Implantable stimulation devices, and methods and systems for use therewith, that automatically adjust stimulation parameters to improve preload in an HF patient

Abstract

Methods, systems and devices described herein can be used for automatically adjusting one or more cardiac resynchronization therapy (CRT) pacing parameters (and more generally stimulation parameters), to achieve a long term reduction in left ventricular (LV) diastolic pressure (and more generally, preload) of a heart failure (HF) patient. A reduction in LV diastolic pressure is indicative of a reduction in preload (the force of blood the fills the left ventricle), which is typically indicative of an improvement in a patient's HF condition. In accordance with certain embodiments, when a set of stimulation parameters is tested, the set is tested for a period that is sufficiently long enough to allow the patient's compensatory mechanisms to react to the set of stimulation parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the using the set of stimulation parameters. Such techniques are believed to provide better results than achieved using acute hemodynamic optimization techniques.

Description

FIELD OF THE INVENTION

Embodiments of the present invention generally pertain to implantable cardiac stimulation devices that provide cardiac resynchronization therapy (CRT), and methods for use therewith. Embodiments of the present invention can also be used with devices capable of delivering other types of therapy that can affect preload, such as devices that deliver neurostimulation.

BACKGROUND OF THE INVENTION

In recent years, it has been demonstrated repeatedly that there is little tangible improvement in clinical outcomes from performing acute hemodynamic optimization of paced pulse timing. There is a reason for this. Since the heart is not a fatigable muscle, a hemodynamic sensor by itself gives no indication if a pacing intervention improves hemodynamics at the expense of greater energy expenditure, which could trigger maladaptive neurohormonal mechanisms within minutes to hours, or if the pacing intervention truly unloads the left ventricle.

The goal of cardiac resynchronization therapy (CRT) is to synchronize mechanical activation, which can relieve compensatory mechanisms and unload the heart. Preload (the force of blood that fills the left ventricle) and afterload (the force against which the left ventricle must work to eject blood) are the two factors that determine cardiac output, in addition to the force of contraction. Increasing preload is a mechanism used by the body to compensate for poor cardiac function. Though there is some nonlinearity in the pressure-volume preload relationship, maintaining higher filling pressure allows a greater volume of blood to fill the left ventricle.

In particular, the Frank-Starling law explains how preload helps to maintain cardiac output (CO). The curves shown in FIG. 1 are used to illustrate a relationship between preload and CO. In FIG. 1, preload is indicated by left ventricular end-diastolic pressure (LV EDP), which is closely related to the left atrial pressure (LAP) when blood enters the left ventricle during diastolic filling. The curves at the left in FIG. 1 show different possible Frank-Starling curves as a function of contractility. The curves at the right in FIG. 1 show different Frank-Starling curves and as a function of afterload, expressed as arterial resistance. In advanced heart failure (HF), a curve may even have a negative slope at elevated filling pressure.

Still referring to FIG. 1, the Frank-Starling curves show CO as a function of LV EDP, where LV EDP is a surrogate of preload. All of the curves show that increasing preload leads to an increase in CO, which may not be true in advanced HF. At the left, the curves demonstrate that higher contractility can also increase CO. At the right, the curves show that higher afterload (expressed by arterial resistance) reduces CO.

Except in extreme deterioration, such as decompensated HF, the body's powerful neurohormonal mechanisms compensate in various ways to maintain CO. Even if a sub-optimal pacing configuration is programmed, the body attempts to preserve CO. Some of these adaptations are considered hallmark signs of HF, such as an increase in resting heart rate and over-activation of the renin-angiotensin-aldosterone system. It may be less easily measured, but is certainly no less important, that the body may decrease the amount of blood distributed to organs of the body to accumulate blood and maintain a higher filling pressure in an attempt to compensate for poor cardiac function. When all other factors are kept unchanged, the ventricles will be able to expel a greater amount of blood during systole if the force bringing blood into the ventricles during diastole is greater.

Thus, it may be concluded that the acute change in CO caused by activating a pacing intervention has an unclear relationship to the outcome that will result from long-term use of the pacing intervention. Acute CO changes are, rather, a measure of the delay to action of the body's compensatory mechanisms. Similarly, it is likely that there will be neither a clear acute change in LAP morphology, nor even in its mean value over the cardiac cycle, immediately after starting a pacing intervention.

SUMMARY

Embodiments of the present invention generally pertain to implantable cardiac stimulation devices that provide cardiac resynchronization therapy (CRT), systems that include such devices, and methods for use with such devices and/or systems. Certain such embodiments can be used for automatically adjusting one or more CRT pacing parameters to achieve a long term reduction in left ventricular (LV) diastolic pressure of a heart failure (HF) patient. A reduction in LV diastolic pressure is indicative of a reduction in preload (the force of blood the fills the left ventricle), which is indicative of a satisfactory matching of venous return to the heart with the level of cardiac output appropriate to the body's needs.

Certain methods involve, for each of a plurality of sets of pacing parameters, pacing the patient's heart using the set of pacing parameters for a time period that is sufficiently long enough to allow the patient's compensatory mechanisms to react to the set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the set of pacing parameters. This can include, for example, pacing the patient's heart using a first set of pacing parameters (i.e., a first pacing intervention), for a first time period that is sufficiently long enough to allow the patient's compensatory mechanisms to accommodate the first set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the first set of pacing parameters; and pacing the patient's heart using a second set of pacing parameters (i.e., a second pacing intervention), for a second time period that is sufficiently long enough to allow the patient's compensatory mechanisms to accommodate the second set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the second set of pacing parameters. Preferably, only one pacing parameter in each set of pacing parameters is different than a corresponding pacing parameter in the other set(s). For example, only one pacing parameter in the first set of pacing parameters is different than a corresponding pacing parameter in the second set.

In certain embodiments, there is a cycling through of the plurality of sets of pacing parameters at least twice. For example, there can be an alternating back and forth, at least twice, between pacing the patient's heart using the first set of pacing parameters for the first time period and pacing the patient's heart using the second set of pacing parameters for the second time period.

In accordance with certain embodiment, the above described process is performed a plurality of times for each of at least two different pacing parameters.

In accordance with preferred embodiments of the present invention, the length of each time period is at least 1 hour. In accordance with certain embodiments, the length of each time period is approximately 24 hours, which should account for circadian variability. In other embodiments, each of the time periods spans a same portion of separate 24 hour periods, which again should account for circadian variability. For example, each first time period and each second time period spans a same portion of separate 24 hour time periods. In still other embodiments, the time periods (e.g., the first and second time periods) can differ from one another, but should each still be long enough to allow the patient's compensatory mechanisms to react to the set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the set of pacing parameters, and preferably should also account for circadian variability.

For each of the plurality of sets of pacing parameters used to pace the patient's heart, a corresponding measure indicative of the patient's LV diastolic pressure achieved using the set of pacing parameters is obtained. For example, a first measure, indicative of the patient's LV diastolic pressure achieved using the first set of pacing parameters, is obtained; and a second measure, indicative of the patient's LV diastolic pressure achieved using the second set of pacing parameters, is obtained. Preferably, each measure is indicative of the substantially steady-state LV diastolic pressure achieved by pacing the patient's heart using one of the sets of pacing parameters.

