<Li> those with a so - called non-diagnostic or normal ECG . However, a normal ECG does not rule out acute myocardial infarction . </Li> <P> The current guidelines for the ECG diagnosis of the ST segment elevation type of acute myocardial infarction require at least 1 mm (0.1 mV) of ST segment elevation in the limb leads, and at least 2 mm elevation in the precordial leads . These elevations must be present in anatomically contiguous leads . (I, aVL, V5, V6 correspond to the lateral wall; V3 - V4 correspond to the anterior wall; V1 - V2 correspond to the septal wall; II, III, aVF correspond to the inferior wall .) This criterion is problematic, however, as acute myocardial infarction is not the most common cause of ST segment elevation in chest pain patients . Over 90% of healthy men have at least 1 mm (0.1 mV) of ST segment elevation in at least one precordial lead . The clinician must therefore be well versed in recognizing the so - called ECG mimics of acute myocardial infarction, which include left ventricular hypertrophy, left bundle branch block, paced rhythm, early repolarization, pericarditis, hyperkalemia, and ventricular aneurysm . </P> <P> There are heavily researched clinical decision tools such as the TIMI Scores which help prognose and diagnose STEMI based on clinical data . For example, TIMI scores are frequently used to take advantage of EKG findings for prognosing patients with MI symptoms . Based on symptoms and electrocardiographic findings, practitioners can differentiate between unstable angina, NSTEMI and STEMI, normally in the emergency room setting . Other calculators such as the GRACE and HEART scores, assess other major cardiac events using electrocardiogram findings, both predicting mortality rates for 6 months and 6 weeks, respectively . </P> <P> Sometimes the earliest presentation of acute myocardial infarction is the hyperacute T wave, which is treated the same as ST segment elevation . In practice this is rarely seen, because it only exists for 2--30 minutes after the onset of infarction . Hyperacute T waves need to be distinguished from the peaked T waves associated with hyperkalemia . </P>

What changes can occur on an ecg due to myocardial infarction