Patent Application
20130190582
1. Field of the Invention
The present invention generally relates to ischemia detection, and in particular to detection of ischemic heart regions based on constituent concentration measurements in coronary venous blood.
2. Description of the Prior Art
Ischemia is the lack of oxygen supply to cells. In animals, including humans, the underlying cause of ischemia is typically a cardiovascular disease, where blood vessels may be affected by atherosclerosis. Cardiac ischemia is caused by restriction of blood flow in the coronary blood vessel, e.g. due to atherosclerosis. This reduced blood flow and the resulting lack of oxygen to the myocytes in the heart may lead to several effects, including contractile dysfunction and hibernating cells. These various effects may in turn decrease the hemodynamic performance of the heart, which ultimately can result in worsening heart failure and further decrease in pumping capacity.
Ischemic heart disease (IHD) is very common. IHD may be symptomatic, such as in angina pectoris, causing the patient to experience severe discomfort and pain. However, a majority of ischemic periods are silent and therefore hard to detect and classify. Most ischemic episodes, regardless of being symptomatic or silent, are reversible but still influence the risk of arrhythmias, the functional state and long-term remodeling of the heart.
A common technique in the art to detect cardiac ischemia is to measure oxygen saturation (SO2) in coronary sinus blood, such as disclosed in U.S. Pat. No. 5,156,148; U.S. Pat. No. 5,199,428; US 2005/0154370; US 2008/0177194 and EP 1 386 637. These prior art documents generally state that cardiac ischemia is detected as a decrease in SO2 in the coronary sinus blood.
The prior art techniques basically operate according to an on-off principle. In other words, they either detect presence of an ischemic event or they conclude that there is no detectable ischemic event. However, it is generally preferred to be able to obtain a more accurate detection of the particular heart region where the ischemic event takes place. Such detailed ischemic analysis is not possible or at least very hard with to the above mentioned prior techniques.
It is a general objective to enable detection of the particular region of a heart that suffers from an ischemic event.
This and other objectives are met by embodiments as disclosed herein.
An aspect of the embodiments relates to an ischemia detecting system comprising an implantable medical device comprising a connector. The connector is connectable to a left ventricular cardiac catheter equipped with at least two sensor elements arranged on the catheter to be positioned on either side of a branching vein in the coronary venous system of a subject's heart. A first sensor signal is generated for the first sensor element to be representative of the concentration of a constituent in coronary venous blood in a first portion of the coronary venous system. A corresponding second sensor signal is generated for the second sensor element to be representative of the concentration of the constituent in coronary venous blood in a second, different portion of the coronary venous system. The sensor signals are stored in a memory of the implantable medical device and are co-processed by an ischemic region detector. The ischemic region detector is configured to detect an ischemic heart region based on a relation between the sensor signals.
Another aspect of the embodiments defines a method of detecting ischemia. The method comprises recording a first sensor signal representative of the concentration of a constituent in coronary venous blood in a first portion of the coronary venous system of a subject's heart at a site on a first side of a branching vein of the coronary venous system. A second sensor signal representative of the concentration of the constituent in coronary venous blood is recorded for a second portion of the coronary venous system at a site on a second, opposite side of the branching vein. The sensor signals are then co-processed to detect an ischemic region of the heart based on a relation between the sensor signals.
The embodiments are thereby able to not only detect the presence of cardiac ischemia but are also able to identify the particular region of the heart where the ischemia has occurred. This provides valuable diagnostic information and can also be used as a basis for more effective treatment.
The embodiments generally relate to ischemia detection, and in particular to detection of ischemic heart regions based on constituent concentration measurements in coronary venous blood or, as it is sometimes denoted, coronary sinus blood.
The ischemia detection of the embodiments enables identification of the particular heart region where an ischemic event has occurred. Hence, the embodiments enable pinpointing the particular region in the heart that has suffered from ischemia. The detailed information of the particular ischemic heart region constitutes valuable diagnostic information to the patient's physician in determining appropriate therapy to the patient and detecting any trend or worsening heart condition that may subsequently lead to severe conditions, such as myocardial infarction or heart failure. The localization of the ischemic heart region is also of value in selecting a particular pacing mode for a pacemaker or implantable cardioverter-defibrillator (ICD) of the patient.
