192: Treatment of unexplained syncope: A multicenter, randomized trial of cardiac pacing guided by adenosine 5’-triphosphate testing

Background The origin of 40% of syncope remains unknown even after a complete diagnostic work-up. Previous studies have suggested that adenosine 5’-triphosphate (ATP) testing has value in selecting successful therapy. This patient-blinded, multicenter, randomized superiority trial tested whether, in patients with syncope of unknown origin (SUO), selecting cardiac pacing in those with a positive ATP test results in fewer recurrences than those who do not receive pacing. Methods and Results From 2000 to 2005, 80 consenting patients (mean age 75.9±7.7 years; 81% women; 56% without diagnosed structural heart disease) with syncope of unknown origin and atrioventricular or sinoatrial block lasting longer than 10 seconds (average 17.9±6.8 seconds) under ATP administration (20 mg IV bolus) were recruited from 10 hospitals, implanted with programmable pacemakers and randomized to either active pacing (dual-chamber pacing at 70 beats per minute (bpm) or backup pacing (atrial pacing at 30 bpm). Patients were followed regularly for up to five years for any syncope recurrence, the primary outcome. Mean follow-up was 16 months. Syncope recurred in eight (21%) of 39 patients randomized to active pacing and in 27 (66%) of 41 randomized to backup pacing (control), yielding a hazard ratio of 0.25 (95% CI: 0.12–0.56). After recurrence, the 27 recurrent control patients were reprogrammed to active pacing and only one reported subsequent syncope. Conclusions This study suggests that, in elderly patients with syncope of unknown origin and positive ATP tests, active dual-chamber pacing reduces syncope recurrence risk by 75% (95% confidence interval, 44–88).