Doubly Committed Juxtaarterial VSD #1: Anatomy and Physiology

1. Definition and Morphologic Anatomy

A doubly committed juxtaarterial ventricular septal defect (DCJA VSD) is an outlet VSD located immediately beneath both the aortic and pulmonary valves. It is also commonly termed a doubly committed subarterial, subpulmonary, or supracristal VSD. Its defining morphologic feature is deficiency or absence of the muscular outlet septum and subpulmonary infundibular tissue that normally separates the aortic and pulmonary roots. As a result, the aortic and pulmonary valves are in direct fibrous continuity at the superior margin of the defect.

From the right ventricular aspect, the defect opens high within the right ventricular outflow tract (RVOT), immediately beneath the pulmonary valve. The superior border may contain little or no muscular tissue; instead, the adjacent semilunar valve hinges effectively form part of the roof of the defect. The posteroinferior border is usually muscular.

This anatomy is clinically important because the missing outlet septal support leaves the adjacent aortic cusp—most commonly the right coronary cusp (RCC)—susceptible to progressive deformation and prolapse into the VSD.

2. Mechanism of Aortic Cusp Prolapse

Aortic cusp prolapse in outlet VSD is not simply a consequence of the magnitude of the ventricular shunt. Classic morphologic and angiographic observations indicate that two interacting mechanisms are involved: lack of anatomic support beneath the aortic cusp and hemodynamic forces acting across the defect [1].

Normally, the semilunar valve apparatus is supported by the surrounding ventricular and arterial root structures. In DCJA VSD, the absence of the conal or infundibular septum removes part of the structural support beneath the adjacent aortic cusp. During systole, flow across the VSD then repeatedly draws or displaces the unsupported cusp toward the right ventricle. Over time, progressive cusp elongation and deformation may develop [1].

The sequence can therefore be conceptualized as:

Absent outlet septal support → repetitive systolic displacement of the aortic cusp → cusp prolapse into the VSD → progressive leaflet deformation → impaired coaptation → aortic regurgitation

The RCC is affected most frequently, although other cusps may become involved depending on the precise spatial relationship between the VSD and the aortic root.

3. Aortic Regurgitation as the Critical Natural-History Problem

The major natural-history concern in DCJA VSD is progressive aortic regurgitation (AR). Unlike many muscular VSDs, spontaneous anatomic closure is uncommon, and apparent reduction in the effective VSD size may actually reflect progressive incorporation of the prolapsing aortic cusp into the defect.

This distinction is clinically important. As the RCC increasingly prolapses into the VSD, the effective left-to-right orifice may become smaller and Doppler velocity may increase. The patient may therefore demonstrate less pulmonary overcirculation even while the aortic valve lesion is becoming more severe.

Consequently, the severity of a DCJA VSD should not be judged solely by:

• VSD diameter,
• Doppler gradient,
• Qp:Qs,
• left ventricular volume loading, or
• symptoms of pulmonary overcirculation.

Serial assessment of aortic cusp morphology and AR is equally important.

Once the prolapsing cusp becomes substantially elongated or distorted, VSD closure alone may not completely restore normal valve coaptation. This provides the rationale for timely closure before irreversible aortic valve pathology develops.

4. Hemodynamic Physiology

The basic shunt physiology follows the same principles as other ventricular communications. After pulmonary vascular resistance falls during infancy, blood flows from the left ventricle through the VSD into the RVOT and pulmonary circulation.

For a large effective defect:

LV → VSD → RVOT/PA → pulmonary overcirculation → increased pulmonary venous return → LA/LV volume loading

Affected infants may therefore develop tachypnea, feeding difficulty, poor weight gain, or clinical heart failure.

However, shunt magnitude and aortic valve risk are partially dissociated in DCJA VSD. A patient with a modest left-to-right shunt may still develop progressive cusp prolapse. Conversely, increasing cusp prolapse can reduce the effective shunt by partially occluding the VSD.

Thus, the absence of significant LV volume overload does not necessarily imply benign anatomy.

5. Quantifying Aortic Cusp Deformation

Echocardiographic severity indices have been proposed to provide a more objective assessment of RCC prolapse. In a study of 316 patients with outlet VSD, Tomita and colleagues evaluated the right coronary cusp deformity index (RCCD) and an R/L cusp imbalance ratio in relation to subsequent AR [2].

In that cohort, patients with:

RCCD <0.30 and R/L <1.30

generally maintained trivial, nonprogressive AR and could be observed if AR remained stable. In contrast, the presence of:

RCCD ≥0.30 or R/L ≥1.30

identified a group at greater risk of clinically important AR and supported consideration of VSD closure [2].

These numerical thresholds are useful conceptual tools but should not be regarded as universal operative guidelines. They were derived from an observational cohort and should be integrated with the patient's age, defect morphology, degree and progression of cusp prolapse, AR severity, ventricular loading, and institutional practice.

The broader principle remains more important than the individual cutoff:

Progressive structural deformation of the aortic cusp is itself an indication to reconsider continued observation, even when the ventricular shunt is not hemodynamically large.

