| Objective:The aim of this study was to determine ECG parameters, assess the role of STelevation in the leads V5and V6to locate the culprit artery accurately as compared tocoronary angiography in inferior acute myocardial infarction. Furthermore, comparingthe degree of ST-segment elevation in lead V6with that in lead III is useful forpredicting the culprit artery.Background:Inferior wall acute myocardial infarction (AMI) characteristically causes ST-segment elevation in some or all of the inferior leads (II, III, and aVF). Duringinferior acute myocardial infarction, ST-segment elevation often occurs in leads V5and V6, but its clinical implications remain unclear. Some investigators havesuggested that ST-segment elevation in precordial leads V5to V6represents a lateralextension of the infarction, whereas some suggests that it is predictive of the leftcircumflex artery, as opposed to right coronary artery occlusion. Therefore, thepresumption prediction of a culprit artery based on the electrocardiographic recordedat the time of admission is of clinical importance to predict the outcome of patients. Inthis study, we describe electrocardiographic (ECG) criteria for quantitating the extentof coronary artery distribution in patients with inferior wall AMI and we explore therelation between the size, distribution, and the presence of ST segment elevation inleads V5to V6.The electrocardiogram is an essential part of diagnostic tool of patients withsuspected AMI. Acute or evolving changes in the ST–T wave forms and Q waveforms, when present, allow the clinicians to time the event, to identify the infarct-related artery, to estimate the amount of myocardium at risk as well as prognosis, and to determine therapeutic strategy. More profound ST-segment changes or T waveinversion involving multiple leads and territories is associated with a greater degree ofmyocardial ischemia and a worse prognosis. The current guidelines for the ECGdiagnosis of acute myocardial infarction require at least≥1mm (≥0.1mV) of STsegment elevation in the limb leads, and at least≥2mm elevation in theprecordial leads. These elevations must be present in an anatomically contiguousleads, leads I, aVL, V5, V6correspond to the lateral wall; V1-V4correspond to theanterior wall; and II, III, aVF corresponds to the inferior wall. The ST elevation ismeasured60ms from the J point.Methods:We retrospectively analyzed390patients having an acute inferior wall MI,admitted and underwent coronary angiography in the cardiovascular department of thefirst hospital of Norman Bethune College of medicine under Jilin University fromJanuary1st2012to December31st2012. Only160patients (male132and female28)met our inclusion criteria of chest pain for≥30minutes before hospital admission.Elevation of creatinine kinase (CK-MB) greater than twice the upper limit.(Normal:0-3.5ng/ml). The ECG shows ST segment≥0.1mV (1mm) in at least2of3inferior leads (II, III, aVF). Coronary angiography showing total occlusion or criticalstenosis>70%in single vessel either RCA or LCX. Whereas, exclusion criteriaincludes lack of ST elevation≥0.1mV (1mm) in the inferior leads (II, III, aVF),previous history of acute myocardial infarction, coronary artery bypass surgery orpercutaneous coronary intervention prior to current hospitalization, evidence of recentleft bundle branch block or left ventricular hypertrophy on ECG, and significantstenosis in both LCX and RCA or triple vessel disease so that a single infarct relatedartery could not be defined. Results:A total of160patients with a first inferior wall AMI (male132and female28)were included in the study. Patients were divided according to the presence (n-62)and absence (n-98) of ST elevation of≥2mm in leads V5and V6on admission.Patients with ST elevation in leads V5and V6were further subdivided into the2groups according to the degree of ST elevation in lead III and in lead V6. STelevation in lead III greater than in V6(n-45) and ST elevation in lead III equal to orless than in V6(n-17). There were no significant differences between3groups inbaseline clinical characteristics and prevalence of risk factors. The mean age for NoST-elevation in leads V5and V6, ST elevation in leads V5and V6with ST elevationin lead III greater than in V6, and ST elevation in leads V5and V6with ST elevationin lead III equal to or less than in V6are58.37±12.075,59.33±10.96, and58.79±11.59respectively. ST elevation in leads II, III and