Different Dynamic Aspects of the Repolarization Morphology between LQT1 and LQT2 Forms of Congenital Long QT Syndrome

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Because of the limitation of electrocardiographic findings for diagnosis of congenital long QT syndrome (LQTS), we assessed the diagnostic value of rate-dependent dynamics of the repolarization morphology for genotyping of LQTS. Methods: CM5 lead digital Holter ECG was recorded for 24-hour in 12 patients with LQT1, 12 with LQT2 and 16 controls. The QT/RR, T-amp/RR and T-area/RR linear regression lines were analyzed. Results: The QT/RR slope was greater in both LQT1 and LQT2 patients compared to controls (0.15±0.02 and 0.2±0.02 vs 0.13±0.03, p<0.01), and was greater in LQT2 than in LQT1. QT interval (sec) at RR interval of either 0.6 or 1.2 sec was longer in LQTS than in controls. Moreover, QT at RR interval of 1.2 sec was longer in LQT2 than in LQT1. Both slopes of T-amp/RR (mV/sec) and T-area/RR (mV) regression lines were smaller (p<0.01) in LQT2 (0.36±0.14 and 0.24±0.17) compared to both LQT1 (1.23±0.31 and 0.7±0.17) and controls (1.19±0.31 and 0.69±0.18). Both T-amplitude (mV) and T-area (mV·sec) at RR interval of either 0.6 or 1.2 sec were smaller in LQT2 patients than other groups. Conclusions: Enhanced QT prolongation during bradycardia was demonstrated in both LQT1 and LQT2 patients; however, impaired rate-dependent increment of both the amplitude and the area of T-wave were characteristic of patients with LQT2.