Relationships between heart rate variability, functional capacity and leftventricular function following myocardial infarction: An evaluation after one week and six months

Background: Relationships between heart rate (HR) variability and different prognostic markers such as ejection fraction, functional capacity, and pat ency of the infarct-related artery, as well as the comparison of their time courses are not fully elucidated. Hypothesis: The aim of study was to assess prospectively the early postinfa rction changes in HR variability and its evolution over a period of 6 month s; the relationships between HR variability and functional capacity in exer cise testing; left ventricular function in cardiac catheterization; status of the infarct-related artery; and the comparison of their time courses. Methods: In 42 patients with anterior myocardial infarction, a study was ma de of the early changes in HR variability analyzed by the complex demodulat ion method, its evolution over a period of 6 months, and the relationships between HR variability and(1) functional capacity in exercise testing, (2) left ventricular function in cardiac catheterization, and (3) status of the infarct-related artery. Results: At 1 week HR variability parameters correlated directly with funct ional capacity indicators such as METS, percent change in HR from rest to p eak exercise (%Delta HR), difference between initial and peak HR (HR range) , percent peak theoretical HR (% peak HR), left ventricular ejection fracti on (EF), and, inversely, with end-systolic volume (ESV). Stepwise multiple regression analysis to establish HR variability parameters (recorded at 1 w eek) as related to functional capacity and left ventricular function at 1 w eek and 6 months postinfarction established the following variables: (1)At 1 week: standard deviation (SD) of the RR cycles in relation to %Delta HR ( r = 0.60, p<0.0001), HR range (r = 0.43, p < 0.01), and EF (r = 0.79, p<0.0 001). (2) At 6 months, the sole accepted HR variability parameter was the S D in relation to %<Delta>HR (r = 0.38, p < 0.05) and HR range (r=0.45, p<0. 01). No variability parameter was accepted in relation to METS, % peak HR, or ESV. Relationship between EF or ESV and HR variability parameters was no t significant when both were evaluated at 6 months. At that time, there was a significant increase in all HR variability parameters among all survivin g patients (n = 39) with the exception of the LF/HF ratio and mean RR cycle . The percent increase in HR variability between the first week and 6 month s was greater among those patients with the lowest basal EE No relation was established between HR variability and patency of the infarct-related arte ry. Conclusion: The decrease in HR variability observed following myocardial in farction is associated with a diminished functional capacity and an increas ed alteration of the EE This does not affect the recovery of HR variability , which was observed in all surviving patients.