FLOW-FUNCTION RELATIONS DURING GRADED CORONARY OCCLUSIONS IN THE DOG - EFFECTS OF TRANSMURAL LOCATION AND SEGMENT ORIENTATION

Objective: The sensitive relationship between regional myocardial perf usion and local systolic deformation during acute myocardial ischemia is not independent of the transmural location or segment orientation. The aim of this study was to determine the effects of fiber orientatio n and transmural location on the relationships between regional myocar dial flow and three-dimensional systolic wall strain during graded cor onary artery occlusions, Methods: Transmural distributions of three-di mensional strain (by biplane radiography of implanted radiopaque marke rs) and myocardial blood flows (using fluorescent microspheres) were m easured in the ischemic region during graded left anterior descending (LAD) coronary artery occlusions in 12 anesthetized dogs. Results: Occ lusion of the coronary artery did not significantly alter mean heart r ate or end-systolic pressure. As flow decreased during graded occlusio ns, ischemia significantly changed systolic circumferential, longitudi nal, radial, fiber and cross-fiber strains (p < 0.004). There was a si gnificant effect of transmural position on circumferential, cross-fibe r and radial strains, but not on fiber or longitudinal strains. Ischem ia significantly altered all normal strains: circumferential, longitud inal, fiber, cross-fiber and radial. There was a strong interaction ef fect between transmural location and blood flow for circumferential, c ross-fiber and radial strains, but not fiber or longitudinal strains. Conclusion: During non-transmural ischemia, there is evidence of stron g transmural tethering in the cross-fiber direction, whereas the fiber -strain flow relation is independent of transmural position. Thus, whe ther the relationship between local myocardial bloodflow and systolic strain during acute ischemia is dependent on transmural location, depe nds on segment orientation. (C) 1998 Elsevier Science B.V.