Clinical Significance Of ST Segment Elevation In Posterior Leads V7, V8and V9in Patients With Acute Inferior Wall Myocardial Infarction

Objectives: The aim of the study was to assess the role of ST segment elevation in theposterior leads （V7, V8, V9） that compare with coronary angiography and otherparameters like CPK MB and ejection fraction for the diagnosis of posterior wallacute myocardial infarction.Background: The diagnosis of a posterior wall myocardial infarction is difficult toaccomplish through the standard12lead ECG, especially in the acute stage. Theposterior wall MI may occur as an isolated event or often associated with an inferiorwall myocardial infarction. Posterior leads V7, V8and V9are usually ignored butsome investigators have suggested that these leads can provide ECG information thatis useful for characterization of inferior AMI and diagnosis of posterior wall MI.12lead ECG with posterior lead should be performed to correctly diagnose culprit arteryin inferior wall MI.ST elevation in posterior leads （V7, V8and V9） is frequently seenin posterolateral infarction that is usually associated with occlusion of the leftcircumflex artery, large infarct zone and complications like reinfarction, postinfarction angina and mortality. The electrocardiogram is the main diagnostic tool forthe diagnosis and initial evaluation of the patients with chest pain. ECG recording iseasy, convenient, inexpensive bedside tool which gives an idea of infarct size,prognosis and localization of the epicardial coronary artery occlusion responsible formyocardial infarction. It is the gold standard test for the physiological assessment ofthe heart conduction. The diagnosis of AMI is based on the ST-T changes in at least2contiguous leads or the presence of new left bundle branch block （LBBB）. ECGmanifestations of Acute Myocardial Ischemia （in absence of left ventricularhypertrophy and LBBB）: ST elevation: New ST elevation at the J point in twocontiguous leads with the cut off points equal or>0.2mV in men; equal or>0.15mVin female in chest leads and/or>0.1mV in limb leads. ST depression and T wavechanges: New horizontal or down sloping ST depression equal or>0.05mV in contiguous leads: and/or T inversion equal or>0.1mV in two contiguous leads withprominent R wave or R/S ratio>1. Shortly after coronary artery occlusion, serial ECGchanges are detected by leads facing ischemic zone. There are3grades of ischemiadepending upon ECG changes: For Rs configuration （chest leads）Grade I ischemia: Tall symmetrical T wave without ST elevationGrade II ischemia: ST elevation without changes in QRS complexGrade III Ischemia: ST elevation with the distortion of terminal portion ofQRS complex; no S waveFor qR configuration （limb leads）Grade I: Tall symmetrical T wave without ST elevationGrade II: ST elevation with emergence of J point at <50%of the R wave amplitude （Jpoint/R wave ratio <0.5）Grade III: ST elevation with emergence of J point at> or equal50%of the R waveamplitude （J point/R wave ratio>0.5）.A new ST segment deviation even only0.05mV remains an important and specificmeasure of ischemia and possible prognosis.[15]19The presence of T wave inversionleading to ischemia has good sensitive but has less specific, unless it is marked （>0.3mV）[16]20ST elevation0.1mV in at least two contiguous leads has sensitivity around90%. ECG findings are confirmed by further tests like cardiac biomarkers andcoronary angiography. Coronary angiography is a minimally invasive procedure withis used to diagnose occlusion, stenosis, restenosis, thrombosis or aneurismalenlargement in the coronary circulation. This is the gold standard diagnostic tool forthe confirmation of the culprit epicardial vessel occlusion. However coronaryangiography provides no information regarding the arterial wall and severeatherosclerosis that do not encroach the arterial wall may not detect.Methods:121patients （male102and female19） with mean age of58.74±12yearswere included in the study having chest pain lasting for more than30minutes beforehospital admission, elevation of creatinine kinase （CK-MB） greater than twice theupper limit （normal:0-3.5ng/ml）, ECG shows ST segment elevation>0.1mV （1mm） in at least2of3the inferior leads （II, III and aVF）, ST segment elevation>0.05mV（0.5mm） in posterior leads V7, V8, V9, and coronary angiography shows totalocclusion or