Q-T interval in congenital complete heart block.

The rate-corrected Q-T interval (Q-Tc) was measured in 273 children with congenital complete heart block. Fifty-nine had prolonged Q-Tc and 50 of these had symptoms. All 10 with isolated complete heart block, prolonged Q-Tc and bundle branch block had symptoms. The ventricular rate (VR) was significantly lower in patients with prolonged Q-Tc than in their age-matched controls. The outcome is worse for children with low VR and long Q-Tc than for those with low VR and normal Q-Tc. In 11 children a prolonged Q-Tc preceded symptoms by more than 1 month. This suggests that prolonged Q-Tc in children with congenital complete heart block can be of prognostic significance.