T‐Wave Alternans Measured by 24‐Hour Ambulatory Recordings Rather Than Exercise Stress Tests as a Risk Stratification Marker in Patients With Long QT Syndrome

Abstract

Background Few small‐sample studies have quantified the T‐wave alternans (TWA) value by 24‐hour ambulatory recordings or exercise stress tests in patients with long QT syndrome (LQTS). The cutoff point of TWA ≥47 μV was based on patients with myocardial infarction. In our study, we aimed to (1) evaluate the association of TWA with life‐threatening arrhythmic events (LAEs); (2) compare the predictive model of LAEs according to the TWA value measured by 24‐hour ambulatory recordings and exercise stress tests; and (3) propose a cutoff point for the high risk of LAEs in patients with LQTS. Methods and Results The study cohort included 110 patients with LQTS referred to our hospital, and the primary outcome was LAEs. Thirty‐one patients with LQTS (31/110 [28.2%]) developed LAEs during the following 24 (12–47) months. Peak TWA value quantified from 12 leads by 24‐hour ambulatory recordings in patients with LQTS with LAEs (LQTS–LAEs group) was significantly higher than LQTS without LAEs (LQTS–non‐LAEs group) (64.0 [42.0–86.0] μV versus 43.0 [36.0–53.0] μV; P <0.01). There was no statistical difference in TWA value measured by exercise stress tests between the 2 groups (69.0 [54.5–127.5] μV versus 68.5 [53.3–99.8] μV; P =0.871). The new cutoff point of the peak TWA value measured by 24‐hour ambulatory recordings was 55.5 μV, with a sensitivity of 75.0% and a specificity of 78.6%. A univariate Cox regression analysis revealed that TWA value ≥55.5 μV was a strong predictor of LAEs (hazard ratio [HR], 4.5 [2.1–9.6]; P <0.001]. A multivariate Cox regression analysis indicated that TWA value ≥55.5 μV remained significant (HR, 2.7 [1.1–6.8]; P =0.034). Conclusions Peak TWA measured by 24‐hour ambulatory recordings was a more favorable risk stratification marker than exercise stress tests for patients with LQTS.