Influence of atenolol and nifedipine on digoxin-induced inotropism in humans

Short term effect of digoxin on left ventricular performance was studied in six healthy volunteers before and during atenolol or nifedipine administration. Left ventricular function was evaluated by systolic time intervals and echocardiography. No changes in left ventricular end diastolic or systolic dimensions occurred throughout the study, indicating unchanged ventricular pre- and afterload. Thus, changes in the systolic time intervals must be attributed to changes in cardiac contractility. Changes in the pre-ejection period index (PEPI) obtained from the systolic time intervals were used as a measure of digoxin-induced inotropism. A concentration-response relationship between plasma digoxin level and changes in PEPI was revealed when digoxin was given alone. Atenolol did not influence the digoxin-induced inotropism at a given serum digoxin level. During nifedipine administration no inotropic effect of digoxin could be demonstrated. Thus, it is concluded that nifedipine attenuates digoxin-induced inotropism, while atenolol seems without this effect. These results are in accordance with previous experiments and reflect the different pharmacological sites of action of beta-adrenoceptor antagonists and calcium channel blocking agents. Plasma digoxin concentration, renal digoxin clearance and creatinine clearance did not change during atenolol or nifedipine.