Optimal antagonism of the Renin-Angiotensin-aldosterone system: do we need dual or triple therapy?

The cardiovascular and cardiorenal disease continuum comprises the transition from cardiovascular risk factors to endothelial dysfunction and atherosclerosis, to clinical complications such as myocardial infarction (MI) and stroke, to the development of persistent target-organ damage and, ultimately, to chronic congestive heart failure (CHF), end-stage renal disease or premature death. The renin-angiotensin-aldosterone system (RAAS) is involved in all steps along this pathway, and RAAS blockade with ACE inhibitors or angiotensin AT(1)-receptor antagonists (angiotensin receptor blockers; ARBs) has turned out to be beneficial for patient outcomes throughout the disease continuum. Both ACE inhibitors and ARBs can prevent or reverse endothelial dysfunction and atherosclerosis, thereby reducing the risk of cardiovascular events. These drugs have further been shown to reduce end-organ damage in the heart, kidneys and brain. Aldosterone antagonists such as spironolactone and eplerenone are increasingly recognized as a third class of RAAS inhibitor with potent risk-reducing properties, especially but not solely with respect to the inhibition of cardiac remodelling and the possible prevention of heart failure. In secondary prevention, head-to-head comparisons of ACE inhibitors and ARBs, such as the recent ONTARGET study, provided evidence that, in addition to better tolerability, ARBs are non-inferior to ACE inhibitors in the prevention of clinical endpoints such as MI and stroke in cardiovascular high-risk patients. However, the combination of both ramipril and telmisartan at the maximally tolerated dosage achieved no further benefits and was associated with more adverse events such as symptomatic hypotension and renal dysfunction. In acute MI complicated by heart failure, the VALIANT trial has shown similar effects of ACE inhibition with captopril and ARB treatment with valsartan, but dual RAAS blockade did not further reduce events. In CHF, meta-analyses of RESOLVD, ValHeFT and CHARM-ADDED have shown that combined RAAS inhibition with an ACE inhibitor and ARB significantly reduced the morbidity endpoint in certain patient subgroups compared with standard therapy. However, in clinical practice, dual RAAS blockade is rarely employed, as seen, for instance, in the CORONA trial. The RALES and EPHESUS trials, investigating the effects of aldosterone blockade on cardiovascular outcomes in CHF patients, revealed that the addition of an aldosterone antagonist to standard heart failure therapy conferred powerful relative risk reductions for both morbidity and mortality. Future studies will elucidate whether this also holds true for patients who are asymptomatic or who have heart failure with preserved ejection fraction. In selected patients with renal disease, several studies have suggested that combined RAAS blockade brings about additional renoprotective antiproteinuric effects independent of blood pressure reduction, and large trials with robust endpoints are underway. In summary, combined therapy with several RAAS inhibitors is not recommended for all patients along the cardiorenovascular continuum. Patients with CHF with incomplete neuroendocrine blockade, as indicated, for example, by repetitive cardiac decompensation or refractory symptoms, might benefit from dual therapy as long as safety issues are well controlled. Finally, novel pharmacological agents such as the direct renin inhibitor aliskiren may provide additional therapeutic tools, but their role has yet to be established.