The embodiments therefore provide a significant improvement to the prior art ischemia detecting systems that basically only are able to detect the presence or absence of cardiac ischemia but without any further detailed information of in which part of the heart the ischemia has occurred.
The IMD 100 is in operation connected to a left ventricular (LV) cardiac catheter or lead 20 comprising multiple, i.e. at least two, sensor elements 30, 32 arranged at different positions on the LV cardiac catheter 20. These sensor elements 30, 32 are employed by the ischemia detecting system 1 in order to monitor the concentration of a selected constituent in coronary venous blood in different parts of the coronary venous system of the heart 15.
The LV cardiac catheter 20 could be a dedicated sensor-carrying catheter. Alternatively, the LV cardiac catheter 20 not only carries the sensor elements 30, 32 but is also used by the IMD 100 for providing cardiac therapy and/or monitoring. For instance, the LV cardiac catheter could be an LV cardiac lead 20 having at least one electrode 22, 24, typically denoted pacing and sensing electrode 22, 24 in the art. In such a case, the IMD 100 is able to deliver pacing pulses to the left ventricle of the heart 15 and sense electrical activity from the left ventricle via the electrode(s) 22, 24 of the LV cardiac lead 20. As is well known in the art, an LV cardiac lead 20 is generally implanted via the coronary venous system. Hence, the LV cardiac lead 20 is therefore highly suitable to carry the sensor elements 30, 32 to position these sensor elements 30, 32 at different positions within the coronary venous system to enable monitoring of the constituent concentration in coronary venous blood.
The IMD 100 can also be connected to other cardiac leads, for instance a right ventricular (RV) cardiac lead and/or an atrial cardiac lead (not illustrated). An RV cardiac lead is typically provided inside the right ventricle of the heart 15 and comprises one or more electrodes that can be used by the IMD 100 to apply pacing pulses to the right ventricle and/or sense electrical activity from the right ventricle. An atrial cardiac lead, typically a right atrial (RA) cardiac lead having at least one electrode arranged in or in connection with the right atrium, can be used by the IMD 100 in order to provide atrial pacing and/or sensing. Instead of or as a complement to an RA cardiac lead, the IMD 100 can be connected to a left atrial (LA) cardiac lead.
The communication module 210 and the data processing device 200 can be separate devices as illustrated in
In a general aspect of the embodiments an ischemia detecting system comprises an implantable medical device comprising a connector that is connectable to an LV cardiac catheter comprising at least a first sensor element and a second sensor element arranged on the LV cardiac catheter. The sensor elements are provided on the LV cardiac catheter to be positioned on either side of a branching vein in the coronary venous system of the subject's heart when the LV cardiac catheter is implanted in the coronary venous system. The first sensor element and the second sensor element either constitute a respective sensor, i.e. the LV cardiac catheter comprises at least a first sensor and a second sensor, or the at least two sensor elements are connectable to a common sensor of the ischemia detecting system. In the former case, the first sensor is configured to generate a first sensor signal representing a concentration of a selected constituent in coronary venous blood in a first portion of the coronary venous system. The second sensor is correspondingly configured to generate a second sensor signal representing a concentration of the constituent in coronary venous blood in a second, different portion of the coronary venous system. In the latter case the common sensor is configured to generate the first sensor signal for the first sensor element and generate the second sensor signal for the second sensor element. The implantable medical device also comprises a memory configured to store the first and second sensor signals. The ischemia detecting system comprises an ischemic region detector configured to co-process the first sensor signal and the second sensor signal to detect an ischemic region of the heart based on a relation between the first sensor signal and the second sensor signal.
Thus, by conducting the constituent concentration measurements at different sites in the coronary venous system and having the sensor elements present on either sides of a branching vein in the coronary venous system, the ischemia detecting system can detect a particular region of the heart that is suffering from ischemia by co-processing the sensor signals and in particular based on a relation between the sensor signals.
For instance, if the first (or second) sensor signal recorded by the first (or second) sensor or the common sensor for the first (or second) sensor element indicates a significant change in the concentration of the constituent while the other sensor signal does not indicate any change or at least a much lesser change in the concentration of the constituent it is possible to locate an ischemic region to be present at a portion of the heart between the positions of the two sensor elements.
