P1
Gross Anatomical Characteristics:
The human heart is approximately the size of an individual's fist and resides within the mediastinum of the thoracic cavity.
Base: Represents the broader, superior aspect of the organ where the great vessels emerge.
Apex: The pointed, inferior-most tip directed anteriorly and to the left.
Structural Layers of the Heart Wall:
Pericardium: A fibroserous, protective double-layered sac enclosing the heart and proximal great vessels, providing mechanical protection and lubrication.
Epicardium: The outer visceral layer of the serous pericardium, composed of mesothelium and connective tissue containing coronary vessels.
Myocardium: The thick, muscular middle layer formed of specialized cardiac myocytes responsible for mechanical contractility and pumping force.
Endocardium: The smooth, thin inner endothelial lining that coats the interior chambers and covers the cardiac valves, providing a frictionless surface for intracardiac blood flow.
Chambers and Internal Blood Flow:
Right Atrium: Receives deoxygenated systemic venous return from the superior vena cava (draining the upper body) and the inferior vena cava (draining the lower body).
Right Ventricle: Propels deoxygenated blood through the pulmonary semilunar valve into the pulmonary artery toward the pulmonary capillary beds.
Left Atrium: Collects oxygen-rich blood returning from the lungs via four pulmonary veins.
Left Ventricle: Thickest, highest-pressure chamber; forcibly ejects oxygenated blood through the aortic semilunar valve into the aorta for distribution across the systemic arterial tree.
Atrioventricular (AV) Valves:
Tricuspid Valve: Positioned between the right atrium and right ventricle, preventing backward regurgitation during ventricular systole.
Mitral (Bicuspid) Valve: Positioned between the left atrium and left ventricle, preventing retrograde systolic leakage.
Cardiovascular Circulatory Circuits:
Pulmonary Circuit: A low-pressure vascular network originating from the right ventricle, delivering blood through pulmonary arteries to alveolar capillaries to unload carbon dioxide and bind oxygen, returning to the left atrium via pulmonary veins.
Systemic Circuit: A high-pressure vascular network delivering oxygenated blood from the left ventricle through the systemic arteries and systemic capillary beds to peripheral organs and tissues, returning oxygen-depleted blood to the right atrium via the vena cavae.
Cardiac Cycle Phases:
Systole: The phase of myocardial contraction and ejection; corresponds to systolic blood pressure (SBP).
Diastole: The phase of myocardial relaxation and ventricular filling; corresponds to diastolic blood pressure (DBP).
Coronary Arterial Vasculature:
Right Coronary Artery (RCA): Branches from the base of the ascending aorta and extends into the posterior artery, perfusing the right side of the heart, the inferior LV wall, and primary conduction centers.
Left Main Coronary Artery: Arises from the left aortic sinus and bifurcates into:
Left Anterior Descending (LAD) Artery: Traverses the anterior interventricular sulcus, perfusing the anterior wall of the left ventricle and anterior two-thirds of the interventricular septum.
Circumflex Artery: Traverses the left coronary sulcus to supply the lateral and posterior left ventricular myocardium.
Collateral Circulation Adaptation: Sustained physical exercise induces physiological shear stress that stimulates coronary collateral vessel angiogenesis, establishing alternative vascular bypass conduits that protect myocardium from localized ischemia.
Cardiac Electrophysiology and Action Potential Dynamics
Cardiac Conduction System:
Sinoatrial (SA) Node: The primary physiological pacemaker situated in the superior right atrium; spontaneously depolarizes to initiate rhythmic electrical wave fronts.
Atrioventricular (AV) Node: Positioned in the inferior interatrial septum; acts as a physiological gatekeeper by introducing a brief temporal delay that allows complete atrial mechanical emptying into the ventricles before ventricular systole.
Bundle of His: Emerges from the AV node and bifurcates into the right bundle branch and left bundle branch within the interventricular septum.
Purkinje Fibers: Extensive terminal arborization network rapidly disseminating electrical depolarizing waves throughout the ventricular myocardium to produce synchronized, apicobasal contraction that optimizes stroke volume.
Phases of the Ventricular Myocyte Action Potential:
Phase 0 (Rapid Depolarization): Voltage-gated fast sodium channels open; massive rapid influx of shifts transmembrane potential from up to ; corresponds surface-wise to the QRS complex on the electrocardiogram (ECG).
