Received: February 3, 2017. Accepted: April 5, 2017.
Abstract
The ST segment corresponds to the plateau phase of ventricular repolarization, ie, phase 2 of the action potential. Heightened awareness of the characteristic patterns of ST-segment changes is paramount to quickly identifying life-threatening disorders. The differential diagnosis of ST-segment elevation includes four major processes: ST-segment elevation myocardial infarction(STEMI); early repolarization; pericarditis; and ST elevation secondary to an abnormality of the QRS complex (left bundle branch block, left ventricular hypertrophy, or preexcitation). Other processes that may be associated with ST elevation include hyperkalemia, pulmonary embolism, and Brugada syndrome. Two particular patterns of ST-segment depression reflect ST-segment elevation myocardial infarction rather than non-ST-segment elevation acute coronary syndrome: ST-segment depression that is reciprocal to a subtle and sometimes overlooked ST-segment elevation, and ST-segment depression that is maximal in leads V1-V3, suggesting true posterior infarction. The clinical setting and specific electrocardiographic criteria often allow identification of the cause.
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