Clinical Application of Remote Ischemic Preconditioning

Ischemic preconditioning1 has been shown to reliably reduce ischemic myocardial cell necrosis in a host of animal models.2 Although preconditioning is one of the most powerful and reproducible phenomena in cardioprotection, it has not readily translated to routine clinical use. One issue is that the timing of the long duration of ischemia must be known in advance and the treatment must be applied before the long duration of ischemia. Thus, although evidence suggests that preinfarction ischemia (angina) before an ST-segment elevation myocardial infarction is associated with smaller infarct size and better clinical outcome,3 there is no reliable way to predict when a myocardial infarction will occur and hence no way to either induce ischemic preconditioning or apply a preconditioning mimetic agent just before the infarction. There are, of course, situations in which myocardial ischemia is planned, eg, during coronary artery balloon angioplasty, during coronary artery bypass surgery, during excision and transportation of a donor heart, and before exercise in a patient with known demand-induced ischemia. Preconditioning has been applied to some of these situations. For example, multiple brief balloon inflations and deflations in the coronary artery reduce the severity of chest pain, ST-segment elevation, and lactate production on subsequent balloon inflations compared with an initial balloon inflation without necessarily recruiting blood flow.4 Intermittent aortic cross clamping before coronary artery bypass surgery has been observed to preserve cardiac high-energy phosphate levels.2 These examples of ischemic preconditioning require an invasive procedure to induce ischemia within the heart and the possibility of showering atherosclerotic emboli either down the coronaries or into the aorta as a coronary angioplasty balloon is repeatedly inflated or deflated or the aortic cross clamp is repeatedly clamped and unclamped.