One of the plurality of sets of pacing parameters is selected, as the preferred set, in dependence on a comparison of the corresponding measures indicative of the patient's LV diastolic pressure achieved using the sets of pacing parameters. For example, one of first and second sets of pacing parameters can be selected as the preferred set in dependence on a comparison of a first measure indicative of the patient's LV diastolic pressure achieved using the first set of pacing parameters and a second measure indicative of the patient's LV diastolic pressure achieved using the second set of pacing parameters. More specifically, in certain embodiments, the one of the sets that resulted in the lower measure of the patient's LV diastolic pressure is selected. Additionally, at least one new set of pacing parameters is selected to replace at least one of the sets of pacing parameters that was not selected as the preferred set. The above process is then repeating, one or more times. In accordance with certain embodiments, each time the pacing using a plurality of sets of pacing parameters is repeated (to enable a comparison of, and a selection among, the sets), one of the sets of pacing parameters is the set of pacing parameters most recently selected based on the comparison between the sets, and the other set(s) of pacing parameters is/are the new set(s) of pacing parameters most recently selected.

In accordance with certain embodiments, each measure indicative of the patient's LV diastolic pressure can be, e.g., a measure of left ventricular pressure (LVP), a measure of left atrial pressure (LAP), a measure of pulmonary artery pressure (PAP), a measure of pulmonary venous pressure (PVP), a measure of pulmonary capillary wedge pressure (PCWP), or a combination of at least two of the above listed measures. Each such pressure measurement can either be a direct measure or a surrogate measure. For example, a measure of PAP can either be a direct measure of PAP, or a surrogate measure of PAP. For a more specific example, a measure indicative of the patient's LV diastolic pressure can be a surrogate measure of PAP that is derived from a first derivative of an RV pressure curve obtained using an RV pressure sensor. This is just one example, which is not meant to be limiting.

In accordance with certain embodiments, each set of pacing parameters defines at least one of the following pacing parameters: an atrio-ventricular (AV) delay, an inter-ventricular (V-V) delay, an intra-ventricular delay, an inter-atrial delay, an LV pacing vector, a pacing rate, a selection among bi-ventricular (BiV) pacing and LV only pacing, a selection among LV pacing electrode configurations, or a selection among single or multiple LV pacing electrode configurations. This list is not intended to be all encompassing, and thus, embodiments of the present invention can also be used to adjust and select among settings for other types of pacing parameters, and more generally, to adjust various different types of stimulation parameters.

In certain embodiments, each set of pacing parameters comprises two or more of the above listed pacing parameters. In certain such embodiments, each time pacing occurs using a plurality of sets of pacing parameters, only one of the at least two pacing parameters in each set of pacing parameters has a different value than a corresponding one of the at least two pacing parameters in the other set(s) of pacing parameters. Additionally, in certain embodiments, when a new set of pacing parameters is selected (to replace a non-selected set), only one of the at least two pacing parameters in the new set of pacing parameters has a different value than a corresponding one of the at least two pacing parameters in the set of pacing parameters being replaced.

In accordance with specific embodiments, a corresponding range of allowable values is specified for each pacing parameter, and each time a new set of pacing parameters is selected each pacing parameter in the new set of pacing parameters remains within its corresponding range of allowable values.

Embodiments of the present invention are also directed to systems that can be used to perform the above described methods. Such systems can be completely implantable. Alternatively, a portion of such a system can be implanted, and a further portion of such a system can be a non-implanted sub-system that wirelessly communicates with the implantable portion of the system. For example, a non-implanted sub-system can perform the aforementioned comparisons and/or selections of one of the first and second sets of pacing parameters, and/or can perform the selection of a new set of pacing parameters. Other variations are also possible, and are within the scope of an embodiment of the present invention.

Additionally, or alternatively, embodiments of the present invention can be used to automatically adjust other types of stimulation parameters, such as neurostimulation parameters, to achieve a long term reduction in LV diastolic pressure of an HF patient.

This summary is not intended to be a complete description of the invention. Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail, in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 includes Frank-Starling curves that illustrate relationships between cardiac output and left ventricular end-diastolic pressure (LV EDP), which is closely related to the left atrial pressure (LAP) when blood enters the left ventricle during diastolic filling.

FIGS. 2A and 2B are high level diagrams that are used to explain specific implementations of embodiments of the present invention.

FIG. 3 is a high level flow diagram that is used to explain that, in accordance with certain embodiments, a clinician or physician can specify a range of allowable values for each of a plurality of pacing parameters, which can be used to select initial and new sets of pacing parameters to be tested.

FIG. 4 illustrates an exemplary graphical user interface (GUI) of an external programmer that enables a clinician or physician to readily specify a range for each of four pacing parameters that may be automatically adjusted using embodiments of the present invention.

FIG. 5A illustrates an exemplary trend in LV diastolic pressure, without any change in pacing parameters settings.

FIG. 5B illustrates an exemplary LV diastolic pressure pattern when an implantable device switches back and forth between the two sets of pacing parameters.

FIG. 6 shows a sequence of comparisons of two sets of pacing parameters having different AV delays and how embodiments of the present invention can be used to converge to a preferred AV delay setting.

FIG. 7A is a simplified, partly cutaway view illustrating an implantable cardiac stimulation device in electrical communication with at least three leads implanted into a patient's heart for delivering multi-chamber stimulation and shock therapy and sensing cardiac activity.

FIG. 7B is a functional block diagram of the multi-chamber implantable cardiac stimulation device of FIG. 7A, illustrating the basic elements that provide pacing stimulation, cardioversion, and defibrillation in four chambers of the heart.

DETAILED DESCRIPTION

The following description is of the best modes presently contemplated for practicing various embodiments of the present invention. The description is not to be taken in a limiting sense but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be ascertained with reference to the claims. In the description of the invention that follows, like numerals or reference designators will be used to refer to like parts or elements throughout. In addition, the first digit of a reference number identifies the drawing in which the reference number first appears.

Certain embodiments of the present invention described herein are related to methods, devices and system for tuning CRT pacing parameters using measures indicative of the patient's LV diastolic pressure, which are preload measures. In certain embodiments, a clinician or physician programs a range of allowed pacing parameters settings. A device or sub-system selects one set of pacing parameters for use during a first time period (e.g., a first day), then switches to a second set of pacing parameters for use during a second time period (e.g., the next day), and continues to switch back and forth (e.g., daily) between the two sets of pacing parameters (first set, second set, first set, second set . . . ). In certain embodiments, the time of switching between sets of pacing parameters is at night when the patient is at rest. Trends in LV diastolic pressure are measured over the entire period, and grouped together according to the pacing intervention (pacing using the first set or pacing using the second set) to reduce other temporal variations. In certain embodiments, after several periods (e.g., several days), the device selects the set of pacing parameters that yields lower LV diastolic pressure, which corresponds to the lower preload. The device picks another set of pacing parameters to compare and repeats the steps to determine which set of pacing parameters is better. The device continues to adjust pacing parameters settings automatically with the goal of maintaining low LV diastolic pressure, and thus, low preload.

In accordance with specific embodiments, each set of pacing parameters defines at least one of the following pacing parameters: an atrio-ventricular (AV) delay, an inter-ventricular (V-V) delay, an intra-ventricular delay, an inter-atrial delay, an LV pacing vector, a pacing rate, a selection among bi-ventricular (BiV) pacing and LV only pacing, a selection among LV pacing electrode configurations, or a selection among single or multiple LV pacing electrode configurations, but are not limited thereto. In certain embodiments, each set of pacing parameters defines at least two of the above mentioned pacing parameters. Additionally, or alternatively, embodiments of the present invention can be used to automatically adjust other types of therapy parameters, such as one or more neurostimulation parameters, to achieve a long term reduction in LV diastolic pressure of an HF patient, and thus, a long term reducing in preload.

The high level diagram of FIG. 2A will now be used to explain specific implementations of embodiments of the present invention. More specifically, FIG. 2A is used to describe methods for automatically adjusting one or more CRT pacing parameters (also referred to simply as pacing parameters) to achieve a long term reduction in LV diastolic pressure in an HF patient, and thus, a reduction in preload. Embodiments of the present invention are believed to provide for better longer-term unloading of the heart by reducing compensatory mechanisms, even if no substantial improvement is seen in any acute hemodynamic measurement.

