Volume of LV and RV myocardium perfused by intramyocardial arteries of maturing pigs

It has previously been shown that the volume of LV myocardium perfused by a coronary artery varies with the artery's lumen cross‐sectional area (CSA) and that the “slope” (S=[mm 3 of perfused myocardium]/[perfusing artery's lumen CSA, mm 2 ]) of that relationship increases with body weight (M, kg), but that this difference was normalized when the slope was divided by M 0.75 , an index of metabolic rate. In order to determine whether this weight‐based relationship holds for maturing animals, we used pigs at 3 ages. Group 1 consisted of 3, 98‐day, fetal piglets (0.43 kg), Group 2 of 3, 1 month‐old, pigs (9.3 kg) and Group 3 of 3, 5 month‐old, pigs (61.7 kg). After anesthesia the coronary arteries were infused with radiopaque Microfil ® . Transmural “biopsies” (approx. 2 cm 3 ) of the right and left ventricular wall (RVW, LVW) and outflow tract (RVO, LVO) regions were obtained and scanned in a micro‐CT scanner at 20μm cubic voxel resolution. The 3D micro‐CT images were used to identify a number (~3/”biopsy”) of 200μm diameter intramural arteries. The inter‐branch lumen segment diameter and myocardial volume perfused by the downstream branches of the trees were used to calculate S for all arterial segments. The mean and SE of S/M 0.75 (mm 3 /mm 2 ) are:These data are consistent with the myocardial microcirculation in the fetal pig being perfused maximally, whereas in the adult it is perfused at about 20% of maximum perfusion capacity. Supported in part by NIH grant EB000305