Correlations between SAECG and HRV parameters in individual patients after myocardial infarction

The effects of alterations in autonomic tone on the signal-averaged ECG (SAECG) have not been evaluated systematically in postinfarction patients. To study the circadian variations of the SAECG and potential link between fluctuations in the SAECG and the autonomic tone, bedside monitoring (10pm-6am) of high resolution ECG´s was performed in 34 patients with myocardial infarction. From 15 min-time segments at the beginning of every hour, SAECG parameters (QRSD LAS40, RMS40) were calculated. In addition, time and frequency domain parameters of heart rate variability (HRV) were determined from each time segment: HR, SD, MSSD; and the HF (0.15-0.40 Hz) power, LF (0.04-0.15 Hz) power and the ratio of LF to HF (LF/HF) power. The variability of LP and HRV parameters was expressed as the coefficient of variation. Spearman´s rank correlation coefficient was used in estimating the link between SAECG and HRV parameters. In 9/43 patients late potentials (LP) were permanently present, in 9/43 patients LP were seen intermittently and in 14/43 patients no LP were observed. Significant positive and negative correlations between SAECG and HRV parameters were found in 7/18 patients with permanent or intermittent LP whereas 11/14 Patients without LP showed significant correlations between SAECG parameters and HR or LF/HF. These findings imply that consideration of the baseline autonomic state may be required for optimal use of the SAECG.