Referring to FIG. 2A, at step 202, a value for N is specified, wherein N indicates how many times a cardiac stimulation device alternates back and forth between pacing using a first set of pacing parameters and pacing using a second set of pacing parameters before respective measures of LV diastolic pressure corresponding to the first and second sets are compared to one another. In other words, as will be appreciated from the following description, N defines how many times steps 206-212 in FIG. 2A are performed before flow continues to steps 218-226 in FIG. 2A. The value for N can be preprogrammed into a cardiac stimulation device. Alternatively, the value for N can be programmed by a clinician or physician using an external programmer that communicates with an implanted cardiac stimulation device. In other embodiments, rather than specifying a specific number (N) of iterations that are to be perform to adjust a specific pacing parameter, steps 206-212 can be repeated until a predefined criterion is satisfied.

At step 204, a count value is set to 1. As will be appreciated from steps 214 and 216 discussed below, this count value is used to keep track of how many times the cardiac device has alternated back and forth between pacing using the first set of pacing parameters and pacing using the second set of pacing parameters before respective measures of LV diastolic pressure corresponding to the first and second sets are compared to one another in order to select one of the sets as a preferred set.

At step 206, pacing is performed using a first set of pacing parameters, for a first time period that is sufficiently long enough to allow the patient's compensatory mechanisms to react to the first set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the first set of pacing parameters. In accordance with an embodiment, the first time period is at least 1 hour, but is preferably longer. For example, in a specific embodiment, the first time period is a full day, i.e., 24 hours. It is also possible that the first time period be some other time between 1 hour and 24 hours, e.g., 2 hours, 3 hours, or 8 hours, etc. In still other embodiments, the first time period is even longer than 24 hours, e.g., is 48 hours. In still other embodiments, if it is found that a particular patient's compensatory mechanisms react relatively fast and achieve a substantially steady-state LV diastolic pressure relatively fast, after a change in pacing parameters, then it is possible that each of the time periods can be less than 1 hour.

At step 208, a measure indicative of the LV diastolic pressure achieved using the first set of pacing parameters is obtained. LV diastolic pressure may be measured directly, or a surrogate measure of LV diastolic pressure can be obtained at step 208. Exemplary surrogate measures of LV diastolic pressure (and more generally, preload), which can be obtained at step 208, include: a measure of left atrial pressure (LAP), a measure of pulmonary artery pressure (PAP), a measure of pulmonary venous pressure (PVP), or a measure of pulmonary capillary wedge pressure (PCWP), but are not limited thereto. It is also possible that two or more of the above listed measures are combined, e.g., using a predefined algorithm, to provide the measure indicative of the LV diastolic pressure. Each such pressure measurement, which is a surrogate measure of LV diastolic pressure, can itself either be a direct measure or a surrogate measure. For example, a measure of PAP can either be a direct measure of PAP, or a surrogate measure of PAP. For a more specific example, a measure indicative of the patient's LV diastolic pressure can be a surrogate measure of PAP that is derived from a first derivative of an RV pressure curve obtained using an RV pressure sensor. In other words, the term “measure” as used herein can either refer to a direct measure or a surrogate measure, unless stated otherwise. In accordance with an embodiment, the measure obtained at step 208 is a single measure obtained just prior to the end of the first time period during which pacing is performed using the first set of pacing parameters. In the embodiment with time periods beginning and ending in the nighttime while the patient is at rest, the measure is taken in a resting position. Alternatively, the measure obtained at step 208 is an average (e.g., a mean, a mode or a median) of a plurality of measures obtained during a latter portion of the first time period (e.g., the last 10% of the first time period) during which pacing is performed using the first set of pacing parameters. Either way, the measure obtained at step 208 is preferably indicative of a substantially steady-state LV diastolic pressure that results after the patient's compensatory mechanisms had an opportunity to react to the first set of pacing parameters.

At step 210, pacing is performed using a second set of pacing parameters, for a second time period that is sufficiently long enough to allow the patient's compensatory mechanisms to react to the second set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the second set of pacing parameters. In accordance with an embodiment, as was the case with the first time period, the second time period is at least 1 hour, but is preferably longer. In a specific embodiment, the second time period is a full day, i.e., 24 hours, which should account for circadian variability. Alternatively the second time period can be some other time between 1 hour and 24 hours, or can be even longer than 24 hours. In accordance with certain embodiments, the length of the first time period and the length of the second time period are the same (e.g., each is 24 hours). Alternatively, the lengths of the first and second time periods are not the same, e.g., the first time period can be 4 hours and the second time period can be 1 hour. Regardless of the actual lengths of the first and second time periods, such time periods should preferably each still be long enough to allow the patient's compensatory mechanisms to react to the set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the set of pacing parameters, and should preferably also account for circadian variability.

At step 212, a measure indicative of the LV diastolic pressure achieved using the second set of pacing parameters is obtained. In a similar manner as was discussed above with reference to step 208, a surrogate measure of LV diastolic pressure (and more generally, preload) can be obtained at step 212, examples of which were discussed above. In a similar manner as was discussed above with reference to step 208, the measure obtained at step 212 can be a single measure obtained just prior to the end of the second time period during which pacing is performed using the second set of pacing parameters, or the measure obtained at step 212 can be an average (e.g., a mean, a mode or a median) of a plurality of measures obtained during a latter portion of the second time period (e.g., the last 10% of the second time period) during which pacing is performed using the second set of pacing parameters. Either way, the measure obtained at step 212 is preferably indicative of a substantially steady-state LV diastolic pressure that results after the patient's compensatory mechanisms had an opportunity to react to the second set of pacing parameters.

In accordance with certain embodiments, where each period of time is less than 24 hours, steps 206-212 are performed when the patient has a predetermined posture and/or activity level, so as to minimize effects on the measures that may be due to differences in posture and/or activity, and more generally, due to diurnal variations. To detect posture and/or activity, an implantable system (e.g., 702 in FIGS. 7A and 7B) that is used to perform the steps described herein can include one or more sensors that can detect a patient's posture and/or level of activity. The sensor can be, e.g., a DC-coupled 3-dimensional accelerometer, such as described in U.S. Pat. No. 6,658,292 (Kroll et al), a multi-axis DC accelerometer, such as described in U.S. Pat. No. 6,466,821 (Pianca et al), or an external field sensor, such as described in U.S. Pat. No. 6,625,493 (Kroll et al), each of which is incorporated herein by reference. Such sensors are able to distinguish among different static positions. In addition, since the sensors can detect motion, they can be used to distinguish between a static vertical position, such as sitting, and a standing position, which due to the dynamics of balance is associated with subtle motion that is not present while sitting. In this way an implantable system, using one of the above mentioned sensors or other sensing modality, can detect a posture and/or level of activity so that that different measures indicative of LV diastolic pressure, which are compared to one another, are obtained when the patient had substantially the same posture and/or level of activity.

Still referring to FIG. 2A, at step 214 there is a determination of whether the count value is equal to N. If the answer to step 214 is no, then flow proceeds to step 216 where the count value is incremented by 1, and then flow returns to step 206 so that an additional iteration of steps 206-212 can be performed. For example, if N=3, then steps 206-212 will be performed a total of three times before flow proceeds to step 218.