Phase 1 (Early Repolarization / Peak): Characterized by abrupt closure and inactivation of voltage-gated fast sodium channels along with initial potassium efflux, creating a transient downward notch.
Phase 2 (Plateau Phase): Influx of through slow sodium-calcium (L-type calcium) channels balances outward repolarizing efflux; this influx triggers calcium-induced calcium release from the sarcoplasmic reticulum to initiate cross-bridge cycling and sustained muscular contraction.
Phase 3 (Rapid Repolarization): Closure of calcium channels alongside extensive opening of delayed-rectifier voltage-gated channels; prominent outward efflux restores negative polarity toward the resting potential; corresponds to the T wave on the surface ECG.
Phase 4 (Resting Membrane Potential): The cell membrane stabilizes at approximately ; active electrogenic transport by the ATPase pump ( expelled for every imported) restores and maintains transmembrane ionic concentration gradients.
Refractory Periods:
Absolute Refractory Period (ARP): Encompasses Phase 0, Phase 1, Phase 2, and the initial segment of Phase 3.
During this interval, fast sodium channels remain completely inactivated; cardiac myocytes are entirely unresponsive to further depolarizing stimuli, regardless of current strength.
Physiological Imperative: Prevents sustained tetanic spasm, guarantees obligatory mechanical relaxation intervals required for ventricular diastolic filling, and shields the myocardium against re-entrant fatal tachyarrhythmias.
Ischemic Heart Disease and Angina Pectoris
Acute Coronary Syndrome (ACS) Spectrum:
Represents a continuum of acute myocardial ischemia ranging from unstable angina (UA) to acute non-ST-segment elevation myocardial infarction (NSTEMI) and ST-segment elevation myocardial infarction (STEMI).
Angina Pectoris: Transient clinical discomfort or chest pain induced by reversible myocardial ischemia in the absence of acute myocyte necrosis.
Ischemic Pathophysiology:
Develops when local myocardial oxygen requirements outstrip oxygen delivery via the coronary arteries.
Cells transition to anaerobic glycolysis, producing lactic acid that stimulates cardiac sensory nociceptors in regional autonomic nerve fibers.
Etiological contributors include fixed atherosclerotic narrowing, transient coronary thrombus formation, severe vasospasm, microvascular dysfunction (ischemia with non-obstructive coronary arteries [INOCA]), or severe systemic anemia.
Distinct Clinical Entities:
Stable Angina:
Mechanism: Fixed luminal narrowing due to chronic atherosclerotic plaque.
Pattern: Predictable onset; triggered reproducibly by physical exertion or intense emotional stress.
Duration: Typically lasts .
Relief: Rapidly resolves upon cessation of exertion (rest) or administration of sublingual nitroglycerin.
Tissue Impact: Transient ischemia; zero permanent necrosis.
Prinzmetal's (Variant or Vasospastic) Angina:
Mechanism: Episodic focal spasm of an epicardial coronary artery, occurring either in normal vessels or in the presence of atherosclerotic CAD.
Pattern: Unpredictable; frequently occurs at rest, during early morning hours, or during rapid eye movement (REM) sleep.
Etiology: Unclear pathogenesis involving endothelial dysfunction, focal nitric oxide deficiency, and localized hyperreactivity.
Triggers & Associations: Cigarette smoking, systemic inflammatory states (elevated high-sensitivity C-reactive protein [hs-CRP]), stimulants, alcohol, hyperventilation; low serum potassium worsens vasospasm. Occasionally associated with Raynaud's phenomenon and migraine headaches.
Therapy: Responds to calcium channel blockers or nitrates; carries elevated risks of ventricular arrhythmias, acute infarction, and sudden cardiac death.
Unstable Angina (UA):
Mechanism: Plaque erosion or rupture accompanied by transient, labile platelet aggregation and thrombus formation (clot transiently occludes vessel for roughly ) alongside vasoconstriction.
Pattern: New-onset severe angina, crescendo angina (progressively increasing in frequency, duration, or intensity), or angina occurring at rest.
Relief: Refractory to rest and nitroglycerin; classified as a medical emergency due to impending irreversible infarction.
Clinical Manifestations of Angina:
Presentation: Crushing, squeezing, heavy, retrosternal chest pain.
Levine's Sign: Patient clenches a closed fist over the sternum to describe ischemic pressure.
Radiation Pattern: Discomfort radiates broadly to the left shoulder, left or bilateral arms, jaw, neck, and upper epigastrium.
Pain characteristics remain static regardless of positional shifts, cough, or respiratory phase changes.
