It is not difficult to diagnose atrial fibrillation (AF) according to typical ECG manifestations. However, AF complicating electrolyte disorder, drug poisoning or other arrhythmia challenges its clinical diagnosis. It is very important to identify these kinds of arrhythmias for making clinical decisions. This paper mainly makes a brief description about ECG changes of AF complicated by the above circumstances.

Objective  To study the clinical value of ST-segment changes and QRS duration in leads V₄ and Ⅲ in identifying different involvements of the left anterior descending (LAD) artery among patients with acute inferior ST-segment elevation myocardial infarction (STEMI). Methods  Retrospective analysis was performed on 189 patients with inferior STEMI who had undergone coronary angiography. Among these patients, 64 were divided into LAD occlusion group (LAD obstruction≥99%, n=17), LAD stenosis group (50%＜LAD obstruction＜99%, n=21) and normal LAD group (without LAD obstruction, n=26) according to different degrees of LAD obstruction in a single culprit vessel (the right coronary artery or left circumflex artery). The clinical data of the three groups were compared; the receiver operating characteristic (ROC) curve was utilized to determine the related cut-off values of ST-segment deviation and QRS duration in leads V4 and Ⅲ. ResultsThe proportion of patients with hypertension or cerebral infarction in the normal LAD group is lower than that in the LAD occlusion group and the LAD stenosis group; the proportion of patients with diabetes or cardiac function of Killip Ⅲ-Ⅳ in the LAD occlusion group is higher than that in the normal LAD group (P＜0.05). The left ventricular ejection fraction in the LAD occlusion group is significantly lower than that in the other two groups(P＜0.01), and the serum NT-proBNP level of the normal LAD group is the lowest (P＜0.01).In terms of electrocardiogram, the deviation of ST-segment depression in lead V4 (STV4↓), the difference between ST-segment depression in lead V4 and STsegment elevation in lead Ⅲ (STV4↓-STⅢ↑), and QRS duration in lead V4 (QRSV4) of patients in the LAD occlusion and LAD stenosis groups are higher than those of patients in the normal LAD group (P＜0.05). QRS duration of lead Ⅲ in the LAD occlusion group is widened as compared to the normal LAD group (P＜0.05). ROC curve analysis indicates that STV4↓-STⅢ↑＞-1.46 mm and QRSV4＞97.38 ms are of high predictive value for patients with inferior myocardial infarction complicating LAD involvement (including LAD occlusion or stenosis). The sensitivity of these two indexes are  separately 83.3% and 68.4% while the specificity are 57.1% and 80.8%, respectively.   A combination of the two are improved in diagnostic performance  with a sensitivity of 76.3% and a specificity of 84.6%. Conclusion  Inferior STEMI patients with LAD lesion have many comorbidities, especially in the presence of LAD occlusion, their cardiac function would be worse. The indexes of STV4↓-STⅢ↑ and QRSV4 could provide  clues for diagnosing  complicated LAD lesions in patients with inferior STEMI.

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