Noninvasive assessment of left ventricular function related to serum digoxin levels in neonates

Eighteen neonates in heart failure were investigated to assess whether high or low serum digoxin levels had differing effects on left ventricular function as determined by systolic time intervals obtained by echocardiography. Nine patients had digoxin levels of 1.99 +/- 0.35 ng/ml (group 1). Nine others had levels of 3.62 +/- 0.95 ng/ml (group 2). Systolic time intervals were obtained by echocardiography before and at 5 days after digoxin and correlated with serum levels. The heart rate, preejection period (PEP), left ventricular ejection time (LVET), electromechanical systole (QS2) and the PEP/LVET ratio were measured. LVET and electromechanical systole were indexed. These measurements were analyzed and the two groups were compared using Student's t test. The clinical improvement in both groups was similar and no difference in ECG changes were noted. Therapy with digoxin produced changes in heart rate and systolic time intervals in both groups. Both showed significant shortening of electromechanical systole index; group 1 significantly shortened the LVET index and PEP/LVET ratio, whereas group 2 significantly shortened the PEP. Statistical analysis comparing the two groups showed no difference between them. Digoxin produces measurable changes in the indices of left ventricular function. The magnitude of these changes suggests no therapeutic advantage to the higher levels.