Define congentinal heart disease

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Congenital Heart Disease (CHD)

Definition

Congenital heart disease refers to structural abnormalities of the heart or great vessels that are present at birth, arising from abnormal cardiac development during fetal life. These defects affect the cardiac architecture in ways that interfere with normal blood flow - disrupting systemic or pulmonary venous drainage, septation of cardiac segments, sequential attachment of cardiac segments (including the great vessels), or valvular function.

Miller's Anesthesia, 10e: "Congenital heart disease is the most common congenital disorder in newborns and is the most common cause of death during infancy."

Epidemiology

Statistic	Figure
Prevalence at birth	3-10 per 1,000 live births
Global burden (2019)	~13.3 million people living with CHD
Global deaths (2019)	~216,896 deaths (42.7% decline since 1990)
Deaths under age 5	~174,442 of all CHD deaths

The incidence is higher in low-SDI (sociodemographic index) countries, where the burden falls disproportionately. Globally, from 1990 to 2019, there was a 28% increase in total persons living with CHD due to improved survival - Fuster and Hurst's The Heart, 15th Ed..

Etiology

The cause of most CHDs remains unknown. Identified contributors include:

Chromosomal/Genetic (< 15% of cases):
- Trisomy 21 (Down syndrome), Trisomy 18, Trisomy 13
- Turner syndrome (45,X)
- DiGeorge syndrome (22q11 deletion)
- Single gene defects: 3-5% of all cases
- Chromosomal syndromes overall: ~10% of CHDs
Environmental/Maternal factors:
- Maternal diabetes mellitus
- Maternal obesity
- Alcohol use during pregnancy
- Rubella infection in the first trimester
Miller's Anesthesia, 10e: "Overall, genetic defects can account for less than 15% of congenital heart defects."

Pathophysiology

Congenital heart lesions produce one or more of three key pathophysiologic states:

Ventricular volume overload - from left-to-right shunts causing pulmonary overcirculation
Ventricular pressure overload - from obstructive lesions (e.g., stenosis, coarctation)
Hypoxemia - from right-to-left shunts or mixing lesions delivering deoxygenated blood to the systemic circulation

These ultimately risk myocardial failure or pulmonary vascular disease.

Classification

CHD is broadly classified into four physiologic categories (Miller's Anesthesia):

1. Shunt Lesions

Intracardiac or extracardiac connections between cardiac chambers or vessels:

Left-to-right shunts (acyanotic): Blood recirculates through the lungs - causes pulmonary overcirculation, volume overload, and eventually elevated pulmonary vascular resistance. Examples: ASD (atrial septal defect), VSD (ventricular septal defect), PDA (patent ductus arteriosus).
Right-to-left shunts (cyanotic): Deoxygenated blood enters systemic circulation - causes hypoxemia and cyanosis.
If untreated, left-to-right shunts can reverse to right-to-left (Eisenmenger syndrome).

2. Mixing Lesions

Complete mixing of oxygenated and deoxygenated blood (e.g., truncus arteriosus, single ventricle physiology, transposition of the great arteries).

3. Obstructive/Flow Obstruction Lesions

Structural obstruction to blood flow, causing pressure overload:

Right-sided: Pulmonary stenosis, pulmonary atresia
Left-sided: Aortic stenosis, coarctation of the aorta, hypoplastic left heart syndrome

4. Regurgitant Valves

Abnormal valve function allowing backward blood flow, leading to volume overload.

Cyanotic vs. Acyanotic Classification

A traditional and clinically practical classification:

Category	Mechanism	Examples
Cyanotic CHD	Right-to-left shunt or mixing	Tetralogy of Fallot, Transposition of Great Arteries, Truncus Arteriosus, Tricuspid Atresia, Total Anomalous Pulmonary Venous Return (TAPVR)
Acyanotic CHD	Left-to-right shunt or obstruction	VSD, ASD, PDA, Aortic Stenosis, Coarctation of Aorta

Cyanosed patients typically have more complex disease. Clinical cyanosis may be hard to detect in artificial light and causes clubbing of finger and toe nails. Complex hematological abnormalities (including impaired blood clotting) are common.

High-Risk Groups (Surgical Perspective)

Three groups identified as high-risk before surgical correction (Pye's Surgical Handicraft):

Cyanosed patients - More complex disease, haematological abnormalities, impaired coagulation
Neonates and infants - Virtually a surgical subspecialty; optimal centres perform 100+ operations per year
Pulmonary vascular disease - Occurs when high-pressure left-sided blood passes into the pulmonary artery (e.g., large VSD), leading to pulmonary arteriolar hypertrophy. Fully developed changes may preclude surgery.

Clinical Considerations

Most congenital heart defects are repaired in childhood, with a trend toward earlier intervention.
Not all operations are corrective; many unavoidably damage the myocardium, leading to postoperative low cardiac output syndrome.
With increasing survival into adulthood, pulmonary arterial hypertension (PAH) is an important long-term complication. Among patients with long-term PAH, 72% had a form of CHD (Braunwald's Heart Disease).
Modern classification now combines anatomic and physiologic (AP) parameters, captured in the International Pediatric and Congenital Cardiac Code (IPCCC), which forms the basis for ICD-11 codes.

Sources: Miller's Anesthesia 10e | Fuster and Hurst's The Heart 15e | Braunwald's Heart Disease | Pye's Surgical Handicraft 22e

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