Address correspondence to Kathleen Tate, MD, Dept of Obstetrics and Gynecology, Vanderbilt University Medical Center, R--1214 Medical Center North, Nashville, TN 37232--2521. Ph: 615-343-8801, Fax: 615-343-8806 ¶ Dept. of Pediatric Cardiology, § Dept. of Radiology

Synonyms: Double inlet ventricle, single ventricle, univentricular heart.

Definition: A single ventricle of indeterminate, left, or right ventricular type1 with two separate atrioventricular valves or a common valve. A rudimentary chamber is present with ventricles of the left ventricular type, and may be present when the dominant ventricle has a right  ventricular morphology2.

Prevalence: Single ventricle heart (single or double inlet) malformations account for 1% of all cardiac anomalies and about 4% of neonates with congenital heart defects3. As heart defects have an incidence of 70 per 10,000 live births4, single ventricle heart has an incidence of about 0.05-- 0.1:10,000 live births.

Etiology: The etiology is multifactorial inheritance with genetic predisposition.

Pathogenesis: A single ventricle results from failure of development of the two-trabecular heart components: the left ventricular from the “primitive ventricle” and the right ventricular from the “bulbus”.

Diagnosis: Prenatal: a single ventricular chamber on a four-chamber view of the heart with two atrioventricular valves. Postnatal: Ultrasound examination confirms the presence of a single ventricular chamber as well as the anatomy of the atrioventricular valves and the ventriculoarterial connections. Examination of ventricular outflow and aortic arch anatomy are critical because of associated anomalies.

Differential diagnosis: The differential diagnosis should include large ventricular septal defect, corrected transposition of the great arteries with a ventricular septal defect, atrioventricular canal, complete transposition of the great arteries with ventricular septal defect, and double outlet right ventricle.

Associated anomalies: These include anomalies of the valves entering the cardiac chambers, including stenosis, overriding, or straddling imperforate valves. In over 90% of cases of left single ventricle, the great arteries will be transposed¹. Atresia of the pulmonary or aortic valves or trunks, truncus arteriosus and subaortic stenosis may also be associated.

Prognosis: The prognosis is variable and is heavily influenced by the structure and function of the atrioventricular valves and ventriculoarterial connections. The survival for univentricular hearts without surgical intervention of the Mayo Clinic was 30% at 16 years².

Management: If the diagnosis is made before 24 weeks, the option of termination can be offered to the parent. Otherwise, after regular monitoring to detect signs of fetal hydrops, birth is recommended in a tertiary care center.

Postnatal management: Options for treatment include pulmonary artery banding, systemic to pulmonary artery shunting, the Fontan operation, and the septation operation (see text).

MESH Heart defects, congenital ICD9 745.3 CDC 745.300

Introduction

Single ventricle heart with double inlet is a rare congenital anomaly, comprising 1% of all congenital heart defects. The prenatal diagnosis of this rare birth defect has rarely been described¹⁰. The diagnosis is suspected on a four-chamber view and confirmed by echocardiographic analysis.

Case # 1

A 22-year old G₂P₁₀₀₁ was seen at Vanderbilt Hospital and diagnosed at 17 weeks gestation with a double inlet single ventricle. Fetal biometry was consistent with last menstrual period. At 21 weeks, she presented for a second opinion and ultrasound at the University of Utah Medical Center where the diagnosis was confirmed.

On ultrasound examination, there was a single ventricle with double inlet (fig. 1) and a subaortic outlet chamber with a bulboventricular foramen. The right--sided atrioventricular valve annulus was smaller than the left--sided atrio­ventricular valve annulus, as were the arteries (fig. 2). The pulmonary artery was to the right and posterior to the aorta, consistent with L--transposition. There was a pulmonary stenosis. An anomalous pulmonary venous return from a right upper lobe vein into the superior vena cava was observed (fig. 3). The Doppler and M--mode tracings demonstrated a second degree heart block. Amniocentesis at 21 weeks revealed a normal male karyotype. Follow-up on this fetus is not available.

Case # 2

A 28-year-old G₄P₂₀₁₂ was referred to Vanderbilt at 39 weeks gestation because of an outside suspicion of single ventricular heart. She had a previous ultrasound at 20 weeks, at which the anomaly was not seen. The third trimester scan was ordered because of size--dates discrepancy. The family history was significant for maternal grandfather with bicuspid stenotic aortic valve that had required surgery.

