The morphology of the QT interval predicts torsade de pointes during acquired bradyarrhythmias

Abstract

Objectives: The purpose of this study was to define the electrocardiographic (ECG) predictors of torsade de pointes (TdP) during acquired bradyarrhythmias.

Background: Complete atrioventricular block (CAVB) might lead to downregulation of potassium channels, QT interval prolongation, and TdP. Because potassium-channel malfunction causes characteristic T-wave abnormalities in the congenital long QT syndrome (LQTS), we reasoned that T-wave abnormalities like those described in the congenital LQTS would identify patients at risk for TdP during acquired bradyarrhythmias.

Methods: In a case-control study, we compared 30 cases of bradyarrhythmias complicated by TdP with 113 cases of uncomplicated bradyarrhythmias. On the basis of the criteria used for the congenital LQTS, T waves were defined as LQT1-like (long QT interval with broad T waves), LQT2-like (notched T waves), and LQT3-like (small and late) T waves.

Results: Neither the ventricular rate nor the QRS width at the time of worst bradyarrhythmia predicted the risk of TdP. However, the QT, corrected QT (QTc), and T(peak)-T(end) intervals correlated with the risk of TdP. The best single discriminator was a T(peak)-T(end) of 117 ms. LQT1-like and LQT3-like morphologies were rare during bradyarrhythmias. In contrast, LQT2-like "notched T waves" were observed in 55% of patients with TdP but in only 3% of patients with uncomplicated bradyarrhythmias (p < 0.001). A 2-step model based on QT duration and the presence of LQT2-like T waves identified patients at risk for TdP with a positive predictive value of 84%.

Conclusions: Prolonged QT interval, QTc interval, and T(peak)-T(end) correlate with increased risk for TdP during acquired bradyarrhythmias, particularly when accompanied by LQT2-like notched T waves.