Abstract 18986: Collateral Flow In the Canine Heart Derived From Coronary Wedge Pressure Overestimates Actual Collateral Flow Measured by Fluorescent Microspheres

Abstract

Purpose: In severe coronary artery disease, coronary collateral flow may prevent distal ischemia. Clinically the ratio between coronary wedge pressure and aortic pressure is used as index of collateral flow. The aim of this study was to validate this method by selective microsphere injections in the LAD during obstruction of LCX flow. Methods: The study was conducted in ten mongrel dogs and was performed in accordance with the Principles of laboratory animal care (NIH) as well as local IACUC. Under anesthesia a thoracotomy was performed and a guide wire equipped with both a pressure and a Doppler velocity sensor was introduced in the LCX. Fluorescent microspheres were injected into the LAD with partial and full occlusions of the LCX. Collateral flow derived from pressure was expressed as the fractional flow reserve, FFRcoll_p calculated according to its definition as; FFRcoll_p = FFRmyo - FFRcor where FFRmyo is the assumed true myocardial FFR. FFRcor_p is zero by definition during full occlusion and unity in the absence of any stenosis resistance. At full occlusion FFRcoll_p equals the ratio between distal wedge pressure, Pw, and aortic pressure Pa. At partial occlusion FFRcoll_p can be calculated from distal pressure, Pd, and Pa by means of the linear FFR model. With microspheres, FFRcoll_m is measured as the ratio between microsphere density in the LCX and that in the LAD perfusion territory but corrected for the estimated contribution of septal 28%, and right, 21%, coronary contribution to LCX collateral flow as derived from literature data. Results: Both, FFRcoll_p and FFRcoll_m were inversely related to the ratio between LCX flow velocity by the maximal hyperemic coronary flow velocity in the LCX. FFRcoll_p overestimated FFR_m at all occlusion degrees by a factor of 3 in average. At full occlusion this difference was significant according to Wilcoxon paired test with P<0.0005. Conclusions: These results show that during severe occlusion pressure-derived measurement of collateral flow overestimates collateral flow as determined from microsphere distributions. Pressure based assessment of collateral flow may thus yield an incorrect estimate of collateral flow.