Asymptomatic Asystolic Carotid Sinus Hypersensitivity Predicts Asystolic Events During ILR Monitoring in Reflex Syncope Patients

BACKGROUND The diagnosis of carotid sinus syndrome requires the reproduction of spontaneous symptoms during carotid sinus massage (CSM) alongside clinical features indicative of a reflex mechanism. In contrast, the significance of asymptomatic asystolic carotid sinus hypersensitivity (CSH) remains uncertain, as it is frequently observed in older adults without syncope. OBJECTIVES This study aimed to evaluate the correlation between asymptomatic asystolic CSH and spontaneous events documented via implantable loop recorder (ILR). METHODS In this study, 92 reflex syncope patients with an asymptomatic pause >3 seconds during CSM (average 4.9 ± 1.7 seconds) received an ILR and were followed for a median of 23.1 months. The control group consisted of reflex syncope patients with negative CSM drawn from a historical ILR population and matched with the propensity score method to the CSH group based on clinical variables. RESULTS During the observation period, 38 (41.3%) CSH patients had recurrence of syncope, which was associated with asystole of 8.0 seconds (95% CI: 5.3-13.5 seconds) in 29 (76.3%) cases. Although the actuarial rate of total syncope recurrence in CSH group was similar to that in the control group (HR: 1.22; P = 0.40), CSH patients showed a higher rate of asystolic syncope (HR: 2.13; P = 0.011) and asystolic pauses (HR: 2.06; P = 0.009). CONCLUSIONS Patients with asymptomatic asystolic CSH were more likely to experience spontaneous asystolic syncope than those without CSH. Among CSH patients who experienced a recurrence of syncope documented by an ILR, the positive predictive value of an asystolic pause detected during CSM was 76.3%.