Influence of Pacing Modes on Microvolt T-Wave Alternans

Objective: Cardiac resynchronization therapy (CRT) is known to be effective for left ventricular dysfunction associated with left bundle branch block. However, CRT does not necessarily decrease the risk of sudden cardiac death. Recent studies have shown that epicardial left ventricular pacing may lead to prolongation of the QT interval and the development of torsades de pointes. Microvolt T-wave alternans (TWA) has been associated with increased susceptibility to ventricular tachyarrhythmias. We compared the influence of right atrial pacing, right ventricular pacing, left ventricular pacing and biventricular pacing (RAP, RVP, LVP and BVP) on TWA. Methods: TWA was measured per pacing mode during incremental pacing from 70 to 120 bpm in 18 CRT patients with a mean ejection fraction of 32±5%. TWA was considered positive if alternans voltage (Valt)>1.9 μV and alternans ratio (AR)>3.0 were observed for at least 1 minute. The incidence of TWA is reported as the percentage of impulse applications during which it was observed. Results: TWA was observed as follows: BVP, 73%; RVP, 50%; LVP, 60%; and RAP, 60%. Mean Valt (μV) was 2.44±0.35, 0.36±0.11, 1.44±0.65, and 1.95±0.45, respectively (P<0.01 BVP vs. RVP). Mean alternans ratio during BVP, RVP, LVP, and RAP was 8.21±2.4, 4.28±1.3, 5.66±2.3, and 7.36±2.0, respectively (P<0.05 BVP vs. RVP). Conclusion: BVP may increase the temporal inhomogeneity of ventricular repolarization, which may lead to the development of ventricular tachyarrhythmia.