Culprit artery in evolving inferior wall acute myocardial infarction: RCA vs LCx: reply

With interest we read the comment by Fiol et al.1 on our study 2 demonstrating a low diagnostic accuracy of the well-established algorithm 3 to predict the culprit artery in an all-comer cohort of patients with inferior wall ST-segment elevation myocardial infarction (STEMI). In a previous publication, Fiol et al. showed that ST-segment depression in standard lead I of the 12-lead electrocardiogram (ECG) showed the highest sensitivity (92%) to predict right coronary artery occlusion in inferior STEMI patients. 4 The investigators could identify the culprit artery in more than 95% of cases after extension of the ECG algorithm with the ratio of summed ST-segment depression in the right precordial leads and summed ST-segment elevation in the inferior leads. In contrast, ST-segment depression in lead I in our study had a sensitivity of only 79% as previously reported in this journal. 2 Furthermore, application of the complete algorithm (including the abovementioned ratio) to our data set did only modestly improve diagnostic accuracy (to 79%) and therefore did not correspond with the 95% accuracy as stated by Fiol et al. In our view, this discrepancy may be caused by dissimilarities between the above-mentioned study cohorts. In the study by Fiol et al. , coronary flow through the infarct-related artery at the time of ECG recording was unknown and the site of occlusion (proximal vs. distal to the first right ventricular branch of the right coronary artery) was not reported. 4 Moreover, we were not informed about the summed ST-segment deviation of all 12 leads of the index ECG. As presented in our paper, these parameters largely influenced ECG algorithm accuracy. 2 It might well be that the percentage of patients with either a total occlusion of infarct-related artery, with a proximal occlusion, or with extensive ST-segment deviation is higher in the patient population described by Fiol et al. Furthermore, the investigators studied a small and highly selected cohort of patients with no previous history of myocardial infarction and with single-vessel disease. This may have caused an important selection bias resulting in a higher ECG algorithm accuracy. In accordance with the plea for lead V4R formulated in the editorial comment by Wellens, 5 we would like to urge the importance of this lead in the non-invasive diagnosis of the infarct-related artery in inferior STEMI. In addition, ST-segment elevation in lead V4R indicates right ventricular involvement and herewith is a predictor of major in-hospital complications. 6 In our opinion, recording of this additional lead should be a standard act in the initial evaluation of patients with acute chest pain. Unfortunately, we did not systematically record V4R in our study and agree with Dr Wellens that a large cohort of patients with inferior STEMI should be studied to confirm the diagnostic accuracy of lead V4R. Conflict of interest: none declared.