Association of long QT syndrome loci and cardiac events among patients treated with β-blockers

Context Data on the efficacy of beta-blockers in the 3 most common genetic long QT syndrome (LQTS) loci are limited. Objective To describe and assess outcome in a large systematically genotyped population of beta-blocker-treated LQTS patients. Design, Setting, and Patients Consecutive LQTS-genotyped patients (n=335) in Italy treated with beta-blockers for an average of 5 years. Main Outcome Measures Cardiac events (syncope, ventricular tachycardia/torsades de pointes, cardiac arrest, and sudden cardiac death) while patients received beta-blocker therapy according to genotype. Results Cardiac events among patients receiving beta-blocker therapy occurred in 19 of 187 (10%) LQT1 patients, 27 of 120 (23%) LQT2 patients, and 9 of 28 (32%) LQT3 patients (P<.001). The risk of cardiac events was higher among LQT2 (adjusted relative risk, 2.81; 95% confidence interval [CI], 1.50-5.27; P=.001) and LQT3 (adjusted relative risk, 4.00; 95% CI, 2.45-8.03; P<.001) patients than among LQT1 patients, suggesting inadequate protection from beta-blocker therapy. Other important predictors of risk were a QT interval corrected for heart rate that was more than 500 ms in patients receiving therapy (adjusted relative risk, 2.01; 95% CI, 1.16-3.51; P=.01) and occurrence of a first cardiac event before the age of 7 years (adjusted RR, 4.34; 95% CI, 2.35-8.03; P<.001). Conclusion Among patients with genetic LQTS treated with β-blockers, there is a high rate of cardiac events, particularly among patients with LQT2 and LQT3 genotypes.