The IMD 100 comprises a connector 110 connectable to the LV cardiac catheter and therefore comprises connector terminals 115-117 configured to be connected to the sensor elements of the LV cardiac catheter. In
In an embodiment, each sensor element constitutes a respective sensor. Hence, the LV cardiac catheter then comprises at least a first sensor and a second sensor arranged on the LV cardiac catheter to be positioned on either side of the branching vein in the coronary venous system. The first sensor then generates the first sensor signal representing the concentration of the selected constituent in coronary venous blood in the first portion of the coronary venous system and the second sensor generates the second sensor signal representing the concentration of the selected constituent in coronary venous blood in the second portion of the coronary venous system. The connector 110 then preferably comprises a respective connector terminal 115-117 for each of the sensors along the LV cardiac catheter.
In another embodiment, the LV cardiac catheter comprises a common sensor that is connected to each sensor element. The common sensor could then be positioned anywhere along the LV cardiac catheter but is typically proximally arranged relative to the sensor elements, i.e. closer to the end of the LV cardiac catheter that is to be connected to the IMD 100 and the connector 110 as compared to the positions of the sensor elements on the LV cardiac catheter. Each sensor element then comprises at least one respective sensor connection to the common sensor. The common sensor generates the sensor signals for each of the sensor elements and forwards them to the connector 110. In such a case, it could be sufficient to only include a single connector terminal 115-117 in the connector 110 that is connectable to the common sensor, although multiple parallel connector terminals 115-117 to the common sensor are indeed possible.
A further embodiment houses a common sensor not on the LV cardiac catheter but rather within the housing of the IMD 100. Each sensor element on the LV cardiac catheter then preferably comprises at least one respective connection to the common sensor through at least one respective connector terminal 115-117 in the connector 110. The common sensor (not illustrated) in the IMD 100 then generates the sensor signals for the different sensor elements.
The selected constituent which is monitored by the at least one sensor can be any substance or molecule present in coronary venous blood and that can be used for ischemia detection. A particular preferred example of such constituent is to monitor oxygen concentration in coronary venous blood. The at least one sensor is then an implantable oxygen sensor. The implantable oxygen sensor does not necessarily have to be able to produce a sensor signal that represents an absolute oxygen concentration value. It is sufficient if the implantable oxygen sensor can be used to monitor variations in oxygen concentration and thereby produce a sensor signal that represents relative oxygen concentration values.
There are various implantable oxygen sensors disclosed in the art and that can be used according to the embodiments. For instance, the implantable oxygen sensor can be a partial oxygen pressure (pO2) sensor, such as an electrochemical pO2 sensor, or a sensor that measures oxygen saturation (SO2), such as an optical SO2 sensor, or indeed any other type of implantable sensor that outputs a sensor signal that represents variations of oxygen concentration in venous blood in the coronary venous system.
In an embodiment, the implantable oxygen sensor could use a measurement sampling frequency to generate an oxygen concentration sample every heartbeat, or multiple such samples per heartbeat. Also a low sampling frequency could be used, such as every second heart beat or even lower. Instead of basing the sampling frequency on the heart rate, the implantable oxygen sensor could generate a measurement sample once every 0.1-10 seconds as illustrative but non-limiting examples.
In an embodiment, the LV cardiac catheter comprises multiple oxygen sensors each generating a respective sensor signal as previously discussed herein. The oxygen sensors could then, for instance, be electrochemical pO2 sensors or indeed optical SO2 sensors. If a common oxygen sensor is to be used, either arranged on the LV cardiac catheter or inside the housing of the IMD 100, the common oxygen sensor is preferably an optical SO2 sensor. In such a case, one or a pair of optical fibers runs from the common optical SO2 sensor up to each sensor element along the LV cardiac catheter. Light with a particular wavelength is produced by the common SO2 sensor, such as a diode of the common SO2 sensor, and guided to each sensor element by a respective optical fiber. Returning light is then forwarded by these optical fibers or the other optical fibers in the case of a pair of optical fibers per sensor element back to the common SO2 sensor for generating the sensor signals.
Alternatively other substances besides oxygen could be monitored and used by the ischemia detecting system 1. Examples of such other substances include nitric oxide (NO) and carbon dioxide (CO2) in coronary venous blood.
