VSD Patch Closure for Perimembranous VSD with “Outlet” Extension

Perimembranous ventricular septal defects (VSDs) occupy the region normally closed by the membranous septum and lie in fibrous continuity with the tricuspid and aortic valves.[1,2]PubMed+1

When the defect extends cranially into the outlet septum, the superior rim becomes shallow and abuts the right coronary cusp and right ventricular outflow tract (RVOT). This outlet extension creates a crowded relationship between the patch, the aortic leaflet, and the RVOT, and it is the key anatomic feature that shapes the surgical strategy.[1]PubMed

Exposure and definition of the defect

After cardioplegic arrest, the defect is usually approached through a right atriotomy with inspection across the tricuspid valve. The superior margin may be partially hidden by the right coronary cusp; a supplemental dose of cardioplegia allows the aortic root to relax and helps define the true border of the VSD.

If visualization remains suboptimal—particularly in cranially oriented defects—temporary detachment of the tricuspid valve, most commonly the anterior or septal leaflet, is an effective maneuver. The leaflet is incised along its annulus while preserving chordal insertions and is later reattached to the annulus or to the patch. This provides a wide, orthogonal view of the outlet component and the relationship of the patch to the aortic valve and RVOT, with reliable restoration of tricuspid competence when carefully repaired.[2,5]PubMed+1

Relationship to the conduction system

The atrioventricular conduction axis is intimately related to the posteroinferior margin of a perimembranous VSD. From the compact atrioventricular (AV) node at the apex of the triangle of Koch, the penetrating bundle crosses the fibrous continuity between the tricuspid and aortic valves and enters the crest of the ventricular septum at the inferior rim of the defect.[2,3]PubMed+1

Phase-contrast CT and classic histologic studies show that the penetrating and non-branching His bundle lie within only 1–2 mm of the septal crest and posteroinferior edge of the defect.[3]PubMed

Distal to this point, the bundle divides into the left bundle, which fans over the upper left ventricular septal surface, and the right bundle branch (RBB). In outlet-type perimembranous defects, the posterior limb of the trabecula septomarginalis (TSM) runs just inferior to the VSD and partially shields the RBB as it courses intramurally toward the right ventricular free wall.[1,4]PubMed+1

The RBB then emerges on the right ventricular septal surface near the medial papillary muscle complex, where it becomes particularly vulnerable to deep stitches taken at the base of the papillary muscle or along the valley between the TSM limbs.[1,3,4]PubMed+2PubMed+2

Quantitative anatomical and imaging studies therefore converge on a practical rule: the conduction axis lies consistently along the posteroinferior rim of a perimembranous defect, within a few millimetres of the edge, and emerges superficially near the medial papillary muscle. Precise awareness of this three-dimensional course is essential when designing the suture line for patch closure.[1,3,4]PubMed+2PubMed+2

Conduction-safe suture strategy

Traditionally, surgeons placed sutures 2–5 mm away from the VSD margin to “back off” from the conduction tissue. However, histologic–clinical correlation showed that deep, distant bites can actually intersect the intramyocardial RBB and result in a high incidence of complete right bundle branch block (RBBB).[3,5]PubMed+1

Fukuda and colleagues demonstrated that shallow stitches placed close to the rim of the perimembranous defect reduced complete RBBB from ~44% to ~6%, without increasing complete AV block.[5]PubMed

More recently, Kim et al. confirmed in a large contemporary series that shallow suturing at the postero-inferior margin significantly lowers late RBBB and tricuspid regurgitation compared with traditional, deeper sutures.[6]PubMed

In practical terms, for a perimembranous VSD with outlet extension:

Superior/anterior rim. The initial sutures are often placed along the anterosuperior margin, close to the aortic annulus. Here the priority is to protect the right coronary cusp—taking fine, shallow bites and periodically checking that the cusp coapts freely and does not prolapse into the defect.
Posteroinferior (conduction) rim. Along the inferior border, the patch is anchored with closely spaced, shallow, longitudinal stitches placed on the right ventricular side of the septal crest, hugging the rim but avoiding the valley between the limbs of the TSM and the base of the medial papillary muscle, where the RBB becomes superficial.[3–5]PubMed+2PubMed+2
Tricuspid valve relationship. Any detached leaflet is reimplanted onto the patch or annulus with fine interrupted or running sutures, creating a smooth coaptation line and avoiding restriction or residual regurgitation.

