Cardioinhibitory carotid sinus hypersensitivity predicts an asystolic mechanism of spontaneous neurally mediated syncope.

AIMS: We correlated the finding of cardioinhibitory carotid sinus hypersensitivity (CSH) with that observed during a spontaneous syncopal relapse by means of an implantable loop recorder (ILR). METHODS AND RESULTS: We included 18 consecutive patients with suspected recurrent neurally mediated syncope and positive cardioinhibitory response during carotid sinus massage (max pause 5.5 +/- 1.6 s) who had subsequent documentation of a spontaneous syncope by means of an ILR. They were compared with a 2:1 age- and sex-matched group of 36 patients with a clinical diagnosis of recurrent neurally mediated syncope and negative response to carotid sinus massage, tilt testing and ATP test. Asystole >3 s was observed at the time of the spontaneous syncope in 16 (89%) of CSH patients and in 18 (50%) of the control group (P = 0.007). Sinus arrest was the most frequent finding among CSH patients but not among controls (72 vs. 28%, P = 0.003). After ILR documentation, 14 CSH patients with asystole received dual-chamber pacemaker implantation; during 35 +/- 22 months of follow-up, 2 syncopal episodes recurred in 2 patients (14%), and pre-syncope occurred in another 2 patients (14%). Syncope burden decreased from 1.68 (95% confidence interval 1.66 - 1.70) episodes per patient per year before to 0.04 (0.038-0.042) after pacemaker implant (98% relative risk reduction). CONCLUSIONS: In patients with suspected neurally mediated syncope, the finding of cardioinhibitory CSH predicts an asystolic mechanism at the time of spontaneous syncope and, consequently, suggests a possible benefit of cardiac pacing therapy.