Congenital Heart Disease

Overview

CHD = cardiac abnormality present from birth, commonest important heart disease of early life, ~0.5% of newborns (higher in preemies). Mostly unknown cause — multifactorial (genetic+environmental): maternal rubella, maternal drugs, heavy maternal alcohol use.

Classified as shunts (left-right or right-left) or obstructions — complex anomalies combine both.

Dextrocardia

Apex points right. May accompany situs inversus (all organs transposed — heart normal relative to others). Isolated dextrocardia (no situs inversus) → associated major cardiac anomalies.

Left-to-right shunts

Volume-overloads right heart → pulmonary HTN → RVH. Over time right pressure may exceed left → shunt REVERSES (Eisenmenger physiology) → late cyanosis.

VSD — commonest CHD (~30%). Small ones close spontaneously. 90% membranous septum (near bundle of His — conduction risk). RV volume hypertrophy, valve changes, LA/LV volume hypertrophy.

ASD — ~10%. Often silent till pulmonary HTN develops. 3 types: fossa ovalis/ostium secundum (90%, commonest), ostium primum (5%, near AV valves, cleft mitral leaflet), sinus venosus (5%, near SVC). RA/RV volume hypertrophy; LA/LV volume ATROPHY.

PDA — normally closes functionally day 1-2; patent >3 months abnormal, from ongoing PGE2 synthesis (linked to RDS; closed pharmacologically with indomethacin — PGE2 synthesis inhibitor). ~10%, 90% isolated. LA/LV volume hypertrophy.

Right-to-left shunts (cyanotic)

Shunt-obstruction combos → functional right-to-left flow → early cyanosis.

Tetralogy of Fallot — commonest cyanotic CHD (~10%). 4 features: VSD (shunt) + aorta overriding VSD + pulmonary stenosis (obstruction) + RVH.

• Cyanotic form: PS dominates, mild VSD → right-left shunt, cyanosis
• Acyanotic form: VSD dominates, mild PS → left-right shunt, no cyanosis (same 4 features, balance determines physiology)

TGA — malposition of great arteries/AV relationships.

• Complete TGA (commonest): aorta from RV, pulmonary trunk from LV → cyanosis from birth
• Corrected TGA (uncommon): great arteries AND veins both transposed → physiologically corrected despite anatomic transposition

PTA — rare, aortopulmonary septum fails → single common vessel (3-6 cusps) from both ventricles, usually + VSD. Left-right shunt, early cyanosis, poor prognosis.

Tricuspid atresia/stenosis — rare, absent/malformed tricuspid orifice. Interatrial defect → right-left shunt. Cyanotic from birth, survival weeks-months.

Obstructions

Coarctation of aorta — localised narrowing.

• Postductal (adult): distal to closed ductus, “cinched like suture.” Upper-limb HTN, weak lower pulses, claudication. Collaterals via enlarged intercostal arteries → rib notching.
• Preductal (infantile): proximal to patent ductus, longer segment, often +ASD. RVH+small LV. Cyanosis confined to LOWER body (upper vessels arise proximal, spared). Poor prognosis.

Aortic stenosis/atresia — commonest anomaly = bicuspid aortic valve (usually silent, predisposes to later calcification). Atresia rare, incompatible with survival. Stenosis: valvular/subvalvular/supravalvular — all → LV/LA pressure hypertrophy.

Pulmonary stenosis/atresia — isolated forms NOT cyanotic (acyanotic group). PS = commonest obstructive CHD (~7%), fused cusps → diaphragm-like obstruction; may be isolated or part of TOF. Atresia — no RV-lung communication, blood bypasses RV via ASD, reaches lungs via PDA.

Clinical relevance

Eisenmenger reversal = single most important dynamic concept — explains why “acyanotic” lesions present decades later as cyanotic, why early correction of large shunts matters. TOF’s cyanotic/acyanotic split from identical 4 features = clean example that in combined shunt-obstruction lesions, BALANCE (not presence alone) determines picture. Coarctation’s postductal/preductal split hinges entirely on relationship to ductus — one positional fact predicts an entire divergent presentation. PDA’s PGE2 dependence directly yields a treatment (indomethacin) — rare clean link from basic science to bedside intervention.

