Hypoplastic Left Heart Syndrome

Published on 07/06/2015 by admin

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15 Hypoplastic Left Heart Syndrome

Rima S. Bader, James C. Huhta

I. CASE

A 22-year-old African American woman, gravida 2, para 1+0, was referred by the obstetrician at 26 weeks’ gestation for ventricular disproportion (right ventricle [RV] larger than left ventricle [LV] for gestation). The mother has a bicuspid aortic valve.

A. Fetal echocardiography findings

1. The fetal echo reveals situs solitus of the atria, levocardia, left aortic arch, and increased cardiothoracic ratio (0.45).

2. The LV is severely hypoplastic, with atretic mitral and aortic valves.

3. There is evidence of increased echogenicity at the ventricular walls and papillary muscles of the mitral valve. The LV shows endocardial fibroelastosis with decreased function. The RV is dilated, with large tricuspid and pulmonary valves that were not dysplastic and had no significant regurgitation.

4. The transverse and distal aortic arch are of normal size and by color and pulsed Doppler there was flow reversal into the distal arch. Usually, the distal arch is the largest aspect of the arch in a patient with hypoplastic left heart syndrome (HLHS), presumably because it receives the greatest amount of flow.

5. The RV Tei index (myocardial performance index) is normal (0.4).

6. There are no signs of hydrops fetalis.

7. The interatrial septum is intact (no flow across the atrial septum) (Fig. 15-1). The left atrium (LA) is mildly enlarged, with bowing of the interatrial septum toward the right atrium (RA).

8. The pulmonary veins in the LA are decompressed through a vertical vein, which is obstructed at the site of the left pulmonary artery and left bronchus (mean gradient, 6-7 mm Hg). The pulmonary venous flow is abnormal, with a significant a wave reversal in systole and no forward flow in early ventricular diastole, suggesting severely elevated LA pressure.

9. The pulsatility index is increased in the proximal pulmonary artery, suggesting elevated fetal pulmonary vascular resistance (PVR).

Fig. 15-1 Intact atrial septum on a four-chamber view of the fetal heart. Note the thickened and intact atrial septum (vertical arrow) and the dilated pulmonary veins (horizontal arrows). RA, right atrium; RV, right ventricle.

B. Cardiovascular profile score

1. The cardiovascular profile score is 9/10.

2. One point was deducted for cardiomegaly.

C. Associated syndromes and extracardiac anomalies

D. Fetal management and counseling

1. Amniocentesis was performed before referral and showed normal fetal karyotype and negative fluorescent in situ hybridization (FISH) analysis for 22q11 microdeletion.

2. Fetal intervention.

a. Rationale and consent.

(1) The patient was informed of the poor prognosis for the fetus. A few days after the diagnosis she gave written informed consent for an attempt at in utero interatrial laser septostomy (IALS) at 26 weeks’ gestation.

(2) The aim was to increase the chances of survival in the immediate neonatal period and in the long term.

(1) Under ultrasound guidance and local anesthesia and using a percutaneous approach, an 18-gauge needle was inserted into the RA.

(2) A 600 contact Nd:YAG (neodymium:yttrium-aluminum-garnet) laser fiber was passed through the lumen of the needle and placed against the atrial septum.

(3) The septum was opened with short bursts of 5 to 10 watts of energy.

(4) Color Doppler confirmed flow of blood from the LA to the RA.

(5) A hemopericardium of 6 mL was drained with a 22-gauge needle without complications.

c. Follow-up included serial antenatal studies at weekly intervals initially and then every 2 to 4 weeks.

(1) The size, mean gradient, and direction of flow across the foramen ovale were monitored after the successful laser septostomy (normal right to left).

(2) The size, gradient, and pattern of flow were monitored in the pulmonary veins. An α wave reversal in systole suggests elevated LA pressure (Fig. 15-2). Prenatal pulmonary vein flow patterns, looking at the magnitude of a wave reversal in HLHS, and presence or absence of forward flow in ventricular systole can identify the fetus at risk of severe LA hypertension at birth.

(a) Patients with type A or B flow (in which there is forward flow during ventricular systole and early ventricular diastole, with some a wave reversal) can be clinically stable at birth.

(b) Patients with a type C pattern (forward flow only in ventricular systole with no flow in early ventricular diastole and significant a wave reversal) are critically ill as newborns, with clinical evidence of severe LA hypertension.

(3) Development of regurgitation of the tricuspid or pulmonary valves or RV systolic or diastolic dysfunction could result in the evolution of cardiovascular compromise and hydrops fetalis. Pulmonary regurgitation with a normal valve is usually an ominous sign indicating ventricular dysfunction with poor fetal outcome.

(4) Size and function of the LV was monitored. Size of the transverse aortic arch was compared to the ductus size. The direction of flow in the aortic arch was monitored (reversal of flow—pulmonary to aortic—confirms the presence of aortic atresia). Progression of endocardial fibroelastosis was monitored. All of this should not matter where there is mitral and aortic atresia rather than isolated aortic stenosis.

