---

Pharmacology and Drug Treatment of Heart Failure

---

1. Pathophysiology — The Framework for Treatment

• HFrEF (Heart Failure with Reduced Ejection Fraction, EF <40%) — systolic failure, the dilated, weak heart
• HFpEF (Heart Failure with Preserved Ejection Fraction, EF >50%) — diastolic failure, the stiff, hypertrophied heart

Key pathophysiological mechanisms driving HFrEF:

---

2. Heart Failure Staging

---

3. Drug Treatment of Chronic HFrEF

Treatment Principle I: Neurohumoral Modulation (RAAS Blockade)

ACE Inhibitors (ACEIs)

• Mechanism: Inhibit conversion of Angiotensin I → Angiotensin II; reduce aldosterone; lower preload and afterload; attenuate cardiac remodeling
• Key trial: CONSENSUS (1987) — enalapril reduced mortality ~40% in NYHA class IV. SOLVD (1991) — ~16% reduction in NYHA II–III
• Examples: Enalapril, lisinopril, captopril, ramipril
• Adverse effects: Dry cough (bradykinin accumulation), angioedema (contraindication to further use), hyperkalemia, hypotension, teratogenicity
• Clinical use: All patients with HFrEF (Stage B–D) unless contraindicated

Angiotensin Receptor Blockers (ARBs)

• Mechanism: Selectively block AT₁ receptors — same downstream benefits as ACEIs without bradykinin-mediated cough
• Examples: Valsartan, candesartan, losartan
• Use: When ACEIs are not tolerated (mainly due to cough); not to be combined with ACEIs due to increased adverse effects without additional benefit

Angiotensin Receptor–Neprilysin Inhibitor (ARNI)

• Drug: Sacubitril/valsartan (LCZ696)
• Mechanism: Sacubitril inhibits neprilysin (which degrades natriuretic peptides BNP, ANP), thereby enhancing vasodilation, natriuresis, and anti-remodeling effects. Combined with valsartan (ARB)
• Key trial: PARADIGM-HF (2014) — sacubitril/valsartan reduced all-cause mortality by ~16% vs. enalapril in 8,442 patients
• Guideline recommendation: Replace ACEI/ARB with ARNI in NYHA II–III patients who can tolerate it. Cannot be combined with an ACEI (risk of angioedema); a 36-hour washout is required when switching from ACEI

Mineralocorticoid Receptor Antagonists (MRAs)

• Drugs: Spironolactone, eplerenone
• Mechanism: Block aldosterone receptors in kidney (reduce Na⁺ retention, K⁺ loss) and heart (reduce fibrosis)
• Key trials:
  • RALES (1999): Spironolactone reduced mortality ~30% in severe HF (EF <35%) on background of ACEI + diuretics
  • EMPHASIS-HF: Eplerenone reduced mortality in mild HF
• Adverse effects: Hyperkalemia (monitor K⁺ and renal function), gynecomastia/menstrual disorders (spironolactone only — due to sex steroid receptor cross-reactivity; eplerenone is more selective)
• Contraindicated if CrCl <30 mL/min or K⁺ ≥5 mmol/L

---

Treatment Principle II: Preload Reduction (Diuretics)

Loop Diuretics (First-line)

• Drugs: Furosemide, bumetanide, torsemide
• Mechanism: Block Na⁺-K⁺-2Cl⁻ co-transporter in the thick ascending limb of Henle — potent natriuresis
• Furosemide starting dose: 20–40 mg/day; titrate to 40–240 mg/day
• Adverse effects: Hypokalemia, hyponatremia, hypomagnesemia, hyperuricemia, ototoxicity (at high doses), nephrotoxicity

Thiazide Diuretics (Adjunct)

• Drugs: Hydrochlorothiazide, chlorthalidone
• Used in combination with loop diuretics to break diuretic resistance ("sequential nephron blockade")
• Adverse effects: Hypokalemia, hyperuricemia, hypercalcemia, glucose intolerance

Potassium-Sparing Diuretics

• Drugs: Spironolactone, eplerenone (as MRAs), amiloride, triamterene
• Used to prevent hypokalemia; risk of hyperkalemia when combined with ACEIs/ARBs

---

Treatment Principle III: Afterload Reduction

Hydralazine + Isosorbide Dinitrate (ISDN)