Where N is greater than 1, there will be multiple (i.e., N) measure indicative of the patient's LV diastolic pressure achieved using the first set of pacing parameters, and multiple (i.e., N) measures indicative of the patient's LV diastolic pressure achieved using the second set of pacing parameters. Accordingly, steps 218 and 220 are performed to obtain measures that can be compared to one another. More specifically, at step 218, a first measure indicative of the patient's LV diastolic pressure achieved using the first set of pacing parameters is determined by combining measures obtained at the most recent N instances of step 206. Such measures obtained at the most recent N instances of step 206 can be combined, e.g., by determining an average (e.g., mean, mode or median) of them. Alternatively, the measures can simply be added. At step 220, a second measure indicative of the patient's LV diastolic pressure achieved using the second set of pacing parameters is determined by combining measures obtained at the most recent N instances of step 212. Such measures obtained at the N most recent instances of step 212 can be combined, e.g., by determining an average (e.g., mean, mode or median) of them. Alternatively, the measures can simply be added. Preferably, the combining performed at step 220 is performed in the same manner as the combining at step 218. Other ways of combining the measures at steps 218 and 220 to obtain the first and second measures indicative of the patient's LV diastolic pressure achieved using the first and second sets of pacing parameters are possible, and are also within the scope of embodiments of the present invention.

At step 222, the first measure (indicative of the patient's LV diastolic pressure achieved using the first set of pacing parameters) obtained at step 218 is compared to the second measure (indicative of the patient's LV diastolic pressure achieved using the second set of pacing parameters) obtained at step 220. At step 224, one of the first and second sets of pacing parameters is selected as the preferred one of the two based on results of the comparison performed at step 222. More specifically, since a goal is to identify pacing parameters that achieve reduced LV diastolic pressure, and more generally preload, the set that achieved the lower LV diastolic pressure is most likely selected at step 222. It is presumed that in most cases pacing using one of the first and second sets will achieve a lower LV diastolic pressure than pacing using the other one of the sets. However, if the pacing using both sets achieves substantially the same LV diastolic pressure, then either one of the sets can be selected at step 226. In certain embodiments, where there is a desire to maintain at least a specified minimum level of LV diastolic pressure, the one of the first and second sets of pacing parameters that achieved a higher LV diastolic pressure may be selected if pacing using one set results in an LV diastolic pressure below the minimum desired level, and the other does not, or if pacing using each of the sets resulted in an LV diastolic pressure lower than the desired minimum.

In accordance with certain embodiments, each set of pacing parameters defines at least two pacing parameters, and each time steps 206 and 210 are performed only one of the at least two pacing parameters in the first set of pacing parameters used at step 206 differs from a corresponding one of the at least two pacing parameters in the second set of pacing parameters used at step 210. For example, if each set of pacing parameters includes an atrio-ventricular delay value and an inter-ventricular delay value, then when the first and second sets of pacing parameters have different atrio-ventricular delay values than one another the two sets should have the same inter-ventricular delay values. This enables the comparisons performed at instances of step 222 to be comparisons of a common pacing parameter, which would be atrio-ventricular delay in the above example.

Still referring to FIG. 2A, at step 226 a new set of pacing parameters is selected to replace the set not selected at step 224, thereby enabling this new set to be compared to the set selected at step 224 during the next iteration of steps 204-224. The new set of pacing parameters can be selected in any one of various different manners, such as, but not limited to, selecting random parameters within an allowable range of parameters, incrementing or decrementing values of certain parameters, employing a search tree to identify an optimal parameter value using gradient descent techniques to converge on the optimal parameter value, and/or the like. In certain embodiments, only one pacing parameter in the new set of pacing parameters selected at step 224 is different than in the set of pacing parameters being replaced. For example, the new set of pacing parameters and the set being replaced can include the same inter-ventricular (V-V) delay, the same intra-ventricular delay, and the same LV pacing vector, but include different AV delays. In other words, a single pacing parameter at a time can be changed.

In certain embodiments, each of the first and second periods of time (associated with steps 206 and 208) is one full day, and N=7. This would mean that the first set of pacing parameters would be used every other day for a two week period, and the second set of pacing parameters would be used the other days of the two week period. Such embodiments ensure that each of the first and second sets of pacing parameters is tested for each day of the week and reduces that chances that changes in LV diastolic pressure are due to non-pacing variations such as diet, medications and lifestyle. A benefit of testing each set of pacing parameters for a whole day is that it confirms if there is an anomaly in the patient's LV diastolic pressure, which would be indicative of an anomaly in the patient's daily filling pressure pattern. In an alternate embodiment, one of the sets of pacing parameters (e.g., the most recently newly selected set) is only tested for a few hours in the middle of the night. In certain embodiments, if a dramatic undesirable change in LV diastolic pressure (and thus, afterload) occurs, the device can revert back to a safe state, such as a previous set of pacing parameters that resulted in an LV diastolic pressure within an acceptable range. Reverting to a safe state could similarly be done for any embodiment described herein.

In accordance with certain embodiments, the process described with reference to steps 206-226 are repeated a predetermined number of times (e.g., three times) for a specific pacing parameter (e.g., atrio-ventricular delay), after which the process described with reference to steps 206-226 is then repeated a further predetermined number of times (e.g., three more times) for another pacing parameter (e.g., inter-ventricular delay). Such a process can be repeated until each of the different types of pacing parameters in the first and second sets of parameters had a chance to be adjusted in an attempt to reduce LV diastolic pressure. Alternatively, a clinician or physician can specify that only certain pacing parameters should be adjusted using the above described methods, while other pacing parameters should remain fixed. How many times steps 206-226 are repeated for a specific pacing parameter can be fixed, can be specified by a clinician or physician, or can be variable. For example, in certain embodiments steps 206-226 can be repeated for a specific pacing parameter until a specific criteria is met. For a more specific example, steps 206-226 can be repeated for a specific pacing parameter until two (or some other specified number of) consecutive iterations of steps 206-226 result in the same set of pacing parameters being selected at step 224. Use of other criteria are also possible and within the scope of an embodiment of the present invention.

In accordance with certain embodiments, once steps 206-226 have been performed (once, or a plurality of times) for each of a plurality of different pacing parameters, the set most recently selected at step 224 is used indefinitely for continued CRT pacing. In other embodiments, once steps 206-226 have been performed (once, or a plurality of times) for each of a plurality of different pacing parameters, the process is repeated again, indefinitely, so that there is a continually attempt to reduce LV diastolic pressure (and more generally, preload) as the patient's HF condition gradually changes. In still other embodiments, the above described process can be repeated until a clinician or physician stops the process.

Even though the sets of pacing parameters continually adapt, a rationale for switching between two sets of pacing parameters repeatedly before making a decision as to which set results in a preferred (e.g., lower) LV diastolic pressure is to avoid moving to an inappropriate set of pacing parameters because of one anomalous period of time (e.g., one anomalous day) in the patient's life. The repeated tests help to average out noise by considering multiple time periods (e.g., multiple days) at each setting. However, should a device actually try out a setting that becomes uncomfortable to the patient, the patient may be equipped with an “override” button on a non-implanted device (e.g., a bedside monitor) that wirelessly communicates with the patient's implanted device, or may have some other means such as a personal web page that allows the patient to override the setting. There should also be careful monitoring to report an alert if the patient continually overrides pacing interventions. Similarly, a clinician or physician can have the ability to cancel a test intervention, which could be done in clinic or if regulatory bodies permit, remotely.

The method described with reference to FIG. 2A can be reduced to the steps shown in FIG. 2B where N=1. In other words, in a specific embodiment of the present invention, there is no alternating back and forth between the first and second sets of pacing parameters before corresponding measures of LV diastolic pressure are compared to one another at step 222. This would also have the effect of reducing steps 208 and 218 to a single step, shown as 208/218 in FIG. 2B, and reducing steps 212 and 220 to a single step, shown as step 212/220 in FIG. 2B.

