Microvolt T-Wave Alternans as a Predictor of Ventricular Tachyarrhythmias: A Prospective Study Using Atrial Pacing

Background—Microvolt T-wave alternans (TWA) is reported to be closely associated with sudden cardiac death (SCD) and ventricular tachycardia (VT). Animal experiments revealed that microvolt TWA is highly dependent on heart rate. The purpose of this study was to determine whether patients with TWA at relatively low heart rates have increased vulnerability to ventricular tachyarrhythmias. Methods and Results—Subjects were 248 consecutive patients (158 men, 90 women; mean age, 59±17 years) who underwent electrophysiological study from 1997 to 2000. TWA recording was made in sinus rhythm and at atrial pacing rates of 90, 100, 110, and 120 bpm with the Cambridge Heart CH2000 system. Alternans voltage (Valt) was measured when the alternans ratio was >3 for a period of >1 minute in VM, X, Y, Z, or 2 adjacent precordial leads. Study end point was the first appearance of VT, ventricular fibrillation (VF), appropriate implantable cardioverter-defibrillator therapy with pacing or shocks, or SCD. During the 37±12-month follow-up period, 22 patients had sustained VT, and 5 patients died of SCD. In patients with >1.9-μV Valt at rates of 90, 100, and 110 bpm, the incidence of VT/VF/SCD was 56%, 28%, and 18%, respectively. Valt of >2.9 μV at a heart rate of 90 bpm had a 70% positive predictive value for VT/VF/SCD. However, when Valt was <0.9 μV at a rate of 120 bpm, negative predictive value was 100%. Conclusions—Patients with TWA at relatively low heart rates are susceptible to ventricular tachyarrhythmias.