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CVS PATHOLOGY - DAY 3 NOTES

CH 12: THE HEART

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PART 1: HEART FAILURE (CONGESTIVE HEART FAILURE)

Definition & Epidemiology

• Definition: Heart failure is a systemic clinical syndrome where the heart cannot pump blood at a rate sufficient to meet the metabolic oxygen demands of peripheral tissues, OR can do so only from abnormally elevated ventricular filling pressures.
• Epidemiology: Affects >5 million individuals in the US (~2% of the population); drives >1 million annual hospitalizations; contributes to ~300,000 deaths/year.
• Prognosis: ~50% of patients die within 5 years of definitive diagnosis.
• Clinical Evolution: Represents the common end-stage of most chronic cardiac diseases; typically emerges insidiously from chronic work overloads (valvular disease, hypertension) or ischemic heart disease.
• Acute Precipitants: Rapid fluid volume overload, acute valvular rupture, acute MI.

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Early Compensatory Mechanisms

1. Frank-Starling Mechanism

• Increased filling volume stretches myocytes → pulls actin-myosin filaments to optimal alignment → maximizes cross-bridge formation → boosts contractile force and stroke volume.

2. Sympathetic Nervous System (SNS)

• Adrenergic nerves release norepinephrine → binds myocardial receptors → elevates HR and contractile velocity → constricts peripheral vessels → increases SVR.

3. RAAS (Renin-Angiotensin-Aldosterone System)

• Perfusion drops → kidneys release renin → cascade drives systemic vasoconstriction + aldosterone-mediated salt and water retention → expands circulating blood volume.

4. Atrial Natriuretic Peptide (ANP)

• Released from stretched atrial walls → counterbalances RAAS via targeted diuresis and vascular smooth muscle relaxation (endogenous brake mechanism).

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The Two Functional Pathways to Heart Failure

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Cardiac Hypertrophy and Progression to Failure

• Protein Synthesis: Hypertrophy requires increased protein synthesis to assemble sarcomeres and duplicate mitochondria.
• Nuclear Ploidy: Hypertrophic cardiomyocytes have enlarged or multiple nuclei - DNA replicates without cell division.

Pressure vs. Volume Overload - Sarcomere Assembly

• Diagnostic Note: Total heart weight (not wall thickness) is the definitive yardstick to measure cardiac hypertrophy because dilation can thin hypermuscular walls.

Metabolic Mismatch in Hypertrophy

• Cardiac mass spikes significantly BUT capillary proliferation does NOT match myocyte growth.
• Perfusion Gap: Diffusion distance for O2 increases → fragile, inadequate blood supply.
• Oxygen Demand Surge: Larger muscle mass + higher wall tension + elevated contractility.
• Ischemic Decompensation: Hypertrophied heart is highly vulnerable to ischemia → myocyte death → heart failure.
• Interstitial Fibrosis: Chronic stress deposits non-contractile collagenous scar → increases wall rigidity → impairs diastolic filling.

Molecular & Genetic Reprogramming

1. Immediate-Early Gene Response: FOS, JUN, MYC, EGR1 activated → ramp up protein synthesis.
2. Fetal Gene Reprogramming: Adult cardiomyocyte re-expresses fetal proteins - fetal myosin heavy chain, natriuretic peptides, fetal collagen type.

Pathologic vs. Physiologic Hypertrophy

• Resistance Training Note: Heavy weightlifting triggers mild concentric hypertrophy without the adaptive microvascular benefits of aerobic conditioning.

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Forward vs. Backward Failure

• Forward Failure: Decreased cardiac output → inadequate arterial tissue perfusion → systemic hypoxia, weakness, organ dysfunction.
• Backward Failure: Blood pools upstream in venous system → fluid leaks into tissues → pulmonary edema, peripheral edema, or both.
• Independent left- or right-sided failure eventually increases strain on the opposite chamber → global heart failure.

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LEFT-SIDED HEART FAILURE

Etiology

• Ischemic Heart Disease (IHD), Systemic Hypertension, Aortic/Mitral Valvular Diseases, Primary Myocardial Diseases (cardiomyopathies).

Pathophysiologic Triad

1. Passive pulmonary congestion (hydrostatic pressure backing into pulmonary circulation)
2. Chamber stasis (blood stagnating in left-sided cavities)
3. Forward hypoperfusion (inadequate arterial perfusion to downstream organs)

Morphology

Cardiac Alterations

• LV is hypertrophied and dilated (in most cases).
• Left atrial dilation from high LV filling pressures → disrupts local conduction tissue → risk of atrial fibrillation.
• Cascade: LV failure/dilation → Mitral Regurgitation + High LA pressure → LA Dilation → AF + Blood Stasis → Thrombus formation in appendage → Systemic Embolization.
• Microscopic: Non-specific - myocyte hypertrophy + patchy interstitial fibrosis.

Pulmonary Remodeling and Edema - 3 Stages:

1. Perivascular Edema - fluid leaks into connective tissue and interlobular septa.
2. Septal Widening - progressive hydrostatic accumulation widens alveolar septa.
3. Alveolar Flooding - hydrostatic forces overwhelm barriers, fluid pours into alveolar spaces.

• Heart Failure Cells: High pulmonary hydrostatic pressure → fragile capillaries leak RBCs into alveolar spaces → macrophages phagocytose RBCs → break down hemoglobin → store residual iron as brown hemosiderin pigment → hemosiderin-laden macrophages = telltale sign of previous pulmonary edema.
• Pleural Effusions: Elevated pressures → transudation of clear, protein-poor serous fluid into pleural cavities.

Symptoms - Respiratory Dyspnea Cascade

1. Exertional Dyspnea & Cough
2. Orthopnea (dyspnea when lying flat; relieved by sitting/standing)
3. Paroxysmal Nocturnal Dyspnea (PND) - sudden nighttime suffocation
4. Dyspnea at Rest

• Fine Lung Rales (Crackles): Fluid-filled lungs produce crackles at lung bases - caused when edematous alveoli snap open during inspiration.

