What is the purpose and procedure of the Blalock-Taussig (BT) shunt in pediatric patients with congenital heart defects?

Blalock-Taussig Shunt: Purpose and Procedure

Primary Purpose

The Blalock-Taussig shunt is a palliative surgical procedure that increases pulmonary blood flow and enhances systemic oxygen saturation in pediatric patients with cyanotic congenital heart disease characterized by severe obstruction to pulmonary flow. 1

The procedure serves two main clinical scenarios:

• Bridge to definitive repair in patients with biventricular anatomy (e.g., tetralogy of Fallot) 1
• Staged palliation in patients with functionally univentricular circulation as part of progression toward Fontan completion 1, 2

Surgical Technique

Modified vs. Classic Approach

The modified Blalock-Taussig shunt using an interposition polytetrafluoroethylene (Gore-Tex) tube graft is the current standard, having replaced the classic direct subclavian-to-pulmonary artery anastomosis 1, 2. The modified technique accounts for 99.6% of contemporary procedures 2.

Technical Details

• Shunt placement: Predominantly right-sided (90% of cases), most commonly from right subclavian artery to right pulmonary artery 2
• Surgical access: Can be performed via thoracotomy or median sternotomy 3, 2
• Shunt material: Polytetrafluoroethylene (Gore-Tex) interposition graft 1

Approach Selection

Thoracotomy approach is preferred over median sternotomy when feasible, as sternotomy is associated with longer ventilation duration (183 vs. 53 hours), increased inotropic requirements (33.3% vs. 4.2%), longer ICU stay (9.14 vs. 3.3 days), and prolonged hospitalization (14.59 vs. 5 days) 3. However, sternotomy approach is a risk factor for in-hospital mortality on multivariable analysis 2.

Clinical Indications

Primary Indications

The shunt is indicated for severe cyanosis due to:

• Valvular or subvalvular pulmonary stenosis 1
• Pulmonary atresia 1
• Critical pulmonary stenosis with intact ventricular septum (after decompressive procedure) 1
• Complex cyanotic lesions with inadequate pulmonary blood flow 4, 2

Patient Population

• Median age at operation: 8 days (range 0 days to 18.5 years) 2
• Median weight: 3.2 kg (1.5 to 51 kg) 2
• Procedure can be safely performed in neonates less than 1 week of age 4

Expected Outcomes and Complications

Mortality Risk

Hospital mortality varies significantly by underlying anatomy:

• Biventricular lesions: 3% mortality 2
• Univentricular lesions: 15% mortality 2
• Overall contemporary mortality: 8-15% depending on patient complexity 4, 5, 2

Risk Factors for Mortality

Multivariable analysis identifies these high-risk features:

• Use of cardiopulmonary bypass 2
• Sternotomy approach 2
• Innominate artery-to-PA shunt location 2
• Pulmonary atresia 5
• Genetic syndromes and extracardiac malformations 5
• Weight ≤2.5 kg 5
• Higher shunt size/weight ratio 5

Shunt Patency and Function

Actuarial shunt survival is 87% ± 9% at 1 year and 78% ± 12% at 2 years 6. Approximately 73% of patients successfully bridge to the next stage of palliation or repair 5, 2.

Thrombotic Complications

Shunt thrombosis is a life-threatening complication occurring in 9.3% of patients, with 20% occurring shortly after surgery 1. Complete shunt occlusion requires immediate recognition and emergent management:

• Immediate heparin bolus (50-100 U/kg) 1
• Increase systemic blood pressure with phenylephrine to maximize shunt perfusion 1
• Controlled ventilation to optimize oxygen delivery 1
• Consider emergent catheterization for thrombectomy or ECMO if initial measures fail 1

Other Complications

• Unplanned cardiac reoperation: 14% in single ventricle patients vs. 7% in biventricular patients 5
• ECMO requirement: 12% in single ventricle patients vs. 4% in biventricular patients 5
• Potential for pulmonary artery distortion from residual Gore-Tex tube causing "tenting" in growing children (requires long-term follow-up) 1

Clinical Examination Findings

Physical examination in patients with functioning BT shunt reveals:

• Continuous murmur of aortopulmonary shunt 1
• Cyanosis and clubbing (though improved from pre-shunt baseline) 1
• Absent or diminished brachial pulse on the side of the shunt 1
• Single second heart sound 1

Transition to Definitive Repair

Median duration from BT shunt to complete repair or next palliation stage is 6.5 months (range 0 days to 15.3 years) 2. The shunt provides excellent pulmonary artery growth, with ipsilateral and contralateral PA/descending aorta ratios improving from 0.70-0.73 to 0.95-0.99 over 550 days 6.

Shunt Closure

When the shunt becomes unnecessary after definitive repair, transcatheter occlusion is the preferred closure method over surgical ligation, as it avoids risks of phrenic nerve injury, recurrent laryngeal nerve injury, thoracic duct injury, and prolonged hospitalization 1. Transcatheter closure demonstrates high success rates (95-100%) with minimal complications 1.