Complete AVSD Repair with Two-Patch Technique: Key Anatomy and VSD Closure

1. Introduction

Complete atrioventricular septal defect (AVSD) is a malformation of the atrioventricular junction rather than simply the combination of an atrial septal defect (ASD) and a ventricular septal defect (VSD). The lesion is characterized by a common atrioventricular junction, a five-leaflet atrioventricular valve, an ostium primum interatrial communication, and an inlet ventricular communication of variable depth. Successful repair requires ventricular and atrial septation, construction of two competent atrioventricular valves, preservation of the conduction axis, and maintenance of unobstructed ventricular outflow [1].

This chapter consolidates four operative teaching points from the surgeon's perspective: the three-dimensional anatomy, assessment of leaflet partitioning, the displaced conduction system, and geometry of the VSD patch. Although the illustrations depict a two-patch strategy, the underlying principles apply to other reconstructive techniques.

2. Surgical Anatomy of Complete AVSD

2.1. Common atrioventricular junction and bridging leaflets

Viewed through the right atrium, the common valve includes the superior and inferior bridging leaflets, the right anterosuperior leaflet, and the right and left mural leaflets. The bridging leaflets extend across the ventricular septal crest and form substantial portions of both eventual atrioventricular valve components. Their relationship to the septum, chordae, and papillary muscles determines the distribution of valve tissue and the depth of the interventricular communication [1].

The Rastelli classification describes the configuration of the superior bridging leaflet: type A has chordal attachments to the septal crest, type B has anomalous attachment to a right ventricular papillary muscle, and type C has a relatively free-floating superior bridging leaflet. This classification helps anticipate operative exposure and leaflet mobilization but does not by itself determine patch choice.

The ventricular defect lies beneath the bridging leaflets. The primum ASD lies above the common valve, with the inferior atrial septal margin deficient. The coronary sinus, inferior bridging leaflet, and posterior atrial structures establish crucial orientation when the repair approaches the conduction axis.

2.2. Unwedged aorta and left ventricular outflow

The aortic root is unwedged: it does not occupy its usual position between the right and left atrioventricular valve components. The resulting inlet–outlet disproportion produces an elongated, relatively narrow left ventricular outflow tract (LVOT), sometimes described as a gooseneck configuration [1,2].

This anatomy affects reconstruction. Excessive anterior displacement of a VSD patch, distorted bridging-leaflet attachments, or unfavorable chordal geometry can further compromise the LVOT. Preoperative echocardiography should characterize ventricular balance, the superior bridging leaflet, subaortic chordal attachments, papillary muscles, associated valve abnormalities, and any preexisting LVOT narrowing [2].

3. Leaflet Assessment Before Septation

3.1. Establishing the intended valve partition

The common atrioventricular valve must be divided functionally into right and left components without sacrificing the effective area of the left atrioventricular valve (LAVV). Following aortic and bicaval cannulation, cardioplegic arrest, and right atriotomy, the surgeon assesses leaflet mobility, chordal distribution, annular dimensions, and the ventricular septal crest. The final partition should be based on leaflet coaptation and subvalvar support, not simply on the geometric midpoint of the common annulus.

Saline testing helps predict where the superior and inferior bridging leaflets should meet on the left side. A temporary marking or approximation stitch at the planned junction can preserve this relationship while the leaflets are elevated for VSD exposure. The stitch is a reference point, not a substitute for repeated functional testing.

The intended LAVV area must remain sufficient. Partitioning too far toward the left may create a restrictive left-sided orifice; partitioning too far toward the right may compromise leaflet apposition or right-sided valve support. Additional abnormalities—including a double-orifice LAVV, deficient mural leaflet, abnormal papillary muscle position, or complex chordal attachments—may require individualized reconstruction [2,4].

3.2. Zone of apposition

The apparent “cleft” of the LAVV is more accurately a zone of apposition between the left-sided portions of the bridging leaflets. This differs morphologically from a cleft in an otherwise normal mitral valve. Closure is commonly performed to improve leaflet competence, but its extent must respect available valve area, tissue quality, and adjacent chordae.

