الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
Despite major advances in cardiac imaging, Electrocardiography (ECG) is still the most accessible and cheapest means to assess patients with symptoms of acute myocardial ischemia. The ECG findings form an essential part of the decision making process, particularly in relation to reperfusion therapy. In acute coronary syndrome (ACS), the number of electrocardiographic leads with ST. Segment deviation (either elevation or depression) is a marker of the extent of ischemiaDifferent studies have been done to assess the usefulness of ECG and validated diagnostic criteria have been established, such as ST elevation in lead aVR and extensive endocardia injury. Yamaji et al compared the ECG finding for LMCA, left anterior descending artery (LAD) and right coronary artery (RCA) obstruction. The authors concluded that greater ST.elevation in lead aVR than in lead V1 predicts LMCA obstruction. The left main coronary artery (LMCA) supplies approximately 75% of the left ventricular myocardial mass and therefore its obstruction leads to life- threatening hemodynamic deterioration. Hence, predicting acute left main coronary obstruction is vital and important regarding selection of the best treatment approach as well as estimation of the patients survival. Augmented vector right (aVR) lead is commonly “ignored” and designated as the “neglected lead”. However, recent investigations have shown that an analysis of ST-segment shift in lead aVR provides useful information on the coronary anatomy and risk stratification in ACS . Recently, the use of lead aVR for predicting appearance and progression of left main lesion has been a subject of great interest. Significant lesions in lead to trans-mural ischaemia in the basal part of the septum can result in ST elevation in lead aVR of electrocardiogram. Several studies has confirmed that raised ST-segment in lead aVR is usually present in LMCA stenosis.However,in other studies it has been shown that ST-Segment elevation in aVR is not specific for LMCA blockage, but there are some other diagnoses such as triple vessel disease(causing subendocardial ischemia due to insufficient blood flow)and a very proximal LAD occlusion (causing transmural infarction of the basal septum )that could cause this finding as well . Lead V1 reflects the right basal septal area, which is supplied by septal branches from the LAD artery alone or together with the conal branch of the right coronary artery (dual circulation). Accordingly, ST-segment elevation in lead aVR and in lead V1 predict LAD lesion proximal to the first septal branch, along with insufficient or absent flow from the conusbranch . Our study was conducted during the period of 6 months between September 2015 and February 2016.It was an observational prospective study that included 822 patients. Of them 186 (22.63%) patients with acute Myocardial Infarction (AMI) and 100(12.17%) patients with Unstable Angina (UA)admitted to our coronary care unit of Asyut University Hospitals and 536 (65.2%) patients who underwent coronary angiography within 6 months after discharge from hospital during this period . To study the value of ST- segment elevation in lead aVR in predicting LMCA or severe proximal LAD stenosis in ACS, we compared the population of the three previous groups. Patients in each group were further divided into two subgroups, based on ECG findings with or without ST- segment elevation in lead aVR. On our study the ST-segment elevation in lead aVR in the patient with clinically suspected ACS suggests a strong possibility of LMCA obstruction as we found that about 80 % of patients with raised ST-segment in lead aVR in STEMI had significant LM coronary artery disease and about 92.3 % of patients with raised ST-segment in lead aVR in UA had significant LM coronary disease. from the study, the sensitivity of ST-segment elevation in lead aVR for predicting LMCA obstruction was determined to be 83.72% and the specificity to be 96.41%.Also in the present descriptive study, we compared the findings on the electrocardiograms (ECGs) of patients with acute LMCA obstruction with those of patients with acute LAD and RCA obstruction, by using simple and multivariate analyses , focusing on the findings of ST segment shifts in leads aVR and V1. According that ,the relationship between the ST segment elevation in lead aVR and V1 would differ between acute LMCA and LAD obstruction.
We found that about 83.7% of cases with raised ST-segment in lead aVR associated with LM disease while only 4 cases (3.5%)of cases with raised ST-segment in lead V1 associated with LM disease in contrast to 102 cases (90.3%)of cases with raised ST-segment in lead V1 associated with LAD disease. While according to relation of RCA obstruction with raising ST-segment in aVR we notice very low sensitivity(60.47%) and specifity (55.97).