The new concept of univentricular heart

Abstract

The concept of univentricular heart moved from hearts with only one ventricle connected with atria [double inlet ventricle or absent atrioventricular (AV) connection] to hearts not amenable to biventricular repair, namely hearts with two ventricles unable to sustain separately pulmonary and systemic circulations in sequence. In the latter definition, even hearts with one hypoplastic ventricle are considered "functional" univentricular hearts. They include pulmonary/aortic atresia or severe stenosis with hypoplastic ventricle, and rare conditions like huge intramural cardiac tumors and Ebstein anomaly with extreme atrialization of right ventricular cavity. In this setting, the surgical repair is univentricular with "Fontan" operation, bypassing the ventricular mass. In other words, functionally univentricular heart is a condition in which, after surgery, only one ventricle sustain systemic circulation. Univentricular hearts (double inlet or absent AV connection) almost invariably show two ventricular chambers, one main and one accessory, which lacks an inlet portion. The latter is located posteriorly when morphologically left and anteriorly when morphologically right. As far as double inlet left ventricle, this is usually associated with discordant ventriculo-arterial (VA) connection (transposition of the great arteries) and all the blood flow to the aorta, which takes origin from the hypoplastic anterior right ventricle, is ventricular septal defect (bulbo-ventricular foramen) dependent. If restrictive, an aortic arch obstruction may be present. Double inlet left ventricle may be rarely associated with VA concordance (Holmes heart). As far as double inlet right ventricle with posterior hypoplastic left ventricular cavity, ventriculo-arterial connection is usually of double outlet type; thus the term double inlet-outlet right ventricle may be coined. Absent right or left AV connection may develop in the setting of both d- or l-loop, whatever the situs. In this condition, the contra-lateral patent AV valve may be either mitral or tricuspid in terms of morphology and the underlying ventricle (main chamber) either morphologically left or right. Establishing the loop, whatever right or left (also called right or left ventricular topology), is a fundamental step in the segmental-sequential analysis of congenital heart disease.

Keywords: aortic atresia; double inlet ventricle; mitral atresia; pulmonary atresia; single ventricle; tricuspid atresia; univentricular heart.

Figures

Figure 1

Segmental analysis of congenital heart disease. The normal heart consists of three segments: atria, ventricles, and the great arteries connected each other at atrioventricular and ventriculo-arterial junctions [partially modified from Refs. (12, 13)].

Figure 2

Univentricular atrioventricular connection. (A) The atrioventricular connection is univentricular when both atria drain mostly into a single ventricular chamber through two patent or a common atrioventricular valves (double inlet connection) or through a single valve in case of absent right or left connection. Note the anterior position of the right ventricle and the posterior position of the left ventricle when the main chamber is of left or right morphology, respectively. In the absence of ventricular septum, the main ventricular chamber is of indeterminate morphology (IV). (B). Absent right atrioventricular connection (tricuspid atresia), viewed from the right atrium: no orifice is present at the right atrial floor. (C) Double inlet ventricle: two separate valves drain into a main ventricular chamber of left morphology: note the hypoplastic right ventricle. The right atrioventricular valve is overriding the interventricular septum. (D) Absent left atrioventricular connection (mitral atresia): no orifice is present at the left atrial floor and the left ventricle is slit-like. A, atrium; IV, indeterminate ventricle; LV, left ventricle; RV, right ventricle; V, ventricle. [partially modified from Ref. (12)]

Figure 3

Double inlet left ventricle. (A) Both the AV valves drain into a posterior ventricular chamber of left morphology. (B) External view of the heart: the hypoplastic right ventricle is located in antero-superior position and gives origin to the aorta (discordant ventriculo-arterial connection). Note the restrictive ventricular septal defect (bulbo-ventricular foramen). The arrow indicates the surgical repair of the aortic arch obstruction.

Figure 4

Double inlet left ventricle with concordant ventriculo- arterial connection (Holmes heart). (A) View of the dominant left ventricle in which both the atria mostly drain through two patent AV valves. (B) External view of the heart with hypoplastic right ventricle and normally related great arteries. The aorta takes origin from the posterior ventricular chamber of left morphology and the pulmonary artery from the anterior hypoplastic ventricle of right morphology (concordant ventriculo-arterial connection).

