Effect of beta-blockade on quantitative microvolt T-wave alternans in 24-hour continuous 12-lead ECG recordings in patients with long QT syndrome.

Abstract

The aim of study was to investigate effects of beta-blockade on microvolt T-wave alternans (TWA), a precursor of lethal arrhythmia, in patients with long QT syndrome (LQTS). Eleven consecutive LQTS patients, types 1 (n=6), 3 (n=2), and "non-1, non-2, non-3" (n=3) were enrolled. All patients underwent 24-hr continuous 12-lead ECG monitoring before and after initiation of beta-blockade therapy. TWA was measured using the modified moving average method. Seven (63.6%) of the 11 patients studied were symptomatic, with history of cardiac arrest or documented Torsade de Pointes (TdP) in 4 and syncope in three patients. After a median follow-up of 34months, beta-blockade reduced the number of symptomatic patients to 1 with TdP (p<0.02), in whom TdP frequency decreased from 25 events/60months (0.42 event/month) to seven events/69months (0.1 event/month). In association with this reduction in symptoms, peak TWA decreased by 47% in the cohort after a median of eight months of beta-blockade therapy [from 95 (74-130) to 50 (39.5-64.5) µV, p=0.01]. All patients exhibited TWA ≥42µV before beta-blockade therapy, which eliminated these episodes in four patients. Daily frequency of TWA ≥42µV episodes decreased by 87% [from 15 (6-26) to 2 (0-5) episodes/day, p=0.009]. This study is limited by the small sample size and is mainly hypothesis generating. TWA monitoring deserves further evaluation as a risk marker and a guide to therapy in LQTS patients in future large-scale studies.