Digoxin therapy and left ventricular performance in premature infants with patent ductus arteriosus.

Left ventricular systolic time intervals were assessed in 16 preterm infants with symptomatic left-to-right ductal shunts, before, during and after digoxin therapy. An intravenous loading dose of digoxin, 20 micrograms/kg, resulted in a serum digoxin concentration of 1.94 +/- 0.44 nmol/l (mean +/- 1 SD) but in no significant change in heart rate or systolic time intervals. Digoxin maintenance, 2.5 micrograms/kg/12 h, led 3-7 days later to serum concentrations of 2.57 +/- 1.06 nmol/l with an associated shortening of left ventricular ejection time (p less than 0.05) which probably reflected a reduced ductal shunt. Digoxin therapy was withdrawn after ductal closure. The terminal serum half-life was 87 +/- 17 h. Decreasing digoxin concentrations were associated with prolongation of left ventricular ejection time (p less than 0.01). Digoxin therapy did not seem to influence left ventricular systolic time intervals while ductal patency persisted. This may be attributed to limitations of the method or the left ventricle already working at its maximum.