How would you interpret the 12-lead ECG shown in the figure below? This tracing was obtained from a 51-year-old man with new-onset chest pain. What is the likely “culprit” artery?

Although there is much artifact (especially in leads II and III), this does not prevent appreciation of the obvious abnormalities on this tracing. The rhythm is sinus tachycardia at a rate of just over 100/minute. The PR and QRS intervals are normal; the QT interval appears prolonged. The axis is normal. There is no chamber enlargement. There are small and narrow Q waves in most inferolateral leads. R wave progression is normal, with transition occurring between leads V2 to V3. There are dramatic ST-T wave changes. There is over 10 mm of J-point ST segment depression in several anterior leads. All lateral leads show marked ST segment elevation, which nearly attains 10 mm in lead V6.

There is an obvious acute ST elevation myocardial infarction (STEMI). Localization of ST segment elevation to the lateral leads strongly suggests acute occlusion of the left circumflex (LCx) artery. This is supported by the finding of several millimeters of ST elevation in lead II, but virtually none in leads III and aVF. In contrast, with acute right coronary artery (RCA) occlusion, ST elevation is localized to the inferior leads, with the relative amount of ST elevation typically more in lead III compared to lead II. The dramatic anterior ST depression strongly suggests acute posterior as well as lateral infarction. This distribution of marked and acute inferolateral wall involvement is seen with acute occlusion of a dominant LCx artery.

Fortunately, this large acute STEMI was immediately recognized. Cardiac catheterization with prompt reperfusion of a dominant LCx artery resulted in rapid resolution of virtually all ST-T wave abnormalities. Coupled with no more than minimal troponin elevation and complete resolution of symptoms, it is likely that almost all jeopardized myocardium was salvaged with minimal long-term damage from this acute event. Cardiac catheterization revealed severe underlying multi-vessel coronary disease, which helps account for the extreme amount of ST-T wave deviation seen in this case.

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