T-WAVE ALTERNANS IN IDIOPATHIC LONG QT SYNDROME

Objectives. The study evaluates the association between T wave alternans and the risk of cardiac events (syncope, aborted cardiac arrest or cardiac death) in a large population of patients with idiopathic long QT syndrome. Background. T wave alternans is an infrequently recorded electrocardiographic (ECG) finding in patients with delayed repolarization, and its clinical significance is not clear. Methods. A total of 4,656 ECG recordings in 2,442 patients enrolled in the International Long QT Syndrome Registry were reviewed for episodes of T wave alternans. To determine the risk associated with T wave alternans, independent of corrected QT interval (QTc) duration, patients with T wave alternans were matched for QTc value (every 0.025 s(1/2)) to patients with long QT syndrome without T wave alternans. Results. T wave alternans was identified in 30 patients (25 of whom had a QTc interval >0.50 s(1/2)). A strong association between QTc prolongation and T wave alternans was observed (odds ratio 1.23 per 0.01-s(1/2) unit increase in QTc, p < 0.0001). Conditional logistic regression analyses with adjustment for age, gender, status and QTc value revealed that T wave alternans did not make a significant independent contribution to the risk of cardiac events. The risk of experiencing a major cardiac event was primarily related to length of QTc. Conclusions. T wave alternans, a marker of electrical instability and regional heterogeneity of repolarization, identifies a high risk subset of patients with prolonged repolarization. Patients with T wave alternans have an increased risk of cardiac events, but this risk is primarily related to the magnitude of repolarization delay (QTc prolongation). T wave alternans does not make an independent contribution to the risk of cardiac events after adjustment for QTc length.