Cardiac Signs

• Cardiomegaly, tachycardia, S3 (volume overload during rapid filling), S4 (atrial contraction into stiff ventricular wall).
• Mitral Restructuring: Progressive LV dilation → papillary muscles displaced outward → mitral leaflets fail to coapt → secondary mitral regurgitation.
• Cascade: Chronic ventricular dilation → Outward displacement of papillary muscles → Mitral regurgitation → LA dilation → AF → Loss of atrial kick + Reduced stroke volume.

Systemic Organ Hypoperfusion

1. Renal Feedback Loop (Prerenal Azotemia)

• Diminished renal perfusion → RAAS activation → aggressive salt and water retention → overloads vascular circuit → spikes backward hydrostatic pressures → worsens pulmonary edema.
• If hypoperfusion worsens → kidneys lose filtration pressure → Prerenal Azotemia (nitrogenous waste buildup in blood).

2. Cerebral Pathway (Hypoxic Encephalopathy)

• Far-advanced heart failure → central perfusion drops → Hypoxic encephalopathy.
• Progression: irritability → loss of attention → restlessness → stupor → coma → irreversible ischemic brain injury.

Systolic (HFrEF) vs. Diastolic (HFpEF) Failure

• Note: Constrictive pericarditis mimics primary diastolic dysfunction.

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RIGHT-SIDED HEART FAILURE

Primary Etiology

• Most common cause: Left-sided heart failure (LV failure → increased hydrostatic back-pressure into pulmonary circulation → chronic pressure load on right ventricle).
• Isolated right-sided HF typically develops secondary to intrinsic lung diseases or pulmonary vascular disorders.

Cor Pulmonale (Pulmonary Heart Disease)

• Right-sided HF driven by severe sustained rise in pulmonary vascular resistance.
• Causes:
  • Parenchymal lung disease: COPD, diffuse interstitial fibrosis.
  • Vascular degradation: Primary pulmonary hypertension, recurrent pulmonary thromboembolism.
  • Vasoconstrictive surges: Obstructive sleep apnea, chronic altitude sickness.
• Sequence: Pulmonary hypertension → RV and RA hypertrophy and dilation → (in extreme cases) interventricular septum bulges to the left, impairing LV filling.

Systemic Pathology of Right-Sided HF

1. Hepatoportal System (Congestive Liver)

• Congestive Hepatomegaly: Liver enlarges due to passive blood pooling in central veins.
• Nutmeg Liver: Pericentral zones (Zone 3) = deep red-brown from intense blood pooling; periportal regions (Zone 1) = normal tan. Resembles cut nutmeg.
• Centrilobular Necrosis: Combined left+right HF → Zone 3 cells experience oxygen starvation → ischemic cell death.
• Cardiac Cirrhosis: Longstanding severe right HF → dead pericentral zones undergo fibrous scarring → fibrous bands bridge central areas.
• Congestive Splenomegaly: High portal pressures → spleen expands → blood pooling → premature platelet trapping and destruction (platelet sequestration).
• Bowel Wall Edema: Intestinal walls become thick and edematous → impairs absorption of nutrients and oral medications.

2. Serous Cavity Effusions

• Pleural Effusion: Large effusions can compress lung → atelectasis.
• Pericardial Effusion: Fluid in pericardial sac.
• Ascites: Massive abdominal fluid collection → presses upward on diaphragm → mechanical dyspnea.

3. Subcutaneous Tissue Infiltration

• Pedal and Pretibial Edema: Fluid in dependent portions (ambulatory patients) - feet, ankles, shins.
• Presacral Edema: Gravity shifts fluid to lower back/sacrum in bedridden patients.
• Anasarca: Massive, generalized whole-body swelling (far-advanced failure).

Renal and Cerebral Impact of Right-Sided HF

• Renal Congestion: Backward hydrostatic pressure travels up renal veins → renal venous congestion → blocks normal drainage → disrupts glomerular filtration pressure → kidneys retain fluid → peripheral edema + congestive azotemia.
• CNS Hypoxia: Venous congestion travels up jugular veins → blocks cranial drainage → venous stasis + local hypoxia → cognitive deficits (disorientation, memory lapses).

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Clinical Management of CHF

Diagnostic Tools

Pharmacotherapy

1. Preload Reduction: Dietary salt restriction, Diuretics.
2. Inotropic Stimulation: Positive inotropic medications (increase contractile velocity and force).
3. Afterload Reduction: Beta-blockers, ACE Inhibitors.

• ACE Inhibitors: Beyond lowering afterload, provide major long-term survival benefit by disrupting neurohumoral cascades that cause maladaptive myocyte hypertrophy and structural ventricular remodeling.

Advanced Armamentarium

• Cardiac Resynchronization Therapy (CRT): Biventricular pacemakers synchronize electrical impulses to both ventricles - restores coordinated mechanical squeezing in hearts with bundle branch blocks.
• Ventricular Assist Devices (VADs): Implantable mechanical pumps that take over the failing ventricle's workload.

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PART 2: CARDIAC DEVELOPMENT & CONGENITAL HEART DISEASE

Cardiac Development

• Heart begins generating pulsatile blood flow within 3 weeks of fertilization.
• Hemodynamic forces direct cardiac development just as they influence hypertrophy/dilation in adult hearts.
• CHD caused by errors during complex cellular migration, folding, and alignment steps of cardiac morphogenesis.

Two Heart Fields

• Focal FHF anomalies → damage LV; Focal SHF anomalies → damage RV/outflow.

Chronological Development

• Day 20: Midline cardiac precursors fuse → single beating tube.
• Day 28: Linear heart tube undergoes complex looping → basic cardiac chambers + Neural Crest Migration + Endocardial Cushion Expansion.
• Day 50: Final structural septation of ventricles, atria, and AV valves → fully functioning 4-chambered heart.

Transcription Networks

• Key pathways: Wnt, Hedgehog, VEGF, BMP, TGF-β, FGF, Notch.
• Many inherited CHD involve mutations in genes encoding transcription factors → partial loss of function, autosomal dominant inheritance.
• Micro-RNAs (miRNAs) act as master epigenetic controllers of transcription factor expression.

