Drugs for Heart Failure

The video begins by explaining the basic pathophysiology of heart failure, distinguishing between heart failure with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF). It highlights the commonality of decreased cardiac output in both types and how this activates compensatory mechanisms like the sympathetic nervous system and the Renin-Angiotensin-Aldosterone System (RAAS). These compensatory mechanisms, while initially protective, lead to detrimental effects over time, such as increased oxygen demand, reduced coronary perfusion, left ventricular hypertrophy, and dilation, ultimately worsening the disease and increasing mortality. The discussion also covers the role of Brain Natriuretic Peptide (BNP) in opposing RAAS effects and the development of pulmonary and peripheral edema due to venous congestion.

Beta blockers are introduced as a crucial class of drugs that reduce mortality in heart failure. Specific beta blockers mentioned include metoprolol succinate, bisoprolol, and carvedilol. Their mechanism involves blocking beta-1 receptors on the heart, leading to decreased heart rate and contractility, which reduces oxygen demand and prolongs diastole, improving coronary perfusion. Carvedilol, additionally, blocks alpha-1 receptors, causing vasodilation and reducing afterload and preload. These drugs are particularly beneficial for HFrEF patients, especially those post-MI or with coronary artery disease. Adverse effects include bradycardia, decreased contractility (contraindicating use in decompensated heart failure), bronchospasm, and hypoglycemia unawareness.

RAAS inhibitors are vital for reducing mortality in heart failure. This category includes ACE inhibitors (e.g., lisinopril, enalapril), Angiotensin Receptor Blockers (ARBs) (e.g., losartan, valsartan), and aldosterone antagonists (e.g., spironolactone, eplerenone). ACE inhibitors and ARBs block the effects of Angiotensin II, leading to reduced systemic vascular resistance (afterload), decreased venous return (preload), inhibited ADH and aldosterone production (reducing sodium and water retention), and beneficial effects on renal function by reducing proteinuria and chronic kidney disease progression. Aldosterone antagonists are add-on therapy for symptomatic patients with low EF despite ACEI/ARB and beta-blocker use. Common adverse effects include hyperkalemia, increased creatinine, and, specifically for ACE inhibitors, dry cough and angioedema. These drugs are contraindicated in pregnancy.

To further block the RAAS effects, combination drugs like sacubitril/valsartan (Entresto), an Angiotensin Receptor Neprilysin Inhibitor (ARNI), increase BNP by inhibiting neprilysin, an enzyme that breaks down BNP. This leads to profound reduction in Angiotensin II activity, improving cardiac remodeling and reducing blood volume. ARNIs are alternatives for patients on maximal ACEI/ARB therapy who remain symptomatic or have contraindications. Adverse effects are similar to RAAS inhibitors, including hypotension and cough/angioedema due to increased bradykinin levels. Direct-acting vasodilators, such as hydralazine (arterial dilator) and isosorbide dinitrate (venous dilator), offer an alternative for patients with declining renal function or African American patients, effectively reducing afterload and preload without significant renal impact. Orthostasis and reflex tachycardia are potential side effects.

Diuretics (loop and thiazide) are used primarily for symptomatic relief by reducing fluid overload, pulmonary edema, and peripheral edema, often seen in heart failure. They work by inhibiting sodium and water reabsorption in the kidneys, decreasing blood volume and preload. While they do not directly reduce mortality, they significantly improve quality of life. Ivabradine is a medication for refractory HFrEF patients with EF ≤ 35%, normal sinus rhythm, and heart rate > 70 bpm, who are on maximal beta-blocker therapy or have contraindications. It works by blocking funny sodium channels in the SA node, slowing heart rate, prolonging diastole, improving ventricular filling, and coronary perfusion. Adverse effects include bradycardia and luminous vision changes.

Positive inotropic agents increase cardiac contractility. Digoxin is used in refractory HFrEF patients or those with atrial fibrillation and HFrEF. It inhibits the Na+/K+-ATPase pump, increasing intracellular calcium and contractility. It also has negative chronotropic effects by stimulating the vagus nerve, slowing heart rate. Digoxin does not increase mortality but can reduce hospitalizations when levels are appropriate. Adverse effects include arrhythmias, hyperkalemia (due to pump inhibition), and dose-dependent toxicity (exacerbated by hypokalemia). Dobutamine and milrinone are IV inotropic agents reserved for acute heart failure with cardiogenic shock, as they increase mortality. Dobutamine is a beta-agonist (inodilator), increasing contractility and causing vasodilation. Milrinone is a phosphodiesterase-3 inhibitor, increasing cyclic AMP, leading to increased contractility and vasodilation. Both can cause hypotension, sometimes requiring co-administration with vasopressors like norepinephrine.

Chronic heart failure management follows the New York Heart Association (NYHA) classification, categorizing patients based on symptoms, structural heart disease, and risk factors. Class A (risk factors only, no symptoms/structural changes): ACE inhibitor or ARB. Class B (structural heart disease, no symptoms): ACE inhibitor/ARB + beta-blocker. Class C (symptoms, structural heart disease, risk factors): ACE inhibitor/ARB + beta-blocker + aldosterone antagonist. If maximal ACEI/ARB doesn't control symptoms, switch to ARNI. If African American or with renal dysfunction, consider hydralazine/isosorbide dinitrate instead of ACEI/ARB. Add diuretics for symptomatic edema. Class D (refractory symptoms despite optimal therapy): Add ivabradine (if criteria met) and/or digoxin.

Acute heart failure exacerbations require immediate management based on the Forrester classification, which assesses perfusion and congestion. Warm and dry (normal perfusion, no congestion): stable, outpatient management. Warm and wet (normal perfusion, congested): diuresis. Cold and dry (poor perfusion, no congestion): cardiac ICU, inotropes. Cold and wet (poor perfusion, congested): cardiac ICU, highest mortality risk. This worst-case scenario demands aggressive intervention: reduce congestion with high-dose IV diuretics (e.g., loop + thiazide combo) and preload-reducing venodilators (nitroglycerin, morphine). Improve perfusion by addressing afterload reduction (for hypertensive patients, e.g., high-dose nitroglycerin, hydralazine) or by increasing contractility with positive inotropes (dobutamine, milrinone for hypotensive patients in shock), often with vasopressors to maintain blood pressure. Beta-blockers and RAAS inhibitors should be held if the patient is hypotensive or in cardiogenic shock.