| Abstract: | Left ventricular performance was assessed with echocardiography in 10 normal subjects before and during maintenance therapy with digoxin (0.5 mg/day orally) in the basal state and after acute pressure loading with intravenously administered phenylephrine. During digoxin therapy, despite a decrease in mean heart rate of 5 beats/min in the basal state, mean left ventricular ejection fraction increased from 74 +/- 2 to 79 +/- 1 percent (standard error, P less than 0.03); percent shortening of a left ventricular minor dimension increased from 37 +/- 2 to 41 +/- 1 percent (P less than 0.04) and the mean rate of left ventricular dimension shortening increased from 5.66 +/- 0.22 to 6.31 +/- 0.23 cm/sec (P = 0.05). During acute pressure loading with phenylephrine there was no change in mean heart rate after digoxin and mean ejection fraction increased from 69 +/- 3 to 75 +/- 2 percent; mean percent shortening increased from 33 +/- 2 to 38 +/- 2 percent; mean rate of shortening increased from 5.46 +/- 0.32 to 6.48 +/- 0.33 cm/sec and mean normalized rate of shortening increased from 1.11 +/- 0.06 to 1.29 +/- 0.05 sec-1 (all P less than 0.01). In a few subjects the response to digoxin did not coincide with the mean data for the whole group. This variability was largely due to difficulties in exactly matching heart rate between the control and digoxin studies. These data (1) support the concept that long-term oral digoxin therapy exerts a positive inotropic effect on the normal left ventricle, and (2) demonstrate the usefulness of echocardiography in nonivasive assessment of the effects of drugs on left ventricular performance. |