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Congenital Heart Disease (CHD)

Clinical Overview

• Definition: Abnormalities of heart or great vessels present at birth.
• Gestational Window: Most CHD from faulty embryogenesis during gestational weeks 3-8.
• Severity Spectrum: Most severe anomalies incompatible with intrauterine survival; circumscribed defects compatible with live birth.
• Compatible Malformations: Septal defects (ASD, VSD), Stenotic lesions (hypoplastic left heart), Outflow tract anomalies.
• Diagnostic Timeline: ~50% diagnosed within the first year of life; milder forms (e.g., ASD) may remain hidden until adulthood.

Epidemiology

• Small muscular VSDs/ASDs detected in >5% of live births by neonatal echo (but typically close spontaneously → excluded from true burden).
• Bicuspid Aortic Valve: 1-2% incidence; often undetected until late adulthood.
• Serious structural defects: slightly less than 1% worldwide; CHD is one of the most prevalent birth defects.
• A core group of 12 distinct disorders accounts for ~85% of all clinical CHD cases.
• Nearly 1.5 million adults in the US live with CHD (driven by surgical advances).
• Surgical Limitations: Irreversible remodeling, arrhythmogenic substrates, prosthetic complications, gestational stress.

Etiology and Pathogenesis

• Precise cause unknown in ~90% of cases.

Key Genetic Notes

• Trisomy 21 (Down Syndrome): Most common known genetic cause of CHD; ~40% have heart defects; most affect structures from the 2nd heart field (AV septae).
• 22q11.2 Deletion (DiGeorge Syndrome): Deranges development of 4th branchial arch and 3rd-4th pharyngeal pouches (thymus, parathyroid, heart); TBX1 deletion is primary culprit; strongly associated with adult-onset schizophrenia.
• Haploinsufficiency: 50% reduction in gene activity sufficient to derange cardiac morphogenesis.
• NOTCH Pathway: NOTCH1 mutations → bicuspid aortic valve; JAG1 and NOTCH2 mutations → Tetralogy of Fallot.
• Marfan Syndrome (Fibrillin mutations): Structural ECM flaws → valvular defects + aortic aneurysms; fibrillin normally negative regulator of TGF-β; mutations → hyperactive TGF-β signaling.

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Clinical Patterns of CHD

Three Major Operational Categories

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RIGHT-TO-LEFT SHUNTS (Cyanotic CHD)

Clinical Profile

• Cyanosis: Deoxygenated blood into systemic arterial supply → dusky blueness of skin and mucous membranes.
• Paradoxical Embolism: DVTs bypass lungs through structural defect → systemic arterial tree → ischemic stroke or organ infarction.
• Compensatory Polycythemia: Chronic systemic hypoxia → erythropoietin release → increased circulating RBCs.
• Digital Clubbing: Long-standing cyanosis causes distal blunting and enlargement of fingertips and toes; may accompany periosteal bone changes (hypertrophic osteoarthropathy).

The "5 T's" of Cyanotic CHD

1. Tetralogy of Fallot (TOF) - most common
2. Transposition of the Great Arteries (TGA)
3. Truncus Arteriosus (Persistent)
4. Tricuspid Atresia
5. Total Anomalous Pulmonary Venous Connection (TAPVC)

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LEFT-TO-RIGHT SHUNTS & EISENMENGER PATHWAY

• Sequence: Left-to-Right Shunt → Chronic high volume/pressure in pulmonary circuit → Medial hypertrophy of small muscular pulmonary arteries → Irreversible obstructive intimal lesions + pulmonary atherosclerosis → RV failure → Pulmonary vascular resistance surpasses systemic resistance → Shunt reverses Right-to-Left → EISENMENGER SYNDROME (late-onset cyanosis).
• Critical Care Note: Once Eisenmenger syndrome develops, structural defects are irreparable - surgical closure will cause acute right heart failure and death. Early surgical intervention is mandatory.

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EMBRYOLOGY OF THE ATRIAL SEPTUM

1. Septum Primum Ingrowth → crescentic sheet grows downward; remaining gap = Ostium Primum.
2. Ostium Secundum Formation → before ostium primum seals, fenestrations coalesce in upper septum primum = Ostium Secundum.
3. Septum Secundum Ingrowth → second rigid muscular sheet grows to the right of the primum, covering the ostium secundum (like a sliding door).
4. Foramen Ovale → gap beneath septum secundum; allows necessary fetal right-to-left shunting.

Perinatal Conversion

• Intrauterine: High pulmonary vascular resistance → right atrial pressure > left atrial pressure → septum primum flap pushed open (right-to-left).
• Postnatal: Lung expansion → drop in pulmonary vascular pressure + rise in left atrial pressure → septum primum presses flat against septum secundum → functional closure. Permanently fuses in most individuals before adulthood.

ASD vs. PFO

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ATRIAL SEPTAL DEFECT (ASD)

Morphological Classification

Clinical Features

• Adulthood Detection Bias: VSDs have higher incidence at birth but most close spontaneously. ASDs less likely to close → most common congenital heart defect diagnosed in adults.
• Hemodynamic Forces: Driven by two factors:
  • Pulmonary vascular resistance < systemic vascular resistance.
  • RV wall much more compliant than LV wall.
• Pulmonary Volume Overload: Blood volume through pulmonary circuit can reach 2-8 times normal.

Clinical Timeline

Auscultation

• Classic murmur = mid-systolic ejection murmur from massive blood volume forcing through a normal pulmonic valve (NOT from blood crossing the septal hole).
• Fixed, wide splitting of the second heart sound (S2).

Surgical Management

• Open or intravascular patch closures; exceptionally low mortality; post-op survival tracks with unaffected general population.

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PATENT FORAMEN OVALE (PFO)

• Foramen ovale permanently fuses in ~80% of individuals by age 2; remains patent in 20%.
• Functions as a passive one-way flap valve - stays closed under normal left-atrial pressures.
• Opens if right-atrial pressure spikes above left-atrial pressure (chronic pulmonary hypertension, severe right HF, or transient Valsalva surges - straining, coughing, sneezing).
• Paradoxical Embolization: DVT clot bypasses lungs through PFO → arterial system → stroke.

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VENTRICULAR SEPTAL DEFECT (VSD)

• Most common overall form of CHD at birth.
• Incomplete closure of interventricular septum → high-pressure communication between right and left ventricles.

