Comparative study of the electrocardiograms of healthy fullterm and premature newborns.

The electrocardiograms of 421 healthy fullterm and premature newborns, recorded on the fifth day of life, were evaluated for possible systematic differences related to gestational age. All newborns were appropriate for gestational age and were divided into four groups according to birthweight. As birthweight increased, we noted: (a) a progressive rightward shifting of the QRS axis in the frontal plane; (b) an increase in the amplitude mainly of the precordial R and S waves reflecting the right ventricle and both ventricles combined, whereas a less significant increase or even a decrease was noted in the R and S waves reflecting the left ventricle; (c) a more frequent occurrence of diphasic and positive T waves in the right precordial leads; and (d) a prolongation in the duration of the P wave and the QRS complex. These findings reflect both an increase in total myocardial mass as well as a progressive right ventricular predominance, as birthweight or gestational age increases. Practical implications for electrocardiographic identification of cardiac hypertrophy in newborns of different gestational age are discussed.