Anginal Equivalents: Non-classical presentations presenting as dyspnea, unexplained diaphoresis, lightheadedness, presyncope, dizziness, or epigastric discomfort; frequent in females, elderly individuals, and patients with diabetic autonomic neuropathy.
Acute Myocardial Infarction: Pathology and Complications
Pathological Progression of Infarction:
Arises when persistent, occlusive coronary thrombosis completely cuts off blood supply for longer than , initiating irreversible ischemic coagulative necrosis.
Zonation of Myocardial Damage:
Zone of Infarction (Central Core): Non-viable, necrotic tissue showing altered electrical depolarization and continuous leakage of intracellular enzymes/proteins (cardiac troponins I and T).
Zone of Injury: Hypoperfused tissue bordering the core; viable if collateral perfusion is restored; manifests electrocardiographically as ST-segment changes.
Zone of Ischemia: Peripheral outer region of stunned but viable tissue; electrophysiologically manifests as T-wave inversions.
Reperfusion Injury and Myocardial Stunning:
Restoration of physiological arterial blood flow and oxygen to ischemic zones can paradoxically induce secondary myocardial damage termed reperfusion injury.
Driven by localized bursts of oxidized free radicals generated by infiltrating white blood cells (WBCs), resulting in mitochondrial damage, cellular hypercontracture, sustained myocardial stunning (depressed inotropic function), and reperfusion arrhythmias.
Atypical and Silent Infarction:
Silent MI: Total absence of typical anginal symptoms during transmural necrosis, documented primarily in diabetic populations due to sensory denervation.
Post-Myocardial Infarction Complications:
Lethal Dysrhythmias: Peak vulnerability occurs within hours post-infarction; ischemic zones conduct impulses abnormally slowly, generating electrical re-entry circuits that trigger ventricular tachyarrhythmias.
Papillary Muscle Rupture: Ischemia and necrosis of left ventricular papillary muscles causes acute mitral valve insufficiency (regurgitant murmur), provoking massive retrograde backflow into the left atrium and pulmonary circulation, precipitating acute pulmonary crackles and severe dyspnea.
Mural Thromboembolism: Akinesis or hypokinesis of infarcted myocardium promotes local blood stasis and hypercoagulability, creating intraventricular thrombi capable of systematic embolization to the cerebral or peripheral circulation.
Ventricular Aneurysm and Free Wall Rupture: Necrotic ventricular muscle weakens, dilates, and thins under high intraventricular pressures, ballooning outward into a ventricular aneurysm; rupture of this necrotic wall leads to catastrophic hemopericardium, requiring emergent surgical correction.
Pericarditis and Dressler's Syndrome:
Acute Pericarditis: Develops post-MI as transmural inflammation irritates the epicardium; produces a scratchy pericardial friction rub and sharp, pleuritic chest discomfort exacerbated by supine positioning and deep inspiration.
Dressler's Syndrome: A delayed hypersensitivity or autoimmune reaction against necrotic myocardial autoantigens occurring weeks post-MI, characterized by recurrent pericarditis, pleuritis, and pericardial effusions.
Cardiogenic Shock:
Represents severe end-stage ventricular pumping failure where cardiac output cannot maintain vital organ perfusion.
Acute myocardial infarction accounts for of all documented cases of cardiogenic shock.
Characterized by profound hypotension, decreased cardiac output, elevated ventricular filling pressures, oliguria, and fatal multi-system organ failure.
Inflammatory and Infectious Heart Diseases
Infective Endocarditis (IE):
Severe microbial infection of the endocardium, primarily damaging the heart valves.
Primary Pathogen: Staphylococcus aureus is the predominant bacterial culprit.
Predisposing Risk Factors: Prosthetic heart valves, implanted pacemakers/defibrillators, central venous catheters, intravenous (IV) drug abuse, and bacteremia secondary to invasive dental procedures, pneumonia, or pyelonephritis.
Vegetation Formation: Amorphous vegetations formed of bacteria, platelets, and fibrin develop on cardiac valves, causing leaflet perforation, acute regurgitation, and fragmentation that sheds septic emboli into the systemic circulation.
Myocarditis (Inflammatory Cardiomyopathy):
Diffuse inflammation of the myocardium ranging from subclinical courses to lethal pump failure.
Etiology: Enteroviruses, influenza, herpesviruses, hepatitis viruses, autoimmune conditions (systemic lupus erythematosus), or cardiotoxic exposure.
