RANDOMIZED CROSS-OVER EVALUATION OF 2 ADAPTIVE PACING ALGORITHMS FOR THE TERMINATION OF VENTRICULAR-TACHYCARDIA

Objective: In a randomized, cross-over study we evaluated the efficacy of rate adaptive constant cycle length (BURST) and autodecremental (R AMP) pacing for termination of sustained monomorphic ventricular tachy cardia. Methods: An external device capable of delivering the same typ es of antitachycardia pacing as the newer generation implantable cardi overter defibrillators was used. Thirty-one patients with ischemic and nonischemic cardiomyopathy and documented clinical ventricular tachyc ardia or ventricular fibrillation were examined during routine invasiv e electrophysiological studies. RAMP and BURST pacing were each attemp ted in 54 matched pairs of induced ventricular tachycardia. After a th erapy was applied, the tachycardia was reinitiated and the other thera py applied during the second episode so that a total of 108 ventricula r tachycardia episodes were studied. Results: Overall efficacy of vent ricular tachycardia pace termination was 69% and the time required to stop ventricular tachycardia was 14.1 +/- 11.3 seconds. The ability to terminate ventricular tachycardia by RAMP (72%) or BURST (65%) pacing was not significantly different. However, time to terminate ventricul ar tachycardia by RAMP (11.8 +/- 8.5 sec) was significantly shorter th an by BURST (16.4 +/- 13.5), P < 0.001. Acceleration of ventricular ta chycardia was uncommon with both pacing modes, 7/108 (7%). The ability to pace terminate ventricular tachycardia was cycle length dependant. The highest success was with ventricular tachycardia cycle length bet ween 300 and 350 msec. The success rate decreased with faster and also slower ventricular tachycardia. Conclusions: 1. Rate adaptive pacing methods for ventricular tachycardia termination are effective and safe . 2. Autodecremental RAMP pacing afford quicker ventricular tachycardi a termination than constant cycle length BURST pacing. 3. The ability to terminate ventricular tachycardia is cycle length dependent with cy cle length range of 300-350 msec being most responsive to pace termina tion.