Atrioventricular Malconnection

Atrioventricular Septal Defects
Double Inlet Ventricle
Tricuspid Atresia
Ebstein's Anomaly
Mitral Stenosis and Atresia
Mitral Regurgitation

General Consideration

During embryological development, the atrioventricular valves are formed over the future left ventricle, and the right atrioventricular portion migrates to become situated over the future right ventricle. The right atrioventricular valve is distinguished by the attachment of the chordae tendineae (of the septal leaflet) to the ventricular septum, and the left by attachment to the (anterolateral and posteromedial) papillary muscles. A ventricular septal defect is generally present in anomalies of the atrioventricular valves, and is variously referred to as the outlet foramen, intraventricular foramen (IVF), or bulboventricular foramen (BVF).

Complete failure of the right atrioventricular valve to migrate to the right ventricle results in double inlet left ventricle, a situation in which both atrioventricular valves are located over the left ventricle. The right ventricle is generally rudimentary in this situation, because blood is directed principally to the left ventricle, which develops normally. The only source of blood flow to the right ventricle enters through the intraventricular foramen.

Partial migration of the right atrioventricular valve to the right ventricle results in overriding of the atrioventricular valve, a situation in which the right atrioventricular valve is variably positioned over the left ventricle. If the right atrioventricular valve is over-riding the ventricular septum by greater than 50%, than double inlet left ventricle is said to be present. The development of the right ventricle in these situations will be dependent upon the degree of over-riding, (the greater the degree the less well developed the right ventricle will be), and the presence of an intraventricular foramen.

Complete migration of the right atrioventricular valve, but with persistent attachment of some or all of the chordae to the left ventricular septum results in straddling of the atrioventricular valve. Straddling of the right atrioventricular valve results in maldevelopment of the right ventricle by directing blood flow away from the right ventricle and towards the left ventricle. Straddling may also preclude a two-ventricle repair for technical reasons alone, even in the presence of a normally developed right ventricle. Straddling and over-riding of the atrioventricular valve my coexist in the same heart.

Complete maldevelopment of the right atrioventricular valve results in tricuspid atresia, which is characterized by the lack of a right atrioventricular connection. The floor of the right atrium is completely muscular, and is separated from the ventricular mass by the atrioventricular sulcus. The right ventricle is generally maldeveloped, and is characterized by total absence of the inlet portion and varying degrees of maldevelopment of the trabecular and infundibular portions. A intraventricular foramen is generally present between the maldeveloped right ventricle and the left ventricle.

Atrioventricular Septal Defects

Cleft Mitral Valve

Partial atrioventricular septal defect

Complete atrioventricular septal defect

Morphology & Embryology

Atrioventricular septal defects represent a spectrum of lesions that are associated with maldevelopment of the atrioventricular septum and adjoining atrioventricular valves. Perhaps the simplest of these lesions is that of a cleft mitral valve, which, if being the solitary cardiac anomaly, is almost invariable silent. The next level of complexity is that of a partial atrioventricular septal defect, in which there is a cleft mitral valve along with a defect in the atrioventricular septum above the level of the atrioventricular valve annulus. This common combination, in the absence of mitral regurgitation, is pathophysiological and clinically analogous to a secundum atrial septal defect, although the operative repair is entirely different. The most complex combination is that of a defect of the atrial portion on the atrioventricular septum, a nonrestrictive ventricular septal defect, and complex morphology of the atrioventricular valves. This latter combination is referred to as complete atrioventricular septal defect, while defects with a restrictive ventricular septal defect are referred to as transitional or intermediate forms of atrioventricular septal defect. Unbalanced atrioventricular septal defect refers to the situation in which the two atrioventricular valves (or the common atrioventricular valve) overrides the ventricular septum to an such an extent that one of the ventricles is well developed (most commonly the left), and the other ventricle is hypoplastic. Major associated cardiac anomalies in atrioventricular septal defect include a patent arterial duct in 10%, abnormalities of ventriculoarterial connection in 12%, (tetralogy of Fallot 10%, double outlet right ventricle 2%, and transposition of the great arteries rarely), and completely unroofed coronary sinus with left superior vena cava (3%).

