RESUMO
BACKGROUND: Reproducibility of heart rate (HR) and heart rate variability (HRV) indices from ambulatory electrocardiograms (AECGs) is a prerequisite for their use as predictors or monitors of disease progression, or response to therapeutic interventions. HYPOTHESIS: This study sought to determine the stability over time of HR and HRV indices in patients with coronary artery disease. METHODS: Five AECGs, recorded at 1-week intervals in 21 clinically stable patients, were used to calculate minimum, average, and maximum HR, and three commonly used HRV indices in data samples of 15, 30, 60, 120, daytime and nighttime intervals (complete data were available on 17 patients). RESULTS: All parameters studied were stable over time (p = NS). Diurnal variation was found only for the average and maximum HR, with values being higher for daytime than for nighttime. Intercorrelations of the HR and HRV indices were poor and varied among the five AECGs, suggesting that these parameters reflect different aspects of HRV. The HR and HRV variables calculated from short-time intervals correlated poorly with the corresponding information from 24-h recordings, and such relationships varied among the five AECGs. CONCLUSIONS: Thus, HR and HRV indices from five consecutive AECGs recorded at 1-week intervals are reproducible. The poor intercorrelations between pairs of the studied indices suggest that none of these parameters can be used as surrogate of the others. Finally, the poor performance of HR and HRV indices, deriving from short-time intervals, indicate that they cannot be employed in lieu of parameters calculated from 24-h AECGs.
