Complete AVSD Repair with Two-Patch Technique #1: Anatomy from the Surgeon’s Standpoint

1. Complete AVSD Is a Malformation of the Atrioventricular Junction

Complete atrioventricular septal defect (AVSD) should not be conceptualized as the simple coexistence of a primum atrial septal defect, an inlet ventricular septal defect, and a “cleft mitral valve.” Its defining feature is a common atrioventricular junction guarded by a common atrioventricular valve. Deficiency of the normal atrioventricular septal structures produces atrial- and ventricular-level communications, an abnormal five-leaflet valve, altered ventricular inflow geometry, elongation of the left ventricular outflow tract, and displacement of the atrioventricular conduction axis.

Repair is therefore a three-dimensional reconstruction. The surgeon must create separate right and left atrioventricular orifices while closing both septal components, preserving leaflet mobility and coaptation, maintaining unobstructed ventricular inflow and left ventricular outflow, and avoiding the conduction tissue. The ventricular patch, valve partition, and atrial patch should be regarded as one integrated reconstruction.

2. The Common Atrioventricular Junction

In the normal heart, the tricuspid and mitral valves occupy separate atrioventricular junctions, with the septal tricuspid leaflet inserting more apically than the mitral valve. In complete AVSD, a single oval common junction spans both ventricles. The normal atrioventricular valve offset is absent, and the common valve crosses the plane of the ventricular septum.

The distribution of the common junction determines whether the defect is balanced or unbalanced. In a balanced defect, both ventricles receive sufficient valve tissue and inflow for biventricular repair. In an unbalanced defect, one ventricle receives a disproportionately small component of the junction, often with ventricular hypoplasia or restricted inflow. Preoperative imaging should assess ventricular size, atrioventricular valve commitment, inflow dimensions, papillary muscle arrangement, and bridging-leaflet attachment, but direct operative assessment remains essential.

3. Architecture of the Common Atrioventricular Valve

The common atrioventricular valve is usually described as having five leaflets:

1. Superior bridging leaflet
2. Inferior bridging leaflet
3. Left mural leaflet
4. Right mural leaflet
5. Right anterosuperior leaflet

The bridging leaflets cross the ventricular septum and contribute to both future atrioventricular valves. The left mural leaflet forms the lateral component of the reconstructed left valve, whereas the right mural and right anterosuperior leaflets complete the right-sided orifice.

These structures should not be interpreted as normal mitral and tricuspid valves separated by a defect. The surgically created left septal leaflet remains morphologically different from the normal anterior mitral leaflet. It is more rectangular than triangular and has a less organized subvalvar apparatus. Only 8.7% of its tendinous cords divided through three generations, compared with 55.5% in normal mitral valves, whereas 60.8% remained undivided, compared with 25% in normal valves [1]. Durable repair therefore depends on optimizing abnormal native geometry rather than attempting to recreate a normal mitral valve.

The intended partition line must preserve adequate leaflet area on both sides. It should be inferred from leaflet coaptation, ventricular commitment, chordal distribution, and papillary muscle support rather than determined only by the visible septal crest.

4. Superior and Inferior Bridging Leaflets

The bridging leaflets are central to the anatomy and the repair. Their free margins meet over the ventricular septal crest, while their chordae may insert into the septum, papillary muscles, or ventricular free walls. The superior bridging leaflet usually has the greater right ventricular extension and forms the basis of the Rastelli classification.

Rastelli Type A

The superior bridging leaflet is attached to the ventricular septal crest, usually through chordal tissue.

Rastelli Type B

The superior bridging leaflet is supported by an anomalous papillary muscle arising in the right ventricle. This morphology is uncommon.

Rastelli Type C

The superior bridging leaflet has no direct attachment to the ventricular septal crest and extends relatively freely into the right ventricle.

Rastelli type predicts exposure of the ventricular component and the relationship between the patch and the superior bridging leaflet, but it does not describe the entire operative problem. In a series of 138 patients, four associated valve morphologies were linked to a higher incidence of postoperative moderate-or-greater regurgitation or stenosis: abnormal papillary muscles with a hypoplastic mural leaflet, dense superior-leaflet chordal insertion obscuring the septal crest, a double-orifice valve, and severe disparity in the lengths of the left-sided zone of apposition [2].

The surgeon should therefore define the density, direction, and ventricular insertion of secondary chordae. Chordal anatomy determines whether the ventricular patch can be positioned without leaflet tethering, residual shunting, or valve distortion.

5. The Left-Sided Zone of Apposition

On the left side, the superior and inferior bridging leaflets meet along a zone of apposition. The term “cleft” is commonly used clinically, but this is not a cleft within a normally formed anterior mitral leaflet. It is the natural junction between two distinct bridging leaflets.