critical stenosis more than70%in single vessel either LCX or RCA.Inclusion criteria includes chest pain lasting for more than30minutes before hospitaladmission, elevation of creatinine kinase （CK-MB） greater than twice the upper limit（normal:0-3.5ng/ml）, ECG shows ST segment elevation>0.1mm in at least2of3theinferior leads （II, III and aVF）, ST segment elevation>0.05mm in posterior leads V7,V8, V9, and Coronary angiography shows total occlusion or critical stenosis morethan70%in single vessel either LCX or RCA. Exclusion criteria includes lack of STelevation>0.1mV in the inferior leads （II, III, aVF）, the patients with inferior MI nothaving posterior leads （V7to V9） estimation, previous history of acute myocardialinfarction, coronary artery bypass surgery or percutaneous coronary intervention priorto current hospitalization, evidence of recent left bundle branch block or leftventricular hypertrophy in ECG, and significant stenosis in both LCX and RCA ortriple vessel disease so that a single infarct related artery could not be defined.Results: The mean age for group A is60.00±0.05（50to70years）, the mean age forgroup B is57.65±12.86（45to70years）. The disease is very common in male thanfemale （83.47%vs16.53%）. The ECG of inferior wall MI with ST elevation in leadIII>II is frequently associated group B patients than group A patients （n=72,59.5%vsn=19,15.7%, p=0.0001） whereas ST elevation II>III favors group A patients thanGroup B patients （n=22,18.2%vs n=8,6.6%, P=0.0001）. Group A patients hadsignificantly larger infarcts compared to group B patients which is shown byCPK-MB values （90.12+₃3.42vs45±38.28, p=0.0001）. However, there is nodifference in ejection fraction between two groups. The patients with inferiorwall STEMI have a normal ST segment in leads V1to V3which was more frequentlyseen in group B patients （n=74[61.2%] vs n=29[24%], p=0.0001）. Out of121patients,69.42%has RCA as the culprit artery whereas30.58%has LCX occlusion asshown in figure12. TIMI O coronary flow is found in94patients （77.4%）. Nodifferences were found between two groups regarding TIMI0flow score. The infarct related artery （IRA） was identified through coronary angiography in355patients and121patients were included for the study which fulfilled the criteria. The leftcircumflex coronary artery （LCX） disease was found significantly higher proportionin group A （n=33,27.3%） than in group B （n=4,4.3%, p=0.0001） whereas the rightcoronary artery （RCA） disease was found very frequently in group B （n=76,62.8%）than group A （n=8,6.6%, p=0.0001）. In our study,33.88%（n=41） patients had STsegment elevation in posterior leads V7-V9whereas66.12%（n=80） patients had noinvolvement of posterior wall of the left ventricle. The sensitivity, specificity, positivepredictive value and negative predictive value with ST elevation in posterior leadsV7-V9to predict LCX are84%,90%,80%and92%respectively whereas thesensitivity, specificity, positive predictive value and negative predictive value withoutST elevation in posterior leads V7-V9for RCA are90%,84%,92%and80%respectively. The>0.1mv （1mm） ST elevation in inferior leads II, III and aVF issignificant in the diagnosis of inferior wall STEMI. The ratio of ST elevation in leadsII and III has clinical implication to predict culprit artery. In our study, ST elevation inlead III>II was seen in91patients （75.21%） whereas ST elevation in lead II>III wasseen in30patients （24.79%）. RCA was very habitually involved in ECG with STelevation in lead III>II （n=77,63.6%, p=0.0001） whereas LCX was the culprit arteryin patients having a ST elevation in lead II>III （n=23,19.3%, p=0.0001）. Thesensitivity, specificity, positive predictive value and negative predictive value with STelevation in lead III>II to predict RCA as a culprit IRA were90%,61%,83%and75%respectively. The sensitivity, specificity, positive predictive value and negativepredictive value with ST elevation in lead II>III for LCX were61%,90%,75%and83%respectively.Conclusion: We recommend routine recording of posterior leads V7, V8and V9in allpatients admitted to the hospital with an acute inferior MI. The left circumflex arteryis more frequently implicated in inferior wall MI with ST elevation in the posteriorleads. ST segment elevation in posterior leads associated with large area ofjeopardized myocardium, might argue in favor of reperfusion therapy.