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Prediction of Infarct-Related Coronary Artery of Patients With Acute Inferior Myocardial Infarction By a Predischarge Exercise Test Index

Posted on: Sunday, 5 December 2004, 03:00 CST

The predictive accuracy of electrocardiographic markers in identifying the infarct-related artery of myocardial infarctions has been a subject of extensive investigation. The present study was designed to test whether the index L II/L III ratio adapted to exercise electrocardiograms could be utilized as a marker to distinguish right coronary and left circumflex arteries as culprit coronaries in acute inferior myocardial infarctions. For this purpose, 82 patients with a positive-symptom-limited and/or submaximal treadmill exercise test with modified Bruce protocol after an acute inferior myocardial infarction were studied. Those patients with ST segment elevation during the stress test were included in the study. ST segment index was defined as the ratio of exercise-induced ST elevation amplitude in L II/L III. Patients were classified as having an index > 1 (n = 24) and < 1 (n = 58), and the findings were compared with the findings on coronary angiography. The groups were comparable with respect to age, gender, peak exercise level, and double products achieved. Circumflex artery was the infarct-related one in the majority (21/24; 88%) of patients with an index > 1, whereas most (51/58; 88%) patients with an index < 1 had the culprit lesion in their right coronary artery (p < 0.001). The ratio of exercise-induced ST elevations in leads L II and L III has a significantly high ability to discriminate the infarct-related coronary artery in patients with uncomplicated inferior myocardial infarction. Considering the prognostic importance of the type of coronary involvement, this index could be a part of predischarge evaluation in this patient group.

Introduction

Inferior myocardial infarction accounts for 40-50% of all acute infarctions.1 The relatively more heterogeneous clinical course it has in comparison with anterior infarctions is determined by the localization of the culprit artery, that is, the right coronary artery (RCA) or the left circumflex (LCX) artery in patients suffering an acute inferior myocardial infarction. Right ventricular involvement, arrhythmias, and hemodynamic complications are more commonly observed in right coronary artery occlusions, whereas patients in whom the culprit lesion is in the left circumflex artery have fewer complications and better prognosis.2-5 Therefore, the early recognition of the culprit artery would be helpful for the clinician in predicting the patient's prognosis.

Some types of ST segment deviations on resting electrocardiogram (ECG) have been suggested as predicting the culprit coronary artery in acute inferior infarctions.6-8 These changes in leads (L) L I, L II, L III, aVL, and V^sub 5-6^ are prone to vanish after the myocardial ischemia is treated, but they may reappear when the ischemia is induced by stress. In the present study we sought to examine whether an index derived from exerciseinduced ST segment elevations in leads L II and L III would predict the culprit coronary artery at an early stage of inferior wall myocardial infarction.

Materials and Methods

The study group consisted of 118 patients who suffered from acute inferior myocardial infarction. Eighty-two patients with acute inferior myocardial infarction, ST segment elevation in leads L II, L III on predischarge exercise test, and a single culprit artery detected on coronary angiography in the early phase were enrolled into the study group. The remaining 36 patients were excluded because of ST segment depression in L II and/or L III during the test. Excluded were patients with complete heart block, WPW syndrome, electrolyte imbalance, left ventricular hypertrophy on ECG, pretest ST segment deviation > 1 mm, resting heart rate > 110 bpm, digitalis or antiarrhythmic drug use, and multivessel disease.

Exercise stress testing was performed with a treadmill system, using a symptom-limited or submaximal exercise stress testing according to modified Bruce protocol (Quinton 5000, USA).9,10 Exercise-induced ST segment deviation was measured relative to the TP segment at 60 ms from the J point. ST segment index was defined as the ratio of ST segment elevation on L II to L III, and patients were classified according to an ST segment index of > 1 or < 1 as Group 1 and Group 2, respectively.

Patients who demonstrated a positive stress test underwent selective coronary angiography within 13 3 days of infarction by Judkins technique (Philips Integris 3000 H, Holland).11 Two cardiologists who were blinded to findings of stress tests performed the examinations. The culprit coronary artery lesion was defined as 1) major branch occlusion or ≥ 70% stenosis at RCA or LCX, or 2) presence of intraluminal thrombus at arteriography. Patients in whom 2 criteria exist in both of these arteries were excluded from the study.

Numerical values were expressed as mean SD and significance was set at a p < 0.05. Continuous and categorical variables were compared with Student's t test and Chi-square test, respectively. Sensitivity, specificity, and predictive accuracy of a positive test were calculated in the usual fashion. All statistical computations were performed with an SPSS Program for Windows 98.