Clinical Features: Systemic fever, arthralgias, myalgias, palpitations, audible pericardial friction rub, and an gallop (indicative of acute ventricular volume overload).
Pericardial Effusion and Cardiac Tamponade:
Pericardial Effusion: Pathological accumulation of serous, purulent, or hemorrhagic fluid within the pericardial space.
Cardiac Tamponade: Rapid or excessive fluid accumulation within the inelastic pericardial sac that dramatically increases intrapericardial pressure, mechanically compressing cardiac chambers and impeding diastolic ventricular filling.
Pathognomonic Manifestations of Tamponade:
Beck's Triad: Hypotension, jugular venous distention (JVD), and muffled (distant) heart sounds.
Pulsus Paradoxus: An exaggerated, pathological drop in systolic blood pressure of or greater during normal inspiration.
Cardiac Dysrhythmias and Conduction Disorders
Classification Principles:
Supraventricular Dysrhythmias: Arise proximal to the bifurcation of the bundle of His (SA node, atrial myocardium, or AV node).
Ventricular Dysrhythmias: Originate within the specialized ventricular conduction network or the ventricular myocardium.
Rate Distinctions: Tachyarrhythmias (heart rate exceeding ) versus bradyarrhythmias (heart rate below ).
Conduction Blocks: Pathological disruption of electrical wave progression; complete heart block involves absolute AV dissociation where atria and ventricles beat independently without synchronization.
Atrial Fibrillation (AFib):
Characterized by chaotic, rapid, disorganized atrial depolarization without uniform mechanical atrial systole.
ECG Features: Complete absence of distinct P waves, replaced by irregular baseline fibrillatory waves and irregularly irregular QRS responses.
Clinical Complications: Loss of atrial kick decreases stroke volume; circulatory stasis in the left atrial appendage promotes thrombus formation and thromboembolic cerebrovascular accidents (stroke).
Premature Ventricular Contractions (PVCs):
Ectopic depolarizations arising from an irritable ventricular focus.
ECG Features: Early, wide, and bizarre QRS complexes uncoupled from preceding P waves.
Patterns: Bigeminy (every alternating beat is a PVC), trigeminy (every third beat), and quadrigeminy (every fourth beat).
Represents the most frequent dysrhythmia observed following acute MI.
Sporadic, isolated PVCs require no active pharmacotherapy; high-risk indicators requiring intervention include couplets (two consecutive PVCs) or a frequency exceeding .
Ventricular Tachycardia (VT):
A consecutive run of wide, bizarre QRS complexes at a rate greater than , devoid of P or T waves.
Extreme ventricular pacing prevents adequate diastolic filling, dramatically collapsing cardiac output; triggers dyspnea, lightheadedness, palpitations, syncope, and swift progression into ventricular fibrillation.
Ventricular Fibrillation (VF):
Disorganized, chaotic electrical quivering of ventricular fibers without any coherent mechanical pumping activity.
Frequently triggered by an R-on-T phenomenon, where a premature ventricular contraction depolarizes myocardial tissue during the vulnerable relative refractory period of the preceding T wave.
Causes instantaneous loss of cardiac output, rapid loss of consciousness, and brain death within minutes unless reversed by electrical defibrillation.
Hemodynamics and Compensatory Mechanisms in Heart Failure
Fundamental Hemodynamic Concepts:
Cardiac Output (CO): The volume of blood ejected by the left ventricle per minute, calculated as , averaging approximately in a healthy adult at rest.
Cardiac Index (CI): Hemodynamic parameter normalizing cardiac output to individual body surface area ().
Left Ventricular Ejection Fraction (LVEF): The volumetric percentage of total end-diastolic blood ejected per systolic contraction; normal baseline values range from .
Preload: The volume and stretch within the ventricle at the conclusion of diastole (End-Diastolic Volume, EDV).
According to the Frank-Starling mechanism, higher EDV stretches myocardial sarcomeres, augmenting mechanical contraction force and increasing stroke volume up to an optimal physiological plateau.
Afterload: The wall tension and systemic vascular resistance (SVR) that the left ventricular myocardium must generate and overcome to force open the aortic valve and eject blood; elevations in afterload impede ventricular emptying and reduce forward cardiac output.
Inotropic vs. Chronotropic Properties:
Inotropy: The inherent force of myocardial contraction. Positive inotropes include sympathetic adrenergic stimulation and intracellular ; negative inotropic states impair pumping force.
