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Fundamentals of reperfusion injury for the clinical cardiologist.

Case presentation: S.B. is a 48-year-old man who suffered an acute anterior myocardial infarction and received fibrinolytic therapy. The patient died ≈12 hours after reperfusion. K.R. is a 68-year-old diabetic woman who underwent conventional coronary artery bypass graft surgery and developed low output syndrome after reperfusion postoperatively. V.A. is a 55-year-old man who developed a stunned myocardium after percutaneous coronary reperfusion. What is reperfusion injury, and why is it important?

Reperfusion of coronary flow is necessary to resuscitate the ischemic or hypoxic myocardium. Timely reperfusion facilitates cardiomyocyte salvage and decreases cardiac morbidity and mortality. Reperfusion of an ischemic area may result, however, in paradoxical cardiomyocyte dysfunction, a phenomenon termed “reperfusion injury.” Modalities for reperfusion include not only thrombolysis, but also percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG), and cardiac transplantation. Reperfusion injury has been observed in each of these situations. We discuss here the fundamental principles of reperfusion injury from a mechanistic and pharmacological standpoint.

### What is reperfusion injury, and why is it important? 

The myocardium can tolerate brief periods (up to 15 minutes) of severe and even total myocardial ischemia without resultant cardiomyocyte death. Although the cardiomyocytes suffer ischemic injury, the damage is reversible with prompt arterial reperfusion. Indeed, such transient periods of ischemia are encountered in the clinical situations of angina, coronary vasospasm, and balloon angioplasty, and are not associated with concomitant myocyte cell death.1,2⇓ With increasing duration and severity of ischemia, however, greater cardiomyocyte damage can develop, with a predisposition to a spectrum of reperfusion-associated pathologies, collectively called reperfusion injury.3 Reperfusion injury results in myocyte damage through myocardial stunning, microvascular and endothelial injury, and irreversible cell damage or necrosis (termed lethal reperfusion injury; Figure 1).3,4⇓ 



Figure 1. Mechanisms and mediators of reperfusion injury. Reperfusion strategies are required to resuscitate the ischemic myocardium. In the clinical realm, these include …