An effective pre-patch examination identifies the likely origin of regurgitation. A central coaptation defect, a deficient zone of apposition, and regurgitation caused by chordal tethering may require different corrections. Excessively aggressive suturing can generate stenosis even when the saline test initially suggests improved competence.

4. Conduction System and the Vulnerable Septal Margin

4.1. Displaced atrioventricular node and bundle

In complete AVSD, the atrioventricular node is displaced posteriorly and inferiorly relative to its position in the normally septated heart. The penetrating atrioventricular bundle then follows an abnormal course toward the ventricular septum, passing beneath the region of the inferior bridging leaflet before continuing as the nonbranching bundle and dividing into the right and left bundle branches [1,3].

Consequently, the conventional apex of Koch's triangle cannot be used as an unmodified guide. In a morphologic study of 94 AVSD specimens, Seo and colleagues identified the position at which the inferior bridging leaflet crosses the ventricular septum as the most useful gross surgical landmark for the penetrating conduction axis [3].

The nonbranching bundle can lie close to the posterior and inferior margins of the inlet VSD. Its precise relationship to the septal crest varies. Neither a schematic line nor a constant distance from the defect can substitute for careful recognition of the abnormal anatomy.

4.2. Suture strategy

The most consequential part of VSD closure is the posteroinferior segment. Deep, full-thickness septal bites near the projected bundle may produce complete atrioventricular block. A common protective strategy is to use superficial bites on the right ventricular side of the crest, keeping the suture line away from the anticipated conduction tissue. In especially vulnerable posterior regions, a surgeon may incorporate appropriately supported right atrioventricular valve tissue rather than taking deep septal bites.

This strategy must be adapted to tissue strength and valve geometry. A superficial or valve-based stitch that avoids heart block but leaves a residual VSD or deforms the valve is not an adequate repair. Posterior leaflet anchoring, subsequent ASD patch sutures, and any revision stitches also require deliberate protection of the displaced node and penetrating bundle.

5. VSD Patch Design and Closure

5.1. What the patch must accomplish

The VSD patch is not merely a barrier between the ventricles. It creates a new septal foundation for the bridging leaflets and partly determines the geometry of both reconstructed valve orifices. Its anteroposterior length and vertical height must be considered independently.

An oversized patch may elevate or spread the bridging leaflets, stretch chordae, enlarge the functional LAVV annulus, or reduce the area of leaflet coaptation. Conversely, a patch that is excessively short or shallow can place the valve under tension, distort the zone of apposition, or leave a residual ventricular communication. Surgical descriptions have advocated modest patch undersizing to avoid annular distortion; this is a technique-dependent judgment rather than a validated universal measurement [4–6].

The educational diagram depicts an anteroposterior patch dimension of approximately 80% of the illustrated span and warns against excessive depth. These are schematic design cues, not standardized targets applicable to every complete AVSD. Patch dimensions must follow the observed septal defect, leaflet reach, chordal attachments, and intended valve level.

5.2. Operative sequence

1. Expose and define the defect. Retract the bridging leaflets gently, identify the septal crest and posteroinferior conduction-risk zone, and confirm the intended leaflet partition with the marking stitch.
2. Tailor the ventricular patch. Use suitable patch material sized to reconstruct the ventricular septum without lifting the valve or encroaching on the LVOT. Reassess the height against the bridging-leaflet hinge points.
3. Secure the septal margin. Place carefully oriented sutures along the crest, using shallower or more right-sided bites near the projected conduction axis. Preserve chordal attachments and avoid septal tissue that will not provide durable purchase.
4. Anchor the bridging leaflets. Continue the superior patch attachment through the selected leaflet tissue at the predetermined partition line. Maintain symmetric leaflet support and avoid twisting or shortening either bridging leaflet.
5. Complete the patch–leaflet–patch junction. Incorporate the lower margin of the ASD patch where appropriate, creating a stable neoseptal attachment. The atrial component is then completed with attention to the coronary sinus and conduction region.

