Abstract 9687: Vagal Reflexes as a Simple Clinical Tool to Stratify Risk Among LQT1 Patients

Abstract

Background We demonstrated that lower baroreflex sensitivity (BRS) values can identify Long QT Syndrome 1(LQT1) patients at lower risk for life-threatening arrhythmias, suggesting a protective role of “blunted” autonomic responses. However, the complexities of the phenylephrine method to assess BRS have limited its use for risk stratification in clinical practice. Objectives To identify an easily quantifiable marker of reflex vagal activation that might perform as well as BRS in predicting a differential risk for life-threatening arrhythmias in LQT1 patients. Specifically, to test the predictive value of heart rate (HR) recovery during the first minute after cessation of an exercise stress test. Methods In a South African LQT1 founder population segregating KCNQ1-A341V, 44 mutation carriers (MCs) underwent an exercise stress test and a phenylephrine test off-β-blockers. The HR decrease during the first minute of recovery from the peak of exercise (Δ 1min-rec ) was measured and subsequently correlated with BRS values among symptomatic (syncope, cardiac arrest, sudden death) and asymptomatic patients. Results Asymptomatic MCs had a smaller decrease in HR during the first minute of recovery from peak exercise (Δ 1min-rec ) than symptomatic MCs (13±5 vs 19±7 bpm, p< 0.05). A Δ 1min-rec <15 bpm, which corresponds to the first tertile of its distribution, predicted a much lower probability of being symptomatic (OR 0.13, 95%CI 0.028-0.63, p<0.05). The Δ 1min-rec values were significantly correlated with BRS values (r=0.64, p=0.001). Both tests performed similarly and quite accurately in discriminating between MCs with or without cardiac events (AUC 0.77 and 0.80). Conclusions LQT1 patients are at risk for life-threatening arrhythmias especially in association with rapid HR changes in either direction. Blunted autonomic responses, identified by lower values of BRS and - as vagal reflexes are concerned - by smaller HR reductions at the end of exercise, can usefully contribute to their risk stratification in a novel, simple, and inexpensive way.