ABSTRACT
BACKGROUND: Our aim was to compare the distribution and determinants of heart rate variability (HRV) measures in a middle-aged population with patients of the same sex and age after an acute myocardial infarction (AMI), and to show, whether HRV values defined as abnormal from the general population are indicative for a worse prognosis even in AMI patients. METHODS: HRV was studied in a random sample of 149 middle-aged men and 137 women from the general population (45-65 years) as well as 129 consecutive AMI patients (25-74 years). Spectral analysis was used to compute low frequency (LF), high frequency (HF), and total frequency power. To the AMI population of age 45-65 years (N = 85) a sample out of the general population was matched by age and sex by 2:1 matching (N = 149). All AMI patients were followed for a median of 43 months (range 1-47) for death or malignant arrhythmia. RESULTS: All measures of HRV were significantly and substantially lower in AMI patients than the general population (P < 0.001). Expression in relative terms revealed that the proportionate contributions of HF and LF to total power were significantly different in the two populations with relatively lower LF power in AMI patients (P < 0.01). The negative correlation with heart rate and HRV measures was significantly more pronounced in AMI patients (P < 0.01). The 2.5th percentile of the LF power distribution in the general population (3.08 ln ms2) corresponds to the 25th percentile in the AMI population. Subjects of the whole AMI population with values below this LF cutpoint revealed a significant increased risk of death or malignant arrhythmia during follow-up (odds ratio 5.1; 95% confidence interval: 1.3; 23). CONCLUSIONS: AMI patients had strongly diminished HRV compared to the general population. The relatively lower LF power indicates an alteration of the sympathico-vagal balance, and the significantly stronger correlation of heart rate with HRV may be indicative for a more pronounced effect of sympathetic activation on autonomic modulation in the case of myocardial infarction. Finally, a value below the 2.5th percentile of the population LF power distribution may identify subjects at risk and warrant further testing.
