UNDERSENSING DURING VENTRICULAR TACHYARRHYTHMIAS IN A 3RD-GENERATION IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR - DIAGNOSIS USING STORED ELECTROGRAMS AND CORRECTION WITH PROGRAMMING

Third-generation implantable cardioverter defibrillators with stored e lectrograms allow diagnosis of various sensing problems that may lead to an inappropriate device response. Undersensing of ventricular tachy arrhythmias is a potentially serious problem, as it may lead to failur e to deliver therapy. To determine the incidence of this problem, we r eviewed 98 patients with Ventritex Cadence defibrillator systems and f ound 2 patients in whom defibrillation therapy was delayed or aborted because of undersensing during induced ventricular tachyarrhythmias. I n both cases, examination of stored electrograms revealed variation in electrogram amplitude, which presumably resulted in failure of the au togain feature to increase its sensitivity enough to count each comple x. During charging, criteria for redetection of sinus rhythm were met because of this undercounting, leading to failure to deliver defibrill ation therapy. This problem was detected in both patients 4-6 weeks fo llowing device implant during device testing, and both patients had be en started on antiarrhythmic drug therapy prior to this testing. Progr amming the sinus redetection parameter from nominal to slow, increasin g the number of beats necessary to confirm resumption of sinus rhythm, corrected the problem in both patients. Device testing in the electro physiology laboratory, routinely postoperatively and following initiat ion of antiarrhythmic drug therapy, and the ability to retrieve stored electrograms are useful in detecting such sensing anomalies.