Morphological Classification

Clinical Features

• Majority of symptomatic pediatric VSDs = complex multi-component anomalies (e.g., TOF); only 20-30% are isolated.
• VSD detected first time in adult = almost always an isolated lesion.
• Spontaneous Closure Rate: ~50% of small muscular VSDs close during childhood.
• Large Lesion Catastrophe: Massive high-pressure left-to-right shunt → early RV hypertrophy and pulmonary hypertension → Eisenmenger transition.
• Surgical Timing: Asymptomatic VSDs - delay to allow spontaneous closure; large VSDs - early repair mandatory.

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PATENT DUCTUS ARTERIOSUS (PDA)

• Anatomy: Normal fetal vascular channel from main pulmonary artery → aorta (just distal to left subclavian artery).
• Intrauterine Function: Fetal lungs collapsed, high resistance → PDA shunts RV output from pulmonary artery → aorta, bypassing lungs.

Physiologic Closure (Term Infant)

1. Arterial oxygenation surge → ductus constricts.
2. Pulmonary vascular resistance crash → reverses blood flow direction.
3. Prostaglandin E2 collapse → (placental separation/lung clearance) PGE2 falls → PDA closes.

• Anatomic Obliteration: Functional constriction → complete structural fibrosis → solid fibrous cord = ligamentum arteriosum.

Delayed Closure

• Neonatal hypoxia (IRDS, cyanotic heart disease).
• Concurrent large VSDs.
• PDAs account for ~7% of all serious CHD; 90% are isolated structural defects.

Clinical Features

• Classic Sign: Continuous, harsh, "machinery-like" murmur through both systole and diastole (aortic pressure always > pulmonary artery pressure throughout cardiac cycle).
• Hemodynamic Stages: Initially asymptomatic → vascular remodeling → Eisenmenger flip → cyanosis.

Pharmacological Management

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TETRALOGY OF FALLOT (TOF)

Four Cardinal Features (The TOF Tetrad)

1. Ventricular Septal Defect (VSD) - large opening in interventricular septum.
2. Subpulmonic Stenosis - obstruction of right ventricular outflow tract.
3. Overriding Aorta - aortic valve shifts anteriorly, straddles the VSD.
4. Right Ventricular Hypertrophy - secondary consequence of severe chronic pressure overload.

• Embryonic Culprit: Anterosuperior displacement of the infundibular septum simultaneously creates VSD, narrows outflow tract, and misaligns the aorta.

Morphology

• Boot-Shaped Heart (coeur en sabot): Classic characteristic appearance due to massive RV hypertrophy lifting and blunting the cardiac apex.
• VSD typically large with aortic valve at superior border → overriding aorta draws blood from both ventricles.
• Right ventricular outflow obstruction = primarily infundibular (subpulmonic stenosis) ± true pulmonary valvular stenosis.
• Pulmonary Atresia Variant: Life depends on collateral flow through PDA/dilated bronchial arteries.
• Associated Anomalies: Aortic valve insufficiency, concurrent ASD, right-sided aortic arch in ~25% of cases.

Clinical Dynamics

• Clinical phenotype depends on severity of subpulmonic stenosis.

• Growth Mismatch: As child grows, heart muscle expands but rigid stenotic pulmonic orifice fails to expand → relative obstruction worsens over time.
• Pulmonary Shield: Subpulmonic stenosis physically limits blood flow to lungs → protects from Eisenmenger syndrome.
• Decompression Pathway: VSD acts as escape hatch → decompresses RV; true RV failure is rare in childhood.
• Surgery: Complete surgical correction is highly successful; complex in severe pulmonary atresia.

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TRANSPOSITION OF THE GREAT ARTERIES (TGA)

Dextro-TGA (d-TGA) - Complete

• Defect: Ventriculoarterial discordance - ventricles connect to incorrect outflow tracts.
• Aorta arises from RV; Pulmonary artery emanates from LV.
• AV connections remain normal.
• Embryonic Culprit: Failure of embryonic spiraling truncal and aortopulmonary septae to rotate normally.
• Result: Two entirely independent closed vascular loops running in PARALLEL rather than in series.
  • Systemic loop: deoxygenated blood → RA → RV → aorta → tissues (without oxygenation).
  • Pulmonary loop: oxygenated blood → LA → LV → pulmonary artery → lungs (useless re-oxygenation).
• Completely incompatible with extrauterine life unless a structural shunt exists for cross-mixing.

Hemodynamic Shunts

• ~35% of cases: Concurrent VSD → stable bidirectional mixing.
• ~65% of cases: Depend solely on PFO or PDA → immediate life-threatening danger when these close.
• Intervention: Emergent Balloon Atrial Septostomy to tear open interatrial septum and preserve life.

Ventricular Shifts

• RV undergoes severe concentric hypertrophy (generates systemic pressures).
• LV undergoes atrophy and thins out (only supports low-resistance pulmonary bed).
• Surgery: Early Arterial Switch Operation - transects and replants great vessels into correct ventricles.

Levo-TGA (l-TGA) - Congenitally Corrected Transposition

• Double Discordance: Abnormalities at both inlet and outlet levels cancel each other out functionally.
  • RA → morphologic LV → Pulmonary arteries (ventriculoarterial discordance)
  • LA → morphologic RV → Aorta (AV discordance)
• Blood still flows in series → no cyanosis.
• Often asymptomatic; diagnosed incidentally in adulthood.
• Long-Term: Morphologic RV not designed for systemic pressures → eventually hypertrophies → systemic RV heart failure. Also associated with VSDs, ASDs, PFO.

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TRICUSPID ATRESIA

• Definition: Complete occlusion and absence of tricuspid valve orifice - blocks direct RA-to-RV communication.
• Embryonic Cause: Unequal division of the AV canal during development.

Structural Consequences

• Mitral Valve Expansion: Common AV canal favors left side → mitral valve larger than normal.
• Right Ventricular Hypoplasia: Completely bypassed → severe hypoplasia.
• Mandatory Shunts for Survival:
  • Systemic venous return → RA → Mandatory Interatrial Shunt (ASD or PFO) → LA → Enormous mitral valve → LV.
  • From LV: Aortic systemic track + Mandatory Ventricular Shunt (VSD) → blood passes into hypoplastic RV → lungs.

