Concept and epidemiology of congenital heart defects
A congenital heart defect (CHD) is a structural defect of the heart or great vessels present from birth. Most of these defects disrupt hemodynamics in both the systemic and pulmonary circulations. CHDs develop during embryonic development between weeks 2 and 8 and occur with a frequency of 6–8 cases per 1,000 births, accounting for about 30% of all developmental malformations and placing them among the three most common congenital anomalies.
Classification of congenital heart defects
The detailed clinical classification distinguishes five groups of defects:
- with intracardiac blood shunting and increased pulmonary blood flow;
- with intracardiac blood shunting and decreased pulmonary blood flow;
- with blood flow obstruction;
- with valvular regurgitation;
- combined defects.
A more common classification in educational practice divides defects into three groups:
- Acyanotic defects (left-to-right shunt): atrial septal defect (ASD), ventricular septal defect (VSD), patent ductus arteriosus.
- Cyanotic defects (right-to-left shunt): tetrad of Fallot, transposition of the great vessels, hypoplasia of the right atrioventricular septum.
- Defects with obstruction to ventricular outflow: aortic stenosis, aortic coarctation, pulmonary trunk stenosis.
Septal defects and patent ductus arteriosus
ASD. Since the pressure in the left atrium is higher, arterial blood is shunted into the right atrium, increasing the volume of blood entering the right ventricle and the pulmonary circulation. Volume overload of the pulmonary circulation develops along with malignant pulmonary hypertension. Correction is possible in two ways: endovascular placement of an occluder via a catheter (requires sufficient septal rims for fixation) or open surgery under cardiopulmonary bypass with defect repair using a rectangular pericardial patch with a continuous double-ended suture.
VSD. During systole, arterial blood is shunted from the left ventricle to the right, causing pulmonary hypervolemia and pulmonary hypertension. Endovascular correction with an occluder or open patch repair under cardiopulmonary bypass is used.
Patent ductus (Botallo's) arteriosus. In utero, the ductus shunts blood from the pulmonary trunk to the aorta, bypassing the non-functioning pulmonary circulation. If the ductus fails to close within the first year of life, it is regarded as a CHD and leads to a continuous shunt of arterial blood into the pulmonary circulation with the development of hypervolemia. Surgical treatment is indicated for all patients and includes: ligation with transfixion, clipping, or division of the ductus with closure of both ends.
Fallot's triad, tetrad, and pentad
Fallot's triad includes ASD, right ventricular outflow tract stenosis (pulmonary stenosis), and right ventricular myocardial hypertrophy. Correction is performed in a single stage or in stages: relief of pulmonary stenosis (e.g., Brock valvulotomy) and closure of the ASD with a pericardial patch. After surgery, cyanosis disappears and pressure in the right ventricle decreases.
Tetralogy of Fallot is characterized by four features: a large VSD, right ventricular outflow tract obstruction with pulmonary valve stenosis, right ventricular hypertrophy, and dextroposition of the aorta. Blood is shunted from the left ventricle to the right, an inadequate volume enters the pulmonary circulation, and mixed, oxygen-depleted blood enters the aorta. Radical correction includes closing the VSD with a patch, excision of thickened muscle bundles narrowing the right ventricular outflow tract, and relieving pulmonary stenosis: if the valve is preserved, division of fused cusps (Brock valvulotomy); if the valve size is inadequate, widening of the orifice with a patch.
Fallot's pentad adds an ASD to the features of the tetrad. The radical operation is similar to that for the tetrad, but complicated by the need to close the interatrial defect.
Coarctation of the aorta
Coarctation of the aorta is a localized narrowing of the aortic lumen, leading to hypertension in the upper extremities, left ventricular hypertrophy, and inadequate perfusion of the abdominal organs and lower extremities. Treatment is exclusively surgical. The ideal option is resection of the stenotic segment with an end-to-end anastomosis. If the defect is extensive or there are marked sclerotic changes in the vessel wall, aortic replacement with a synthetic graft is performed. Plastic repair of the narrowed segment with a synthetic patch or using the subclavian artery is also possible. Some patients undergo balloon dilation in an X-ray operating room.
Key points
- CHDs develop during weeks 2–8 of embryogenesis and account for about 30% of all developmental malformations.
- Acyanotic defects (ASD, VSD, PDA) are accompanied by a left-to-right shunt and volume overload of the pulmonary circulation.
- Cyanotic defects (tetralogy of Fallot, TGA) produce a right-to-left shunt and are accompanied by cyanosis.
- Radical correction of septal defects is possible endovascularly using an occluder or openly with pericardial patch repair.
- Patent ductus arteriosus after the first year of life requires ligation, clipping, or division.
- Tetralogy of Fallot includes VSD, pulmonary stenosis, right ventricular hypertrophy, and dextroposition of the aorta.
- Brock valvulotomy is used to relieve pulmonary stenosis when the valve is preserved.
- Aortic coarctation is treated with resection and anastomosis, graft replacement, or balloon dilation.