Closed Loop Stimulation in Vasovagal Syncope

Study Questions:

Does dual-chamber pacing with closed loop stimulation (DDD-CLS) reduce the frequency of syncope in patients with cardioinhibitory vasovagal syncope?


This was a randomized, double-blind, controlled study of patients age ≥40 years, with high burden syncope, and a cardioinhibitory head-up tilt test (HUT). Patients were randomized to DDD-CLS pacing for 12 months followed by sham DDI mode pacing (at 30 ppm for 12 months (Group A), and sham DDI mode during 12 months followed by DDD-CLS pacing for 12 months (Group B). Patients in both arms were crossed-over after 12 months of follow-up or when a maximum of three syncopal episodes occurred within 1 month.


Forty-six patients completed the protocol; 22 males, mean age 56 ± 11 years. The mean number of previous syncopal episodes was 12. The proportion of patients with ≥50% reduction in the number of syncopal episodes was 72% with DDD-CLS compared to 28% with DDI sham mode (p = 0.017). Four patients (9%) had events during DDD-CLS and 21 (46%) during sham DDI (hazard ratio, 6.7; 95% confidence interval, 2.3-19.8). Kaplan-Meier curve was significantly different between groups in time to first syncope (29.2 months vs. 9.3 months; odds ratio, 0.11; p < 0.0001).


DDD-CLS pacing significantly reduced syncope burden and time to first recurrence by sevenfold, prolonging time to first syncope recurrence in patients ≥40 years with HUT-induced vasovagal syncope compared to sham pacing.


Prior to this publication, the most promising study of pacing in vasovagal syncope was ISSUE-3. That study used significant pauses on an implantable loop recorder as an entry criterion, rather than tilt test response, and specifically tested dual-chamber pacing with what is known as the rate-drop response algorithm, where upon detection of an intrinsic rate drop, the device paces at a higher rate for a period of time. Interestingly, on post hoc analysis, ISSUE-3 showed benefit of pacing only in patients who had negative cardioinhibitory response during tilt test. The present study, which used a positive tilt test response for entry, employs a proprietary closed loop stimulation (CLS) algorithm, which is triggered by changes in right ventricular contractility. CLS is activated before cardioinhibition and vasodilation manifest, offering the potential for earlier and more effective pacing intervention. Unfortunately, the tilt test is plagued by limited sensitivity and specificity, and poor reproducibility, making it unclear how to best select patients for CLS pacing.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias

Keywords: Arrhythmias, Cardiac, Pacemaker, Artificial, Primary Prevention, Syncope, Syncope, Vasovagal, Tilt-Table Test, Vasodilation

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