Patent Application
20100280563
1. Field of the Invention
The present invention generally relates to cardiac pacing systems and, in particular, to methods and medical devices for detecting and treating myocardial infarctions.
2. Description of the Prior Art
Due to the in general poorer medical status of pacemaker and ICD patients they are subjected to an increased risk of myocardial infarction (MI). The term myocardial infarction refers to the death of myocardial or heart tissue caused by a partial or complete blockage of in one the arteries that supply blood to the heart (coronary arteries), resulting in an interruption in the blood supply to the heart. In the classical acute MI there is a sudden occlusion of a coronary artery due to thrombosis resulting in the death of part of either the right or left ventricular wall. The thrombus occurs due to atheromatous changes in the blood vessel wall.
When heart tissue is deprived of blood-borne oxygen for longer than 30 minutes (called ischemia), it begins to die. Ischemia causes electrical instability within the chambers of the heart, preventing the heart from adequately pump blood throughout the body.
Cardiac repair after MI is a complex process involving diverse inflammatory components, extracellular matrix remodelling and responses of the cardiomyocytes to ischemia. After necrosis of the cardiomyocytes and a long inflammatory phase, the ischemic zone is subsequently replaced by fibrotic tissue. This permanent damage of the heart muscle increases the risk of developing congestive heart failure (CHF).
It is critical to begin treatment of the areas affected by ischemia as soon as possible after the myocardial infarction. Intensive research over the last 20 or more years has demonstrated that prompt treatment can decrease damage from a heart attack and increase the chance for survival. If such therapy is initiated within 1 hour of the inset of symptoms, less irreparable damage may occur.
In light of this, a number of approaches have been made to detect and/or to treat myocardial infarction in implantable medical devices such as pacing devices. For example, in EP 467 695 A2 a method and apparatus for detecting and treating myocardial infarctions in antitachy-arrhythmia and bradycardia pacing devices are disclosed. Electrical activity of the patient's heart is sensed and signalled in order to detect the presence of an MI and a thrombolytic drug is released into the bloodstream upon such detection. Thus, this solution improves the supply of blood at the detection of an MI but, however, it does not treat potential damages of the cardiac tissue caused by the MI.
In EP 1 384 433, by the same applicant, a monitor for early detection of an ischemic heart disease of a patient using intracardiac impedance is shown. According to this solution, the impedance changes due to the increased stiffness of the cardiac tissue caused by the ischemic heart disease are detected. However, EP 1 384 433 is not concerned with the treatment of a detected ischemia.
Furthermore, EP 1 690 566, U.S. Pat. No. 6,604,000 and U.S. Pat. No. 6,256,538 also present implantable medical devices incorporating an ischemia detector responsive to measured intracardiac impedance.
US 2004/0260367 shows a method for treating a detected myocardial infarction of a patient's heart. According to this solution, a light source adapted to generate therapeutic light in the visible to near-infra-red wavelength range using so called low level light therapy (“LLLT”) or phototherapy is positioned relative to the patient's heart on the torso of the patient. The therapeutic light penetrates the intervening tissue and the cardiac tissue is irradiated according to a treatment protocol. Thus, the solution according to US 2004/0260367 is impaired with the problem that a detection of the myocardial infarction and a determination of the location of the myocardial infarction are required before the treatment can be initiated. As discussed above, the heart tissue begins to die if it is deprived of blood-borne oxygen for longer than 30 minutes and hence it is critical to begin treatment of the areas affected by ischemia as soon as possible after the myocardial infarction. Therefore, the cardiac tissue may already have been affected with damages, which may be irreparable, when the treatment can be initiated.
Thus, there remains a need within the art of a method and medical device that are capable of detecting the occurrence and location of a myocardial infarction and initiating a treatment of the cardiac tissue suffering from the myocardial infarction subsequently to the detection.
An object of the present invention is to detect the occurrence and location of a myocardial infarction is detected and to administer a treatment to the cardiac tissue suffering from the myocardial infarction is initiated.
According to another object of the present invention, the occurrence and location of a myocardial infarction is automatically detected and a treatment of the cardiac tissue suffering from the myocardial infarction is automatically initiated subsequently to the detection.
According to a further object of the present invention, a commencement of a myocardial infarction and the location of the myocardial infarction can be detected at an early stage.
