Renin-angiotensin-aldosterone system blockade for cardiovascular diseases: current status

Abstract

Activation of the renin-angiotensin-aldosterone system (RAAS) results in vasoconstriction, muscular (vascular and cardiac) hypertrophy and fibrosis. Established arterial stiffness and cardiac dysfunction are key factors contributing to subsequent cardiovascular and renal complications. Blockade of RAAS has been shown to be beneficial in patients with hypertension, acute myocardial infarction, chronic systolic heart failure, stroke and diabetic renal disease. An aggressive approach for more extensive RAAS blockade with combination of two commonly used RAAS blockers [ACE inhibitors (ACEIs) and angiotensin receptor blockers (ARBs)] yielded conflicting results in different patient populations. Combination therapy is also associated with more side effects, in particular hypotension, hyperkalaemia and renal impairment. Recently published ONTARGET study showed ACEI/ARB combination therapy was associated with more adverse effects without any increase in benefit. The Canadian Hypertension Education Program responded with a new warning: 'Do not use ACEI and ARB in combination'. However, the European Society of Cardiology in their updated heart failure treatment guidelines still recommended ACEI/ARB combo as a viable option. This apparent inconsistency among guidelines generates debate as to which approach of RAAS inhibition is the best. The current paper reviews the latest evidence of isolated ACEI or ARB use and their combination in cardiovascular diseases, and makes recommendations for their prescriptions in specific patient populations.

Figure 1

RAAS. Renin, produced by the juxtaglomerular cells of the kidney converts angiotensinogen to A-I. Angiotensinogen is an alpha-2-globulin mainly produced by the liver. A-I is biologically inactive and is activated by ACE, mainly produced by the lungs to form A-II. A-II acts on A-II receptors. The angiotensin type 1 (AT1) receptor governs most physiological effects. The net effects of activation of the RAAS include vasocontriction, increased arterial blood pressure, increased myocardial contractility, sodium and water retention which subsequently increases the effective circulating volume. Renin–angiotensin–aldosterone blockade can be achieved by direct renin inhibitor, ACEI, ARB and AA. A-II can also be produced by alternative pathways by enzymes like chymase and cathepsin G, which form the basis of ‘A-II escape’. This is also the rationale for using dual blockade of the system by ACEI and ARB.