Predicting torsade de pointes in acquired long QT syndrome: optimal identification of critical QT interval prolongation.

OBJECTIVES: To determine the optimal method of ventricular repolarization assessment in predicting torsade de pointes (Tdp) in acquired long QT syndrome (LQTS) within the context of the recommended cutoff levels of concern for QT/corrected QT (QTc) interval prolongation.

METHODS: Twenty-nine patients with LQTS and Tdp (age 66 ± 11 years) and matched controls were studied. Standard 12-lead electrocardiograms were utilized to evaluate ventricular repolarization by using six different QT/JT heart rate correction methods. We compared the distribution of QT/QTc and JT/corrected JT intervals of patients who experienced Tdp with (1) the corresponding intervals in the matched controls and (2) the recommended cutoff levels for QT/JT interval prolongation.

RESULTS: Patients with Tdp (23 with narrow QRS, 6 with wide QRS) had longer ventricular repolarization intervals than controls (p < 0.001). For patients with narrow QRS, the QTc interval as determined firstly by the method of Hodges (t = 7.56, c = 0.933, p < 0.001), followed by the Nomogram and Fridericia methods, best discriminated Tdp patients from controls and provided the optimal balance between sensitivity and specificity at all three cutoff levels. For patients with wide QRS, the JT interval or, alternatively, the Hodges method seemed most useful.

CONCLUSIONS: Assessment of ventricular repolarization by the Hodges, Nomogram and Fridericia methods performs best in identifying subsequent Tdp.