Functional anatomical site of intramural collaterals in dogs

The objectives of the present study were to determine quantitatively whether the retrograde flow measurement reflects the total flow from collateral vessels or overestimates or underestimates collateral flow, and to determine the functional anatomical origin of intramural collaterals in the native dog heart. In an isolated heart preparation, three experimental procedures were used. 1) The left circumflex coronary artery was embolized with microspheres of different sizes; then retrograde flows and the peripheral coronary pressures were measured. 2) Epicardial collaterals were cauterized, and retrograde flows were measured before and after cautery. 3) Epicardial collaterals were cauterized followed by embolization of the circumflex coronary artery with different size spheres. We found that 1) the retrograde flow measurement underestimates the total collateral flow to the circumflex coronary artery by approximately 25%, 2) intramural collateral flow constitutes 58 +/- 3.5% of the retrograde flow measurement, 3) the antegrade component of blood flow that is not measured during a retrograde flow measurement is from the intramural collateral circulation, and 4) the functional site of origin of intramural collaterals is greater than 25 microns but less than 80 microns in diameter. We conclude that, in our preparation, retrograde flow underestimates total collateral flow, and that intramural collateral flow is a major component of retrograde flow in the native dog heart.