Doubly Committed Juxtaarterial VSD #1: Anatomy and Physiology

Anatomy, Physiology, and Aortic Valve Risk

A doubly committed juxtaarterial ventricular septal defect (DCJA VSD) is an outlet-type VSD located immediately beneath the semilunar valves. It is also referred to as a doubly committed subarterial, supracristal, or subpulmonary VSD. The defining anatomical feature is absence or marked deficiency of the infundibular septum, resulting in direct fibrous continuity between the aortic and pulmonary valves [1].

This defect is clinically important not only because it creates a left-to-right ventricular shunt, but also because it places the aortic valve—particularly the right coronary cusp—at risk for progressive prolapse and aortic regurgitation [1, 2].

1. Core Anatomical Concept

In the normal heart, the infundibular septum separates the aortic and pulmonary outflow tracts. In DCJA VSD, this muscular structure is absent or deficient. As a result, the defect lies immediately beneath the pulmonary valve and adjacent to the aortic valve, creating a shared outlet region.

Key anatomical features include:

• Subpulmonary location: the defect opens into the right ventricular outflow tract immediately beneath the pulmonary valve.
• Aortic–pulmonary valve continuity: the aortic and pulmonary valves are separated by little or no muscular infundibular tissue.
• Aortic cusp vulnerability: the right coronary cusp is commonly unsupported and may progressively prolapse into the defect [1, 3].
• Surgical exposure: because of its subpulmonary position, the defect is frequently well visualized through a transpulmonary approach [4, 5].

This morphology makes DCJA VSD fundamentally different from a typical perimembranous VSD. The lesion should be understood as an outlet septal defect with semilunar valve involvement, rather than simply as a ventricular-level communication.

2. Hemodynamic Physiology

The basic hemodynamic physiology is a left-to-right shunt from the left ventricle to the right ventricle. When the defect is large or nonrestrictive, this may result in:

• Increased pulmonary blood flow
• Left atrial and left ventricular volume loading
• Pulmonary overcirculation
• Heart failure symptoms in infancy
• Failure to thrive or recurrent respiratory symptoms

However, DCJA VSD may sometimes appear relatively restrictive, especially when the aortic cusp partially prolapses into the defect. This can reduce the apparent shunt while simultaneously worsening aortic valve distortion. Therefore, the magnitude of the shunt alone does not fully define the risk of this lesion.

3. Mechanism of Aortic Cusp Prolapse

The most characteristic natural-history problem is progressive aortic cusp prolapse, most often involving the right coronary cusp [1, 2].

Several mechanisms contribute:

1. Loss of anatomical support

The absent infundibular septum removes the normal structural support beneath the aortic cusp.

2. Systolic flow effect

The left-to-right jet through the defect may draw the aortic cusp toward the VSD, progressively deforming cusp geometry.

3. Cusp elongation and malcoaptation

Over time, the prolapsing cusp may elongate and lose normal coaptation with the remaining cusps.

4. Development of aortic regurgitation

Once cusp coaptation becomes abnormal, aortic regurgitation may appear and may progress if the defect remains unrepaired [2, 3].

This sequence is central to the management of DCJA VSD: the problem is not only the hole, but also the progressive distortion of the aortic valve.

4. Natural History

DCJA VSD has a higher-risk natural history than many small muscular or restrictive perimembranous VSDs. Spontaneous closure is generally uncommon, and the main clinical concern is progressive aortic valve involvement.

Reported surgical and echocardiographic series have shown a high prevalence of aortic valve prolapse and aortic regurgitation before repair. Aortic cusp prolapse has been reported in approximately 65–79% of patients, while aortic regurgitation has been reported in approximately 48–65% before surgery in major series [1, 2, 5].

Important natural-history principles:

• Aortic cusp prolapse can develop even when the VSD is not hemodynamically large.
• Aortic regurgitation tends to progress once cusp deformity becomes established.
• Restriction of the shunt by cusp prolapse does not necessarily indicate clinical improvement.
• Delayed closure after the onset of aortic regurgitation may increase the risk of persistent postoperative regurgitation [2, 6].

Thus, surveillance should focus not only on chamber enlargement and pulmonary blood flow, but also on subtle changes in aortic cusp position, cusp coaptation, and early aortic regurgitation.

5. Timing of Surgical Closure

The central surgical principle is:

DCJA VSD should be closed before progressive aortic cusp prolapse produces significant or irreversible aortic regurgitation.

In many VSDs, timing of repair is driven by symptoms, pulmonary overcirculation, pulmonary hypertension, or failure to thrive. In DCJA VSD, timing is additionally driven by aortic valve preservation [2, 3, 6].

Evidence from surgical series supports early intervention. Patients repaired before development of cusp prolapse or aortic regurgitation have a low risk of postoperative aortic valve deterioration, whereas those with established aortic regurgitation—especially if surgery is delayed after AR onset—are more likely to have persistent or progressive postoperative AR [2, 3, 6].

Practical indications for closure include:

• Definite DCJA/subarterial VSD morphology
• Aortic cusp prolapse, especially right coronary cusp prolapse
• Any new or progressive aortic regurgitation
• Significant left-to-right shunt or pulmonary overcirculation
• Progressive aortic valve distortion even with a restrictive shunt

The goal is not simply shunt elimination. The goal is prevention of aortic valve deformation.