In accordance with certain embodiments, it is not necessary that the obtained measures indicative of the patient's LV diastolic pressure be accurate values of the LV diastolic pressure. Rather, since the obtained measures are primarily being used to select preferred sets of pacing parameters, the measures only need to be capable of being compared to one another such that the set the resulted in a preferred (e.g., lower) LV diastolic pressure can be identified. According, the sensor(s) used to obtain measures indicative of the patient's LV diastolic pressure need not be a high fidelity sensor.

In accordance with certain embodiments, prior to the method of FIG. 2A or 2B being performed, a range of allowable values for each of a plurality of pacing parameters can be specified, as indicated at step 302 in FIG. 3. A clinician or physician can program the range of allowed pacing parameters settings, e.g., using an external programmer. FIG. 4 illustrates an exemplary graphical user interface (GUI) of an external programmer that enables a clinician or physician to readily specify a range for each of four pacing parameters. It is also possible, that a device is pre-programmed with a range of allowable pacing parameter settings, which may or may not be adjustable by a clinician or physician. Returning to FIG. 3, at step 304 a first set of pacing parameters within the allowable ranges is identified, and at step 306 a second set of pacing parameters within the allowable ranges is identified. Steps 304 and 306 can be used to select the initial first and second sets of pacing parameters used at initial instances of step 206 and 210. Additionally, one of steps 304 or 306 can be used to specify new sets of pacing parameters at instances of steps 226. In certain embodiments, all of the pacing parameters except one are the same in the first and second sets of pacing parameters. For example, the first and second sets of pacing parameters can include the same inter-ventricular (VV) delay, the same intra-ventricular (LV-LV) delay, and the same LV pacing vector, but include different atrio-ventricular (AV) delays. In certain embodiments, the first and second sets of pacing parameters identified at steps 304 and 306 are specified by a clinician or physician. Alternatively, a device can be programmed to automatically identify the first and second sets of pacing parameter. In still another embodiment, a clinician or physician can specify one of the first and second sets of pacing parameters and the device can specify the other one of the two. Other variations are also possible, and within the scope of an embodiment of the present invention.

By employing the methods of the present invention described with reference to FIGS. 2A and 2B, a medical device or system can learn a patient's history over time, which makes the device better at picking the next candidate new set of pacing parameters at step 226. It should be noted that the methods do not assume there is a true optimum set of pacing parameters. Rather, in accordance with certain embodiments, one of the methods described herein is continually used to adapt dynamically to a patient's changing HF condition, and may return to previously tested pacing parameters. As the patient's HF condition improves, and is able to relieve filling pressure, the device can continue to find more appropriate pacing parameter settings for further improvement in the patient's HF condition. If the patient's HF condition deteriorates, the device continues to search for settings that are less uncomfortable and with lesser rise in filling pressure (indicated by a lower LV diastolic pressure), in an attempt to palliate.

Embodiments of the present invention described herein can be implemented entirely by an implantable medical device, such as, but not limited to, the exemplary device described below with reference to FIGS. 7A and 7B. Alternatively, certain features can be performed by an implanted device, while other features are performed by non-implanted sub-system that wirelessly communicates with the implanted device. For example, a non-implanted sub-system can perform steps associated with comparing and selecting sets of pacing parameters, such as, but not limited to, steps 222, 224 and 226 described above, while an implanted device can perform steps associated with pacing and obtaining measures indicative of LV diastolic pressure, such as, but not limited to, steps 206, 208, 210 and 212. That is, a system that performs the methods described herein can be completely implanted, or can be partially implanted and partially non-implanted. Other variations are also possible, and are within the scope of an embodiment of the present invention.

FIG. 5A illustrates an exemplary trend in LV diastolic pressure (and more generally preload) without any change in pacing parameter settings. In this exemplary plot, the middle trace 502 in FIG. 5A is indicative of median LV diastolic pressure, and the lower trace 504 and upper trace 506 are respectively indicative of 5% and 95% values of LV diastolic pressure recorded within a time window. In this example, each vertical line corresponds to 3:00 a.m. The pattern suggests a typical rise in median LV diastolic pressure each morning (as well as a decrease in the highest pressure readings).

FIG. 5B illustrates how the traces 502, 504 and 506 might look if the implantable device switched back and forth (daily) between the two sets of pacing parameters (first set, second set, first set, second set . . . ) at 3:00 a.m. In FIG. 5B, each “A” corresponds to the first set of pacing parameters, and each “B” corresponds to the second set of pacing parameters. In the pattern shown in FIG. 5B, there is an increase in LV diastolic pressure associated with each day that CRT is performed using the second set of pacing parameters (corresponding to “B”), compared to the days CRT is performed using the first set of pacing parameters (corresponding to “A”). Actual patient data may not be so pronounced, or may have a time constant of minutes to hours before the change in preload occurs, but should still display a distinct pattern if the compensatory mechanisms cause preload to increase (or decrease) for one intervention but not for the other. The daily pressure pattern could be reduced to a single number by taking a median, percentile or mean, or by fitting to a pattern observed for the patient.

FIG. 6 shows a sequence of comparisons of two sets of pacing parameters having different AV delays. More specifically, FIG. 6 illustrates how pacing using first and second sets can be alternated between (e.g., daily) during a first period (e.g., a first two week period), wherein the first set includes an AV delay of 120 ms and the second set includes an AV delay of 200 ms. At the end of the first period, the device selects the first set which includes the AV delay of 120 ms as the preferred set (because the device determined that pacing using an AV delay of 120 ms achieved a lower LV diastolic pressure than pacing using an AV delay of 200 ms), and the device replaces the second set of pacing parameters with a new second set of pacing parameters including an AV delay of 160 ms. During a second period (e.g., a second two week period), the devices alternately tests the first and second sets of pacing parameters, wherein the first set includes an AV delay of 120 ms, and the second set includes an AV delay of 160 ms. At the end of the second period, the device selects the second set which includes the AV delay of 160 ms as the preferred set (because the device determined that pacing using an AV delay of 160 ms achieved a lower LV diastolic pressure than pacing using an AV delay of 120 ms), and replaces the first set of pacing parameters with a new first set of pacing parameters including an AV delay of 140 ms. During a third period (e.g., a third two week period), the device alternately tests the first and second sets of pacing parameters, wherein the first set includes an AV delay of 140 ms, and the second set includes an AV delay of 160 ms. At the end of the third period, the device selects the first set which includes the AV delay of 140 ms as the preferred set. Each of the first, second and third periods can be, e.g., two weeks, but is not limited thereto. Assuming each of the periods is two weeks, FIG. 6 shows how a device can converge to a preferred AV delay of 140 ms over six weeks. In certain embodiments, at the end of such a six week period, the device can then spend the next six weeks using a similar process to select a new value for another pacing parameter, such as inter-ventricular (VV) delay. Such a process can then be repeated for still other pacing parameters, such as, an intra-ventricular delay, inter-atrial delay, an LV pacing vector, pacing rate, a selection among bi-ventricular (BiV) pacing and LV only pacing, a selection among LV pacing electrode configurations, and/or a selection among single or multiple LV pacing electrode configurations, but is not limited thereto. The device can then return to testing different values for AV delay, etc.

