Echocardiography-Guided Risk Stratification for Long QT Syndrome

Background: The ability to identify those patients at the highest phenotypic risk for long QT syndrome (LQTS)-associated life-threatening cardiac events remains suboptimal.

Objectives: This study sought to validate the association between electromechanical window (EMW) negativity, as derived from echocardiography, and symptomatic versus asymptomatic status in patients with LQTS.

Methods: We analyzed a cohort of 651 patients with LQTS (age 26 ± 17 years; 60% females; 158 symptomatic; 51% LQTS type 1; 33% LQTS type 2; 11% LQTS type 3; 5% multiple mutations) 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.

Results: 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, heart rate-corrected QT interval (QTc), 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 to 1.48; p < 0.0001). EMW outperformed QTc in predicting symptomatic patients (area under the curve: 0.78 vs. 0.70; p = 0.01). After training and implementation, EMW correlation from echocardiographic sonographers showed excellent reliability (intraclass correlation coefficient: 0.93; 95% confidence interval: 0.89 to 0.96).

Conclusions: 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. In December 2019, our institution's echocardiography clinical practice committee approved use of EMW for patients with LQTS, making it a routinely reported echocardiographic finding.