The examination performed at 39 weeks revealed a biometry consistent with the last menstrual period. There was a double inlet single ventricle with a left ventricular morphology on the four--chamber view (fig. 4). A large pulmonary artery was connected to the ventricle and a smaller, hypoplastic aorta appeared to arise from a rudimentary outflow chamber (fig. 5). A diagnosis of double inlet single ventricle was made and was confirmed by pediatric cardiology consultation.

The patient had an induced labor and delivered a 2827g infant with Apgars of 9 at one minute and 8 at five minutes. Postnatal echocardiography revealed a double inlet left ventricle with rudimentary right ventricle, subaortic stenosis, a patent ductus arteriosus, and L--transposition of the great arteries. Coarctation of the aorta was sus­pected. The communication between the single ventricular chamber and the rudimentary outflow chamber was restrictive (subaortic stenosis). These dia­gnoses were confirmed at cardiac catheterization. Therapeutic options discussed with the family included Norwood repair, orthotopic cardiac transplantation, and compassionate care. The infant subsequently underwent a Stage I Norwood repair and is doing well at 8 months of life.

Discussion

The prenatal diagnosis of single ventricle double inlet heart has not previously been published. It is a rare congenital anomaly but should be easily diagnosed or suspected on an abnormal four--chamber view.

Definition

There are three types of cardiac anomalies associated with the single ventricle double inlet heart:

• a single ventricle of the indeterminate type, or of
• left or
• right ventricular type with a rudimentary contralateral chamber¹.

A dominant left ventricle with rudimentary right ventricular chamber is the most common form of double inlet ventricle. These forms of single ventricle can sometimes be differentiated by prenatal ultrasound.

Aspects of anatomy requiring special attention in the postnatal period include:

• the size and position of the communication between the single ventricle and the outflow chamber,
• the bulboventricular foramen,
• the anatomy and function of the atrioventricular valves, and
• the anatomy of the pulmonary and aortic outflow tracts.

Pulmonary and aortic outflow tract obstruction may occur and impact significantly on patient prognosis and management. Subpulmonary obstruction may be due to posterior deviation of the infundibular septum, atrioventricular valve tissue or subvalvular fibrous tissue¹. Varying degrees of hypoplasia of the ascending aorta, aortic valve, and outflow chamber, or a restrictive bulboventricular foramen may result in aortic outflow tract obstruction. These aspects of anatomy may be confirmed at catheterization but may be elucidated by echocardiography.

Embryology

In normal development of the heart, the left ventricle trabecular component is formed from the inlet segment of the primitive ventricle of the primary heart tube, while the right ventricle trabecular component forms from the outlet segment of the bulbus. A failure of development of these trabecular components results in a single ventricle¹.

Diagnosis

The anomaly can be detected on the four--chamber view of the heart: the ventricular septum is absent, and the two atria empty into a single ventricular chamber (fig. 6).

Prognosis

The prognosis is difficult to generalize due to the complexity of this lesion and its associated anomalies. Patients without aortic outflow tract obstruction and with moderate restriction of pulmonary blood flow generally remain well compensated in infancy. A Rashkind atrial septostomy is required in the presence of stenosis of the posterior atrioventricular valve to relieve pulmonary venous obstruction.

Infants with unobstructed pulmonary blood flow develop symptoms of congestive failure in the first months of life.

Infants with severe obstruction to pulmonary blood flow require intervention in the neonatal period to ensure adequate pulmonary blood flow. Similarly, infants with severe obstruction to systemic blood flow, such as the first infant above, require intervention before ductal closure to insure adequate systemic blood flow. Without further surgery to separate the systemic and pulmonary circulations, individuals with double inlet left ventricle are subject to the complications of cyanosis and chronic ventricular volume overload, and survival beyond the second decade of life is rare.

Treatment

Palliative procedures in early infancy include pulmonary artery banding to limit pulmonary blood flow in patients without obstruction to pulmonary blood flow, or creation of an aortopulmonary shunt to ensure pulmonary blood flow in individuals with marked pulmonary outflow tract obstruction or pulmonary atresia.

The Norwood repair, discussed later, may also be considered in the neonatal period, for those infants with systemic outflow tract obstruction.

