Evaluation of the QT interval in patients with drug‐induced QT prolongation and torsades de pointes

Abstract

Background: Data on the optimal location of the electrocardiogram (ECG) leads for the diagnosis of drug-induced long QT syndrome (diLQTS) with torsades de pointes (TdP) are lacking. Methods: We systematically reviewed the literature for the ECGs of patients with diLQTS and subsequent TdP. We assessed T wave morphology in each lead and measured the longest QT interval in the limb and chest leads in a standardized fashion. Results: Of 84 patients, 61.9% were female and the mean age was 58.8 years. QTc was significantly longer in chest versus limb leads (mean (SD) 671 (102) vs. 655 (97) ms, p = .02). Using only limb leads for QT interpretation, 18 (21.4%) ECGs were noninterpretable: 10 (11.9%) due to too flat T waves, 7 (8.3%) due to frequent, early PVCs and 1 (1.2%) due to too low ECG recording quality. In the chest leads, ECGs were noninterpretable in nine (10.7%) patients: six (7.1%) due to frequent, early PVCs, one (1.2%) due to insufficient ECG quality, two (2.4%) due to missing chest leads but none due to too flat T waves. The most common T wave morphologies in the limb leads were flat (51.0%), broad (14.3%), and late peaking (12.6%) T waves. Corresponding chest lead morphologies were inverted (35.5%), flat (19.6%), and biphasic (15.2%) T waves. Conclusions: Our results indicate that QT evaluation by limb leads only underestimates the incidence of diLQTS experiencing TdP and favors the screening using both limb and chest lead ECG.

Lessons Learned During the Pandemic: Correlation of QT Intervals Between Telemetry and 12-Lead Electrocardiogram

“…A prolonged QT interval is defined as 460 milliseconds (ms) or longer in women and 450 ms or longer in men [1]. Previous guidelines have recommended that one of the ECG limb leads should be used to measure QT, but in patients with drug-induced long QT syndrome, the most accurate measurement is obtained by using both limb and precordial leads [2].…”