Implantable antitachycardia cardioverter/defibrillator

Abstract: An algorithm for classifying cardiac arrhythmias comprising multiple stages and dual chamber sensing. A first stage includes the steps of comparing ventricular and atrial rates and declaring that the heart is in atrial tachycardia or atrial fibrillation on the one hand, or that the heart is in ventricular fibrillation on the other hand. The second stage is entered if no determination is made in the first stage and, in particular, when the atrial rate equals the ventricular rate. A third stage is entered in which the heart is paced (ventricular, atrial or both) at a predetermined rate for a set period of time. Cardiac rhythm classification is made based on heart responses during and after pacing.

Description: Background of the Invention The present invention relates to an implantable antitachycardia cardioverter/defibrillator according to the preamble of claim 1. Poor discrimination between supraventricular tachycardia and ventricular tachycardia results in unnecessary delivery of shocks in patients with implantable defibrillators. This problem is seen in more than ten percent of patients with implantable cardiac defibrillators. Prior approaches to solve this problem have not focused on distinguishing between supraventricular tachycardia (SVT) and ventricular tachycardia (VT) using dual chamber sensing. One prior approach using dual chamber sensing only concentrates on distinguishing between sinus tachycardia (ST) and ventricular tachycardia. It is desirable that an implantable device be able to recognise and distinguish all forms of supraventricular tachycardia, as well as to discriminate sinus tachycardia from ventricular tachycardia. Document U.S. 5,107,850 discloses an apparatus for classifying and treating cardiac arrhythmias based on atrial and ventricular activity according to the preamble of claim 1. This apparatus is directed to classify cardiac arrhythmias and to determine the appropriate therapy based on the type of arrhythmia detected. Therefore, the apparatus comprises sensing means for sensing the atrial and ventricular depolarization rates of the heart and cardiac arrhythmia classifying means for determining the ventricular and atrial rate of contraction, comparing the ventricular rate with a preset threshold value, comparing the ventricular rate with an atrial rate if the ventricular rate exceeds that preset threshold value and classifying the rhythm of the heart has ventricular fibrillation or ventricular tachycardia if the ventricular rate is greater than the atrial rate. Furthermore, the apparatus is provided with means for delivering pacing pulses, cardioverter shocks or defibrillating shocks according to the classification of the rhythm of the heart. In order to prepare the classification of an arrhythmia the standard deviation of the ventricular and atrial rates may be computed to determine the regularity of these quantities. However, this document discloses not an implantable antitachycardia cardioverter/defibrillator having so-called third stage means comprising means for monitoring the response to a pacing of the heart at a predetermined rate for a predetermined period of time and means for declaring the specific arrhythmia. In addition, EP 436 517 discloses an apparatus for antitachycardia pacing in a dual chamber arrhythmia control system having means for detecting tachycardias and pulse generating means being responsive to said tachycardia detecting means for generating heart stimulating pulses for the atrium and for the ventricle. Although this document discloses a pacing device having means for detecting tachycardia as well as means for generating heart stimulating pulses it is not disclosed to provide combined means for pacing the heart, monitoring the response of said pacing and means declaring the specific arrhythmia based on the pacing and monitoring of the heart. It is a primary object of the present invention to provide a implantable antitachycardia cardioverter/defibrillator for determining the type of cardia arrhythmia based on responses to pacing pulses. This object is solved by an implantable antitachycardia cardioverter/defibrillator of the type noted above having the features of the characterizing portion of claim 1. The inventive implantable antitachycardia cardioverter/defibrillator is capable of carrying out an algorithm that is designed for use in an implantable antitachycardia cardioverter/defibrillator that requires accurate detection of underlying rhythm for proper functioning. In particular, the present invention provides for recognition of the nature of rhythm (normal vs. abnormal) and the precise type (VT vs. SVT) for accurate application of therapy. The algorithm employs dual chamber sensing and a pacing algorithm to improve sensing potential in a multi-stage technique towards tachycardia recognition, resulting in improved chances of accurate detection. In particular, the algorithm used in the present invention is divided into three stages. In the first stage, the atrial and ventricular activity is sensed and the respective rates compared. If the atrial rate exceeds the ventricular rate, it is declared that the heart is in atrial tachycardia or atrial fibrillation. If the ventricular rate exceeds the atrial rate, it is declared that the heart is in ventricular tachycardia. The second stage is entered when no determination is reached in stage one, specifically, when the atrial rate equals the ventricular rate. In this stage, the time interval between atrial depolarization and ventricular depolarization is examined and several determinations are made to arrive at an accurate diagnosis. Finally, if no determination