In accordance with specific embodiments, the methods described above with reference to FIGS. 2A and 2B which have a goal of reducing LV diastolic pressure (and thus, reducing preload) can be combined with another goal. For example, while it could be a goal to reduce and maintain a low LV diastolic pressure, it may also be a goal to not allow the LV diastolic pressure to drop below a minimum threshold. To achieve both goals, the criteria of the selection at step 224 can be appropriately modified. In other words, at step 224, the set that achieved the lower LV diastolic pressure is selected, so long as that set does not result in an LV diastolic pressure below a specified minimum threshold. If both sets result in an LV diastolic pressure below the minimum threshold, than the set that achieves the higher LV diastolic pressure can be selected. For another example, it could be desired to maintain low LV diastolic pressure, but not allow the V wave of LAP morphology to indicate mitral regurgitation. For still another example, it might also be desired to combine the goal of low LV diastolic pressure with a target heart rate variability, or combining low LV diastolic pressure with a controlled resting heart rate. These are just a few examples which are not meant to be all encompassing, as there are certainly other possibilities for improving multiple factors that are also within the scope of embodiments described herein. Further, in certain embodiments there can be specified limit to how low LV diastolic pressure (and thus, preload) should be reduced. In other words, while a general goal may be to achieve a long term reduction in LV diastolic pressure, there can be a specified minimum LV diastolic pressure level below which the patient′ actual LV diastolic pressure preferably does not fall below. Such a minimal level can be taken into account when there is a selection among different sets of pacing parameters that have been tested.

Embodiments of the present invention can additionally, or alternatively, be used to automatically adjust other types of therapy parameters, such as neurostimulation parameters, to achieve a long term reduction in LV diastolic pressure of an HF patient, and more generally, a long term reduction in preload. Neurostimulation parameters can, for example, be used to specify electrode configuration, pulse amplitude, pulse width, pulse pattern and/or pulse repetition rate parameters that are used to stimulate portions of a patient's central nervous system, such as portions of spinal cord, spinal nerves, and/or brain. In other words, more than just cardiac pacing parameters can be adjusted using embodiments of the present invention. Rather, various different types of therapy parameters, including, but not limited to, cardiac stimulation and/or neurostimulation parameters, can be automatically adjusted in accordance with embodiments of the present invention to achieve a long term reduction in LV diastolic pressure of an HF patient, and thus, a long term reduction in preload.

In the above description, there was often a testing of two sets of pacing parameters, after which one of the two sets was selected as the preferred one of the two sets based on corresponding measures indicative of the patient's LV diastolic pressure, and thereafter a new set of pacing parameters was selected to replace the set not selected. In other embodiments, there can be a testing of three or more sets of pacing parameters, after which one of the sets is selected as the preferred one of the sets based on corresponding measures indicative of the patient's LV diastolic pressure, and thereafter one or more new sets of pacing parameters are selected to replace one or more of the sets not selected. More generally, embodiment of the present inventions can include, for each of a plurality of sets of pacing parameters, pacing the patient's heart using the set of pacing parameters for a time period that is sufficiently long enough to allow the patient's compensatory mechanisms to react to the set of pacing parameters and achieve a substantially steady-state LV diastolic pressure corresponding to the pacing using the set of pacing parameters. For each of the plurality of sets of pacing parameters used, a corresponding measure is obtained that is indicative of the patient's LV diastolic pressure achieved using the set of pacing parameters. One of the plurality of sets of pacing parameters is selected as the preferred set in dependence on a comparison of the corresponding measures indicative of the patient's LV diastolic pressure achieved using the sets of pacing parameters. At least one new set of pacing parameters is selected to replace at least one of the sets of pacing parameters not selected. In certain embodiments, each of the sets except the preferred set is replaced with a new set. Other variations are also possible. The above steps are repeated, one or more times, wherein each time pacing using a plurality of sets of pacing parameters is repeated, one of the sets of pacing parameters comprises the set of pacing parameters most recently selected as the preferred set, and at least one of the other sets of pacing parameters comprises the at least one new set of pacing parameters most recently selected.

For completeness, additional details of an exemplary cardiac stimulation device within which embodiments of the present invention can be implemented will now be describe with reference to FIGS. 7A and 7B. FIG. 7A provides a simplified block diagram of a cardiac stimulation device, which is a dual-chamber stimulation device 702 capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation, including multi-site left ventricular (MSLV) pacing. This cardiac stimulation device 702 is an example of a device that can be used to implement the embodiments described above with reference to FIGS. 2A-6. To provide atrial chamber pacing stimulation and sensing, cardiac stimulation device 702 is shown in electrical communication with a heart 713 by way of a left atrial (LA) lead 720 having an atrial tip electrode 722 and an atrial ring electrode 723 implanted in the atrial appendage. Cardiac stimulation device 702 is also in electrical communication with the heart by way of a right ventricular (RV) lead 730 having, in this embodiment, a ventricular tip electrode 732, a RV ring electrode 734, a RV coil electrode 736, and a superior vena cava (SVC) coil electrode 738. Typically, the RV lead 730 is transvenously inserted into the heart so as to place the RV coil electrode 736 in the RV apex, and the SVC coil electrode 738 in the superior vena cava. Accordingly, the RV lead is capable of receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle (also referred to as the RV chamber).

To sense left atrial and ventricular cardiac signals and to provide left chamber pacing therapy, cardiac stimulation device 702 is coupled to a multi-pole LV lead 724 designed for placement in the “CS region” via the CS os for positioning a distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium (also referred to as the LA chamber). As used herein, the phrase “CS region” refers to the venous vasculature of the left ventricle, including any portion of the CS, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the CS. Accordingly, an exemplary LV lead 724 is designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using a set of four LV electrodes 726₁, 726₂, 726₃, and 726₄ (thereby providing a quadra-pole lead), left atrial pacing therapy using at least a LA ring electrode 727, and shocking therapy using at least a LA coil electrode 728. In certain embodiments, the LV lead 724 includes the LV electrodes 726₁, 726₂, 726₃, and 726₄, but does not include the LA electrodes 727 and 728. Such a lead can be, e.g., the Quartet™ left ventricular pacing lead developed by St. Jude Medical Inc. (headquartered in St. Paul, Minn.), which includes four pacing electrodes on the left ventricular lead-enabling up to 10 pacing configurations.

The LV electrode 726₁ is shown as being the most “distal” LV electrode (with relation to how far the electrode is from where the LV lead 724 connects to the cardiac stimulation device 702). The LV electrode 726₄ is shown as being the most “proximal” LV electrode. The LV electrodes 726₂ and 726₃ are shown as being “middle” LV electrodes, between the distal and proximal LV electrodes 726₁ and 726₄. Accordingly, so as to more aptly describe their relative locations, the four LV electrodes 726₁, 726₂, 726₃, and 726₄ can be referred to respectively as electrodes D1, M2, M3 and P4 (where “D” stands for “distal”, “M” stands for “middle”, and “P” stands from “proximal”, and the numbers are arranged from most distal to most proximal).

It is also possible that more or fewer LV electrodes are provided. However, for much of the remaining discussion, it will be assumed that the multi-pole LV lead 724 includes the four LV electrodes 726₁, 726₂, 726₃, and 726₄ (i.e., LV electrodes D1, M2, M3 and P4, respectively).

The four LV electrodes can be used to provide various different pacing vectors and sensing vectors. Some of the vectors are intraventricular LV vectors (vectors between two LV electrodes); whereas others are interventricular vectors (e.g., vectors between a LV electrode and the RV coil 736). Below is a list of exemplary vectors that can be used for pacing and/or sensing using the LV electrodes D1, M2, M3 and P4 with and without the RV coil 736. In the following list, the first electrode in each row (i.e., the electrode to the left of the arrow) is assumed to be connected as the cathode, and the second electrode in each row (i.e., the electrode to the right of the arrow) is assumed to be connected as the anode, but that need not be the case, especially where neither electrode is a coil.

D1→RV coil

M2→RV coil

M3→RV coil

P4→RV coil

D1→M2

D1→P4

M2→P4

M3→M2

M3→P4

P4→M2

Although only three leads are shown in FIG. 7A, it should also be understood that additional leads (with one or more pacing, sensing and/or shocking electrodes) might be used and/or additional electrodes might be provided on the leads already shown, such as additional electrodes on the RV or LV lead. It is also possible that less than three leads be used.