Clinical Features

• Early-onset cyanosis from birth (complete mixing of deoxygenated and oxygenated blood in LA).
• High early infant mortality unless managed with staged surgical palliations.

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COARCTATION OF THE AORTA

• Definition: Pathological narrowing/constriction of the aortic lumen.
• Sex Distribution: 2x more frequent in males; females with Turner syndrome (Monosomy X) have strong predisposition.
• Associated Pathology: Bicuspid aortic valve in 50% of cases; also associated with congenital aortic stenosis, ASD, VSD, mitral regurgitation, intracranial berry aneurysms within Circle of Willis.

Two Classic Morphological Forms

Preductal Coarctation with PDA (Neonatal Crisis)

• Differential Cyanosis: Upper body = fully oxygenated blood from LV via aortic arch branches; Lower body = deoxygenated blood shunted from RV through PDA into descending aorta.
• Pink upper body + lower body cyanosis = hallmark sign of preductal coarctation.
• High early mortality without urgent surgical/catheter-based intervention.

Postductal Coarctation without PDA (Adult Phenotype)

• Acts as chronic, isolated pressure barrier.
• Usually asymptomatic until adult life.
• Upper extremity hypertension; lower extremity hypotension.
• Bounding radial pulses; weak, delayed femoral pulses.
• Symptoms: chronic headache, dizziness, stroke risk (upper); leg claudication, cold extremities (lower).

Compensatory Collateral Pathways & Rib Notching

• Blood diverts: high-pressure subclavian arteries → internal mammary (thoracic) arteries → anterior intercostal arteries → posterior intercostal arteries → descending aorta below narrowing.
• Rib Notching: Engorged intercostal arteries dilate, lengthen, become tortuous → continuous mechanical pulsing erodes adjacent bone → visible erosions along undersurfaces of ribs on chest X-ray.
• Auscultatory Markers: Persistent heart murmurs throughout systole + palpable vibratory "thrill" over chest wall/upper back.
• Myocardial Remodeling: Progressive concentric LV hypertrophy from chronic afterload.
• Surgical Management: Resection of narrowed segment + end-to-end anastomosis or synthetic prosthetic graft.

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PULMONARY STENOSIS AND ATRESIA

• Relatively frequent congenital malformation; obstruction ranges from mild narrowing to complete atresia.
• Can be isolated or part of complex cyanotic anomalies (TOF, TGA).
• RV Hypertrophy: Progressive concentric hypertrophy due to increased workload.
• Poststenotic Dilation: High-velocity turbulent streams slam against main pulmonary artery wall → structural weakening → abnormal expansion.
• TOF Exception: If valvular narrowing coexists with subpulmonic infundibular stenosis, muscular infundibulum chokes blood flow before the valve → pulmonary trunk shielded → remains small and hypoplastic.

Total Pulmonary Atresia - Mandatory Shunts for Survival

• Deoxygenated venous return → RA → Mandatory ASD/PFO → LA → LV → Aorta → PDA (ductal lifeline) → pulmonary arteries → lungs.
• RV completely cut off from workload during fetal development → severely underdeveloped and hypoplastic.

Clinical Features

• Mild stenosis: asymptomatic; compatible with long, normal lifespan.
• Severe/symptomatic stenosis: requires timely surgical correction or balloon valvuloplasty.
• Cavopulmonary Routing (Fontan procedure): Routes deoxygenated venous blood directly from SVC and IVC into pulmonary arteries when RV is too hypoplastic.

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CONGENITAL AORTIC STENOSIS AND ATRESIA

Three Anatomical Locations

Hypoplastic Left Heart Syndrome (HLHS)

• When aortic valve orifice is severely narrowed or entirely missing → LV completely cut off from workload during development.
• Result: LV and ascending aorta remain extremely small and underdeveloped (HYPOPLASIA).
• Endocardial Fibroelastosis: Stagnant, high-pressure LV develops thick porcelain-like coating.
• Absolute Critical Point: Entire systemic circulation + coronary arteries rely 100% on PDA to get blood from RV.
• Natural ductal closure in first week = uniformly lethal unless immediate PGE1 infusion to maintain patency.
• Surgery: Staged open-heart surgeries (Norwood, Glenn, Fontan procedures) - RV takes over as primary systemic pump.

Subvalvular (Subaortic) Stenosis

• Dense endocardial fibrous tissue forms rigid ring below aortic valve cusps.
• Turbulent systolic flow → prominent systolic ejection murmur ± palpable vibratory thrill.

Supravalvular Aortic Stenosis

• Localized thickening, inelasticity, and constriction of ascending aortic wall just above coronary sinuses.
• Genetic Basis: Inherited or sporadic elastin gene mutations → disrupts elastin fiber-smooth muscle cell interactions → overgrowth of disorganized fibrotic wall tissue.

Common Features

• Regardless of location, LV generates high pressures to eject blood past the obstruction → marked concentric LV pressure hypertrophy.
• Generally well-tolerated in childhood and early adulthood.
• Sudden Cardiac Death: Severe LV hypertrophy carries persistent risk - hyperplastic, oxygen-starved muscle can trigger lethal ventricular arrhythmias under stress.

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PART 3: ISCHEMIC HEART DISEASE (IHD)

Definition & The Patho-Biological Ischemic Loop

• Group of related clinical entities from myocardial ischemia - critical imbalance between myocardial oxygen supply and metabolic demands.
• 3 Mechanisms of Ischemic Injury:
  1. ATP collapse (mitochondrial oxidative phosphorylation shuts down).
  2. Nutrient deprivation (halts delivery of essential substrates).
  3. Toxic waste stasis (lactic acid builds up, poisons local tissue).
• Ischemia vs. Hypoxemia: Ischemia = complete stagnation of flow → cuts off nutrients AND causes toxic waste buildup → far less tolerated than pure hypoxemia (where perfusion is intact but O2 content is low, as in anemia, cyanotic heart disease).

Etiology

• >90% of cases: Reduced blood flow due to obstructive atherosclerotic plaques in epicardial coronary arteries.
• IHD frequently called Coronary Artery Disease (CAD).
• Silent Window: Coronary lesions undergo long silent progression spanning decades before sudden onset of clinical symptoms.
• Alternative Causes: Coronary emboli, vasculitis, vascular spasm (Prinzmetal angina).

