# US 6,058,328 A · Implantable stimulation device having means for operating in a preemptive pacing mode to prevent tachyarrhythmias and method thereof > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,058,328 A - Document ID: US6058328A - Status: Granted - Kind: A - Application number: 08/788,152 - Filed: 1997-01-24 - Granted: 2000-05-02 - Earliest claimed: 1997-01-24 - Assignees: Pacesetter, Inc. - Inventors: Paul A. Levine; Jason A. Sholder; Gene A. Bornzin; Joseph J. Florio; Kenneth Valikai; Lisa P. Weinberg - Web page: https://patentgrep.com/patent/US6058328A ## CPC - A61N 1/3956: {Implantable devices for applying electric shocks to the heart, e.g. for cardioversion} - A61N 1/3622: {comprising two or more electrodes co-operating with different heart regions} - A61N 1/36585: {controlled by two or more physical parameters} - A61N 1/3688: {configured for switching the pacing mode, e.g. from AAI to DDD} - A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B) ## Abstract Preemptive tachyarrhythmia pacing is provided in an implantable cardiac-stimulation device, such as an implantable pacemaker or defibrillator, by modifying the operation of the implantable device in a way that minimizes the likelihood of occurrence of a tachyarrhythmia. The behavior modification is achieved through the use of an appropriate preemptive tachyarrhythmia pacing control routine stored within the memory of the device. Depending upon the needs of the patient, preemptive tachyarrhythmia pacing is invoked continuously or on demand. If invoked on demand, Preemptive tachyarrhythmia pacing is triggered only upon the sensing of one or more conditions suggest that the onset of a tachyarrhythmia is imminent. When thus invoked, preemptive tachyarrhythmia pacing remains invoked only for as long as the onset-of-a-tachyarrhythmia-is-imminent conditions persist. Various preemptive tachyarrhythmia pacing control routines are contemplated, including those based on overdrive pacing, pacing with randomicity, and mode switching. Overdrive pacing, when used, is based on an automatically-determined diurnal rate, an automatic stepped increase over the average atrial rate, or a rate set by a cycle-to-cycle negative hysteresis. Conditions which suggest the imminency of the onset of a tachyarrhythmia include, but are not limited to, a sudden change in the patient's cardiac cycle from a previously-determined normal cardiac cycle. ## Claims ### Claim 1 A method of operating an implantable medical device in one of a main operating mode or a preemptive tachyarrhythmia preventive pacing operating mode, the implantable medical device including pulse generating means for generating pacing pulses and directing such pulses to cardiac tissue of a patient, the pulse generating means being controlled by a processor, the processor being coupled to a memory wherein an operating program for controlling the operating modes may be stored, the method comprising the steps of: (a) sensing at least one parameter associated with the physiology of the patient's heart for an indication that a tachyarrhythmia may soon occur; (b) determining when the at least one parameter exceeds a prescribed threshold, thereby indicating that a tachyarrhythmia may soon occur; (c) automatically operating the implantable medical device in accordance with the main operating mode whenever the at least one parameter suggests that a tachyarrhythmia may not soon occur, wherein the main operating program is aimed at controlling the implantable medical device so that it performs its intended function; and (d) automatically operating the implantable medical device in accordance with the preemptive tachyarrhythmia preventive pacing operating mode whenever the at least one parameter exceeds the prescribed threshold thereby indicating that a tachyarrhythmia may soon occur, wherein the preemptive tachyarrhythmia preventive pacing operating mode is aimed at preventing a tachyarrhythmia from occurring. ### Claim 2 (depends on 1) The method, as set forth in claim 1, wherein the step of sensing the at least one parameter for an indication that a tachyarrhythmia may soon occur comprises: sensing a first value of a first parameter at a time when a tachyarrhythmia is not present, the first value being indicative of a normal, non-tachyarrhythmia, condition; and storing the first value of the first parameter indicative of a normal, non-tachyarrhythmia, condition as a reference value; and sensing a second value of the first parameter during subsequent cardiac cycles of the patient; and wherein the determining step comprises: comparing the second value of the first parameter to the reference value; defining the patient's rhythm as one in which a tachyarrhythmia may soon occur when the first parameter has changed by at least a prescribed amount from the reference value; and defining the patient's rhythm as one in which