Autonomic Markers as Predictors of Nonfatal Acute Coronary Events after Myocardial Infarction

Abstract

Autonomic markers, such as heart rate variability (HRV), heart rate turbulence (HRT), and baroreflex sensitivity (BRS) provide information on the risk of all-cause mortality after an acute myocardial infarction (AMI), but their value in predicting nonfatal cardiac events is not well known. A consecutive series of 675 patients with an AMI were followed up to 30 months. At baseline, the patients underwent a 24-hour Holter recording, and assessment of BRS using phenylephrine test. Several parameters of HRV and HRT were determined. After the follow-up, 98 patients (15%) had a nonfatal acute coronary event. Among the studied variables, the short-term scaling exponent alpha1 (P = 0.002), power-law slope beta (P = 0.008), low-frequency component of HRV power spectrum (P < 0.001), turbulence slope (P < 0.001), and BRS (P < 0.001) had the strongest association with the occurrence of nonfatal acute coronary events in univariate comparisons. After adjustment with relevant clinical variables (such as age, gender, ejection fraction, functional class, medication, diabetes) in the Cox proportional hazards model, alpha1 and beta remained as statistically significant predictors of nonfatal acute coronary events (HR = 2.0 [1.2-3.2, 95% CIs, P = 0.006] for alpha1 < or = 1.025), (HR = 1.9 [1.2-3.1, P = 0.008] for beta < or =-1.507). Several autonomic markers provide information on the risk of recurrent nonfatal coronary events after an AMI. Altered fractal heart rate behavior seems to be the strongest independent predictor of such events.