What is the management and treatment of Major Aortopulmonary Collateral Arteries (MAPCAS)?

Major Aortopulmonary Collateral Arteries (MAPCAs): Management and Treatment

MAPCAs are congenital vessels arising from the aorta that provide pulmonary blood flow in patients with compromised pulmonary circulation, most commonly associated with pulmonary atresia with VSD, and require a strategic approach balancing surgical unifocalization, transcatheter occlusion, or conservative management depending on the specific anatomy, degree of shunting, and clinical presentation. 1

Definition and Pathophysiology

• MAPCAs are persistent segmental arteries that connect the aorta or its branches to the pulmonary arterial vasculature, serving as the primary or supplementary source of pulmonary blood flow 2
• These vessels occur in three anatomic patterns: unifocal with confluent good-sized pulmonary arteries supplied by a patent ductus arteriosus; multifocal with confluent but hypoplastic pulmonary arteries supplied by multiple MAPCAs; and multifocal with non-confluent pulmonary arteries supplied by MAPCAs 1
• The clinical presentation varies dramatically based on pulmonary blood flow—patients with reduced flow present with cyanosis and failure to thrive, while those with excessive flow through large MAPCAs develop heart failure and may progress to segmental pulmonary hypertension 1

Diagnostic Approach

Echocardiography serves as the first-line diagnostic technique, showing absence of direct right ventricular-to-pulmonary artery flow with continuous flow on color Doppler from multiple MAPCAs. 1

• Cardiac catheterization is mandatory to determine sources of pulmonary blood supply, size of pulmonary arteries, assess pulmonary hypertension, and evaluate MAPCA anatomy 1
• CMR and CT are required to fully characterize the pulmonary vascular anatomy, with imaging findings critical for surgical and interventional planning 1, 2
• Clinical examination reveals continuous murmurs at the back suggesting MAPCAs, with profound cyanosis in unrepaired patients even with minimal physical effort 1
• Chest X-ray demonstrates a boot-shaped cardiac contour with abnormal, decreased pulmonary vascularity alternating with areas of increased vascularity through large MAPCAs 1

Management Strategy: A Decision Algorithm

For Patients with Pulmonary Atresia and MAPCAs

The primary goal is achieving complete repair with incorporation of all lung segments while maintaining low right ventricular pressure. 3, 4

Early Unifocalization Approach (Preferred Strategy)

• Perform early unifocalization at 3-6 months of age, with VSD closure if 15 or more out of 20 lung segments can be recruited 3
• Patients with confluent, good-sized pulmonary arteries and a pulmonary trunk are suitable for Fallot-like repair using a transannular patch 1
• Patients with good-sized pulmonary arteries but without a pulmonary trunk require repair with an RV-PA conduit 1
• For confluent but hypoplastic pulmonary arteries, place an arterial shunt or reconstruct the RVOT without VSD closure to enhance pulmonary artery growth, then reassess for later repair with a valved conduit 1

Staged Unifocalization for Complex Anatomy

• For non-confluent pulmonary arteries with borderline vasculature, leave the VSD open with a limiting RV-PA conduit as an interim or definitive circulation 3
• Rehabilitation of small native vessels with central shunts can be effective, but optimal outcomes require unifocalization of MAPCAs together with native vessels when present 3
• Patients with non-confluent pulmonary arteries and adequate but not excessive pulmonary blood flow can survive into adulthood without surgery 1

For Transcatheter Occlusion of MAPCAs

The decision to occlude MAPCAs depends on three critical factors: degree of left-to-right shunting, degree of cyanosis and effective pulmonary flow, and degree of dual supply between the MAPCA and native pulmonary artery. 1

Class I Indications (Must Occlude)

• Transcatheter occlusion is indicated for MAPCAs with documented large left-to-right shunting in biventricular or single-ventricle physiology causing congestive heart failure, pulmonary overcirculation, respiratory compromise, pleural effusion, or protein-losing enteropathy 1

Class IIb Indications (May Consider)

• Transcatheter occlusion may be considered for moderate-sized collaterals in asymptomatic single-ventricle patients undergoing routine pre-Glenn or pre-Fontan catheterization 1
• Occlusion may be considered in consultation with surgeons for patients with pulmonary atresia and MAPCAs that have adequate dual supply from native pulmonary arteries 1

Class III Contraindications (Do Not Occlude)

• Never perform transcatheter occlusion in patients with significant cyanosis due to decreased pulmonary flow, as MAPCAs provide beneficial augmentation of pulmonary blood flow 1
• Do not occlude MAPCAs in patients with pulmonary atresia when vessels can be unifocalized into native pulmonary arteries 1

For Adult Patients Previously Considered Unoperable

All unrepaired adult patients should be critically re-evaluated in specialized centers, as modern surgical and interventional techniques may now offer benefit even in complex cases. 1

• Patients with good-sized confluent pulmonary arteries may benefit from repair, particularly if they have not developed severe pulmonary vascular disease due to protecting stenoses 1
• Large MAPCAs anatomically suitable for unifocalization without advanced RV or LV dysfunction should be considered for repair 1
• Many unrepaired patients remain unsuitable for surgery due to pulmonary vasculature complexity 1

Critical Pitfalls and Complications

Procedural Risks

• The primary risk of transcatheter occlusion is inadvertent device embolization into important systemic arteries, particularly when MAPCAs arise from head vessels (carotid or subclavian arteries) 1
• Select devices that can be accommodated by the collateral vessel to prevent fallout during implantation 1
• Contrast extravasation may occur with catheter manipulation into small collaterals 1

Long-Term Complications in Unrepaired Patients

• Haemoptysis occurs from rupture of small collateral vessels or small pulmonary artery thrombosis 1
• Chronic heart failure develops from multifactorial causes including chronic cyanosis, early excessive pulmonary blood flow, increased pulmonary vascular resistance, RV dysfunction, and aortic regurgitation 1
• Progressive ascending aorta dilation with increasing aortic regurgitation may occur, with aortic dissection as a rare complication 1
• Endocarditis is particularly compromising in patients with limited cardiovascular reserve and significant cyanosis 1
• Arrhythmia and sudden cardiac death are not uncommon 1

Surgical Outcomes and Contemporary Results

• In a 20-year institutional experience with 780 patients, complete repair was achieved in 90% of patients, with 67% achieving complete repair during the first surgery 4
• Median right ventricular to aortic pressure ratio after complete repair was 0.34, indicating excellent hemodynamic results 4
• Cumulative mortality at 10 years was 15%, with no difference across surgical eras 4
• Risk factors for mortality include Alagille syndrome (HR 2.8), preoperative respiratory support (HR 2.0), and palliative first surgery (HR 3.5) 4

Specialized Care Requirements

All patients with MAPCAs require management in specialized centers with access to congenital cardiac surgeons, adult congenital heart disease cardiologists, and cardiac anesthesiologists with congenital heart disease expertise. 5

• Collaboration and careful planning between interventionalists and surgeons is essential, with the ultimate goal of maximizing and evenly distributing true pulmonary flow while minimizing pulmonary pressure 1
• Advanced imaging including cardiac MRI and CT should be available 5