Treatment of Congestive Heart Failure (CHF) - 2nd MBBS Pharmacology

PART 1: THERAPEUTIC OBJECTIVES IN CHF

1. Reduce symptoms - relieve dyspnea, orthopnea, paroxysmal nocturnal dyspnea, and peripheral edema
2. Reduce preload - decrease venous return and cardiac filling pressures (by diuretics, nitrates, ACE inhibitors)
3. Reduce afterload - decrease systemic vascular resistance (by ACE inhibitors, ARBs, vasodilators)
4. Improve cardiac contractility - increase force of contraction (by digoxin, inotropes)
5. Reduce neurohormonal activation - blunt the RAAS and sympathetic systems that drive cardiac remodeling (by ACE inhibitors, beta-blockers, spironolactone)
6. Reduce morbidity and mortality - slow disease progression and prevent death
7. Prevent cardiac remodeling - reverse ventricular hypertrophy and dilation
8. Treat precipitating/contributing factors - control hypertension, arrhythmias, infection

PART 2: DRUGS USED IN CHF - ENUMERATION

A. Diuretics

• Loop diuretics: Furosemide, Bumetanide, Torsemide
• Thiazides: Hydrochlorothiazide (mild CHF only)
• Potassium-sparing: Spironolactone, Eplerenone (aldosterone antagonists)

B. RAAS Inhibitors

• ACE inhibitors: Enalapril, Captopril, Lisinopril, Ramipril
• ARBs: Losartan, Valsartan, Candesartan
• ARNI: Sacubitril/Valsartan (Entresto)

C. Beta-Blockers

• Carvedilol, Metoprolol (succinate), Bisoprolol, Nebivolol

D. Cardiac Glycosides

• Digoxin (drug of choice)

E. Vasodilators

• Nitrates: Isosorbide dinitrate (venodilator - reduces preload)
• Hydralazine (arteriolar dilator - reduces afterload)
• Fixed combination: Hydralazine + Isosorbide dinitrate (BiDil - for Black patients)
• Nitroprusside (acute CHF - both preload and afterload reduction)

F. Positive Inotropes (acute/short-term use only)

• Dobutamine (beta-1 agonist)
• Milrinone (phosphodiesterase inhibitor)
• Dopamine (low doses - renal vasodilation; higher doses - inotropic)

G. Newer Drugs

• SGLT2 inhibitors: Dapagliflozin, Empagliflozin
• Ivabradine (I_f channel blocker - reduces heart rate)

PART 3: ANY 4 GROUPS USEFUL IN CHF - MOA, CLASSIFICATION, USE

GROUP 1: ACE INHIBITORS

• All ACE inhibitors are effective as a class effect
• Examples: Enalapril, Captopril, Lisinopril, Ramipril, Quinapril

• Block angiotensin-converting enzyme (ACE), preventing conversion of angiotensin I → angiotensin II
• Angiotensin II is a potent vasoconstrictor - its inhibition reduces afterload (decreased peripheral resistance) and preload (decreased aldosterone → less Na+/water retention)
• ACE inhibitors also prevent breakdown of bradykinin → vasodilation
• Blunt angiotensin II-mediated release of epinephrine and aldosterone
• Inhibit RAAS-driven cardiac remodeling, fibrosis, and ventricular hypertrophy
• Result: Decreased preload, decreased afterload, increased cardiac output, reverse remodeling

• First-line in all patients with HFrEF (reduced ejection fraction), from asymptomatic LV dysfunction to severe CHF
• Reduce both morbidity and mortality (shown in multiple large RCTs)
• Effective even in patients without edema

GROUP 2: BETA-BLOCKERS

• Carvedilol (non-selective beta + alpha-1 blocker)
• Metoprolol succinate (beta-1 selective)
• Bisoprolol (beta-1 selective)
• Nebivolol (beta-1 selective + releases NO)

• Block beta-1 adrenoceptors on the heart → reduce heart rate and myocardial oxygen demand
• Prevent deleterious effects of sustained sympathetic activation on myocardial cells (catecholamine-induced cardiotoxicity)
• Inhibit renin release from kidneys → decrease RAAS activation
• Prevent beta-adrenergic receptor downregulation in failing heart
• Over months, improve ejection fraction and reverse ventricular remodeling

• Proven mortality benefit in HFrEF
• Must be started at low doses and titrated slowly (acute blockade of catecholamine support can transiently worsen HF)
• Improvement in EF may take several months
• Not all beta-blockers are effective - only carvedilol, metoprolol, bisoprolol, nebivolol have mortality data

GROUP 3: ALDOSTERONE ANTAGONISTS (Potassium-sparing diuretics)

• Spironolactone (non-selective - also blocks androgen and progesterone receptors)
• Eplerenone (selective aldosterone receptor blocker)

