Systemic-Pulmonary Shunt #4: Surgical Configurations

Systemic-to-pulmonary artery shunts were developed to augment pulmonary blood flow in patients with cyanotic congenital heart disease and inadequate native pulmonary perfusion. Although each configuration shares the same fundamental physiologic purpose—delivering systemic arterial blood into the pulmonary circulation—the surgical anatomy, flow characteristics, and late consequences differ substantially.

The evolution from direct arterial anastomoses to prosthetic interposition grafts reflects a central principle of modern congenital heart surgery: pulmonary blood flow should be sufficient to relieve cyanosis, but controlled enough to avoid pulmonary overcirculation, systemic diastolic runoff, coronary hypoperfusion, ventricular volume overload, and pulmonary vascular injury. Systemic-to-pulmonary shunts remain an important palliative strategy, particularly when definitive repair is not immediately appropriate or when pulmonary blood flow must be stabilized before the next stage of reconstruction [1].

1. Physiologic Purpose of a Systemic-Pulmonary Shunt

A systemic-pulmonary shunt creates a communication between a high-pressure systemic artery and a low-pressure pulmonary artery.

The major goals are:

• To increase pulmonary blood flow in cyanotic lesions with pulmonary stenosis, pulmonary atresia, or inadequate antegrade pulmonary perfusion
• To improve systemic arterial oxygen saturation
• To provide temporizing palliation before definitive biventricular repair or staged single-ventricle palliation
• To support pulmonary artery growth before later reconstruction or cavopulmonary connection
• To stabilize pulmonary blood flow when ductal patency is unreliable or when ductal stenting is not anatomically favorable

The key physiologic balance is controlled pulmonary blood flow.

Insufficient shunt flow may cause persistent hypoxemia, poor pulmonary artery growth, or shunt thrombosis. Excessive shunt flow may cause pulmonary overcirculation, low systemic diastolic pressure, coronary hypoperfusion, systemic hypoperfusion, ventricular volume overload, respiratory failure, and heart failure.

2. Original Blalock-Taussig-Thomas Shunt

The original Blalock-Taussig-Thomas shunt was a direct anastomosis between the subclavian artery and the ipsilateral pulmonary artery.

Surgical Configuration

The subclavian artery was divided and anastomosed directly to the pulmonary artery, usually through a thoracotomy. This created a direct systemic-to-pulmonary arterial connection without an interposition graft.

Flow Characteristics

Pulmonary blood flow depended on:

• Native subclavian artery caliber
• Anastomotic geometry
• Systemic arterial pressure
• Pulmonary vascular resistance
• Distal pulmonary artery size and resistance
• Growth and distortion of the pulmonary artery over time

Because the subclavian artery itself served as the inflow vessel, shunt flow was partly constrained by native vessel size. This provided some intrinsic limitation of flow but reduced the surgeon’s ability to precisely calibrate pulmonary blood flow.

Surgical and Anatomic Limitations

Important limitations included:

• Sacrifice of distal subclavian artery continuity
• Potential arm ischemia or impaired upper extremity growth
• Limited ability to select shunt size
• Dependence on native vessel size and orientation
• Potential distortion of the pulmonary artery
• Technical limitations in very small neonates or complex anatomy

The original shunt was historically transformative because it established surgical palliation for cyanotic congenital heart disease. However, it has largely been replaced by prosthetic interposition graft techniques that provide greater technical flexibility and more reproducible flow control.

3. Modified Blalock-Taussig Shunt

The modified Blalock-Taussig shunt uses a prosthetic graft, most commonly PTFE, between a systemic artery and a pulmonary artery.

Surgical Configuration

The inflow vessel is usually the subclavian artery or innominate artery. The graft is anastomosed end-to-side to the systemic artery and end-to-side to the pulmonary artery.

Common configurations include:

• Right subclavian artery to right pulmonary artery
• Innominate artery to right pulmonary artery
• Left subclavian artery to left pulmonary artery

The shunt may be placed through thoracotomy or median sternotomy, depending on the cardiac lesion, associated procedures, pulmonary artery anatomy, and institutional strategy.

Advantages

The modified BT shunt became the contemporary standard for many indications because it provides a more controlled and reproducible source of pulmonary blood flow.

Major advantages include:

• Preservation of native subclavian artery continuity
• Ability to select graft size according to body weight, anatomy, and desired pulmonary blood flow
• More predictable shunt caliber than direct arterial anastomosis
• Technical adaptability to different anatomic configurations
• Reduced risk of severe pulmonary artery distortion compared with older side-to-side shunts
• Compatibility with staged palliation and later definitive repair

Flow Considerations

Shunt flow is influenced by:

• Graft diameter
• Graft length
• Systemic arterial pressure
• Pulmonary vascular resistance
• Distal pulmonary artery size
• Geometry and angle of the graft
• Competitive antegrade pulmonary blood flow, if present

In neonates, small changes in graft diameter can produce large changes in flow because resistance is highly dependent on radius. Therefore, graft size selection is not only a technical decision; it is a physiologic decision.

