Determinants of frequency domain measures of heart rate variability in the acute and convalescent phases of myocardial infarction

OBJECTIVE: Low heart rate variability after acute myocardial infarction is associated with an increased risk of cardiac mortality. The aim of this study was to investigate the determinants of frequency domain measures of heart rate variability in acute myocardial infarction. METHODS: Heart rate variability in the frequency domain was compared in 43 patients in the early (0-12 h from the onset of pain) and convalescent (1 week after) phases of myocardial infarction and related to location (22 patients with anterior infarction and 21 patients with inferior infarction) and size of the infarct, occurrence of ventricular ectopic activity, and thrombolytic therapy. RESULTS: In the early phase of infarction all the power spectral components of heart variability were significantly lower in the patients with anterior infarcts than in those with inferior infarcts (p < 0.05 for all), but heart rate variability did not differ significantly between anterior and inferior infarct groups in the convalescent phase. High frequency power of heart rate variability was significantly lower in the convalescent phase than in the early phase in both the anterior and inferior infarction groups (p < 0.05 and p = 0.001, respectively), but other measures of variability did not change significantly. The ejection fraction was correlated with total power (p < 0.05), low frequency power (p < 0.01), and very low frequency power of heart rate variability (p < 0.05), and the low frequency and high frequency power components were significantly lower in the patients with non-sustained ventricular tachycardia than in those without repetitive ventricular activity in the convalescent phase of myocardial infarction (p < 0.05). Thrombolytic therapy had no influence on the measures of heart rate variability. CONCLUSIONS: The frequency domain measures of heart rate variability are mostly determined by the location of myocardial infarction in the early phase, whereas a correlation between heart rate variability and left ventricular function and arrhythmic propensity is more obvious in the convalescent phase.