Free radical and granulocyte-mediated injury during myocardial ischemia and reperfusion.

The success of thrombolytic/reperfusion therapy in limiting the extent of myocardial infarction may be limited by reperfusion injury. Damage from acute ischemia is not due solely to the interruption of blood flow; rather, ischemia initiates a cascade of reactions involving partially reduced oxygen, inflammatory mediators, mechanical capillary obstruction by granulocytes and other events that lead to irreversible injury. A surprising consequence is that reperfusion by delivering oxygen and granulocytes may counteract some of the benefits of restoring flow. Mechanisms of neutrophil and free radical injury include superoxide radical formation and lipid peroxidation, progressive leukocyte capillary plugging and capillary no-reflow, and edema. The interaction of various specific mechanisms of injury in the heart (i.e., xanthine oxidase, mitochondrial superoxide leak, neutrophil superoxide, degranulation and capillary plugging, and neutrophil-derived vasoconstrictors) deserves further study.