is made in stage two, the present invention features a third stage which is entered in which the heart is paced for a predetermined period of time and the responses to the pacing are examined to diagnose the heart rhythm. The above and other objects and advantages will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of the system for performing the dual chamber sensing algorithm used in the present invention. Figure 2 is a flow diagram illustrating first and second stages of the dual chamber sensing algorithm used in the present invention. Figures 3A-3C are flow diagrams illustrating a third stage in which pacing diagnosis is performed as part of the dual chamber sensing algorithm used in the present invention. DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 illustrates, in general terms, the hardware for performing the dual chamber sensing algorithm used in the present invention. The detailed steps and computations of the sensing algorithm (shown in Figures 2 and 3A-3C) are performed by the arrhythmia analyzer shown at 10. A microprocessor or computer may be used as the arrhythmia analyzer 10. Ventricular and atrial sensing electrodes 12 and 14 are provided about the heart in the appropriate positions to sense the ventricular and atrial electrical activity respectively. These signals are fed to the arrhythmia analyzer 10 by the leads 16 and 18, respectively. A pacer unit 20 is provided and connected to the arrhythmia analyzer 10 and to ventricular and atrial pacing electrodes 22 and 24 via leads 26 and 28, respectively. In addition, a defibrillation/cardioversion unit 30 is provided and connected to the arrhythmia analyzer 10. The defibrillation/ cardioversion unit 30 is connected to ventricular electrode 12 which can serve as a sensing and defibrillation electrode and to the subcutaneous electrode 32. Additional defibrillation electrodes may be provided; however, the particular defibrillation electrode arrangement is not an essential requirement of the present invention. The dual chamber sensing algorithm is implemented by software run on the machine embodying the arrhythmia analyzer 10. Referring now to Figure 2, the first and second stages of the dual chamber sensing algorithm will be described. The first stage comprises steps 40-48 and the second stage comprises steps 50-68. Initially, in step 40, the ventricular and atrial rates are derived from the signals detected by electrodes 12 and 14. In step 42, a comparison is made between the ventricular and atrial rates to determine if the atrial rate is greater than the ventricular rate. If so, it is declared in step 44 that the heart is in an atrial tachycardia or atrial fibrillation. Otherwise, the rates are compared again to determine if the ventricular rate is greater than the atrial rate in step 46. When the ventricular rate exceeds the atrial rate in step 46, it is declared that the heart is in a ventricular tachycardia in step 48. If the ventricular and atrial rates are equal, the algorithm continues at step 50 to either the pacing diagnosing routine (third stage of the algorithm) shown in Figures 3A-3C or to the second portion of the algorithm. The decision to go directly to the third stage or to the second stage may be based upon clinical and arrhythmia characteristics of a given patient. Preferably, the second stage is entered if no determination is made in stage one. The first step in the second stage is to compute the A-V time interval in step 52. Next, in step 54 the computed A-V interval is compared with a baseline A-V value to determine if the computed value exceeds the baseline value by less than 10 msecs. If the criteria in step 54 is met, it is declared in step 56 that the heart is in a sinus tachycardia (ST). Otherwise, it is determined in step 58 whether the computed A-V interval falls between -100 msecs and 50 msecs and is clearly not equal to a baseline value. A positive value of less than 50 msecs on a negative value of the A-V time interval indicates that ventricular systole is occurring before atrial systole (actually a V-A interval). If the criteria in step 58 is met, it is declared in step 60 that the heart is in A-V nodal reentry. Next, in step 62, it is determined whether atrial depolarization occurs after ventricular depolarization, but before the end of the ventricular electrogram (the signal sensed from the ventricle). If the test in step 62 proves positive, then it is declared in step 66 that the heart is in A-V nodal reentry. Otherwise, a test is made in step 64 to determine if the A-V interval is less than -100 msecs, meaning that ventricular systole preceded atrial systole by 100 msecs. If the A-V interval meets this test, then it is determined in step 68 that the heart is in atrial tachycardia, A-V reentry or ventricular tachycardia. If not, then the algorithm jumps to the third stage, called the pacing diagnosis routine. The third stage, called the pacing diagnosis routine, is illustrated in Figures 3A-3C. Figure 3A illustrates the details of the atrial pacing diagnosis routine. Initially, in step 70 atrial pacing pulses are delivered to the heart at a rate approximately 20-40 (programmable) beats-per-minutes (BPM) above the sensed tachycardia rate for ten cardiac cycles. During the ten cycles of pacing, the responses of the heart are monitored and classified. Specifically, the ventricular rate is monitored in step 72 and if there is no change as a result of the atrial pacing pulses, then it is declared in step 74 that the heart is in ventricular tachycardia. Next, it is determined in step 76 whether the ventricular rate accelerated as a result of the atrial pacing pulses from the first captured beat. If so, it is declared