• Competitively block aldosterone receptors in the distal tubule and collecting duct
• Prevent aldosterone-mediated Na+ retention and K+ excretion → produce mild diuresis with K+ retention
• Block aldosterone-mediated cardiac fibrosis and ventricular remodeling (key benefit beyond diuresis)
• In CHF, RAAS activation causes high aldosterone → progressive cardiac and vascular fibrosis; spironolactone blocks this

• Should be considered in all patients with moderate to severe CHF (reduce both morbidity and mortality - Katzung)
• Combination with ACE inhibitor or ARB provides additive neurohormonal blockade
• Risk of hyperkalemia when combined with ACE inhibitors - monitor K+ levels

GROUP 4: DIURETICS

• Loop diuretics: Furosemide, Bumetanide (inhibit Na+/K+/2Cl- cotransporter in thick ascending loop of Henle)
• Thiazides: Hydrochlorothiazide (inhibit NaCl cotransporter in distal tubule)
• Potassium-sparing: Spironolactone, Amiloride

• Reduce plasma volume by promoting Na+ and water excretion
• Decrease venous return (preload) and reduce pulmonary/peripheral edema
• Loop diuretics are most powerful - mainstay in CHF with edema
• Thiazides may be adequate in mild CHF only
• Secondary benefit: reduce cardiac filling pressure, relieve dyspnea

• Sodium removal (dietary restriction + diuretic) is the mainstay of symptomatic CHF management, especially when edema is present (Katzung)
• Furosemide is drug of choice in moderate-severe CHF
• Risk: Hypokalemia - especially hazardous if patient is on digitalis (increases digitalis toxicity)

PART 4: USE OF ACE INHIBITORS IN CHF - PHARMACOLOGICAL BASIS

• Causes intense arteriolar vasoconstriction → increases afterload
• Stimulates aldosterone secretion → Na+/water retention → increases preload
• Stimulates ADH release → water retention
• Directly promotes cardiac fibrosis, hypertrophy, and remodeling
• Stimulates sympathetic nervous system activation

1. Block Ang II formation → reduce afterload (vasodilation) and preload (less Na+/water retention)
2. Inhibit aldosterone → less edema
3. Reduce sympathetic tone
4. Prevent and reverse cardiac remodeling/hypertrophy
5. Preserve bradykinin (vasodilatory, natriuretic) by blocking its breakdown by ACE

• Improve cardiac output
• Reduce symptoms
• Significantly improve survival in all subsets of HFrEF (asymptomatic to severe)
• Slow progression of ventricular dilation
• First-line drug in CHF without edema

• Bilateral renal artery stenosis (may precipitate acute renal failure)
• Hyperkalemia (can worsen with aldosterone antagonists)
• Pregnancy (teratogenic - category D/X)
• History of angioedema (switch to ARB instead)
• Do not replace digoxin with ACE inhibitor if patient is already on digoxin (patients deteriorate)

PART 5: USE OF CARDIAC GLYCOSIDES (DIGOXIN) IN CHF - PHARMACOLOGICAL BASIS

MOA of Digitalis (KDT-style)

• Digoxin binds to and inhibits the Na+/K+-ATPase (sodium pump) in the sarcolemmal membrane of cardiac myocytes
• This reduces the active pumping of Na+ out of the cell → intracellular Na+ accumulates

• Elevated intracellular Na+ reduces the driving gradient for the Na+/Ca2+ exchanger (NCX), which normally extrudes Ca2+ out of the cell in exchange for Na+ entry
• NCX activity decreases → intracellular Ca2+ increases

• The increased cytosolic Ca2+ is stored in the sarcoplasmic reticulum
• On excitation, a greater Ca2+ release occurs → stronger cross-bridge formation → positive inotropic effect
• Cardiac output increases and the ventricular function curve shifts upward (Lippincott, Fig 10.9)

• Enhanced vagal tone → slows heart rate (negative chronotropy) and slows AV conduction (negative dromotropy)
• Slows conduction velocity through AV node → useful in atrial fibrillation
• At toxic doses: increased automaticity (due to depolarized resting membrane potential) → risk of arrhythmias

• Low-dose digoxin inhibits sympathetic activation (baroreflex sensitization) → reduces RAAS activation
• This is an important additional benefit independent of inotropic effect

• Large volume of distribution (accumulates in muscle); dosage based on lean body weight
• Long half-life (~36 hours) - renal excretion; reduce dose in renal failure
• Target serum concentration: 0.5-0.9 ng/mL for HFrEF (Lippincott)

• Indicated in patients with HFrEF who are symptomatic on optimal pharmacotherapy (beta-blockers + ACE inhibitors + diuretics)
• Particularly useful in CHF with atrial fibrillation (controls ventricular rate)
• Only ~50% of patients in normal sinus rhythm respond significantly
• Does NOT reduce mortality but reduces symptoms and hospitalizations
• Only cardiac glycoside available in most countries

