Clinical markers and clinical consequences of stunned myocardium

Clinical markers must be identified to distinguish between stunned and acutely ischemic myocardial tissue, as well as to assess the viability of myocardium. Evaluation of electrocardiographic ST segment abnormalities can distinguish transmural oxygen deprivation from subendocardial oxygen declines, but stunned myocardium may have normal ST segments. Myocardial contrast echocardiography can estimate regional myocardial blood flow but ultrasound measurement of blood flow is not always able to discern stunned from nonviable myocardium. Change in extracellular pH has been used to study ischemia, but has not yet been shown to reflect differences between stunned and ischemic myocardium. A combination of clinical markers of flow, delivery, and oxygen consumption may be necessary in order to differentiate between stunned and ischemic regions. This distinction can have important therapeutic consequences because patients with acutely ischemic but viable myocardium may be ultimately harmed by inotropic drugs that increase myocardial oxygen demand. In contrast, inotropes may be indicated for stunned myocardial tissue. The determination of the reversibility of myocardial dysfunction can also impact on decisions to use mechanical cardiocirculatory support. Differentiation of stunned and ischemic myocardium might also streamline ICU assignments and lead to more effective use of high technology resources.