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 infarctio n is associated with an increased risk of cardiac mortality. The aim o f this study was to investigate the determinants of frequency domain m easures of heart rate variability in acute myocardial infarction. Meth ods: Heart rate variability in the frequency domain was compared in 43 patients in the early (0-12 h from the onset of pain) and convalescen t (1 week after) phases of myocardial infarction and related to locati on (22 patients with anterior infarction and 21 patients with inferior infarction) and size of the infarct, occurrence of ventricular ectopi c activity, and thrombolytic therapy. Results: In the early phase of i nfarction all the power spectral components of heart variability were significantly lower in the patients with anterior infarcts than in tho se with inferior infarcts (p < 0.05 for all), but heart rate variabili ty did not differ significantly between anterior and inferior infarct groups in the convalescent phase. High frequency power of heart rate v ariability was significantly lower in the convalescent phase than in t he early phase in both the anterior and inferior infarction groups (p < 0.05 and p = 0.001, respectively), but other measures of variability did net change significantly. The ejection fraction was correlated wi th total power (p < 0.05), low frequency power (p < 0.01), and very lo w frequency power of heart rate variability (p < 0.05), and the low fr equency and high frequency power components were significantly lower i n the patients with non-sustained ventricular tachycardia than in thos e without repetitive ventricular activity in the convalescent phase of myocardial infarction (p < 0.05). Thrombolytic therapy had no influen ce on the measures of heart rate variability. Conclusions: The frequen cy domain measures of heart rate variability are mostly determined by the location of myocardial infarction in the early phase, whereas a co rrelation between heart rate variability and left Ventricular function and arrhythmic propensity is more obvious in the convalescent phase.