[Development of the heart rate in the first year of life and infant ill health]

Abstract

Heart rate during the 1st year of life decreases from 149 to 117/min (mean) and 227 to 186 (upper range), as determined by Holter monitoring. There is little change in those at the lower frequencies. A decrease in nocturnal rhythm becomes evident by 3 months of age. In comparison to these controls, near-miss infants or their sibs and infants with "spells" demonstrate a lower basal rate with longer pauses and wider range of instantaneous variability from the 1st days of life. Near-miss infants and sibs of sudden infant death syndrome infants are harder to differentiate. However, the "sibs" + "spells" groups show prolonged pauses over 1 second in the first weeks of life and become even more prominent at 3 months. This vagal hyperreactivity may be due to immature or poorly regulated cholinergic bulbar centers.