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

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

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.

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.

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%.

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.