In a conventional two-patch repair, the ventricular patch, bridging-leaflet tissue, and atrial patch form a coordinated reconstruction. Variations in suture sequence, leaflet division, and patch material are legitimate differences among established surgical techniques [4,5].

5.3. Completion assessment

After ventricular septation, inspect the left and right valve components for adequate orifice area, symmetric support, and unrestricted leaflet motion. Perform saline testing, address the LAVV zone of apposition as indicated, and complete atrial septation. When repair is finished, transesophageal or epicardial echocardiography should evaluate residual VSD or ASD, LAVV and right atrioventricular valve regurgitation or stenosis, LVOT obstruction, ventricular function, and any other residual lesions.

A significant residual VSD, important new valve regurgitation, a restrictive LAVV, or new LVOT obstruction should prompt an active decision about immediate revision rather than routine acceptance of the finding.

6. Technique Selection and Clinical Outcomes

Classic two-patch repair separates ventricular and atrial closure. Modified single-patch repair attaches the common valve to the ventricular septal crest without a separate VSD patch and is most attractive when the ventricular component is relatively shallow. In deeper defects, preserving leaflet height and avoiding excessive downward traction may favor a two-patch reconstruction [4,5].

Comparative evidence is largely observational. In an Australian cohort of 819 repairs, including 223 propensity-matched pairs, modified single-patch and double-patch techniques had similar overall and event-free survival, without significant differences in reoperation for LAVV regurgitation or LVOT obstruction [8]. Smaller comparative series have reached broadly similar conclusions, although case selection and anatomic complexity may differ [7]. Neither technique should be considered universally superior.

The broader operative risk remains clinically important. In 2,399 complete AVSD repairs entered into the Society of Thoracic Surgeons database during 2008–2011, hospital mortality was 3.0%, major complications occurred in 9.8%, and 2.7% required permanent pacemaker implantation. These are historical registry estimates, not predictions for a specific contemporary center [9].

The Pediatric Heart Network study of 120 children found no significant difference in residual defects or LAVV regurgitation according to repair type; moderate or greater LAVV regurgitation was present in 22% at six months [10]. Persistent postoperative LAVV dysfunction is therefore a central determinant of outcome. A separate 138-patient series identified moderate or greater regurgitation at discharge as a strong predictor of reoperation [11].

More recent evidence also supports nuanced surveillance. In a cohort of 220 complete AVSD repairs, 87 developed moderate LAVV regurgitation; approximately 45% of that subgroup progressed to severe regurgitation, whereas some remained stable or improved. A jet centered at the zone of apposition was associated with worsening and reoperation [12]. Reoperation may also be required for residual shunting or subaortic obstruction [13].

7. Postoperative Assessment and Follow-up

Early management should distinguish expected postoperative loading changes from residual anatomic problems. Echocardiography assesses atrioventricular valve function, shunts, ventricular systolic performance, and LVOT velocity; ECG and telemetry screen for atrioventricular conduction disturbance. Significant LAVV regurgitation may produce elevated left atrial pressure, pulmonary edema, and low cardiac output despite technically complete septal closure.

Follow-up must assess both immediate repair quality and later evolution of valve competence and LVOT geometry. New regurgitation may reflect growth-related changes, annular dilation, recurrent zone-of-apposition separation, or progressive leaflet restriction. A new subaortic gradient warrants investigation of intrinsic LVOT configuration and postoperative obstruction rather than attribution to the patch alone.

8. Key Surgical Principles

• Map the common valve before septation: preserve the intended left-sided orifice and leaflet coaptation geometry.
• Use the inferior bridging leaflet as a conduction landmark: the atrioventricular node and penetrating bundle are displaced posteroinferiorly.
• Protect the posteroinferior VSD rim: avoid deep septal bites in the projected conduction zone.
• Tailor both patch dimensions: modest undersizing may prevent leaflet distortion, but no fixed percentage is universal.
• Maintain leaflet height and chordal freedom: avoid tension, tethering, and LVOT encroachment.
• Assess the completed physiology: residual shunts, valve dysfunction, heart block, and outflow obstruction determine whether further revision is required.

References

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