Improvement of cardiac function by angiotensin converting enzyme inhibition. Sites of action

The discovery of new properties of angiotensin converting enzyme (ACE) inhibitors in addition to their well-known ability to lower blood-pressure, such as antiproliferative actions and antiadrenergic and vagal-stimulating effects, has contributed to the usefulness of this class of agents in the prevention and treatment of cardiovascular diseases.

The contribution of an activated endocrine and/or cardiac paracrine renin-angiotensin system to the progression of cardiovascular diseases with the exception of renovascular hypertension is not fully understood. In particular, the following questions were addressed: 1) Is the facilitation of noradrenaline release in the genesis of arrhythmias a target for ACE inhibition? 2) Is an impaired nutritional cardiac blood flow in heart failure a target for ACE inhibition? 3) Is the intimal hyperplasia that results from coronary angioplasty a target for ACE inhibition? 4) Is the diastolic dysfunction associated with left ventricular hypertrophy in essential hypertension a target for ACE inhibition? In an isolated rat heart preparation with ischemia-induced arrhythmias, none of the ACE inhibitors nor an angiotensin II antagonist was able to significantly suppress the incidence or severity of arrhythmias. In 12 patients with New York Heart Association functional class II-IV heart failure, a fall in cardiac filing pressures after ACE inhibition was associated with an immediate rise in cardiac output and an increase in coronary blood flow of almost 30%. In 24 patients with angina at rest, a preceding percutaneous transluminal coronary angioplasty, and a second angioplasty, control angiograms at 6 months revealed a high degree of restenosis in both ACE inhibitor-treated and placebo patients. Luminal narrowing amounted to 72% in the placebo group and 61% in the ACE inhibitor group. The differences between placebo and enalapril were statistically not significant. In 12 patients with essential hypertension treated with 5 mg cilazapril, left ventricular mass was reduced by 30%, which was closely related to the change in mean arterial blood pressure. The concomitant normalization of the diastolic filling pattern by ACE inhibition, however, was not related to the respective changes in blood pressure.

Promising experimental data regarding the antiproliferative effects of ACE inhibitors in preventing restenosis could not be transferred into clinical benefits for patients who underwent repeat coronary angioplasty. Possible antiarrhythmic effects of ACE inhibitors are not likely to be caused by their suppression of noradrenaline release during myocardial ischemia. ACE inhibition was effective in reducing coronary resistance in patients with severe heart failure, thereby augmenting nutritional cardiac blood flow. ACE inhibition also effectively induced a regression of left ventricular hypertrophy in essential hypertension. The associated normalization of diastolic filling pattern may represent an important goal in the treatment of hypertension.