Surgical anatomy
Although the variant of atrioventricular septal defect with common atrioventricular valve is the commonest type of lesion, and there is almost always the potential for shunting in such anomalies at both atrial and ventricular levels, as we have emphasized in the previous review in this section of our supplement,1 the essence of the malformation remains an atrioventricular septal defect in the setting of a common atrioventricular junction. The anatomic hallmarks of the lesion, therefore, are the scooped-out ventricular septum, the elongated left ventricular outflow tract, and, of course, the trifoliate nature of the left atrioventricular valve.2 All of these anatomic features are of surgical importance. Shunting through the atrioventricular septal defect depends on the relationships between the bridging leaflets of the common atrioventricular valve and the scooped-out crest of the ventricular septum. The degree of disproportion between the inlet and outlet dimensions of the ventricular septum are no different between the variant with a common atrioventricular valve, discussed in this review, and the so-called “ostium primum” defect, in which shunting is confined at atrial level because the bridging leaflets are usually firmly attached to the ventricular septal crest.3 There is greater deficiency of the middle part of the septum in the setting of a common valve, but the inferior bridging leaflet is almost always closely related to the most inferior part of the septum, favouring direct closure of this part of the atrioventricular septal defect. The ventricular component of the defect is usually considered to represent an “inlet” defect, and there is no question but that the defect opens between the ventricular inlets. It is also possible, however, to find muscular defects opening between the ventricular inlets, so it is less than satisfactory to consider the ventricular component of the septal defect simply as an “inlet defect”. This is the more so, since the ventricular septal deficiency extends also to open towards the outlet of the right ventricle, particularly when there is greater degrees of bridging of the superior leaflet, as in the so-called Rastelli type C malformation.4 It is no coincidence that there is always significant bridging of this leaflet into the right ventricle when there is associated double outlet from the right ventricle or tetralogy of Fallot, the lesions to be considered in the next review of this supplement.5 It is the direction of opening of this part of the defect towards the outlet of the right ventricle that makes possible complete surgical repair in many hearts with double outlet from the right ventricle, and as we will discuss, this feature also underscores the need for a ventricular patch in the repair of many infants with common valve, albeit that those with the so-called Rastelli type A variant can also be repaired by suturing the superior bridging leaflet directly to the right ventricular aspect of the ventricular septum.6, 7 The close relationship between the superior bridging leaflet and the superior part of the scooped-out ventricular septum also underscores the fact that obstructive lesions of the left ventricular outflow tract are more frequent with the so-called Rastelli type A lesion, albeit not as frequent as with the ostium primum defect, when the bridging leaflets are directly adherent to the septal crest. These problems involving the outflow tract from the left ventricle, however, along with lesions such as a solitary papillary muscle supporting the leaflets of the left atrioventricular valve, should always be suspected when the left ventricle itself is hypoplastic. Indeed, in the setting of severe hypoplasia of the left ventricle, it may prove judicious to opt for functionally univentricular repair. The pathognomonic feature of the anomaly, nonetheless, is the common atrioventricular junction, and it is this feature which underscores the grossly abnormal location of the conduction tissues when compared to the normal heart (Fig. 1). Unlike the normal situation, where the atrioventricular node is centrally positioned at the apex of the triangle of Koch, the node is displaced inferiorly in the setting of the common atrioventricular junction. There is a nodal triangle which serves as the surgical landmark to the node, but its borders are markedly different from the normal triangle of Koch. In the setting of common atrioventricular junction, the borders of the triangle are the hinge of the inferior bridging leaflet and the leading edge of the atrial septum, with the coronary sinus forming the base of the triangle (Fig. 1). Irrespective of the size and location of the orifice of the coronary sinus, it is usually possible to place the patch to close the atrial component of the septal defect so that the coronary venous return drains to the right side of the heart, albeit that on occasion it may be necessary to place sutures in the leaflet tissue of the newly reconstructed left atrioventricular valve in the region of penetration of the atrioventricular bundle. This point is found at the apex of the nodal triangle. Having penetrated, there is a long non-branching bundle, which extends down the inferior rim of the scooped-out septum beneath the inferior bridging leaflet. This bundle is potentially at risk when the inferior leaflet is sutured to the septal crest, or a patch is placed to close the inferior component of the ventricular defect. The axis of conduction tissue, however, branches at the midpoint of the scooped-out septum, so that the left ventricular outflow tract, unlike the situation in the normal heart, is unrelated to the left bundle branch.
Figure 1. The cartoon shows the surgical landmarks and course of the atrioventricular conduction axis in atrioventricular septal defect with common valvar orifice. The inset shows how the axis can be avoided in the stitches placed in the inferior bridging leaflet are deviated to the left, this manoeuvre avoiding the need to cross the axis.
