HYPOPLASTIC LEFT HEART SYNDROME

- SHONE SYNDROME

Hypoplastic left heart is a syndrome in which the left ventricular cavity is markedly reduced in size (hypoplastic left ventricle) associated with aortic and mitral valvular stenosis / atresia.

7-9 % of congenital cardiac lesions (1). 2:1 male predominance. 0.5%-2% recurrence risk (1,2), in siblings of an affected child.

ULTRASOUND (3,4)

Left ventricle	Usually very small to almost normal. Size is dependent on the degree of mitral pathology Hypoplastic left ventricle.
Right ventricle	Constitutes the cardiac apex ("apex forming ventricle") Significantly larger than the left ventricle.
Aorta	Very small (hypoplastic) but may enlarge at sinus of Valsalva. Absent vesel (aorta) on 3 vessel view in aortic atresia
Aortic valve	Stenosis / atresia of the aortic valve (small, echogenic) May be either valvular, subvalvular or supravalvular
Ascending aorta	Hypoplasia of the ascending aorta In mitral valve atresia or severe stenosis, shunting of blood across a VSD from right to left may result in a normal appearing LV and ascending aorta. Despite the LV size, it cannot maintain systemic circulation after birth
Mitral valve	Hypoplastic or stenotic - Chordae are short and thick, papillary muscles are small, annulus is hypoplastic Atresia:   - Membranous band instead of valve leaflets   - Right to left shunting of blood through VSD.
Aortic and Mitral valve	Size of LV depends on the degree of mitral valve hypoplasia In aortic valve atresia and mitral valve stenosis or hypoplasia resulting in a small slit like ventricle If aortic valve is atretic and mitral valve is normal the left ventricle may appear larger.
Pulmonary artery	Usually enlarged in combination with a large RV and RA.
Pulmonary veins	Usually enlarged due to pulmonary congestion.
Interatrial septum	May be bowed to left due to anomalous pulmonary venous drainage or severe tricuspid incompetence.
Endocardium	Endocardium is hyperechoic, stiff and poorly contractile Fibroelastosis giving rise to a small LA, small LV and small ascending aorta.
M-mode echocardiography	Diagnostic criteria are:   - Left ventricular end-diastolic diameter <9mm   - Aortic root diameter <6mm.
Color and pulsed doppler	Blood flow to the head and neck vessels and coronary arteries are supplied in a retrograde manner by the ductus arteriosus Retrograde flow is present in the ascending aorta and aortic arch Tricuspid incompetence (seen in >50% of cases) Mitral stenosis/atresia can be easily diagnosed Flow in the atretic ascending aorta can be assessed.
Cardiac failure	Congestive cardiac failure may result from RV overload, but fetal hydrops is uncommon.

Hypoplastic Left Heart Syndrome Hypoplastic left heart - gray scale (1) Hypoplastic left heart - mitral stenosis (1) Hypoplastic left ventricle – mitral stenosis Hypoplastic left heart - mitral atresia (1)

ASSOCIATED ANOMALIES

Link to Associated Anomalies

HEMODYNAMICS

Hemodynamics results in adequate perfusion of the head and neck vessels. The right ventricle supplies both pulmonary and systemic circulations. Congestive cardiac failure is only seen in the presence of incompetence of the atrioventricular valves (rare). Intrauterine growth is usually normal.

PROGNOSIS

25% mortality within the first week of life with all untreated infants dying within the first 6 weeks.

REFERENCES

1. Schaffer RM, Corio FJ. Sonographic diagnosis of hypoplastic left heart syndrome in utero. J Diag Med Sonography 1988;6:319-320.
2. Yagel S, Mandelberg A, Hurwitz A et.al. Prenatal diagnosis of hypoplastic left ventricle. Am J Perinatol 1986;3:6-8.
3. Sahn DJ, Shenker L, Reed KL et.al. Prenatal ultrasound diagnosis of hypoplastic left heart syndrome in utero associated with hydrops fetalis. Am Heart J 1982;104:1368-1372.
4. Silverman NH, Enderlein MA, Golbus MS. Ultrasonic recognition of aortic valve atresia in utero. Am J Cardiol 1984;53:391.