Pulmonary Artery Banding

Anatomy and Physiology

Before considering pulmonary artery banding as a potential palliation strategy, several anatomic features need to be considered. It is important to consider the length of the main pulmonary artery (MPA) to allow placement of a band in the mid-portion of MPA without impinging pulmonary valve in the proximal segment and branch pulmonary arteries (PA) distally. The inferior aspect of the right PA typically arises slightly more proximally on the MPA than the left PA and also arises in a more acute angle. Therefore right PA tends to be at a higher risk of impingement when the band is placed, as any migration of the band distally may result in distortion of the RPA, although this can occur with the left pulmonary artery as well. Given the higher pulmonary to systemic blood flow ratio, MPA tends to be larger than aorta with a more thin-walled vessel, thereby increasing the risk of vessel wall rupture at the time of surgery.

Patients with a large ventricular septal defect and low pulmonary vascular resistance will ultimately develop pulmonary over-circulation. This will manifest clinically with signs of congestive heart failure, including tachypnea, poor feeding, and pulmonary edema. In the short term, these symptoms may be managed with diuretics, systemic afterload reduction, and potentially nasogastric feeding supplementation. However, long term pulmonary over-circulation may lead to irreversible vascular changes, with progressive vascular medial hypertrophy and the development of pulmonary hypertension from increased vascular resistance. This is particularly true with conditions of high pressure and high volume flow (i.e., large VSD), as opposed to low-pressure but high-volume flow (i.e., large ASD).

A PAB creates narrowing in the mid-segment of MPA, increases subpulmonic ventricular afterload, thereby reducing left to right shunting and decrease in pulmonary blood flow via physical restriction of flow. This protects pulmonary vasculature from being exposed to high pressures and thus attenuates deleterious remodeling. The reduction in shunt volume will consequently increase systemic cardiac output and blood pressure. In cardiac defects that require adequate mixing of pulmonary and systemic blood to maintain reasonable systemic oxygen saturation (i.e., transposition of the great arteries), PAB might not be tolerated, especially in the presence of a restricted atrial septal defect. Therefore surgical septectomy or balloon septostomy might need to be performed before attempting PAB.[12][10][13]

Indications

Pulmonary artery banding is performed with predominantly two objectives:

1) Reduce pulmonary blood flow in patients with significant pulmonary over circulation secondary to significant left-to-right shunting in as palliation prior to later definitive surgical repair.

2) Increase afterload to the morphological left ventricle (which functions as a low-pressure pulmonary ventricle) in order to prepare or "train" the ventricle to become a systemic ventricle prior to an arterial switch procedure in patients with transposition of the great arteries (TGA). 

Clinical scenarios in which pulmonary blood flow requires limitation via PAB include:[14][12]

1) Muscular "Swiss cheese" ventricular defects (VSD) which may be technically challenging to repair and/or require ventriculotomy in infants.

2) Multiple or single VSD with confounding surgical comorbidities (i.e., very low birth weight, sepsis, pneumonia, intracranial hemorrhage, multiorgan failure, etc.).

3) Unbalanced AVC defects with borderline left ventricular hypoplasia as palliation prior to committing to potential biventricular repair after further development and growth.

4) High-risk infants with hypoplastic left heart syndrome with bilateral PAB and patent ductus arteriosus stenting for short term surgical palliation.[15][16][17][18]

Clinical scenarios for the patient requiring LV training include:[12]

1) Preparation of left ventricle in patients with D-TGA presenting late (>1month) for a subsequent staged arterial switch operation, where the LV has become "deconditioned" by functioning as the pulmonary ventricle.

2) Preparation of left ventricle in patients with L-TGA for a subsequent staged double switch procedure.

3) Reduction of tricuspid regurgitation in patients with L-TGA without VSD. In this scenario, the pressure load to the pulmonary LV induces a shift of interventricular septum that improve coaptation of tricuspid valve leaflets in the systemic right ventricle.