According to an aspect of the present invention, there is provided an implantable medical device including a pulse generator emits cardiac stimulating pacing pulses and that is connectable to at least one medical lead for delivering the pulses to cardiac tissue of a heart of a patient. The implantable medical device has a myocardial infarction detection means, which myocardial infarction detection unit that detects a myocardial infarction and identifies a location of the myocardial infarction. Further, the implantable medical device has therapy circuitry connected to a number of light emitting units arranged in the at least one medical lead adapted to emit therapeutic light, and a control circuit connected to the myocardial infarction detection unit and to the light emitting units, the control circuit being configured to initiate a therapy session in which one or more of the light emitting units is/are selectively activated to emit the therapeutic light toward a detected location of the myocardial infarction upon detection of an occurrence of the myocardial infarction.
According to a second aspect of the present invention, there is provided a method for treating cardiac tissue of a heart of a patient with therapeutic light using an implantable medical device including a pulse generator adapted to produce cardiac stimulating pacing pulses and being connectable to at least one medical lead for delivering the pulses to cardiac tissue of a heart of a patient. The method includes the steps of intracorporeally detecting a myocardial infarction and identifying a location of the myocardial infarction, and initiating a therapy session by selectively activating one or more of a number of intracorporeally placed light emitting units arranged in the at least one medical lead to emit therapeutic light toward the detected location of the myocardial infarction upon detection of an occurrence of the myocardial infarction.
According to a third aspect of the present invention, there is provided a computer-readable medium, directly loadable into an internal memory of an implantable medical device according to the first aspect of the present invention, encoded with software code that causes the implantable medical device to perform steps in accordance with a method according to the second aspect of the present invention.
The invention utilizes the technique photobiomodulation, also called Low Level Laser Therapy (LLLT), Cold Laser Therapy (CLT), Laser Biomodulation, phototherapy or Laser therapy, wherein certain wavelengths of light at certain intensities are delivered for a certain amount of time. More specifically, the present invention is based on the insight of using such therapeutic light to treat cardiac tissue after a myocardial infarction. This is based upon the findings that photobiomodulation has been proven to be a successful therapy in wound healing see, for example, “Effect of NASA light-emitting diode irradiation on wound healing”, H. T. Whelan et al., Journal of Clinical Laser Medicine and Surgery, 19, (2001) p 305. It was also confirmed by Whelan et al. that the cell growth of various cell types in human and rat could be increased by up to 200% by irradiation of light of certain wavelengths. Furthermore, it has also been shown, for example, in “Low energy laser irradiation reduces formation of scar tissue after myocardial infarction in rats and dogs”, U. Oron, et al., Circulation, 103, (2001), p 296, that light therapy improves the regeneration of the cardiac cells and decreases the scar tissue formation following a myocardial infarction.
Thus, the present invention provides a number of advantages, for example, an occurrence and location of a myocardial infarction can be detected at an early stage and the treatment of the myocardial infarction can thus be initiated at an early stage. This is of high importance since it has been shown that it is critical to initiate the treatment of the areas of cardiac tissue affected by ischemia as soon as possible after the myocardial infarction. Intensive research over the last 20 or more years has demonstrated that prompt treatment may decrease damage from a heart attack and increase the chance for survival. If a therapy is initiated within 1 hour of the onset of the infarct, less irreparable damage may occur. A further advantage of the present invention is that the regeneration of cardiac cells after a myocardial infarction is improved.
According to an embodiment, the therapy circuit is adapted to activate the light emitting unit or units to emit the therapeutic light according to a treatment protocol, wherein the treatment protocol includes treatment parameters comprising: emitting intervals of the therapeutic light, intensity of the emitted therapeutic light, wavelength of the emitted light, and/or intermittence of the emitted therapeutic light.
In one embodiment, each of the light emitting units is formed by at least one light emitting diode. The light emitting units, according to other embodiments, may be arranged in an array along an outer surface of a lead body of respective medical lead.
According to an embodiment of the present invention, the electrodes are arranged in an array along the outer surface of a lead body of respective medical lead.
In a further embodiment, each of the light emitting units includes at least one optical fiber adapted to conduct light emitted from at least one light source arranged in the implantable medical device, and the therapy circuit selectively activates the at least one light source and/or at least one optical fibre such that light conducted in one or more optical fibres emanates from the one or more optical fibers toward the detected location.
