Definition and Embryological Basis
Congenital heart defects (CHDs) are structural or functional anomalies of the cardiovascular system that develop as a result of a disruption in one of the stages of embryonic development. At a certain stage of organogenesis, a failure occurs in the formation of chambers, septa, valves, or great vessels, or the process of cleavage of a particular structure is impaired.
To understand the pathogenesis of CHDs, it is necessary to remember basic hemodynamics. The systemic circulation begins in the left ventricle: blood enters the aorta, is distributed to organs and tissues, collects through the capillary bed into the venous system, and returns to the right atrium. The pulmonary circulation originates in the right ventricle: deoxygenated blood enters the lungs via the pulmonary artery, is oxygenated, and returns to the left atrium via the pulmonary veins. Normally, the right and left sides are isolated, and the pressure in the left chambers is significantly higher than in the right.
Atrial septal defect
ASD is a communication between the left and right atria. The interatrial septum is formed from two leaflets (primum and secundum), each of which has physiological openings during embryogenesis. Failure of these openings to close leads to two main variants: ostium primum and ostium secundum. Clinical significance is determined not so much by the type as by the size of the defect.
Since the pressure in the left atrium is higher, blood shunts from left to right, creating volume overload of the right heart and pulmonary circulation. Patients remain asymptomatic for a long time; eventually, the following appear:
- exertional dyspnea, decreased exercise tolerance;
- frequent respiratory infections in children (due to hemodynamic changes rather than immunodeficiency);
- rhythm disorders after the age of 40 — often multifocal atrial tachycardia as the first manifestation;
- dilatation of the right atrium followed by right ventricular failure.
Ventricular Septal Defect and Patent Ductus Arteriosus
The VSD is most frequently localized in the membranous (basal) part of the septum. Left-to-right shunting is more pronounced here due to the high systolic gradient between the ventricles. Overload of the right ventricle, systemic congestion, pulmonary overload, and chronic heart failure develop. With long-standing defects, Eisenmenger syndrome may develop: pressure in the right chambers exceeds that in the left, the shunt reverses, and deoxygenated blood enters the systemic circulation.
The patent ductus (Botallo's) arteriosus is the persistence of a communication between the aorta and the pulmonary artery after birth. Intrauterinely, the ductus unloads the non-functioning lungs: blood flows from the pulmonary artery into the aorta because the pressure in the pulmonary circulation is higher. After birth, pulmonary pressure drops, and if the ductus fails to close, a reverse shunt occurs — from the aorta to the pulmonary artery, causing volume overload of the pulmonary circulation and left ventricle.
Aortic Coarctation and Aortic Stenosis
Aortic coarctation is a localized narrowing of the aorta, most commonly at the junction of the aortic arch and the descending segment. Perfusion is reduced below the stenosis and increased above it. Characteristic manifestations include:
- headaches, epistaxis, sensation of pulsation in the head and neck;
- significant blood pressure gradient between the upper and lower extremities;
- weakness, fatigue, heaviness in the legs due to hypoperfusion.
Congenital aortic valve stenosis is most commonly associated with a bicuspid aortic valve — the absence of cleavage of the right and left coronary cusps. During systole, the cusps do not open fully, the pressure gradient between the left ventricle and the aorta increases, concentric left ventricular hypertrophy develops, along with arrhythmias and subsequently heart failure. Unlike degenerative calcific stenosis in adults, this is a primary malformation of the valve structure.
Diagnostics
The key method is echocardiography: only it allows visualization of septal defects, assessment of shunts, valve status, chamber sizes, and pulmonary pressure.
Auxiliary methods merely raise suspicion and guide further diagnostic steps:
- auscultation — systolic murmur at valve auscultation points;
- ECG — signs of chamber hypertrophy, rhythm disorders;
- pulse oximetry — decreased saturation in right-to-left shunting;
- chest X-ray — cardiomegaly, altered pulmonary vascular pattern;
- contrast-enhanced CT or MRI — the method of choice for aortic coarctation, as visualization of the arch is limited on echocardiography.
Principles of Treatment and Follow-up
Therapeutic tactics consist of three areas:
- Drug therapy — treatment of complications: heart failure, arrhythmias, pulmonary hypertension. The anatomical defect itself cannot be eliminated with medications.
- X-ray endovascular interventions — occluder placement for ASD and VSD, balloon dilatation and stenting for aortic coarctation, endovascular closure of a patent ductus arteriosus.
- Cardiosurgical operations — patch repair of large defects, valve replacement, correction of complex defects (Tetralogy of Fallot, transposition of the great arteries, Ebstein's anomaly), which are typically operated on in childhood.
All patients with CHDs require lifelong dispensary follow-up by a cardiologist with regular echocardiographic monitoring. Severe forms of defects are corrected in pediatric practice; adult general practitioners more often encounter patients with relatively benign or surgically repaired defects.
Key points
- CHDs are a consequence of embryogenesis disorders of the cardiovascular system.
- The initial direction of the shunt is left-to-right due to higher pressure in the left heart.
- ASD remains asymptomatic for a long time; it frequently manifests with atrial arrhythmias after the age of 40.
- VSD and PDA lead more rapidly to pulmonary overload and heart failure; shunt reversal (Eisenmenger syndrome) is possible.
- Aortic coarctation manifests as a blood pressure gradient between the upper and lower extremities.
- Congenital aortic stenosis is most commonly associated with a bicuspid valve and leads to left ventricular hypertrophy.
- Echocardiography is the primary diagnostic method; CT/MRI are informative for coarctation.
- Treatment includes medical management of complications, endovascular and cardiosurgical interventions, and mandatory dispensary follow-up.