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In these cases, the clinician may rely on the history and physical examination or order a transthoracic echocardiogram to facilitate the decision whether to proceed with acute reperfusion therapy. The reported percentage of patients with false activation of the p-PCI protocol because of nonischemic STE varies from 14% to over 40%,[5, 7-9] although it has recently been suggested that a http://www.selleckchem.com/products/a-1331852.html goal.[10] It seems that this percentage is highly dependent on the prevalence of abnormal baseline ECGs in the population served by the individual medical center. It has to be also remembered that not all patients with positive cardiac markers who present with STE and found to have angiographically proven coronary artery disease, even with significant stenosis, have true STE-ACS. Some may have NSTE-ACS with baseline nonischemic STE, so-called ��pseudo-STEMI.��[11] In adjudicated true STE-ACS, the pattern of ST-segment deviation should be compatible with the site of occlusion of the coronary artery and resolution of the ECG changes is expected if timely reperfusion therapy is successful. Aborted STEMI adds to the confusion: if the coronary artery occlusion recanalizes rapidly, either spontaneously or with reperfusion therapy, even transmural ischemia due to complete occlusion of an epicardial artery may resolve without (significant) elevation of cardiac markers.[12] Stress-induced (takotsubo) cardiomyopathy may present http://www.selleck.cn/products/PLX-4720.html with STE, fulfilling reperfusion criteria, on the 12-lead ECG. By definition, these patients have neither significant culprit artery stenosis nor intracoronary http://www.selleckchem.com/products/avelestat-azd9668.html thrombi. However, preexisting coronary artery disease does not exclude the possibility of stress-induced cardiomyopathy in an individual patient, resulting in differential diagnostic challenges.[4] Acute transmural ischemia may affect the QRS-complex, the ST-segment, and the T-wave morphology. The pattern of ECG changes enables the reader to estimate the site of coronary artery occlusion, the size and extent of the ischemic area at risk, the severity of ischemia, and prognosis.[11, 13-15] In the chronic phase of myocardial infarction, Q waves are regarded as a sign of irreversible necrosis. However, about 50% of patients presenting within 1 hour of onset of STE-ACS already have Q waves in the leads with STE, especially in the anterior leads.[14] These Q waves may be transient and not necessarily represent irreversible damage. It is believed that intense ischemia may cause a transient loss of electrical activity in the region at risk (��myocardial concussion��). Thus, Q waves on presentation may reflect either irreversible damage and/or a large ischemic zone, and thus portend a large final infarction.