A small graft may produce inadequate oxygenation or predispose to thrombosis. A large graft may produce pulmonary overcirculation, low diastolic pressure, coronary hypoperfusion, and ventricular volume overload.

Outcomes and Complications

Contemporary studies of modified BT shunts report early operative mortality of approximately 4.3%, with overall mortality ranging from approximately 7.2% to 16% across cohorts [2]. Major complications include shunt thrombosis, shunt stenosis, infection, and pulmonary overcirculation [3]. Thrombosis is particularly important because acute shunt occlusion can rapidly produce severe hypoxemia and cardiovascular collapse.

Risk factors for adverse outcomes include low body weight, particularly weight less than 2.5 kg, and markers of poor systemic perfusion such as lactic acidosis [2]. These findings reinforce the importance of careful patient selection, precise graft sizing, meticulous anastomotic technique, and aggressive perioperative monitoring.

4. Waterston Shunt

The Waterston shunt is a side-to-side anastomosis between the ascending aorta and the right pulmonary artery.

Surgical Configuration

The ascending aorta is connected directly to the right pulmonary artery through a side-to-side anastomosis. Unlike the modified BT shunt, no prosthetic interposition graft is used.

Flow Characteristics

The ascending aorta is a high-pressure, high-flow source. Therefore, the Waterston shunt can provide substantial pulmonary blood flow, but flow control is imprecise. Once pulmonary vascular resistance falls, the shunt may produce excessive pulmonary blood flow and significant systemic runoff.

Major Limitations

The Waterston shunt is associated with important anatomic and physiologic disadvantages:

• Excessive pulmonary blood flow
• Pulmonary hypertension
• Right pulmonary artery distortion or stenosis
• Uneven pulmonary blood flow distribution
• Difficulty during later complete repair
• Potential need for complex pulmonary artery reconstruction

Because the anastomosis directly involves the ascending aorta and right pulmonary artery, distortion of the right pulmonary artery can compromise later reconstruction. These limitations contributed to the abandonment of the Waterston shunt in routine contemporary congenital cardiac surgery.

5. Potts Shunt

The Potts shunt is a side-to-side anastomosis between the descending aorta and the left pulmonary artery.

Surgical Configuration

The descending thoracic aorta is connected directly to the left pulmonary artery, usually through a left thoracotomy.

Flow Characteristics

Like the Waterston shunt, the Potts shunt provides a direct systemic arterial source to the pulmonary circulation without a prosthetic graft. Flow may be substantial and difficult to regulate.

Major Limitations

Important limitations include:

• Excessive pulmonary blood flow
• Pulmonary vascular disease
• Left pulmonary artery distortion
• Differential pulmonary artery growth
• Persistent systemic-to-pulmonary runoff
• Technical difficulty at later takedown or definitive repair

The direct relationship between the descending aorta and left pulmonary artery may complicate later repair. The risk of uncontrolled flow and pulmonary artery distortion led to the decline of this shunt in standard palliation.

6. Central Shunt

A central shunt uses an interposition graft between the ascending aorta and the main pulmonary artery or central pulmonary artery confluence.

Surgical Configuration

The graft is placed between the ascending aorta and the main pulmonary artery or central pulmonary artery segment, typically through a median sternotomy.

Clinical Use

A central shunt may be considered when:

• Branch pulmonary arteries are small
• More central and bilateral pulmonary blood flow distribution is desired
• Subclavian or innominate artery anatomy is unfavorable
• Median sternotomy is already required for associated procedures
• Pulmonary blood flow must be provided in the setting of complex pulmonary artery anatomy

Flow Characteristics

Because the ascending aorta is the inflow source, central shunts can provide robust pulmonary blood flow. However, this also creates a risk of excessive systemic runoff if the graft is too large or if pulmonary vascular resistance falls rapidly after birth.

Advantages and Concerns

Potential advantages include:

• Central distribution of pulmonary blood flow
• Avoidance of subclavian artery manipulation
• Applicability in selected complex anatomy
• Usefulness when performed with other procedures through sternotomy

Potential concerns include:

• Pulmonary overcirculation
• Low systemic diastolic pressure
• Coronary hypoperfusion
• Need for precise graft size selection
• Adhesions and technical considerations at later reoperation

7. Shunt Geometry and Pulmonary Artery Growth

The modified BT shunt should not be viewed simply as a tube connecting a systemic artery to a pulmonary artery. Its geometry may influence pulmonary artery growth and flow distribution.

Computed tomography-based analysis has suggested that a more vertical modified BT shunt angle is associated with greater pulmonary artery growth [4]. This observation supports an important surgical concept: the configuration of the shunt affects not only immediate oxygenation but also the geometry of pulmonary blood flow and subsequent pulmonary artery development.