a tachyarrhythmia may not soon occur when the first parameter has not changed by at least a prescribed amount from the reference value. ### Claim 3 (depends on 1) The method, as set forth in claim 1, wherein the step of sensing the at least one parameter for an indication that a tachyarrhythmia may soon occur comprises: sensing a first set of values for a first set of parameters at a time when a tachyarrhythmia is not present, the first set values being indicative of a normal, non-tachyarrhythmia, condition; storing the first set of values of the first set of parameters at the time when a tachyarrhythmia is not present as a reference template; and sensing a second set of values for the first set of parameters during subsequent cardiac cycles of the patient; and wherein the determining step comprises: comparing the first set of values of the first set of parameters during a subsequent cardiac cycle to the reference template; defining the patient's rhythm as one in which a tachyarrhythmia may soon occur when the first set of parameters has changed by at least a prescribed amount from the reference template; and defining the patient's rhythm as one in which a tachyarrhythmia may not soon occur when the first set of parameters has not changed by at least a prescribed amount from the reference template. ### Claim 4 (depends on 1) The method, as set forth in claim 1, wherein the preemptive tachyarrhythmia pacing operating mode comprises operating in an overdrive pacing mode. ### Claim 5 (depends on 4) The method, as set forth in claim 4, wherein operating in an overdrive pacing mode comprises setting a pacing rate based on a predetermined diurnal rate. ### Claim 6 (depends on 4) The method, as set forth in claim 4, further comprising automatically determining a diurnal rate, and operating in an overdrive pacing mode by setting a pacing rate based on the automatically determined diurnal rate. ### Claim 7 (depends on 6) The method, as set forth in claim 6, wherein automatically determining the diurnal rate comprises gathering heart rate data over at least a 24-hour period, filtering the heart rate data with a digital recursive low-pass filter using a delay of at least 20 seconds, and using the resulting filtered output as an indicator of the diurnal rate. ### Claim 8 (depends on 7) The method, as set forth in claim 7, wherein the diurnal rate comprises a diurnal base rate (DBR), and wherein determining the diurnal base rate comprises: setting a desired "Sleeprate" parameter as a desired heart rate to be allowed when sleeping; computing a running average of the gathered heart rate data at prescribed increments of "Delay2" seconds; finding a difference, "DIFF2(t)", between the running average after each prescribed increment of "Delay2" seconds; determining an effective time constant, "ACT.sub.-- SD2(t)", after each prescribed increment of "Delay2" seconds, as ACT.sub.-- SD2(t)=(1/j) [DIFF2(t)]+[(j-1)/j]ACT.sub.-- SD2(t-Delay2), where j is an integer having a value of at least 30, and ACT.sub.-- SD2(t-Delay2) is the most recent value of the effective time constant determined during the most-recent increment prior to the present increment; computing the diurnal base rate (DBR) corresponding to the prescribed increment as DBR(t)=Slope2[ACT.sub.-- SD2(t)]+Sleeprate, where "Slope2" is a predetermined parameter. ### Claim 9 (depends on 8) The method, as set forth in claim 8, further comprising selecting the value of "Delay2" to be at least 25 seconds, and setting the value of "j" to be at least 60. ### Claim 10 (depends on 8) The method, as set forth in claim 8, further comprising selecting the value of "Delay2" to be a prescribed number, n2, of cardiac cycles, where n2 is at least 30. ### Claim 11 (depends on 4) The method, as set forth in claim 4, wherein the preemptive tachyarrhythmia pacing operating mode comprises operating in an atrial overdrive pacing mode. ### Claim 12 (depends on 11) The method, as set forth in claim 11, wherein operating in the atrial overdrive pacing mode comprises setting a pacing rate based on an automatic stepped increase over an average atrial rate. ### Claim 13 (depends on 12) The method, as set forth in claim 12, further comprising: (a) determining the average atrial rate by monitoring at least three consecutive P-to-P intervals; (b) setting the pacing rate to a new base rate value that is a prescribed step increase greater than the average atrial rate; (c) pacing the atria at a rate faster than the new base rate value for a prescribed number n.sub.P of cardiac cycles; and (d) returning to the new base rate value after the prescribed number n.sub.P of cardiac cycles. ### Claim 14 (depends on 13) The method, as set forth in claim 13, wherein the number of cardiac cycles n.sub.P that are paced faster than the new base rate value comprises at least three. ### Claim 15 (depends on 13) The method, as