Major aortopulmonary collateral arteries (MAPCA) occur in cyanotic congenital heart diseases with decreased pulmonary blood flow (tetralogy of Fallot like physiology). They are a natural protective mechanism to improve pulmonary blood flow. MAPCAs are more likely to occur in pulmonary atresia than in simple tetralogy of Fallot.
MAPCAs can also occur in conditions other than the typical pulmonary atresia with ventricular septal defect. In a retrospective review of such cases, 33 had single ventricle anatomy while the rest had two ventricle anatomy. Among those with single ventricle, 15 had unbalanced complete atrioventricular canal, 6 had pulmonary atresia with intact ventricular septum and 12 with other forms of single ventricular physiology. Among the 17 patients with MAPCAs and two ventricles, 5 had complete atrioventricular canal, 4 had corrected transposition, 3 had double outlet right ventricle, 3 had scimitar syndrome and 2 had complex D-transposition of great arteries .
A study from Stanford University reported on all infants undergoing first cardiac surgery for tetralogy of Fallot/MAPCAs from 2001 to 2019 . 1068 MAPCAs were noted in 276 patients. 55% had incompletely arborizing pulmonary arteries, 17% had normally arborizing pulmonary arteries and 16% had absent pulmonary arteries. Unilateral MAPCAs were noted in 11%. Each of the 18 pulmonary segments could be supplied either by a MAPCA, central pulmonary artery or both. But all these variations were conducive of a good repair. Patients with low total MAPCA and/or pulmonary artery cross-sectional area were less likely to undergo complete surgical repair. Total cross-sectional area of central pulmonary arteries and MAPCAs is an important driver of outcome .
Unifocalization of MAPCAs is an important initial procedure in the surgical repair of patients with cyanotic congenital heart disease and MAPCAs. When the lungs are supplied by multiple MAPCAs, they are unifocalized prior to definitive surgical repair. Connecting the distal end of MAPCAs to a single vessel is known as unifocalization. In a report of 50 patients with anatomy other than the typical pulmonary atresia with ventricular septal defect, the initial cardiac operation was unifocalization/shunt in 34 cases .
Two important measures on the size of pulmonary arteries are the McGoon ratio and the Nakata index. McGoon ratio is the sum of the diameters of pulmonary arteries divided by the diameter of the aorta . Nakata index is the sum of the cross-sectional area of the pulmonary arteries divided by the body surface area. Nakata index was initially described as pulmonary artery or PA index by Nakata S et al .
As the intrapulmonary pulmonary arteries are often larger than the intrapericardial pulmonary arteries in tetralogy of Fallot/MAPCAs, pulmonary artery diameters measured at the first lobar bifurcation in the anteroposterior projection is used to calculate a modified Nakata index. This is assuming a circular cross section of the pulmonary arteries. Sum of cross-sectional areas of single supply MAPCAS and single supply branches from mixed supply MAPCAs divided by body surface area is defined as MAPCA index. Modified Nakata index and MAPCA index were added to get a total neo-pulmonary artery index (TNPAI). Patients with larger TNPAI are more likely to undergo single stage repair .
MAPCAs can originate from either of the subclavian arteries or their branches, transverse aorta, descending thoracic aorta, abdominal aorta at or below the level of the diaphragm or coronary artery .