The at least one light source may be a laser source adapted to emit coherent and monochromatic light having a wavelength in the range of 600 nm-1000 nm. Furthermore, in one embodiment, an intensity of 1-500 mW/cm2 and a total dosage of about 1-4 J/cm2 are applied. In another embodiment, an intensity of 6-50 mW/cm2 and a total dosage of about 1-4 J/cm2 may be applied.
According to an embodiment of the present invention, the myocardial infarction detection unit includes an impedance measuring circuit connected to the electrodes arranged in the medical leads. The impedance measuring device is adapted to apply excitation current pulses between respective electrode pairs including at least a first and at least a second electrode and to measure the impedance in the tissues between the at least first and the at least second electrode of the electrode pairs to the excitation current pulses. Further, the myocardial infarction detection means includes a myocardial infarct detector adapted to evaluate the measured impedances by detecting changes in the impedances being consistent with a myocardial infarction and to determine a location of the myocardial infarction using the evaluation. The impedance measuring circuit may measure the impedance between a number of different combinations of electrodes. The impedance measuring circuit may be adapted to periodically initiate impedance measuring sessions according to a myocardial infarction monitoring protocol, wherein the impedance between different pairs of electrodes is measured according to a predetermined sequence (e.g. one pair after another during consecutive cardiac cycles or all pairs simultaneously during a number of consecutive cardiac cycles) to be able to detect and locate a myocardial infarction. That is, during each impedance measuring session, a number of impedance measurements from the different electrode pairs are obtained. Consequently, it is possible to continuously monitor the cardiac tissue to enable a reliable detection of the occurrence and location of a myocardial infarction.
According to embodiments of the present invention, the myocardial infarct detector compares measured impedances with a stored reference impedance template to detect an occurrence of a myocardial infarction and a location of the myocardial infarction from the result of the comparison. The template may alternatively be obtained or created by the myocardial infarction detection means during a period when no changes of the monitored signals, e.g. impedance or electrical activity of the cardiac tissue, are of a sufficient magnitude to indicate the possibility of the commencement of a condition such as a myocardial infarction. Such a template may also be updated periodically by performing new measurements of the impedance and/or the electrical activity.
In one example, impedance value ratios for a cardiac cycle is determined by determining a maximum impedance and a minimum impedance, respectively, measured by the impedance measuring circuit during a cardiac cycle. Further, an impedance value ratio being below a predetermined impedance value ratio threshold is determined to be consistent with a myocardial infarction; and the impedance value ratio being smallest of the impedance value ratios being below the predetermined impedance value ratio threshold is determined to indicate the location of the myocardial infarction.
Alternatively, or as a complement to the impedance value ratio determination, the myocardial infarct detector may be adapted to calculate a respective maximum time derivative of the measured impedance curves, to determine a maximum impedance time derivative being below a predetermined impedance time derivative threshold to be consistent with a myocardial infarction and to determine the maximum impedance time derivative being lowest of the maximum impedance time derivatives being below the predetermined impedance time derivative threshold to indicate the location of the myocardial infarction.
In yet another embodiment of the present invention, the myocardial infarction detection unit has an intracardiac electrogram measuring circuit connected to the electrodes of respective medical leads and which measuring circuit is adapted to measure intracardiac electrograms using one or more electrodes of the medical leads. Furthermore, the myocardial infarction detection unit includes a myocardial infarct detector adapted to evaluate the intracardiac electrograms to detect changes being consistent with a myocardial infarction and to determine a location of the myocardial infarction using the evaluation. A reference template, which template may be a stored reference impedance template, may be used in this evaluation. The template may alternatively be obtained or created by the myocardial infarction detection means during a period when no changes of the monitored signals, e.g. the electrical activity of the cardiac tissue, are of a sufficient magnitude to indicate the possibility of the commencement of a condition such as a myocardial infarction. Such a template may also be updated periodically by performing new measurements of the electrical activity. Consequently, it is possible to continuously monitor the cardiac tissue to enable a reliable detection of an occurrence and location of a myocardial infarction.
In a specific embodiment of the present invention, the myocardial infarct detector is adapted to determine a ST segment elevation being above a predetermined ST segment threshold as being consistent with the occurrence of a myocardial infarction and determine the intracardiac electrogram having the largest ST segment elevation of the ST segments being above a predetermined ST segment threshold as indicating the location of the myocardial infarction.
Furthermore, according to embodiments of the present invention, a combination of impedance measurements and intracardiac electrograms is used to detect an occurrence and location of a myocardial infarction. For example, both ST segment elevations and maximum impedance time derivatives may be used to detect myocardial infarctions. Thereby, it is possible to obtain a more reliable detection of the myocardial infarction and the location of the myocardial infarction.