Why should patients with a common valve not be repaired in early infancy?
Until recently, surgeons working in most centres were reluctant to attempt repair of the common valve in the very first months of life due to the fragility of the left atrioventricular valve. It is true that the tissue of the left component of the common valve can be fragile and immature in the neonate and the premature infant. After the age of one month, nonetheless, the valve becomes more mature and stronger. It remains a potentially weak structure, but is amenable to safe suturing provided that no undue tension remains on the valvar tissue postoperatively. The myocardial tissue is probably equally, if not more, fragile but closure of the ventricular component of the septal defect can be safely accomplished in neonates using appropriate techniques.
The main advantage of seeking to achieve very early repair is the avoidance of the acquired lesions that substantially complicated this type of surgery in the past. Pulmonary vascular obstructive disease is known to occur very early in the setting of a common atrioventricular valve, not only because of the propensity for this complication in those patients with Down's syndrome, but also because of the significant left-to-right shunting which usually occurs when there is a large ventricular component to the septal defect. It is also advantageous that the introduction of nitric oxide has simplified the management of post-operative pulmonary hypertension crises, but the recent experience with early repair shows that this complication has virtually disappeared, making unnecessary the cumbersome measurements of pulmonary arterial pressure. Extubation can be achieved very rapidly in absence of residual lesions, even after a few hours in those units with proactive teams in the intensive care unit. The other worrisome acquired lesion encountered in the past was the progressive dilation of the common atrioventricular junction leading to regurgitation across the left atrioventricular valve. In this setting, repair of the left valve can become an additional procedure, which was oftentimes unsuccessful in the past, leading to reoperation and potentially to insertion of a prosthetic valve. When there are questions about the adequacy of the left ventricle to support the systemic circulation, then early repair offers a real window of opportunity to induce postoperative ventricular growth. Early repair also seems the safest option when there is associated tetralogy of Fallot, with repair being performed as soon as the cyanosis becomes concerning. Such early repair prevents undue right ventricular hypertrophy, and hence avoids right ventricular diastolic dysfunction in the postoperative course. When a common atrioventricular valve is found in the setting of isomerism of the atrial appendages and double outlet right ventricle, however, the situation is markedly different.8 In part, this is because of the frequent presence of associated totally anomalous pulmonary venous connection, but also because of the need to construct a long tunnel from the subaortic component of the septal defect to the aorta. In this setting, therefore, it is mandatory, or at least preferable, to achieve repairs in two stages.
The question then remains as to how early is too early? In our opinion, the repair can be undertaken between 2 and 4 months according to the degree of congestive cardiac failure. Repair during the first month of life does not seem necessary for most of the patients, and avoiding the neonatal period permits maturation of the leaflets of the common atrioventricular valve. Patients with moderate hypoplasia of the left ventricle, nonetheless, judged to be amenable for induction of left ventricular growth when the end-diastolic left ventricular volume is from 15 to 20 millilitres per metre squared, may benefit from repair in the first month of life.
Surgical techniques appropriate for repair during early infancy
In reality, the technique is not markedly different from that employed in the older patient. Some modifications, nonetheless, have substantially simplified the procedure in the infant with small weight. The operative procedure has four objectives. These are, first, to close the ventricular component of the septal defect without creating subaortic obstruction, second, to repair the left atrioventricular valve so that there is no postoperative regurgitation or stenosis, third to close the atrial component of the defect, and finally to repair the right-sided component of the common atrioventricular valve. The quality of the functional results is directly related to the intra-operative achievements. Obtaining an optimal intra-operative reconstruction, therefore, is essential. The advent of perioperative transoesophageal echocardiography has contributed to the improved recent results. Any significant residual lesion detected by the echocardiographic interrogation, particularly those involving the left atrioventricular valve, should be an indication for revision of the repair.
There are past and ongoing controversies concerning the optimal surgical techniques. One major step in the operation is to define the geometrical centre of the common atrioventricular valve (Fig. 2).9, 10 Injection of saline into the left ventricle causes the common valve to bulge, and this permits the geometrical centre to be readily defined, and marked by a stitch placed at this point within the zone of apposition of the superior and inferior bridging leaflets (Fig. 2). A greater controversy, perhaps, has been whether or not to close the left ventricular component of the zone of apposition between the bridging leaflets, the so-called cleft. In our eyes, this issue now seems to be resolved. There is no question but that the zone of apposition should be closed. The evidence supporting this approach has been ably marshalled by the group working in Bonn,11 who showed not only the rate of late reoperation was significantly greater when the zone of apposition was not closed, but more importantly that the late mortality was significantly more elevated when the so-called cleft was left open.
