Congenital Heart Disease

## Congenital Heart Disease ## Summary **Congenital Heart Disease (CHD)** refers to structural or functional abnormalities of the heart and circulatory system present at birth, arising from altered embryonic development. It affects approximately 0.8% of live births and can be associated with extracardiac anomalies. CHDs are broadly classified as **acyanotic** (left-to-right shunts) or **cyanotic** (right-to-left shunts), and by complexity into simple and complex defects. The etiology is often unknown but can involve environmental factors like maternal infections or substance use, and genetic factors such as chromosomal abnormalities. Normal embryonic development involves the formation of a straight cardiac tube that folds and septates to form the four chambers and great arteries. Abnormalities in this process lead to specific defects. **Acyanotic CHDs** include **Atrial Septal Defects (ASD)**, **Ventricular Septal Defects (VSD)**, **Patent Ductus Arteriosus (PDA)**, and **Coarctation of the Aorta**. **Cyanotic CHDs** include **Tetralogy of Fallot (TOF)**, **Transposition of the Great Arteries (TGA)**, **Ebstein's anomaly**, **Truncus arteriosus**, and **Eisenmenger syndrome**. ## Key Points * **Definition**: An abnormality in cardio-circulatory structure or function present at birth. * **Epidemiology**: Affects ~0.8% of live births; extracardiac anomalies are common. * **Etiology**: Unknown in ~90%; associated with maternal rubella, thalidomide, alcohol, and genetic factors (e.g., Trisomies, Turner syndrome). * **Classification**: **Acyanotic** (Left-to-Right shunt) vs. **Cyanotic** (Right-to-Left shunt). * **ASD Types**: **Ostium secundum** (most common), **Ostium primum** (associated with Down syndrome), **Sinus venosus**, and **Coronary sinus**. * **PFO**: **Persistent foramen ovale** in ~25% of adults, linked to **paradoxical embolism**. * **VSD**: Most common CHD (25%); haemodynamic effects depend on size. * **PDA**: Persistence of the **ductus arteriosus**, often associated with prematurity; causes a **machinery murmur**. * **Eisenmenger Syndrome**: Irreversible reversal of a Left-to-Right shunt to a Right-to-Left shunt due to **pulmonary hypertension**. * **TOF**: Most common cyanotic CHD; characterized by **VSD**, **pulmonary stenosis**, **overriding aorta**, and **RVH** (Right Ventricular Hypertrophy). * **TGA**: **Aorta from RV**, **PA from LV**; incompatible with life without mixing (ASD/VSD/PDA). * **Ebstein's Anomaly**: **Apical displacement of the tricuspid leaflet**; associated with maternal lithium use. * **Coarctation of Aorta**: Narrowing of the aorta; causes **hypertension in upper limbs** and **hypotension in lower limbs**. ## Embryological Development ### Cardiac Tube Formation (Month 1) 1. **Sinuatrium** 2. **Primitive ventricle** 3. **Bulbus cordis** 4. **Truncus arteriosus** ### Septation and Folding (Month 2) * **Atrial Septum**: **Septum primum** grows to create **ostium primum**, then perforates to form **ostium secundum**. **Septum secundum** forms the **fossa ovalis**. * **Ventricular Septum**: Cephalic growth of the **main ventricular septum** fuses with **endocardial cushions**. * **Great Arteries**: **Truncus arteriosus** divides and rotates to create the spiral relationship between the **aorta** and **pulmonary artery**. ## Acyanotic CHD (Left-to-Right Shunts) ### Atrial Septal Defect (ASD) * **Ostium secundum (75%)**: A midseptal defect; often associated with **mitral valve prolapse**. * **Ostium primum (15%)**: A lower septal defect; associated with **Down syndrome** and **AV valve clefts**. * **Sinus venosus (10%)**: An upper septal defect; associated with **anomalous pulmonary venous return**. ### Ventricular Septal Defect (VSD) **VSD** is the most common CHD overall. * **Types**: **Muscular**, **Membranous** (most common), and **Doubly committed subarterial**. * **Pathophysiology**: Large defects lead to **LV volume overload** and can eventually progress to **Eisenmenger syndrome**. ### Patent Ductus Arteriosus (PDA) A **Patent Ductus Arteriosus** is a persistent connection between the proximal left pulmonary artery and the descending aorta. Clinically, it presents with a **continuous machinery murmur**. It can be treated with **Indomethacin** to close it, or **Prostaglandins** may be administered to keep it open (e.g., in cases of TGA where mixing is essential). ## Cyanotic CHD (Right-to-Left Shunts) ### Tetralogy of Fallot (TOF) **Tetralogy of Fallot** is the most common cyanotic CHD, characterized by four components: * **VSD** (Ventricular Septal Defect) * **Pulmonary Stenosis** * **Overriding Aorta** * **RVH** (Right Ventricular Hypertrophy) Clinically, patients may experience "**Tet spells**" (episodes of cyanosis, often relieved by squatting, which increases systemic vascular resistance to improve oxygenation). A chest X-ray typically shows a "**boot-shaped heart**". ### Transposition of the Grea