At an infarction, certain hormones or chemical substances are released or are produced in a higher concentration than normal, for example, creatine phosphatinase, FABP (Fatty Acid Bonding Proteins), LDH (Lactic Dehydrogenase), or GOT (Glutamic-Oxalatic Transaminase). In one embodiment of the present invention, this is utilized by arranging a sensor in the implantable medical device or in the medical leads adapted to sense such a hormone or substance. A semiconductor sensor may be used where a reactance material is applied on a surface of the sensor, which reactance material is specific to react with the substance of interest.
According to embodiments of the present invention, signals being indicative of the healing process of the myocardial infarction is monitored, continuously or periodically, during the therapy session to determine whether the therapy has been successful and should be ended or whether the therapy parameters, i.e. the parameter of the treatment protocol, should be adjusted in order to make the treatment more potent during a certain phase of the healing process or to make the treatment less potent. A more potent treatment may be a higher degree of intensity of light or a constant intensity of light but with a changed intermittence, i.e. longer periods of light delivery or a more frequent light delivery with a constant period of light delivery. A less potent treatment may instead be a lower degree of intensity of light or a constant intensity of light but with a changed intermittence, i.e. shorter periods of light delivery or a less frequent light delivery with a constant period of light delivery.
According to one embodiment of the present invention, the myocardial infarct detector, after an initiation of a therapy session, monitors impedances obtained by at least an electrode pair indicating the location of the myocardial infarction to determine whether the impedances indicate that the therapy session should be terminated and/or the treatment parameters should be adjusted or maintained.
Furthermore, the myocardial infarct detector may be adapted to determine impedance value ratios for successive cardiac cycles and to determine that the therapy session should be terminated if a predetermined number of the impedance value ratios are found to be above the impedance value ratio threshold.
In another embodiment, the myocardial infarct detector may be adapted to calculate maximum time derivatives of the measured impedance curves for successive cardiac cycles and to determine that the therapy session should be terminated if a predetermined number of the maximum impedance time derivatives are found to be above a predetermined impedance time derivative threshold.
According to further embodiments, the myocardial infarct detector is adapted to monitor intracardiac electrograms obtained by at least an electrode pair indicating the location of the myocardial infarction to determine whether the intracardiac electrograms indicate that the therapy session should be terminated and/or the treatment parameters should be adjusted or maintained.
In a certain embodiment, the myocardial infarct detector is adapted to determine ST segments for successive cardiac cycles and determine that the therapy session should be terminated if a predetermined number of the ST segment elevations are found to be below a predetermined ST segment elevation threshold.
Moreover, according to other embodiments of the present invention, a combination of impedance measurements and intracardiac electrograms is used to determine whether the therapy should be terminated or whether the therapy parameters should be adjusted or maintained. For example, both ST segment elevations and maximum impedance time derivatives may be used to evaluate the therapy. Thereby, it is possible to obtain a more reliable judgement of the healing process and the therapy.
According to an embodiment of the present invention, the implantable medical device is provided with a power transmission unit that operates by inductive coupling in order to provide the implantable medical device with additional energy for a healing process. A receiver coil with a rectifier is arranged in the implantable medical device. An external sending coil is arranged to emit AC-fields in frequencies of a few kHz to about 500 kHz. This additional energy may be supplied directly to the light emitting means, for example, the diodes or may be used to charge a re-chargeable battery of the implantable medical device.
In a further embodiment, a warning system is arranged in the implantable medical device adapted to notify the patient (e.g. by means of a beep signal or a generated vibration) and/or a care institution such a hospital. For example, the hospital can be notified via message transmitted via an RF (Radio Frequency) unit of the implantable medical device and telecommunication system containing, inter alia, information related to the patient and a detected myocardial infarction stored in the implantable medical device. A decision at the hospital how to proceed with the treatment of the infarct can be based on the transmitted information collected by the sensors of the implantable medical device. For example, medical personnel is able to tune the light therapy by programming the device and the device can be provided with additional power or energy can be supplied from an external power source shortly after the onset of the infarct. The patient is also able to contact medical personnel via a home monitoring equipment installed at his/hers home at notification of a detection of an infarct.