Relevant technical considerations include:

• Site of systemic arterial inflow
• Site of pulmonary artery insertion
• Graft length
• Graft curvature
• Angle of insertion into the pulmonary artery
• Avoidance of kinking or compression
• Avoidance of branch pulmonary artery distortion
• Anticipated future reconstruction

A technically patent shunt is not necessarily an optimal shunt. The ideal shunt provides stable oxygenation while preserving pulmonary artery architecture for the next operation.

8. Comparison of Major Shunt Configurations

9. Why the Modified BT Shunt Became the Standard

The modified BT shunt is favored because it separates the systemic inflow source from the pulmonary target using a prosthetic graft of predetermined diameter. This allows more deliberate control of pulmonary blood flow than older direct side-to-side shunts.

The major conceptual advantages are:

• Flow can be calibrated by graft diameter
• Subclavian artery continuity can be preserved
• Pulmonary artery distortion is generally reduced compared with older direct shunts
• The operation is reproducible across different centers
• The shunt can be adapted to patient size, anatomy, and future surgical plan
• The configuration can be selected to optimize later repair or staged palliation

Long-term comparative data from the single-ventricle population suggest that the choice between a modified BT shunt and a right ventricle-to-pulmonary artery shunt may have limited association with some late outcomes after Norwood palliation, although early hemodynamics, interstage risk, reinterventions, and ventricular effects remain important considerations [5].

10. Surgical Decision-Making

Selection of a shunt configuration depends on multiple factors:

• Cardiac diagnosis and final surgical pathway
• Single-ventricle versus biventricular strategy
• Degree of cyanosis and ductal dependence
• Size and anatomy of the branch pulmonary arteries
• Presence of pulmonary artery discontinuity, stenosis, or hypoplasia
• Arch anatomy and systemic arterial access
• Neonatal weight and prematurity
• Pulmonary vascular resistance
• Ventricular function
• Presence of competitive antegrade pulmonary blood flow
• Need for concomitant intracardiac, pulmonary artery, or aortic arch procedures
• Anticipated timing and technical requirements of the next operation

A systemic-pulmonary shunt should not be considered an isolated procedure. It is part of a staged surgical strategy. The initial shunt configuration can influence pulmonary artery growth, ventricular loading, reentry risk, later reconstruction, and the feasibility of definitive repair.

11. Key Teaching Points

Systemic-pulmonary shunts augment pulmonary blood flow in patients with inadequate native pulmonary perfusion.

The original Blalock-Taussig-Thomas shunt established the principle of surgical palliation but required direct use of the subclavian artery.

The Waterston and Potts shunts provided effective pulmonary blood flow but were limited by poor flow control, pulmonary overcirculation, pulmonary artery distortion, and difficulty at later repair.

The central shunt remains useful in selected patients, especially when central pulmonary artery perfusion is desired or when sternotomy is already required.

The modified BT shunt has become the dominant contemporary systemic-pulmonary shunt configuration because it provides more controlled, reproducible, and anatomically adaptable pulmonary blood flow.

Contemporary MBTS outcomes are influenced by patient weight, systemic perfusion status, shunt patency, graft geometry, and the balance between pulmonary and systemic blood flow.

The central surgical principle is controlled palliation: enough pulmonary blood flow to relieve cyanosis and promote pulmonary artery growth, but not so much that systemic perfusion, coronary perfusion, ventricular function, or pulmonary vascular development are compromised.

References

[1] Ruiz Pérez LE. Systemic-to-pulmonary artery shunt: a surgical strategy with no expiration date. Frontiers in Pediatrics. 2026. doi:10.3389/fped.2026.1767112.

[2] Tarca A, Peacock G, McKinnon E, Andrews D, Saundankar J. A single-centre retrospective review of modified Blalock-Taussig shunts: a 22-year experience. Heart, Lung and Circulation. 2023. doi:10.1016/j.hlc.2022.12.005.

[3] Rajiah P, Sardá M, Ashwath R, Goerne H. Palliative procedures for congenital heart disease: imaging findings and complications. Radiographics. 2023. doi:10.1148/rg.220049.

[4] Lee S, Kwak JG, Kim WH. Change in pulmonary arteries after modified Blalock-Taussig shunt procedure: analysis based on computed tomography. Journal of Chest Surgery. 2024. doi:10.5090/jcs.23.128.

[5] Goldberg C, Trachtenberg FL, Gaynor JW, Mahle W, Ravishankar C, Schwartz SM, Cnota J, Ohye R, Gongwer R, Taylor MD, Paridon S, Frommelt P, Afton K, Atz A, Burns KM, Detterich J, Hill K, Cabrera A, Lewis AB, Pizarro C, Shah A, Sharma B, Newburger J. Longitudinal follow-up of children with HLHS and association between Norwood shunt type and long-term outcomes: the SVR III Study. Circulation. 2023. doi:10.1161/CIRCULATIONAHA.123.065192.