Closure generally improves central coaptation and reduces residual left atrioventricular valve regurgitation, but it must be individualized. Excessive closure can reduce effective valve area or create stenosis, particularly when the left mural leaflet is hypoplastic or papillary muscles are closely spaced. Incomplete closure may leave a persistent central regurgitant jet.

Leaflet retraction and secondary attachments to the ventricular septal crest can increase tension on the medial left-sided leaflet and flatten its coaptation surface. This may produce both regurgitation and left ventricular outflow tract obstruction after closure. Detachment of restrictive attachments with patch augmentation of the bridging leaflet has been described to restore leaflet area and reduce tension in selected anatomies [3]. This is an anatomic solution for a deficient or tethered leaflet, not a routine maneuver.

6. The Ventricular Component and the Scooped-Out Septum

The ventricular communication is commonly called an inlet ventricular septal defect, but it is better understood as deficiency of the inlet ventricular septum beneath the common valve. Its superior boundary is formed by the bridging leaflets and chordal attachments, whereas its inferior boundary is the muscular septal crest.

A characteristic feature is the scooped-out septum. The depth of the scoop determines the distance between the muscular septum and the common valve and therefore the required ventricular patch height. A patch placed too low may leave a residual shunt. A patch that is too high, bulky, or taut may elevate the bridging leaflets, impair coaptation, or project into the left ventricular outflow tract.

The patch must also pass on the correct side of crossing chordae. Chordal tunnels can hide portions of the defect, and failure to identify them may cause residual communication or leaflet entrapment. The goal is to reconstruct the missing inlet septum while preserving the native relationship between the common valve and both ventricles.

7. The Primum Atrial Component

The primum atrial communication lies immediately above the common atrioventricular valve. Its inferior margin is deficient because the lower atrial septal structures have not fused with the atrioventricular junction. The posteroinferior region lies near the coronary sinus and displaced atrioventricular node.

The atrial patch connects the valve-partition line to the native atrial septal rim. The coronary sinus may be left on the right atrial side or routed to the left atrium, depending on the chosen suture line. This must be intentional because an imprecise posteroinferior patch line can distort the valve, obstruct the coronary sinus, leave residual interatrial shunting, or endanger the conduction axis.

8. The Unwedged Aortic Root and Left Ventricular Outflow Tract

In the normal heart, the aortic root is wedged between the separate atrioventricular junctions. In complete AVSD, the common junction prevents normal wedging, and the aortic root lies more anteriorly and superiorly. This produces the unwedged aortic valve and elongates the distance from the left ventricular inlet to the aortic root.

The left ventricular outflow tract may therefore have a long, narrow “gooseneck” configuration. Obstruction may result from superior bridging-leaflet tissue, restrictive chordae, accessory valve tissue, abnormal papillary muscle position, septal hypertrophy, or ventricular patch geometry.

The outflow tract should be inspected before and after reconstruction. Tightening the zone of apposition in the presence of restrictive secondary attachments may increase leaflet tension and worsen subaortic narrowing [3]. Valve competence must therefore be balanced against preservation of an adequate outflow tract.

9. Displaced Atrioventricular Node and Conduction Axis

The atrioventricular node lies posteroinferiorly, near the coronary sinus ostium and inferior common atrioventricular junction, rather than at the usual apex of the normal triangle of Koch. The penetrating bundle then courses anteriorly along the inferior margin of the ventricular component.

Deep sutures near the coronary sinus, inferior junction, or lower rim of the ventricular patch may produce complete atrioventricular block. The conduction tissue should be regarded as an extended danger zone rather than a single point. The posteroinferior atrial patch line should remain superficial, and inferior ventricular sutures should avoid unnecessary deep septal bites.

10. High-Risk Anatomic Variants

The operative assessment should systematically identify:

• Hypoplastic left mural leaflet
• Abnormal or closely spaced papillary muscles
• Dense superior bridging-leaflet chordal insertion
• Double-orifice left atrioventricular valve
• Marked disparity in the zone of apposition
• Straddling or overriding chordae
• Accessory valve tissue
• Unbalanced ventricular commitment
• Intrinsic left ventricular outflow tract narrowing

These variants directly influence patch placement, valve partition, and the feasibility of complete closure of the zone of apposition. The morphologies described by Ando and Takahashi interfered with ventricular patch positioning and accurate leaflet approximation and remained associated with postoperative dysfunction despite individualized repair [2].

A small mural leaflet or restricted papillary muscle arrangement limits the available left-sided valve area. Dense chordae can obscure the septal crest and force the patch away from the ideal plane. A double-orifice valve requires preservation of both functional openings. Recognition of these patterns before the final suture line is essential.