set forth in claim 13, wherein step (c) comprises pacing the atria at a rate that is both faster than the new base rate value and that varies from cycle to cycle for each of the n.sub.P cardiac cycles. ### Claim 16 (depends on 15) The method, as set forth in claim 15, further comprising pacing the atria at a rate that is increasingly faster than the new base rate value for each of the n.sub.P cardiac cycles. ### Claim 17 (depends on 15) The method, as set forth in claim 15, further comprising pacing the atria at a rate that is decreasingly faster than the new base rate value for each of the n.sub.P cardiac cycles. ### Claim 18 (depends on 15) The method, as set forth in claim 15, further comprising pacing the atria at a rate that is randomly faster than the new base rate value for each of the n.sub.P cardiac cycles. ### Claim 19 (depends on 13) The method, as set forth in claim 13, wherein the prescribed step increase above the average atrial rate to which the new base rate value is set comprises at least 5 bpm. ### Claim 20 (depends on 13) The method, set forth in claim 13, further comprising periodically decreasing the atrial pacing rate to test for the occurrence of P-waves; and if P-waves are detected, determining the average atrial rate by monitoring at least three consecutive P-to-P intervals and resetting the pacing rate to yet a newer base rate value that is a prescribed step increase greater than the most-recently determined average atrial rate, whereby the base rate value is dynamically reset as needed as a function of the most-recently determined average atrial rate. ### Claim 21 (depends on 11) The method, as set forth in claim 11, wherein operating in the atrial overdrive pacing mode comprises setting a pacing rate using a negative hysteresis scheme. ### Claim 22 (depends on 21) The method, as set forth in claim 21, further comprising: setting the atrial pacing rate at a programmed base rate or a sensor indicated rate, whichever is faster; increasing the atrial pacing rate to an atrial hysteresis rate, where the hysteresis rate is a programmed amount delta greater than the faster of the programmed base rate or the sensor-indicated rate, whenever an intrinsic P-wave is sensed within an atrial escape interval of the current cardiac cycle so that the next cardiac cycle is subjected to the atrial hysteresis rate; maintaining the atrial hysteresis rate for at least one cardiac cycle; and returning the atrial pacing rate to the faster of the programmed base rate or the sensor-indicated rate. ### Claim 23 (depends on 22) The method, as set forth in claim 22, further comprising returning the atrial pacing rate to the faster of the programmed base rate or the sensor-indicated rate in one step so that the following cardiac cycle is subjected to the faster of the programmed base rate or the sensor-indicted rate. ### Claim 24 (depends on 22) The method, as set forth in claim 22, further comprising returning the atrial pacing rate to the faster of the programmed base rate or the sensor-indicated rate gradually over several cardiac cycles. ### Claim 25 (depends on 1) The method, as set forth in claim 1, wherein the preemptive tachyarrhythmia preventive pacing operating mode aimed at preventing a tachyarrhythmia from occurring comprises introducing randomicity into a base rate of the implantable medical device. ### Claim 26 (depends on 25) The method, as set forth in claim 25, further comprising: gathering heart rate data; processing the gathered heart rate data to determine a correlation dimension, D.sub.2 ; and varying the pacing rate of the pacing pulses applied to the cardiac tissue to maintain D.sub.2 above a prescribed correlation dimension threshold level. ### Claim 27 (depends on 26) The method, as set forth in claim 26, further comprising adjusting the pacing rate as required to maintain correlation dimension D.sub.2 above a value of about 2.0. ### Claim 28 (depends on 26) The method, as set forth in claim 26, further comprising adjusting the pacing rate as required to maintain overdrive pacing and to maintain D.sub.2 above a value of about 2.0. ### Claim 29 (depends on 1) The method, as set forth in claim 1, further comprising switching the operating mode of the implantable medical device from its main operating mode to a preemptive operating mode whenever a tachyarrhythmia is determined to soon occur. ### Claim 30 (depends on 29) The method, as set forth in claim 29, wherein the at least one parameter that suggests a tachyarrhythmia may soon occur is selected from a group of physiological parameters that includes: blood pressure, contractility, pre-ejection interval, intra-chamber impedance, stroke volume, and oxygen saturation. ### Claim 31 (depends on 29) The method, as set forth in claim 29, wherein sensing the at least one parameter which suggests a tachyarrhythmia may soon occur comprises sensing