A simplified block diagram of internal components of the cardiac stimulation device 702 is shown in FIG. 7B. While a particular cardiac stimulation device is shown, this is for illustration purposes only, and one of skill in the art could readily duplicate, eliminate or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) with cardioversion, defibrillation and pacing stimulation. The housing 740 for cardiac stimulation device 702, shown schematically in FIG. 7B, is often referred to as the “can”, “case” or “case electrode” and may be programmably selected to act as the return electrode for all “unipolar” modes. The housing 740 may further be used as a return electrode alone or in combination with one or more of the coil electrodes, 728, 736 and 738, for shocking purposes. The housing 740 further includes a connector (not shown) having a plurality of terminals, 742, 743, 744₁-744₄, 746, 748, 752, 754, 756 and 758 (shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). As such, to achieve RA sensing and pacing, the connector includes at least a RA tip terminal (A_R TIP) 742 adapted for connection to the atrial tip electrode 722 and a RA ring (A_R RING) electrode 743 adapted for connection to RA ring electrode 723. To achieve left chamber sensing, pacing and shocking, the connector includes a LV tip terminal 744₁ adapted for connection to the D1 electrode and additional LV electrode terminals 744₂, 744₃ and 744₄ terminals adapted for connection to the M2, M3 and P4 electrodes of the quadra-pole LV lead.

The connector also includes a LA ring terminal (A_L RING) 746 and a LA shocking terminal (A_L COIL) 748, which are adapted for connection to the LA ring electrode 727 and the LA coil (A_L COIL) electrode 728, respectively. To support right chamber sensing, pacing and shocking, the connector further includes a RV tip terminal (V_R TIP) 742, a RV ring terminal (V_R RING) 743, a RV shocking terminal (V_R COIL) 756, and an SVC shocking terminal (SVC COIL) 758, which are adapted for connection to the RV tip electrode 732, RV ring electrode 734, the RV coil electrode 736, and the SVC coil electrode 738, respectively.

At the core of cardiac stimulation device 702 is a programmable microcontroller 760 that is used to controls the various modes of stimulation therapy. As is well known in the art, the microcontroller 760 (also referred to herein as a control unit or controller) typically includes one or more microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, the microcontroller 760 includes the ability to process or monitor input signals (data) as controlled by a program code stored in a designated block of memory. The details of the design and operation of the microcontroller 760 are not critical to the invention. Rather, any suitable microcontroller 760 may be used that carries out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art.

As shown in FIG. 7B, an atrial pulse generator 770 and a ventricular pulse generator 772 generate pacing stimulation pulses for delivery by the RA lead 720, the RV lead 730, and/or the LV lead 724 via an electrode configuration switching circuitry 774. It is understood that in order to provide stimulation therapy in each of the four chambers of the heart, the atrial and ventricular pulse generators, 770 and 772, may include dedicated, independent pulse generators, multiplexed pulse generators or shared pulse generators. The pulse generators, 770 and 772, are controlled by the microcontroller 760 via appropriate control signals, 776 and 778, respectively, to trigger or inhibit the stimulation pulses.

The microcontroller 760 includes timing control circuitry 761 to control the timing of the stimulation pulses, including, but not limited to, pacing rate, atrio-ventricular (AV) delay, interatrial conduction (AA) delay, interventricular conduction (VV) delay and/or intraventricular delay (e.g., LV1-LV2 delay). The timing control circuitry 761 can also keep track of the timing of refractory periods, blanking intervals, noise detection windows, evoked response detection windows, alert intervals, marker channel timing, etc., which is well known in the art.

The microcontroller 760 further includes an arrhythmia detector 762. The detector 762 can be utilized by the stimulation device 702 for determining desirable times to administer various therapies. The detector 762 may be implemented in hardware as part of the microcontroller 760, or as software/firmware instructions programmed into the device and executed on the microcontroller 760 during certain modes of operation.

The microcontroller 760 further includes a CRT controller 764, which can be used to implement various algorithms and/or methods described herein. The CRT controller may be implemented in hardware as part of the microcontroller 760, or as software/firmware instructions programmed into the device and executed on the microcontroller 760 during certain modes of operation. Additional components of the microcontroller include a MSLV controller 765 to control the actual delivery of MSLV pacing. The CRT controller 764 and/or the MSLV controller 765 can communicate with and/or be implemented together with the timing controller 761.

Depending upon the implementation, the various components of the microcontroller may be implemented as separate software modules or the modules may be combined to permit a single module to perform multiple functions. For example, the MSLV controller 765 and the CRT controller 764 can be combined. In addition, although shown as being components of the microcontroller, some or all of these components may be implemented separately from the microcontroller, using application specific integrated circuits (ASICs) or the like.

Switching circuitry 774 includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, the switching circuitry 774, in response to a control signal 780 from the microcontroller 760, determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art. The switching circuitry 774 also switches among the various LV electrodes.

Atrial sensing circuits 782 and ventricular sensing circuits 784 may also be selectively coupled to the RA lead 720, LV lead 724, and the RV lead 730, through the switching circuitry 774 for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing circuits, 782 and 784, may include dedicated sense amplifiers, multiplexed amplifiers or shared amplifiers. The switching circuitry 774 determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity. Each sensing circuit, 782 and 784, preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic gain control enables cardiac stimulation device 702 to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation. The outputs of the atrial and ventricular sensing circuits, 782 and 784, are connected to the microcontroller 760 which, in turn, are able to trigger or inhibit the atrial and ventricular pulse generators, 770 and 772, respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart.

For arrhythmia detection, cardiac stimulation device 702 utilizes the atrial and ventricular sensing circuits, 782 and 784, to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. As used in this section “sensing” is reserved for the noting of an electrical signal, and “detection” is the processing of these sensed signals and noting the presence of an arrhythmia, an evoked response, an intrinsic event, or some other event being monitored for. The timing intervals between sensed events (e.g., AS, VS, and depolarization signals associated with fibrillation which are sometimes referred to as “F-waves” or “Fib-waves”) can be classified by the microcontroller 760 by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, atrial tachycardia, atrial fibrillation, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, antitachycardia pacing, cardioversion shocks or defibrillation shocks). The arrhythmia detector 762, mentioned above, can be used to detect and characterize such arrhythmias.

Cardiac signals are also applied to the inputs of an analog-to-digital (A/D) data acquisition system 790. The data acquisition system 790 is configured to acquire intracardiac electrogram signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external programmer 704 or a bedside monitor or personal advisory module (PAM) 705. The data acquisition system 790 is coupled to the RA lead 720, the LV lead 724, and the RV lead 730 through the switching circuitry 774 to sample cardiac signals across any pair of desired electrodes. The microcontroller 760 is further coupled to a memory 794 by a suitable data/address bus 796, wherein the programmable operating parameters used by the microcontroller 760 are stored and modified, as required, in order to customize the operation of cardiac stimulation device 702 to suit the needs of a particular patient. Such operating parameters define, for example, the amplitude or magnitude, pulse duration, electrode polarity, for both pacing pulses and impedance detection pulses as well as pacing rate, sensitivity, arrhythmia detection criteria, and the amplitude, waveshape and vector of each pacing and shocking pulse to be delivered to the patient's heart within each respective tier of therapy. Other pacing parameters include base rate, rest rate and circadian base rate.

