Definition and Morphology
The nomenclature for single ventricle has been a subject of debate for years. Double-inlet ventricle is commonly defined as the morphologic arrangement in which more than 50% of both atria are connected to one dominant ventricular chamber. The connection can be either through two separate atrioventricular (AV) valves (one of them may be imperforate) or through a common AV valve, excluding tricuspid or mitral atresia ( Box 55.1 ). Van Praagh first introduced the terms “single” and “common” ventricle to describe the outlet chamber in general and nonmorphologic terms. The term single ventricle is often used in patients with a double-inlet ventricle, although in most instances, a rudimentary second ventricle is present. The rudimentary and hypoplastic ventricle may receive direct drainage from the atrium. However, by definition, more than 50% of the corresponding AV valve must override the ventricular septum and drain into the dominant and functional ventricular chamber.
Atrial Arrangement
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Situs solitus
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Situs inversus
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Atrial isomerism (right or left)
Atrioventricular Connection
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Univentricular AV connection; by definition, more than 50% of both valves committed to the dominant ventricle
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The mode of atrioventricular connection can be:
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two patent valves,
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one patent valve plus one imperforate valve (right or left),
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one totally committed valve plus one straddling valve (right or left; >50% rule),
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two straddling valves (>50% rule), or
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a common valve (which may or may not straddle).
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Ventricles
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Dominant ventricle may be left (most common), right, or very occasionally, indeterminate
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Ventricular morphology is usually determined by:
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the AV valves;
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the relative ventricular position (left ventricle is a posterior chamber, whereas right ventricle is an anterior chamber); or
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apical trabeculations (fine in left ventricle, coarse in right ventricle).
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Ventriculoarterial Connection
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Discordant (transposed great arteries, common); the VSD may be restrictive, leading to subaortic stenosis.
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Pulmonary stenosis (valvular and subvalvular) is common and may protect the pulmonary vascular bed from pulmonary vascular disease.
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Concordant (so-called Holmes heart, uncommon)
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Double outlet
The most common clinical scenario is a double-inlet left ventricle in the setting of situs solitus with transposed great vessels or double-outlet right ventricular connection, as confirmed by Uemura et al. ( Fig. 55.1 ). The right nondominant ventricle is usually small, precluding a biventricular repair. There is one or occasionally multiple ventricular septal defects (VSDs) that may or may not be restrictive, leading to subaortic stenosis where there is ventriculoarterial discordance. Pulmonary stenosis (valvular and subvalvular), and occasionally pulmonary atresia, are often associated.
Full appreciation of the morphology helps in understanding the different clinical patterns, the natural history, and the surgical options available, including surgical septation, and potential long-term complications.
Conduction System
The anatomy of the specialized conduction tissue in double-inlet ventricles is of particular interest to surgeons, specifically when septation or muscular resection is considered. The atrial situs determines the position of the sinoatrial node. Dual nodes are seen in right atrial isomerism, and hypoplastic nodes occur in left atrial isomerism. The AV conduction is determined by the AV connection and ventricular morphology. A ring of conduction tissue associated with the AV valve annulus forms the AV node(s) and bundles. In the usual situation of a dominant left ventricle (also called the l-loop configuration), the AV node and bundles are anterior and to the right, with the bundle across the anterior aspect of the outflow tract, then onto the right margin of the VSD. If the VSD in this situation is restrictive and needs enlargement (to relieve subaortic stenosis), septal resection must be done posteriorly.
Associated Lesions
Associated cardiac lesions are frequent. AV valve anomalies in the form of valvular hypoplasia, straddling, leaflet dysplasia, and clefting are prevalent, potentially leading to valvular stenosis or insufficiency. Valvular pulmonary stenosis or atresia occurs secondary to leaflet dysplasia or to a hypoplastic annulus. Subvalvular pulmonary stenosis occurs due to muscle hypertrophy, infundibular hypoplasia, septal displacement, or a restrictive VSD. Subaortic stenosis is usually due to a restrictive VSD. Aortic arch abnormalities (hypoplasia, coarctation, or interruption) are also common.
Genetics and Epidemiology
Double-inlet ventricle is an uncommon defect. It has been diagnosed in 1.5% of patients with congenital heart disease at the Hospital for Sick Children in Toronto. Similarly in Belgium, there were 9 (0.98%) cases diagnosed with single ventricle out of 921 children with congenital heart disease in 2002.
Recurrence of congenital heart disease was 2.8% among siblings of children with double-inlet ventricles. This was much higher among patients with left atrial isomerism (28%). As in the majority of patients with single-ventricle physiology, no chromosomal abnormalities have been associated with double-inlet ventricles.
The incidence of univentricular cardiac lesions may change in the future. As illustrated in Denmark, the incidence of children born with common ventricle decreased significantly in the last decade with an increase in termination of pregnancy. After more than 30 years of follow-up, survival increased over the study period, and 50% of their cohort with double-inlet ventricle were alive at the end of the study in 2009. The adult congenital population with single-ventricle physiology is growing and will bring new challenges.