• Mechanism: Hydralazine = arterial vasodilator (reduces afterload); ISDN = venodilator (reduces preload via NO generation)
• Key indication: Black patients with NYHA III–IV HF (A-HeFT trial showed ~43% mortality reduction in African Americans vs. placebo)
• Also used when ACEIs/ARBs/ARNI are contraindicated (e.g., severe renal impairment, bilateral renal artery stenosis)
• Fixed-dose formulation: 37.5 mg hydralazine + 20 mg ISDN (BiDil)
• Adverse effects: Headache (nitrate-related), reflex tachycardia (hydralazine), lupus-like syndrome with prolonged high-dose hydralazine use

---

Treatment Principle IV: Increasing Cardiac Contractility

Digoxin (Cardiac Glycoside)

• Mechanism:
  1. Inhibits Na⁺/K⁺-ATPase → raises intracellular Na⁺ → reduces Na⁺/Ca²⁺ exchanger activity → more intracellular Ca²⁺ → positive inotropy
  2. Vagomimetic effect → slows AV conduction → rate control in atrial fibrillation
  3. Reduces SNS activation by sensitizing baroreceptors
• Key trial: DIG (1997) — digoxin did not reduce all-cause mortality but reduced HF hospitalizations by ~27%
• Therapeutic range: 0.5–0.8 ng/mL (narrow therapeutic index — target the lower end)
• Adverse effects/toxicity: Nausea, vomiting, visual disturbances (yellow-green halos), cardiac arrhythmias (especially at toxic levels: PVCs, heart block, VT)
• Toxicity precipitants: Hypokalemia, hypomagnesemia, renal insufficiency (digoxin is renally cleared)
• Antidote: Anti-digoxin Fab fragments (Digibind) — purified ovine antibody fragments

---

Treatment Principle V: Heart Rate Reduction

β-Blockers (Beta-Adrenergic Antagonists)

• Rationale: Chronic SNS activation in HF causes β-receptor downregulation, increased energy consumption, fibrosis, arrhythmias, and cardiomyocyte death. β-Blockers interrupt this maladaptive process
• Mechanism in HF: Competitive antagonism of β₁ (and β₂/α₁ for some agents); long-term benefit: reversal of the "HF gene program," improvement in LVEF after 3–6 months, reduced sudden cardiac death
• Clinical paradox: Acutely depress cardiac function but chronically improve EF and survival
• Key agents approved for HFrEF:

• Key trials: MERIT-HF (metoprolol) and CIBIS-II (bisoprolol) both showed ~34% reduction in all-cause mortality
• Critical prescribing rules:
  • Initiate only in clinically stable patients
  • Start at one-eighth of target dose
  • Titrate every 4 weeks ("start low, go slow")
  • Do NOT initiate in acute decompensation or new-onset HF
• Adverse effects: Bradycardia, hypotension, bronchospasm (avoid in reactive airway disease), fluid retention (may require diuretic adjustment), fatigue
• CYP2D6: Metoprolol and carvedilol are CYP2D6 substrates — poor metabolizers (8% of Caucasians) have 5-fold higher Cₘₐₓ

Ivabradine

• Mechanism: Selective inhibitor of cardiac HCN pacemaker channels (Iₓ) → reduces heart rate without affecting contractility or blood pressure
• Indication: NYHA II–III HFrEF, HR >70 bpm in sinus rhythm on maximally tolerated β-blocker dose (guideline Class IIa)
• Adverse effects: Bradycardia, phosphenes (transient visual brightness), increased risk of atrial fibrillation
• Evidence: SHIFT trial (Swedberg et al., 2010) — reduced HF hospitalizations and HF mortality, but not total or cardiovascular mortality

---

Treatment Principle VI: SGLT2 Inhibition

• Drugs: Dapagliflozin, empagliflozin, canagliflozin
• Primary mechanism: Block sodium-glucose co-transporter 2 (SGLT2) in the proximal tubule → glycosuria + natriuresis ("a better diuretic effect")
• Off-target mechanisms (proposed): Inhibition of Na⁺/H⁺ exchanger (NHE), reduction of myocardial sodium overload, anti-inflammatory effects
• Key trials:
  • EMPA-REG OUTCOME (empagliflozin) — initial cardiovascular outcomes trial in diabetic patients; showed major HF benefit
  • DAPA-HF (McMurray 2019) — dapagliflozin reduced the composite of worsening HF or cardiovascular death by 26% in HFrEF, independent of diabetes status
• Approval: Dapagliflozin was the first SGLT2 inhibitor approved for HF in the U.S. (2020)
• Adverse effects: Genital mycotic infections, diabetic ketoacidosis (rare), volume depletion

The "Fantastic Four" of modern HFrEF therapy (GDMT): ACEI/ARB/ARNI + β-blocker + MRA + SGLT2 inhibitor — this combination is now guideline-directed medical therapy (GDMT).

