Cyanotic congenital heart disease

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Cyanotic Congenital Heart Disease

Cyanotic congenital heart disease (CHD) refers to structural cardiac defects that result in right-to-left shunting of deoxygenated blood into the systemic circulation, causing hypoxemia and clinical cyanosis. The classic group is remembered by the "5 Ts": Tetralogy of Fallot, Transposition of the Great Arteries, Tricuspid Atresia, Truncus Arteriosus, and Total Anomalous Pulmonary Venous Return (TAPVR). All cause cyanosis through right-to-left shunting, though the underlying mechanisms differ.

Pathophysiology: Why Cyanosis Occurs

Right-to-left shunting bypasses the pulmonary circulation, allowing deoxygenated (venous) blood to enter the systemic arterial circulation. This produces:

Hypoxemia (low PaO2)
Central cyanosis (visible when reduced hemoglobin > 5 g/dL)
Compensatory polycythemia (chronic hypoxemia stimulates erythropoiesis)
Clubbing of fingers/toes (chronic hypoxemia)

The classification by pulmonary blood flow is clinically useful:

Cyanotic CHD classification by pulmonary blood flow

Fig. Clinical clues to diagnosis of cyanotic CHDs based on pulmonary blood flow and ECG findings (Rosen's Emergency Medicine)

The Five Classic Lesions

1. Tetralogy of Fallot (TOF)

Most common cyanotic CHD beyond infancy - ~1 in 2,500 live births.

Four anatomical defects (all arising from a single embryologic defect - anterosuperior displacement of the infundibular septum):

Large, unrestrictive, misaligned VSD
Right ventricular outflow tract obstruction (RVOTO) - subpulmonic stenosis
Aorta overriding the VSD
Right ventricular hypertrophy (secondary to pressure overload)

Fig. (A) Classic TOF: right-to-left VSD shunt when subpulmonic stenosis is severe. (B) Complete TGA: with and without VSD (Robbins Pathology)

Clinical presentation:

Degree of cyanosis depends on severity of RVOTO
Pink TOF: mild obstruction, may have left-to-right shunt initially
Severe TOF: profound cyanosis from birth, requires PGE1 to maintain ductal patency
Systolic ejection murmur at left sternal border
Right axis deviation + RVH on ECG
Boot-shaped heart on CXR (coeur en sabot) - concave pulmonary artery segment, normal heart size, decreased pulmonary vascular markings
Right-sided aortic arch in ~25% of cases

Tet Spells (Hypercyanotic/Hypoxic Spells): Peak incidence at 2-4 months. Triggered by anything that suddenly lowers SVR (crying, feeding, defecation, hypovolemia, tachycardia). The mechanism is a vicious cycle:

SVR falls → Increased R-to-L shunt across VSD → ↓PaO2, ↑PCO2, ↓pH → Hyperpnea → ↑Venous return to RV → ↑R-to-L shunting → Worsening cyanosis

Management of Tet Spells:

Intervention	Mechanism
Knee-to-chest position	↑SVR, ↓R-to-L shunt
Supplemental O2	Limited benefit alone
Morphine 0.1-0.2 mg/kg IV/IM	Sedation, ↓hyperpnea, ↓SVR
Fentanyl 1 µg/kg IV/IM	Alternative to morphine
Propranolol IV	↓Infundibular spasm (β-blockade)
Phenylephrine (α-agonist)	↑SVR directly
IV fluids	Correct hypovolemia
NaHCO3	Correct metabolic acidosis

Surgical treatment:

Definitive: VSD patch closure + RVOTO relief (transatrial/transpulmonary approach preferred to spare RV function)
Palliative (if not ready for repair): Modified Blalock-Taussig shunt (subclavian-to-pulmonary artery anastomosis), pioneered in 1944 by Blalock, Taussig, and Vivien Thomas at Johns Hopkins
Long-term sequelae include pulmonary regurgitation requiring pulmonary valve replacement in adulthood

2. Transposition of the Great Arteries (D-TGA)

2-3 per 10,000 live births. The aorta arises from the RV and the pulmonary artery from the LV - ventriculoarterial discordance with normal AV connection. This creates two parallel, independent circuits: systemic venous blood goes RV→Aorta→body (never oxygenated), and pulmonary venous blood goes LV→PA→lungs (never reaches body). Survival requires mixing between the two circuits via ASD, VSD, or PDA.

Clinical features:

Extreme cyanosis from birth (especially with intact septum - TGA-IVS)
Single, loud S2; minimal or no murmur (unless VSD/PS present)
ECG: RAD and RVH (RV acts as systemic ventricle)
CXR: "Egg on a string" - narrow mediastinum (parallel great vessels), cardiomegaly, increased pulmonary vascular markings

Management:

PGE1 infusion - maintains ductal patency to improve mixing and pulmonary blood flow
Balloon atrial septostomy (Rashkind procedure) - creates/enlarges ASD for atrial-level mixing, temporizes until surgery
Arterial switch operation (Jatene procedure) - definitive repair; great arteries transected and switched back to the correct ventricles, coronary arteries reimplanted; must be performed within first 2 weeks of life before LV "de-trains" from the low-resistance pulmonary circuit

3. Tricuspid Atresia

Complete absence of the tricuspid valve with a hypoplastic RV and pulmonary artery. Requires ASD, PDA, or VSD to survive (to allow right heart blood to reach the lungs via left heart).

