Partial Atrioventricular Septal Defect (AVSD) — #1 Anatomy from the Surgeon’s Viewpoint

Date
October 21, 2025
URL
https://x.com/WithAScalpel/status/1980604836392382779
Categories
AVSD

Partial Atrioventricular Septal Defect (Partial AVSD) — #1 Anatomy from the Surgeon’s Standpoint

image

Partial AVSD is defined by a common atrioventricular (AV) junction with two separate AV valve orifices and no interventricular communication. The atrial component is a primum ASD contiguous with the AV valve plane; the left AV valve (LAVV, mitral analogue) has a true zone of apposition (“cleft”) between the superior and inferior bridging leaflets, the principal substrate for regurgitation [1, 2]. The left AV valve is typically trifoliate (small mural leaflet plus two bridging leaflets), and the cleft usually points toward the LV outflow tract (LVOT) [2].

Embryologic Basis

Partial AVSD results from incomplete fusion of the superior and inferior endocardial cushions, leaving an inferior atrial septal deficiency (primum ASD) and abnormal bridging leaflets that “straddle” the septal crest. Ventricular septation is intact, but the annulus is common across right and left sides—key to its distinctive valve geometry and conduction relationships [1, 2].

Core Surgical Anatomy (mapped to your figures)

  • Primum ASD: sits just superior to the AV valves, abutting the annulus. The posteroinferior rim is deficient and blends with the coronary sinus ostium and the triangle of Koch.
  • Left AV valve: superior and inferior bridging leaflets create a cleft directed toward the LVOT; the cleft may extend to the annulus.
  • Right AV valve: tricuspid-like but with chordal insertions that reflect the common AV junction.
  • Conduction system: inferiorly displaced AV node near the coronary sinus with the His bundle coursing along the posteroinferior margin of the primum defect—an ever-present hazard when suturing the patch along this rim [2, 9].

Hemodynamics and Pathophysiology

Two elements dominate:

  1. Left-to-right atrial shunt through the primum ASD, leading over time to RA/RV dilation and pulmonary overcirculation; and
  2. LAVV regurgitation through the cleft or from leaflet/chordal dysplasia, producing left-sided volume load.

    3. A “gooseneck” LVOT configuration and occasional subaortic stenosis from accessory chordae/fibromuscular tissue may coexist and should be actively sought [1, 7].

Clinical Presentation

Infants range from asymptomatic to tachypneic with poor weight gain when shunt and/or LAVV regurgitation are substantial. Classic findings: fixed split S2, a pulmonary flow murmur, and an apical holosystolic murmur when the cleft is hemodynamically relevant. Older children often present with exercise intolerance or faltering growth.

Imaging Essentials

Transthoracic echocardiography establishes the diagnosis: a primum ASD contiguous with the AV valve plane, a scooped septal crest with common AV junction and bridging leaflets, and a mitral cleft directed toward the LVOT (color Doppler for severity and jet direction). Evaluate ventricular size/function, LVOT morphology, and any subaortic tissue. Transesophageal echo refines valve/cleft anatomy in larger children when planning repair [1].

Associated Lesions

Persistent left SVC to coronary sinus, accessory clefts or commissures, papillary muscle anomalies (single/malpositioned papillary muscle, short secondary chordae), partial anomalous pulmonary venous connection, and rarely coarctation should be considered and excluded pre-op [1].

Indications and Timing for Surgery

Elective repair is generally undertaken in early childhood once body size allows safe cannulation and before pulmonary vascular disease develops; excellent outcomes are reported with a median repair age near 1.5 years [3]. Contemporary data support deferring elective repair beyond infancy when feasible, because propensity-matched analyses show lower long-term survival after infant repair (with similar reoperation rates) compared with repair later in childhood; many infant cases carry additional risk from heart failure and significant LAVV regurgitation at presentation [4, 8]. Practically, operate earlier for moderate–severe LAVV regurgitation, failure to thrive, recurrent pulmonary infections, or a significant shunt (e.g., Qp:Qs ≥1.5) [1, 3].

