Alfred Blalock and Helen Taussig ushered in the surgical treatment of congenital heart disease with the introduction in clinical practice of a systemic artery-to-pulmonary artery (PA) shunt in 1944. In the current era of early complete correction of congenital heart disease, the Blalock–Taussig shunt still plays an important role in the surgical management of newborns and infants with inadequate pulmonary blood flow.^1–3 The paradigm shift emphasizing early complete repair is based on contemporary data demonstrating the deleterious effects of palliative physiology, coupled with the realization that most infants can tolerate operative correction. However, some malformations still require a staged approach toward eventual correction, while others may necessitate a palliative procedure when anatomic or patient factors preclude complete repair. A staged repair is often favored when there are extenuating technical issues that stem from morphologic complexity or severe extracardiac pathology that would make one-stage correction prohibitive. The functionally single ventricle (Chapter 77) is an example of this strategy, by which a staged palliative approach eventually achieves the goal of separating the pulmonary and systemic circulations.

Palliative or staged procedures are primarily designed to modify pulmonary blood flow, enhance intracardiac mixing, or rehabilitate a ventricle prior to definitive surgery. For example, aortopulmonary shunts will increase pulmonary blood flow, while a pulmonary artery band (PAB) will limit pulmonary perfusion. Although conceptually simple, palliative operations pose several unique challenges. Intraoperatively, the infants are often low birth-weight or even preterm, and might have other extracardiac factors that have mitigated against complete repair. Postoperatively, the palliated state complicates patient management, as equipoise must be achieved between the pulmonary and systemic circulations (Chapter 60), also inviting the opportunity for interstage attrition.

As early complete repair has become increasingly more common, indications for systemic-to-PA shunts are in some respects controversial. However, a shunt still remains the initial procedure for duct-dependent single-ventricle lesions and also specific lesions with inadequate pulmonary blood flow in the presence of two adequate ventricles. In those instances, a systemic-to-PA shunt may be necessary for early survival, at the expense of further surgical procedures.

A systemic-to-PA shunt could be indicated in any anomaly that presents with obstruction of blood flow either entering or exiting the right heart (in specific types of tricuspid atresia, or pulmonary stenosis or atresia not amenable to percutaneous intervention, for example). Other indications include anomalies with unbalanced pulmonary blood flow where a systemic-to-PA shunt (alone or, rarely, with a PAB) can be used to provide a controlled source of pulmonary blood flow.

Classic Blalock–Taussig Shunt

The development of palliative procedures began at the Johns Hopkins Hospital with the goal of providing improved blood flow to the pulmonary vascular bed in cyanotic children; the subclavian-to-right PA shunt was introduced clinically in 1944.³ This method of systemic-to-PA shunt followed the pioneering experimental work by Alfred Blalock and Vivien Thomas, who created a canine model of PA hypertension by anastomosing the subclavian artery to the transected end of the PA; this concept was adopted as a palliative attempt to augment pulmonary blood flow in patients with tetralogy of Fallot. In the 2 years following the first successful case, hundreds of cyanotic children traveled to Baltimore to undergo a classic Blalock–Taussig shunt. The reported early mortality was 16 percent, and only 6 percent of the patients were refused surgery.

The shunt is performed on the side opposite the aortic arch, by anastomosing the subclavian artery to the ipsilateral PA in an end-to-side fashion. There is usually an innominate artery on the side opposite the aortic arch, and it provides adequate length and orientation to allow for the subclavian to form a gentle curve inferiorly toward the PA. Access to the subclavian artery is typically obtained via an anterolateral thoracotomy (Fig. 62-1). The branches of the subclavian artery are also ligated. Additional mobilization can be obtained by freeing the proximal carotid artery from surrounding tissues. The subclavian artery is then brought through the loop of the recurrent laryngeal nerve, oriented down toward the PA, and sewn to the main PA. Division of the inferior pulmonary ligament will often help in facilitating this anastomosis.

Even though the classic Blalock–Taussig shunt has the distinct advantage of avoiding the use of prosthetic material, this procedure has been largely abandoned because of concerns regarding ipsilateral arm or hand ischemia. Although an asset in the era preceding the advent of open cardiac surgical intervention, the growth potential of this shunt may provide excessive pulmonary blood flow and therefore additional volume-load to the ventricle, which can be extremely detrimental in single ventricle patients. At the time of corrective surgery, the shunt may be taken down via median sternotomy by entering the plane posterior to the superior vena cava (SVC).