the patient's heart rate variability; and wherein the determining step comprises determining a marked reduction in heart rate variability (HRV). ### Claim 32 (depends on 29) The method, as set forth in claim 29, wherein sensing the at least one parameter which suggests a tachyarrhythmia may soon occur comprises sensing the patient's right ventricular electrogram through a single endocardial lead; and wherein the determining step comprises determining high frequency cardiac activity signals above the prescribed threshold thereby indicating the presence of ischemia. ### Claim 33 (depends on 29) The method, as set forth in claim 29, wherein sensing the at least one parameter which suggests a tachyarrhythmia may soon occur comprises sensing the patient's right ventricular electrogram through a single endocardial lead; and wherein the determining step comprises determining electrical alternans of the QT interval above the prescribed threshold. ### Claim 34 A method of operating an implantable tissue-stimulating medical device in a preemptive tachyarrhythmia pacing mode for the purpose of preventing the occurrence of a tachyarrhythmia, said method comprising: sensing a value of at least one physiological condition capable of predicting the occurrence of a tachyarrhythmia; detecting when the value of the at least one physiological condition provides an indication that a pre-tachycardia condition exists; and when such pre-tachyarrhythmia condition is detected, modifying the behavior of the implantable tissue-stimulating medical device so as to minimize the likelihood of occurrence of a tachyarrhythmia. ### Claim 35 (depends on 34) The method, as set forth in claim 34, further including returning the behavior of the implantable tissue-stimulating medical device to what it was before being modified in response to detecting the pre-tachyarrhythmia condition upon the occurrence of a prescribed event. ### Claim 36 (depends on 35) The method, as set forth in claim 35, further comprising returning the behavior of the implantable tissue-stimulating medical device to what it was initially upon a timing out of a prescribed period of time, whereby the behavior of the implantable tissue-stimulating medical device is modified for only the prescribed period of time. ### Claim 37 (depends on 35) The method, as set forth in claim 35, further comprising returning the behavior of the implantable tissue-stimulating medical device to what it was initially upon the completion of a prescribed number of consecutive cardiac cycles. ### Claim 38 (depends on 35) The method, as set forth in claim 35, further comprising returning the behavior of the implantable tissue-stimulating medical device to what it was initially upon detecting the absence of the pre-tachyarrhythmia condition. ### Claim 39 (depends on 35) The method, as set forth in claim 35, further comprising returning the behavior of the implantable tissue-stimulating medical device to what it was initially upon detecting the return of a sensed parameter back to a value it had before the pre-tachyarrhythmia condition was detected. ### Claim 40 (depends on 34) The method, as set forth in claim 34, wherein the step of modifying the behavior of the implantable tissue-stimulating medical device comprises introducing a degree of randomicity into the stimulation rate of the device so that a minimum specified correlation dimension is maintained. ### Claim 41 (depends on 34) The method, as set forth in claim 34, wherein the step of modifying the behavior of the implantable tissue-stimulating medical device comprises switching its operating mode. ### Claim 42 (depends on 34) The method, as set forth in claim 34, wherein the implantable tissue-stimulating device comprises a device adapted to stimulate cardiac tissue, and wherein the step of modifying the behavior of the implantable tissue-stimulating medical device comprises operating the device in an overdrive pacing mode which provides stimulation pulses at a rate faster than a natural underlying heart rate. ### Claim 43 (depends on 42) The method, as set forth in claim 42, wherein overdrive pacing comprises pacing at a rate that is a prescribed amount faster than an automatically determined diurnal rate. ### Claim 44 (depends on 42) The method, as set forth in claim 42, wherein overdrive pacing comprises pacing at a rate that is an automatic stepped increase over an average heart rate. ### Claim 45 (depends on 42) The method, as set forth in claim 42, wherein overdrive pacing comprises pacing every cardiac cycle using a negative hysteresis scheme. ### Claim 46 (depends on 34) The method, as set forth in claim 34, wherein the implantable tissue-stimulating medical device comprises a device adapted to stimulate cardiac tissue of a patient in order to maintain a desired heart rhythm, and wherein the step of detecting a pre-tachyarrhythmia condition