Effect of Ischemic Preconditioning Based on Different Epicardial Branching Patterns of the Left Coronary Artery in the Rabbit Heart

The aim of this study was to characterize the effect of increasing numbers of preconditioning cycles on the different branching patterns (bifurcation/trifurcation) of the coronary artery in the rabbit heart. Fifty-six NZW rabbits were assigned to a bifurcation group and subjected to 0, 1, 3, 5, or 7 (B0, B1, B3, B5, or B7 subgroup, respectively) cycles of preconditioning (PC) (5 min of regional ischemia plus 10 min of reperfusion/cycle) and this was followed by 45 min of sustained ischemia and 72 h of reperfusion; 16 rabbits were assigned to a trifurcation group and subjected to 0, 1, 3, or 5 (T0, T1, T3, or T5 subgroup, respectively) cycles of PC. The ratio of necrotic zone (NZ) to ischemic zone (IZ) was calculated. The bifurcation group showed higher mortality (28.6%) than the trifurcation group (0%). The volume of the ischemic zone (expressed as a percentage of volume of the left ventricle) and the volume of the necrotic zone were larger in the bifurcation group than in the trifurcation group. The ratio of the necrotic zone to the ischemic zone was significantly lower in the B5 and B7 subgroups than in the B0, B1, and B3 subgroups. In the trifurcation group, the ratio of the necrotic zone to the ischemic zone showed a diminishing tendency in the subgroups as the PC cycle number increased, but without statistical significance. Thus, in the trifurcation pattern of the rabbit coronary artery there could be little effect on preconditioning, but in the bifurcation pattern the number of preconditioning is recommended to be 5 to 7 cycles. In this regard, different branching patterns of the epicardial branching of the rabbit coronary artery should be considered when interpreting experimental results on ischemic preconditioning.