11. Translating the Anatomy into a Two-Patch Repair

The two-patch technique reconstructs the defect at three interconnected levels:

1. The ventricular patch closes the communication beneath the common valve.
2. The common valve is partitioned into right and left components.
3. The atrial patch closes the primum communication above the reconstructed valve.

Before completing the repair, the surgeon should confirm that the partition preserves adequate valve area on both sides, chordae are not trapped or displaced, the left-sided zone of apposition closes without stenosis, the right-sided orifice remains adequate, the ventricular patch does not obstruct the left ventricular outflow tract, the coronary sinus has been routed intentionally, and the inferior suture lines avoid the conduction axis.

Clinical series support the reproducibility of the two-patch strategy when combined with careful valve reconstruction. In 100 consecutive patients undergoing two-patch repair with complete closure of the left-sided zone of apposition, freedom from reoperation for left atrioventricular valve dysfunction was 94% at 10 years, and freedom from reoperation for left ventricular outflow tract obstruction was 99% [4]. In a contemporary series of 138 complete AVSD repairs, 92% used a two-patch technique; moderate-or-greater left atrioventricular valve regurgitation at discharge was the strongest predictor of later reoperation, with a hazard ratio of 10.85 [5].

Longer-term data similarly identify residual valve dysfunction as the principal determinant of reintervention. In a 29-year experience including 508 AVSD repairs, left atrioventricular valve regurgitation was the main indication for reoperation, and moderate or severe regurgitation at discharge predicted reoperation [6]. The immediate post-repair valve result is therefore a major predictor of long-term durability.

When important regurgitation develops after primary repair, valve re-repair should be pursued whenever feasible. Patch augmentation may be useful when leaflet deficiency or tethering prevents durable primary closure; in one reoperation series, patch augmentation was associated with greater repair durability than repeat primary closure [7]. Valve replacement in young children carries major burdens, including anticoagulation, prosthesis–patient mismatch, ventricular dysfunction, and future reoperation.

Key Surgical Perspective

Complete AVSD is a disorder of the entire atrioventricular junction. The primum atrial communication, ventricular component, bridging leaflets, abnormal subvalvar apparatus, unwedged aortic root, elongated left ventricular outflow tract, and displaced conduction axis are linked expressions of the same developmental malformation.

The objective of the two-patch technique is not simply to close two septal defects. It is to create two competent, adequately sized atrioventricular valves while reconstructing the inlet septum, preserving ventricular inflow and outflow, and protecting the conduction axis. Durable repair depends on recognizing high-risk leaflet and chordal variants before they are converted into postoperative regurgitation, stenosis, residual shunting, outflow obstruction, or heart block.

References

[1] Kanani M, Elliott M, Cook A, Juraszek AL, Devine W, Anderson RH. Late incompetence of the left atrioventricular valve after repair of atrioventricular septal defects: the morphologic perspective. J Thorac Cardiovasc Surg. 2006;132(3):640-646.e3.

[2] Ando M, Takahashi Y. Variations of atrioventricular septal defects predisposing to regurgitation and stenosis. Ann Thorac Surg. 2010;90(2):614-621.

[3] Baird CW, Kreutzer C, Sanders SP, Borisuk MJ, del Nido PJ. Augmentation of bridging leaflets in repair of atrioventricular canal defects. Ann Thorac Surg. 2017;104(1):e101-e103.

[4] Bakhtiary F, Takács J, Cho MY, Rázek V, Dähnert I, Doenst T, Walther T, Borger MA, Mohr FW, Kostelka M. Long-term results after repair of complete atrioventricular septal defect with two-patch technique. Ann Thorac Surg. 2010;89(4):1239-1243.

[5] Xie O, Brizard CP, d’Udekem Y, Galati JC, Kelly A, Yong MS, Weintraub RG, Konstantinov IE. Outcomes of repair of complete atrioventricular septal defect in the current era. Eur J Cardiothorac Surg. 2014;45(4):610-617.

[6] Schleiger A, Miera O, Peters B, Schmitt KRL, Kramer P, Buracionok J, Murin P, Cho MY, Photiadis J, Berger F, Ovroutski S. Long-term results after surgical repair of atrioventricular septal defect. Interact Cardiovasc Thorac Surg. 2019;28(5):789-796.

[7] Malhotra SP, Lacour-Gayet F, Mitchell MB, Clarke DR, Dines ML, Campbell DN. Reoperation for left atrioventricular valve regurgitation after atrioventricular septal defect repair. Ann Thorac Surg. 2008;86(1):147-152.