Complete AVSD Repair with Two-Patch Technique #2: Leaflet Assessment Before Septation

1. Operative Objective

Repair of complete atrioventricular septal defect requires more than closure of the atrial and ventricular septal components. The common atrioventricular valve must be transformed into competent right and left atrioventricular valves while preserving leaflet mobility, chordal function, adequate inflow area, and an unobstructed left ventricular outflow tract. The surgeon therefore determines not only where the septal patches will be placed, but also how the superior and inferior bridging leaflets will be allocated between the two ventricles.

A temporary marking stitch provides a reversible simulation of the intended line of septation. It helps define the relationship between the future right and left valve components, demonstrates the anticipated left atrioventricular valve coaptation line, and permits reassessment before the bridging leaflets are committed to the patches. The central objective is to preserve sufficient left-sided leaflet tissue and valve area without compromising the right-sided valve.

This assessment should be completed before definitive leaflet-to-patch sutures are placed. Once the bridging leaflets have been incorporated between the two patches, their effective height, orientation, and distribution become substantially less adjustable.

2. Functional Anatomy of the Common Atrioventricular Valve

The common atrioventricular junction is guarded by a single valve complex rather than separate tricuspid and mitral valves. The valve generally contains five major components:

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

The superior and inferior bridging leaflets cross the ventricular septum and contribute to both reconstructed valve orifices. The future left atrioventricular valve is formed by the leftward portions of these leaflets and the left mural leaflet. The future right atrioventricular valve consists of the rightward bridging-leaflet portions together with the right anterosuperior and right inferior leaflets.

This anatomy cannot be reduced to a geometric division through the center of the common annulus. Rastelli classification describes superior bridging-leaflet attachment, but the operative geometry also depends on the inferior bridging leaflet, mural leaflet, papillary muscles, and subvalvar apparatus. In one morphologic study, patients with Rastelli type C anatomy and an undivided inferior bridging leaflet showed less progression of valve regurgitation than those with Rastelli type A anatomy or a divided inferior leaflet, illustrating that intrinsic leaflet configuration influences valve competence [1].

3. The Reconstructed Left Valve Is Not a Normal Mitral Valve

The left atrioventricular valve created during AVSD repair should not be conceptualized as a normal mitral valve. Its septal component is surgically constructed from bridging-leaflet tissue, and its chordal architecture remains intrinsically abnormal.

Morphologic comparison has shown that the reconstructed septal leaflet is relatively rectangular, whereas the aortic leaflet of a normal mitral valve is triangular. The chordal arrangement is also deficient and disorganized. Only 8.7% of chordae in repaired AVSD divided through three generations, compared with 55.5% in normal mitral valves, while 60.8% remained undivided, compared with 25% in normal valves [2]. Surgery can restore coaptation and septal continuity, but it cannot normalize the underlying leaflet and subvalvar architecture.

The practical implication is that the repair should preserve native mobility rather than force the valve into a visually “normal” configuration. Excessive tension, over-closure of the zone of apposition, or rigid fixation to the septal patches may create immediate competence at the cost of restricted motion and reduced durability.

4. Systematic Inspection Before Septation

After right atriotomy and exposure, the surgeon should inspect the valve before placing definitive patch sutures. Assessment should include:

• Relative right and left ventricular size
• Superior and inferior bridging-leaflet morphology
• Width and mobility of the left mural leaflet
• Length and depth of the left-sided zone of apposition
• Chordal attachments to the ventricular septum
• Papillary muscle position and separation
• Accessory or crossing chordae
• Double-orifice anatomy
• Leaflet deficiency, dysplasia, or asymmetry
• Relationship to the ventricular septal crest and left ventricular outflow tract

Saline testing helps identify the natural closing pattern, but it must be interpreted together with leaflet tension and orifice area. Static inspection alone may underestimate chordal tethering, prolapse, or mural-leaflet deficiency.

Specific malformations are associated with increased postoperative regurgitation or stenosis. In a two-patch repair series, four important patterns were abnormal papillary muscles with a hypoplastic mural leaflet, dense superior bridging-leaflet chordal insertion obscuring the septal crest, a double-orifice valve, and marked disparity in the lengths of the superior and inferior zones of apposition [3]. These variants can complicate ventricular patch positioning and accurate leaflet approximation and should be recognized before septation.

