[Study of heart rate variability in acute myocardial infarction and its relationship with ventricular function and other clinical variables].

BACKGROUND: The influence of ventricular function (VF) on prognosis in acute myocardial infarction (AMI) is well known. Heart rate variability (HRV), as a neurohumoral parameter could predict VF after discharge in AMI patients. Our goal is to investigate the possible relation among HRV, VF and another clinical variables in AMI.

PATIENTS AND METHODS: We studied 37 patients with AMI after hospital discharge. Age, AMI type, location, enzymes, treatment (thrombolysis versus no thrombolysis) were evaluated. The left ventricular ejection fraction (LVEF) was assessed by radionuclide ventriculography in 27 subjects. Twenty nine subjects without cardiopathy were the control group. Twenty four hour electrocardiographic recordings were obtained and a proper software was used to measure HRV. This was evaluated with time domain measures: RR interval, standard deviation of the mean RR interval (SDNN), standard deviation of the average of the RR intervals measured every 5 minutes during 24 hours (SDANN) and number of two consecutive RR intervals with a variability > 50 ms (pNN50). We considered a decreased variability if SDANN was less than 100 ms. Two groups were established: 1) low heart rate variability (LHRV) if SDANN was less than 100 ms, and 2) normal heart rate variability (NHRV) if SDANN was larger than 100 ms. Continuous variables were examined by the t-test, chi square for discrete ones and linear regression analysis was used to assess the relation among variables. A p < 0.05 was considered significant.

RESULTS: The percentage of infarcted patients in the group of LHRV is 75%, whereas it is 14% in the control group (p < 0.05). SDANN, SDNN and pNN50 values are significantly lower (p < 0.05) in the AMI than in the control group. LHRV was more frequent in patients with complicated AMI with congestive heart failure. LVEF was significantly lower (35% vs 56%) in the LHRV than in the NHRV group. No significant differences were found among: site, type infarct, treatment or ventricular ectopy in the Holter before discharge. There is good correlation (r = 0.635; p < 0.05) between LVEF and HRV measures. No correlation was found between HRV and age, or the enzymatic size of infarction.

CONCLUSIONS: 1) LHRV is frequent in the late phase of AMI, and 2) LHRV can be an indirect index of left ventricular failure.