4) As an adjunct procedure in patients with single ventricle anatomy and antegrade pulmonary blood flow at the time of bidirectional Glenn shunt placement to maintain some antegrade flow but maintain low superior vena cava pressure.

Contraindications

1) Infants with certain single ventricle defects (i.e., double inlet left ventricle or tricuspid atresia with TGA where there exists a potential future risk of subaortic obstruction) or with aortic arch anomalies:[19] Pulmonary artery banding can cause ventricular/conal hypertrophy leading to worsening of subaortic stenosis.[20]

2) Patients with pressure gradient across the systemic outflow tract/subaortic region >15-20 mmHg: This may create a scenario of "double banding" where both the systemic and pulmonary outflow tracts have significant outflow gradients and therefore impose a pressure overload on both ventricles.

3) Severe AV valve regurgitation of the pulmonary ventricle (or of the systemic AV valve in single-ventricle patients): The increased afterload imposed by the band in this scenario may worsen the AV valve regurgitation and is generally considered a relative contraindication.

4) Truncus arteriosus: The short MPA in type 1 truncus arteriosus may be difficult to the band and may impinge onto the right PA. Furthermore, patients with Type 2 & 3 truncus arteriosus would require bilateral PAB, balancing blood flow to bilateral lungs remains extremely challenging. Finally, PAB placement in scenarios of both systolic and diastolic pulmonary flow, such as truncus arteriosus, may be less effective in limiting pulmonary flow due to the continuous nature of flow (as opposed to purely systolic flow in patients with a VSD). Thus, for several anatomic and physiology reasons, PAB is generally avoided in these patients.

Personnel

A multidisciplinary team comprising of healthcare workers including cardiothoracic surgeons, pediatric cardiologists, cardiac anesthesiologists, surgical and intensive care nurses, and perfusionists carries outy the pre-surgical planning, intra-procedural support, and post-surgical care.

Preparation

Pre-operative evaluation should include echocardiography for detailed anatomic definition. Additional imaging with magnetic resonance imaging and/or cardiac catheterization may be helpful to provide a further anatomical and physiological evaluation in complex defects, although these are generally not required for simple defects such as a VSD. The focus of pre-operative management should be to minimize left to right shunt by providing systemic afterload reduction and aggressive diuresis, especially in patients with congestive heart failure symptoms. In patients with severe pulmonary over circulation, respiratory support may be required, and adequate oxygenation and ventilation are maintained using mechanical ventilator support, especially in the setting of pulmonary edema. Attention to avoid excessive oxygen is important, as the pulmonary vasodilatory effective of inspired oxygen will act as a pulmonary vasodilator that will augment pulmonary flow.

Technique or Treatment

The standard surgical approaches to pulmonary artery banding include: 1) Anterior left thoracotomy through the 2nd/3rd intercostal space, 2) Left lateral thoracotomy through 3rd/4th intercostal space, 3) Median sternotomy. In the case of anterior/lateral thoracotomy, MPA is exposed by retracting thymus and dissecting the pericardium anterior to the left phrenic nerve. When median sternotomy is pursued, especially during concomitant surgeries such as atrial septectomy, the use of cardiopulmonary bypass is indicated. In patients with TGA or single ventricle anatomy, median sternotomy is preferred as it gives excellent exposure to MPA.

Surgical technique: After exposure to the aorta and MPA, the band is prepared for placement. Various materials are used for banding. The umbilical tape is preferred by few surgeons due to its low affinity to erode through the vessel wall and can be easily modified to be used as an adjustable band by passing it through a silastic snare. Trusler formula has classically been used to help determine the optimal band circumference.[21] This formula has specified the following dimensions as a good initial guide: non-cyanotic mixing lesions = 20 mm + 1 mm/kg; mixing lesions = 24 mm + 1 mm/kg; single ventricular physiology with a plan for future palliative Fontan surgery = 22 mm + 1 mm/kg. Final band circumference is determined by the pressure gradient through the band, distal pulmonary artery pressures, and potentially by the degree of desaturation if the patient has single ventricle physiology.