Chronotropy: Heart rate. Positive chronotropes (sympathetic tone) elevate heart rate; negative chronotropes (parasympathetic tone) decrease it.
Starling Forces and Edema Pathogenesis:
Governed by the dynamic balance between capillary hydrostatic pressure (filtration force pushing water into the interstitium) and oncotic pressure (absorption force pulling water into the intravascular space).
Ventricular pump failure leads to retrograde venous volume accumulation, elevating downstream capillary hydrostatic pressure, overcoming plasma oncotic forces, and driving peripheral or pulmonary edema.
Neurohormonal Compensatory Systems:
Renin-Angiotensin-Aldosterone System (RAAS):
Renin: Secreted by renal juxtaglomerular cells in response to low renal arterial perfusion; converts circulating hepatic angiotensinogen into angiotensin I.
Angiotensin-Converting Enzyme (ACE): Located primarily within pulmonary capillary endothelial walls; cleaves angiotensin I into active angiotensin II.
Angiotensin II: Potent systemic vasoconstrictor that elevates total systemic afterload, induces direct cellular hypertrophy and maladaptive ventricular remodeling, and triggers the adrenal cortex to release aldosterone.
Aldosterone: Synthesized in the adrenal cortex; enhances distal tubule sodium and water retention, expanding effective circulatory plasma volume and worsening myocardial preload.
Natriuretic Peptides and Regulatory Mediators:
Atrial Natriuretic Peptide (ANP): Synthesized and secreted by atrial myocytes in response to wall stretch; induces natriuresis, diuresis, vasodilation, and inhibition of renin and aldosterone.
Brain (B-type) Natriuretic Peptide (BNP): Released by ventricular myocytes under excessive ventricular distention; serves as a quantitative clinical biomarker for the diagnosis and staging of heart failure.
Neprilysin: An endogenous metalloprotease responsible for enzymatic degradation of ANP and BNP; pharmaceutical neprilysin inhibitors preserve natriuretic peptide levels to sustain vasodilation and natriuresis.
Endothelin: A potent endothelial-derived peptide elevated post-MI; stimulates severe arterial vasoconstriction and accelerated ventricular remodeling.
Tumor Necrosis Factor-alpha (TNF-): Inflammatory cytokine promoting cardiomyocyte apoptosis, interstitial fibrotic collagen deposition, and negative inotropic depression.
Nitric Oxide (NO): Endothelial autacoid inducing potent vascular smooth muscle relaxation and vasodilation.
Antidiuretic Hormone (ADH / Vasopressin): Secreted by the posterior pituitary following baroreceptor unloading; drives water reabsorption across renal collecting ducts, expanding total intravascular volume.
Autonomic Nervous System: Decreased cardiac output disinhibits carotid/aortic baroreceptors, prompting sympathetic nervous system (SNS) output that acts via beta-1 adrenergic receptors to increase heart rate and contractility while driving vasoconstriction; parasympathetic nervous system (PNS) tone acts via cholinergic receptors to depress heart rate.
Heart Failure Etiologies, Classifications, and Clinical Manifestations
Etiological Drivers of Heart Failure:
Systemic Arterial Hypertension: The primary underlying risk factor; chronic pressure overload drives concentric left ventricular hypertrophy (LVH), which narrows ventricular chamber filling space and elevates myocardial oxygen consumption beyond coronary supply capacity.
Ischemic Heart Disease: Infarction destroys functional myocytes, substituting compliant muscle with rigid fibrotic scar tissue.
Cardiomyopathies:
Ischemic: Extensive myocardial fibrosis following recurrent coronary ischemia.
Dilated: Marked chamber enlargement with global systolic contractile impairment.
Restrictive: Excessive myocardial stiffness preventing adequate diastolic filling.
Hypertrophic: Genetic mutations (primary) or longstanding hypertension (secondary) driving marked asymmetric myocyte hypertrophy.
Cor Pulmonale: Isolated right-sided ventricular failure caused by chronic pulmonary parenchymal or vascular disorders (COPD, hypoxia, pulmonary fibrosis) that trigger chronic pulmonary vasoconstriction and pulmonary arterial hypertension.
Valvular Pathology: Chronic aortic stenosis forces the left ventricle to generate elevated pressures, inducing LVH and failure; severe mitral regurgitation produces left atrial and pulmonary venous volume overloads.
