ABSTRACT
While acquiring data for the International Long QT Syndrome Registry, we noticed that a number of patients referred for long QT syndrome (LQTS) were affected by asthma. The effect of asthma comorbidity on clinical course of LQTS has not been studied. This study aimed to evaluate the prevalence of asthma in patients with LQTS, determine the influence of asthma comorbidity on outcome of LQTS patients, and to investigate the confounding effects of beta mimetics and beta blockers on the occurrence of cardiac events in asthmatic patients. The influence of asthma on risk of cardiac events (syncope, aborted cardiac arrest, or LQTS death) was evaluated after accounting for age, gender, QTc, and RR interval duration, beta-blocker and beta-mimetic use. Asthma was identified in 226 (5.2%) of 4,310 studied LQTS family members. Longer QTc duration was associated with higher incidence of asthma (p <0.001). Asthma was independently associated with significantly increased risk of cardiac events in affected LQTS patients (hazard ratio 1.32; p = 0.048) and in borderline-affected family members (hazard ratio 2.08; p = 0.004) after adjustment for QTc, RR interval, and gender. An increased risk of cardiac events in asthmatic patients observed before beta-blocker therapy was reduced after initiation of treatment with beta blockers. In conclusion, the occurrence of asthma in LQTS patients increases with QTc duration. Asthma comorbidity in LQTS patients is associated with an increased risk of cardiac events. The asthma-associated increase in the risk of LQTS-related cardiac events is diminished after initiation of beta-blocker therapy, suggesting a possible role of beta-receptor modulation underlying asthma-LQTS association.