Modified Blalock–Taussig Shunt

A significant modification of the classic Blalock–Taussig shunt, first performed by Redo and Ecker in 1963, involved the interposition of a prosthetic graft to connect the systemic circulation to the PA (Fig. 62-2).^4–6 This procedure was later reported by Gazzaniga in 1976 and termed the “modified” Blalock–Taussig shunt by deLeval in 1975.⁷ This modification provides several advantages over the standard Blalock–Taussig shunt: less tendency to deform hypoplastic PAs, less need for mediastinal dissection, preservation of upper extremity blood flow, consistent shunt flow (regulated by the internal diameter of the ostia of the innominate or subclavian arteries), and adequate length. Disadvantages include a 10 to 15 percent incidence of seroma formation and the rare possibility of endocarditis or thrombosis (3–5 percent). Because of these significant advantages, the modified Blalock–Taussig shunt remains the most widely used systemic-to-PA shunt today. Initial concerns that there may be a risk of impaired growth of the contralateral PA have been discredited by current literature, which demonstrates that equivalent growth without distortion can be accomplished with the modified shunt.⁵ Compared to the classic Blalock–Taussig shunt, the modified Blalock–Taussig shunt has a more predictable life span, which is limited by the lack of growth potential. These shunts are destined for short-interval use and generally require some other surgical intervention to provide a reliable source of pulmonary blood flow as the child grows.

The modified Blalock–Taussig shunt can be performed through either right or left thoracotomy, or via a median sternotomy. The decision to perform a sternotomy versus a thoracotomy is usually dictated by surgeon preference. However, in some circumstances the approach is dependent on the vascular anatomy and on the location of the ductus arteriosus. For instance, the shunt should be placed on the side of the dominant SVC (so as to facilitate pulmonary arterioplasty at the time of bidirectional cavopulmonary shunt placement) and opposite to the ductus arteriosus. The three different approaches have subtle advantages and disadvantages. Some authors have suggested that a right-sided shunt is easier to take down, while others suggest that a thoracotomy is preferred because, at the time of the next operation, the pericardium will be relatively free of adhesions. A median sternotomy prevents post-thoracotomy scoliosis, allows for duct ligation, a shorter and more centrally located shunt with less distortion and eventual loss of the upper lobe PA branch, and affords the ability to initiate cardiopulmonary bypass in case of hemodynamic instability or intolerable levels of hypoxemia. Currently, the sternotomy approach is favored by most centers in the United States.

In performing the procedure via thoracotomy, the chest is usually entered through the fourth intercostal space. The lung is retracted inferiorly and medially and the mediastinal pleura opened posterior to the SVC. The innominate and/or subclavian arteries are dissected free from the surrounding tissues and controlled with vessel loops. During this portion of the dissection, great care is taken to avoid the recurrent laryngeal nerve, which, on the right side, courses around the distal innominate artery at its bifurcation into subclavian and common carotid arteries. Next, the PA is mobilized, first proximally toward the pericardial reflection and then distally to the first bifurcation. The vessels are controlled with vascular tapes. An expanded polytetrafluoroethylene (ePTFE, Gore-Tex) graft is then beveled with scissors to conform to the natural curve of the systemic artery. A Cooley or Castaneda vascular clamp is applied to the innominate artery, encompassing the origin of the right subclavian artery and an arteriotomy is made on the inferior aspect of the artery. The anastomosis is performed with a 7-0 monofilament suture in a running fashion. Some authors prefer systemic heparinization prior to systemic vessel clamping; we prefer to heparinize the patient after the first anastomosis is complete. The clamp is then repositioned on the graft to minimize systemic arterial trauma. If at this point the azygos vein lies in the direct path of the shunt, it is ligated and divided. The distal anastomosis is performed by first placing a stay suture in the direct center of the superior margin of the unmanipulated PA to make sure that there will be no torsion or kinking during occlusion. Prior to initiating the anastomosis, vascular tapes are used for a test-occlusion of the PA. Once the surgeon is assured that the patient will tolerate single-lung perfusion, the pulmonary arteriotomy is made by excising a circular portion of the PA. The excised portion should be larger than the diameter of the graft so as to avoid proximal stenosis. The graft is then cut to length, attempting to avoid any redundancy. The anastomosis is again performed with a 7-0 monofilament suture in a running fashion. Clamps and tapes are then released, hemostasis is assured, and the chest closed with a pleural drain. There should be a nearly instantaneous increase in the patient’s oxygen saturation and a drop in the diastolic blood pressure, with a palpable thrill in both shunt and PA.

