Differing rate dependence and temporal distribution of repolarization alternans in patients with and without...

Repolarization alternans (RPA) may reflect repolarization heterogeneities underlying VT, yet its temporal dynamics are poorly understood. We hypothesized that RPA occurring late, rather than early, within repolarization reflects a temporal variation in recovery that may predispose to wavefront fractionation and the initiation of reentrant VT, and that this temporal distribution may vary with heart rate.

ECG leads I, aVF, and V1 were recorded in 40 patients during electrophysiologic study. RPA across the JT interval was computed spectrally for 64-beat sequences at paced cycle lengths (CLs) of 600, 500, and 400 msec, and expressed as the T wave alternans ratio (TWAR) on the vector ECG lead. Significant RPA (TWAR > or = 3) was reconstructed into the time domain, and its center of area used to represent its temporal distribution. Twenty-two patients were inducible into VT and 18 were not. RPA was of larger magnitude in inducible than noninducible patients (TWAR = 11.1 vs 4.42, P = 0.035; 38.3 vs 5.74, P = 0.004; and 88.8 vs 4.28, P = 0.001 in each, respectively), and was distributed later (P < 0.02; CL 600 msec). Applying TWAR > or = 3 to the distal half of the JT segment produced greater specificity for inducible VT (88.9%, 66.7%, and 69.2% at each CL, respectively) than did RPA of the entire JT segment (77.8%, 53.3%, and 69.2%).

RPA is more specific for inducible VT when distributed late rather than elsewhere in repolarization, and this temporal distribution is heart rate sensitive. Further study is required to interpret these findings in the context of temporal dispersion of refractoriness.