Introduction: Although T wave alternans (TWA) is a promising risk marker for myocardial electrical instability, it remains unclear how the presence of TWA is related to myocardial damage. Methods and Results: TWA was measured in 28 patients with hypertrophic cardiomyopathy (HCM), 29 patients with hypertensive left ventricular hypertrophy (HLVH), and 15 normal volunteers using a CH2000 system. The amplitude of TWA (Valt) was measured at the lead with the maximum amplitude. Cardiac biopsy was performed in 12 HCM patients, who were divided into two groups (severe and mild) based on histologic findings of myocardial disarray and fibrosis. TWA was positive (Valt > 1.9 μV) in 61% of HCM and 31% of HLVH, despite a nearly identical left ventricular mass index (176 ± 65 g/m2 vs 175 ± 39 g/m2). Valt at heart rate = 110 beats/min was significantly greater in HCM with severe disarray and fibrosis than in HCM with mild disarray and in HLVH. Conclusion: In HCM patients, a positive TWA test probably is related to abnormal myocardial arrangement (disarray) and/or fibrosis, and it may reflect electrical instability of the myocardium.
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