Beta-Blockers and Exercise Performance in Children with Long QT Syndrome

BACKGROUND Young people taking beta-blockers for long QT syndrome (LQTS) have concerns about exercise performance. OBJECTIVES This study sought to determine whether objective measures of cardiopulmonary fitness are influenced by beta-blocker dose in LQTS. METHODS In a retrospective chart review of treadmill cardiopulmonary exercise tests (CPETs), we measured peak oxygen consumption (Vo2), respiratory exchange ratio (RER), blood pressure, and percent predicted heart rate at peak exertion (%PHR), each analyzed with a linear mixed-effects model. We analyzed nadolol data (noncardioselective) as our primary analysis, then analyzed a validation cohort of atenolol data (cardioselective). RESULTS We evaluated 220 CPETs in 93 patients with LQTS. The mean age at first CPET was 12 ± 3.9 years. In multivariable analysis, %PHR decreased by 13% for every 1 mg/kg/d increase in beta-blocker dose, demonstrating physiologic beta-blocker effects. However, we identified no correlation between nadolol dose and measures of cardiopulmonary fitness. Neither peak Vo2 nor peak RER was correlated with nadolol dose. Only mild blood pressure changes were observed (<9 mm Hg decrease at peak exertion per 1 mg/kg increase in nadolol dose). Increased atenolol dose was also associated with stable peak Vo2 and peak RER. CONCLUSIONS In children with LQTS, we did not observe any relationship between higher nadolol doses and objective measures of effort (peak RER) or cardiopulmonary fitness (peak Vo2), despite a linear dose-response between nadolol dose and %PHR. These results suggest that treatment with nadolol for LQTS does not affect most patients' peak exercise performance. These data were validated in patients from an earlier era who had been prescribed atenolol.