comprises: monitoring, during a time when the patient is at rest and the cardiac rhythm is stable, cardiac events of the patient for a sufficiently long period of time to learn a particular sequence and rate of cardiac events that can thereafter be used to represent a normal condition for the patient; and detecting, after learning the sequence and rate of cardiac events that represent a normal condition for the patient, the pre-tachyarrhythmia condition as any cardiac events that vary a prescribed amount from the learned sequence and rate of cardiac events representing a normal condition for the patient. ### Claim 47 (depends on 34) The method, as set forth in claim 34, wherein the implantable tissue-stimulating medical device comprises a device adapted to stimulate cardiac tissue of a patient in order to maintain a desired heart rhythm, and wherein the step of detecting a pre-tachyarrhythmia condition comprises: monitoring, during a time when the patient is not experiencing a tachyarrhythmia, at least one physiological parameter of the patient and saving the value of such at least one physiological parameter as a threshold reference; and detecting, after saving the threshold reference, the pre-tachyarrhythmia condition by continuing to monitor the at least one physiological parameter and detecting when its monitored value differs from the threshold reference by more than a prescribed amount. ### Claim 48 (depends on 47) The method, as set forth in claim 47, wherein the at least one physiological parameter is selected from a group of cardiac-related physiological parameters comprising: blood pressure, heart rate, blood temperature, blood O.sub.2 saturation, contractility, pre-ejection interval, intra-chamber impedance, stroke volume, heart rate variability, and detection of ischemia. ### Claim 49 A method of operating an implantable tissue-stimulating device, the device having generating means for generating electrical stimulating pulses of specified energies and applying the pulses to body tissue at specified times, and means for sensing natural muscle contractions of the body tissue, the method comprising: predicting when a tachyarrhythmia may occur; operating in a preemptive tachyarrhythmia pacing mode whenever a tachyarrhythmia is predicted to occur, the preemptive tachyarrhythmia pacing mode triggering the generation of electrical stimulating pulses to the tissue at controlled times and energy levels designed to minimize the occurrence of a tachyarrhythmia in the tissue being stimulated; and operating the tissue-stimulating device in a non-preemptive tachyarrhythmia pacing mode whenever a tachyarrhythmia is not predicted to occur. ### Claim 50 (depends on 49) The method, as set forth in of claim 49, further comprising sensing at least one body parameter over a specified period of time; determining whether the at least one body parameter satisfies specific criteria, the specific criteria defining a threshold condition which, when exceeded, is indicative of a body tissue condition conducive to the occurrence of a tachyarrhythmia; operating the tissue-stimulating device in the preemptive tachyarrhythmia pacing mode when the at least one body parameter satisfies the specific criteria; and operating the tissue-stimulating device in the non-preemptive tachyarrhythmia pacing mode when the at least one body parameter does not satisfy the specific criteria. ### Claim 51 An implantable cardiac tissue-stimulating device comprising: pulse generating means for generating electrical stimulating pulses of specified energies; lead/electrode means for delivering the stimulating pulses to cardiac tissue; sensing means for sensing natural muscle contractions of the cardiac tissue; means for determining when a pre-tachycardia condition exists; and processing/control means for operating in a preemptive tachyarrhythmia pacing mode when the pre-tachyarrhythmia condition exists and in a non-preemptive mode when the pre-tachyarrhythmia does not exist, the preemptive tachyarrhythmia pacing mode comprising means for triggering the pulse generating means of the tissue-stimulating device to apply electrical stimulating pulses to the cardiac tissue at controlled times and energy levels designed to minimize the occurrence of a tachyarrhythmia in the tissue being stimulated. ### Claim 52 (depends on 51) The implantable cardiac tissue-stimulating device, as set forth in claim 51, wherein: the means for determining when a pre-tachycardia condition includes: means for sensing at least one body parameter over a specified period of time; and means for determining whether the at least one body parameter satisfies specific criteria, the specific criteria defining a threshold condition which when exceeded is indicative of a body tissue condition conducive to the occurrence of a tachyarrhythmia; and the processing/control means includes: means for