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Double-Inlet Ventricle


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.

BOX 55.1
Double-Inlet Ventricle: The Morphologic Spectrum

Atrial Arrangement

  • Situs solitus

  • Situs inversus

  • Atrial isomerism (right or left)

Atrioventricular Connection

  • Univentricular AV connection; by definition, more than 50% of both valves committed to the dominant ventricle

  • The mode of atrioventricular connection can be:

    • two patent valves,

    • one patent valve plus one imperforate valve (right or left),

    • one totally committed valve plus one straddling valve (right or left; >50% rule),

    • two straddling valves (>50% rule), or

    • a common valve (which may or may not straddle).

Ventricles

  • Dominant ventricle may be left (most common), right, or very occasionally, indeterminate

  • Ventricular morphology is usually determined by:

    • the AV valves;

    • the relative ventricular position (left ventricle is a posterior chamber, whereas right ventricle is an anterior chamber); or

    • apical trabeculations (fine in left ventricle, coarse in right ventricle).

Ventriculoarterial Connection

  • Discordant (transposed great arteries, common); the VSD may be restrictive, leading to subaortic stenosis.

  • Pulmonary stenosis (valvular and subvalvular) is common and may protect the pulmonary vascular bed from pulmonary vascular disease.

  • Concordant (so-called Holmes heart, uncommon)

  • 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.

Figure 55.1, Magnetic resonance image from a patient with double-inlet left ventricle. A, Note that both atria connect with a smoothly trabeculated ventricle (morphologically left). B, Discordant ventriculoarterial connection from the same patient, with more than 50% of the anteriorly placed aorta arising from the rudimentary right ventricle. Note bilateral infundibula causing subvalvular pulmonary stenosis. Ao , Aorta; LA , left atrium; LV , left ventricle; PA , pulmonary artery; RA , right atrium; RV , right ventricle.

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.

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