Left heart hypoplasia syndrome

Hypoplastic left heart syndrome consists of hypoplasia of the left ventricle and ascending aorta, underdevelopment of the aortic and mitral valves, atrial septal defect, and a wide patent ductus arteriosus. If physiological closure of the ductus arteriosus is not prevented by prostaglandin infusion, cardiogenic shock will develop and the child will die. A loud single second heart sound and nonspecific systolic murmur are often heard. The diagnosis is based on emergency echocardiography or cardiac catheterization. Radical treatment is staged surgical correction or heart transplantation. Endocarditis prophylaxis is recommended.

Hypoplastic left heart syndrome accounts for 1% of congenital heart defects. Oxygenated blood returning to the left atrium from the lungs fails to enter the hypoplastic left ventricle. Instead, the blood enters the right heart via the interatrial communication, where it mixes with deoxygenated venous blood. This relatively deoxygenated blood exits the right ventricle and enters the lungs via the pulmonary arteries and the systemic circulation via the ductus arteriosus. The systemic circulation receives blood only via the right-to-left shunt of the ductus arteriosus; therefore, the prognosis for life immediately after birth depends on maintaining an open ductus arteriosus.

Symptoms of hypoplastic left heart syndrome

Symptoms appear when the ductus arteriosus begins to close during the first 24 to 48 hours of life. Signs of cardiogenic shock (eg, tachypnea, dyspnea, weak pulse, cyanosis, hypothermia, pallor, metabolic acidosis, lethargy, oliguria, and anuria) develop. If systemic circulation is compromised, cerebral and coronary perfusion may be reduced, leading to signs of myocardial or cerebral ischemia. Death occurs rapidly if the ductus arteriosus fails to reopen.

Physical examination reveals vasoconstriction of the vessels of the extremities and a gray-blue tint to the skin (due to cyanosis and hypoperfusion). The second heart sound is loud and single. Sometimes a soft non-specific murmur is heard. The presence of severe metabolic acidosis disproportionate to Po and PCo is characteristic.

Diagnosis of hypoplastic left heart syndrome

The diagnosis is suggested by clinical data and confirmed by two-dimensional echocardiography with color Doppler. Cardiac catheterization is usually necessary to clarify the anatomy of the defect before surgery.

Radiographs show cardiomegaly and pulmonary venous congestion or pulmonary edema. ECG almost always shows right ventricular hypertrophy.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ]

Treatment of hypoplastic left heart syndrome

All infants should be admitted immediately to a neonatal intensive care unit. Vascular access should be established, usually via an umbilical venous catheter, followed by an infusion of prostaglandin E1 [PGE1; initial dose 0.05-0.1 mcg/(kg x min) IV] to prevent closure of the ductus arteriosus or to reopen it. Neonates should generally be intubated and ventilated. Metabolic acidosis is corrected with sodium bicarbonate infusion. Severely ill neonates with cardiogenic shock may require inotropic agents and diuretics to improve cardiac function and control circulating volume.

Subsequently, neonates require a stepwise correction, after which the right ventricle begins to function as a systemic ventricle. The first stage, the Norwood operation, is performed in the first week of life. The pulmonary trunk is divided, the distal branch is closed with a patch, and the arterial duct is ligated. Then, a right-sided bypass according to Blalock-Taussig or the formation of a channel between the right ventricle and the pulmonary artery (Sano modification) is performed; the interatrial septum is enlarged, and the proximal pulmonary artery and hypoplastic aorta are connected to an allograft of the aorta or pulmonary artery to form a new aorta. The 2nd stage, which is performed after 6 months, consists of a bidirectional bypass operation - the Glenn operation (end-to-side anastomosis between the superior vena cava and the right pulmonary artery) or hemi-Fontan operation (see "Tricuspid atresia"). Stage 3, performed approximately 12 months after stage 2, involves a modified Fontan procedure; blood from the inferior vena cava is diverted into the pulmonary circulation, bypassing the right ventricle entirely. Survival is 75% after stage 1, 95% after stage 2, and 90% after stage 3. Five-year survival after surgical correction is 70%. Many patients develop neurodevelopmental disabilities, which are more likely to be due to underlying CNS abnormalities than to the surgery.

In some centers, heart transplantation is the treatment of choice; however, prostaglandin E1 infusion should be continued until a donor heart is known to be available. Availability of donor hearts is also very limited; approximately 20% of newborns die while waiting for a donor heart. Five-year survival after heart transplantation and after multistage correction is approximately the same. Immunosuppressants are required after heart transplantation. These drugs make patients more susceptible to infections and cause pathological changes in the coronary arteries of the transplant in more than 50% of patients after 5 years. The only known treatment for coronary artery disease in the transplant is retransplantation.

All patients should receive endocarditis prophylaxis before dental or surgical procedures that may result in bacteremia.