MAPCAs are persistent intersegmental arteries-persistence of the branches from the dorsal aorta. These normally regress during fetal life if there is an adequate flow to the native pulmonary arteries(5). These can arise from descending thoracic aorta, subclavian artery, aortic arch, ascending aorta, rarely from the abdominal aorta, intercostal and coronary arteries.  

Are they bronchial arteries?

• MAPCAs do not branch in their mediastinal course and anastomose with the intrapulmonary arteries typically at or near the pulmonary hilum instead of in the periphery.

• MAPCAs may accompany bronchi but do not form a nutritive plexus around bronchi and are never connected to intercostals arteries. 

• Histologically, MAPCAs have an elastic wall structure resembling PA or aorta which is absent in bronchial arteries(6).

Types of MAPCAs

Depending upon the arterial supply to the lung in TOF with pulmonary atresia, various classifications describe MAPCAs

In Barbero-Marcial classification, pulmonary atresia with VSD is divided into 3 types based on the supply of the bronchopulmonary segments.

Type A - All the bronchopulmonary segments are connected to the central PAs.

Type B - Some bronchopulmonary segments are supplied by branches of the central PAs whereas other segments are supplied by MAPCAs.

Type C - All the bronchopulmonary segments are supplied exclusively by MAPCAs, and central PAs are absent(7,8).

In congenital heart surgery nomenclature and database project, published in 2000 by The Society of Thoracic Surgeons, patients with PA-VSD were divided into 3 types, according to the anatomy and morphology of the pulmonary circulation bronchopulmonary segments.

Type A: Native pulmonary arteries(NPA)were present. No MAPCAs.

Type B: Both NPA and MAPCAs are present.

Type C: No NPA. MAPCAs supplying the pulmonary circulation (9).

Somerville classification of pulmonary atresia is as follows(10):

Type I: Atresia of pulmonary valve with complete PA development.

Type II: Atresia of pulmonary valve and MPA. RPA and

LPA are present, which may be separate or joined.

Type III: Atresia of pulmonary valve, MPA, and one main

branch.

TypeIV: Atresia of the pulmonary valve, MPA, and both

MPA branches.

Robimovitch classification followed by some surgeons is based on origin of the systemic collateral arteries, with type I being a branch of bronchial artery, type II direct aortic and type III indirect aortic branch(11).

The physiologic status of the patient determines the timing and type of initial surgical intervention(12).

The presence of the main pulmonary artery with confluent pulmonary arteries is a minimum requirement for a single-stage complete surgical repair. Patients with severely hypoplastic MPA or hypoplastic/stenotic branch pulmonary arteries need to undergo preliminary surgical procedures such as systemic- pulmonary shunt to prepare the pulmonary circulation for a complete repair(13, 14).

Unifocalisation is defined by Puga FJ et al as “the group of surgical procedures directed toward the restoration of segmental and lobar pulmonary arterial confluence by creation of a central, single, and accessible source of pulmonary flow”(15).

MAPCAS can be unifocalized as a single stage procedure with complete repair or multistage unifocalisation followed by final complete repair.

In single stage procedure, complete repair is done if the pulmonary arterial size was more than 75% of expected or perfuse more than 15 segments of the lung(1).

Early single-stage unifocalization decreases the time they are subjected to systemic pressures (15,16)

The surgical management of the MAPCAs depends on multiple factors based on the following

Origin:  The large central MAPCAs originating close to the MPA can be easily unifocalized at the time of complete repair through a median sternotomy. For the ease of localizing the MAPCA, the clock position of its origin, as viewed by the surgeon from the foot end of the patient and the level of origin in relation to the vertebral body, carina or main bronchi is preferred.

Size and length: The MAPCAs are considered small if they are < 2mm in size (~ size of an intercostal artery) or significant of they are > 2mm in size(~ size of internal mammary artery).  MAPCAs with a calibration of 2 mm or less may not be good candidates for unifocalization. Whether the MAPCAs are sufficient in length to reach the site of anastomosis in unifocalisation.

Type of supply to lung:

The MAPCAs can be the only source of blood supply to the lung or they can be present with native pulmonary artery.  If dual blood supply to a lung segment from the native pulmonary arteries and MAPCAs is documented, the MAPCAs can be occluded in the catheterization or ligated at the time of unifocalization. If MAPCAs are the only source of blood supply to lungs, then it is important to preserve the supply.

Protected vs Unprotected:

The MAPCAs can develop stenosis as they have high flow at higher systemic pressure. While the protected MAPCAs have proximal stenosis leading to obstructed low pressure flow, the unprotected MAPCAs without stenosis have unobstructed flow. Unprotected MAPCA segments are prone to develop irreversible pulmonary vascular disease,  there by the repair in older patients have questionable outcome.

Native pulmonary arteries:

It is important to know the state of native pulmonary arteries and arborisation. If the NPA are present, whether they are normal sized or hypoplastic, confluent or non confluent. These factors help assess the requirement for central shunt/RV-to-PA conduit.

Presence of patent ductus arteriosus(PDA), AP window. The length of PDA, presence of stenosis.