Coronary microvascular reactivity after ischemic cold storage and reperfusion

The coronary microvascular system is important in the regulation of myocardial perfusion. Preservation of microvascular reactivity may be important in those hearts undergoing ischemic storage for transplantation. Endothelium-dependent relaxation of right and left ventricular coronary microvessels was examined in a canine model of heart transplantation.

Canine hearts underwent topical cooling, antegrade arrest, and 3 hours' ischemic cold storage at 4 degrees C using crystalloid cardioplegia (n = 8), Roe's solution (n = 8), and University of Wisconsin solution (n = 8). All groups underwent 1 hour of reperfusion in an isolated heart circuit. Noninstrumented canines were used as controls (n = 10). Coronary microvessels (100 to 200 microns in diameter) were examined in a pressurized, no-flow state with video microscopic imaging and electronic dimension analysis.

Endothelium-dependent microvascular relaxation was examined in response to the receptor-dependent acetylcholine and to the receptor-independent calcium ionophore. Microvascular relaxation to acetylcholine in Roe's solution and University of Wisconsin solution was preserved (p = not significant) in the left ventricle, whereas crystalloid cardioplegia failed to preserve (p < 0.05) microvascular relaxation when compared with the control groups. Right ventricular microvascular relaxation was always (p < 0.05) less than left ventricular microvascular relaxation. Endothelium-independent microvascular relaxation to nitroprusside was similar to that in controls, indicating normal smooth muscle responsiveness.

Ischemic cold storage with Roe's solution and University of Wisconsin solution preserved microvascular relaxation in the left ventricle, whereas crystalloid cardioplegia failed to preserve microvascular relaxation. Right ventricular microvascular relaxation was impaired in all groups, but University of Wisconsin solution was superior to crystalloid cardioplegia and Roe's solution. This suggests that microvascular dysfunction may be partially responsible for right ventricular dysfunction after heart transplantation. The choice of preservation solution may be important in preservation of the microvascular endothelium.