Operative Principles

  1. Primum ASD closure with a single patch (autologous pericardium or synthetic) sewn to the true AV annulus and septal crest.
    • Conduction protection: on the posteroinferior rim, keep sutures shallow and on the left atrial side near the coronary sinus to avoid the AV node/His bundle [2, 9].
    • The coronary sinus usually continues to drain to the RA; tailor strategies for unroofed variants.
  2. Cleft closure of the LAVV using interrupted (often pledgeted) sutures from the free edge toward—but not invariably to—the annulus to avoid stenosis and to preserve diastolic area. Add commissuroplasty/annuloplasty if annular dilation persists.
  3. Address subvalvar/LVOT issues: lengthen or resect restrictive secondary chordae, remove fibrous tags, and correct lesions that threaten LVOT obstruction [7].

    4. These steps—ASD patching, thoughtful cleft approximation, and LVOT management—summarize the operative “triad” for partial AVSD repair [7].

Outcomes and Late Sequelae

When repaired in childhood, long-term survival is excellent, with ~94% survival at 30 years in a large, modern series; nonetheless, ~25% of patients may require reoperation, predominantly for LAVV regurgitation [5, 6]. Reintervention may also target recurrent subaortic stenosis, and a minority need pacemakers. The dominant reasons for late surgery—cleft-related LAVV failure and LVOT obstruction—mirror the key anatomic substrates of the lesion [6, 7]. These observations underscore the value of meticulous cleft management and proactive LVOT assessment at the index operation. Continuous surveillance into adulthood is recommended because reoperation, although not universal, is not rare [5].

References

[1] Calkoen EE, Hazekamp MG, Blom NA, Elders BBLJ, Gittenberger-de Groot AC, Haak MC, Bartelings MM, Roest AAW, Jongbloed MRM. Atrioventricular septal defect: From embryonic development to long-term follow-up. Int J Cardiol. 2016;202:784-795. PubMed

[2] Anderson RH, Wessels A, Vettukattil JJ. Morphology and morphogenesis of atrioventricular septal defect with common atrioventricular junction. World J Pediatr Congenit Heart Surg. 2010;1(1):59-67. PubMed

[3] Devlin PJ, Backer CL, Eltayeb O, Monge MC, Hauck AL, Costello JM. Repair of partial atrioventricular septal defect: Age and outcomes. Ann Thorac Surg. 2016;102(1):170-177. PubMed

[4] Konstantinov IE, Buratto E. Repair of partial atrioventricular septal defects in infancy: a paradigm shift or a road block? Heart. 2018;104(17):1388-1389. PubMed

[5] Buratto E, McCrossan B, Galati JC, Bullock A, Kelly A, d’Udekem Y, Brizard CP, Konstantinov IE. Repair of partial atrioventricular septal defect: a 37-year experience. Eur J Cardiothorac Surg. 2015;47(5):796-802. PubMed

[6] Stulak JM, Burkhart HM, Dearani JA, Cetta F, Barnes RD, Connolly HM, Schaff HV. Reoperations after repair of partial atrioventricular septal defect: a 45-year single-center experience. Ann Thorac Surg. 2010;89(5):1352-1359. PubMed

[7] Manning PB. Partial atrioventricular canal: pitfalls in technique. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2007:42-46. PubMed

[8] Buratto E, Daley M, Ye XT, Radford DJ, Alphonso N, Brizard CP, d’Udekem Y, Konstantinov IE. Propensity score matched analysis of partial atrioventricular septal defect repair in infancy. Heart. 2018;104(12):1014-1018. PubMed

[9] Ho SY, Gerlis LM, Toms J, Lincoln C, Anderson RH. Morphology of the posterior junctional area in atrioventricular septal defects. Ann Thorac Surg. 1992;54(2):264-270. PubMed