[Electrocardiography changes in newborn infants during the 1st 6 weeks of life in Mexico City. Physiological implications].

The electrocardiograms of 150 newborns who were born in Mexico City (2,240 m. above sea level) were obtained in the first 24 hours of life and six weeks later. The electrocardiographic changes were similar to those observed at sea level; AQRS shifted to the left, the T waves became negative in the right precordial leads and the R/S relation increased in the left precordial leads. Mid-altitude does not affect the pulmonary vascular maturation of the normal newborn.