A New Algorithm to Solve Endless Loop Tachycardia in DDD Pacing: A Multi-Center Study of 91 Patients

ELTs (endless loop tachycardias) are a common occurrence associated with DDD pacing. In order to detect and treat ELTs, an innovative automatic pacemaker algorithm was devised and evaluated. The basic principle of the algorithm rests on the relative stability of the ventriculoatrial conduction time (VACT) during ELTs. ELTs are suspected when the VACT remains stable and adheres to certain programmable limits referred to as VACT stability (16 or 31 msec); it is confirmed when the VACT remains stable after a programmable shortening of the AV delay (AVD) value, referred to as AVD shortening (47 or 63 msec). Ninety-one patients, 54 males and 37 females, were implanted with such an algorithm-specific device between January 10 and September 9, 1989. The reasons for implantation were as follows: 55 patients were implanted for AV block, 31 for sinus node dysfunction, and 2 for carotid sinus syndrome. Pacing parameters were programmed to favor ELT initiation (long AVD, short postventricular atrial refractory period [PVARP] and high atrial sensitivity) followed by basic programming of the algorithm (VACT stability set at 16 msec and AVD shortening set at 47 msec. Once this was done, a 24-hour Holter recording was obtained. Eighty-eight patients were thus analyzed, three being excluded from the final report due to the poor quality of the Holter tracings. In 43.2% of the sampling (38 patients), multiple episodes of ELT were identified, exhibiting a mean rate of 120 beats/min. In 26 of 38 cases (68.4%), the rate of ELT was found to be slower than the upper rate limit (URL).(ABSTRACT TRUNCATED AT 250 WORDS)