in step 78 that the heart is in atrial tachycardia. Finally, if no match is made in steps 72 and 76, then it is determined in step 80 whether there is A-V dissociation initially followed by a 1:1 A-V ratio. If so, then it is declared in step 82 that the heart is in A-V nodal reentry, A-V reentry, or ventricular tachycardia. In addition, the responses to the atrial pacing are monitored after the ten cycles of pacing. In step 84, if the A-V interval is less than or equal to 10 msecs, then it is declared in step 86 that the heart is in sinus tachycardia. In step 88, if the A-V interval is more than 10 msecs greater than the baseline A-V interval within 3-5 cardiac cycles, then it is declared in step 90 that the heart is in an atrial tachycardia. In step 92, if the A-V interval is less than or equal to 50 msecs but greater than or equal to -100 msecs, then it is declared in step 94 that the heart is in A-V nodal reentry. Furthermore, if the A-V interval is greater than 100 msecs as determined in step 96, then it is declared in step 98 that the heart is in ventricular tachycardia. Finally, in step 100, if the atrial pacing pulses terminated the tachycardia with prior A-V block during pacing, then it is declared that the heart is in atrial tachycardia. Otherwise, if the atrial pacing pulses terminated the tachycardia with prior 1:1 A-V conduction, then it is determined that the heart is in atrial tachycardia or A-V nodal reentry. Figure 3B illustrates the routine for ventricular pacing diagnosis. In step 102, ventricular pacing pulses are initially delivered to the heart at a rate approximately 20 BPM greater than the sensed tachycardia rate for eight cycles or five captured cycles. Like the atrial pacing diagnosis, the responses to the ventricular pacing are monitored during the application of the pacing pulses. If there is no change detected in the atrial rate in step 104, then it is declared that the heart is in atrial tachycardia in step 106. If it is determined in step 108 that the heart is in atrial dissociation at the onset of the pulses but in a 1:1 ratio near the end of the pulses, then it is determined in step 110 that the heart is in atrial tachycardia, or A-V nodal reentry. Finally, if the heart has a 1:1 A-V relationship from the onset of capture in step 112, then it is determined that the heart is in A-V reentry or ventricular tachycardia 114. In addition, the responses after application of the pacing pulses are examined and classified in the same manner as that in the atrial pacing diagnosis routine, illustrated by steps 84-100 in Figure 3A. Figure 3C illustrates the simultaneous atrial/ventricular pacing diagnosis routine. In step 116, pacing pulses are simultaneously delivered to an atrium and ventricle of the heart at a rate approximately 20 BPM above the tachycardia rate for five to eight cycles. The responses to the pacing pulses are examined in the same manner as shown in stages 52-68 (Fig. 2). The foregoing description is intended by way of example only and is not intended to limit the present invention in any way except as set forth in the following claims.

Claims: Implantable antitachycardia cardioverter/defibrillator comprising an arrhythmia analyzer (10), a ventricular and an atrial sensing electrode (12, 14), a pacer unit (20), a ventricular and atrial pacing electrode (22, 24) and a defibrillation/cardioversion unit (30) in which the arrhythmia analyzer (10) senses cardiac activity and classifies the condition of the heart whereby the sensing and classifying means comprises: a first stage means including: means for sensing atrial and ventricular depolarization rates of the heart; means for comparing the atrial depolarization rate with the ventricular depolarization rate; means for declaring the heart condition based on information of said means for comparing if the atrial depolarization rate does not equal the ventricular depolarization rate; and a second stage means being implemented if the atrial depolarization rate equals the ventricular depolarization rate, said second stage means including: means for computing an A-V time interval between consecutive atrial and ventricular depolarizations; means for comparing the A-V time interval with a baseline value; means for declaring the heart condition based on the difference between the A-V time interval and the baseline value; characterized by a third stage means being implemented if no declaration is made by said second stage means, said third stage means including: means for pacing the heart at a predetermined rate for a predetermined period of time; means for monitoring the response to said pacing during and after said predetermined period of time; and means for declaring the specific arrhythmia based on the response of the heart during said pacing and after said predetermined period of time. Implantable antitachycardia cardioverter/defibrillator according to claim 1, wherein said second stage means further comprises: means for declaring that the heart is in sinus tachycardia if said A-V time interval differs from said baseline value by a predetermined amount; means for determining if said A-V time interval is within a predetermined threshold interval if said A-V time interval differs from said baseline value by more than said predetermined amount; means for declaring that the heart is in A-V nodal reentry if said A-V time interval is within said predetermined threshold interval; means for determining if atrial depolarization occurs before ventricular depolarization but before the end of the ventricular electrogram if said A-V time interval is outside of said predetermined threshold interval; means for declaring that the heart is in A-V nodal reentry