---

4. AHA/ACC Treatment Algorithm for HFrEF (Stage C)

1. Establish HFrEF diagnosis → Initiate ACEI or ARB + β-blocker; diuretics as needed
2. Consider additional therapy (choices not mutually exclusive):
   • NYHA II–IV + CrCl >30 + K⁺ <5 → Add MRA
   • NYHA II–III, tolerating ACEI/ARB → Switch to ARNI (sacubitril/valsartan)
   • NYHA III–IV in Black patients → Add ISDN + hydralazine
   • NYHA II–III, LVEF ≤35% → ICD (implantable defibrillator)
   • NYHA II–IV, QRS >150 ms with LBBB → CRT (cardiac resynchronization therapy)
   • NYHA II–III, HR >70 bpm on max β-blocker → Ivabradine
3. Reassess → If refractory (Stage D): heart transplantation or LVAD

---

5. Drug Treatment of Acutely Decompensated Heart Failure (ADHF)

a) Diuretics (IV loop diuretics — first-line)

• IV furosemide 40–80 mg bolus, then infusion
• Titrate based on symptoms and urine output
• Adding a thiazide (small dose) can overcome loop diuretic resistance
• Avoid excessive doses → hypotension, reduced GFR, electrolyte imbalance, neurohumoral activation

b) Vasodilators

• Nitroglycerin and sodium nitroprusside reduce preload and afterload
• Best for patients with elevated blood pressure; avoid if systolic BP <110 mmHg
• Nesiritide (recombinant BNP): Reduces preload/afterload via cGMP; FDA-approved for ADHF but evidence for improved outcomes is weak
• Main risk: Hypotension (associated with poor outcomes)

c) Positive Inotropic Agents (in cardiogenic shock / severe low-output states)

• Dobutamine (β₁-agonist): Increases myocardial contractility; used short-term in hemodynamically unstable patients
• Dopamine (low dose: DA₁ renal vasodilation; high dose: α₁ vasoconstriction)
• Milrinone (PDE3 inhibitor): Increases cAMP → inotropy + vasodilation ("inodilator"); useful in patients on chronic β-blockers; increased risk of arrhythmias and mortality with prolonged use

d) Myofilament Calcium Sensitizers

• Levosimendan: Binds troponin C → increases Ca²⁺ sensitivity of myofilaments (inotropy without increasing intracellular Ca²⁺ → fewer arrhythmias); also opens K⁺ATP channels (vasodilation); approved in Europe, not the U.S.
• Role: Possibly superior to dobutamine in select patients; no clear mortality benefit

---

6. Drug Treatment of HFpEF

• Treat the underlying comorbidities: optimize blood pressure, control diabetes and obesity
• Use diuretics for congestion/symptom relief
• ACEIs, ARBs, spironolactone, sildenafil (PDE5 inhibitor) — all failed in clinical trials
• SGLT2 inhibitors are a promising emerging option (EMPEROR-Preserved trial with empagliflozin showed benefit in HFpEF)
• Exercise training is the only intervention that reliably improves exercise capacity in HFpEF

---

7. Key Landmark Clinical Trials Summary

---

8. Important Drug Failures — Lessons Learned

The central lesson: Drugs that stimulate the failing heart short-term can deplete energy reserves and increase arrhythmic risk. Sustained benefit requires unloading the heart and blocking the maladaptive neurohumoral cascade — not simply increasing contractility.

---

Summary: The Pillars of HFrEF Pharmacotherapy

NEUROHUMORAL BLOCKADE
├── RAAS: ACEI → ARB → ARNI (sacubitril/valsartan)
├── SNS: β-blockers (bisoprolol, carvedilol, metoprolol XL)
└── Aldosterone: MRA (spironolactone, eplerenone)

VOLUME/HEMODYNAMIC MANAGEMENT
├── Diuretics: Loop (furosemide) ± thiazides
└── Vasodilators: Hydralazine+ISDN (especially Black patients)

NOVEL MECHANISMS
└── SGLT2 inhibitors: Dapagliflozin, empagliflozin

SYMPTOM/RATE CONTROL
├── Digoxin (rate control + symptom relief)
└── Ivabradine (HR reduction when β-blockers insufficient)

---