Four Classic Clinical Presentations

The Tachycardiac Paradox

• Tachycardia exerts simultaneous dual assault:
  1. Spikes demand: more contractions per unit time → accelerated ATP consumption.
  2. Cuts off supply: coronary perfusion occurs almost exclusively during diastole; tachycardia shortens diastole → chokes blood supply.

Epidemiology

• Leading global killer: IHD accounts for >12% of all global deaths; >7.5 million casualties annually in industrialized nations.
• Death rate in the US has dropped by over 50% since mid-1960s peak:
  • Primary/Secondary Prevention: smoking reduction, cholesterol management, hypertension control, weight loss, exercise, glycemic control.
  • Technological Advances: thrombolysis, angioplasty with stenting, CABG; prophylactic aspirin, statins, VADs, AICDs.
• Acute MIs develop in only a fraction of individuals with advanced coronary atherosclerosis → complex underlying genetic variations dictate plaque stability and ischemic susceptibility.

Arterial Pathogenesis

Lumen Occlusion Thresholds

Collateral Vessels and Flow Reserve

• Obstruction developing slowly over years → chronic ischemia stimulates angiogenesis → extensive intercoronary collateral vessel network → shields downstream myocardium from necrosis.
• Physical percentage of narrowing on angiogram does NOT always reflect clinical severity → clinicians use coronary flow reserves (e.g., FFR - Fractional Flow Reserve).

Anatomic Distribution of Coronary Plaques

• Plaques occur most frequently within the first several centimeters of LAD and LCX.
• Atherosclerosis of intramyocardial (penetrating) branches is exceptionally rare → almost all significant coronary stenoses can be accessed via percutaneous coronary catheterization.

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ACUTE PLAQUE CHANGE AND ACUTE CORONARY SYNDROMES (ACS)

The Metamorphosis of an Arterial Wall

• Inflammatory Driver: Active inflammatory cells secrete metalloproteinases → degrade matrix collagen → thin protective fibrous cap → highly vulnerable to mechanical shear stresses.

Pathophysiological Consequences

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ANGINA PECTORIS

• Paroxysmal, usually recurrent attacks of substernal/precordial chest discomfort.
• Driven by transient myocardial ischemia lasting 15 seconds to 15 minutes - insufficient to cause irreversible necrosis.
• Pathway of Pain: Ischemia-induced metabolic shifts → deprived myocytes release adenosine and bradykinin → stimulate sympathetic and vagal cardiac afferent nerve fibers.
• Silent Ischemia Paradox: Common in geriatric population and diabetic neuropathy patients (autonomic sensory nerve degradation).

Three Angina Patterns

• Stable Angina Referred Pain: Crushing/squeezing substernal sensation radiating to left arm or left jaw - because cardiac afferents enter spinal cord at T1-T4 (same as somatic dermatomal nerves).
• Unstable Angina = Infarction Harbinger: Represents actively mutating unstable thrombus - critical warning sign of imminent complete vascular occlusion.

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MYOCARDIAL INFARCTION (MI)

Epidemiology

• ~1.5 million individuals/year in the US; ~610,000 annual deaths.
• 10% of MIs in individuals younger than 40 years.
• 45% of MIs in individuals younger than 65 years.
• Pre-menopausal: Estrogen protects women; men at higher relative risk.
• Post-menopausal: Drop in estrogen → accelerated CAD; IHD = most common cause of death in older women.
• HRT Paradox: Post-menopausal HRT fails to offer cardiovascular protection; can exert pro-thrombotic effects.

Pathogenesis of Standard Coronary Occlusion

1. Acute Plaque Disruption - exposes subendothelial type I collagen and thrombogenic necrotic lipid core.
2. Platelet Activation & Vasospasm (Seconds) - platelets adhere, aggregate, activate; degranulate → TxA2, ADP, serotonin → further platelet recruitment + arterial smooth muscle constriction.
3. Coagulation Cascade Activation (Seconds to Minutes) - exposed tissue factor + factor VII → extrinsic/intrinsic pathways → thrombin generation → fibrin meshwork around aggregated platelets.
4. Complete Luminal Occlusion (Minutes) - evolving atherothrombotic mass completely blocks coronary artery.

Angiographic Timeline Paradox

• Plaque Burden Paradox: Catastrophic acute thrombi usually develop at arterial sites with MILD-TO-MODERATE plaques (thin, unstable fibrous caps) - NOT at sites of critical fixed stenosis (>70%).

MI Without Atherothrombosis (~10%)

1. Dynamic Vasospasm: Intense sustained smooth muscle constriction (with or without pre-existing atherosclerosis); often triggered by platelet hyperaggregation or vasoactive sympathomimetic drugs (cocaine, ephedrine).
2. Coronary Embolization: From LA/LA appendage (during AF), left-sided ventricular mural thrombi, bacterial/fungal vegetations of infective endocarditis, fragments from prosthetic valves/patches, paradoxical emboli through PFO/ASD.
3. Small-Vessel, Metabolic & Structural Mismatches: Microvascular disorders (vasculitis), hematologic abnormalities (sickle cell crisis), extracellular amyloid deposition in microscopic coronary vessel walls, vascular dissection (spontaneous coronary artery dissection), extreme hypertrophy + shock states.

Metabolic Timeline of Cardiomyocyte Injury

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SUBENDOCARDIAL WAVEFRONT OF NECROSIS

• Subendocardial zone = first to die (within 20-30 minutes of severe ischemia).
• Two reasons it's most vulnerable:
  1. Terminal Perfusion: Most distal territory supplied by epicardial coronary arteries (end of the line).
  2. Compressive Forces: Exposed to highest intramural pressures during systole → mechanically compresses microscopic vessels.

Determinants of Infarct Geometry & Extent

• Obstruction characteristics (location, degree, rate of development).
• Vascular anatomy (size of bed supplied).
• Time (duration of total occlusion).
• Tissue kinetics (baseline metabolic activity).
• Collateral flow.
• Dynamic spasm.
• Systemic status (HR, rhythm, blood oxygenation).