Early Presentation and Management
The clinical presentation of patients with double-inlet ventricle is determined by the degree of pulmonary blood flow and associated lesions ( Box 55.2 ).
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Neonates may be cyanotic if pulmonary obstruction is severe, as seen in patients with valvular and subvalvular pulmonary stenosis or in double-inlet left ventricle with ventriculoarterial concordance and a severely restrictive ventricular septal defect.
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Unobstructed pulmonary blood flow causes a left-to-right shunt, resulting in congestive heart failure with a relative decrease in systemic perfusion as seen in double-inlet left ventricles with ventriculoarterial discordance. These patients are at risk of developing irreversible pulmonary vascular disease.
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Coexisting coarctation, arch hypoplasia, or interruption result in more severe heart failure and earlier presentation.
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Patients with balanced pulmonary and systemic circulation, moderate to severe pulmonary stenosis, and unobstructed systemic blood flow often survive well beyond the neonatal period and have the best overall long-term prognosis. Such patients may present quite late, with minimal cyanosis and a long ejection systolic heart murmur due to pulmonary stenosis.
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The diagnosis is usually established fully by means of echocardiography. Further anatomic definition may be determined by magnetic resonance imaging, whereas additional hemodynamic data can be obtained from cardiac catheterization.
Management
The majority of patients with double-inlet ventricle are not suitable for biventricular repair and are considered for staged palliative procedures with a view to an ultimate Fontan operation (see Chapter 12 ).
Early interventions usually address one or more of the following:
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Pulmonary blood flow:
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Augmentation of flow (for patients with pulmonary stenosis and atresia) with a systemic-to-pulmonary arterial shunt or a bidirectional cavopulmonary anastomosis; the former is preferred when pulmonary vascular resistance is elevated.
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Reduction of flow with pulmonary artery banding for patients with unobstructed pulmonary flow who are at risk of pulmonary hypertension.
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Relief of outflow tract obstruction with:
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VSD enlargement in patients with discordant ventriculo-arterial connections and a restrictive VSD leading to subaortic stenosis; the latter may not be obvious from the outset and may develop following pulmonary artery banding. Outflow obstruction is also frequent in patients who underwent aortic arch repair for coarctation or interruption. Infants with these anatomic substrates, therefore, need early reassessment of the subaortic outflow tract (with cardiac catheterization and angiography, if necessary), after pulmonary artery banding and/or aortic arch surgery. VSD enlargement may leave residual stenosis and/or cause postoperative complete heart block. VSD enlargement by means of resection at the inferior part of the septum results in fewer complications, and therefore muscular resection has become the treatment of choice in a number of institutions.
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A Damus-Kaye-Stansel (D-K-S) operation is the alternative approach for relieving subaortic stenosis in this setting. It consists of an aortopulmonary window with distal ligation of the main pulmonary artery, thus using both left and right ventricular outflow tracts to supply the aorta and effectively relieve subaortic stenosis. When a D-K-S procedure is considered and pulmonary artery banding is required, the latter should be wrapped closer to the bifurcation of the pulmonary arteries (ie, distal to the pulmonary valve). This maneuver provides adequate length for anastomosing the proximal pulmonary artery with the ascending aorta for subsequent completion of the D-K-S connection.
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Atrial septectomy occasionally, particularly if there is stenosis or atresia of one of the AV valves with a restrictive atrial septum.
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These palliative procedures are followed by a cavopulmonary anastomosis and finally a Fontan completion. Ventricular septation is performed in only a minority of patients.
The age for the Fontan procedure (see Chapter 12 ) has been brought forward in recent years with a view to preserving long-term ventricular function. Many children with double-inlet ventricle would be considered for a Fontan completion during the first half of the first decade of life. Occasionally, patients may require concomitant relief of subaortic stenosis. Early postoperative mortality of patients with double-inlet ventricle undergoing a Fontan procedure is comparable to that of patients with other cardiac morphology. The operative mortality rate has been less than 10% and in most contemporary series, less than 5%, regardless of whether the dominant ventricle was morphologically right or left. The presence of subaortic obstruction, ventricular hypertrophy, and diastolic dysfunction, in addition to atrial isomerism and primary or secondary pulmonary obstruction, conveys an increased perioperative risk. Fenestration during the Fontan procedure is highly recommended if one or more of these risk factors are present.
Ventricular septation allows for biventricular repair and physiology and should be considered for patients with a slightly enlarged dominant ventricle (compared with a well-developed second ventricle) with two competent nonstenotic AV valves, little or no aortic overriding, and no subaortic stenosis. Septation should be performed early, before the age of 10 years and ideally before the age of 2 years. The operative mortality cited in small series has been high, up to 40%. In a subset of “ideal patients” with a “large” left ventricle, normal situs and left-sided subaortic chamber, and no associated defects, no immediate postoperative death was seen, although the majority of patients were in complete heart block after the operation. The proportion of patients with double-inlet ventricle who may be suitable for septation (about 20%) reduces significantly with time, owing to the development of ventricular hypertrophy, pulmonary hypertension, and/or subaortic stenosis.
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