The mid-portion of MPA is identified, paying close attention to the location of the pulmonary valve and branch PAs, in an attempt to avoid impingement of brand PAs and distortion of the pulmonary valve. Adventitia between aorta and MPA is dissected to avoid migration of the band. The band is passed across the transverse sinus encircling the pulmonary trunk. The band is then carefully passed between aorta and MPA through the previous dissection site, thereby avoiding the need to pass a clamp across MPA and potentially injuring the vessel. The marked sites of the band are aligned along the anterior wall of MPA and snared by passing it through polyethylene tubing. A pericardial pledget is placed underneath the snare to avoid injury to the vessel, and hemoclips are used to fix the snare.

The addition or removal of hemoclips helps reduce or increase the circumference of the band, respectively. Occasionally resorption of infoldings of MPA over the course of a few weeks will reduce the restriction across the MPA, thereby loosening the band. Therefore a technique to perform v-shaped arteriotomy of the MPA distal to sinotubular junction has been described. This is done using a C-clamp before placing the band to avoid the future risk of loosening the band. Cardiovascular hemodynamics to be achieved post-PAB include: 1) PA pressured 30 to 50% of systemic pressures 2) Oxygen saturation of approximately 90% at 50% FiO2, 3) Increase in systemic blood pressure by 5 to 10 mmHg. In patients with single ventricle physiology, lower arterial oxygenation targets are acceptable.

The takedown of PAB is usually performed after the staged intracardiac repair is completed. The scar tissue around the PAB is dissected, and removal of the band usually demonstrates the evidence of stenosis of MPA. This is corrected either by resection of the stenotic segment followed by end-to-end anastomosis or vertical incision of the stenotic segment with patch augmentation of the stenotic segment. In patients with whom the PA bands have been in place several months or less, this PA plasty is often not necessary.

Complications

Potential complications of pulmonary artery banding include:

1. Stenosis or distortion of one or both branch PAs
2. Alterations in the function of the pulmonary valve
3. Impingement of circumflex artery
4. Erosion of band into the pulmonary artery
5. Pseudoaneurysm of pulmonary artery 
6. Hemolysis
7. Thrombosis
8. Ineffective band placement leading to irreversible changes to pulmonary vasculature cause pulmonary hypertension
9. Local infection

Clinical Significance

Successful PAB often results in significant improvement in cardiac hemodynamics, resolution of signs/symptoms of congestive heart failure, improvement in pulmonary over circulation, and reduction in ventricular end-diastolic volume. The mortality rate among patients undergoing PAB is more reflective of the complexity of underlying congenital heart defects rather than the procedure itself. The patients who often undergo PAB in preparation for a staged surgical repair may have been considered high risk for a definitive repair. Therefore, early studies reported approximately 25% mortality with PAB.[22] However, subsequent improvement in surgical techniques, appropriate timing of PAB placement, and improvements in perioperative care have significantly reduced the mortality rate by approximately 5%.[23][24][25][26]

Enhancing Healthcare Team Outcomes

Pulmonary artery banding (PAB) is a palliative surgical technique used for the correction of congenital cardiac defects, characterized by pulmonary over-circulation caused by left-to-right shunting of blood. PAB is reserved for palliation in a certain subset of infants with complex congenital heart disease.[1] [Level 3] PAB protects pulmonary vasculature by reducing excessive pulmonary blood flow, thereby preventing the onset of irreversible remodeling of the pulmonary vasculature and pulmonary hypertension.

In patients with D & L transposition of great arteries (TGA), PBA helps "train" the left ventricle in preparation for a staged arterial switch procedure. A multidisciplinary team of healthcare workers, including cardiothoracic surgeons, pediatric cardiologists, cardiac anesthesiologists, surgical and intensive care nurses, and perfusionists, is involved in the pre-surgical planning, intra-procedural support, and post-surgical care.