In one embodiment of the present invention, the light emitting units are activated such that therapeutic light is emitted according to a treatment protocol including treatment parameters comprising one, more or all of: emitting intervals of the therapeutic light, intensity of the emitted therapeutic light, wavelength of the emitted light, intermittence of the emitted therapeutic light, or treatment periods. The protocol may thus comprise a predetermined treatment scheme. In an alternative embodiment, the treatment is varied in dependence of one or more treatment response parameters.
In embodiments of the present invention, the light emitting units emit coherent and monochromatic light having a wavelength in the range of 600 nm-1000 nm. Furthermore, an intensity of 1-500 mW/cm2 and a total dosage of about 1-4 J/cm2 may be used.
As will be apparent to those skilled in the art, steps of the method of the present invention, as well as preferred embodiment thereof, are suitable to realize as a computer program or an encoded computer readable medium.
The features that characterize the invention, both as to organization and to method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawings. It is to be expressly understood that the drawings is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that follows is read in conjunction with the accompanying drawings.
a schematically illustrates an embodiment of the implantable medical device according to the present invention.
b schematically illustrates another embodiment of the implantable medical device according to the present invention.
a schematically illustrates an embodiment of the myocardial infarction detection unit in accordance with the present invention.
b schematically illustrates another embodiment of the myocardial infarction detection unit in accordance with the present invention.
In the following, the present invention will be discussed in the context of medical systems including at least an implantable pacemaker, and medical leads such as an atrial lead and a ventricular lead.
With reference first to
Turning now to
The leads 22a and 22b can be electrically coupled to the pacemaker 20 in a conventional manner. The leads 22a, 22b carry one or more electrodes, such as a tip electrode or ring electrodes, arranged to, inter alia, measure the impedance or transmit pacing pulses for causing depolarization of cardiac tissue adjacent to the electrode(-s) generated by a pace pulse generator 21 under influence of a controller or controlling circuit 24 including a microprocessor. The controller 24 controls, inter alia, pace pulse parameters such as output voltage and pulse duration.
Moreover, a storage unit 25 is connected to the controller 24, which storage unit 25 may include a random access memory (RAM) and/or a non-volatile memory such as a read-only memory (ROM). The storage unit 25 is connected to the controller 24. Detected signals from the patient's heart are processed in an input circuit (not shown) and are forwarded to the controller 24 for use in logic timing determination in known manner.
Furthermore, the implantable medical device 20 has a myocardial infarction detection unit 27, which will be described below in more detail with reference to
In this embodiment, a plurality of light emitting units (see
The implantable medical device 20 is powered by a battery (not shown), which supplies electrical power to all electrical active components of the implantable medical device 20 including the light emitting units arranged in the medical leads 22a and 22b and the myocardial infarction detection unit 27. The implantable medical device 20 may also be provided with means for power transmission via inductive coupling in order to provide the implantable medical device 20 with additional energy for a healing process. A receiver coil (not show) with a rectifier is arranged in the implantable medical device 20. An external sending coil is arranged to emit AC-fields in frequencies of a few kHz to about 500 kHz. This additional energy may be supplied directly to the light emitting units, for example, the diodes or may be used to charge a re-chargeable battery of the implantable medical device 20.
The implantable medical device 20 further has a communication unit (not shown), for example, an RF telemetry circuitry for providing RF communications. Thereby, for example, data contained in the storage means 25 can be transferred to an external programmer device (not shown) via the communication unit and a programmer interface (not shown) for use in, for example, analyzing system conditions, patient information, etc.
Moreover, the implantable medical device 20 may further has a notifying device (not shown) adapted to, at detection of an occurrence of a myocardial infarction, notify said patient of the event that a myocardial infarct has been detected and/or that therapy has been initiated. In one embodiment, the notifying device is a vibration unit adapted to vibrate in the event that a myocardial infarct has been detected and/or that therapy for treating such an infarct has been initiated and thereby notify the patient.
Referring to
Referring now to
Furthermore, myocardial infarction detection means 27′ comprises a myocardial infarct detector 35 adapted to evaluate the measured impedances by detecting changes in the impedances that is consistent with a myocardial infarction and to determine a location of the myocardial infarction using the evaluation. In one embodiment, the myocardial infarct detector 35 is adapted to compare the measured impedances with a reference impedance template stored in a template memory 36 to detect an occurrence of a myocardial infarction and a location of the myocardial infarction from the result of the comparison. Alternatively, the reference impedance template may be stored in the storage means 25. Moreover, the reference template can be obtained and created before the parameter monitoring session is initiated, e.g. the impedance measurement session, and updated periodically. In one embodiment, the impedance measurements sessions are synchronized with the heartbeats of the patients, for example, at the end of diastole.