αVF with ST elevation in lead V5and V6was more common in more male than in female (81%vs19%). In the ECGof ST elevation in the inferior leads (II, III and αVF), ST elevation in leads III>II wasfrequently associated with ST elevation V5and V6with ST elevation in lead III>V6than in ST elevation in lead V5and V6with ST elevation in lead III≤V6(84%vs53%)(p=0.027), whereas ST elevation in lead II>III was more associated with STelevation in lead V5and V6with ST elevation in lead III≤V6than in ST elevationin V5and V6with ST elevation in lead III> V6(46%vs15%)(P=0.027).However, ST segment depression in V1-V3was greater in both patients with STelevation in leads V5and V6with ST elevation in lead III>V6and ST elevation inleads V5and V6with ST elevation in lead III≤V6(71%vs70%) than No STelevation in leads V5-V6(37%)(P-0.0001). There was no much difference in creatinine kinase (CK-MB) and ejection fraction between three groups. Among62patients with ST elevation in leads V5and V6, the infarct related artery was rightcoronary artery in41patients (66%) and left circumflex artery in19(31%). In No STelevation in leads V5and V6and ST elevation in leads V5and V6with ST elevationin lead III> V6were strongly associated with RCA occlusion;73%and82%respectively. Whereas, ST elevation in leads V5and V6with ST elevation in lead III≤V6was associated with LCX,71%occlusion. TIMI0coronary flow was found in145patients (91%). No differences were found between three groups regarding TIMI0flow score. The right coronary artery (RCA) disease was found significantly higherproportion in ST elevation in leads V5and V6with ST elevation in lead III> V6(n-37;82%) than in ST elevation in leads V5and V6with ST elevation in lead III≤V6(n-4;23%)(p=0.0001), whereas the left circumflex artery (LCX) disease was foundvery frequently in ST elevation in leads V5and V6with ST elevation in III≤V6(n-12;71%) than in ST elevation in leads V5and V6with ST elevation in lead III>V6(n-7;16%)(p-0.0001).In our study, out of160patients;61%(n-98) had no ST elevation in leads V5and V6,39%(n-62) patients had ST elevation in leads V5and V6in relation to STelevation in the inferior leads (II, III and αVF). Out of62patients,73%(n-45) had STelevation in leads V5and V6with ST elevation in lead III> V6, whereas27%(n-17)had ST elevation in leads V5and V6with ST elevation in lead III≤V6. According tocoronary angiography findings the sensitivity, specificity and positive predictivevalue and negative predictive value in ST elevation in leads V5and V6with STelevation in lead III>V6to predict right coronary artery (RCA) as a culprit artery are90%,63%,84%and75%respectively. And, the sensitivity, specificity, positive predictive value and negative predictive value in ST elevation in leads V5and V6with ST elevation in lead III≤V6to predict left circumflex artery (LCX) as a culpritartery are63%,90%,75%and84%respectively.The ST segment elevation of≥1mm (>0.1mv) in inferior leads II, III and aVF issignificant to make the diagnosis of acute inferior wall STEMI. The ratio of STelevation in leads II and III has a clinical implication to predict the culprit artery. Inour study, ST elevation in lead II>III was seen in36(23%) patients, and in lead III>IIin124(78%) patients. Right coronary artery (RCA) was frequently involved in ECGwith ST elevation in lead III>II (n-100;81%)(p-0.0001) and left circumflex artery(LCX) in lead II>III (n-21;58%)(p-0.0001). The sensitivity, specificity, positivepredictive value and negative predictive value for ST elevation in lead II>III topredict LCX as a culprit artery are51%,88%,62%and83%, respectively, whereassensitivity, specificity, positive predictive value and negative predictive value for STelevation in lead III>II to predict RCA as a culprit artery are88%,51%,83%and62%respectively.ConclusionIn conclusion, ST segment elevation in leads V5and V6suggests a greater riskarea in patient with acute inferior wall myocardial infarction. The right coronaryartery occlusion was most common in ST elevation in leads V5and V6with STelevation in lead III>V6and the left circumflex artery occlusion in ST elevation inleads V5and V6with ST elevation in lead III≤V6. And, while evaluating risk in anacute inferior wall myocardial infarction, we should also look for ST elevation inleads V5and V6, as it signify a larger perfusion territory and demands for moreaggressive reperfusion therapy. |
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