Four Pillars of Heart Failure with Reduced Ejection Fraction: Mechanisms and Side Effects
All patients with HFrEF should receive quadruple therapy consisting of ARNI (or ACEI/ARB), beta-blockers, mineralocorticoid receptor antagonists (MRAs), and SGLT2 inhibitors—these are the four foundational pillars that reduce mortality and hospitalizations. 1
The Four Pillars
1. Renin-Angiotensin System Inhibition
Mechanism of Action:
- ARNIs (Angiotensin Receptor-Neprilysin Inhibitors): Block angiotensin II receptors while simultaneously inhibiting neprilysin, which increases natriuretic peptides, bradykinin, and other vasodilator peptides. This provides balanced vasodilation and reduces adverse ventricular remodeling 1
- ACE Inhibitors: Block conversion of angiotensin I to angiotensin II, reducing vasoconstriction and aldosterone secretion. Also inhibit kininase, increasing bradykinin levels 2
- ARBs: Directly block angiotensin II receptors without affecting kininase 2
Common Side Effects:
- Hypotension (symptomatic blood pressure drops)
- Hyperkalemia (potassium >5.0 mEq/L)
- Worsening renal function (particularly when creatinine clearance <30 mL/min)
- Angioedema (ACEIs > ARNIs > ARBs)
- Cough (ACEIs only, due to bradykinin accumulation) 1, 2
2. Beta-Blockers
Mechanism of Action:
- Block sympathetic nervous system activation, reducing heart rate, myocardial oxygen demand, and preventing catecholamine-induced myocyte toxicity
- Reduce adverse ventricular remodeling and arrhythmias 1
Common Side Effects:
- Bradycardia
- Hypotension
- Fatigue
- Worsening symptoms initially (may occur during titration)
- Bronchospasm (in patients with reactive airway disease) 1
3. Mineralocorticoid Receptor Antagonists (MRAs)
Mechanism of Action:
- Block aldosterone receptors, reducing sodium retention, potassium excretion, and myocardial fibrosis
- Target the renin-angiotensin-aldosterone system at the aldosterone level 1
Common Side Effects:
- Hyperkalemia (most significant concern, especially when combined with ARNI/ACEI/ARB)
- Worsening renal function
- Gynecomastia (with spironolactone)
- Discontinue if potassium >5.0 mEq/L or creatinine clearance <30 mL/min 1
4. SGLT2 Inhibitors (Sodium-Glucose Cotransporter-2 Inhibitors)
Mechanism of Action:
- Block glucose and sodium reabsorption in the proximal renal tubule
- Provide natriuresis, reduce preload, improve myocardial energetics, and reduce inflammation
- Benefits emerge within weeks of initiation 1, 3
Common Side Effects:
- Genital mycotic infections
- Urinary tract infections
- Volume depletion (mild)
- Euglycemic diabetic ketoacidosis (rare)
- Generally well-tolerated with rapid clinical benefit 3
Management of Common Side Effects
Hypotension:
- First exclude over-diuresis, non-cardiovascular medications causing hypotension (anticholinergics, prostate medications), and autonomic dysfunction
- Do NOT reduce GDMT doses until other causes are addressed
- Use best-tolerated doses rather than discontinuing therapy 1
Hyperkalemia or Worsening Renal Function:
- Use less than target doses of ARNI/ACEI/ARB
- Discontinue MRA if creatinine clearance <30 mL/min or potassium >5.0 mEq/L
- Low-dose ACEI still provides survival benefit and may be preferred in renal insufficiency with marginal blood pressure 1
Critical Implementation Principles
Start all four pillars immediately—delayed initiation is associated with never initiating therapy 1. The contemporary approach is "four drugs in 4 weeks" with rapid initiation and structured up-titration 3.
Titrate to target doses even if patients are stable or symptoms improve, as target doses are associated with best outcomes 1. Titration should occur within 6-12 weeks of diagnosis 4.
Diuretics are essential for symptom control but do not modify disease progression—they relieve congestion which drives symptoms and hospitalizations 1.
Additional Therapies (Not Core Pillars)
- Hydralazine/Isosorbide Dinitrate: First-line for self-identified African Americans, provides balanced vasodilation and oxidative stress modulation 1
- Ivabradine: Second-line for elevated heart rate (>70 bpm despite beta-blocker) 1
- Vericiguat: Soluble guanylyl cyclase stimulator for patients with recent decompensation 5
The key pitfall is undertreating due to fear of side effects—most adverse effects can be managed through dose adjustment and addressing confounding factors rather than discontinuing life-saving therapy 1.