Overview

Congenital heart disease (CHD) — cardiac abnormality present from birth — is the most common and important heart disease of early life, affecting ~0.5% of newborns (higher in premature infants). Cause is unknown in most cases; attributed to multifactorial inheritance (genetic + environmental), with implicated factors including maternal rubella infection, maternal drug use, and heavy maternal alcohol use during pregnancy.

Classification: shunts (left-to-right or right-to-left) or obstructions to flow — complex anomalies often combine both.

I. Malposition: Dextrocardia

Cardiac apex points right. May accompany situs inversus (all organs transposed together — heart is then normally positioned relative to the other organs). Isolated dextrocardia (without situs inversus) is associated with major cardiac anomalies — transposed atria relative to ventricles, or transposed great arteries.

II.A Left-to-Right Shunts (Acyanotic → Late Cyanotic)

Left-to-right shunting volume-overloads the right heart → pulmonary hypertension → right ventricular hypertrophy. Over time, right-sided pressure may exceed left-sided pressure, reversing the shunt (Eisenmenger physiology) and producing late cyanosis.

Ventricular septal defect (VSD) — the single most common CHD (~30%). Small defects often close spontaneously; large ones remain patent. 90% involve the membranous septum (close to the bundle of His — clinically relevant for conduction risk); the remaining 10% are subpulmonic, subaortic, or multiple muscular defects. Effects: RV volume hypertrophy, tricuspid/pulmonary valve changes, RV endocardial hypertrophy, RA pressure hypertrophy, LA/LV volume hypertrophy, mitral/aortic valve changes.

Atrial septal defect (ASD) — ~10% of CHD; often unnoticed until pulmonary hypertension develops (late cyanosis, right heart failure). Three types: fossa ovalis/ostium secundum (~90%, most common), ostium primum (~5%, low in septum near AV valves, may have a cleft aortic mitral leaflet), sinus venosus (~5%, high septum near SVC entry). Effects: RA/RV volume hypertrophy, tricuspid/pulmonary valve changes, RA/RV endocardial hypertrophy, LA/LV volume atrophy, small mitral/aortic orifices.

Patent ductus arteriosus (PDA) — the ductus normally closes functionally by day 1–2 of life; patency beyond 3 months is abnormal, likely from continued PGE2 synthesis (supported by PDA’s association with respiratory distress syndrome, and pharmacologic closure using indomethacin to suppress PGE2). ~10% of CHD; 90% isolated, remainder associated with VSD/coarctation/aortic-pulmonary stenosis. Effects: LA/LV volume hypertrophy, mitral/pulmonary valve changes, ascending aorta enlargement.

II.B Right-to-Left Shunts (Cyanotic Group)

These entries are not pure shunts but shunt-obstruction combinations, producing functional right-to-left flow and early cyanosis from poorly-oxygenated blood entering the systemic circulation.

Tetralogy of Fallot — the most common cyanotic CHD (~10% of cardiac anomalies). Four features: (1) VSD (the “shunt”), (2) aorta displaced right, overriding the VSD, (3) pulmonary stenosis (the “obstruction”), (4) right ventricular hypertrophy.

Severity depends on the balance between pulmonary stenosis severity and VSD size:

• Cyanotic tetralogy — pulmonary stenosis dominates, VSD mild → right-to-left shunt, cyanosis. Effects: RA/RV pressure hypertrophy, smaller/abnormal tricuspid valve, smaller LA/LV, enlarged aortic orifice.
• Acyanotic tetralogy — VSD dominates, pulmonary stenosis mild → left-to-right shunt, increased pulmonary flow, no cyanosis. Effects: RV/RA pressure hypertrophy, LA/LV volume hypertrophy, enlarged mitral/aortic orifices.

Transposition of great arteries — malposition of aorta/pulmonary trunk/AV orifices/atria-ventricle relationships.

