Endless-loop tachycardias: description and first clinical results of a new fully automatic protection algorithm.

Endless-loop tachycardia (ELT) is one of the most common pacemaker mediated tachycardia. An innovative ELT protection algorithm has proven to be clinically effective. A new improved version that will eliminate the need to program any parameter is now under clinical evaluation. Nine patients entered the study: six men and three women, aged 52 +/- 22 years. This automatic algorithm needs only 10 cycles to detect and confirm an ELT. Three hundred thirty-three ELTs lasting more than 9 cycles have been induced and analyzed. The total results are the following: mean duration: 6.7 sec +/- 3.1; mean ELT rate: 137 +/- 21.9 bpm, mean programmed upper rate limit (URL): 142.5 +/- 26.5 bpm (Only 70% of ELTs presented rates equal to programmed URL). (1) ELTs reduced by postventricular atrial refractory period (PVARP) extension on one cycle: 291 ELTs (87%). ELT rate: 128.5 +/- 18.2 bpm. (2) Retrograde block: algorithm operation may induce a retrograde block due to a short atrioventricular delay (AVD) applied during the confirmation phase to discriminate an ELT from a stable sinus rhythm. Thirty-two ELTs (10%) have been reduced and detected on a retrograde block occurrence. (3) Algorithm failure due to an unstable ventriculoatrial conduction time (VACT) even at fixed rate or to a retrograde Wenckebach behavior on AVD reduction during the confirmation phase. A total of 10 algorithms failed to detect or confirm an ELT have been recorded (3%). Mean duration: 8.2 +/- 4.2 sec, mean ELT rate: 148.9 +/- 14.3 bpm. This new fully automatic algorithm has reduced 97% of ELTs, including high rate episodes (100-175 bpm).(ABSTRACT TRUNCATED AT 250 WORDS)