Sugrue, van Zyl M, Enger N, et al.
Echocardiography-Guided Risk Stratification for Long QT Syndrome. J Am Coll Cardiol 2020;76:2834-2843.
Is it possible to identify a subset of patients at the highest risk for long QT syndrome (LQTS)–associated life-threatening cardiac events by examining the electromechanical window (EMW) negativity, as derived from continuous-wave Doppler echocardiography?
There were 651 patients with LQTS (mean age, 26 years; 60% females; 158 symptomatic; 51% LQTS type 1; 33% LQTS type 2; 11% LQTS type 3) and 50 healthy controls. EMW was calculated as the difference between the interval from QRS onset to aortic valve closure midline, as derived for continuous-wave Doppler, and the electrocardiogram-derived QT interval for the same beat.
A negative EMW was found among nearly all patients with LQTS compared to controls, with more profound EMW negativity in patients with symptomatic LQTS compared to those with asymptomatic LQTS (-52 ± 38 ms vs. -18 ± 29 ms; p < 0.0001). Logistic regression identified EMW, corrected QT interval, female sex, and LQTS genotype as univariate predictors of symptomatic status. After multivariate analysis, EMW remained an independent predictor of symptomatic status (odds ratio for each 10-ms decrease in EMW, 1.37; 95% confidence interval, 1.27-1.48; p < 0.0001). EMW outperformed corrected QT interval in predicting symptomatic patients. EMW correlation across sonographers showed excellent reliability.
In this validation study, patients with a history of LQTS-associated life-threatening cardiac events had a more profoundly negative EMW. EMW outperformed heart rate–corrected QT interval as a predictor of symptomatic status. EMW is now a clinically validated risk factor.
So far, efforts at risk prediction in LQTS have mainly focused on the electrical manifestations of this condition such as corrected QT interval and T-wave morphology. This fascinating manuscript ties together the abnormalities in electrical conduction with mechanical function abnormalities observable on echo with high interobserver reliability. In normal adults, the end of electrical systole occurs slightly before the end of mechanical systole, resulting in a positive EMW. A negative EMW occurs when there is a mismatch between the end of electrical and mechanical systole as a result of prolongation of electrical systole. The exact mechanism is speculative, and it is possible that EMW is a surrogate marker that highlights impaired relaxation and inhomogeneity across the ventricle as the substrate for arrhythmogenesis. EMW should be evaluated prospectively in the QTS population and potentially many other arrhythmogenic conditions.