• Regular (complete) transposition — most common; aorta emerges from RV, pulmonary trunk from LV → cyanosis from birth.
• Corrected transposition — uncommon; great arteries and great veins are both transposed (pulmonary veins → RA, systemic veins → LA), producing a physiologically corrected circulation despite the anatomic transposition.

Persistent truncus arteriosus (PTA) — rare; the aortopulmonary septum fails to form, leaving a single common vessel (3–6 cusps) receiving blood from both ventricles, usually with an associated VSD; left-to-right shunt with frequent early systemic cyanosis; generally poor prognosis.

Tricuspid atresia/stenosis — rare; absent tricuspid orifice (atresia, with a dimple in the RA floor) or small malformed tricuspid ring/cusps (stenosis); an interatrial defect usually allows right-to-left shunting. Cyanotic from birth; survival typically weeks to months.

III. Obstructions (Obstructive CHD)

Coarctation of aorta — localised aortic narrowing.

• Postductal (adult) type — narrowing just distal to a (usually closed) ductus arteriosus, aorta “cinched like a suture,” dilated on either side. Recognised in adulthood: upper-extremity hypertension, weak lower-extremity pulses/pressure, claudication/coldness in the legs. Collateral circulation develops between pre- and post-stenotic branches, enlarging intercostal arteries enough to cause rib notching (erosions on the rib’s inner surface).
• Preductal (infantile) type — narrowing proximal to a (usually patent) ductus, gradual, involving a longer proximal aortic segment; often with an associated ASD. Produces RV hypertrophy with a small LV; cyanosis confined to the lower body (upper body vessels arise proximal to the coarctation and are spared). Poor prognosis.

Aortic stenosis/atresia — the commonest congenital aortic anomaly is a bicuspid aortic valve (usually functionally silent, but predisposes to later calcification). Congenital atresia is rare and incompatible with survival. Congenital stenosis: valvular (malformed, irregularly thickened cusps), subvalvular (fibrous ring below the valve), or supravalvular (fibrous constriction above the sinuses of Valsalva, rarest) — all produce LV/LA pressure hypertrophy and aortic root dilatation.

Pulmonary stenosis/atresia — isolated forms do not cause cyanosis (acyanotic group). Pulmonary stenosis is the commonest obstructive CHD (~7% of all CHD); fused valve cusps form a diaphragm-like obstruction, with pulmonary trunk dilatation; may occur isolated or as part of Tetralogy of Fallot. Pulmonary atresia — no RV-to-lung communication; blood bypasses the RV via an ASD, then reaches the lungs via a PDA.

Clinical Relevance

• The left-to-right shunt group’s eventual reversal into late cyanosis (Eisenmenger physiology) is the single most important dynamic concept in this topic — it explains why an “acyanotic” lesion can present decades later as cyanotic, and why early correction of large shunts matters clinically, not just anatomically.
• Tetralogy of Fallot’s cyanotic-versus-acyanotic split, both arising from the identical four anatomic features, is a clean illustration that in combined shunt-obstruction lesions, the balance between competing abnormalities (not the presence of either alone) determines the physiologic and clinical picture.
• Coarctation of the aorta’s postductal-versus-preductal distinction (adult-recognised with rib notching versus infantile with lower-body-only cyanosis) hinges entirely on the anatomic relationship to the ductus arteriosus — a single positional fact that predicts an entire divergent clinical presentation.
• PDA’s dependence on ongoing PGE2 synthesis is a rare case in this topic where the underlying molecular mechanism directly yields a treatment (indomethacin, a prostaglandin synthesis inhibitor) — worth remembering as the mechanistic link between a basic-science fact and an actual bedside intervention.

• Eisenmenger reversal: left-to-right shunt evolving into late right-to-left cyanotic shunt
• Tetralogy of Fallot: same four anatomic features branching into cyanotic vs acyanotic physiology depending on the pulmonary-stenosis/VSD balance
• Coarctation of aorta: postductal vs preductal anatomy and their divergent clinical pictures