Figure 2. The geometrical centre of the common atrioventricular valve is defined by injecting saline into the ventricles.
One modification of our technique, therefore, used over the past five years, is to close the left ventricular component of the zone of apposition between the bridging leaflets as the first step of the procedure (Figs. 2–4). In our experience, such initial closure simplifies substantially the subsequent stabilization of the overall structure, and in defining clearly the size and the shape of the ventricular component of the septal defect. The zone of apposition, therefore, is sutured all the way to the insertion of the first primary cords in the left ventricle, using either 6/0 or 7/0 separate sutures (Fig. 4). In presence of a parachute left atrioventricular valve, however, the zone should be only partially closed, as also in the setting of double orifices, taking care to check the diameter of the newly constructed valve using sizing scales and a Hegar dilator.
Figure 3. The location of the geometrical centre, as identified subsequent to injection of saline, is marked by a stitch. This site corresponds to the septal extent of the left ventricular component of the zone of apposition between the bridging leaflets of the common atrioventricular valve.
Figure 4. The first step in the surgical repair is to close the entirety of the left ventricular component of the zone of apposition between the bridging leaflets, using separate sutures.
The manner of closure of the ventricular component of the defect is the other major controversy. Should we insert one patch, two patches, or no patch? The first technique used in repair, that of inserting a single patch, is still favoured in some centres.12 In our opinion, use of a solitary patch is more challenging technically, due to the difficulty of anchoring the leaflets of the newly reconstructed left valve at the appropriate height, and because of the need to divide the superior bridging leaflet when it extends significantly into the right ventricle, as in the Rastelli type C variant. We favour inserting two patches, albeit that we have recently modified this technique so that the part of the defect beneath the inferior bridging leaflet is closed by suturing the leaflet itself directly to the right ventricular aspect of the ventricular septum (Fig. 5). Along with the modification of closing the zone of apposition as the initial step of the repair, direct closure of the part of the defect related to the inferior bridging leaflet helps in defining more clearly the superior component of the defect, which is then closed using a patch (Fig. 6).
Figure 5. The inferior part of the ventricular component of the septal defect is closed by suturing the inferior bridging leaflet directly to the right ventricular aspect of the septum, using pledgetted sutures.
Figure 6. The superior portion of the ventricular component of the septal defect is closed with a patch.
Over recent years, it has been shown that patients can be repaired in satisfactory fashion by closing the entirety of the ventricular component of the defect by suturing the bridging leaflets to the right ventricular aspect of the scooped-out ventricular septum.6, 7 The appeal of this technique is its simplicity, and it is justified by the anatomic principle that it replicates the situation produced by nature in the so-called “ostium primum” defect. The anatomic arrangement, however, also indicates that there could be a risk of producing subaortic obstruction when repair if performed in this fashion. Another feature of potential concern is the tension that is applied to the valvar tissue in systole, particularly in young infants. This appealing technique, therefore, requires further follow-up before it can be considered as safe for the repair of infants aged from 2 to 4 months. Our modification, using a small patch to close the superior component of the defect, involves only a minimal technical burden, serves to prevent undue tension subsequent to the repair, and avoids any potential obstruction to the left ventricular ouflow tract.
Subsequent to the completion of these stages of the surgical repair, it is essential to check the result by injecting saline again in the ventricle. When the surgical procedure is performed early in infancy, the result is usually very satisfactory, as it is unusual for the common atrioventricular junction itself to be dilated. Should the injection of saline show that the repair is less than satisfactory, however, additional commissuroplasties are carried out at the appropriate points within the newly reconstructed left valve until a perfect result is achieved.
The atrial component of the atrioventricular septal defect can then be closed safely, seeking to leave the venous return from the coronary sinus draining to the right atrium, and taking care to place the stitches securing the patch in the leaflet tissue of the newly reconstructed left atrioventricular valve in the area of the conduction tissue (see Fig. 1). One anatomical detail of importance is to how deal with a very small atrial component of the defect, should this be encountered. Often times the leading edge of the atrial septum extends down to the level of the atrioventricular junction, decreasing the size of the atrial component. In such circumstances, the muscular bridge between the oval fossa and the atrial component of the atrioventricular septal defect must be divided to provide access to reconstruct the leaflets of the left atrioventricular valve. The muscular bridge should be reconstructed subsequent to repair of the left valve, and prior to closure of the atrial component of the defect, as it provides stability for the inferior part of the annulus of the common atrioventricular valve. The final step in the repair is to pay attention to the newly created septal component of the right atrioventricular valve. Cross-clamping both the aorta and the pulmonary trunk helps in evaluating the integrity of this valve by injection of saline into the ventricle, making further repairs as deemed appropriate.