The myocardial infarct detector 35 may be adapted to determine impedance value ratios for each cardiac cycle by determining a maximum impedance and a minimum impedance for each electrode pair during the cardiac cycle. By comparison with the template, it is possible to identify whether a myocardial infarction has occurred. For example, an impedance value ratio being below an impedance value ratio threshold is determined to be consistent with a myocardial infarction. Further, by comparing the impedance value ratios being below the threshold, a location of the myocardial infarction can be determined. In this embodiment, the impedance value ratio being smallest is determined to indicate the location of the myocardial infarction. That is, the electrode pair providing the impedance measurement curve having the smallest difference between the maximum impedance value and the minimum impedance value during a cardiac cycle is determined to be the electrode pair being closest to the detected myocardial infarction and, hence, the location of the myocardial can be determined. The myocardial infarct detector 35 is adapted to send an instruction or message to the controller 24 informing the controller 24 that a myocardial infarction has been detected and the location of the myocardial infarction, i.e. as defined by the electrode pair being determined to be closest to the detected myocardial infarction.
In another embodiment of the present invention, the myocardial infarct detector 35 is adapted to calculate a maximum time derivative of each measured impedance curve, i.e. for each electrode pair. By comparing the calculated maximum time derivates with the template, it is possible to identify whether a myocardial infarction has occurred. For example, a maximum impedance time derivative being below a predetermined impedance time derivative threshold is determined to be consistent with a myocardial infarction. Further, in this embodiment, the maximum impedance time derivative being the lowest of the maximum impedance time derivatives being below the impedance time derivative threshold is determined to indicate the location of the myocardial infarction. That is, the electrode pair providing the impedance measurement curve having the lowest maximum impedance time derivative is determined to be the electrode pair being closest to the detected myocardial infarction. The myocardial infarct detector 35 is adapted to send an instruction or message to the controller 24 informing the controller 24 that a myocardial infarction has been detected and the location of the myocardial infarction, i.e. as defined by the electrode pair being determined to be closest to the detected myocardial infarction.
Those skilled within the art appreciate that there are a number of other conceivable variations or alternatives to the embodiments described above.
For example, the morphology of the obtained impedance curves may be compared with an impedance template to determine the occurrence and location of a myocardial infarction. In one embodiment, the part of the impedance curve at systole, i.e. after the QRS-complex, is studied and compared with a reference curve obtained with the same electrode configuration at normal conditions, i.e. at conditions when no myocardial infarction is present.
Moreover, the myocardial infarct detector may be adapted to, after an initiation of a therapy session, monitor impedances obtained by at least the electrode pair that indicated the location of the myocardial infarction to determine whether the obtained impedances indicate that the therapy session should be terminated and/or whether treatment parameters should be adjusted. The therapy parameters can be adjusted during the treatment procedure. For example, a higher light intensity can be used during an initial therapy period and the light intensity can be reduced during a second period after the initial period. Alternatively, a constant light intensity but an adjusted intermittence can be utilized, e.g. the periods of light delivery can be adjusted or shorter intervals between the periods of light delivery are used.
In one embodiment, the myocardial infarct detector is adapted to determine impedance value ratios for successive cardiac cycles and to determine that the therapy session should be terminated if a predetermined number of the impedance value ratios are found to be above a predetermined impedance value ratio threshold. Alternatively, the therapy parameters can be adjusted, for example, shorter intervals between the periods of light delivery can be used if a predetermined number of the impedance value ratios are found to be below a predetermined impedance value ratio threshold.
In a further embodiment, the myocardial infarct detector is adapted to calculate maximum time derivatives of the measured impedance curves for successive cardiac cycles and to determine that the therapy session should be terminated if a predetermined number of the maximum impedance time derivatives are found to be above a predetermined impedance time derivative threshold. Alternatively, the therapy parameters can be adjusted, for example, shorter intervals between the periods of light delivery can be used if a predetermined number of the impedance value ratios are found to be below a predetermined impedance value ratio threshold.
