The right timing for post-ischemic stunning

Excerpt

Myocardial stunning refers to a state of prolonged contractile dysfunction of post-ischemic myocardium in which normal myocardial function is gradually restored after a given recovery period. The first description of this phenomenon dates back to the early 30’s, where Tennant and Wiggers demonstrated in their seminal experiments in open-chest dogs that, within 60 seconds of coronary occlusion, myocardial contractions in the ischemic zone change from active systolic shortening to passive systolic lengthening.1 Forty years later, Heyndrickx and colleagues revealed that while regional electrograms normalize within seconds and coronary flow is restored within minutes, contractile dysfunction lasts for up to 2 hours after a 5-minutes occlusion and for up to 24 hours after a 15-minutes occlusion.2 Two important concepts were born: Post-ischemic stunning is determined by (i) the severity and (ii) the duration of myocardial ischemia. This phenomenon is explained by changes induced in contractile proteins and in the cellular ionic environment by a brief coronary occlusion which may outlast normalization of blood flow by several hours. In fact, after experimental coronary occlusion, myocardial ATP concentration declines quickly and metabolites of ATP such as adenosine, hypoxanthine, and inosine accumulate. Since the myocardium is permeable to these substances, they are washed out from the ischemic myocardium during reperfusion. As a consequence, the re-synthesis of ATP is delayed and the period of reduced ATP concentration is prolonged.3,4 …