6. Echocardiographic Assessment

Echocardiography should establish the morphology of the defect rather than merely labeling it by ventricular location. Important findings include:

1. A VSD immediately beneath the semilunar valves.
2. Deficiency of the muscular outlet septum.
3. Aortic–pulmonary valvar continuity.
4. Morphology and mobility of the RCC and other aortic cusps.
5. Presence and severity of cusp prolapse.
6. Presence, direction, and severity of AR.
7. Effective VSD size and Doppler gradient.
8. LA and LV volume loading.
9. RV and pulmonary artery pressure.
10. Associated intracardiac or outflow tract lesions.

Serial comparison is critical. New cusp prolapse or increasing AR may be more important than the absolute size of the VSD.

7. Timing of Closure

The decision to close a DCJA VSD is therefore based on two overlapping indications:

Hemodynamic indication: significant pulmonary overcirculation or left-heart volume loading.

Aortic valve–preservation indication: development or progression of cusp prolapse and AR.

Surgical series support an approach favoring closure before advanced aortic valve deformation develops [3,4]. The objective is not simply to eliminate the left-to-right shunt but to remove the pathway into which the aortic cusp is prolapsing and restore structural support beneath the aortic root.

For this reason, DCJA VSD should be regarded as a lesion in which the natural history of the aortic valve may determine operative timing more strongly than the magnitude of the intracardiac shunt.

Doubly Committed Juxtaarterial VSD #2: Surgical Repair—VSD Patch Closure

1. Objectives of Surgical Repair

Patch closure remains the standard surgical treatment for DCJA VSD [3]. The operation has three fundamental objectives:

1. Completely eliminate the ventricular-level shunt.
2. Restore structural support beneath the aortic root.
3. Preserve the geometry and competence of both semilunar valves.

The third objective is particularly important because the superior margin of the defect lies immediately adjacent to the aortic and pulmonary valve hinges. A technically complete closure that distorts either valve is not an optimal repair.

2. Transpulmonary Approach

The transpulmonary approach provides direct exposure of the defect because the VSD lies immediately beneath the pulmonary valve.

After institution of cardiopulmonary bypass, aortic cross-clamping, and cardioplegic arrest, the main pulmonary artery is opened. The pulmonary valve is inspected, and the leaflets are gently retracted to expose the subpulmonary ventricular septum.

This view allows the surgeon to define:

• the entire circumference of the VSD,
• the deficient superior muscular rim,
• the pulmonary valve annulus and leaflet hinges,
• the adjacent aortic valve,
• the degree of RCC prolapse,
• and the muscular posteroinferior margin.

The aortic cusp may sometimes be seen directly through the VSD, emphasizing how closely the two semilunar valves are related.

Alternative exposure may be required when associated anatomy is present or when direct aortic valve repair is anticipated, but the transpulmonary route provides a particularly direct approach to the characteristic anatomy of an isolated DCJA VSD.

3. The Superior Margin: The Key Technical Feature

The superior margin is the most distinctive component of the repair.

Because the infundibular septum is absent, there may be no substantial muscular tissue between the VSD and the pulmonary valve. Conventional deep myocardial bites cannot therefore be taken uniformly around the entire circumference.

The patch must instead be anchored securely along the superior margin close to the pulmonary valve annulus or leaflet hinge, depending on the exact anatomy and the surgeon's preferred technique.

Several technical principles are important:

• Clearly identify the pulmonary leaflet insertion before placing sutures.
• Avoid incorporating mobile pulmonary leaflet tissue.
• Avoid excessively deep bites that could enter or distort the adjacent aortic valve apparatus.
• Avoid excessive traction that alters pulmonary commissural geometry.
• Ensure that the patch adequately covers the superior edge without leaving a residual juxtavalvar shunt.
• Orient the patch so that it reconstructs a smooth outlet septal plane rather than protruding into the RVOT.

Secure closure must therefore be balanced against preservation of semilunar valve mobility.

4. Conduction System Anatomy

The conduction axis in a classic DCJA VSD differs importantly from that in a perimembranous VSD.

When a complete muscular posteroinferior rim separates the defect from the membranous septum, the atrioventricular conduction axis is remote from the VSD margin. This generally reduces the risk of conduction injury during patch placement along the posteroinferior border.

However, not all outlet defects are morphologically identical. If the defect extends toward the membranous septum or has combined juxtaarterial and perimembranous features, the conduction tissue may again approach the defect.

The practical surgical rule is therefore:

Identify the actual borders of the VSD rather than assuming that every subarterial defect has a conduction-free posteroinferior margin.

5. Management of the Prolapsing Aortic Cusp

Before patch placement, the surgeon should carefully evaluate the aortic valve, particularly the prolapsing RCC.

Closure of the VSD eliminates the abnormal pathway into which the cusp has been displaced and re-establishes structural support beneath the aortic root. Therefore, not every prolapsing cusp requires direct aortic valve repair.

When AR is absent, trivial, or mild and the cusp retains satisfactory tissue quality and coaptation, VSD closure alone may be sufficient. Early surgical series support closure before progressive valve deformation becomes established [3,4].