(5) The maternal hyperoxygenation test was performed after 30 weeks’ gestation.

(a) This test can allow improved functional assessment of the reactivity of the pulmonary vascular bed in the fetus.

(b) In the case of fetal pulmonary hypoplasia, experts agree that a superior method is that of the hyperoxygenation test to assess the fetal lung and the pulmonary vascular reactivity.

(c) This observation does not yet change the outcome, but it gives an idea about the pulmonary vascular reactivity.

Fig. 15-2 Pulsed Doppler in the pulmonary vein (PV) at 23 weeks’ gestation shows no diastolic flow and a biphasic pattern suggesting significant obstruction.

E. Delivery

If the fetus remains well compensated and the lesion is isolated, delivery can be at term in a tertiary care center.

F. Neonatal management

1. Therapeutic options.

a. Compassionate care with either no treatment from delivery or withdrawal of treatment once the diagnosis has been confirmed.

b. Medical treatment.

(1) Treatment with prostaglandin E₁ (PGE₁) infusion.

(2) Optional emergent or urgent cardiac catheterization for further atrial septoplasty.

(3) Possible stent placement to decompress the LA if there is severe LA hypertension. Stent implantation in the ductus arteriosus may be performed while waiting for a donor heart or as a palliative alternative to Norwood stage 1 with bilateral pulmonary artery banding.

c. Staged palliative surgery (Norwood procedure).

d. Cardiac transplantation, particularly in patients with cardiac pathology that can complicate single ventricle palliation, such as significant RV dysfunction or severe tricuspid valve regurgitation.

2. Medical treatment.

a. PGE₁ infusion to keep the ductus open to provide a pathway to the systemic circulation and improve the body perfusion.

b. Administration of oxygen is normally not advisable in neonates with HLHS because this can cause a decrease in the PVR with increased pulmonary blood flow that further steals from the systemic circulation. However, in a neonate with severe restriction of the atrial septum and LA hypertension, oxygen administration can contribute to an improvement in the systemic oxygen levels.

c. Blood gas revealing severe metabolic acidosis and slightly decreased Po₂, a characteristic finding of HLHS, could be due to poor cardiac output. However, babies with severe LA hypertension due to atrial level restriction are both severely cyanotic (Pao₂ < 25-30 mm Hg) and metabolically acidotic. In this setting, therapeutic balloon atrial septostomy can help decompress the LA.

d. The hematocrit should be maintained above 45% to increase the oxygen-carrying capacity.

e. Usually, volume and inotropic support (such as milrinone 0.5 μg/kg/min infusion) may be indicated to improve ventricular function.

3. Surgical treatment.

a. Single ventricle palliation.

(1) Norwood stage 1 can be performed at the first 1 to 2 weeks of life, which carries a surgical mortality of 5% to 15% in the majority of larger pediatric heart centers in North America.

(2) For optimal surgical outcome, the newborn should be allowed to recover from the insults of birth before surgery is undertaken, except when there is an element of obstruction to the pulmonary venous return (total pulmonary venous drainage or restriction at the foramen ovale).

(3) The ultimate goal is to deliver the infant to the operating room in good condition to expect a good surgical outcome.

(4) This operation consists of:

(a) Dividing the main pulmonary artery and closing the distal stump.

(b) Establishing a right sided Gore-Tex shunt (usually a 3.5-4 mm tube) to provide pulmonary blood flow or, more recently, an RV–to–pulmonary artery conduit (Sano procedure).

(c) Excising the atrial septum for adequate decompression of the LA and pulmonary venous return.

(d) Connecting the diminutive ascending aorta to the main pulmonary artery.

(e) Reconstructing the aortic arch between the proximal main pulmonary artery and the hypoplastic ascending aorta, often using homograft material.

(f) Reconstructing the distal arch to the descending aorta, often using homograft material.

(5) At 3 to 6 months of age, performing a bidirectional Glenn operation (anastomosis of the SVC to the right pulmonary artery). This procedure carries a surgical mortality of less than 5%. Before this procedure, cardiac catheterization is necessary to assess the pulmonary artery anatomy and resistance, the ventricular function, and the ascending aorta and reconstructed arch anatomy.

b. Corrective surgery.

(1) At 2 to 5 years, the child undergoes a modified Fontan procedure (or total cavopulmonary anastomosis) in which the inferior vena cava (IVC) return is rerouted to the pulmonary arteries, often through an extracardiac conduit or with a baffle in the RA.

(2) Before this procedure, another cardiac catheterization is performed to be certain that the anatomy and hemodynamics of the patient are adequate for a Fontan procedure.

(3) Significant ventricular dysfunction or AV valve regurgitation, for instance, would not be tolerated by this circulation. The Fontan circulation requires:

(a) Low PVR.

(b) No anatomic obstruction from the systemic veins to the pulmonary vascular bed and through the pulmonary veins.

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