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MORPHOLOGICAL PATTERNS OF MI

Coronary Dominance

• Right Dominance (~80%): RCA supplies posterior third of septum + posterobasal LV wall → RCA occlusion can cause significant LV damage + RV infarction.
• Left Dominance (~20%): LCX wraps around to supply posterior third.

Three Classic Structural Patterns

• Diffusion Shield: Narrow preserved rim (~0.1 mm) of viable subendocardial myocardium survives by directly absorbing O2 from ventricular blood via passive diffusion.

Coronary Infarction Frequencies (Right Dominant System)

• RV Extension: 15-30% of MIs from RCA occlusion extend into adjacent RV free wall.

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MACROSCOPIC (GROSS) TIMELINE

• TTC Stain: Viable myocardium = brick-red (LDH trapped in cells reacts with TTC); Necrotic zone = unstained pale zone (LDH leaked out through ruptured membranes). Can expose early necrosis within 2-3 hours of death.

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HISTOPATHOLOGIC (MICROSCOPIC) EVOLUTION

Mechanics of Repair

• Centripetal Repair: MI heals strictly from outer borders toward geometric center → larger infarcts take longer to heal and heal less completely.
• Factors Retarding Healing: Systemic malnutrition, poor underlying vasculature, exogenous corticosteroids (suppress macrophage cleanup + halt fibroblast collagen synthesis → increase rupture risk).
• Scar Equalization: Once completely healed, a scar's age is impossible to distinguish (8 weeks = 10 years microscopically).

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REPERFUSION & REPERFUSION INJURY

• Primary therapeutic goal: salvage maximum ischemic muscle before irreversible necrosis ("time is myocardium").
• Timely reperfusion via thrombolysis, percutaneous coronary angioplasty/stenting, or CABG.
• Reperfusion injury can account for up to 50% or more of the final infarct size.

Mechanisms of Reperfusion Injury

1. Free Radical Surge: Sudden O2 return → massive ROS production within minutes → alter cell proteins and phospholipids.
2. Calcium Overload: Ischemia impairs calcium cycling and damages sarcolemma → reperfusion drives massive influx of extracellular calcium → hyperactivates actin-myosin.
3. Mitochondrial Ruin: Ischemic changes alter mitochondrial membrane permeability → outer membrane swells and ruptures → releases pro-apoptotic proteins.

• Leukocyte Aggregation / "No-Reflow" Phenomenon: Activated neutrophils/leukocytes physically clump → occlude ischemic microvasculature → release proteases and elastases that kill adjacent myocytes → prevent returning blood from actually perfusing tissue.
• Platelet & Complement Activation: Complement activates → damages vascular endothelium → recruits platelets → microvascular plugging → worsens no-reflow.

Morphology of Reperfused Myocardium

• Gross Hemorrhage: Reperfused infarcts are characteristically hemorrhagic (red-purple) - initial ischemia structurally damages capillaries; restored high-pressure arterial flow leaks blood into dead tissue.
• Contraction Band Necrosis: Classic microscopic hallmark of reperfused MI - massive influx of extracellular calcium → hyperactivates actin-myosin → uncontrolled fierce squeeze → sarcomeres pack tightly into dense, dark, eosinophilic cross-bands → locked in permanent tetanic spasm (cannot unbind; no ATP).

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DYNAMIC MYOCARDIAL STATES: STUNNING vs. HIBERNATION

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CLINICAL CHARACTERISTICS, ECG & BIOMARKERS OF MI

Clinical Symptoms

• Severe chest discomfort lasting >30 minutes; heavy, crushing, stabbing, squeezing substernal sensation + rapid, weak pulse.
• Autonomic Reflex: Profuse sweating (diaphoresis), nausea, vomiting - most pronounced with posterior-inferior LV infarcts (intense secondary vagal stimulation).
• Pulmonary Backflow: Dyspnea from ischemic muscle losing contractile power → blood backs up into LA → acute pulmonary congestion and alveolar edema.
• 25% Asymptomatic ("Silent MIs"): Common in diabetic neuropathy and geriatric populations; discovered incidentally via later ECG changes or routine blood panels.

ECG: STEMI vs. NSTEMI

• Microinfarctions: may yield non-specific wave changes or remain electrocardiographically silent.

Serum Lab Evaluation

• Cardiac-specific Troponins T and I (cTnT and cTnI) = gold-standard diagnostic biomarkers.
• CK-MB was historically tracked (now secondary).
• Total serum troponin volume reflects total mass of dead myocardium.
• Acute Transverse Injury Curve: Also seen in acute myocarditis and blunt myocardial trauma.
• Chronic "Troponin Leak": Persistent flat lower-level elevations in CHF, severe pulmonary embolism, chronic renal failure, sepsis - serial spaced blood measurements mandatory to separate evolving MI from chronic leak.

Pharmacological Management

• Oxygen supplementation (for systemic hypoxia/respiratory distress).
• Nitrates (Nitroglycerin): Dilate coronary vessels + peripheral veins → decrease cardiac preload + reverse coronary vasospasms.
• Antiplatelet Combinations: Immediate chewable Aspirin + ADP receptor inhibitors (clopidogrel) or GP IIb/IIIa inhibitors.
• Anticoagulant Infusions: Unfractionated heparin, LMWH, direct thrombin inhibitors, or factor Xa inhibitors.
• Beta-Blockers: Slow HR + decrease contractility → drop O2 demand + protect from catecholamine-induced arrhythmias (strictly contraindicated in decompensated HF).
• Emergent Reperfusion: Fibrinolytic medications (tPA) or mechanical transcatheter interventions (angioplasty + stenting).
• Hemodynamic Stabilization: Address anemia, anxiety, pain, blood pressure fluctuations.
• Continuous ECG Monitoring: Telemetry to catch early lethal arrhythmias from fresh infarct border zones.

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CONSEQUENCES & COMPLICATIONS OF MI

• Modern early intervention = in-hospital mortality rate of 7-8% (10% STEMI; 6% NSTEMI).
• ~75% of survivors experience one or more secondary complications.
• Out-of-hospital STEMI mortality: ~one-third die within first hour of symptom onset (typically from lethal arrhythmia).

