Effect of digoxin on left ventricular contractility in newborns and infants estimated by echocardiography.

In view of the known susceptibility of newborns to digoxin intoxication this study was undertaken in order to evaluate the effect of a relatively low digoxin dose on left ventricular contractility of newborn infants. Left ventricular ejection time, enddiastolic diameter and endsystolic diameter were measured by echocardiography before digitalization as well as between 2 and 4 h after the first digoxin dose (group 1 : 16 patients) or after full digitalization (group 2 : 12 patients). From these data, shortening fraction (SF) and mean velocity of fiber shortening (mean Vcf) were calculated. We found that SF and mean Vcf increased significantly in both groups after the first digoxin dose and after full digitalization. The increase was equal in newborns and infants. The mean plasma digoxin concentration after full digitalization was 2.2 ng/ml (range 0.7--4.4 ng/ml). These results demonstrate clearly the positive inotropic effect of a relatively low digoxin dose in newborns.