Temporal Variability of the Electromechanical Window in Long-QT Syndrome and Drug-Induced QT Prolongation: Value for Enhanced Arrhythmia-Risk Assessment

BACKGROUND: Arrhythmia-risk assessment in congenital long-QT syndrome (LQTS) and drug-induced QT prolongation (diQTP) is primarily based on clinical, genetic, and electrical parameters. Electromechanical window (EMW) (aortic-valve closure time minus QT interval) assessment outperformed heart rate-corrected QT interval (QTc) as a predictor of symptomatic status in LQTS. OBJECTIVE: The study aimed to investigate the relationship between temporal QTc and EMW dynamics, and ventricular tachyarrhythmia (VT) timing in LQTS and diQTP. METHODS: 47 patients with LQTS/-VT, 18 patients with LQTS/+VT, 9 patients with diQTP/+VT, and 26 controls were included. QTc and EMW were obtained from standard 12-lead electrocardiograms and electrocardiogram-echocardiograms at 2 or 3 time points. Patients with +VT were included if EMW/QTc assessments were performed within 2 weeks before or after VT. RESULTS: In control subjects, EMW remained stably positive over time. In patients with LQTS/-VT, EMW was negative without significant variation. In patients with LQTS/+VT and diQTP/+VT, transient accentuations of EMW negativity were observed at the time point closest to VT (2 days 1-7 to arrhythmia), regardless of whether measured before or after VT. Temporary EMW negativity accentuation was driven by foreshortening of the mechanical systole despite concurrent QT prolongation. EMW recovery after VT was similar for patients with or without beta-blocker therapy. Multiple logistic regression analysis identified EMW negativity and EMW dynamics (ΔEMW) as independent predictors of imminent VT in LQTS. An EMW of -75 ms and a ΔEMW of -39 ms were optimal cutoffs to predict emergent arrhythmic deterioration in the LQTS cohort. CONCLUSION: Temporary accentuation of EMW negativity is a marker of impending VT in patients with LQTS and diQTP.