Modified Blalock-Taussig-Thomas Shunt

Congenital heart disease (CHD) is the most common form of congenital disability, affecting approximately 8 out of every 1000 live births. In many developing countries, CHD often goes undiagnosed until after birth or even later in life, sometimes presenting during childhood or adulthood. About 25% of infants born with a heart defect have critical CHD, necessitating surgical intervention or other procedures within the first year of life. A commonly used palliative procedure for patients with CHD is the modified Blalock-Taussig-Thomas (mBTT) shunt. This procedure improves blood flow to the lungs, reduces cyanosis, promotes pulmonary artery growth, and helps maintain optimal cardiac preload, afterload, and coronary artery perfusion. The mBTT shunt is commonly performed in developing countries as a precursor to more definitive corrective surgery but has become less prevalent in developed nations. Advances in surgical techniques, technology, and the availability of specialized expertise have enabled early corrective surgeries in these regions. Modern surgical decision-making relies on a blend of experience and careful consideration of competing performance goals. For example, the conduit must be sufficiently large to ensure adequate blood flow to the pulmonary vasculature for optimal oxygenation. However, excessive pulmonary blood flow can lead to complications such as pulmonary edema and heart failure. Additional risks associated with shunt hemodynamics include the potential for shunt stenosis or thrombosis, distortion of the pulmonary arteries, impaired coronary perfusion, and uneven growth of the pulmonary arteries. The mBTT shunt, a previous iteration of the classical Blalock-Taussig (BT) shunt, is a palliative surgical procedure designed to treat patients with cyanotic heart diseases that are characterized by decreased pulmonary artery flow. The first BT shunt was performed at the Johns Hopkins Hospital in 1944, resulting from the collaborative efforts of 3 individuals—pediatric cardiologist Dr Helen Taussig, cardiac surgeon Dr Alfred Blalock, and laboratory assistant Mr Vivien Thomas. The term "Blalock-Taussig shunt" was first used by de Leval when reporting on a series of patients who underwent the procedure between 1975 and 1979. In 2003, a request was made to include the eponym "Thomas" to acknowledge the significant contributions of Mr Vivien Thomas to the success of the procedure. The mBTT shunt is designed to provide adequate blood flow to the pulmonary artery, relieving cyanosis while avoiding pulmonary overcirculation. The classical BT shunt procedure involved a lateral thoracotomy, where the subclavian artery was divided and anastomosed to the pulmonary artery in an end-to-side manner. This original technique has undergone extensive modifications, evolving into the mBTT shunt, which uses an interposition polytetrafluoroethylene (PTFE) graft to create a systemic-to-pulmonary shunt without sacrificing the subclavian artery or any of the brachiocephalic tributaries. In 1976, Gazzaniga and colleagues reported using a PTFE graft to construct an aortopulmonary shunt (see  Comparison of Classical Blalock-Taussig and Modified Blalock-Taussig-Thomas Shunts).  The mBTT shunt provides several advantages over the original iteration. By utilizing an interposition PTFE graft, the takedown procedure is simplified, blood flow to the ipsilateral upper limb is preserved, and shunt flow can be more precisely regulated by adjusting the diameter and length of the graft and selecting the appropriate anastomotic site.