Correlation of Severity of ST Segment Elevation with Respect to the Site of Right Coronary Artery Lesion

Introduction: Electrocardiogram a widely available tool may predict infarct related artery in acute inferior wall myocardial infarction. Severity of ST segment elevation may correlate with proximity of lesion in right coronary artery. Methods: Patient with acute ST segment elevation inferior wall myocardial infarction who underwent coronary angiogram was studied. Differences in electrocardiogram among right coronary and left circumflex groups were evaluated. Severity of ST segments elevation in relation to site of lesion in right coronary was studied. Results: The mean age of presentation was 59.52 ± 11.01 years. Total 36 (72%) were men. A total of 42 (84%) had lesion in right and 8 (16%) in left circumflex. Age, sex,diabetes,hypertension, smoking, dyslipidemia and physical activity showed no correlation with lesion in right or circumflex coronary artery. ST segment elevation in III>II (P=0.01), ST segment depression in AVL> I (P<0.01) and ST elevation in V4R (P=0.04), correlated with right coronary lesion. Sum of ST elevation in inferior leads were 10.90 ±1.30 mm for proximal, 7.38±1.19 mm for mid and 5.50± 0.53 mm for distal right coronary with significant correlation (P<0.01). Conclusions: Electrocardiogram was reliable tool to difference right and left circumflex lesion. Severity of sum of ST segment elevations in inferior leads correlated with the proximity of lesion in right coronary. _______________________________________________________________________________________


INTRODUCTION
ST segment elevation myocardial infarction (STEMI) represents the most lethal form of Acute Coronary Syndrome (ACS). 1 About one third of myocardial infarction (MI) are STEMI. 2Acute inferior STEMI is characterized by ST segment elevation in leads II, III, and aVF.Infarct related artery (IRA) of inferior MI can be right coronary artery (RCA) or left circumflex artery (LCX). 3RCA supplies several important structures in heart, so they can be involved if IRA is RCA.
Electrocardiogram (ECG) is a simple and easily available tool.Several ECG criteria has been recommended for the IRA prediction with variable results. 4,5Predicting the site of occlusion in RCA by ECG is worthwhile as proximal occlusion is likely to cause larger myocardial damage.
The objective of the study was to determine IRA focusing correlation between RCA lesion site and severity of ST segment elevation in inferior leads in inferior MI in our setup.

METHODS
A cross-sectional prospective study was conducted at Department of Cardiology, Shahid Gangalal National Heart centre (SGNHC) Kathmandu from February to July 2013.Ethical approval was taken from the Institutional Review Board (IRB) of National Academy of Medical Sciences (NAMS) and the informed consent was obtained from all the participants.All the participants needed to have had coronary angiogram (CAG) done either during the primary percutaneous intervention (PCI) or before discharge from hospital to be included in the study.Patients with previous history of coronary artery disease, with left bundle branch block, a paced rhythm, an accelerated Idioventricular rhythm or severe artifacts causing difficulty for accurate ST segment measurement were excluded.Patients who didn't go angiogram or with diffuse angiographic lesions involving more than one segment in RCA or involving both RCA and LCX were excluded.Patients who didn't give consent for the study were also excluded.
A total of 50 consecutive patients of acute ST segment elevation inferior wall MI were included.Among the patients who presented with clinical features suggestive of MI, acute inferior wall STEMI was diagnosed on the basis of ≥1 mm ST elevation in at least 2 inferior leads ECG measured 0.08 seconds after the J points with reciprocal ST segment depression in I and aVL and rise of cardiac enzymes (CPK-MB or Troponin I).The patients were evaluated focusing the variables to be tested.Those who practice at least 30 minute of moderate exertional activity each day were considered physically active.ECGs were recorded at 25 mm/s speed, and calibrated to 1 mV/cm.The right sided ECG and posterior ECG was taken in all with the suspicion of RV infarction (ST elevation ≥ 1mm in V4R) and posterior infarction (ST elevation ≥ 1mm in V7-V9 ) respectively.
The patients were followed up for coronary angiogram.Angiograms were evaluated for IRA as RCA or LCX.RCA, further was categorized in proximal [from ostium to the first Acute Marginal (AM)], mid (from First to last AM) or distal (from last AM onwards). 6The lesion with highest degree of stenosis was accepted as culprit lesion.
Data were entered and analyzed using SPSS version 14 for windows.For demographic profiles frequencies and percentage distribution were calculated for each variable.Chi square test were used to detect the level of significance.Means were compared using one way ANOVA.P values were calculated and values less than 0.05 were considered statically significant.

RESULTS
Among the 50 enrolled patients of acute inferior wall MI, majority 36 (72%) were male.The age ranged between 33 to 82 years with mean age of presentation being 59.52 ± 11.01 years.Hypertension and diabetes were present in 20 (40%) and 13 (26%) respectively.A total of 19 (38%) were current smoker (Table 1).There was no significant difference in the baseline characteristics between the RCA and LCX group.Similarly Niels J Verouden et al found RCA as a culprit in 79%. 12There was no significant difference in baseline characteristics in between the RCA and LCX group.Chun-Yen Chiang et al found similar results. 13Another study showed LCX occlusion significantly higher in older age with no significant differences in other baseline characterstics. 7e criteria of ST elevation III>II and ST depression aVL>I were more likely to be present in RCA group.
5][16] Herz el al found 84% sensitivity and 88% positive predictive value for the first and 82% sensitivity and 80% positive predictive value for the second criteria mentioned above.When both above criteria were combined the specificity and positive predictive value both were 100%. 17Al Hussain et al also reported a significant correlation of above mentioned criteria for determination of IRA with P values <0.001 in both cases. 11The study found ST elevation V4R also had a positive correlation with IRA as RCA ( P = 0.04).Braat et al showed specificity and positive predictive value of 100% and sensitivity of 59% of the criterion of ST elevation V4R ≥ 1mm. 5 The The findings of positive correlation of severity of sum of ST segment elevation in inferior leads seen in our set up was in consistent with the previously reported literatures.
The study had certain limitations.This was a single center based study done within a short time frame including small number of participants.The study only included clear cut lesions of either RCA or LCX artery.Cases with lesion in both of arteries can have different ECG manifestations.Larger studies to address the above shortcoming is encouraged and expected in future.

CONCLUSIONS
ECG, an easily available and essential tool for the diagnosis of acute myocardial infarction could predict the infarct related artery in acute ST elevation inferior wall MI if it is RCA or LCX.The sum of ST segment elevation in inferior leads correlated with the site of lesion in right coronary artery in our set up, the more proximal lesions had greater values.These findings will help to formulate the plan for their further management.

Table 5 . Total ST segment elevation in inferior leads, (II + III + aVF).
11mkhada.Correlation of Severity of ST Segment Elevation with Respect to the Site of Right Coronary Artery Lesion mm in mid and 5.8 ± 0.2 mm in distal RCA lesions.11 6The study of Ala Hussain Abbase et al found the sum of ST segment elevation of 11.7 ± 1.8 mm in proximal, 7.2 ± 0.97