Figure 5

Double inlet–outlet right ventricle. (A) View from the atria: both the atria drain mostly into a main ventricular chamber of right morphology through two separate atrioventricular valves. The left atrioventricular valve straddles and overrides the interventricular septum (star): note the posterior small ventricular chamber of left morphology. (B) View of the large right ventricle with coarse trabeculations in which both the atrioventricular valves drain.

Figure 6

Double inlet–outlet right ventricle. (A) View of the right-sided cardiac chambers: a common atrioventricular valve is present and drains the blood from both atria, predominantly into an anterior ventricular chamber of right morphology. (B) View of the left-sided cardiac chambers: note the hypoplasia of the posterior left ventricle. (C) From the right ventricle both the aorta and the pulmonary artery take origin. The pulmonary outlet is stenotic. Note the common atrioventricular valve mostly connected to the right ventricle.

Figure 7

Double inlet indeterminate ventricle. Both the atrioventricular valves drain into a ventricular chamber with coarse trabeculations of indeterminate morphology. A second separate ventricle was not identified.

Figure 8

Absent left atrioventricular connection (mitral atresia) with discordant ventriculo-arterial connection. (A) External view of the heart with the aorta in right anterior position and the pulmonary artery in left posterior position. (B) At the floor of the left atrium, there is no orifice (absent left atrioventricular connection). (C) A good sized, right-sided, morphologically right ventricle (d-loop) is present from which the aorta takes origin (discordant ventriculo-arterial connection). The pulmonary artery takes origin from the left ventricle (not shown).

Figure 9

Absent right AV connection (tricuspid atresia) with concordant VA connection. (A) There is no connection between the right atrium and the underlying right ventricle. The diminutive right ventricle is located interiorly and on the right (d-loop) lacks of an inlet portion and gives origin to a hypoplastic pulmonary artery. The two ventricles communicate through a ventricular septal defect. (B) The left atrium drains through a mitral valve into the left ventricle.

Figure 10

Absent left AV valve (tricuspid atresia) with truncus arteriosus. (A) There is no orifice in the floor of the right atrium. (B) A common arterial trunk arises from the heart, prevalently from the left ventricle, and gives origin to both systemic and pulmonary circulations. Note the dysplastic, tricuspid truncal valve.

Figure 11

Absent right atrioventricular connection in l-loop with single aortic outlet (pulmonary atresia). (A) A morphological tricuspid valve joins the left atrium with a main ventricular chamber of right morphology (l-loop), from which the aorta takes origin. The pulmonary valve is atretic (single aortic outlet). (B) At the floor of the right atrium there is no orifice. The underlying ventricular chamber is hypoplastic, posterior, right-sided and of left ventricular morphology (l-loop).

Figure 12

Single outlet ventriculo-arterial connections with functionally univentricular heart. (A) Aortic atresia with intact ventricular septum (single pulmonary outlet). Four chamber echocardiographic cut of the heart showing the severe hypoplasia of the left cardiac chambers. Note the tiny inlet portion of the left ventricle. This heart is only suitable for Norwood univentricular repair. (B) Pulmonary atresia with intact ventricular septum (single aortic outlet) with hypoplastic right ventricle. The size of the right ventricle is such that this heart may be suitable for one and half ventricle repair.

Figure 13

Pulmonary atresia with intact ventricular septum (single aortic outlet). (A) View from the right cardiac chambers: the right ventricle is hypoplastic and hypertrophic. (B) View of the outflow of the same case: note the endocardial fibroelastosis of the diminutive right ventricle. This heart may be suitable for one and half ventricle repair.

Figure 14

Ebstein anomaly of the tricuspid valve. (A) View from the apex of the right ventricle. A prosthetic valve was inserted ad the AV annulus. A large atrialized area is situated between the AV annulus and the displaced leaflets of the tricuspid valve. Note the thin wall of the right ventricle. In this patient, heart transplantation was performed because the dilated right ventricle was unable to sustain the pulmonary circulation. (B) Close up of the same specimen showing the atrialized area.

Figure 15

Aortic stenosis with hypoplastic left heart. (A) View from the left ventricular chambers: the left ventricle is hypoplastic with hypertrophic free wall. Note the hypoplastic mitral valve and the severe endocardial fibroelastosis of the left ventricle. (B) A severe aortic stenosis is present with dysplastic aortic valve. This heart may be amenable for one and half ventricle repair.