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Introduction:Inferior wall ST elevation MI (inf STEMI) may be caused by acute occlusion of the right coronary artery (RCA) or left circumflex artery (LCx). The ECG criteria of ST elevation (STE) in III greater than II with ST depression (STD) in aVL greater than I has been reported to predict RCA culprits; conversely, LCx culprits have been suggested to not satisfy these criteria.Objective:To evaluate the ECG criteria for predicting the culprit artery in inf STEMIs.Methods:We analyzed ECGs and coronary angiograms of 213 adult patients who presented to our institution from January 2009 to December 2013 with acute inf STEMI. ECGs were read by 2 investigators blinded to angiograms; likewise, coronary angiograms were read by 2 investigators blinded to ECGs. We recorded the coronary dominance (right, left, and co-dominant) and affected segments of the culprit lesions.Results:Of 213 patients with inf STEMI, 177 (83%) had RCA culprits and 36 (17%) had LCx culprits. The ECG criteria had 76% sensitivity, 69% specificity, 92% PPV, and 37% NPV for identifying the RCA versus LCx as the culprit. Dominance-stratified data is as shown (Table 1).Conclusion:We found that this commonly used ECG criteria for predicting culprit artery in inf STEMI had relatively low sensitivity, specificity, and NPV but excellent PPV. Our study highlights the importance of coronary circulation dominance in interpreting these results. The LCx is rarely the culprit unless it is a dominant or co-dominant vessel (27 out of 36). The excellent PPV is in large part due to the high prevalence of RCA culprits in inf STEMI. The low specificity is in part due to false positives from culprit dominant and co-dominant LCx (8 out of 11). The low NPV is a consequence of the low prevalence of LCx culprits in inf STEMI and the high number of false negatives. Nearly all false negatives (41 out of 42) are right dominant which demonstrates the limitations of these ECG criteria for identifying culprit artery in inf STEMI.