if atrial depolarization occur before ventricular depolarization but before the end of the ventricular electrogram. Implantable antitachycardia cardioverter/defibrillator according to claim 2, wherein said second stage means further comprises: means for comparing a A-V time interval between ventricular depolarization and atrial depolarization with a predetermined threshold value if atrial depolarizations do not occur before ventricular depolarizations; and means for declaring that the heart is in atrial tachycardia, A-V nodal reentry or ventricular tachycardia if said V-A interval is less than said predetermined threshold value. Implantable antitachycardia cardioverter/defibrillator according to claim 1, wherein said means for pacing of said third stage means comprises means for pacing an atrium of the heart at said predetermined rate for said predetermined period of time, and said means for monitoring comprises means for determining if the ventricular depolarization rate accelerates or does not change during said pacing, and said means for declaring of said third stage means comprises means for declaring that the heart is in ventricular tachycardia if the ventricular depolarization rate does not change, declaring that the heart is in atrial tachycardia if the ventricular depolarization rate accelerates, or declaring that the heart is in A-V nodal reentry or ventricular tachycardia if the ventricular depolarization rate decelerates. Implantable antitachycardia cardioverter/defibrillator according to claim 4, wherein said means for monitoring of said third stage means comprises means for comparing an A-V time interval after pacing with said baseline value, and said means for declaring the specific arrhythmia comprises means for declaring that the heart is in sinus tachycardia if said A-V time interval after pacing differs from said baseline value by said predetermined amount or declaring that the heart is in atrial tachycardia if said A-V time interval after pacing differs from said baseline value more than said predetermined amount. Implantable antitachycardia cardioverter/defibrillator according to claim 4, wherein said means for monitoring after pacing further comprises: means for determining if said A-V time interval is within a predetermined threshold interval if said A-V time interval differs from said baseline value by more than said predetermined amount; means for comparing a V-A time interval between ventricular depolarization and atrial depolarization with a predetermined threshold value if atrial depolarizations do not occur before ventricular depolarizations; and wherein said means for declaring the specific arrhythmia further comprises: means for declaring that the heart is in atrial tachycardia, A-V nodal reentry or ventricular tachycardia if said V-A interval is less than said predetermined threshold value; and declaring that the heart is in A-V nodal reentry if said A-V time interval is within said predetermined threshold interval. Implantable antitachycardia cardioverter/defibrillator according to claim 1, wherein said means for pacing of said third stage means comprises means for pacing a ventricle of the heart at said predetermined rate for said predetermined period of time, and said means for monitoring comprises means for determining if the ventricular depolarization rate accelerates or does not change during said step of pacing, and said means for declaring the specific arrhythmia of said third stage means comprises: means for declaring that the heart is in ventricular tachycardia if the ventricular depolarization rate does not change, declaring that the heart is in atrial tachycardia if the ventricular depolarization rate accelerates, or declaring that the depolarization is in A-V nodal reentry or ventricular tachycardia if the ventricular heart rate decelerates. Implantable antitachycardia cardioverter/defibrillator according to claim 7, wherein said means for monitoring after pacing comprises means for comparing an A-V time interval with said baseline value, and said means for declaring the specific arrhythmia comprises means for declaring that the heart is in sinus tachycardia if said A-V time interval after pacing differs from said baseline value by said predetermined amount or declaring that the heart is in atrial tachycardia if said A-V time interval after pacing differs from said baseline value more than said predetermined amount. Implantable antitachycardia cardioverter/defibrillator according to claim 7, wherein said means for monitoring after pacing further comprises: means for determining if said A-V time interval is within a predetermined threshold interval if said A-V time interval differs from said baseline value by more than said predetermined amount; means for comparing a V-A time interval between ventricular depolarization and atrial depolarizations with a predetermined threshold value if atrial depolarization do not occur before ventricular depolarizations; and wherein said means for declaring the specific arrhythmia further comprises: means for declaring that the heart is an atrial tachycardia, A-V nodal reentry or ventricular tachycardia if said V-A interval is less that said predetermined threshold value; and declaring that the heart is in A-V nodal reentry if said A-V time interval is within said predetermined threshold interval. Implantable antitachycardia cardioverter/defibrillator according to claim 1, wherein said predetermined rate of said means for pacing is a predetermined amount above a tachycardia rate of the heart.

Inventors: AKHTAR MASOOD, AKHTAR, MASOOD
Applicants: AKHTAR MASOOD, AKHTAR, MASOOD
Application year: 1993
Main classification: A61N1
IPC codes: A61N1, A61B5