6. Surgical Perspective

Because the defect lies just beneath the pulmonary valve, a transpulmonary approach often provides direct exposure of the defect and its relationship to the semilunar valves [4, 5]. Patch closure is commonly performed, with careful attention to the pulmonary valve superiorly and the aortic cusp adjacent to the defect.

Important technical considerations include:

• Define the superior rim beneath the pulmonary valve.
• Identify the relationship between the patch and the aortic cusp.
• Avoid distortion of the pulmonary valve annulus or leaflet tissue.
• Avoid residual shunt near the semilunar valves.
• Evaluate aortic cusp coaptation after closure.
• Decide whether VSD closure alone is sufficient or whether aortic valve repair is required.

In many patients with mild cusp prolapse or mild AR, VSD closure alone may stabilize or improve aortic regurgitation [3, 9]. However, in patients with moderate or severe AR, significant cusp elongation, or persistent malcoaptation, additional aortic valve repair may be necessary [7, 8].

7. Postoperative Aortic Valve Outcomes

Postoperative outcome is closely related to the preoperative condition of the aortic valve. When closure is performed before significant cusp deformity, long-term aortic valve function is usually excellent. Large surgical series have reported excellent survival and generally favorable aortic and pulmonary valve outcomes after repair [4, 5].

However, established aortic regurgitation does not always disappear after closure. The probability of residual or progressive AR is higher when:

• AR is already moderate or severe before surgery.
• Cusp prolapse has been present for a long period.
• Cusp elongation or deformity is advanced.
• The interval between onset of AR and repair is prolonged [2, 6].

Therefore, postoperative follow-up should include serial assessment of:

• Residual VSD
• Aortic regurgitation grade
• Aortic cusp coaptation
• Pulmonary valve function
• Right ventricular outflow tract geometry
• Left ventricular size and volume loading

8. Clinical Take-Home Message

A doubly committed juxtaarterial VSD is a deceptively important lesion. Even when the shunt appears small, the anatomical position of the defect places the aortic valve at risk.

The essential concept is:

DCJA VSD is not only a shunt lesion; it is an aortic valve preservation problem.

Timely closure, often through a transpulmonary approach, is aimed at eliminating the defect, restoring outlet septal support, and preventing progression of right coronary cusp prolapse and aortic regurgitation.

Summary

A doubly committed juxtaarterial VSD lies immediately beneath the pulmonary valve because of absence of the infundibular septum, creating direct aortic–pulmonary valve continuity. Its major natural-history risk is right coronary cusp prolapse, which may lead to progressive aortic regurgitation. Because spontaneous closure is uncommon and aortic valve deformation may progress despite a small shunt, timely surgical closure is often recommended to preserve long-term aortic valve competence.

References

[1] Schmidt KG, Cassidy SC, Silverman NH, Stanger P. Doubly committed subarterial ventricular septal defects: echocardiographic features and surgical implications. J Am Coll Cardiol. 1988;12(6):1538-1546.

[2] Komai H, Naito Y, Fujiwara K, Noguchi Y, Nishimura Y, Uemura S. Surgical strategy for doubly committed subarterial ventricular septal defect with aortic cusp prolapse. Ann Thorac Surg. 1997;64(4):1146-1149.

[3] Tomita H, Arakaki Y, Ono Y, Yamada O, Tsukano S, Yagihara T, Echigo S. Evolution of aortic regurgitation following simple patch closure of doubly committed subarterial ventricular septal defect. Am J Cardiol. 2000;86(5):540-542.

[4] Sim EKW, Grignani RT, Wong ML, Quek SC, Wong JC, Yip WCL, Lee CN. Outcome of surgical closure of doubly committed subarterial ventricular septal defect. Ann Thorac Surg. 1999;67(3):736-738.

[5] Devlin PJ, Russell HM, Mongé MC, Patel A, Costello JM, Spicer DE, Anderson RH, Backer CL. Doubly committed and juxtaarterial ventricular septal defect: outcomes of the aortic and pulmonary valves. Ann Thorac Surg. 2014;97(6):2134-2140.

[6] Jung H, Cho JY, Lee Y. Progression of aortic regurgitation after subarterial ventricular septal defect repair: optimal timing of the operation. Pediatr Cardiol. 2019;40(8):1696-1702.

[7] de Leval MR, Pozzi M, Starnes V, Sullivan ID, Stark J, Somerville J, Anderson RH, Deanfield JE. Surgical management of doubly committed subarterial ventricular septal defects. Circulation. 1988;78(5 Pt 2):III40-III46.

[8] Brauner R, Birk E, Sahar G, Blieden L, Vidne BA. Surgical management of ventricular septal defect with aortic valve prolapse: clinical considerations and results. Eur J Cardiothorac Surg. 1995;9(6):315-319.

[9] Hisatomi K, Taira A, Moriyama Y. Is direct closure dangerous for treatment of doubly committed subarterial ventricular septal defect? Ann Thorac Surg. 1999;67(3):756-758.