Blalock-Taussig shunt

Blalock-Taussig shunt Microchapters
Overview
Historical Perspective
Classification
Goals of BT shunt
Indications
Risk Factors
Preparation for BT Shunt
Complications
Prognosis
Alternative Shunts

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Usman Ali Akbar, M.B.B.S.[2]

Synonyms and keywords: Blalock Taussig Procedure, Procedure, Blalock-Taussig, Subclavian Pulmonary Artery Shunt, Blue Baby Operations, Modified Blalock-Taussig Procedure

Overview

The Blalock-Taussig shunt is a palliative surgical procedure done for cyanotic heart defects. This procedure is used to deviate blood flow to lungs from the systemic circulation to relieve cyanosis while a definitive corrective surgery can be performed at a later time. Connection between subclavian artery and pulmonary artery is usually made. Usually, two types of shunts are used i.e classic or original Blalock-Taussig shunt and modified Blalock Taussig shunt. The classic/original BT shunt has been modified into modified Blalock-Taussig Shunt (mBTS). In this modified procedure, a graft from innominate artery or subclavian artery is placed to the corresponding pulmonary artery. This type of BT shunt has superior prognostic value over the classical shunt leading to a greater rate of shunt patency in 3-5 years as compared to the classic or original BT Shunt.

Historical Perspective

Classic or Original Shunt

• The classic or original BT shunt procedure was named after a surgeon in Baltimore, Alfred Blalock (1899–1964), and a cardiologist in Baltimore/Boston, Helen B. Taussig (1898–1986), who along with Blalock's African American laboratory technician Vivien Thomas (1910–1985), developed and described the procedure.
• Taussig noticed that the children with cyanosis along with congenital heart disease accompanied by patent ductus arteriosus have a longer lifetime than those without PDA.
• In 1943, Dr. Taussig approached Blalock and Thomas in their Hopkins laboratory to work on this shunt as it was hypothesized that a shunt mimicking PDA can relieve the cyanosis and improve oxygenation in congential cyanotic diseases.

Original Blalock-Taussig shunt diagram. Source: Dr. Laurent Bilodeau.

Modified Blalock-Taussig Shunt

• In 1962, a modified method of inserting a shunt was developed by Klinner using teflon as a prosthetic graft material between the subclavian artery and the pulmonary artery in order to prevent scarring of the subclavian artery.

Modified Blalock-Taussig shunt diagram. Source: Dr. Laurent Bilodeau.

Classification

Classic/Original Blalock-Taussig Shunt

• For classic Blalock-Taussig shunt, an end-to-end anastomosis opposite to the aortic arch is performed between the subclavian and pulmonary arteries to minimize the kinking of subclavian artery as it crosses aortic prominence.

Classic/Original Blalock-Taussig Shunt

Advantages	Disadvantages
The relative diameter of subclavian artery prevents excessive blood flow to lungs	Thrombosis of shunt due to less diameter
Easily Reversible	Risk of Dissection
Increased rate of anastomosis growth	Subclavian artery is lost during the procedure

Modified Blalock Taussig Shunt

• In 1962, it was first described and performed by Klinner et al.
• It is the most commonly used procedure nowadays and holds a superb prognosis over the classic one.
• An Interposition PTFE or Gore-Tex graft is placed between the subclavian artery and the pulmonary artery. Hence no scarring of subclavian artery results.

Modified Blalock Taussig Shunt

Advantages	Disadvantages
It can be done on the same side of the arch	Thrombosis
More patency than Classic BT shunt i.e >90 % at 2 years	Pseudoaneurysm
Pulmonary artery is less distorted	Chylothorax, Chylopericardium, chylous ascites

Goals of BT shunt

• The ultimate endpoint goals of BT shunt are as follows:
  • To stabilize the preload hence preventing hemodilution.
  • To maintain systemic vascular resistance (afterload) hence, adequate diastolic pressure to maintain coronary perfusion.
  • Increase the blood flow to the pulmonary vasculature in a supervised manner.

Indications

• Following is a list of indications for Blalock-Taussig shunt:
  • Tricuspid atresia
  • Tetralogy of Fallot
  • Ebstein's Anomaly
  • Hypoplastic Left Heart syndrome
  • Pulmonary atresia
  • Inadequate pulmonary arteries

Risk Factors

• Following multiple risk factors have been identified to be associated with high morbidity and mortality in neonates:
  • Sternal approach for MBTS construction
  • Univentricular heart
  • Complicated surgery (CABG)
  • Weight <3 kg
  • Pre-operative ventilation support
  • Pre-operative acidosis and shock
  • Use of Innominate artery-PA shunt
  • Diagnosis of Ebstein's Anomaly

Preparation for BT Shunt

• To perform a BT shunt following pre-operative preparation is done:
  • Preoperative psychological counselling of the patient
  • Preoperative fasting
  • Preoperative medications
• Anesthesia induction is based on the following patient and surgery related factors:

Patient-Related Factors

• Diagnosis of relative congenital cardiac anomaly
• Age of the patient
• Weight <3 kg leads to high mortality and morbidity
• Premature infants
• Any non-cardiac coexisting congenital anomaly like Tracheoesophageal fistula, cleft lip and palate, renal anomalies and skeletal defects.
• Atlantoaxial instability or subluxation in down syndrome that should be considered when managing airway.
• Fatigue, dyspnea on feeding or any other factor showing exercise intolerance
• Use of medications that can lead to increase in operative mortality such as aspirin, warfarin, anti-depressants, diuretics, angiotensin converting enzyme (ACE ) inhibitors, antiarrhythmic.
• Congenital conditions such as subglottic stenosis that can lead to difficulty in access for intubation.
• Optimal right ventricular function.

