1. Operative Concept
Complete atrioventricular septal defect (AVSD) is characterized by deficiency of the atrioventricular septal structures, a common atrioventricular junction, a primum atrial septal defect, an inlet ventricular septal defect (VSD), and a common atrioventricular valve composed of superior and inferior bridging leaflets and right- and left-sided mural leaflets. Surgical repair must simultaneously accomplish ventricular septation, atrial septation, and reconstruction of competent right and left atrioventricular valves while preserving the atrioventricular conduction axis.[1]
In the classic two-patch repair, the ventricular and atrial components are closed separately. A VSD patch reconstructs the ventricular septum and establishes the ventricular-level attachment of the bridging leaflets; a second patch closes the primum ASD. The supplied operative sequence emphasizes a particularly useful technical concept: VSD patch → bridging leaflet → ASD patch, followed by left atrioventricular valve (LAVV) zone-of-apposition closure and completion of atrial septation. Complete AVSD Repair with Two-P…
The two-patch technique is not the only acceptable repair. Modified single-patch and other individualized approaches can achieve comparable results in appropriately selected anatomy. The principal objective is therefore not adherence to a particular patch strategy, but creation of competent atrioventricular valves, unobstructed ventricular outflow tracts, complete septation, and intact conduction.[1]
2. Anatomy From the Surgeon’s Standpoint
After right atriotomy, the surgeon views the common atrioventricular valve from above. The major structures requiring identification are the:
- Superior bridging leaflet
- Inferior bridging leaflet
- Right mural leaflet
- Left mural leaflet
- Primum ASD
- Inlet VSD beneath the bridging leaflets
- Coronary sinus
- Ventricular septal crest
- Displaced atrioventricular conduction axis
The superior and inferior bridging leaflets span the ventricular septal defect to varying degrees according to morphology. Their relationship to the septum, chordal attachments, papillary muscles, and ventricular cavities determines both the geometry of the VSD patch and the feasibility of alternative repair strategies.
A fundamental feature of AVSD is the altered location of the conduction system. Because normal atrioventricular septation is absent, the atrioventricular node is displaced posteriorly and inferiorly, and the nonbranching atrioventricular bundle follows an elongated course before reaching the ventricular septum.[2,3] The usual triangle of Koch therefore cannot be applied as though the heart had normal septal anatomy.
The inferior bridging leaflet where it crosses the ventricular septum is an important operative landmark for predicting the region where the conduction axis penetrates.[2] Appreciation of this relationship is particularly important during the posteroinferior portion of VSD closure and subsequent ASD patch placement.
3. Initial Valve Assessment and Marking Stitch
Before septal reconstruction, the common atrioventricular valve should be assessed carefully. Saline testing and direct inspection help define the intended left and right atrioventricular valve orifices, the coaptation surfaces of the bridging leaflets, the LAVV zone of apposition, and any additional abnormalities such as a double-orifice valve, deficient leaflet tissue, abnormal chordal attachment, or mural leaflet hypoplasia.
A marking stitch can be placed at the intended point of coaptation between the superior and inferior bridging leaflets. This provides a reproducible reference for dividing the common valve into appropriate left- and right-sided components and prevents loss of orientation once the leaflets are elevated to expose the VSD.
This step is more than an anatomic marker. The final valve geometry depends on establishing the correct relationship among the VSD patch, bridging leaflets, and LAVV zone of apposition. Incorrect leaflet positioning can create residual regurgitation even when the septal defects themselves are completely closed.
4. Protecting the Conduction System
The conduction axis should be conceptually mapped before VSD suturing begins. In complete AVSD, the atrioventricular node is situated posteriorly, near the inferior aspect of the atrial septal deficiency, with an elongated nonbranching bundle extending toward the ventricular septum.[2,3]
The most hazardous area is the posteroinferior ventricular septal margin, where deeply placed sutures may injure the penetrating or nonbranching bundle. Sutures in this region should therefore respect the expected conduction pathway rather than simply following the apparent edge of the defect.
The supplied operative illustration appropriately separates the displaced AV node, penetrating bundle, nonbranching bundle, and branching bundle, underscoring that protection of conduction tissue must be incorporated into the geometry of the repair rather than considered only after septation. Complete AVSD Repair with Two-P…
Modern anatomic studies have reinforced that the conduction axis in AVSD may show clinically relevant variation, further supporting an anatomy-based rather than formulaic suture strategy.[3]
5. VSD Patch Closure
The ventricular component is addressed first. The VSD patch is tailored to reproduce the intended ventricular septal plane without distorting the atrioventricular valve or narrowing either ventricular outflow tract.
The patch is typically secured along the ventricular septal crest from one side of the defect to the other. Particular attention is required posteriorly because of the conduction axis. Anteriorly, the patch must remain appropriately positioned relative to the left ventricular outflow tract.