Post-Infarct Complication Matrix

1. Mechanical & Pump Dysfunction

• Contractile Dysfunction: LV pump failure in direct proportion to volume of damaged muscle → hypotension, pulmonary congestion, alveolar edema.
• Cardiogenic Shock: ~10% of patients with transmural MIs; typically associated with infarctions damaging 40% or more of total LV mass.
• Papillary Muscle Dysfunction: Ischemic papillary muscles → acute post-infarct mitral regurgitation (MR); long-term → chronic MR from fibrosis/global ventricular remodeling.
• Right Ventricular Infarction: Proximal RCA occlusion → acute right-sided HF; clinically presents as systemic venous pooling (JVD) + systemic hypotension + clear lung fields.

2. Myocardial Rupture Syndromes (1-5% of MIs; very high mortality)

• Peak Vulnerability Window: 3-7 days - exact phase when macrophage-driven lysis peaks; infarct zone is soft, weak, friable granulation tissue not yet reinforced by dense collagen.
• Three Fatal Rupture Sites:
  • LV Free Wall Rupture → blood tears through outer wall → Hemopericardium + Tamponade → uniformly fatal.
  • Ventricular Septal Rupture → necrosis rips open dividing septum → Acute left-to-right shunt (acquired VSD) → overwhelms right heart.
  • Papillary Muscle Rupture → tethering muscle snaps completely → Acute severe Mitral Regurgitation → massive volume overload.
• Rupture Risk Factors: Age >60, female sex, anterior/lateral wall locations, absence of LV hypertrophy, first MI (prior infarct survivors have protective scar tissue).

3. Electrical Instability (Arrhythmias)

• ~90% of patients develop some form of rhythm disturbance.
• First-Hour Peak: Risk for life-threatening arrhythmias (VF) is highest in very first hour → declines steadily thereafter.
• Variants: variable-degree heart blocks (including complete AV block, asystole), sinus bradycardia, supraventricular tachyarrhythmias, VPCs, VT.

4. Inflammatory Pericarditis

• Early Acute Pericarditis: 2-3 days post-infarct; localized fibrinohemorrhagic pericarditis; sharp anterior chest pain + audible pericardial friction rub; typically resolves spontaneously; rarely → dense fibrous adhesions → constrictive pericarditis.
• Late Immune Pericarditis (Dressler Syndrome): Weeks to months after MI; immune-mediated; autoantibodies against cardiac antigens exposed during acute necrotic event.

5. Late Structural Remodeling: Thrombi and Aneurysms

• Chamber Dilation: Necrotic muscle stretches, thins, and expands; most prominent in large anteroseptal infarctions.
• Mural Thrombus Formation (Virchow's Triad analog):
  • Attenuated contractility/stasis + Chamber dilation + Endocardial damage/exposed matrix → Mural thrombus → Left-sided thromboembolism → ischemic strokes or organ infarcts.
• Ventricular Aneurysm: Late complication from large transmural anteroseptal MI; heals into thin, stretched, non-contractile fibrous scar wall. Despite harboring large mural thrombi, triggering chronic arrhythmias, and worsening HF, they do NOT rupture (dense consolidated collagen resists tearing).

Complication Timeline Summary

Risk Geometry

• Subendocardial Shield: Subendocardial infarcts rarely result in pericarditis, structural wall rupture, or ventricular aneurysms - outer healthy muscle layers preserve structural integrity.

Poor Prognostic Factors (STEMI)

• Advanced age (>70 years): reduced cardiovascular reserve, slowed healing.
• Female sex: higher post-infarct complication rates.
• Diabetes Mellitus: accelerates diffuse coronary disease, silent delayed presentations (autonomic neuropathy).
• Previous MI: less functional unscarred muscle to handle fresh workload.

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VENTRICULAR REMODELING POST-MI

• Initial Compensatory Phase: Healthy myocytes undergo concentric hypertrophy to compensate for dead scar → initially hemodynamically beneficial.
• Deleterious Progressive Phase:
  • Ventricular dilation → chamber wall stretches and thins → heart changes from oval to spherical shape → stiffens ventricle.
  • Energetic starvation → thickened muscle demands more O2 → exacerbates local ischemia → drops cardiac output.
• Pharmacological Blockade: ACE Inhibitors block Angiotensin II → lower systemic afterload + interrupt hormonal signaling pathways driving ventricular stretching and dilation.

Long-Term Prognosis

• Most critical factor: Residual LV function (EF) + severity of remaining vessel blockages.
• Year-One Cliff: Total mortality rate within first year post-MI can be as high as 30%.
• Chronic Attrition Rate: Each subsequent year carries additional 3-4% mortality risk among survivors.
• Primary Prevention: Controlling metabolic risk factors (smoking, lipids, hypertension) in individuals who have never had an MI.
• Secondary Prevention: Antiplatelets, statins, beta-blockers, lifestyle changes in MI survivors.

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CHRONIC ISCHEMIC HEART DISEASE (Ischemic Cardiomyopathy)

• Frequently termed ischemic cardiomyopathy - progressive, slow-onset CHF from accumulated ischemic myocardial damage and/or failure of compensatory remodeling.
• Patients with chronic IHD account for almost 50% of all cardiac transplant recipients.

Two Pathological Pathways to Decompensation

1. Post-Infarction Decompensation: Follows one or more large healed infarctions → functional burden overwhelms healthy hypertrophied muscle → mechanical failure.
2. Purely Ischemic Pump Failure: Develops in absence of major discrete infarct event → severe diffuse multi-vessel obstructive CAD causes widespread chronic tissue starvation.

Morphology

Macroscopic (Gross)

• Cardiomegaly: Markedly enlarged and heavy heart; concentric + eccentric LV hypertrophy + diffuse chamber dilation.
• Coronary Artery Profile: Advanced multifocal stenotic coronary atherosclerosis; evidence of prior bypass grafts or stenting.
• Myocardial Scarring: Discrete firm grey-white fibrous scars (old healed infarctions).
• Endocardial Patches: Patchy opalescent fibrous thickenings of mural endocardium - reactive tissue calluses from years of abnormal wall shear forces.
• Mural Thrombi: Old or freshly organizing thrombi in dilated poorly contracting apical walls.

Histopathologic (Microscopic)

Summary

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