In the series reported by Shamsuddin and colleagues, preoperative AR was present in 65% of surgically treated patients. After repair, AR decreased to trivial in 29%, while mild residual AR persisted in a smaller proportion [3]. Although this was a small series, it illustrates that eliminating the VSD can stabilize or improve associated AR without necessarily requiring extensive valve intervention.

6. When Is Aortic Valve Repair Required?

The decision for simultaneous aortic valvuloplasty should be individualized according to the severity and mechanism of regurgitation.

Features increasing the likelihood that direct valve intervention will be required include:

• moderate or severe AR,
• marked cusp elongation or structural deformation,
• inadequate central coaptation after VSD closure,
• prolapse involving more than one cusp,
• older age at intervention,
• and longstanding valve pathology.

A 22-year experience involving 261 patients with VSD-associated AR found that AR grade, VSD size, age at intervention, and the number of prolapsing cusps were significant determinants of the need for aortic valve intervention [5]. Patients with moderate or severe AR, particularly older patients with small VSDs and involvement of multiple cusps, were more likely to require concomitant aortic valve repair [5].

When repair is performed, the objective is to restore effective cusp height and central coaptation while preserving native valve tissue. Valve replacement should be reserved for uncommon situations in which durable reconstruction is not feasible, particularly given the major long-term implications of prosthetic valve implantation in children.

In the same long-term series, freedom from reoperation after aortic valve repair was approximately 82.6% at 15 years, demonstrating reasonable durability but also emphasizing that patients requiring valve intervention remain at risk for late recurrent AR or reoperation [5].

7. Completion of Patch Closure

The patch is sized to cover the VSD without excessive redundancy. Sutures are placed around the muscular margins and carefully along the deficient superior juxtavalvar border.

The final repair should accomplish:

LV separation from RVOT + restoration of outlet septal support + preservation of aortic and pulmonary valve geometry

Particular attention is required at the superior aspect, where inadequate tissue purchase may produce a residual shunt, whereas overly aggressive suturing may distort the pulmonary valve.

In a surgical series of patients undergoing patch closure, trivial residual shunting was observed in approximately 12% [3]. These data support the effectiveness of patch repair while illustrating the technical challenge created by the deficient superior rim.

8. Intraoperative Assessment

After completion of the repair and separation from cardiopulmonary bypass, transesophageal echocardiography should specifically assess:

• residual VSD flow,
• aortic cusp mobility,
• degree of residual or new AR,
• pulmonary valve leaflet mobility,
• pulmonary regurgitation,
• RVOT obstruction,
• biventricular function,
• and overall intracardiac geometry.

A new eccentric AR jet should prompt careful consideration of patch-related distortion or cusp restriction. Similarly, new pulmonary regurgitation or RVOT turbulence may indicate distortion of the pulmonary valve or excessive patch protrusion.

9. Long-Term Follow-Up

Long-term surveillance should focus particularly on the aortic valve. Relevant endpoints include:

• recurrent or progressive AR,
• residual VSD,
• need for subsequent aortic valvuloplasty or replacement,
• LV size and function,
• RVOT obstruction,
• and pulmonary valve function.

Available surgical studies provide substantially more information about residual shunting and aortic valve outcomes than about late pulmonary valve function after transpulmonary patch closure. Therefore, although preservation of pulmonary valve geometry is an essential operative principle, the evidence defining the incidence and determinants of long-term pulmonary regurgitation or stenosis after this specific repair remains limited.

The operative concept can ultimately be summarized as:

DCJA VSD closure is both a septal repair and an aortic valve–preservation operation.

Successful repair requires timely elimination of the defect before irreversible aortic cusp deformation develops, secure patch fixation despite the deficient superior muscular rim, and meticulous preservation of both semilunar valves.

References

[1] Tatsuno K, Konno S, Ando M, Sakakibara S. Pathogenetic mechanisms of prolapsing aortic valve and aortic regurgitation associated with ventricular septal defect: anatomical, angiographic, and surgical considerations. Circulation. 1973;48(5):1028. doi:10.1161/01.CIR.48.5.1028.

[2] Tomita H, Arakaki Y, Ono Y, Yamada O, Yagihara T, Echigo S. Severity indices of right coronary cusp prolapse and aortic regurgitation complicating ventricular septal defect in the outlet septum: which defect should be closed? Circ J. 2004;68:139. doi:10.1253/CIRCJ.68.139.

[3] Shamsuddin AM, Chen YC, Wong A, Lê T, Anderson RH, Corno A. Surgery for doubly committed ventricular septal defects. Interact Cardiovasc Thorac Surg. 2016;23(2):231. doi:10.1093/icvts/ivw129.

[4] Waqar T, Rizvi M, Baig AR. Doubly committed subarterial ventricular septal defect repair: an experience of 51 cases. Pak J Med Sci. 2017;33(5). doi:10.12669/pjms.335.13429.

[5] Krishnasamy S, Sivalingam S, Dillon J, Mokhtar RAR, Yakub A, Singh R. Syndrome of ventricular septal defect and aortic regurgitation—a 22-year review of its management. Braz J Cardiovasc Surg. 2021. doi:10.21470/1678-9741-2020-0207.