The connector 110 may additionally comprise connector terminals 111-114 configured to be connected to matching electrode terminals electrically connected to electrodes on one or more cardiac leads. With reference to
The IMD 100 also comprises a memory 170 that is configured to store the first and second sensor signals. The memory 170 is therefore directly, or as indicated in
In the embodiment illustrated in
In an embodiment, the ischemic region detector 132 performs the co-processing based on a relation between the concentration of the selected constituent in coronary venous blood in a first portion of the heart as represented by the first sensor signal and the concentration of the constituent in coronary venous blood in a second portion of the heart as represented by the second sensor signal.
The co-processing of the first and second sensor signal can be based on calculating a respective average concentration value with regard to the selected constituent in coronary venous blood. Thus, each sensor signal is preferably in the form of a series of signal samples having a respective sample value representing the concentration of the constituent in coronary venous blood. In such a case, the average concentration value can be calculated based on a defined number of, preferably consecutive, signal samples in the sensor signal or based on multiple, preferably consecutive, signal samples in the sensor signal recorded during a defined period of time. The relation between these average concentration values obtained from the first and second sensor signals are then preferably used by the ischemic region detector 132 to identify the correct region of the heart where ischemia has occurred. Averaging the concentration suppresses noise and other disturbing effects in the sensor signals that might occur due to temporary phenomena that are not related to ischemia.
An example of co-processing is to compare a quotient or difference between the (average) constituent concentrations obtained from the sensor signals with a threshold value. This threshold value is then preferably stored in the memory 170 and represents a previously calculated quotient or difference between the (average) constituent concentrations obtained from the sensor signals at a point in time when the heart was not suffering from ischemia. Thus, assume that C1 represents the (average) concentration of the constituent in coronary venous blood in the first portion of the heart represented by the first sensor signal and C2 represents the (average) concentration of the constituent in coronary venous blood in the second portion of the heart represented by the second sensor signal. The ischemic region detector 132 could compare
with the threshold value T1 or compare (C1−C2) (or (C2−C1)) with the threshold value T2.
For instance, in a non-ischemic condition the quotient
is typically equal to or at least close to a normal or default value, represented by the threshold value T1. However, if an ischemic event occurs in the second heart region (but does not affect the first heart region) the coronary venous blood flow past the second sensor element will drop significantly, thereby reducing the amount of the selected constituent that is detected via the second sensor element. The average concentration value C2 will thereby drop significantly. As a result the quotient
will increase significantly above the threshold value T1, i.e. be larger than T1+ΔT where ΔT represents a hysteresis margin to indicate that the normal value of the quotient can fluctuate within the interval T1±ΔT during normal, non-ischemic conditions.
A significant rise in the quotient thereby indicates that an ischemic event has occurred in a region of the heart that affects the concentration of the constituent in the coronary venous blood at the position of the second sensor element but does not significantly affect the concentration of the constituent at the position of the first sensor element in the coronary venous system. Correspondingly, a significant drop in the quotient indicates that an ischemic event has occurred in a region of the heart that affects the concentration of the constituent in the coronary venous blood at the position of the first sensor element but does not significantly affect the concentration of the constituent at the position of the second sensor element in the coronary venous system.
A somewhat smaller rise or drop in the quotient also provides valuable information by indicating that the ischemic event in particular affects the second heart region (in the case of a small rise) or the first heart region (in the case of a small drop) but also, but to a lesser extent, affects the concentration of the constituent in the first heart region (in the case of a small rise) or the second heart region (in the case of a small drop).
This information can be used to accurately pinpoint and detect the region of the heart where the ischemia is present. This is possible since the positions of the different sensing elements along the LV cardiac catheter is known and also the particular vein of the coronary venous system in which the LV cardiac catheter is present.
In an embodiment, the IMD 100 comprises a variability calculator 134, see
During an occlusion in a blood vessel of the coronary venous system causing a local ischemia the variability in the concentration of the constituent will significantly increase as compared to during normal, healthy conditions. Hence, co-processing in the form of performing the detection based on the relation between variability values can be used according to the embodiments.
