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Hypoplastic left heart syndrome consists of hypoplasia of the left ventricle and ascending aorta, maldevelopment and hypoplasia of the aortic and mitral valves (frequently aortic atresia is present), an atrial septal defect, and a large patent ductus arteriosus. Unless normal closure of the patent ductus arteriosus is prevented with prostaglandin infusion, cardiogenic shock and death ensue. A loud, single 2nd heart sound (S2) and nonspecific systolic murmur are common. Diagnosis is by emergency echocardiography. Definitive treatment is staged surgical correction or heart transplantation.
Hypoplastic left heart syndrome accounts for 2% of congenital heart anomalies. Because the mitral valve, left ventricle, and aortic valve are hypoplastic (often with aortic atresia), oxygenated blood coming into the left atrium from the lungs is diverted across the atrial communication into the right heart, where it mixes with desaturated systemic venous return (see Fig. 9: Congenital Cardiovascular Anomalies: Hypoplastic left heart. ). This relatively desaturated blood exits the right ventricle through the pulmonary artery to the lungs and through the ductus arteriosus to the systemic circulation. Systemic blood flow is maintained only through the right-to-left ductal shunt; thus immediate survival depends on patency of the ductus arteriosus.
Symptoms and Signs
Symptoms appear when the ductus arteriosus begins to close during the first 24 to 48 h of life. Subsequently, the clinical picture of cardiogenic shock (eg, tachypnea, dyspnea, weak pulse, pallor, cyanosis, hypothermia, metabolic acidosis, lethargy, oliguria or anuria) rapidly develops. When systemic circulation is compromised, coronary and cerebral perfusion may be reduced, leading to symptoms of myocardial or cerebral ischemia. If the ductus arteriosus is not reopened, death rapidly ensues.
Physical examination shows a very active precordium with a marked parasternal lift associated with very poor peripheral perfusion, cool extremities, bluish gray skin color, and absent or barely palpable pulses. The 2nd heart sound (S2) is loud and single. Occasionally, a soft, nonspecific systolic murmur is present. Severe metabolic acidosis out of proportion to the Po2 and Pco2 is characteristic.
Diagnosis
Diagnosis is suspected clinically and confirmed by emergency echocardiography with color flow and Doppler studies. Cardiac catheterization is rarely required.
Chest x-ray shows cardiomegaly and pulmonary venous congestion or pulmonary edema. ECG shows right ventricular hypertrophy.
Treatment
All affected infants should be stabilized immediately in a neonatal ICU. Vascular access should be established, usually via an umbilical venous catheter; then PGE1 (beginning at 0.05 to 0.1 μg/kg/min IV) is infused to prevent closure of the ductus arteriosus or to reopen a constricted ductus. Neonates usually require intubation and mechanical ventilation. Metabolic acidosis is corrected via infusion of NaHCO3. Severely ill neonates with cardiogenic shock may require inotropic drugs (eg, milrinone) and diuretics to improve cardiac function and control volume status. It is critical to keep pulmonary vascular resistance relatively high and systemic vascular resistance low in order to prevent marked pulmonary overcirculation at the expense of systemic perfusion. These resistance ranges are maintained by avoiding hyperoxia, alkalosis, and hypocarbia, all of which may lead to pulmonary vasodilation. Because O2 is one of the most potent pulmonary vasodilators, infants are ventilated with room air or even hypoxic mixtures to aim for systemic saturations of 70 to 80%. If the infant requires mechanical ventilation, Pco2 can be controlled in the high normal or mildly elevated range. Systemic vascular resistance is managed by avoiding, or minimizing, the use of vasoconstricting drugs (eg, epinephrine or high-dose dopamine). Milrinone may be beneficial because it can cause systemic vasodilation.
Survival ultimately requires staged procedures that enable the right ventricle to function as the systemic ventricle. Stage 1, done during the first week of life, is the Norwood procedure. The main pulmonary artery is divided, the distal stump is closed with a patch, and the ductus arteriosus is ligated. Then, a right-sided modified Blalock-Taussig shunt (see Congenital Cardiovascular Anomalies: Definitive management) or right ventricular-pulmonary artery conduit (Sano modification) is done; the atrial septum is enlarged, and the proximal pulmonary artery and hypoplastic aorta are connected with an aortic or pulmonary artery allograft to create a neoaorta. Stage 2, done at 3 to 6 mo of age, consists of a bidirectional Glenn operation (end-to-side connection of the superior vena cava to the right pulmonary artery). The 3rd stage, done at 18 to 36 mo, is a modified Fontan procedure (see Congenital Cardiovascular Anomalies: Treatment). Survival rate is 75% for stage 1, 95% for stage 2, and 90% for stage 3. Overall survival rate is 70% at 5 yr after surgical correction. Many survivors have neurodevelopmental disabilities, which may be due to preexisting developmental abnormalities of the CNS or to overt or occult CNS hypoperfusion or thromboemboli occurring during the multistage procedures.
In some centers, heart transplantation is the procedure of choice; however, PGE1 infusion must be continued along with careful management of pulmonary and systemic vascular resistance until a donor heart is available. Because availability of donor hearts is very limited, about 20% of infants die while waiting for one. The 5-yr survival rates after transplantation and after multistage surgery are similar. After heart transplantation, immunosuppressants are required. These drugs make patients more susceptible to infections and cause pathologic changes in the coronary arteries of the transplanted heart in > 50% of patients over a 5-yr period. The only known treatment for allograft coronary artery disease is retransplantation.
Endocarditis prophylaxis is recommended preoperatively but is required only for the first 6 mo after repair unless there is a residual defect adjacent to a surgical patch or prosthetic material.
Last full review/revision March 2010 by Lee B. Beerman, MD
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