Early administration of captopril and nitroglycerin in combination after acute myocardial infarction: an invasive haemodynamic study

Enalaprilat decreases plasma endothelin and atrial natriuretic peptide levels and preload in patients with left ventricular dysfunction after cardiac surgery

OBJECTIVE

To study the acute effects of angiotensin-converting enzyme inhibition by intravenous enalaprilat infusion in patients with left ventricular dysfunction after cardiac surgery.

DESIGN

Prospective, consecutive sample, before-after trial.

SETTING

Surgical intensive care unit in a tertiary care university hospital.

PARTICIPANTS

Eight patients with left ventricular dysfunction after cardiac surgery. Patients were defined as having left ventricular dysfunction if the pulmonary capillary wedge pressure persisted above 18 mmHg in spite of conventional vasoactive medication (inotropic or vasodilating and diuretic drugs) and intermittent mandatory ventilation during the first postoperative week.

INTERVENTIONS

Enalaprilat was infused initially at 1 mg/ hour. The rate was doubled every 30 minutes until pulmonary capillary wedge pressure decreased at least 20% or until a maximum total dose of 10 mg was achieved.

MEASUREMENTS AND RESULTS

Central hemodynamics, systemic oxygenation, and hormonal regulation of circulation (plasma renin activity, plasma endothelin, atrial natriuretic peptide, norepinephrine, epinephrine, and vasopressin concentrations, serum angiotensin-converting enzyme activity, and serum levels of aldosterone) were assessed at baseline before enalaprilat infusion, and repeatedly over 2 hours after the infusion. Enalaprilat infusion (median dose, 2.0 mg; infusion time, 48 minutes) caused a significant decrease in pulmonary capillary wedge pressure (p = 0.004), lasting until the end of the 2 hours' follow-up. This coincided with inhibition of serum angiotensin-converting enzyme activity (p < 0.001), an increase in plasma renin activity (p = 0.022), and decreases in plasma endothelin (p = 0.035), atrial natriuretic peptide (p = 0.005), and serum aldosterone (p = 0.001) concentrations. Cardiac output, venous admixture, and oxygen delivery and consumption remained unchanged.

CONCLUSIONS

Adding enalaprilat to conventional therapy makes it possible to unload the left ventricle and to relieve overt neurohormonal activation temporarily while maintaining cardiac function and systemic oxygenation.

A risk-benefit assessment of ACE inhibitor therapy post-myocardial infarction

The use of ACE inhibitors in patients with myocardial infarction (MI) has been the subject of several studies conducted during recent years. These studies have demonstrated the capacity of these agents to improve both survival and morbidity of patients with MI. However, the use of ACE inhibitors in patients with MI has been shown to reduce blood pressure (BP) and so could jeopardise the ischaemic myocardium. A significant reduction in systemic BP has been demonstrated by all the studies of ACE inhibitors in patients with MI, but no relationship has been found between the occurrence of hypotension and a worse clinical outcome. An increased risk of death has been observed exclusively in association with severe and sudden hypotension, the occurrence of which can be largely prevented by the administration of the ACE inhibitor according to an increasing dose-titration scheme. Conversely, a certain degree of long term BP reduction could result in some beneficial effect in patients with MI and contribute to the lower incidence of re-infarction observed in patients with acute MI undergoing long term treatment with captopril. Since the renin-angiotensin system is strictly related to kidney function, its blockade by an ACE inhibitor could result in some degree of renal dysfunction, particularly in patients with MI and impaired ventricular function. The available results from large-scale studies suggest that abnormalities in kidney function (namely an increase in serum creatinine) are observed in 0.9 to 2.4% of patients with MI who, nevertheless, experience some benefit from treatment with ACE inhibitors. Interestingly, the administration of ACE inhibitors does not seem to further compromise severely impaired renal function, and may also represent a useful tool for the treatment of patients with renal dysfunction associated with MI. The use of ACE inhibitors in patients with MI is associated with a satisfactory clinical and laboratory safety profile. The occurrence of significant adverse effects seems to be very low and mainly attributable to a rather modest prevalence of cough (2.4 to 6.8%). Discontinuation of treatment because of biochemical and haematological abnormalities has been observed in less than 1% of treated patients. Thus, the beneficial effects of ACE inhibitor treatment seem to outweigh safety concerns, thereby reinforcing the role of ACE inhibition as a suitable therapeutic strategy in the treatment of patients with MI.

Indications for immediate angiotensin-converting enzyme inhibition in patients with acute myocardial infarction

When initiated a few days after myocardial infarction, angiotensin-converting enzyme inhibition exerts beneficial effects on survival and morbidity in patients with asymptomatic left ventricular systolic dysfunction or symptomatic heart failure. During the acute phase of a myocardial infarction, angiotensin-converting enzyme inhibition appears to be well tolerated, to prevent the development of heart failure in patients with asymptomatic left ventricular systolic dysfunction and to improve the hemodynamic and clinical variables of heart failure when present. Accordingly, early angiotensin-converting enzyme inhibition is clearly indicated in patients with acute myocardial infarction associated with asymptomatic left ventricular dysfunction or clinical evidence of heart failure. Angiotensin-converting enzyme inhibition may also be beneficial when thrombolytic agents fail to restore coronary patency in patients with acute myocardial infarction.