214 Gene-specific effect of beta-adrenergic blockade on QT duration in the Long QT syndrome

Background In the long QT syndrome (LQTS) the clinical efficacy of beta-blocker treatment differs according to the genotype. We aimed to asses the effect of beta-blocker treatment in LQT1 and LQT2 patients. Patients and methods 24-hour Holter ECG were recorded before and after beta-blocking therapy initiation in genotyped LQT1 (n = 30, 8 males, mean age 21 ± 17) and LQT2 patients (n = 16, 8 males, mean age 19 ± 15). QT duration was measured on consecutive 1-minute averaged QRS-T complexes leading to up to 1440 QT-RR pairs for each recording. Then, we computed subject- and condition-specific log/log QT/RR relationships which were used to calculate QT interval duration at RR = 1000 ms (QT1000 = 1000*). Results Before treatment, coefficients were higher in LQT2 than in LQT1 patients (0.53 ± 0.10 vs. 0.40 ± 0.11, p  Beta-blockers significantly prolonged the mean RR interval (RR = 827 ± 161 ms before treatment and 939 ± 197 ms on beta-blocker, p  Conclusions Our results confirm the elevated coefficient of the QT/RR relationship in LQTS patients. LQT2 patients showed higher coefficient and longer QT1000 when compared to LQT1 patients. The effect of beta-adrenergic blockade on QT1000 duration was gene-specific. Given the demonstrated efficacy of beta-blockers in LQT1 and 2 patients, our data suggest that QT1000 might be a poor predictor of outcome under anti-adrenergic therapy.