The embryology of this lesion remains incompletely understood. It is, however, unlikely due to incomplete fusion of endocardial cushions, as is reported in standard textbooks.

Hemodynamics

The hemodynamic consequences of atrioventricular septal defect in infancy include left-to-right shunting in both diastole (atrial level) and systole (ventricular level), or uniquely, between the left ventricle and right atrium. The left atrioventricular valve almost invariable contains a cleft, which may be associated with left atrioventricular valve regurgitation.

Clinical Presentation & Management

Patients with an ostium primum atrioventricular septal defect and no mitral regurgitation present in a manner analogous to those with secundum atrial septal defect. Congestive heart failure may appear between 4 - 12 weeks of age due to increasing pulmonary blood flow or atrioventricular valve insufficiency. Infants who tolerate the intracardiac shunt are at risk of developing pulmonary vascular obstructive disease at a young age (less than one year).

Early repair is indicated to prevent pulmonary vascular obstructive disease. Infants with concomitant diseases precluding repair can be palliated by pulmonary artery banding, although this results in massive ventricular hypertrophy, which may preclude subsequent complete repair. Some surgeons band the pulmonary artery and wait until the child is larger and before left ventricular hypertrophy occurs to complete the repair, but this method has the obvious disadvantage of requiring two operative procedures, and the pulmonary artery and valve may be distorted or severely damaged and require extensive reconstruction.

Complete atrioventricular septal defect and tetralogy of Fallot

This combination is a particularly difficult situation to treat. Postoperatively there is the potential of both right-sided and left-sided heart failure, the sum of which is worse than each type due to the interactions between the right ventricle and left ventricle. When repairing this lesion, you should always ensure a competent pulmonary valve, as PI is very poorly tolerated, especially in the face of biventricular dysfunction and MR and/ or tricuspid regurgitation that may be present postoperatively.

Double Inlet Ventricle

Morphology & Embryology

Double inlet ventricle is a congenital cardiac malformation in which both atria connect to only one ventricular chamber by either two separate atrioventricular valves or a common atrioventricular valve[198, 196, 195]. The ventricle to which both atrioventricular valves or common atrioventricular valve connects is usually well formed, whereas the ventricle not receiving the great majority of the venous return to the heart is often rudimentary. By definition, the term double inlet ventricle is used only if more than 50% of the overriding valve lies over the dominant ventricle. Recent evidence indicates that a ring of specialized tissue encircles the junction of the right and left ventricles in the developing heart tube. Part of this ring is also an atrioventricular junctional structure, rightward expansion of which forms the right atrioventricular junction. Partial or complete failure of rightward expansion is thought to be responsible for maldevelopment of the right atrioventricular junction, and link together the lesions of straddling tricuspid valve, double inlet left ventricle, and tricuspid atresia. The essence of double inlet left ventricle is that, although there has been expansion of the right atrioventricular junction, the right atrial myocardium retains its connection with the dominant left ventricle, while the right ventricle is incomplete and rudimentary. Hence, the left ventricle receives both atrioventricular valves or a common atrioventricular valve. When both atrioventricular valves are present, they often cannot be designated as either mitral or tricuspid, and are commonly straddling or stenotic. The rudimentary chamber is separated from the main chamber by a septum that does not extend to the crux of the heart, and is connected to the main chamber via a ventricular septal defect. The second chamber is of right ventricle morphology, is always anterior, and is located either to the left or the right. The size of the outlet chamber is related to the degree of development and straddling of the tricuspid valve, in addition to the size of the ventricular septal defect. The ventriculoarterial connections are most commonly discordant (Lambert heart) or may be concordant (Holmes heart). Unusual forms of ventriculoarterial connections in double inlet ventricle include double or single (pulmonary atresia) outlet.

Outflow obstruction to the pulmonary artery is common, and is the most important determinant of the clinical course. The obstruction may be subvalvar, valvar, or both, or may be complete (pulmonary atresia). Obstruction to systemic outflow also occurs, usually at the level of the ventricular septal defect in hearts with discordant ventriculoarterial connections, and the presence of aortic coarctation is a strong marker for the presence of a restrictive ventricular septal defect.