In connection with a temporary ischemic event, there is generally a variation in oxygen concentration in coronary venous blood. First, if there is an occlusion of a blood vessel, thereby reducing the blood flow there is an initial decrease in oxygen concentration in coronary venous blood. Correspondingly, if there is a mismatch between the demands for and the supply of oxygen to a portion of the heart ischemia may occur and is initially detectable as reduction in oxygen concentration in coronary venous blood. Such a mismatch between oxygen supply and demand can be due to occlusions in blood vessels, increased oxygen consumption by the myocytes and/or local coagulation disturbances. Secondly, following the temporary ischemic event there is a reperfusion causing an increase in oxygen concentration above the normal levels in coronary venous blood. Hence, a temporary ischemic event generally causes an initial reduction in oxygen concentration below the normal or baseline level followed by a temporary increase in oxygen concentration above the normal level and then a reduction of the oxygen concentration back to the normal level.
If the ischemia detecting system 1 is configured to generate sensor signals representing the concentration of oxygen in coronary venous blood from various regions of the coronary venous system the co-processing of the sensor signals does not necessarily have to be in the form of detecting a significant decrease in oxygen concentration at one or more of the monitoring sensor element sites. It could actually be advantageous to detect a local ischemic region by an initial and temporary decrease in oxygen concentration for that site below the normal baseline concentration followed by an increase in oxygen concentration above the normal baseline concentration and then return back to the normal baseline concentration. Such an approach improves sensitivity in the ischemia detection and the determination of the ischemic heart region as compared to base the detection and determination solely on a decrease in oxygen concentration, i.e. without any following, temporary increase in oxygen concentration above the baseline concentration. The reason is that certain events, such as increased patient activity, can cause a temporary decrease in oxygen concentration although no cardiac ischemia is present. However, such activity-induced temporary reductions in oxygen concentrations generally return back to the baseline concentration without any intermediate overshoot or increase in oxygen concentration before the return to the baseline concentration.
In another embodiment, the LV cardiac catheter 20 is implanted into the lateral vein of the left ventricle. At this position in the coronary venous system the first sensor element is preferably positioned in the coronary sinus or in the great cardiac vein while the second sensor element is positioned in the lateral vein. With such an implantation site for the LV cardiac catheter 20 it could be beneficial to have more than two sensor elements along the LV cardiac catheter 20. Thus, a third sensor element is preferably arranged on the LV cardiac catheter 20 in addition to the first and second sensor elements. This third sensor element can constitute a third sensor or is connectable to the common sensor arranged proximally on the LV cardiac catheter 20 or inside the housing of the IMD. The third sensor or the sensor connected to the third sensor element then generates a third sensor signal representing a concentration of the constituent in coronary venous blood in a third portion of the coronary venous system. The first sensor element is preferably arranged on the LV cardiac catheter 20 to be positioned in the coronary sinus upstream of the posterior vein of the left ventricle and with the third sensor element configured to be positioned in the coronary sinus or the great cardiac vein but downstream of the posterior vein.
The memory 170 of the IMD 100, see
In another embodiment, the LV cardiac catheter 20 is configured to be implanted in the anterior interventricular vein of the heart. The first sensor element could be arranged on the catheter to be position in the coronary sinus or in the great cardiac vein whereas the second sensor element could be arranged on the catheter to be positioned in the anterior interventricular vein. Also this embodiment could benefit from having at least one additional sensor element in addition to the first and second sensor element. The first sensor element is then preferably positioned in the coronary sinus upstream of the posterior vein of the left ventricle and the third sensor element is positioned in the coronary sinus or in the great cardiac vein downstream of the posterior vein. Alternatively, the first sensor element is positioned in the coronary sinus or in the great cardiac vein upstream of the lateral vein of the left ventricle and the third sensor element is positioned in the great vein downstream of the lateral vein. These embodiments may in fact be combined by having access to more than three sensor elements along the LV cardiac vein. Sensor elements can then be present in the coronary sinus or in the great cardiac vein at positions selected among upstream of the small and middle cardiac vein, downstream of the small and middle cardiac vein but upstream of the posterior vein of the left ventricle, downstream of the posterior vein of the left ventricle but upstream of the lateral vein of the left ventricle, and downstream of the lateral vein of the left ventricle. In addition, or alternatively different sensing positions are possible along the anterior interventricular vein.
As is evident from the discussion presented above, in a general embodiment the connector 110 of the ischemia detecting system 1 in
The memory 170 is configured to store these N sensor signals and the ischemic region detector 132 is configured to co-process the N sensor signals as disclosed herein to detect the ischemic region of the heart based on a relation between the N sensor signals.