5. Purpose and Interpretation of the Marking Stitch

The marking stitch is a temporary reference placed at the proposed boundary between the future right and left valve components. It should not be positioned according to the visual midpoint alone. Its location must reflect the functional requirements of both reconstructed valves.

With gentle traction on the stitch and saline filling of the left ventricle, the surgeon can assess:

• The amount of bridging-leaflet tissue assigned to the left side
• The anticipated line and height of left-sided coaptation
• The contribution of the left mural leaflet
• The width of the residual left atrioventricular valve orifice
• Bridging-leaflet mobility
• The adequacy of the right-sided leaflet allocation
• The relationship to chordal attachments and the outflow tract

The stitch remains provisional. If the left-sided orifice appears restrictive or coaptation is inadequate, the proposed partition should be revised. The surgeon should not accept a small valve merely because saline testing produces little regurgitation.

Published outcome studies have not evaluated the marking stitch as an isolated intervention. Its value is therefore best understood as an operative simulation that makes the consequences of leaflet allocation visible before reconstruction becomes irreversible.

6. Preserving Adequate Left Atrioventricular Valve Area

The common valve appears generous before septation because the entire junction is open. The effective left-sided orifice may become substantially smaller after the bridging leaflets are attached to the ventricular patch and incorporated into the atrial patch. Iatrogenic narrowing can result from:

• Partitioning too far toward the left ventricle
• Assigning insufficient bridging-leaflet tissue to the left side
• Taking excessively deep bites into the leaflet
• Positioning the ventricular patch too high
• Incorporating or tethering chordae
• Excessive closure of the zone of apposition
• Distorting a small left mural leaflet
• Aggressive annuloplasty or commissural sutures

The left valve should open without a funnel-shaped configuration or visible tethering. Assessment should account for ventricular balance, mural-leaflet dimensions, patient size, and anticipated growth.

Postoperative imaging confirms that AVSD repair changes valve geometry rather than merely closing a defect. The left atrioventricular valve annulus may become larger and more circular after repair, and this remodeling may contribute to central regurgitation [4]. The initial operation should therefore establish broad coaptation and preserved mobility rather than depend on a narrow line of edge contact.

7. Assessment and Closure of the Zone of Apposition

The junction between the superior and inferior bridging leaflets is commonly called the “cleft,” although anatomically it is the zone of apposition between two distinct leaflet components. Closure is often required to improve competence, but its extent should be individualized.

The surgeon should evaluate leaflet-edge quality, relative leaflet height, the mechanism of regurgitation, residual valve area, and papillary muscle or chordal constraints. Sutures should approximate the edges without rolling, shortening, or excessive tension. Each additional suture should be followed by reassessment of competence and opening area.

Complete closure is appropriate when the leaflets are well developed and an adequate orifice remains. Partial closure may be necessary when the valve is small, the mural leaflet is hypoplastic, or full closure would produce stenosis. Large outcome series support closure when anatomy permits: cleft closure has been identified as an independent predictor of improved survival and reduced reoperation burden, whereas double-orifice left atrioventricular valve anatomy is associated with less favorable outcomes [5]. These data support complete closure as the default strategy in suitable anatomy but do not justify a restrictive repair.

8. Fixing the Geometry with the Two Patches

The ventricular septal defect patch is positioned beneath the bridging leaflets. The leaflet-to-patch suture line converts the provisional marking-stitch geometry into a fixed reconstruction. The patch should support the valve without acting as a rigid splint.

Excessive superior displacement of the bridging leaflets can reduce opening area and alter coaptation. Deep leaflet bites may shorten functional leaflet height, whereas uneven bites may create an irregular attachment line. Important chordae must remain free of the patch and sutures. Patch bulk or protrusion into the left ventricular outflow tract should be avoided, particularly because AVSD already produces an elongated and potentially narrow outflow geometry.

The atrial septal defect patch is subsequently attached to the superior surface of the bridging leaflets and atrial septal margins. Excessive traction from this patch can elevate or rotate the leaflets, shift the coaptation line, or narrow the left-sided orifice. Both patches should therefore support the reconstructed valve in the neutral configuration predicted by the marking stitch.

Before completing the atrial patch, the surgeon should reassess leaflet mobility, left-sided opening area, and the relationship between the partition and the subvalvar apparatus. Any discrepancy is easier to correct before exposure is limited.