A small degree of “undersizing” along the conduction zone—accepting a slightly more right-sided suture line rather than fully “flattening” the defect—is usually well tolerated and is preferable to encroaching on the His bundle or RBB.

Patch placement and completion

Once exposure is adequate and the margins are clearly defined, a tailored patch of autologous pericardium or synthetic material is parachuted into position. Many surgeons begin at the outlet rim, where stitches must simultaneously respect the aortic valve and the RVOT geometry. The suture line is then carried posteriorly and inferiorly in a continuous or interrupted fashion, following the conduction-safe trajectory described above.

When the tricuspid leaflet has been detached, its reimplantation is planned in advance so that the leaflet margin sits naturally on the patch without tension or redundancy. Particular care is taken to avoid suture crossing of chordae or creation of a ridge that could impede leaflet motion or predispose to subaortic stenosis.

Clinical implications

Despite advances in technique, conduction disturbances remain a distinctive risk of perimembranous VSD closure. In modern surgical series, permanent complete AV block requiring pacemaker implantation after isolated perimembranous defect repair is uncommon but not negligible, typically well under 2%.[6,7]PubMed+1

Late RBBB is far more frequent and has been linked to subtle long-term effects on ventricular function and exercise capacity, underscoring the value of conduction-sparing suturing strategies.[5,6]PubMed+1

Transcatheter closure of perimembranous VSDs also carries a recognized risk of both early and delayed AV block, with reported incidences that vary across devices and series and that have prompted caution and evolving device designs.[8,9]PubMed+1

These observations reinforce the central message from surgical anatomy and imaging studies: precise knowledge of the conduction axis and thoughtful suture placement are crucial to minimizing rhythm complications, regardless of the method of closure.

Summary

Successful closure of a perimembranous VSD with outlet extension rests on three practical principles:

Define and protect the superior rim and aortic valve. Understand the relationship between the defect and the right coronary cusp, taking fine, shallow bites to avoid cusp distortion.
Obtain generous exposure. Do not hesitate to detach the tricuspid valve when needed; careful reattachment reliably restores competence and greatly improves visualization.
Design a conduction-safe suture line. Respect the compact AV node, His bundle, and RBB as they course along the posteroinferior rim and emerge near the medial papillary muscle, using shallow stitches close to the rim rather than deep, distant bites.

Applied consistently, these principles allow secure closure of the defect while preserving both valvar function and the integrity of the conduction system.

References

[1] Ueda M, Becker AE. Morphological characteristics of perimembranous ventricular septal defects and their surgical significance. Int J Cardiol. 1985;8(2):149-157.

[2] Anderson RH, Wilcox BR. The surgical anatomy of ventricular septal defect. J Card Surg. 1992;7(1):17-35.

[3] Yoshitake S, Kaneko Y, Morita K, et al. Visualization and quantification of the atrioventricular conduction axis in hearts with ventricular septal defect using phase contrast computed tomography. J Thorac Cardiovasc Surg. 2020;160(2):490-496.

[4] Yoneyama F, Kato H, Mathis BJ, Suetsugu F, Hiramatsu Y. Right bundle branch in ventricular septal defects. Eur J Cardiothorac Surg. 2025;67(4):ezaf105.

[5] Fukuda T, Suzuki T, Kashima I, Sato M, Morikawa Y. Shallow stitching close to the rim of the ventricular septal defect eliminates injury to the right bundle branch. Ann Thorac Surg. 2002;74(2):550-555.

[6] Kim DH, Cho S, Kim WH, et al. Shallow suture at ventricular septal defect may safely reduce right bundle branch block. Cardiol Young. 2023;33(11):2157-2163.

[7] Tucker EM, Pyles LA, Bass JL, Moller JH. Permanent pacemaker for atrioventricular conduction block after operative repair of perimembranous ventricular septal defect. J Am Coll Cardiol. 2007;50(12):1196-1200.

[8] Bai Y, Wang X, Sun Y, et al. Complete atrioventricular block after percutaneous device closure of perimembranous ventricular septal defect: risk factors and clinical outcomes. Heart Rhythm. 2015;12(10):2132-2140.

[9] Jiang D, Chen W, Zhou K, et al. Predictors and long-term outcomes of heart block after transcatheter closure of perimembranous ventricular septal defect. Front Cardiovasc Med. 2022;9:1041852.