Factors Related to Surgical Procedure

• Complex lesions lead to high in-hospital and overall mortality.
• Duration of surgery
• Cardiovascular anomalies that can lead to complexity of procedure like aortic arch anomaly or presence of aberrant subclavian artery
• Injury to recurrent laryngeal nerve or phrenic nerve during the procedure
• Nature and approach of cardiac surgery e.g, Cardiopulmonary Bypass, sternotomy or thoracotomy

Approach

• For right-sided modified Blalock-Taussig shunt (mBTS), left lateral position is used and for left-sided mBTS right lateral position is used. The approach used is usually thoracotomy.
• For central shunts sternotomy is performed.

Complications

• The immediate post-operative complications include:
  • Development of chylothorax, chylopericardium and chylous ascites
  • Phrenic nerve resection leading to diaphragmatic paralysis
  • Anemia
  • Congestive Heart failure resulting from excessive blood flow
  • Modified PTFE grafts can result in formation of seroma or shunt occlusion due to hyperplasia of neo-intima
  • Stenosis of innominate artery
  • Sunt Infection resulting in sepsis

Unilateral pulmonary edema, Blalock-Taussig shunt in pulmonary atresia with a ventricular septal defect. Source: Dr. Charlie Chia-Tsong.

Management of Complications

Shunt failure

• It is the most immediate risk during the post-operative period. It can lead to drop in oxygen saturation secondary due to shunt thrombosis or kinking. Shunt failure is a surgical emergency and should be managed as follows:
  • Anticoagulation should be started. Heparin should be instituted promptly. It should be again administered if there is less risk of bleeding usually after 4 hours post-op ( when the drainage of the chest shows <3ml/kg/h and aPTT is <60s. Heparin induced thrombocytopenia can occur and should be managed accordingly.
  • Patient is put on aspirin which is usually started at 3-5 mg/kg (max. dose 75mg ) OD.
  • Heparin should be continued until there is a second dose of aspirin.

Blockage of BT shunt

• Blockage or shunt thrombosis is another surgical emergency.
• It's incidence has reported around 12%.
• Any recent onset murmur or significant drop in oxygen saturation must be investigated.
• Operative management is usually required and the shunt is usually repaired or replaced if necessary.

High pulmonary blood flow

• The appropriate size of BT shunt is very important to prevent the long term complications regarding high pulmonary blood flow or high oxygen saturation.
• Chest X Ray usually shows edematous lungs with low mixed venous saturation, rising lactate levels or signs of right heart failure, systemic diastolic pressure may be low, persistent metabolic acidosis leading to "pink patient" and pulmonary hemorrhage.

Causes

• High FiO2
• PDA still open leading to excessive blood delivery to lungs
• Large shunt diameter

Treatment

Following treatment is instituted:

• For mild to moderate symptoms fluid resuscitation and diuretics is given. Permissive hypercapnia and lowering of FiO2 is done.
• For severe symptoms systemic vascular resistance and pulmonary vascular resistance is adjusted.
• Refractory to medical management cases are usually treated with a surgical approach that involves pulmonary artery band or clamping.

Prognosis

• Modified Blalock-Taussig Shunt has a superior prognostic value over classic Blalock-Taussig Shunts. Following prognostic factors are compared between the two procedures in multiple studies:
  • Rise in saturation of oxygen is greater in modified than in classic shunt
  • Shunt patency is 88.8 % in modified for 3-5 years versus 90 % in first year, 62 % in two years and 78.0 % in 3 years for classic shunt.
  • The risk of early shunt failure is 20.8 % in modified and 51.7% in the classic shunt.
  • Post-shunt increase in pulmonary arterial index (mm2/m2) is 158 +/- 21 versus 117 +/- 52 in classic Blalock-Taussig shunt.

Blalock-taussig shunt annotated image, Source: Dr. Vincent Tatco.

Alternative Shunts

Central Shunt

• Central shunt is made by making a anastomosis between ascending aorta and main pulmonary artery.
• A short PTFE conduit for this purpose is used.
• It is also known as Mee's shunt.
• Internal mammary artery is used for this purpose and to create a systemic to pulmonary conduit after there has been a failure of previously used BT shunt.
• It leads to adaptation of growth and flow and reduces the risk for graft infection.

Advantages	Disadvantages
Can be done in small children with small vessels	Can not be performed without in patients without patent ductus arteriosus
Distortion of pulmonary vessels is avoided	Entry into pericardium
Equal blood flow is provided to both lungs
Low chance of occlusion rate
Subclavian steal syndrome is usually avoided

Potts shunt

• It can be used as an alternative to Classic BT shunt.
• To avoid the consequences of right heart failure, it has been used as an alternative to offload the right ventricle.
• This improves the cardiac output but the oxygen saturation is lowered and there is decreased oxygen delivery to lower extremities.
• Pott's shunt includes a connection that is made between descending aorta and left pulmonary artery.

Advantages	Disadvantages
Subclavian artery is used hence large diameter so surgery can be easily performed	Increased incidence of pulmonary hypertension
Lower chance of occlusion than CBTS and mBTS	Increased blood flow to one lung while there is kinking of pulmonary artery
	Increased risk of congestive heart failure

Waterston shunt

• It is made by connecting the ascending aorta and right pulmonary artery.
• It has not been clinically performed now due to increased risk of congestive heart failure, pulmonary hypertension, and kinking of the pulmonary artery.

Cooley Shunt

• It is an intrapericardial anastomosis between ascending aorta and the right pulmonary artery.
• Right anterolateral thoracotomy approach is used.

Advantages	Disadvantages
Use of right anterolateral incision for all approaches - Mediastinal dissection is avoided	Improper size of shunt can lead to right heart failure and pulmonary congestion
Total repair can be done after this shunt in future	Risk of intracardiac adhesions
	Complexity of the procedure