Analysis of rhythm variation during spontaneous cardioinhibitory neurally-mediated syncope. Implications for RDR pacing optimization: an ISSUE 2 substudy.

BACKGROUND Little is known of the variations of the heart rate during spontaneous cardioinhibitory neurally-mediated syncope. Their knowledge has both academic and practical implications for the optimization of rate drop response (RDR) pacing mode. METHODS AND RESULTS We describe variations of the rhythm occurring during 48 syncopal episodes documented by implantable loop recorder. The presyncopal phase of 18 s (interquartile range 9-65) was characterized by a fall in heart rate from 83 +/- 20 bpm to maximal bradycardia or (multiple) asystolic pauses which lasted a median of 19 s (10-30). The recovery phase lasted 22 s (7-52). The total duration of the cardioinhibitory reflex was 85 s (47-116). We then calculated the potential increase in benefit that an optimally programmed drop rate detection could provide compared with a reference Lower Rate detection. Compared with Lower Rate detection (defined as two consecutive beats at 40 bpm), drop rate detection (assumed to be drop size = 20 bpm, detection window = 1 min, and drop rate = 50 bpm) would have been able to introduce intervention pacing, a median of 5.7 s (interquartile range -5.1- -10.4) earlier in 28 cases (58%). CONCLUSION Cardioinhibitory neurally-mediated reflex varies widely from a few seconds to some minutes. In our data the total duration was <2 min. Optimal RDR programming, being potentially able to anticipate the detection of the cardioinhibitory reflex by a few seconds, could provide an increase in benefit for cardiac pacing therapy in prevention of syncope.