Results
Between January of 1995, and April, 2006, 110 patients with atrioventricular septal defect and common atrioventricular valvar orifice have undergone surgical repair at the Heart Institute of Denver Children's Hospital. The surgical procedures were performed by three surgeons. In making this analysis, we excluded from consideration those patients with shunting at ventricular level but with two valvar orifices within the common atrioventricular junction. The median age of the patients at the time of repair was 4.5 months, with a range from one month to 40 months. Over the period from 2002 through 2006, the median age was 3.5 months. Almost three-quarters of the patients (72 percent) had Down's syndrome. Associated lesions included an unbalanced ventricular mass in 4 patients, parachute deformity of the left atrioventricular valve in 3, tetralogy of Fallot in 9, and double outlet right ventricle with right isomerism and totally anomalous pulmonary venous connection in 3 and 3 coractation of the aorta. Repair was performed in two stages in 11 patients, who underwent initial palliation by construction of systemic-to-pulmonary shunts in 8, repair of coarctation in 1, repair of totally anomalous pulmonary venous connection along with construction of a shunt in 1, and by banding of the pulmonary trunk in the final patient.
Prior to 2003, the routine procedure had been to insert two patches and close the zone of apposition between the left ventricular components of the bridging leaflets. Since 2003, repair has been performed in 44 patients by closing the zone of apposition as first step. During this later period, the entirety of the ventricular component of the defect was closed in 6 patients by suturing the bridging leaflets to the right ventricular aspect of the septum.
Over the entire period, we lost 4 patients during the hospital stay (mortality of 3.6 percent). Further analysis showed that 2 of 47 patients aged less than 4 months died (4.2 percent mortality), whilst 2 of 63 patients died who were older than 4 months (3.2 percent mortality). This difference was not statistically significant (Fig. 7). In 3 patients, it was necessary to insert a permanent pace maker because of surgically induced atrioventricular block, occurring twice during a replacement of the left atrioventricular valve with a prosthesis. We lost an additional 2 patients subsequent to discharge from hospital, one of these deaths being unrelated to the cardiac procedures. The overall survival at 10.4 years was 94.2 percent. There was neither mortality nor reoperation for the 3 patients with double outlet right ventricle. Freedom from reoperation at 10.4 years was 94.9 percent for patients aged greater than 4 months at the time of the reparative procedure, and 90.9 percent for the patients younger than 4 months at the initial operation. This difference is again not of statistical significance (Fig. 8). In all, we performed 5 reoperations early, and 2 at later dates. In 5 patients, it was necessary to replace the left atrioventricular valve with a prosthesis, in 2 patients because of a solitary papillary muscle supporting the leaflets of the valve. Of the early reoperations, there were 3 needed in the 6 patients in whom we closed the ventricular component of the defect without inserting a ventricular patch (p equals 0.06).
Figure 7. Survival curves for the patients undergoing surgery in Denver between 1995 and 2006.
Figure 8. The need for reoperation on the left atrioventricular valve in the patients undergoing surgery in Denver.
Conclusions
There is now no question but that repair of patients with atrioventricular septal defect in the setting of a common atrioventricular valvar orifice can safely be undertaken between the ages of 2 and 4 months. The fragility of the tissues of the left atrioventricular valve can be controlled by appropriate surgical technique. In our opinion, the safest outcomes can be achieved by inserting two patches to close the septal defects, and by taking care to close the full length of the left ventricular component of the zone of apposition between the bridging leaflets of the common atrioventricular valve. Modifications introduced in our technique have been to close the zone of apposition as the initial step in the operative procedure, and to close the inferior component of the ventricular defect by suturing the inferior bridging leaflet directly to the right ventricular aspect of the scooped-out ventricular septum, these steps serving to simplify the repair as undertaken in early infancy. In our experience, closing the entire ventricular component of the septal defect by direct suture has been associated with an increased requirement for reoperation on the reconstructed left atrioventricular valve. Even when the anatomy seems to favour such primary closure of the ventricular component of the septal defect, we believe that this appealing technique requires further investigation before it is adopted as the technique of choice for repair in early infancy.
Acknowledgements
Robert H. Anderson is supported by grants from the British Heart Foundation together with the Joseph Levy Foundation. Research at the Institute of Child Health and Great Ormond Street Hospital for Children NHS Trust benefits from R&D funding received from the NHS Executive.
