RESUMO
AIMS: To evaluate the predictive value of heart rate turbulence (HRT) and microvolt T-wave alternans (mTWA) for sudden cardiac death (SCD) in patients after myocardial infarction (MI). METHODS AND RESULTS: We studied 111 patients with MI in the previous 60 days (median, 27 [9;84] months) before inclusion (84 men, mean age 64.1 ± 10.5 years, mean left ventricular ejection fraction 46.6 ± 12.2%). Heart rate turbulence and mTWA were evaluated using 24 h ambulatory electrocardiogram monitoring. The primary endpoint was SCD, and the secondary endpoint was all-cause mortality and non-sudden death from cardiovascular causes. During follow-up of 12 months, 15 SCD and 8 non-sudden cardiovascular deaths (including five fatal MI and three fatal strokes) occurred. Non-survivors had significantly higher mTWA values (83 [74;165] vs. 79 [78;94] mcV, P= 0.002), absolute turbulence onset (TO) values (0 [-0.005;0.01] vs. -0.01 [-0.013;-0.004], P= 0.004), and significantly lower absolute turbulence slope (TS) values (3.34 [2.10;4.83], vs. 3.82 [4.48;7.27], P< 0.001) compared with survivors. In patients with SCD, mTWA, and TO were significantly higher (92 [72;213] vs. 74 [65;86] mcV, P= 0.004 and 0 [-0.001;0.01] vs. -0.01 [-0.03;0.01], P= 0.007, respectively) and TS values were significantly lower (2.14 [1.10;4.56] vs. 4.41 [2.1;7.18], P= 0.005) than in patients with non-sudden death. All parameters were significantly worse in non-survivors than in survivors. We defined cut-off values for increased risk of SCD: for TO = -0.005, relative risk (RR) was 12.4 [95% confidence interval (CI) 2.6-38.2, P< 0.001; positive predictive value (PPV) 28.3%, negative predictive value (NPV) 96.9%], and for mTWA > 53.5 mcV at 100 b.p.m., RR was 5.01 (95% CI 1.5-17.0, P= 0.005; PPV 24.4%, NPV 93.9%). Notably, mTWA > 18.5 mcV at 05.00 AM significantly increased all-cause mortality [RR 7.5 (95% CI 1.4-38.7), P= 0.01; PPV 19.6%, NPV 90.8%]. CONCLUSION: In patients who died from cardiovascular causes, mTWA, and TO values were significantly higher and TS values were significantly lower than in survivors, and the subgroup with SCD was characterized by significantly increased mTWA and TO values and decreased TS values. mTWA > 53.5 mcV at 100 b.p.m. was an independent significant predictor of SCD and increased risk of SCD by five-fold.
