Introduction
Drug-induced prolongation of the QT interval (diLQTS) substantially increases the risk for Torsades de Pointes (TdP) and sudden death.1 Offending agents include widely used drugs like antibiotics, antimalarials, antifungals, antivirals, anti-arrhythmic drugs (AAD), psychiatric drugs, and many others.1–3 In the current context of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infections,4 drugs with a risk for diLQTS, like hydroxychloroquine, azithromycin or antiviral drugs, are used widely off-label and are investigated in randomized trials in large patient populations.5 Expert consensus statements therefore recommend ECG screening for QT interval prolongation before treatment initiation and regularly during treatment with these drugs.6,7 However, repeated ECG screening using 12-lead ECG is clinically unfeasible in the large number of isolated, hospitalized or ambulatory patients, may increase the risk for virus transmission and is economically unfeasible in low-income countries.
Mobile ECG devices seem to be able to reconstruct the six ECG limb leads with good reproducibility of basic ECG intervals compared to conventional 12-lead ECGs in patients with normal and prolonged QT interval.8–11 They might therefore offer a lower-cost, clinically more convenient and safer screening modality for QT prolongation in diLQTS used by the patients themselves. However, as T-wave morphology in the limb leads may flatten in very long QT intervals with the highest risk for TdP, the diagnostic accuracy and interpretability of the QT interval might be low if only limb leads are used.12 Currently, systematic data on the diagnostic value of the limb versus chest leads for prolonged QT interval and T-wave morphology in patients with diLQTS and subsequent TdP are lacking.
We therefore aimed to systematically investigate the diagnostic value and interpretability of the limb versus the chest ECG leads in patients with diLQTS, who subsequently experienced TdP.