Features:

Single S2 + systolic regurgitant murmur at LLSB if VSD present
ECG: Superior QRS axis (distinguishes from other cyanotic CHDs) + LVH (LV is the dominant ventricle)
CXR: Normal or slightly enlarged heart, may be boot-shaped

Management: Staged palliative surgeries toward Fontan circulation:

Stage 1 (neonatal): BT shunt or PA banding depending on pulmonary flow
Stage 2 (4-6 months): Bidirectional Glenn (SVC → pulmonary artery)
Stage 3 (2-4 years): Fontan completion (IVC → pulmonary artery via extracardiac conduit)

4. Total Anomalous Pulmonary Venous Return (TAPVR)

Pulmonary veins drain into systemic venous circulation instead of the left atrium. Must have ASD or PFO for survival (for oxygenated blood to reach left heart).

Types (by drainage site):

Type	Drainage	Frequency
Supracardiac	Superior vena cava or innominate vein	Most common (~50%)
Cardiac	Coronary sinus or right atrium	~25%
Infracardiac/Subdiaphragmatic	IVC, portal vein, hepatic vein	~25%, most often obstructed
Mixed	Multiple sites	~5%

Features:

Hyperactive RV impulse, fixed split S2, systolic ejection murmur at LUSB, mid-diastolic rumble at LLSB
ECG: RAD, RVH (RSR' in V1)
CXR: "Snowman" sign (figure-of-8 appearance) from dilated vertical vein + SVC - seen in supracardiac type, rarely before 4 months
Obstructed TAPVR (especially infracardiac): presents with pulmonary edema and severe cyanosis at birth - surgical emergency

Management: Surgical reconnection of the pulmonary venous confluence to the left atrium.

5. Truncus Arteriosus

A single arterial trunk arises from both ventricles and gives rise to the aorta, pulmonary arteries, and coronary arteries. Always associated with a large VSD. Associated with DiGeorge syndrome (22q11 deletion).

Features:

Cyanosis + signs of pulmonary overcirculation (since pulmonary arteries arise from the trunk at systemic pressure before PVR drops)
ECG: Biventricular hypertrophy
Loud single S2, early systolic ejection click, systolic murmur

Management: Early surgical repair - VSD closure, separation of pulmonary arteries from the trunk, and placement of a RV-to-PA conduit (Rastelli-type repair).

Other Cyanotic CHDs

Lesion	Key Features
Pulmonary atresia with intact septum	Duct-dependent; PGE1 + balloon valvotomy or BT shunt
Ebstein anomaly	Apical displacement of tricuspid valve; atrialized RV; Wolff-Parkinson-White often associated; wide split S2, "sail sound"
Hypoplastic left heart syndrome (HLHS)	Hypoplastic LV, aorta, mitral valve; presents in newborn period with circulatory collapse; Norwood → Glenn → Fontan
Double outlet right ventricle (DORV)	Both great vessels arise from RV; management depends on VSD location
Pulmonary atresia with VSD and MAPCAs	Major aortopulmonary collateral arteries supply lungs; requires unifocalization surgery

General Approach to the Cyanotic Newborn

Hyperoxia test (nitrogen washover test): Administer 100% O2 for 10 minutes. If PaO2 rises above 150-200 mmHg, cyanosis is likely pulmonary in origin. If PaO2 remains low (<100 mmHg), cardiac cause is likely (fixed R-to-L shunt).
Immediate stabilization: PGE1 (0.05-0.1 µg/kg/min) if duct-dependent lesion is suspected - opens/maintains ductus arteriosus
Echocardiography - definitive anatomical diagnosis
Chest X-ray: Pulmonary blood flow (increased vs. decreased) and cardiac silhouette guide diagnosis
ECG: Axis and chamber hypertrophy pattern narrow the differential

Diagnostic Summary Table

Lesion	CXR	ECG	Key Murmur
TOF	Boot-shaped, ↓PVM	RAD, RVH	SEM at LMSB/LUSB
TGA	Egg on string, ↑PVM	RAD, RVH	Minimal (unless VSD)
Tricuspid atresia	Boot-shaped, ↓PVM	Superior axis, LVH	Systolic at LLSB (if VSD)
TAPVR	Snowman sign, ↑PVM	RAD, RVH (RSR')	SEM at LUSB + mid-diastolic rumble
Truncus arteriosus	Cardiomegaly, ↑PVM	BVH	SEM + early click
Ebstein anomaly	Massive cardiomegaly, ↓PVM	RBBB, delta waves (WPW)	TR murmur at LLSB

Complications of Chronic Cyanosis

Polycythemia and hyperviscosity - risk of stroke
Brain abscess (R-to-L shunt bypasses pulmonary filter)
Paradoxical embolism
Coagulopathy (thrombocytopenia, clotting factor defects)
Infective endocarditis
Cerebrovascular accidents (thromboembolic or hemorrhagic)
Growth retardation and developmental delay
Gout (hyperuricemia from increased red cell turnover)
Eisenmenger syndrome (irreversible pulmonary hypertension from long-standing L-to-R shunt that reverses)

Sources:

Rosen's Emergency Medicine, 9th Ed. - Cyanotic Congenital Heart Defects section
Sabiston Textbook of Surgery - Congenital Heart Disease, Chapter 113
Robbins & Cotran Pathologic Basis of Disease - Right-to-Left Shunts
Harriet Lane Handbook, 23rd Ed. - Cyanotic CHD
Fuster and Hurst's The Heart, 15th Ed. - Cyanotic CHD categories

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