Addition of phosphodiesterase inhibitors to adrenergic agents in acutely ill patients

Management of perioperative ventricular dysfunction

With the recognition of the clinical importance of the right ventricle; the development of new techniques for the perioperative evaluation of RV function, particularly transesophageal echocardiography; and new treatment modalities (pharmacologic and mechanical), clinicians will be able to more accurately diagnose and precisely manage patients who have sustained RV injury.

A placebo-controlled trial verifying the efficacy of milrinone in weaning high-risk patients from cardiopulmonary bypass

OBJECTIVE

To establish the efficacy of the phosphodiesterase inhibitor milrinone in facilitating weaning from cardiopulmonary bypass of high-risk patients with left ventricular dysfunction and/or pulmonary hypertension.

DESIGN

A double-blinded, placebo-controlled longitudinal study.

SETTING

A university teaching hospital.

PARTICIPANTS

Thirty-two patients with preoperative left ventricular ejection fraction < or = 35% and/or mean pulmonary artery pressure > or = 20 mmHg were studied after their written informed consent.

INTERVENTION

Patients were randomized to commence either intravenous milrinone, 50 micrograms/kg loading dose over 20 minutes followed by 0.5 microgram/kg/min infusion, or matching placebo 15 minutes before withdrawal of cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Two patients were withdrawn from the study and their results not analyzed: one because of early failure of hemodynamic monitoring and the other because of gross surgical bleeding. In the remaining 30 patients, who were well matched for clinical and baseline hemodynamic variables, bypass support was successfully withdrawn in all 15 patients randomized to receive milrinone but in only 5 of the 15 patients randomized to receive placebo. In the 10 patients who initially failed to wean from bypass while on placebo, bypass was reinstituted and open-label milrinone was administered in the dose outlined. After treatment with open-label milrinone, these patients could also be withdrawn from bypass support. During the period of hemodynamic monitoring, cardiac index increased in both milrinone- and placebo-treated patients, although this change was greater in those treated with milrinone. Perhaps related to routine clinical treatment, there were no significant differences between the two groups with mean pulmonary artery or pulmonary capillary wedge pressures, the other major hemodynamic endpoints. There were no significant adverse effects related to milrinone.

CONCLUSIONS

This placebo-controlled, double-blind study has conclusively demonstrated the benefits of milrinone in facilitating weaning of high-risk patients from cardiopulmonary bypass.

Levosimendan potentiates the inotropic actions of dopamine in conscious dogs

We examined the hemodynamic and left ventricular (LV) functional actions of dopamine with and without levosimendan in dogs chronically instrumented for measurement of aortic and LV pressure, +dP/dtmax, subendocardial segment length, and cardiac output (CO). On different experimental days, dogs were randomly assigned to receive dopamine (2.5, 5.0, and 10.0 micrograms kg-1 min-1) in the absence and presence of levosimendan (0.125, 0.25, and 0.5 microgram kg-1 min-1) or levosimendan alone. Dopamine increased heart rate (HR), CO, stroke volume (SV), and pressure-work index (PWI) and decreased systemic vascular resistance (SVR). Dopamine also increased LV systolic and end-diastolic pressures (LVSP and LVEDP) and mean arterial pressure (MAP). Dopamine caused dose-related positive inotropic [increases in preload recruitable stroke work (Mw) and + dP/ dtmax] and lusitropic effects [decreases in the time constant of isovolumic relaxation (tau) and increases in maximum segment-lengthening velocity (dL/dtmax)]. Dopamine also increased the regional chamber thickness constant (Kp) concomitant with increases in LVEDP. In the presence of levosimendan, dopamine-induced increases in HR, PWI, CO, and SV and decreases in SVR were enhanced. Increases in MAP, LVSP, and LVEDP observed with dopamine alone were attenuated by the addition of levosimendan. Dopamine-induced increases in Mw and +dP/dtmax were enhanced by levosimendan. Reductions in tau and increases in dL/dtmax produced by dopamine were similar with and without levosimendan. However, levosimendan abolished increases in Kp caused by dopamine alone. Levosimendan alone caused dose-related improvements in indices of LV systolic and diastolic function. The results indicate that levosimendan potentiates the positive inotropic effects of dopamine in conscious, unsedated dogs, while attenuating the deleterious action of dopamine on chamber compliance.

Support of the perioperative failing heart with preexisting ventricular dysfunction: currently available options

Perioperative support of the patient with preexisting biventricular failure requires simultaneous optimal manipulation of heart rate and rhythm, loading conditions, and contractility. Patients with preexisting ventricular dysfunction will have alterations in beta-adrenergic receptors, resulting in decreased responsiveness to catecholamines. Even patients with previously normal ventricular function can develop ventricular dysfunction caused by reperfusion injury and other potentially damaging effects of extracorporeal circulation. The mainstay of therapeutic agents used to allow separation from cardiopulmonary bypass are catecholamines, which stimulate alpha- and beta-adrenergic receptors. Submaximal responses to beta 1-adrenergic stimulation can occur in the down-regulated heart. The phosphodiesterase inhibitors provide both inotropic support and vasodilatation, which improves both systolic and diastolic function and bypasses beta-adrenergic receptors. When administered in combination, catecholamine and cyclic-AMP-specific phosphodiesterase inhibitors can have additive effects to restore beta 1-adrenergic responsiveness. Combination therapy provides an important therapeutic option to facilitate separation from cardiopulmonary bypass. Pharmacologic intervention for right ventricular dysfunction focuses on reversal of pulmonary vasoconstriction with nitrates, beta 2-adrenergic agents, phosphodiesterase inhibitors and prostaglandin E1.

The role of phosphodiesterase inhibitors in heart failure

Myocardial contractility is dependent on available intracellular calcium and this can be enhanced by increasing intracellular cyclic adenosine monophosphate. One way of achieving this is by inhibiting the phosphodiesterase III enzyme. Over the last 15 years, a number of new drugs with this mechanism of action have been studied in man and have been found not only to have a positive inotropic action on the heart but also a vasodilating action on peripheral blood vessels. This combination of effects produces favourable haemodynamic improvement in patients with chronic heart failure. While some smaller studies showed that this did translate into an improvement in symptoms and functional capacity, a large well-designed and controlled clinical trial showed that survival was decreased when milrinone was used in target daily doses of 40 mg. For this reason, chronic long-term oral therapy with phosphodiesterase III inhibitors is not currently being actively pursued. They may still have a role as acute short-term therapy in severely ill patients who do not respond adequately to optimal standard drug therapy. Milrinone has been one of the most widely studied drugs in this regard. Even during short-term administration, its use should be closely monitored for any evidence of an increase in ventricular arrhythmias or decrease in ventricular function.