CARDIOVASCULAR MEDICINE Different responses to dobutamine in the presence of carvedilol or metoprolol in patients with chronic heart failure

Objective: To determine whether patients with congestive heart failure on different β adrenoreceptor blocking drugs have similar haemodynamic responses to dobutamine. Design: Single centre, single blind, randomised, two period crossover study comparing carvedilol with metoprolol CR/XL. Patients: Ten patients with stable chronic congestive heart failure (ejection fraction < 40%) on chronic treatment with metoprolol CR/XL. Methods: Patients were treated with carvedilol or metoprolol CR/XL (target dose 50 mg twice daily and 200 mg once daily, respectively) for eight weeks. Stress echocardiography was undertaken at the end of each maintenance period, using dobutamine 5 and 15 μg/kg/min. Results: No significant haemodynamic differences were seen at rest on the two treatments. There was a more pronounced increase in heart rate and cardiac output during dobutamine infusion when the patients were on metoprolol than when they were on carvedilol. Mean arterial pressure increased significantly when the patients were on carvedilol, and cardiac output increased during low dose dobutamine, without further change during high dose dobutamine. During the dobutamine infusion, there was no significant difference in ejection fraction between carvedilol and metoprolol treatment. Conclusions: Patients with congestive heart failure on a non-selective β adrenoreceptor blocker or β1 selective blocker responded differently to the inotropic drug dobutamine: the β1 blockade caused by metoprolol could be counteracted by dobutamine, whereas with carvedilol a low dose of dobutamine increased cardiac output, and a higher dose of dobutamine caused a pressor effect. These findings may be clinically relevant when choosing an inotropic drug.