Turning now to
Furthermore, the myocardial infarction detection unit 27″ includes a myocardial infarct detector 45 adapted to evaluate the obtained intracardiac electrograms to detect changes being consistent with a myocardial infarction and to determine a location of the myocardial infarction using the evaluation. In one embodiment, the myocardial infarct detector is adapted to determine a ST segment elevation of each obtained intracardiac electrogram and compare them with a reference template stored in a template memory 46 to detect an occurrence of a myocardial infarction and a location of the myocardial infarction from the result of the comparison. Alternatively, the reference impedance template may be stored in the storage unit 25. Moreover, the reference template can be obtained and created before the parameter monitoring session is initiated, e.g. the impedance measurement session, and updated periodically.
In this embodiment, it is determined whether the ST segment elevation is above a predetermined ST segment threshold and in such a case; it is determined to be consistent with the occurrence of a myocardial infarction. The intracardiac electrogram having the largest ST segment elevation of the ST segments being above the predetermined ST segment threshold is determined to indicate the location of the myocardial infarction. That is, the electrode and/or electrode combination providing the intracardiac electrogram curve having the largest ST segment elevation during a cardiac cycle is determined to be the electrode and/or electrode combination being closest to the detected myocardial infarction and, hence, the location of the myocardial can be determined. The myocardial infarct detector 45 is adapted to send an instruction or message to the controller 24 informing the controller 24 that a myocardial infarction has been detected and the location of the myocardial infarction, i.e. as defined by the electrode and/or electrode combination being determined to be closest to the detected myocardial infarction. In one embodiment, the amplitude of a cardiac signal is measured during a short interval after the detection of R-wave. For example, the interval is about 40-150 ms after the R-wave detection. Measured amplitude is compared with a predetermined reference amplitude value and when the measured amplitude exceeds the reference value, a myocardial infarction is indicated.
Moreover, the myocardial infarct detector may be adapted to, after an initiation of a therapy session, monitor intracardiac electrograms obtained by at least an electrode and/or an electrode combination indicating the location of the myocardial infarction to determine whether obtained intracardiac electrograms indicate that the therapy session should be terminated and/or the treatment parameters should be adjusted. For example, a higher light intensity can be used during an initial therapy period and the light intensity can be reduced during a second period after the initial period. Alternatively, a constant light intensity but an adjusted intermittence can be utilized, e.g. the periods of light delivery can be adjusted or shorter intervals between the periods of light delivery are used.
The myocardial infarct detector may be adapted to determine ST segments for successive cardiac cycles after the initiation of the therapy session and to determine that therapy session should be terminated if a predetermined number of the obtained ST segment elevations are found to be below a predetermined ST segment elevation threshold. Alternatively, the therapy parameters can be adjusted, for example, shorter intervals between the periods of light delivery can be used if a predetermined number of the impedance value ratios are found to be above a predetermined impedance value ratio threshold.
According to a further embodiment of the present invention, the myocardial infarction detection means 27 comprises circuitry for detecting the occurrence and location of a myocardial infarction using both impedances and intracardiac electrogram. In this case, the occurrence and location of a myocardial infarction can be detected by using impedances and the healing process can be monitored by means of intracardiac electrograms, for example, by evaluating the ST elevation.
With reference to
An annular tip electrode 52 is arranged at the tip of the lead and will, after the implantation, abut against the cardiac tissue. A light emitting diode 54 is arranged at the centre of the tip portion of the lead. Further, an array of ring electrodes 55a-55c are arranged along an outer periphery 56 of the medical lead. An array of light emitting diodes 57a-57d is arranged along the outer periphery 56.
Turning now to
On the other hand, if a change that indicates the occurrence of a myocardial infarction is detected, the algorithm proceeds to step 104 where a reference template is obtained. The reference template may be a predetermined template stored in the template memory 36, 46, in the memory of the implantable medical device 20, or a template obtained and created by using measurements performed during a period when no myocardial indicative change in the monitored signals is detected. This created template may be updated periodically. Then, at step 106, the obtained data, e.g. the morphology of the impedance curves, a maximum impedance time derivative for the different impedance curves, or a ST elevation of the different intracardiac electrograms, are compared with the reference template. At step 108, it is checked whether the comparison indicates a deviation such that an occurrence of a myocardial infarction can be established and, thus, whether a delivery of therapy is justified. If the comparison indicates that the deviation is not sufficient to justify an initiation of a therapy, the algorithm returns to step 100.