In a particular embodiment the ischemia detecting system 1 comprises an activity sensor 165 preferably provided inside the housing of the IMD 100 but can alternatively be attached to the outside surface of the housing, be arranged on the LV cardiac catheter or otherwise connected to the IMD 100 through the connector 110.
The activity sensor 165 is configured to generate an activity signal representative of a current activity level of the subject. The ischemic region detector 132 is then responsive to the activity signal and is configured to perform the co-processing of the sensor signals to detect the ischemic heart region if the current activity level of the subject as defined by the activity signal exceeds an activity threshold level. Thus, in this embodiment the ischemia region detecting operation of the ischemia detecting system 1 is only performed when the subject is active and exercises at a level that corresponds at least to the activity threshold level, which is advantageously defined in the memory 170.
A reason for limiting the ischemia region detection to active periods for the subject is that certain ischemic events, in particular rather mild ischemic episodes, only appears and are detectable if the subject is active, such as up and walking.
As an alternative to limiting the ischemia region detection to active periods, the ischemic region detector 132 could perform the co-processing of the sensor signals and the ischemic heart region detection regardless of the current activity level of the subject. However, information of the detected ischemic heart region, such as represented by information of which sensor element(s) that has(have) indicated a significant change in the constituent concentration in coronary venous blood, could be tagged with information of the current activity level, i.e. is associated with a current, optional average, activity signal value.
The activity level information can then be used together with information of the ischemic heart region by the physician to determine any trends in the condition of the heart and select appropriate combating actions if a deterioration is evident.
The ischemic region detector 132 generates, in an embodiment, a notification of the detected heart region. This notification could be a simple identifier of the sensor elements (or sensors) detecting a significant change in the concentration of the constituent in coronary venous blood. Alternatively the memory 170 is preprogrammed with information of, for each sensor element, which heart region(s) that get its(their) blood supply from particular blood vessel in which the sensor element is present. In such a case, the notification can comprise information of such a detected heart region. The notification may additionally comprise information of the current activity level of the subject as discussed in the foregoing.
The IMD 100 could then comprise a message generator 136 configured to generate a notification message comprising the notification of the detected ischemic heart region. The message generator 136 could be configured to generate the notification message in response to the ischemic region detector 132 detecting the ischemic heart region, i.e. basically generating the notification directly following the ischemia detection. The notification message could then be regarded as an alarm message that will inform the subject or the subject's physician in real time of any ischemic periods and regions. The notification message is wirelessly transmitted by a transmitter or transceiver (TRX) 190 to the data processing device (see
The IMD 100 could alternatively store the notifications and any additional information descriptive of the detected ischemic events in the memory 170 to form a register of the subject's ischemia burden. The collected information is then uploaded when the patient visits his/her physician and is used as diagnostic information and/or for determination of optimal drug titration, device settings for the subject or planning revascularization procedures.
In addition to or as a complement to generating notifications of detected ischemic events, the IMD 100 could initiate cardiac therapy to combat or compensate for the ischemic event. The IMD 100 then comprises a pulse generator 140, represented by a ventricular pulse generator 140 in
The pulse generator 140 is connected to and controlled by a pulse generator controller 130, represented by a general controller 130 in
The default pacing mode is the traditional pacing mode selected for the subject by the physician based on the particular cardiac disease of the subject. This means that the pulse generator controller 130 mainly operates according to this default pacing mode. However, in connection with a detected ischemic heart region as signaled by an ischemia signal generated by the ischemic region detector 132 in response to the detection of an ischemic heart region, the pulse generator controller 130 switches to the ischemic pacing mode. The controller 130 could include a dedicated mode selector 138 that is responsive to the ischemia signal and triggers a switch to the ischemia pacing mode based on the ischemia signal.
Compared to the default pacing mode, the ischemic pacing mode could provide a reduced load on the myocardium of the heart, for instance by reducing the maximum tracking rate or the rate response function used in the default pacing mode. Furthermore, or alternatively, the IMD 100 could be configured to be more sensitive to any arrhythmia events when operating in the ischemic pacing mode as compared to the default pacing mode. Generally, the IMD 100 comprises an intracardiac electrogram (IEGM) processor or circuit 160 connected to the connector 110 and configured to generate an IEGM signal based on electrical activity of the heart sensed by at least one electrode connected to the connector 110. The controller 130 could then process the IEGM signal to determine a current heart rate of the subject's heart.