PART 6: USE OF SPIRONOLACTONE IN CHF - RATIONALE

1. RAAS blockade: In CHF, compensatory RAAS activation leads to high circulating aldosterone levels. While ACE inhibitors reduce Ang II (and thus aldosterone), aldosterone can also be produced independently via other pathways ("aldosterone escape"). Spironolactone directly blocks the aldosterone receptor, providing more complete RAAS blockade.
2. Anti-fibrotic effect: Aldosterone promotes collagen deposition and cardiac/vascular fibrosis. Spironolactone blocks this → prevents progressive ventricular fibrosis and remodeling.
3. Diuresis with K+ retention: Spironolactone causes mild Na+ excretion while retaining K+. This is beneficial because:
   • Reduces edema and preload
   • Prevents hypokalemia caused by loop diuretics
   • Reducing hypokalemia reduces the risk of digitalis toxicity
4. Mortality benefit: Clinical trials (RALES trial) showed spironolactone significantly reduces mortality in moderate-severe CHF.
5. Combination benefit: When added to ACE inhibitor + diuretic + digoxin, spironolactone provides additive neurohormonal blockade.

• Risk of hyperkalemia - especially when combined with ACE inhibitors or ARBs
• Monitor serum K+ and creatinine regularly
• Avoid in renal failure (GFR <30 mL/min)
• Gynecomastia with spironolactone (use eplerenone if intolerable)

PART 7: PRECAUTIONS IN CHF DRUG THERAPY

PART 8: POSSIBLE DRUG INTERACTIONS IN CHF

Digoxin Drug Interactions (most important in 2 MBBS)

Spironolactone Drug Interactions

• ACE inhibitors/ARBs: Risk of hyperkalemia (additive K+-sparing)
• K+ supplements: Avoid combination (hyperkalemia)
• NSAIDs: Reduce diuretic and antihypertensive efficacy

ACE Inhibitor Drug Interactions

• K+-sparing diuretics/spironolactone: Hyperkalemia
• NSAIDs: Reduce antihypertensive effect; worsen renal function
• Lithium: ACE inhibitors increase lithium toxicity

PART 9: DIGITALIS TOXICITY - FEATURES AND DRUG TREATMENT

Features of Digitalis Toxicity

• Nausea, vomiting, anorexia, abdominal pain, diarrhea

• Headache, confusion, delirium
• Visual disturbances - xanthopsia (yellow-green vision), blurred vision, halos around lights

• Bradycardia, AV block (1st, 2nd, 3rd degree)
• Paroxysmal atrial tachycardia with block (most characteristic)
• Bidirectional ventricular tachycardia (pathognomonic)
• Ventricular premature beats (especially bigeminy)
• Ventricular fibrillation (can be fatal)

• Hypokalemia predisposes to toxicity (chronic diuretic use)
• Severe acute overdose causes hyperkalemia (K+ leaks from cells)

Drug Treatment of Digitalis Toxicity

1. Withhold digoxin immediately
2. Correct electrolytes:
   • IV Potassium chloride (KCl) - for hypokalemia; K+ competes with digoxin at the Na+/K+-ATPase binding site → reduces toxicity (unless hyperkalemia or AV block - avoid K+ then)
   • Correct hypomagnesemia (magnesium sulfate IV)
3. Antiarrhythmic therapy (for ventricular arrhythmias):
   • Phenytoin (drug of choice for ventricular arrhythmias due to digitalis) - suppresses digitalis-induced automaticity, does not worsen AV block
   • Lidocaine - IV, for ventricular tachyarrhythmias
   • Atropine - for bradycardia or AV block
4. Temporary cardiac pacemaker:
   • For severe bradycardia or high-degree AV block
5. Digoxin-specific antibodies (Digoxin Immune Fab - DigiFab/Digibind):
   • Treatment of choice for severe/life-threatening digitalis toxicity
   • Fab fragments bind digoxin (and other cardiac glycosides) with high affinity
   • Rapidly reverse severe intoxication
   • May also be useful in eclampsia/preeclampsia (endogenous digitalis-like factor)
6. Avoid:
   • Electrical cardioversion (may precipitate VF in digitalis toxicity - avoid unless VF already present)
   • Quinidine (increases digoxin levels further)
   • IV calcium (potentiates toxicity)
   • Class IA antiarrhythmics (worsen toxicity)

SUMMARY TABLE: Drugs + Their Primary Mechanism in CHF

• "The triad of diuretic + ACE inhibitor + beta-blocker" forms the cornerstone of modern HFrEF therapy
• Digoxin is added when symptoms persist despite optimal pharmacotherapy or in CHF with AF
• Spironolactone adds neurohormonal blockade and anti-fibrotic benefit beyond what ACE inhibitors provide
• Digitalis toxicity is treated with Digoxin Immune Fab (digoxin-specific antibody fragments) in severe cases
• Phenytoin/Lidocaine for arrhythmias; K+ correction; avoid cardioversion