operating the tissue-stimulating device in accordance with the preemptive tachyarrhythmia pacing mode when the at least one body parameter satisfies the specific criteria; and means for not operating the tissue-stimulating device in accordance with the non-preemptive tachyarrhythmia pacing mode when the at least one body parameter does not satisfy the specific criteria. ### Claim 53 (depends on 51) The implantable cardiac tissue-stimulating device, as set forth in claim 51, wherein the means for determining when a pre-tachycardia condition includes: means for learning a normal sequence and rate of cardiac events at a time when the patient's cardiac rhythm is stable; storing the normal sequence and rate of cardiac events; and means for detecting as the pre-tachyarrhythmia condition any cardiac events that vary a prescribed amount from the normal sequence and rate of cardiac events. ### Claim 54 (depends on 51) The implantable cardiac tissue-stimulating device, as set forth in claim 51, wherein the means for determining when a pre-tachycardia condition includes: means for learning a normal heart rate variability during a time when the patient's cardiac rhythm is stable; storing the normal heart rate variability; and means for detecting as the pre-tachyarrhythmia condition a heart rate variability that varies a prescribed amount from the normal heart rate variability. ### Claim 55 (depends on 51) The implantable cardiac tissue-stimulating device, as set forth in claim 51, wherein the means for determining when a pre-tachycardia condition includes: means for learning a normal correlation dimension during a time when the patient's cardiac rhythm is stable; storing the normal correlation dimension; and means for detecting as the pre-tachyarrhythmia condition a correlation dimension that varies a prescribed amount from the normal correlation dimension. ### Claim 56 (depends on 51) The implantable cardiac tissue-stimulating device, as set forth in claim 51, wherein the means for determining when a pre-tachycardia condition includes: means for learning a normal a QT interval during a time when the patient's cardiac rhythm is stable; storing the normal QT interval; and means for detecting as the pre-tachyarrhythmia condition alternans which occur in the QT interval that differ by a prescribed amount from the normal QT interval. ### Claim 57 (depends on 51) The implantable cardiac tissue-stimulating device, as set forth in claim 51, wherein the means for determining when a pre-tachycardia condition includes: means for learning normal frequency components of a ventricular cardiac signal during a time when the patient's cardiac rhythm is stable; storing the normal frequency components of the ventricular cardiac signal; and means for detecting as the pre-tachyarrhythmia condition high frequency cardiac signal components which differ by a prescribed amount from the normal frequency components of the ventricular cardiac signal, the high frequency cardiac signal components indicating the presence of ischemia. ### Claim 58 (depends on 51) The implantable cardiac tissue-stimulating device, as set forth in claim 51, wherein the processing/control means for operating in a preemptive tachyarrhythmia pacing mode comprises: means for operating in an overdrive mode which provides stimulation pulses at a rate faster than a natural underlying heart rate. ### Claim 59 (depends on 58) The implantable cardiac tissue-stimulating device, as set forth in claim 58, wherein the means for operating in the overdrive mode comprises: means for providing stimulation pulses at a varying rate faster than a natural underlying heart rate. ### Claim 60 (depends on 58) The implantable cardiac tissue-stimulating device, as set forth in claim 58, wherein the means for operating in the overdrive mode comprises: means for providing stimulation pulses at a randomly-varying rate faster than a natural underlying heart rate. ### Claim 61 (depends on 58) The implantable cardiac tissue-stimulating device, as set forth in claim 58, wherein: the means for determining when a pre-tachycardia condition exists includes means for determining a normal correlation dimension during a time when the patient's rhythm is stable; and the means for operating in the overdrive mode includes means for providing stimulation pulses at a rate which maintains correlation dimension to within a prescribed range about the normal correlation dimension. ### Claim 62 (depends on 58) The implantable cardiac tissue-stimulating device, as set forth in claim 58, wherein: the means for determining when a pre-tachycardia condition exists includes means for determining a normal heart rate variability during a time when the patient's rhythm is stable; and the means for operating in the overdrive mode includes means for providing stimulation pulses at a rate which mimics the normal heart rate variability.