Microvolt T wave alternans in human cardiac hypertrophy: Electrical instability and abnormal myocardial arrangement

Introduction: Although T wave alternans (TWA) is a promising risk marker fo r 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 card iomyopathy (HCM), 29 patients with hypertensive left ventricular hypertroph y (HLVH), and 15 normal volunteers using a CH2000 system. The amplitude of TWA (Valt) was measured at the lead with the maximum amplitude. Cardiac bio psy was performed in 12 HCM patients, who were divided into two groups (sev ere and mild) based on histologic findings of myocardial disarray and fibro sis. TWA was positive (Valt > 1.9 muV) in 61% of HCM and 31% of HLVH, despi te a nearly identical left ventricular mass index (176 +/- 65 g/m(2) vs 175 +/- 39 g/m(2)) Valt at heart rate = 110 beats/min was significantly greate r in HCM with severe disarray and fibrosis than in HCM with mild disarray a nd in HLVH, Conclusion: In HCM patients, a positive TWA test probably is related to abn ormal myocardial arrangement (disarray) and/or fibrosis, and it may reflect electrical instability of the myocardium.