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%.