The conduction tissues, as seen in relationship to the ventricular septal defect, have a directly comparable arrangement to that seen in tricuspid atresia. Unlike tricuspid atresia, however, the AV node is situated anteriorly within the right atrioventricular orifice rather than within the atrial septum. This arrangement is seen irrespective of whether the rudimentary right ventricle is right or left-sided. The position of the rudimentary ventricle affects only the relationship of the atrioventricular bundle to the outflow tract from the dominant left ventricle. This disposition of conduction tissue is readily explained on the basis of its formation from the ring of tissue initially developed between the inlet and outlet components of the ventricular loop.

Associated Cardiac Anomalies

Associated cardiac anomalies occur in about one-third of cases with double inlet ventricle. atrioventricular valve malformations are common, and include straddling, leaflet dysplasia, leaflet cleft and tags and annular hypoplasia. The pulmonary valve may be stenotic due to either annular hypoplasia or leaflet thickening, or may be atretic. Subvalvar pulmonary stenosis may be due to a restrictive ventricular septal defect in cases in which the pulmonary artery arises from the rudimentary chamber, or may less commonly be due to infundibular narrowing. Aortic arch anomalies such as coarctation, interrupted aortic arch and hypoplastic aortic arch are strongly associated with a restrictive ventricular septal defect in cases in which the aorta arises from the rudimentary chamber.

Diagnostic Work-up

Most of the main features of double inlet ventricle can be defined by echocardiography or angiocardiography. Important left atrioventricular valvar stenosis should be sought, as its presence necessitates either atrial septostomy or septectomy. Pulmonary arterial pressure is important, since the choice of operative therapy is largely dictated by the presence of pulmonic stenosis and its severity.

Hemodynamics

There are several important hemodynamic variables in double inlet ventricle, including the completeness of intracardiac mixing at the atrial level, the degree of outlet obstruction, and the presence of atrioventricular valve malfunction. In double inlet ventricle, mixing of systemic and pulmonary venous blood occurs in the main ventricular chamber. This may result in nearly equal oxygen saturation in the aorta and the pulmonary artery. In some cases, streaming of blood within the ventricle results in a substantial difference in oxygen saturation between the aorta and the pulmonary artery. The streaming may be favorable, with aortic saturation being greater than pulmonary arterial saturation, or unfavorable, with pulmonary saturation being greater than aortic. The degree of saturation is also influenced by the severity of pulmonic stenosis, the single most important determinant of the clinical course. Aortic stenosis is also important, although it is much less commonly a hemodynamic factor, and is almost always due to subvalvar stenosis at the level of the ventricular septal defect. Subaortic stenosis often follows palliative pulmonary artery banding, in which the resultant hypertrophy of muscle around the ventricular septal defect may play a contributing role. Atrioventricular valve stenosis is hemodynamically important if the atrial septum is intact or the atrial septal defect is restrictive, in which case venous return may be restricted or obstructed.

Clinical Course

There are two modes of presentation, occurring in the neonatal period or during early infancy, and is dependent on the status of pulmonary blood flow. Patients with reduced blood flow due to pulmonic stenosis or atresia typically present within the first week of life, whereas those with increased pulmonary blood flow usually present within the first few months of life. Patients with balanced pulmonary blood flow may present much later in life. Cyanosis is more striking in cases with obstructed pulmonary blood flow, while congestive cardiac failure is more common in those with unrestricted pulmonary blood flow.

Atresia of the left-sided atrioventricular valve, when combined with a restrictive intra-atrial communication, results in severe pulmonary venous hypertension with its typical chest radiographic appearance and severe respiratory distress in early life. This situation may be masked initially by pulmonary stenosis, only to become unmasked following the creation of a systemic-pulmonary artery shunt. Severe atrioventricular valve regurgitation results in elevated atrial pressure and the early appearance of congestive heart failure.