Patch geometry is critical. An excessively large patch can displace the bridging leaflets superiorly, distort chordal geometry, enlarge the reconstructed LAVV annulus, and promote regurgitation. Some surgical descriptions therefore advocate slight undersizing of the ventricular patch so that the valve remains at its physiologic level rather than being elevated above the ventricular septum.[6]
Conversely, excessive reduction in patch height can place tension on the bridging leaflets or alter subvalvar geometry. The required dimensions depend on the depth of the ventricular component, Rastelli morphology, chordal attachments, and ventricular balance. A deep inlet defect generally favors patch reconstruction rather than direct approximation of the leaflets to the septal crest.
The classic two-patch technique has demonstrated durable results across several surgical series.[1,4] Contemporary modifications may divide portions of the bridging leaflets to facilitate patch placement in selected anatomy, but such maneuvers are technique-dependent rather than universally required.[5]
6. Bridging Leaflet–Patch–ASD Patch Assembly
Once the ventricular margin of the VSD patch has been secured, the repair transitions from ventricular septation to atrioventricular valve reconstruction.
The operative sequence is:
- VSD patch
- Bridging leaflet tissue
- ASD patch
The sutures emerging through the superior aspect of the VSD patch are passed through the corresponding bridging leaflet tissue at the predetermined line separating the reconstructed left and right atrioventricular valves. They are then incorporated into the inferior margin of the ASD patch.
This effectively creates a three-layer junction in which the bridging leaflets are anchored between the ventricular and atrial septal reconstructions. The sequence is clearly illustrated in the supplied material. Complete AVSD Repair with Two-P…
The surgeon must maintain the orientation established by the marking stitch. The objective is not simply to close the VSD but to establish a stable neoseptal attachment for both reconstructed atrioventricular valves.
At this stage, distortion can occur if leaflet bites are asymmetric, if the VSD patch is oversized, or if the bridging leaflets are pulled excessively toward one ventricle. Saline testing before proceeding further can identify malcoaptation while the repair remains readily adjustable.
7. Left Atrioventricular Valve Zone-of-Apposition Closure
After ventricular septation and leaflet fixation, attention turns to the LAVV. The line between the left-sided portions of the superior and inferior bridging leaflets is often termed the “cleft,” although zone of apposition more accurately reflects AVSD morphology.
Approximation of this zone is commonly performed with interrupted sutures from the base toward the free leaflet edge. Historical and contemporary experience supports closure when this can be achieved without producing stenosis.[1,4,6]
The repair should not be performed mechanically to the leaflet tips in every patient. The appropriate extent depends on:
- LAVV orifice size
- Leaflet tissue availability
- Mural leaflet dimensions
- Papillary muscle configuration
- Double-orifice or parachute morphology
- Resulting coaptation
- Risk of iatrogenic stenosis
Bando and colleagues reported favorable intermediate- to long-term valve function with routine approximation of the zone of apposition when anatomically feasible.[7] Conversely, inadequate leaflet tissue or abnormal LAVV morphology may justify partial rather than complete closure.
Repeated saline testing is useful. The objective is a broad and symmetric coaptation surface without restriction of leaflet opening.
8. ASD Patch Closure
The primum ASD is then closed using the atrial patch, commonly autologous pericardium or another suitable patch material. The inferior portion of the ASD patch has already been incorporated into the VSD patch–leaflet junction.
The remaining patch is sutured around the atrial septal defect. Special care is again required near the posterior-inferior margin because of the displaced AV node and conduction axis.
The relationship of the coronary sinus to the patch must be considered. Depending on local anatomy and the chosen suture line, the coronary sinus is usually maintained on the right atrial side. In unusual anatomy with markedly deficient tissue near the coronary sinus and conduction axis, alternative routing may be considered.[6]
The completed reconstruction should restore atrial septation without distorting the atrioventricular valve annuli or systemic and pulmonary venous pathways.
9. Completion Assessment
Before terminating cardiopulmonary bypass, the repair should be assessed systematically.
Valve function is central. The LAVV should demonstrate an adequate orifice, satisfactory coaptation, and no more than trivial or mild regurgitation whenever achievable. The right atrioventricular valve should also be evaluated because its septal component has been reconstructed along the same patch-leaflet junction.
Transesophageal echocardiography should assess:
- Residual VSD
- Residual ASD
- LAVV regurgitation
- Right AV valve regurgitation
- LAVV stenosis
- LVOT obstruction
- RVOT obstruction
- Biventricular function
Significant residual LAVV regurgitation deserves particular attention. In the Australian multicenter experience of 829 CAVSD repairs, moderate residual LAVV regurgitation on postoperative echocardiography was independently associated with subsequent reoperation.[8] A repairable mechanism identified intraoperatively should therefore prompt consideration of immediate revision rather than reliance on spontaneous improvement.
10. Two-Patch Versus Modified Single-Patch Repair
The major conceptual difference between the classic two-patch and modified single-patch techniques lies in management of the ventricular component. In the modified single-patch repair, the bridging leaflets are approximated directly to the ventricular septal crest, eliminating the separate VSD patch.
