Congenital Heart Disease (Shunt, Obstructive, and Cyanotic Lesions)
Shunt lesions
ASD: secundum (mid-septal, often device-closable), primum (part of an AV septal defect), sinus venosus (high, frequently with partial anomalous pulmonary venous return - needs TEE or cross-sectional imaging), and coronary sinus defects. VSD: perimembranous (most common, risk of aortic cusp prolapse and regurgitation), muscular, inlet, and outlet/supracristal (subaortic and subpulmonary, tendency to aortic regurgitation). PDA: measure the narrowest diameter and assess the direction of flow and diastolic runoff. AVSD: common AV valve with a cleft left AV valve leaflet, strongly associated with trisomy 21.
Key principle: shunt direction is set by relative compliance and resistance, not by hole size. A small restrictive VSD gives a loud murmur and a large gradient; a large unrestrictive VSD gives equal pressures and almost no gradient.
Obstructive lesions
Coarctation (suprasternal sawtooth pattern, diastolic runoff, bicuspid aortic valve in a majority), valvar and subvalvar aortic stenosis, pulmonary stenosis (dysplastic valve in Noonan syndrome), subaortic membrane, mitral stenosis, and hypoplastic left heart syndrome.
Cyanotic lesions
The classic five: truncus arteriosus, transposition of the great arteries, tricuspid atresia, tetralogy of Fallot, and total anomalous pulmonary venous return. Tetralogy combines VSD, overriding aorta, subpulmonary obstruction, and RV hypertrophy; the murmur comes from the outflow obstruction, and tet spells reflect worsening obstruction. Transposition presents on day one with severe cyanosis and little or no murmur; the obstruction in TAPVR is a prostaglandin-resistant emergency.
Worked example: Qp/Qs uses the ratio of pulmonary to systemic stroke volumes from the respective outflow and inflow velocities; a value above 1.5 usually indicates a hemodynamically significant shunt.