Absence of slowest oscillations in short term heart rate variability of post-myocardial infarction patients. GISSI-3 arrhythmias substudy. GISSI-3 Arrhythmias Substudy Investigators.

Despite the widely demonstrated association of reduced heart rate variability (HRV) to bad prognosis after myocardial infarction (MI), reference values for HRV parameters are still not available. The GISSI-3 Arrhythmias Substudy studied short-term HRV in a relatively unselected population of patients (324) with recent MI (13 +/- 7 days) providing the statistical description of the main time and frequency domain parameters. All HRV indices, except for the RR interval, showed a non-normal distribution generally skewed around the lowest values. Particularly, no LF power was detected in 75 patients (23%) by power spectral analysis. The absence of LF oscillation in RR spectra was associated to the lower standard deviation of normal RR intervals (SD), aging (> 65 years) and blood pressure hypertension. This result seems to indicate a paradoxical effect of sympathetic overactivity in post-MI patients.