Differing Rate Dependence and Temporal Distribution of Repolarization Alternans in Patients with and without Ventricular Tachycardia

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Abstract
Temporal Dynamics of Repolarization Alternans. Introduction: Repolarization atlternans(RPA) may reflect repolarization heterogeneities underlying VT, yet its temporal dynamics are poorly understood. We hypothesized (hat RPA occurring late, rather than early, with in repolarization reflects a temporal variation in recovery that may predispose to wave front fractionation and the initiation of reentrant VT, and that this temporal distribution may vary with heart rate. Methods and Results: ECG leads I, aVF, and V1 were recorded in 40 patients during; electrophysiologic study. RPA across the JT interval was computed. spectrally for 64‐heatsequences 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 ≥ 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 4.2S. P = 0.001 in each, respectively), and was distributed later (P < 0.02; CL 600msec). Applying TWAR ≥ 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%) Conclusion: RPA is more specific for inducible VT when distributed late rather than else wherein 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.