10.11: Heart Failure Drugs: Inhibitors of Renin-Angiotensin System

The activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS) contributes to cardiac remodeling, and inhibiting the RAAS is a pharmacological target in heart failure management. As a result, neurohumoral modulation is a crucial treatment principle for managing heart failure. This approach involves using medications like ACE inhibitors (ACEIs), angiotensin receptor blockers (ARBs), β-blockers, mineralocorticoid receptor antagonists (MRAs), and neutral endopeptidase inhibitors to counter the harmful effects of neurohumoral activation on the heart, blood vessels, and kidneys.

ACEIs work by reducing angiotensin II levels. They have several physiological effects, including vasodilation, reduced aldosterone release, anti-remodeling effects on the heart, and sympatholytic effects. ACEIs can cause dry cough or rare angioedema due to increased bradykinin and substance P levels. ARBs are highly selective AT₁ receptor antagonists used as alternatives to ACEIs in patients who cannot tolerate them. They can increase hypotension, hyperkalemia, and renal dysfunction. β-blockers reduce the actions of catecholamines on β-adrenoceptors, leading to decreased heart rate, force, and AV conduction. They also suppress arrhythmias and lower renin levels and may have varying effects on bronchoconstriction and vasoconstriction. MRAs, such as spironolactone and eplerenone, block aldosterone receptors and reduce fibrosis. These drugs have a documented life-prolonging effect in heart failure patients but can precipitate dysmenorrhea, gynecomastia, and hyperkalemia. Sacubitril/valsartan, a combination drug, activates the beneficial axis of neurohumoral activation and provides multiple benefits such as natriuresis, vasodilation, inhibition of thrombosis, and cardiac remodeling. ACEIs and ARBs reduce peripheral resistance, afterload, salt/water retention, and sympathetic activity. ACEIs are the preferred initial treatment for left ventricular dysfunction without edema. ARBs are alternatives for patients intolerant to ACEIs.

In heart failure, continuous RAAS activation intensifies cardiac workload, causing fatal tissue remodeling if untreated.

Heart failure pharmacotherapy helps reduce these harmful neurohumoral effects.

Angiotensin-converting enzyme or ACE inhibitors block the conversion of Angiotensin I to II, lowering its levels and enhancing bradykinin and substance P levels.

Next, angiotensin receptor blockers or ARBs selectively antagonize AT₁ receptors modulating Angiotensin II effects. They are therapeutic alternatives for ACE inhibitor-intolerant patients.

Further, mineralocorticoid receptor antagonists or MRAs block nuclear aldosterone receptors and act as K⁺  -sparing diuretics.

These strategies decrease peripheral resistance, cardiac afterload, and sympathetic activity while increasing natriuresis.

However, ACE inhibitors and ARBs have various adverse effects and are contraindicated in pregnancy. Additionally, ACE inhibitors can induce a dry cough, while MRAs may cause allergic reactions and gynecomastia in males.

Lastly, the pharmacotherapeutic arsenal includes β₁- blockers and combination therapies of ARBs with neprilysin inhibitors.