9. Challenging Morphology and Individualized Reconstruction

Abnormal papillary muscles, a hypoplastic mural leaflet, dense septal chordae, double-orifice anatomy, and major disparity between the bridging-leaflet edges may prevent a standard repair from producing a symmetric valve [3]. The surgeon should identify the dominant mechanism of dysfunction rather than rely on routine closure alone.

A small mural leaflet increases dependence on bridging-leaflet tissue for both valve area and coaptation. Dense superior bridging-leaflet chordae may restrict exposure and complicate ventricular patch placement. Double-orifice anatomy requires determination of whether both orifices provide useful inflow or whether one is obstructive or incompetent. Abnormal papillary muscle position may limit leaflet excursion even when the edges appear well approximated.

Not all abnormalities are completely correctable. The operative goal is the best durable balance among competence, inflow area, leaflet mobility, and outflow tract preservation. Additional reconstructive maneuvers should address a defined mechanism and should not introduce excessive tension.

10. Final Intraoperative Assessment

After septation and valve reconstruction, the repair should be reassessed by direct saline testing and transesophageal echocardiography. Evaluation should include:

• Degree and mechanism of left atrioventricular valve regurgitation
• Left atrioventricular inflow gradient
• Right atrioventricular valve competence and inflow
• Residual atrial or ventricular shunting
• Left ventricular outflow tract geometry and gradient
• Ventricular function
• Leaflet and chordal mobility
• Patch position

Residual regurgitation should be analyzed mechanistically. A central jet through the zone of apposition may respond to an additional closure suture. An eccentric jet may instead reflect prolapse, tethering, mural-leaflet deficiency, or papillary muscle abnormality. Revision should not be based on jet severity alone; valve area and mobility must be reassessed after every additional maneuver.

Long-term results demonstrate that a disciplined two-patch repair with complete closure of the zone of apposition can provide durable function. In a series of 100 patients, left atrioventricular valve regurgitation was absent or trivial in 80%, and actuarial freedom from reoperation for left valve dysfunction was 94% at 10 years [6]. Persistent late regurgitation remains possible because the reconstructed valve retains abnormal leaflet and chordal architecture.

11. Key Surgical Principles

• Assess the entire common valve before placing definitive septal patch sutures.
• Treat the right-left partition as a functional allocation of leaflet tissue, not a geometric midpoint.
• Use a temporary marking stitch to simulate the final valve relationship before septation.
• Define the anticipated left atrioventricular valve coaptation line and confirm broad tissue contact.
• Preserve adequate left-sided valve area; do not exchange stenosis for apparent competence.
• Recognize abnormal papillary muscles, mural-leaflet hypoplasia, dense septal chordae, double-orifice anatomy, and leaflet-edge disparity before patch placement.
• Close the zone of apposition completely when anatomy permits, but individualize the repair when closure would restrict the valve.
• Coordinate leaflet allocation, ventricular patch contour, atrial patch tension, and left ventricular outflow tract geometry.
• Reassess competence, inflow gradients, chordal mobility, residual shunting, and outflow obstruction after reconstruction.
• Accept that repair restores function but does not convert the left atrioventricular valve into a normal mitral valve.

References

[1] Suzuki K, Tatsuno K, Kikuchi T, Mimori S. Predisposing factors of valve regurgitation in complete atrioventricular septal defect. J Am Coll Cardiol. 1998. doi:10.1016/S0735-1097(98)00383-0.

[2] 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. doi:10.1016/j.jtcvs.2006.01.063.

[3] Ando M, Takahashi Y. Variations of atrioventricular septal defects predisposing to regurgitation and stenosis. Ann Thorac Surg. 2010. doi:10.1016/j.athoracsur.2010.03.098.

[4] Kaza E, Marx G, Kaza AK, Colan SD, Loyola H, Perrin DP, del Nido PJ. Changes in left atrioventricular valve geometry after surgical repair of complete atrioventricular canal. J Thorac Cardiovasc Surg. 2012. doi:10.1016/j.jtcvs.2011.06.044.

[5] Najm HK, Coles JG, Endo M, Stephens D, Rebeyka I, Williams WG, Freedom RM. Complete atrioventricular septal defects: results of repair, risk factors, and freedom from reoperation. Circulation. 1997.

[6] 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. doi:10.1016/j.athoracsur.2009.11.017.