The Influence of Beta Blocker Therapy on the Hemodynamic Response to Inotrope Infusion in Patients With Acute Decompensated Heart Failure

Overview

Purpose: To compare the hemodynamic effects of dobutamine and milrinone in hospitalized patients who are receiving Beta Blocker Participants: Patients who are admitted to the General Cardiology and Heart Failure Services at the University of North Carolina Hospitals with acute decompensated heart failure, who have maintained steady state concentrations of beta blocker therapy (carvedilol or metoprolol), and who are deemed by the health care team to require pulmonary artery catheter placement and inotropic therapy with dobutamine or milrinone by continuous infusion. Patients that are not currently receiving beta blocker therapy will be enrolled for comparative purposes; however, any patient not at steady state (on or off beta blocker therapy) will not be enrolled. Procedures: After obtaining informed consent, patients will be assigned to the appropriate sub-study group based on beta blocker use (Study A: patients on stable doses of metoprolol and Study B: patients on stable doses of carvedilol). All patients should receive dobutamine followed by milrinone as outlined in the dosing algorithm (see inotrope dosing algorithm attached, as part of the usual standard of practice). Baseline pulmonary artery catheter hemodynamic parameters will be collected prior to administration of inotrope trial of dobutamine followed by milrinone. Hemodynamic parameters will be recorded per the dosing algorithm following initiation and dose titration. Dose titration will be determined by the health care team based upon patient response or lack thereof and tolerability. Changes in hemodynamic parameters in response to dobutamine or milrinone will be compared within study groups. Additionally, data will continue to be collected on patients receiving not beta blocker therapy for comparative purpose.

Background: First-line management of chronic heart failure includes beta blockers and angiotensin converting enzyme (ACE) inhibitors, as these agents have been shown to have significant benefits on morbidity and mortality in large clinical trials. Therefore, a substantial number of patients with chronic heart failure are receiving chronic beta blocker therapy, most commonly metoprolol succinate and carvedilol. However, despite significant advancements in the treatment of chronic heart failure, the natural history of the disease remains progressive and many patients develop acute decompensations requiring hospitalization. In the setting of acute decompensated heart failure, the use of inotropic agents may be required for hemodynamic support. The two most widely used inotropes are dobutamine and milrinone. Dobutamine primarily acts as a beta-1 receptor agonist with some effects on beta-2 and alpha-1 receptors. Milrinone is a phosphodiesterase III inhibitor, thus inhibiting the breakdown of cyclic adenosine monophosphate. As such, milrinone works at a site that is distal to beta receptors and may be less influenced by chronic beta blocker therapy. As such, one may speculate that the presence of a beta blocker would influence the hemodynamic response to dobutamine, but to a much lesser extent to milrinone, if at all. Two small studies have assessed the hemodynamic response to dobutamine in the presence and absence of beta blocker therapy in patients with chronic heart failure. In addition, one of these studies assessed the response to enoximone, another phosphodiesterase III inhibitor. Both studies demonstrated that metoprolol did not significantly affect the hemodynamic response to dobutamine infusion, including its effect on cardiac index, heart rate, stroke volume, and systemic vascular resistance. Conversely, carvedilol was shown to have significant inhibitory effects on cardiac index, heart rate, and stroke volume during dobutamine infusion. In addition, carvedilol appeared to increase mean arterial pressure at higher doses of dobutamine. In the setting of an enoximone infusion, metoprolol increased the cardiac index and stroke volume responses, while maintaining other hemodynamic parameters. There was no significant difference in the hemodynamic response to enoximone infusion in the presence of carvedilol. Why This Study is Needed: Published studies that assessed the hemodynamic response to inotropes in the presence and absence of beta blockers included less than 50 patients combined. As such, the replication of their results is warranted in order to use this data to drive changes in clinical practice. Additionally, and equally as important, no study has been published, to the best of our knowledge, which has assessed the hemodynamic response to milrinone in the presence of metoprolol. . Although enoximone is a phosphodiesterase III inhibitor and is theoretically similar to milrinone, it is not approved for use in the United States, thus making it difficult to extrapolate these findings to milrinone. Lastly, the severity of illness in patients included in current literature does not reflect individuals who will receive the most benefit from therapy i.e. patients with acute decompensated heart failure.