9.3 Congenital & Valvular Heart Disease

9.3 Congenital & Valvular Heart Disease

Quick Answer: Fetal life uses placenta and three shunts (ductus venosus, foramen ovale, ductus arteriosus) to bypass fluid-filled lungs. After birth, falling pulmonary resistance and rising systemic resistance close shunts functionally. Cyanotic congenital heart disease mixes deoxygenated blood into the systemic circuit; acyanotic disease usually left-to-right shunts until pulmonary hypertension reverses flow (Eisenmenger). Rheumatic and infective processes destroy or deform valves through immune mimicry and vegetations.

Fetal Circulation and Transitional Changes

The placenta is the fetal gas-exchange organ. Oxygenated blood returns via the umbilical vein, and a substantial fraction bypasses the liver through the ductus venosus into the inferior vena cava, streaming preferentially toward the foramen ovale into the left atrium—supporting brain and coronary perfusion with relatively oxygen-rich blood. Deoxygenated superior vena caval blood preferentially enters the right ventricle and is pumped into the pulmonary artery; because fetal pulmonary vascular resistance is high (fluid-filled lungs, hypoxic vasoconstriction), most RV output crosses the ductus arteriosus into the descending aorta.

At birth, lung expansion and rising PaO2 drop pulmonary vascular resistance dramatically. Pulmonary venous return increases left atrial pressure, functionally closing the foramen ovale (septum primum against septum secundum). Rising systemic resistance and falling pulmonary pressure reverse ductal flow briefly; rising oxygen and falling prostaglandins promote ductus arteriosus constriction. Umbilical vessel closure eliminates placental low-resistance runoff and ductus venosus flow. Persistent pulmonary hypertension or prostaglandin effects can keep the ductus open—sometimes lifesaving in ductal-dependent congenital lesions, sometimes pathologic (PDA).

Cyanotic vs Acyanotic Lesions: Shunt Logic

Cyanosis of cardiac origin implies deoxygenated blood reaching the systemic arterial tree—right-to-left shunt or parallel circulations with inadequate mixing. Acyanotic shunt lesions are typically left-to-right (higher left pressures drive oxygenated blood into right heart/pulmonary artery), increasing pulmonary blood flow and risking failure to thrive, pulmonary congestion, and eventual pulmonary vascular disease.

Cyanotic: The Classic Set

Tetralogy of Fallot severity tracks the degree of right ventricular outflow obstruction. Mild obstruction may be mostly left-to-right through the VSD (less cyanotic); severe obstruction forces right-to-left VSD shunting (cyanosis). Squatting during spells increases systemic vascular resistance, reducing R→L shunt fraction—classic physiology vignette.

TGA creates two parallel loops: systemic venous blood recycles to body via RV–aorta; pulmonary venous blood recycles to lungs via LV–PA. Survival requires communication (PGE to keep PDA, balloon atrial septostomy conceptually) so oxygenated and deoxygenated blood can mix.

Truncus arteriosus fails to septate the outflow tracts; a single trunk overrides a VSD. Tricuspid atresia blocks RA-to-RV inflow; an atrial communication is mandatory, and pulmonary flow depends on associated pathways (often VSD to a hypoplastic RV or PDA). TAPVR delivers all pulmonary venous blood to the right side; an ASD is needed for systemic output; obstruction of the anomalous pathway causes severe cyanosis and pulmonary edema.

Acyanotic Lesions and Pressure Overload

VSD size and pulmonary vascular resistance determine shunt magnitude. Small muscular defects may be loud (“maladie de Roger”) yet hemodynamically modest; large perimembranous defects transmit pressure and volume to the pulmonary circuit. ASD shunting is driven more by relative ventricular compliance than by a huge pressure gradient; fixed splitting of S2 is a classic bedside correlate. PDA continuous flow reflects the persistent aorta–PA pressure gradient after birth. Coarctation produces upper extremity hypertension with weak femoral pulses; collateral flow through intercostal arteries erodes ribs (notching) over time. In neonates, critical coarctation may be ductal-dependent for lower body perfusion.

Eisenmenger Syndrome

Chronic large left-to-right shunts expose pulmonary arteries to high flow and pressure, driving pulmonary vascular remodeling (medial hypertrophy, intimal proliferation, eventual fixed pulmonary vascular resistance). When pulmonary pressure exceeds systemic pressure, the shunt reverses to right-to-left, producing cyanosis, clubbing, and erythrocytosis—Eisenmenger syndrome. At that stage, simple defect closure can be catastrophic because the right heart depends on the pop-off and the pulmonary vascular disease is irreversible. Exam stems: long-standing unrepaired VSD/PDA/AV canal → progressive cyanosis years later.

Rheumatic Heart Disease

Acute rheumatic fever follows untreated group A streptococcal pharyngitis via molecular mimicry: antibodies and T cells against streptococcal M protein cross-react with cardiac myosin and valvular laminin/other antigens. Pancarditis can occur; chronic rheumatic heart disease produces fibrotic, thickened valves—mitral stenosis most classically (with or without regurgitation), often with aortic involvement. Pathologic hallmarks conceptually include leaflet thickening, commissural fusion, and chordal shortening. The pathophysiologic cascade: elevated LA pressure → atrial enlargement/fibrillation → pulmonary hypertension → right heart strain. This is immune-mediated post-infectious valvulopathy, not direct bacterial invasion of the valve during the acute pharyngitis itself.

Infective Endocarditis Pathophysiology

Infective endocarditis (IE) begins with endocardial injury (turbulent jets across abnormal valves, prosthetic material, or IVDU-related right-sided trauma) → platelet–fibrin deposition (NBTE: nonbacterial thrombotic endocarditis nidus) → bacteremia seeding → vegetation growth. Vegetations destroy leaflets (regurgitation), embolize, and seed metastatic abscesses; immune complexes contribute to glomerulonephritis and vasculitis phenomena.

Left-sided IE showers systemic emboli (brain, spleen, kidney); right-sided IE (IVDU, tricuspid) embolizes to lung (septic pulmonary infarcts). Culture-negative IE may reflect prior antibiotics or fastidious organisms (HACEK group conceptually). The CBSE focus is mechanism: turbulence → nidus → bacteremia → vegetation → regurgitation/embolization/immune sequelae—not antibiotic dosing algorithms.

Putting Congenital and Valvular Themes Together

Congenital stems ask: where is the oxygenated blood going, is pulmonary flow too high or too low, and is survival dependent on a fetal shunt? Valvular acquired disease asks: immune mimicry (rheumatic) versus infection on a nidus (IE), and which chamber pressures rise as a result (MS → LA; acute AR/MR → catastrophic LV/LA volume; chronic lesions → remodeling). Eisenmenger is the bridge concept linking unrepaired shunt congenital disease to cyanosis later in life.

If you can sketch fetal shunts, classify cyanotic anatomy in one sentence each, explain L→R versus R→L driving pressures, and connect viridans/S. aureus/enterococcus to their portals of entry and valve destruction tempo, you have the high-yield core of Section 9.3.