Identification of the Culprit Artery Involved in Inferior Wall Acute Myocardial Infarction Using Electrocardiographic Criteria

The Journal of International Medical Research 2004; 32: 39 – 44 Identification of the Culprit Artery Involved in Inferior Wall Acute Myocardial Infarction Using Electrocardiographic Criteria E BAYRAM1 AND C ATALAY2 1 Department of Cardiology and 2Department of Anaesthesiology, School of Medicine, Atatürk University, Erzurum, Turkey We tested whether particular electrocardiogram (ECG) changes can identify the right coronary (RCA) or left circumflex (LCX) artery as the responsible vessel in inferior wall acute myocardial infarction (AMI) in 73 patients. A standard 12-lead ECG was performed within 6 h of onset of chest pain. Coronary angiography was performed between 1 week and 6 weeks after the infarction. RCA and LCX lesions were detected in 53 and 20 patients, respectively. The most useful ECG parameters for implicating the RCA were a higher ST elevation in lead III than lead II (specificity 94%, sensitivity 86%) and an S/R wave ratio > 0.33 plus ST segment depression > 1 mm in lead aVL (specificity 94%, sensitivity 92%). Absence of these criteria was associated with LCX occlusion (specificity 100%, sensitivity 87%). These results indicate that composite ECG criteria are useful in predicting the artery involved in inferior wall AMI. KEY WORDS: CULPRIT ARTERY; INFERIOR WALL ACUTE MYOCARDIAL INFARCTION; ELECTROCARDIOGRAM Difficulty in differentiating between LCX and RCA occlusion in inferior wall AMI is a common clinical problem.1 Using thallium radionuclide studies, defects in the posterolateral segments are relatively specific for LCX-related AMI, whereas defects in the posterobasal segments are seen with equal frequency in LCX- and RCA-related AMI. With regard to the electrocardiogram (ECG), the lateral limb leads are highly significant in inferior wall AMI. The aVL lead faces the high lateral segment of the left ventricular wall and is the only lead that is truly reciprocal to the inferior wall.2,3 The reciprocal image of the changes should be a Introduction The culprit artery in inferior wall acute myocardial infarction (AMI) is usually the right coronary artery (RCA), less often the left circumflex coronary artery (LCX), and rarely the left anterior descending artery (LAD). Approximately 50% of patients with inferior wall AMI have significant bradycardia or hypotension, usually as a result of total occlusion of the proximal RCA. Early recognition of whether the culprit artery is the RCA or the LCX may facilitate management and, in some instances, may allow particular complications to be avoided. 39 E Bayram, C Atalay Identification of the culprit artery in inferior wall AMI using ECG percutaneous transmural coronary angioplasty showing ECG evidence of bundle branch block or left ventricular hypertrophy were excluded from the study. All patients gave informed written consent and the Medical Faculty of Atatürk University Ethics Committee approved the study. decrease in the amplitude of the R wave and an increase in the negative wave (Q and S) amplitude. When there is no additional ischaemia of the lateral segment, as seen in RCA AMI, the aVL lead should depict a decrease in R wave amplitude and an increase in S wave amplitude.4 The standard lead III is oriented to the right inferior segment, whereas lead II is oriented principally to the left inferior segment and also to the inferior region of the left lateral part of the superior wall of the ventricle. Consequently, lead III is more influenced by RCA-related AMI and lead II by LCX-related AMI.3 To detect the culprit artery in inferior wall AMI, a number of researchers have studied QRS ECG configurations and ST-segment depression in leads I, II, III, aVL and aVF,5 – 10 but most of these studies did not compare combined criteria. This study aimed to determine whether it was possible to detect the culprit artery in inferior wall AMI, using two different criteria based on the results of the 12-lead ECG. ECG Standard 12-lead ECGs performed on admission, within 6 h of the onset of chest pain, were analysed by the principal investigator (EB). ST-segment deviation from the isoelectric line, which was defined as the level of the preceding TP segment, was measured 80 ms after the J point to the nearest 0.5 mm. The following ECG changes were assessed: ST-segment elevation in lead III exceeding that in lead II, defined as a ratio of ST elevation in lead III/elevation in lead II > 1; ST-segment depression in lead aVL, defined as > 1 mm deviation from the isoelectric line; an S/R wave ratio in lead aVL > 0.33. Patients and methods CORONARY ANGIOGRAPHY Coronary angiography was performed between 1 week and 6 weeks after the infarction. Coronary cineangiography films were reviewed by two investigators who were blinded to the ECG findings. The infarctrelated artery was identified from total occlusion or significant stenosis (> 70%) of the RCA or LCX or their major branches, or from arteriographic evidence of intraluminal thrombosis. To minimize the chance of misclassifying the culprit artery, patients with significant stenosis of both the RCA and the LCX were excluded from the study. PATIENTS The study population consisted of patients with a diagnosis of first inferior wall AMI, who were admitted to our coronary and intensive care units between January 1998 and February 2001 and who subsequently underwent coronary angiography during their time in hospital. A diagnosis of inferior wall AMI was made on the basis of: chest pain lasting > 30 min; ST-segment elevation > 1 mm in at least two of the three inferior leads (II, III and aVF); and elevation of creatine kinase enzyme and its myocardial band (MB) fraction to more than twice the upper limit of normal. Patients with a history of previous AMI, coronary artery bypass surgery or STATISTICAL ANALYSIS The ECG findings in the patients with RCArelated and LCX-related infarcts were 40 E Bayram, C Atalay Identification of the culprit artery in inferior wall AMI using ECG compared using the χ2 test and Fisher’s exact lead aVL, and criterion B consisted of ST segment elevation in lead III exceeding that in lead II (i.e. a ratio of ST elevation in lead III/elevation in lead II > 1; Fig. 1). The ECG findings in the RCA and LCX groups are given in Table 1. The sensitivity, specificity and positive and negative predictive values of the two ECG criteria and their combinations are shown in Table 2. The results did not change with variation in the obstruction site along the coronary artery (proximal versus distal; data not shown). We found that, in patients with inferior wall AMI, both criterion A and criterion B were sensitive and specific markers for RCA but not for LCX obstruction. If both criteria are negative, LCX obstruction is likely. test, as appropriate. A P-value < 0.05 was considered statistically significant. Results The study population consisted of 73 patients (68 men and 5 women) with a mean ± SD age of 52 ± 11 years. On coronary angiography, the culprit arter (...truncated)