Contributing Risk Factors: Advanced age, metabolic syndrome, obesity, diabetes mellitus, obstructive sleep apnea, cardiotoxic medications, anabolic steroids, viral myocarditis, alcohol abuse, chronic kidney disease, and massive pulmonary embolism.
Clinical Classifications of Heart Failure:
Heart Failure with Reduced Ejection Fraction (HFrEF / Systolic HF): Left ventricular ejection fraction is depressed (); myocardial contractility is impaired, limiting forward stroke volume.
Heart Failure with Preserved Ejection Fraction (HFpEF / Diastolic HF): Left ventricular ejection fraction remains preserved (); ventricular walls are stiff, hypertrophied, or non-compliant, impairing diastolic filling despite preserved contractile mechanics.
Acute vs. Chronic Heart Failure: Acute HF involves rapid clinical decompensation (e.g., massive MI or cardiogenic shock); chronic HF represents an indolent, progressive decline in functional performance over extended timeframes.
High-Output vs. Low-Output Heart Failure: Low-output failure involves inadequate forward perfusion under normal or elevated metabolic loads; high-output failure involves normal or elevated cardiac output that remains insufficient to meet abnormally elevated systemic metabolic demands (e.g., severe anemia, thyrotoxicosis).
Forward vs. Backward Failure Dynamics:
Forward Failure: The heart cannot propel adequate blood volume forward into arterial beds, producing poor tissue perfusion, muscle weakness, cold extremities, and renal insufficiency.
Backward Failure: Inability to clear venous return causes elevated filling pressures, retrograde venous engorgement, and transudation of fluid into tissues.
Chamber-Specific Manifestations:
Left Ventricular Failure (LVF):
Backward Effects: Elevated left ventricular end-diastolic pressure transmits backward into the left atrium, pulmonary veins, and pulmonary capillary networks, precipitating pulmonary congestion, impaired alveolar gas diffusion, pulmonary crackles, dyspnea, and acute pulmonary edema.
Orthopnea: Dyspnea provoked by lying supine, clinically quantified by the number of pillows required to achieve restful recumbency.
Paroxysmal Nocturnal Dyspnea (PND): Severe, sudden awakening from sleep with sensations of suffocation and night terrors caused by the central redistribution of dependent edema fluid into the pulmonary vasculature while recumbent.
Forward Effects: Inadequate systemic cardiac output causes cerebral hypoperfusion (confusion, memory loss, anxiety), renal hypoperfusion (oliguria), gastrointestinal ischemia, generalized muscle weakness, and cold, pale extremities.
Right Ventricular Failure (RVF):
Predominant Backward Congestion: Elevation of right ventricular end-diastolic pressure raises right atrial pressure and central venous pressure (CVP).
Jugular Venous Distention (JVD): Visible engorgement and elevation of the jugular venous pulsation column.
Hepatosplenomegaly & Ascites: Congestive hepatomegaly and splenomegaly due to hepatic venous pooling; fluid extravasation into the peritoneal cavity produces ascites.
Hepatojugular Reflex: Sustained manual pressure over the liver causes a sustained, visible rise in jugular venous pressure.
Gastrointestinal Congestion: Mucosal venous pooling precipitates nausea, anorexia, and malabsorption.
Peripheral Edema: Bilateral, dependent pitting edema accumulating in the feet, ankles, and pretibial regions.
Biventricular Failure: Primary mechanical failure in one ventricle alters interventricular septal dynamics and increases opposing afterload or preload, culminating in combined failure of both ventricles with overlapping pulmonary and systemic manifestations.
Heart Failure Staging Frameworks:
New York Heart Association (NYHA) Functional Classification:
Class I: Mild; ordinary physical activity does not induce undue fatigue, palpitations, or dyspnea.
Class II: Mild; comfortable at rest, but ordinary physical exertion induces fatigue, dyspnea, or palpitations.
Class III: Moderate; comfortable at rest, but marked limitation of physical activity occurs with less than ordinary exertion.
Class IV: Severe; inability to carry out any physical activity without discomfort; heart failure symptoms persist at rest.
ACC/AHA Structural Staging System:
Stage A: High risk for developing heart failure, without demonstrable structural heart disease or symptoms.
Stage B: Structural heart defect or injury present, but completely asymptomatic.
Stage C: Structural heart disease accompanied by past or present clinical symptoms of heart failure.
Stage D: Advanced, refractory, end-stage heart failure requiring specialized mechanical or inotropic interventions.