If a sternotomy is chosen, the sequence remains the same. Following sternotomy and thymectomy, the pericardium is left undisturbed and the innominate artery is mobilized to the bifurcation. A limited pericardial incision is then made in order to mobilize the PA between the aorta and SVC. The anastomosis is performed as described above. Ligation of the ductus arteriosus or additional sources of pulmonary blood flow are dependent upon individual patient anatomy as well as surgeon’s preference.

The size and the length of the shunt are important factors in controlling the amount of pulmonary blood flow. Decisions regarding shunt dimensions should consider both the size of the patient as well as whether additional sources of pulmonary blood flow exist. Most infants of normal birth weight require a 3.5-mm shunt. Infants weighing less than 3.5 kg should be treated with a shunt of no less than 3 mm, and the distal anastomosis should be constructed almost entirely to the subclavian artery rather than to the innominate artery. Larger infants may receive shunts as large as 4 or 5 mm. Ideal shunt characteristics may be achieved by indexing shunt diameter to the patient’s body size or surface area.^8,9

Regardless of the approach used to create the shunt, it is usually relatively straightforward to take down a modified Blalock–Taussig shunt through a median sternotomy at the time of the next procedure. A right-sided shunt can be found by dissecting the plane between the aorta and SVC. A left-sided shunt presents more difficulty at the time of takedown and is usually identified by dissecting along the left PA, the inferior aspect of the aorta, or by entering the pleural space. The ePTFE graft can be interrupted with hemoclips and simply divided, usually with the proximal end oversewn. The distal (PA) end of the graft does not need to be removed unless access to the PA is required as part of the procedure (e.g., in case of a superior cavopulmonary anastomosis or a pulmonary arterioplasty).

Right Ventricle-to-Pulmonary Artery Conduit

In selected diseases (hypoplastic left heart syndrome (HLHS) and pulmonary atresia with ventricular septal defect (VSD)),¹⁰ a right ventricle-to-pulmonary artery (RV–PA) conduit can be utilized to provide pulmonary blood flow during initial palliation. The RV–PA PA conduit, first utilized in patients with HLHS by Norwood in 1981 in 4 consecutive patients, consisted of large nonvalved PTFE tubes (8 and 12 mm).¹¹ This was quickly abandoned due to uniformly fatal outcome of the 4 patients. Despite these initial failures, however, the concept of a RV–PA conduit has theoretical advantages over a standard systemic-to-PA shunt.^12–14 First, pulmonary blood flow occurs only during ventricular systole, and therefore diastolic runoff and “coronary steal” are eliminated. Second, because of the reduced pulmonary blood flow relative to a systemic-to-PA shunt, volume load on the ventricle is also reduced, which is critically important for single ventricle patients. Postoperative fluctuations in pulmonary and systemic vascular resistance in the single ventricle patients become less critical to control as myocardial perfusion is decoupled. However, there are also disadvantages to the RV–PA conduit. Construction of this shunt requires a ventriculotomy, which could predispose to ventricular dysfunction or enhance the substrate for late arrhythmias. Furthermore, the reduction in pulmonary blood flow could lead to reduced growth of the branch PAs or lead to early cyanosis, necessitating earlier creation of additional sources of pulmonary blood flow (e.g., bidirectional cavopulmonary anastomosis).