Pulmonary artery banding

Pulmonary artery banding carries a 25-50% mortality rate¹. However, functional subaortic stenosis often develops after this procedure, which Freedom reported in 4 of 31 patients⁵. It is believed to be caused by narrowing of the bulboventricular foramen or by concentric muscular hypertrophy of the subvalvular conus, secondary to the increased pressure gradient across the pulmonary artery⁶. Therefore, after placement of a pulmonary artery band, an infant must be monitored for signs and symptoms of subaortic stenosis.

Blalock-Taussig operation

The Blalock--Taussig operation is the most commonly performed shunting operation. In patients with single ventricle, surgical mortality is less than 20%¹.

Fontan repair

To avoid the long term complications of cyanosis and volume overload, later surgery involves separation of the pulmonary and systemic circulations, using the modified Fontan repair. The many variations of this repair all entail the creation of anastomoses between the systemic venous return and the pulmonary arteries, allowing its passive return to the pulmonary bed. The univentricular heart then receives only the pulmonary venous return, which is pumped to the systemic circulation. In this repair, the pulmonary bed must be a low resistance circuit, free of stenoses. Ideal candidates are those with a pulmonary arterial pressure less than 20 mm Hg, pulmonary vascular resistance less than 5 mm Hg, and normal ventricular end diastolic pressure. Long-term complications include arrhythmias and low cardiac output^1,7.

The Norwood procedure

The Norwood procedure is a series of surgeries correcting aortic outflow tract obstruction with eventual conversion to a modified Fontan repair⁸. Patients with significant obstruction to aortic outflow require relief of this obstruction in the neonatal period before closure of the patent ductus arteriosus. The initial surgery consists of reconstruction of the aortic outflow tract through anastomosis of the aorta and main pulmonary artery. The pulmonary blood flow is provided by a systemic to pulmonary artery shunt. If there is obstruction to blood flow through the posterior atrioventricular valve, an atrial septectomy may be performed. In subsequent surgeries during the first two years of life, cavopulmonary anastomoses are created, similar to those of the modified Fontan repair, again separating the circulations⁹.

The septation operation

Another option for treatment is the septation operation. This operation uses a Dacron patch to recreate an interventricular septum. The best outcomes are achieved in patients with double inlet left ventricle and an inverted rudimentary right ventricle. There must be no obstruction to pulmonary artery outflow, and the atrioventricular valves must be normal. There is a 50% mortality with this procedure¹. It is technically difficult if a pulmonary artery banding has already been done, because of development of subaortic stenosis after pulmonary artery banding.

References

1. Elliott LP, Anderson RH, Bargeron LM Jr., et al:  Single ventricle or univentricular heart. In: Adams FH, Emmanouilides GC, Riemenschneider TA (eds.):  Heart disease in infants and children.  Baltimore, MD, Williams and Wilkins, 1989, pp 485--502.

2. Freedom RM, Smallhorn JF: Hearts with a univentricular atrioventricular connection.  In Freedom RM and Benson LN (eds.):  Neonatal heart disease.  New York: Springer Verlag, 1992, pp 497--521.

3.  Rosenberg HS, Donnelly WH: The cardiovascular system. In Wigglesworth JS, Singer DB (eds):  Textbook of fetal and perinatal pathology. Cambridge, Ma:  Blackwell Scientific Publications, p 716, 1991.

4.  Copel JA: Congenital anomalies, Section 5: Congenital heart disease.  In: Eden RD, Boehm FH (eds).  Assessment and care of the fetus. E. Norwalk, CT: Appleton and Lange, 1990.

5.  Freedom RM, Sondheimer H, Dische R, Rowe RD: Development of “subaortic stenosis” after pulmonary arterial banding for common ventricle.  Am J Cardiol 39:78, 1977.

6.  Jonas RA, Castaneda AR, Lang P:  Single ventricle (single-- or double--inlet) complicated by subaortic stenosis:  surgical options in infancy.  Ann Thorac Surg 39:4, 1985, 361 366.

7.  Peters NS, Somerville J: Arythmias after the Fontan procedure. Br Heart J 68:199--204, 1992.

8. Norwood WI, Pigott JD: Recent advances in congenital cardiac surgery. Clin Perinatol 1988; 15:713--719.

9.  Norwood WI, Jr, Jacobs ML, Murphy JD:  Fontan procedure for hypoplastic left heart syndrome.  Ann Thorac Surg 1992; 54:1025--1030.

10. Allan LD: Spectrum of congenital heart disease detected echocardiographically in prenatal life. Br. Heart J 54:523--6, 1985.