Comparative studies have not demonstrated a clear overall clinical superiority of one technique. Backer and colleagues reported satisfactory results with both approaches.[9] A meta-analysis including 10 comparative studies and 724 patients found shorter cardiopulmonary bypass and cross-clamp times with modified single-patch repair but no significant differences in the major postoperative outcomes evaluated.[10]
The anatomy should therefore determine the repair. A relatively shallow ventricular component may be favorable for a modified single-patch approach, whereas a deep VSD, complex chordal architecture, or anatomy in which direct leaflet-to-septum approximation would substantially displace the valve may favor two-patch reconstruction.[6,10]
11. Outcomes and Long-Term Surveillance
Contemporary complete AVSD repair has low operative mortality in experienced congenital centers, but late morbidity remains dominated by LAVV dysfunction, residual or recurrent septal lesions, LVOT obstruction, and less commonly conduction abnormalities.[8,11]
In the Australian four-center cohort, operative mortality was 3.3%, with survival of 91.7%, 90.7%, and 88.7% at 10, 15, and 20 years, respectively. Freedom from reoperation was 82.7%, 81.1%, and 77.0% at the same intervals.[8] These data emphasize that successful initial repair does not eliminate the need for lifelong surveillance.
LAVV regurgitation remains the most frequent indication for reoperation following AVSD repair.[11] Consequently, the quality of the initial valve reconstruction—appropriate VSD patch dimensions, accurate bridging leaflet alignment, individualized zone-of-apposition closure, and avoidance of annular or subvalvar distortion—is a major determinant of long-term durability.
Key Technical Principles
- Define valve geometry before patch placement. Use direct inspection and marking sutures to establish the intended leaflet coaptation line.
- Know the displaced conduction axis. The posteroinferior septal margin requires particular caution.
- Tailor the VSD patch precisely. Avoid excessive patch height or width that distorts the reconstructed valve.
- Preserve the sequence: VSD patch → leaflet → ASD patch. This creates the central neoseptal attachment of the reconstructed AV valves.
- Treat LAVV competence as a primary endpoint. Zone-of-apposition closure should improve coaptation without creating stenosis.
- Assess the entire reconstructed geometry before leaving the operating room. Residual AV valve regurgitation, septal shunts, or outflow obstruction should be evaluated for immediate revision.
- Select the repair according to anatomy. Two-patch and modified single-patch approaches are complementary techniques rather than universally competing strategies.
References
- Mavroudis C, Backer CL. The two-patch technique for complete atrioventricular canal. Semin Thorac Cardiovasc Surg. 1997. PMID: 9109223.
- Seo JW, Zuberbuhler JR, Ho SY, Anderson RH. Surgical significance of morphological variations in the atrial septum in atrioventricular septal defect for determination of the site of penetration of the atrioventricular conduction axis. J Card Surg. 1992. doi:10.1111/j.1540-8191.1992.tb01022.x. PMID: 1482825.
- Yoshitake S, Kaneko Y, Morita K, et al. Reassessment of the location of the conduction system in atrioventricular septal defect using phase-contrast computed tomography. Semin Thorac Cardiovasc Surg. 2020. doi:10.1053/j.semtcvs.2020.03.011. PMID: 32450213.
- Alexi-Meskishvili V, Ishino K, Dähnert I, et al. Correction of complete atrioventricular septal defects with the double-patch technique and cleft closure. Ann Thorac Surg. 1996. doi:10.1016/0003-4975(96)00319-0. PMID: 8694616.
- Pfister R, Myers P, Hosseinpour AR, et al. Complete atrioventricular septal defect: modified 2-patch technique. Multimed Man Cardiothorac Surg. 2022. doi:10.1510/mmcts.2022.103. PMID: 36546680.
- Mosca RS, Quaegebeur JM. The modified single patch technique. Ann Pediatr Cardiol. 2009. doi:10.4103/0974-2069.52809. PMID: 20300270.
- Bando K, Turrentine MW, Sun K, et al. Surgical management of complete atrioventricular septal defects: a twenty-year experience. J Thorac Cardiovasc Surg. 1995. PMID: 7475207.
- Fong LS, Betts K, Ayer J, et al. Predictors of reoperation and mortality after complete atrioventricular septal defect repair. Eur J Cardiothorac Surg. 2021. doi:10.1093/ejcts/ezab221. PMID: 34002204.
- Backer CL, Stewart RD, Bailliard F, Kelle AM, Webb CL, Mavroudis C. Complete atrioventricular canal: comparison of modified single-patch technique with two-patch technique. Ann Thorac Surg. 2007. doi:10.1016/j.athoracsur.2007.04.129. PMID: 18036931.
- Li D, Fan Q, Iwase T, et al. Modified single-patch versus two-patch repair for complete atrioventricular septal defect: a meta-analysis. World J Pediatr Congenit Heart Surg. 2019. doi:10.1177/2150135119859882. PMID: 31496417.
- 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. doi:10.1016/j.athoracsur.2008.03.040. PMID: 18573414.