Hypoplastic Left Heart Syndrome

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15 Hypoplastic Left Heart Syndrome

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).

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.

b. Treatment.

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

    (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.

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.

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.

b. Corrective surgery.

       (a) Low PVR.

G. Follow-up

1. Short-term and medium-term follow up.

a. Follow-up.

b. Medications.

       (a) Foramen ovale.
       (b) Aortic arch.

2. Long-term follow-up (after Fontan operation).

a. Medical therapy:

b. These patients should be excluded from competitive sports.

c. Patients should be checked for:

    (4) Ascites.

II. YOUR HANDY REFERENCE

F. Immediate postnatal management

1. Management of patients without a prenatal diagnosis of HLHS.

a. Overview.

b. Once a patent ductus arteriosus is confirmed, prostaglandins (Box 15-1) are initiated, and maneuvers should be used to minimize systemic vascular resistance and maximize PVR.

c. Observation and monitoring.

d. If the baby is clearly demonstrating problems with either excessive pulmonary blood flow—signs of overcirculation (arterial blood gas showing raised PaO2)—or inadequate systemic perfusion or both, the following measures can be attempted:

e. Surgical treatment has been addressed in the management of the case.

G. New hybrid strategy for palliative management of HLHS

1. Rationale.

2. Strategy.

H. Pathophysiology

1. During fetal life, the PVR is higher than systemic vascular resistance (SVR), and the dominant RV maintains normal blood flow to the upper and lower body as well as to the placenta.

2. The size of the LV is influenced by the morphology of the mitral valve and the presence or absence of a ventricular septal defect. In cases of aortic atresia combined with mitral atresia, the LV cavity is small (Fig. 15-5).

3. If the mitral valve is patent, thus allowing blood inflow, then the LV is usually larger, although still hypoplastic. In such cases, the LV myocardium might show varying degrees of endocardial fibroelastosis.

4. Severe obstruction to the egress of blood from the LV in the presence of an intact ventricular septum is a prerequisite for the presence of endocardial fibroelastosis.

5. Occasionally, the LV cavity can be of normal size with aortic atresia (in 2%-7%). The majority of such cases were associated with a VSD.

6. After birth there normally is a fall in the PVR, with the SVR being higher than the PVR. In addition, the ductus arteriosus typically closes within the first couple of days postnatally.

7. In HLHS, if the lesion is not recognized, there is a progressive increase in pulmonary blood flow that can virtually steal from the systemic circulation (low effective cardiac output).

8. Oxygen content is increased, with large imagep/images (ratio of pulmonary flow to systemic flow). When saturations approach 90%, the systemic blood flow is reduced, causing inadequate tissue perfusion. This can result in severe hypoperfusion, metabolic acidosis, and shock.

9. In patients with too much pulmonary blood flow, particularly with progressive metabolic acidosis, inotropic support (particularly at doses that cause alpha receptor effect) should be minimized because it can increase the pulmonary blood flow by increasing the SVR. Afterload-reducing agents such as milrinone may be helpful.

10. The volume-overloaded single ventricle also suffers from myocardial dysfunction and AV valve regurgitation

image

Fig. 15-5 Hypoplastic left heart syndrome with mitral and aortic atresia. RV, right ventricle.

(Modified from Mullins CE, Mayer DC: Congenital Heart Disease: A Diagrammatic Atlas. New York, Liss, 1988.)

III. TAKE-HOME MESSAGE

REFERENCES

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Taketazu M, Barrea C, Smallhorn JF, et al. Intrauterine pulmonary venous flow and restrictive foramen ovale in fetal hypoplastic left heart syndrome. J Am Coll Cardiol. 2004;43(10):1902-1907.

Tworetzky W, McElhinney DB, Reddy VM, et al. Improved surgical outcome after fetal diagnosis of hypoplastic left heart syndrome. Circulation. 2001;103(9):1269-1273.