Heart rate dependency of cardiac performance in heart failure patients treated with metoprolol

Aims To investigate whether a low heart rate is necessary to maintain impro vement in myocardial function after long-term treatment with a beta-blocker in patients with heart failure. Methods and Results Forty-eight patients with congestive heart failure were investigated: 30 patients with dilated cardiomyopathy participating in a p lacebo-controlled trial (15 on placebo, 15 on metoprolol), and 18 patients treated by metoprolol in an open protocol. Investigations of spontaneous he art rate and of matched paced heart rates were performed at baseline and af ter 3, 6 and 12 months of follow-up by radionuclide angiography. There were significant signs of improvement in systolic indices of the spontaneous he art rate in the metoprolol-treated group (peak ejection rate: 0.98 to 1.32 end-diastolic volume. s(-1), P=0.015) as compared to placebo (1.14 to 1.19 end-diastolic volume.s(-1), not significant). Similar effects were observed during the matched paced heart rate (peak ejection rate: metoprolol 0.91 t o 1.38 end-diastolic volume.s(-1), P=0.037; placebo 1.22 to 1.12 end-diasto lic volume.s(-1) not significant). No effects were observed in the early pe ak filling rate. Left ventricular volumes decreased during metoprolol treat ment, both for the spontaneous heart rate and during matched pacing. Conclusions These data imply that beta-blocker treatment improves the force -frequency relationship of myocardial performance. A lower heart rate is no t necessary to maintain cardiac function on a short-term basis, once myocar dial recovery has occurred.