Arrhythmia detection is traditionally performed by an IMD 100 if the current heart rate exceeds a predefined rate threshold. The IMD 100 could then use two different such rate thresholds, one rate threshold during the default pacing mode and another, typically lower rate threshold during the ischemic pacing mode.
The controller 130 advantageously switches back from the ischemic pacing mode to the default pacing mode after the end of the detected ischemic event. This switch back to the default pacing mode preferably occurs following a defined time period from when the ischemic region detector 132 detects the end of the ischemic event, i.e. when the constituent concentration in coronary venous blood has returned back to the normal concentration level at all sensor element sites. The length of this defined time period is preferably programmed into the IMD 100 by the subject's physician.
The IMD 100 as illustrated in
The IMD 100 may optionally also comprise a corresponding atrial pulse generator and an atrial sensing circuit (not shown in
The ventricular and optional atrial sensing circuits 150 of the IMD 100 may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. The electronic configuration switch 120 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 physician may program the sensing polarity independent of the stimulation polarity. The sensing circuits are optionally capable of obtaining information indicative of tissue capture.
Each sensing circuit 150 preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, band-pass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest.
The outputs of the ventricular and optional atrial sensing circuits 150 are connected to the controller 130, which, in turn, is able to trigger or inhibit the ventricular and optional atrial pulse generators 140, respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart.
The controller 130 of the IMD 100 is preferably in the form of a programmable microcontroller 130 that controls the operation of the IMD 100. The controller 130 typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of pacing therapy, and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, the controller 130 is configured to process or monitor input signals as controlled by a program code stored in a designated memory block. The type of controller 130 is not critical to the described implementations. In clear contrast, any suitable controller 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.
Furthermore, the controller 130 is also typically capable of analyzing information output from the sensing circuits 150 to determine or detect whether and to what degree tissue capture has occurred and to program a pulse, or pulse sequence, in response to such determinations. The sensing circuits 150, in turn, receive control signals over signal lines from the controller 130 for purposes of controlling the gain, threshold, polarization charge removal circuitry, and the timing of any blocking circuitry coupled to the inputs of the sensing circuits 150 as is known in the art.
The optional electronic configuration switch 120 includes a plurality of switches (not shown) for connecting the desired connector terminals 111-117 to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, the electronic configuration switch 120, in response to a control signal from the controller 130, determines the polarity of the stimulating pulses by selectively closing the appropriate combination of switches as is known in the art.
While a particular IMD 100 is shown in
The IMD 100 additionally includes a battery 180 that provides operating power to all of the circuits shown in
In
In an alternative approach, the units 132-138 are implemented as hardware circuits in the IMD 100, preferably connected to the controller 130, such as in the form of special purpose circuits, such as ASICs (Application Specific Integrated Circuits).
In the embodiment discussed above and disclosed in
In such a case, the IMD 100 preferably provides the sensor signals as previously disclosed herein and stores them in the memory 170. Data representing these sensor signals, such as the sample values or a calculated average signal sample per sensor signal, is then composed by the message generator 136 into data packets that are transmitted by the transceiver 190 of the IMD 100 to a receiver or transceiver 210 of or connected to the data processing device 200. In this embodiment, the data processing device 200 comprises the ischemic region detector 232 and the optional variability calculator 234. The operation of these units 232, 234 are basically the same as previously disclosed herein.
In the embodiment of
In particular, the information of ischemic heart regions can be used for titration of medicaments to the subject by monitoring the effect of medicament administration on cardiac ischemia. For instance, administration of correct amounts of medicaments to treat hypertension is not trivial. Too low levels of the medicament will not have the desired effect of reducing the blood pressure. However, if too high levels of the medicament is administered the blood pressure can be reduced too much so that blood supply in the coronary vascular system is not efficiently maintained and ischemia may occur. The information generated by the ischemic region detector 232 can therefore be used, among others, to verify correct levels of administered medicaments, such as anti-hypertensive drugs and anti-coagulants.
The recording of the sensor signals are preferably performed during a predefined time or until a predefined number of signal samples have been obtained as indicated by the line L1.
The sensor signals recorded in steps S1 and S2 are then co-processed in step S2 to detect an ischemic heart region based on a relation between the sensor signals as previously disclosed herein.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