If the deviation indicates that therapy should be initiated, the algorithm proceeds to step 110, where a location of the established myocardial detection is determined by using the obtained data, for example, the impedance curves or the intracardiac electrograms as described above. For example, the ST elevation being the largest or the minimum difference between the maximum impedance value and the minimum impedance value indicate which electrode and/or electrode combination that is closest to the detected myocardial infarction. Then, at step 112, a therapy session is initiated in accordance with a therapy protocol, which may include predetermined or adjustable treatment parameters such as emitting intervals of the therapeutic light, intensity of the emitted therapeutic light, wavelength of the emitted light, or intermittence of the emitted therapeutic light. The therapy protocol may be stored in the storage unit 25 of the implantable medical device 20 or in the memory of the myocardial detection means 27′, 27″.
At step 114, signals being indicative of the healing process are continuously monitored after the initiation of the therapy session. As described above, impedance signals and/or intracardiac electrograms may be used for this determination. At step 116, it is determined whether the therapy should be terminated based on the therapy protocol. If yes, the therapy is ended. On the other hand if no, the algorithm proceeds to step 118, where it is checked whether the therapy parameters should be adjusted. For example, shorter intervals between the periods of light delivery can be used if a predetermined number of the impedance value ratios, i.e. for a number of successive cardiac cycles, are found to be within a predetermined impedance value ratio interval or if the ST elevation, i.e. for a number of successive cardiac cycles, is found to be within a predetermined ST elevation value interval. If yes, the algorithm proceeds to step 120, where the therapy parameters are adjusted in accordance with the therapy protocol. Then, the algorithm returns to step 114, where the therapy is continued with the new adjusted parameters.
Alternatively, the algorithm may proceed to step 112, where a new therapy session is initiated with the new adjusted parameters. On the other hand, if it is determined that the therapy parameters should not be adjusted at step 118, the algorithm proceeds to step 122 where the therapy parameters are maintained. Thereafter, the algorithm returns to step 114, where the therapy is continued with the maintained therapy parameters. Alternatively, the algorithm may proceed to step 112, where a new therapy session is initiated with the maintained parameters.
The present invention applies to implantable medical devices such as implantable pacemakers including bi-ventricular pacemakers, pacemakers capable of delivering pacing to the atrium, the ventricle, or both the atrium and the ventricle (i.e. left ventricle and/or right ventricle), as well as devices, which are capable of delivering one or more cardioversion or defibrillation shocks.
In a further embodiment of the present invention, the control circuit 24 is adapted to, at detection of an occurrence of a myocardial infarction, send a notification to a medical care institution, e.g. a hospital or a care centre, via a communication unit of the medical device 10, 20, 30 and at least one external radio communication network such as wireless LAN (“Local Area Network”), GSM (“Global System for Mobile communications”), or UMTS (“Universal Mobile Telecommunications System”). For a given communication method, a multitude of standard and/or proprietary communication protocols may be used. For example, and without limitation, wireless (e.g. radio frequency pulse coding, spread spectrum frequency hopping, time-hopping, etc.) and other communication protocols (e.g. SMTP, FTP, TCP/IP) may be used. Other proprietary methods and protocols may also be used. The notification may include at least the patient identity, the occurrence of a myocardial infarction and/or the location of the detected infarct within the heart. The communication unit may be adapted to communicate with an extracorporeal communication device, e.g. mobile phone, a pager or a PDA (“Personal Digital Assistant”), which is adapted to receive the notification and to transmit it via said communication network further to the medical care institution. Alternatively, the communication unit may be adapted to communicate with a home monitoring unit located in the home of the patient. The home monitoring unit is adapted to communicate with the care institution via a telephone link. Furthermore, the notification may include a geographical location of the patient, for example, by means of a GPS (“Global Positioning System”) unit arranged in the communication device. Thereby, it is possible for the care institution to obtain an early notification of the infarct of a patient and, additionally, the position of the patient and hence the patient can be given care at an early stage of an infarction.
In a further embodiment of the present invention, an extracorporeal therapy unit may be connected to a medical lead according to the present invention for supplying, for example, power to the light emitting means or, in case of light conducting optical fibres in the medical lead for supplying therapeutic light. Furthermore, an extracorporeal therapy unit comprising a lead in form of a guide wire including light emitting means in accordance with the present invention may be used to treat the detected infarct since the medical personnel controlling the therapy unit may be provided with the location of the detected infarct via the implanted medical device.
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 heron all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE07/00194 | 2/28/2007 | WO | 00 | 5/20/2010 |
