Heart-Rate Dependency of T-Wave Alternans During the Exercise and Recovery TWA dependency on herat rate

Microvolt T-wave alternans (TWA), a subtle every-other-beat fluctuation of the electrocardiographic (ECG) T-wave amplitude, is a risk index for the occurrence of malignant ventricular arrhythmias. It is well-known that TWA increases with HR so that TWA is often analyzed during exercise. Since TWA during recovery is usually not evaluated, it is not clear if there is a HR-TWA one-to-one correspondence, or if TWA depends on how such HR was reached. Thus, the aim of the present study was to investigate TWA during both HR-increasing exercise and HR-decreasing recovery. To this aim, our HR adaptive match filter (AMF) for automatic TWA identification was applied to ECG recordings of 266 patients with implanted cardio-defibrillator (ICD). HR varied from 70 bpm to 125 bpm during exercise and vice versa during recovery. Our results indicate that TWA increased (from 17 mu V to 51 mu V) with increasing HR during exercise, and decreased (from 28 mu V to 17 mu V) with decreasing HR during recovery. However, such TWA changes did not occur symmetrically, but TWA was significantly lower during exercise than during recovery at low HRs (17-18 mu V vs. 20-25 mu V for HR<100 bpm; P<0.05), and vice versa at high HRs (41-51 mu V vs. 28 mu V for HR>100 bpm; P<10(-6)). Thus, there is not a HR-TWA one-to-one correspondence but the value of TWA at a specific HR depends on how such HR was reached.