Advantageously, the operating parameters of the implantable cardiac stimulation device 702 may be non-invasively programmed into the memory 794 through a telemetry circuit 701 in telemetric communication with an external device 704 or bedside monitor 705, such as a programmer, transtelephonic transceiver or a diagnostic system analyzer. The telemetry circuit 701 is activated by the microcontroller by a control signal 706. The telemetry circuit 701 advantageously allows intracardiac electrograms and status information relating to the operation of cardiac stimulation device 702 (as contained in the microcontroller 760 or memory 794) to be sent to the external device 705 through an established communication link 703. An internal warning device 721 may be provided for generating perceptible warning signals to the patient via vibration, voltage or other methods.

Cardiac stimulation device 702 further includes an accelerometer or other physiologic sensor 708, commonly referred to as a “rate-responsive”sensor because it is typically used to adjust pacing stimulation rate according to the exercise state of the patient. However, the physiological sensor 708 may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states) and to detect arousal from sleep. Accordingly, the microcontroller 760 can respond by adjusting the various pacing parameters (such as rate, AV delay, VV delay, etc.) at which the atrial and ventricular pulse generators, 770 and 772, generate stimulation pulses. While shown as being included within cardiac stimulation device 702, it is to be understood that the physiologic sensor 708 may also be external to cardiac stimulation device 702, yet still be implanted within or carried by the patient. A common type of rate responsive sensor is an activity sensor incorporating an accelerometer or a piezoelectric crystal, which is mounted within the housing 740 of cardiac stimulation device 702. Other types of physiologic sensors are also known, for example, sensors that sense the oxygen content of blood, respiration rate and/or minute ventilation, pH of blood, ventricular gradient, stroke volume, cardiac output, contractility, etc.

Cardiac stimulation device 702 further includes a pressure sensor 709 that can be used to detect a measure indicative of LV diastolic pressure, and more generally, afterload. For example, the pressure sensor 709 can be a sensor configured to obtain a measure of left ventricular pressure (LVP), a sensor configured to obtain a measure of left atrial pressure (LAP), a sensor configured to obtain a measure of pulmonary artery pressure (PAP), a sensor configured to obtain a measure of pulmonary venous pressure (PVP), a sensor configured to obtain a measure of pulmonary capillary wedge pressure (PCWP), but is not limited thereto. Each such pressure sensor can either perform a direct measurement of a type of pressure or a surrogate measure of the type of pressure. While shown as being included within cardiac stimulation device 702, it is to be understood that the pressure sensor 709 may be external to cardiac stimulation device 702, yet still be implanted within the patient. It is also possible that the device 702 include more than one pressure sensor 709. The pressure sensor(s) 709 can, for example, be embodied as any pressure-sensitive transducer, including, but not limited to, piezoelectric, capacitive, electromagnetic, piezoresistive, optical, mechanical electrical mechanical system (MEMS) or potentiometric transducers. The pressure sensor(s) 709 can more generally be implemented as any transducer that can obtain actual or surrogate measures of LV diastolic pressure, and more generally, afterload. For one example, a surrogate of LV diastolic pressure may be obtained from a thoracic impedance signal sensed using implanted electrodes.

The cardiac stimulation device additionally includes a battery 710, which provides operating power to all of the circuits shown in FIG. 7B. The battery 710 may vary depending on the capabilities of cardiac stimulation device 702. If the system only provides low voltage therapy, a lithium iodine or lithium copper fluoride cell typically may be utilized. For cardiac stimulation device 702, which employs shocking therapy, the battery 710 should be capable of operating at low current drains for long periods, and then be capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse. The battery 710 should also have a predictable discharge characteristic so that elective replacement time can be detected. Accordingly, appropriate batteries are employed.

As further shown in FIG. 7B, cardiac stimulation device 702 is shown as having an impedance measurement circuit 712, which is enabled by the microcontroller 760 via a control signal 714. Uses for an impedance measurement circuit include, but are not limited to, lead impedance surveillance during the acute and chronic phases for proper lead positioning or dislodgement; detecting operable electrodes and automatically switching to an operable pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance for determining shock thresholds; detecting when the device has been implanted; measuring respiration; and detecting the opening of heart valves, etc. The impedance measurement circuit 712 is advantageously coupled to the switching circuitry 774 so that any desired electrode may be used.

In the case where cardiac stimulation device 702 is intended to operate as an implantable cardioverter/defibrillator (ICD) device, it detects the occurrence of an arrhythmia, and automatically applies an appropriate electrical shock therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller 760 further controls a shocking circuit 773 by way of a control signal 779. The shocking circuit 773 generates shocking pulses of low (up to 0.1 joules), moderate (0.1-10 joules) or high energy (11 to 40 joules or more), as controlled by the microcontroller 760. Such shocking pulses are applied to the heart of the patient through at least two shocking electrodes, and as shown in this embodiment, selected from the LA coil electrode 728, the RV coil electrode 736, and/or the SVC coil electrode 738. The housing 740 may act as an active electrode in combination with the RV electrode 736, or as part of a split electrical vector using the SVC coil electrode 738 or the LA coil electrode 728 (i.e., using the RV electrode as a common electrode). Cardioversion shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with a R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of 7-40 joules), delivered asynchronously (since R-waves may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, the microcontroller 760 is capable of controlling the synchronous or asynchronous delivery of the shocking pulses.

The above described implantable device 702 was described as an exemplary cardiac stimulation device. One or ordinary skill in the art would understand that embodiments of the present invention can be used with alternative types of implantable devices. Accordingly, embodiments of the present invention should not be limited to use only with the above described device.

Embodiments of the present invention have been described above with the aid of functional building blocks illustrating the performance of specified functions and relationships thereof. The boundaries of these functional building blocks have often been defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Any such alternate boundaries are thus within the scope and spirit of the claimed invention. For example, it would be possible to combine or separate some of the steps shown in FIG. 6. For another example, it is possible to change the boundaries of some of the blocks shown in FIGS. 2A, 2B and 3.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the embodiments of the present invention. While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. A method for automatically adjusting one or more stimulation parameters to achieve a long term reduction in preload of a heart failure (HF) patient, the method comprising: (a) alternating back and forth a plurality of times between delivering stimulation in accordance with a first set of stimulation parameters, for a first time period that is long enough to allow the patient's compensatory mechanisms to react to the first set of stimulation parameters and achieve a steady-state preload corresponding to the use of the first set of stimulation parameters, anddelivering stimulation in accordance with a second set of stimulation parameters, for a second time period that is long enough to allow the patient's compensatory mechanisms to react to the second set of stimulation parameters and achieve a steady-state preload corresponding to the use of the second set of stimulation parameters, and(b) obtaining a first measure indicative of the patient's preload achieved using the first set of stimulation parameters, anda second measure indicative of the patient's preload achieved using the second set of stimulation parameters;(c) selecting one of the first and second sets of stimulation parameters in dependence on a comparison of the first measure indicative of the patient's preload achieved using the first set of stimulation parameters and the second measure indicative of the patient's preload achieved using the second set of stimulation parameters;wherein at least steps (c) and (d) are performed automatically using one or more processors.

2. The method of claim 1, further comprising: (d) selecting a new set of stimulation parameters to replace the one of the first and second sets of stimulation parameters not selected at step (c); and(e) repeating steps (a) through (c) one or more times, wherein each time step (a) is repeated, one of the first and second sets of stimulation parameters used at step (a) comprises the set of stimulation parameters most recently selected at step (c), and the other one of the first and second sets of stimulation parameters used step (a) comprises the new set of stimulation parameters most recently selected at step (d).

3. The method of claim 1, wherein the length of each first time period, and the length of each second time period, is one full day.

4. The method of claim 1, wherein the length of each first time period, and the length of each second time period, is at least 1 hour.

5. The method of claim 1, wherein the length of each first time period is at least one hour.