Effects of Maintenance Digoxin Therapy on Systolic Time Intervals and Serum Digoxin Concentrations

Systolic time intervals (STI) and serum digoxin concentrations (SDC) were measured in eight patients with compensated atherosclerotic and/or hypertensive heart disease who received oral digoxin 0.25 mg/day or 0.5 mg/day for alternate two-week periods without a loading dose. Control data were obtained both before and after the four weeks of treatment. After 13 days treatment with digoxin, 0.5 mg/day, there was a significant decrease in total electromechanical systole corrected for heart rate (QS 2 i), pre-ejection period (PEP), pre-ejection period corrected for heart rate (PEP 1 ) and PEP/left ventricular ejection time (LVET). After the thirteenth dose of 0.25 mg/day there was significant shortening of PEP 1 and PEP/LVET. Shortening of QS 2 i correlated significantly with SDC 24 hours after the thirteenth dose of 0.5 mg. These data suggest that after 13 days of treatment with 0.25 and 0.5 mg/day of digoxin, a positive inotropic effect occurs as reflected by STI shortening. A greater effect was recorded with the 0.5 mg dose.