Medical & Surgical Management

The estimated overall survival without treatment of patients born with double inlet ventricle is about 57% at 1 year and 45% at 5 years, although some subsets have reasonably favorable prognosis[198, 196, 195]. Medical management is largely restricted to the management of congestive cardiac failure in cases with unrestricted pulmonary blood flow, or to the use of PGE1 in neonates with severely restricted pulmonary blood flow or with pulmonic atresia. Occasionally, percutaneous balloon or blade atrial septostomy is required to relieve pulmonary venous obstruction in cases with left sided atrioventricular valve stenosis and an intact atrial septum or restrictive atrial septal defect.

Surgical therapy is usually directed with the ultimate goal of achieving a Fontan type of physiology, often requiring a plan of staged-reconstruction. Ventricular septation and cardiac transplantation are also viable options dependent on local practice and philosophy. Ventricular septation may be an option in cases with an enlarged dominant ventricle into which two reasonable atrioventricular valves with little or no overriding or straddling. The ventriculoarterial connection must be amenable to repair with the appropriate ventriculoarterial connection, and there should be little or no pulmonary or systemic outflow obstruction[346]. Stage septation[421] consists of placing an apical patch and a second patch at the superior portion between the atrioventricular valves using widely spaced interrupted sutures, and completing the septation 6 - 18 months later with a third patch.

Staged-reconstruction consists of three stages, the first being a palliative procedure in which the systemic and pulmonary circulations are usually placed in parallel, the second stage consisting of a superior cavopulmonary anastomosis, and the final stage being conversion to a total cavopulmonary connection (Fontan physiology). The Qp:Qs for the three stages are typically 2-3:1, 0.5:1, and 1:1.

Patients with restricted pulmonary blood flow and no subaortic stenosis or left ventricular outflow tract obstruction are treated with a systemic-pulmonary artery shunt[18, 192, 244, 684]. Pulmonary artery reconstruction may or may not be required depending on the presence of discontinuous pulmonary arteries, pulmonary artery stenosis or distortion, or significant aorto-pulmonary collaterals[889].

Patients with a univentricular atrioventricular connections and left ventricular outflow tract obstruction consists of a modified Damus-Kaye-Stansel procedure[216, 221, 393, 394, 395, 396, 397, 490, 499, 540, 613, 677, 732, 818, 896, 902], in which the two great vessels are attached proximally, and pulmonary blood flow is supplied by an systemic-pulmonary shunt, a superior cavopulmonary anastomosis, or a total cavopulmonary connection. If the left ventricular outflow tract obstruction extends into the aortic arch or descending aorta, a Norwood procedure is required in order to relieve the distal obstruction. Finally, the arterial switch operation[216] has also been utilized, transforming the subaortic stenosis to sub-pulmonary stenosis and thereby theoretically protecting the pulmonary vascular bed. Many of the cases undergoing the arterial switch operation for a univentricular atrioventricular connection ultimately require a systemic-pulmonary shunt for insufficient pulmonary blood flow, raising the possibility of increasing the risk of an ultimate Fontan operation.

Patients with unrestricted pulmonary blood flow and no subaortic stenosis or left ventricular outflow tract obstruction may initially be palliated with pulmonary artery banding[499, 689, 644, 393]. Drawbacks to this procedure is the potential for pulmonary artery distortion, developing pulmonary valvar regurgitation or damage to the pulmonary valve, resultant ventricular hypertrophy, decreased ventricular compliance, and development of subvalvar aortic stenosis[499]. The latter may result from both ventricular hypertrophy and geometric changes to the left ventricle. Pulmonary artery banding may therefore increase the risk of a subsequent Fontan procedure[611].

Ventricular septal defect enlargement or resection of the infundibular septum may be required depending on the degree of restriction of the subaortic stenosis[796]. Atrial septectomy may be required in cases with stenosis of the left atrioventricular valve or those with an intact or nearly intact atrial septum.

