Heart Rate Variability and Plasma Catecholamine Levels Early After Acute Myocardial Infarction

Abstract

BackgroundAn imbalance between sympathetic and parasympathetic tone has been shown to contribute to the genesis of malignant arrhythmias after acute myocardial infarction (AMI). To assess a relationship between the magnitude of sympathoadrenal activation and the balance of autonomic input to the heart early after AMI, plasma catecholamine levels and spectral analysis of short‐term heart rate variability (HRV) were evaluated on day 2 and 5 after hospital admission under standardized conditions.MethodsThirty‐two patients with AMI (27 men, 5 women, mean age 58 ± 10 years) were studied, 13 with anterior and 19 with inferior AMI. Mean left ventricular ejection fraction (LVEF), assessed by two‐dimensional echocardiography, was 48%± 10%. Thirty‐minute ECG recordings were performed in recumbent position, between 9–11 A.M., and edited data were used for analysis of HRV in frequency domain. The control group consisted of 9 patients (6 men, 3 women, mean age 49 ± 10 years) without a history of cardiovascular or systemic disease, who had normal findings on physical examination of the cardiovascular system, and normal 12‐lead ECG. All control subjects were admitted to the hospital for eye or dermatological surgery and underwent the same study procedures according to the identical time schedule.ResultsPlasma catecholine levels decreased significantly from day 2 to 5 of AMI, however, compared to control subjects, the only significant difference suggesting early sympathoadrenal activation in AMI patients was elevated plasma norepinephrine on day 2 (1.73 ± 1.6 vs 0.81 ± 0.7, P < 0.049). Among spectral components of HRV, a trend toward decrease from day 2 to 5 was found for both high frequency (HF) (123.8 ± 184.8 vs 66.7 ± 80.1 ms2, P < 0.03) and low frequency (LF) (293 ± 423.3 vs 164.3 ± 235.4 ms2, P < 0.14) components, although statistically significant only for HF components. However, the ratio between LF and HF components remained unchanged (3.4 ± 2.6 vs 3.6 ± 2.7). Significantly lower values of both LF and HF components, total power, and mean NN interval together with a tendency for a higher LF/HF ratio on day 2 were found in patients with anterior AMI as compared to those with inferior AMI or control subjects. This difference already disappeared on day 5 due to a decrease in both components of HRV in patients with inferior localization of the infarct. Patients with depressed LVEF presented with significantly lower HF components (both in absolute and relative units) while no difference was observed in the mean heart rate or in relative LF components. No significant correlations were found between LF or HF components or their ratio and either measure of sympathoadrenal activity (epinephrine, or norepinephrine and dopamine).ConclusionThe findings of increased plasma norepinephrine levels early after AMI confirm initial sympathoadrenal activation, which was probably related to the presence of myocardial ischemia and/or necrosis per se, independently on the site of myocardial infarction and the degree of impairment of LVEF. The observed changes in spectral measures of short‐term HRV assessed at supine rest under standardized conditions appear to reflect the extent of impairment of cardiac autonomic regulation rather than the magnitude of sympathoadrenal activation. Significant depression of HF