Creation of the RV–PA conduit has been described by others.^11–14 Our current preference is as follows: After median sternotomy, a patch of autologous pericardium is harvested and fixed in glutaraldehyde. On the back table, a “skirt” of pericardium is created by punching a calibrated hole in the pericardial patch the exact size as the intended shunt diameter, and anastomosing the pericardium to the intended distal (PA) end of the ePTFE ringed graft using 6-0 Goretex suture. If the RV–PA shunt is performed as part of a modified Norwood operation, cardiopulmonary bypass is initiated and the pericardial skirt is created during systemic cooling. Otherwise, cardiopulmonary bypass is initiated following “skirt” creation. A 5-mm (for infants greater than 3.5 kg) or 6-mm ringed ePTFE graft is selected and the proximal end is beveled for later anastomosis to the right ventricle. Following cardiopulmonary bypass, the ductus arteriosus is ligated, the aorta is cross-clamped and the heart is arrested with a single dose of cardioplegia infused into the aortic root. The PA confluence and branch PAs are widely mobilized and encircled with vessel loops. The RV–PA shunt is most easily constructed slightly to the left side of the PA confluence. The PA is incised sharply and a small oval excised. In the case of a modified Norwood, the PA has been transected and thus a large defect already exists in which to construct the anastomosis. The cuffed PTFE graft is anastomosed to the PA with running 7-0 prolene. The vessel loops are released, and the graft is de-aired and controlled with a straight vascular clamp. Most rings are removed from the proximal aspect of the graft. A right ventriculotomy is created approximately 1.5 to 2.0 cm below the pulmonary valve using a calibrated punch. Care is taken to avoid any conal arterial branches that may be crossing the infundibulum. A small rim of endomyocardium is excised to prevent any late dynamic or muscular obstruction. The beveled end of the ePTFE graft is sutured to the edges of the ventriculotomy using interrupted pledgeted mattress sutures. Alternatively, we have utilized a running suture technique with two long homograft pledgets surrounding the ventriculotomy.

Outcomes of the RV–PA conduit have been extensively studied.^9,11,13 Many studies, including a large cohort of patients studied through Fontan completion from the Children’s Hospital of Philadelphia¹⁵ have found no difference in morbidity and mortality depending on whether a modified Blalock–Taussig or RV–PA conduit was utilized as part of first stage palliation. In the recently completed single ventricle reconstruction trial, prospectively randomized infants with HLHS received either a modified Blalock–Taussig shunt (N = 275) or an RV–PA conduit (N = 274). The trial demonstrated a 1-year transplantation free survival advantage in the RV–PA shunt group (74 percent) compared to the modified Blalock–Taussig shunt group (64 percent; P = 0.01).¹⁴ However, transplantation-free survival was equivalent between both groups at a mean follow-up of 32 ± 11 months. The RV–PA conduit group had more unintended interventions and complications compared to the modified Blalock–Taussig shunt group. Importantly, pulmonary arterial size, as assessed by the Nakata Index, was lower for the RV–PA shunt group, but right ventricular size and function at the age of 14 months was similar among both groups.

Waterston and Potts Shunts

The success of Blalock–Taussig procedure spawned a number of other systemic shunts. In 1946, Potts described an aortopulmonary shunt,¹⁶ performed by creating an anastomosis between the descending aorta and the left PA through a left thoracotomy in patients with a right-sided aortic arch. To facilitate this procedure, a special partial occluding clamp was devised to minimize the risk of paraplegia. The Potts shunt was used throughout the 1940s and 1950s in patients thought to be too small for a classic Blalock–Taussig shunt. The Potts shunt was associated with several serious complications, including PA aneurysms and sizing difficulties, which often led to persistent cyanosis or chronic pulmonary hypertensive changes. In time, the Potts shunt was abandoned owing to its unnecessary difficulty and the risk associated with shunt takedown. Simple ligation of the shunt often leads to uncontrollable hemorrhage, requiring peripheral bypass and circulatory arrest to achieve control and repair.

In 1955 Davidson and colleagues first described a shunt between the ascending aorta and the PA. In 1962, Waterston reported a similar intrapericardial anastomosis between the posterior ascending aorta and the right PA (Fig. 62-3).¹⁷ The procedure was performed through a right thoracotomy; the right PA and ascending aorta are both partially occluded with the same clamp. After making two opposing arteriotomies, the PA and ascending aorta were sewn side to side. This shunt was very effective in infants but was prone to PA kinking, with resultant unequal pulmonary blood flow and subsequent hypoplasia of the underperfused PA. The Waterston shunt is taken down intrapericardially at the time of definitive repair, the aorta is primarily closed, and the PA is patched.