Electrocardigram Identifying the Culprit Site in Patients With Acute Inferior Myocardial Infarction

Background

Acute myocardial infarction (AMI) usually occurs suddenly and is associated with considerably high mortality rate. The infarct-related artery in inferior wall AMI is usually located at right coronary artery (RCA), less often at left circumflex coronary artery (LCX). [1,2] Inferior wall AMI occlusive site above the first right ventricular branch of RCA was more frequently associated with right ventricular infarction, which had higher incidence of bradyarrhythmia, shock, and in-hospital death.[3-7] Early recognition of the site of infarct-related artery and respond promptly may result in a significant reduction in in-hospital mortality and morbidity.[8-10] Coronary angiography is considered to be the gold standard for determining the culprit site of infarct-related artery, but it is an invasive examination. Additionally, not all hospitals have the facility in performing the cardiac catheterization. There were several non-invasive methods to predict the culprit site including: radioneuclear imaging study, echocardiography or electrocardiogram. Among these methods, electrocardiogram is one of the most simple and useful tools. Several studies have used ST segment elevation in lead III > ST segment elevation in lead II and ST segment depression in lead I, aVL or both to predict that culprit site was located at RCA; ST segment elevation in lead I, aVL, V5 and V6 and ST segment depression in V1, V2 and V3 to predict that the culprit site was located at LCX. [11-24] These electrocardiogram readings including lead III, II, I, aVL, V1, V2, V3, V5 and V6 , which can only differentiate RCA and LCX lesions. If clinicians are intended to know whether the culprit site is located at proximal or distal RCA, further evaluation of the ST segment elevation in leads V1 and V4R,would be needed [25] which makes the algorithm involving too many leads and not so easy to remember. Thus, the aim of this study is designing a method which is simple and useful in identifying the culprit sites in inferior wall acute myocardial infarction (AMI).

Methods

Study Patients:

From review of the medical records, patients suffered from first inferior wall AMI will be enrolled in this study. The diagnosis of acute inferior AMI includes: 1) chest pain > 30 minutes; 2) ST elevation > 1mm in at least two of the three inferior lead (II, III, AVF); and 3) 2-fold increase in serum creatine kinase levels. At least 2 of the above 3 criteria are necessary to confirm the diagnosis. Right ventricular infarction is diagnosed by the presence of an ST-segment elevation of 0.1 mV in the V3R or V4R lead (recorded in all patients with inferior wall MI) in the electrocardiogram performed within 15 minutes after arrival at emergent department. Exclusion criteria include previous AMI or coronary artery bypass surgery, electrocardiographic evidence of bundle branch block, undetermined culprit site by coronary angiography, or first electrocardiogram obtained more than 12 hours after the onset of symptoms. Patient's demographic variables, important risk factors and clinical outcomes including atrioventricular block, arrhythmia, shock, mortality during the first hospital days are recorded.