The second stage operation, the bi-directional Glenn procedure, consists of division and anastomosis of the superior vena cava to the pulmonary artery and division and closure of the pulmonary trunk below its bifurcation. A bilateral bi-directional Glenn procedure is required when there is persistence of the left superior vena cava. The bi-directional Glenn procedure can usually be performed in the first 8 - 12 weeks of life, at which time pulmonary vascular resistance is usually sufficiently low to accommodate approximately half of the cardiac output. Insufficient pulmonary blood flow may be augmented by the addition of a small systemic-pulmonary shunt. A persistently high pulmonary vascular resistance results in insufficient pulmonary blood flow and severe cyanosis (systemic saturation less than 60% and a PaO2 less than 25 - 30 torr), manifested by high "Glenn pressures" (superior vena cava pressure over 18 - 20 mm Hg). A high Glenn pressure may significantly decrease cerebral perfusion by decreasing the pressure gradient across the cerebral bed. This may be clinically manifested as fullness of the fontanelle, persistently irritability, systemic hypertension and relative bradycardia. In not medically reversible, the bi-directional Glenn may need to be taken down and a systemic-pulmonary shunt reconstructed. Unusual following the bi-directional Glenn procedure is persistent pleural effusions, although the rare late development of pulmonary arteriovenous malformations may cause severe cyanosis. The latter result in right to left shunting, and, if severe, precludes successful conversion to Fontan operation. Conversion to a Fontan operation completes the single-ventricle pathway in cases with unrestricted pulmonary blood flow.

Tricuspid Atresia

Mophology

There are many forms of tricuspid atresia . . .

Clinical Findings

Diagnosis

Medical Management

Surgical Management

Straddling Tricuspid Valve

Morphology

The central feature of hearts with straddling and overriding of the tricuspid orifice is that they are intermediate between normal hearts with a concordant atrioventricular connection and those with double inlet left ventricle and right-sided rudimentary right ventricle. The disposition of the conduction tissues reflects this intermediate status, since the atrioventricular node is formed at the point at which the ventricular septum, overridden by the abnormal tricuspid orifice, makes contact with the atrioventricular junction. According to the degree of override, the node can be formed at any point around the tricuspid orifice. This arrangement is well accounted for on the basis of partial expansion of the right atrioventricular orifice across the primary ventricular septum. Hearts with such partial expansion represent an intermediate stage between the normal heart and hearts with double inlet left ventricle.

Ebstein’s Anomaly

Morphology

Carpentier described five anatomic characteristics of Ebstein’s anomaly that are relevant to the surgical management of the condition:

• There is displacement of the septal and posterior leaflets of the tricuspid valve toward the apex of the right ventricle.
• The anterior leaflet is attached to the appropriate level of the tricuspid valve annulus, however, it is larger than normal and may have multiple chordal attachments of the ventricular wall
• The segment of the right ventricle from the level of the true tricuspid annulus to the level of attachment of the septal and posterior leaflets is unusually thin and dysplastic and is described as "atrialized". The tricuspid annulus and the right atrium are extremely dilated.
• The cavity of the right ventricle beyond the atrialized portion is reduced in size, usually lacks an inlet chamber, and has a small trabecular component.
• The infundibulum is often obstructed by the redundant tissue of the anterior leaflet as well as by the chordal attachments of the anterior leaflet to the infundibulum.

In addition, he described four clinical variants with progressively increasing severity. In type A, the volume of the true right ventricle is adequate; in type B, the volume of the right ventricle is small, and there is a large atrialized portion of the right ventricle; in type C, the volume of the right ventricle is small, and there is obstruction of the right ventricular outflow tract; and in type D, there is almost complete atrialization of the right ventricle with the exception of a small infundibular component, and the only communication between the atrialized ventricle and the infundibulum is through the antero-septal commissure of the tricuspid valve.

Associated cardiac anomalies

The most common associated anomaly is an atrial septal defect, which occurs in about 50% of cases. In symptomatic neonates, survival is dependent on the presence of a patent arterial duct. As alluded to above, there is a variable degree of right ventricular outflow tract obstruction. A Wolff-Parkinson-White type of accessory pathway, often with associated pre-excitation, is present in about 10% of cases. Rarely, an abnormality of ventriculoarterial connection is associated, including ventricular septal defect and {S,D,D} or {S,L,L} transposition of the great arteries.