The ECG in localizing the culprit lesion in acute inferior myocardial infarction: a plea for lead V4R?

This editorial refers to ‘Distinguishing the right coronary artery from the left circumflex coronary artery as the infarct-related artery in patients undergoing primary percutaneous coronary intervention for acute inferior myocardial infarction’ by N.J. Verouden et al., on page 1517 The electrocardiogram (ECG) is being used for decades as a reliable and inexpensive tool to diagnose acute myocardial infarction in the patient with chest pain. More recently, an emphasis has been made on ECG features that allow better identification of the coronary occlusion site and thereby better estimation of the size of the area at risk, which is important for selection of the preferred type of reperfusion. On average the left anterior descending coronary artery supplies 50% of blood flow and the right coronary artery (RCA) and circumflex (Cx) coronary artery each supply 25% of blood flow to the left ventricular myocardium. In addition, RCA irrigates most of the right ventricle. The closer the occlusion site to the origin of the coronary artery, the larger the ischaemic area and the greater the necessity of a rapid reperfusion attempt. The ECG findings considered to be helpful to localize the occlusion site in the culprit coronary artery have been described by several authors and are summarized elsewhere. 1 In the current issue of the journal, Verouden et al. looked at the value of the standard 12-lead ECG to distinguish the RCA from the Cx coronary artery as an infarct-related vessel in a large series of patients with acute inferior MI undergoing primary percutaneous coronary intervention shortly thereafter. 2 ST-segment elevation in lead III more than in lead II, combined with ST-segment depression in lead I or aVL was used as a marker, suggesting that the culprit lesion was located in RCA. The study is important because of the large number of patients and the short time interval between the 12-lead ECG and the coronary angiogram. The findings can be summarized that using this ECG algorithm a correct diagnosis as to the coronary occlusion site did not reach a pre-specified sensitivity threshold of 90% in the whole group. Of interest is that when the authors applied algorithms published by other investigators using ST-segment deviation in the extremity leads, even lower sensitivity was observed. Only in the case of a total 12-lead ST-segment deviation score of more than 18.5 mm, a sensitivity of more than 90% was found. We are not informed about the accuracy of the algorithm in relation to the degree of ST-segment deviation. Is there a critical threshold of