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). Inferior wall AMI occlusive site before 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. Early recognition of the site of infarct-related artery especially combination with right ventricular infarction and respond promptly may result in a significant reduction in in-hospital mortality and morbidity. There were several non-invasive methods to predict the culprit site, which including: radioneuclear imaging study, echocardiography or electrocardiogram. Among these methods, electrocardiogram is one of the most simple and convenient tool. Several algorisms have investigated but these algorisms included using leads III, II, I, aVL, V1, V2, V3, V5 and V6, which can only differentiate RCA and LCX lesions but cannot assure whether the culprit site is located at proximal or distal RCA. 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).

According to the medical record, patients with inferior wall AMI who have no previous history of MI (or the first AMI attack) will be enrolled. These patients are divided into 3 groups from coronary angiography, depending upon the culprit lesion (1) before (proximal) or (2) after (distal) the right ventricular branch of RCA and (3) LCX. A two-step study strategy will be performed to analyze which electrocardiographic variables are capable of discriminating the culprit site of coronary artery. Using the area under the receiver operating characteristic (ROC) curve analysis, we plan to determine which one of the above variables is the most powerful criterion in discriminating the culprit site of coronary artery. Due to the fact that the case number of the first inferior AMI will be limited, this study will be carried out at 3 hospitals in order to collect more cases with the coming year.

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.

All patients received dual anti-platelates with aspirin and clopidegrol, and anti-coagulant (low molecular weight heparin or unfractured heparin) regimen. Most of the patients have received primary percutanuous coronary intervention. The GpIIb/IIIa antagonists is administered in all patients.

Electrocardiogarphy:

Standard 12-lead electrocardiogram is performed within 12 hours after onset of chest pain in all study patients. ST-segment deviation from isoelectric line will be measured with a calliper at the point of 80 ms after the J point. The preceding TP-segment is considered as the isoelectric line. The magnitudes of ST-segment deviation in 12-lead electrocardiogram and V4R are also assessed.

Coronary angiography:

Coronary angiography is performed during the first day of admission. The cineangiography films are reviewed by 2 interventional cardiologists who are blinded to the electrocardiographic findings. The culprit artery is defined as total occlusion (Thrombolysis in Myocardial Infarction, TIMI grade 0) or significant stenosis (> 70% diameter stenosis) of RCA or LCX and of their major branches with intraluminal thrombosis or supply to hypokinetic territory. The occlusion site of infarct-related coronary artery determined by coronary angiography is classified into three groups: proximal RCA: lesion proximal to the first right ventricular branch of the RCA; distal RCA: lesion distal to the first right ventricular branch of the RCA; and LCX groups.

Statistical analysis:

The data of electrocardiographic findings, patient's characteristics and clinical outcomes are presented as mean ± standard deviation for continuous variables and frequency distribution for discrete variables. Chi-square analysis is used to assess the association of patients' characteristics with site of culprit lesion. One way ANOVA with Bonferroni post hoc test are used to assess the relation between site of culprit lesion and electrocardiographic findings. The value of P ≤ 0.05 is considered statistically significant. The cut-off point of electrocardiographic criteria for predicting culprit coronary artery is determined by receiver operating characteristic (ROC) curve. The area under the ROC curve represents the diagnostic validity of each cut-off points will be determined and compared.

Inclusion Criteria:

• first attacked acute inferior MI patients

Exclusion Criteria:

• those with 1). previous AMI, 2). coronary artery bypass surgery, 3). electrocardiographic evidence of bundle branch block, 4). undetermined culprit site by coronary angiography, 5) first electrocardiogram obtained more than 12 hours after the onset of symptoms.

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.