Spatio-temporal repolarization dispersion before and after exercise in patients with long QT syndrome type 1 vs controls - probing into the arrhythmia substrate.

Abstract

Congenital long QT syndrome (LQTS) carries an increased risk for syncope and sudden death. QT prolongation promotes ventricular extrasystoles which in the presence of an arrhythmia substrate might trigger ventricular tachycardia degenerating into fibrillation. Increased electrical heterogeneity (dispersion) is the suggested arrhythmia substrate in LQTS. In the most common subtype LQT1, physical exercise predisposes for arrhythmia and spatio-temporal dispersion was therefore studied in this context. Thirty-seven patients (57% on beta-blockers) and 37 healthy controls (mean age 31 vs 35, range 6-68 vs 6-72 years) performed an exercise test. Frank vectorcardiography was used to assess spatio-temporal dispersion as Tamplitude, Tarea, the ventricular gradient (VG), and the Tpeak-end interval from 10s-signal averages before and 7±2 min after exercise; during exercise too much signal disturbance excluded analysis. Baseline and maximum heart rates as well as estimated exercise intensity were similar, but heart rate recovery was slower in patients. At baseline QT and heart rate corrected QT (QTcB) were significantly longer in patients (as expected), while dispersion parameters were numerically larger in controls. After exercise QTpeakcB and Tpeak-endcB increased significantly more in patients (18±23 vs 7±10ms and 12±17 vs 2±6ms; p<0.001 and p<0.01). There was, however, no difference in the change in Tamplitude,Tarea and VG between groups. In conclusion, while temporal dispersion of repolarization increased significantly more after exercise in LQT1 patients, there were no signs of exercise-induced increase in global dispersion of action potential duration and morphology. The arrhythmia substrate/mechanism in LQT1 warrants further study.