Results

Groups 1 and 2 comprised 24 patients (18 men, mean age: 53 13 years) and 58 patients (43 men, mean age: 56 8 years), respectively. Comparison of the 82 patients in whom a single culprit artery was detected revealed that the culprit lesion was at the LCX in 21 patients (88%) of Group 1 and 7 patients (12%) of Group 2. On the other hand, RCA was the culprit coronary artery in 3 patients (12%) of Group 1 and 51 patients (88%) of Group 2 (p < 0.05). Angina pectoris on exercise test was present in 15 (63%) and 34 (59%) patients in Groups 1 and 2, respectively (p > 0.05). No statistically significant difference was observed between the groups with respect to the exercise stress test results (Table I). The average metabolic equivalent (MET) levels achieved on tests were 7.6 2 and 7.9 1.8 in Groups 1 and 2, respectively (p > 0.05). Mean exercise duration was 5.45 2 minutes and 5.9 1.9 minutes in Groups 1 and 2, respectively.

The specificity, sensitivity, positive predictive value, negative predictive value, and accuracy values were calculated as 87%, 87%, 94%, 75%, and 88% for RCA lesions, and 87%, 87%, 75%, 94%, and 88% for LCX lesions, respectively.

Discussion

The results of the present study suggest that an index derived from exercise-induced ST segment elevations in leads L II and L III has a significantly high ability to discriminate RCA and LCX occlusions as culprit lesions resulting in an inferior myocardial infarction. An ST segment index of L II/L III ratio < 1 indicates RCA (Figure 1), whereas LCX is the culprit coronary artery when the index is > 1 (Figure 2).

Table I. Patients characteristics, exercise stress testing parameters, and culprit coronary arteries.

This finding is consistent with and extends the previous observations, which demonstrated that patients with a predominant ST elevation in L III during an acute inferior myocardial infarction are likely to have the culprit lesion in their RCA.6,12,13 Chia et al14 reported that an ST elevation ratio in L II and L III of 1 or an isoelectric ST in lead L I is a sensitive and specific marker of left circumflex artery occlusion, whereas an ST L II/L III ratio < 1 or ST depression in lead L I is a sensitive and specific marker of right coronary artery occlusion. Kosuge et al12 suggested that RCA lesions result in an ST elevation in L II exceeding the amplitude of ST depression in V^sub 3^. A recent study by Kabakci et al15 reported that the L III > L II and ST-segment depression in lead LI > aVL criteria on admission ECG defined the RCA as infarct-related artery with moderate sensitivity against a specificity of 100%.

The underlying scenario linking an RCA occlusion to a pronounced L III ST elevation either on resting or exercise ECG could be that the RCA mainly supplies the inferior myocardium, whereas the LCX irrigates the posterior, posterior-lateral, and posterior-inferior regions.6,16,17 Exercise-induced ischemia magnifies the ST elevation amplitudes, influences the cardiac vectors, and exaggerates the differences in ST segment deviations of leads facing the same myocardial region.18,19 RCA occlusion results in a progression of ST- segment vector directed inferiorly and to the right and thus positioned parallel to L III, which faces the inferior portion of the left ventricle. In the event the LCX is the culprit artery, the ST-segment vector becomes parallel to L II by directing toward the posterior-lateral myocardial regions.19 These differences might explain the predictive accuracy of the predominant lead in the estimation of the culprit coronary artery in both resting and exercise electrocardiograms.

Figure 1. ST segment index < 1. In this case the culprit artery was the right coronary artery.

Figure 2. ST segment index is > 1. In this case the culprit artery was the left circumflex coronary artery.

The patients who showed ST segment depression in L II and/or L III were excluded from the study. Myocardial viability and functional significance of the culprit coronary artery could not be assessed since myocardial perfusion imaging was not performed in the study group.

Conclusion

The infarct-r\elated artery in acute inferior myocardial infarctions could be distinguished as RCA or LCX occlusion by a reliable L II/L III ST elevation ratio index on predischarge submaximal exercise electrocardiograms of uncomplicated patients.

REFERENCES

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11. Scanlon PJ, Faxon DP, Audet AM, et al: ACC/AHA guidelines for coronary angiography: A report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines (Committee on Coronary Angiography) developed in collaboration with the Society for Cardiac Angiography and Interventions. J Am Coll Cardiol 33:1756-1824, 1999.

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14. Chia BL, Yip JW, Tan HC, et al: Usefulness of ST elevation II/ III ratio and ST deviation in lead I for identifying the culprit artery in inferior wall acute myocardial infarction. Am J Cardiol 86:341-343, 2000.

15. Kabakci G, Yildirir A, Yildiran L, et al: The diagnostic value of 12-lead electrocardiogram in predicting infarct-related artery and right ventricular involvement in acute inferior myocardial infarction. Ann Non-invasive Electrocardiol 6:229-235, 2001.

16. Huey BL, Beller GA, Kaiser DL, et al: A comprehensive analysis of myocardial infarction due to left circumflex artery occlusion: Comparison with infarction due to right coronary artery and left anterior descending artery occlusion. J Am Coll Cardiol 12:1156-1166, 1988.

17. Newman HN, Dunn RF, Harris PJ, et al: Differentiation between right and circumflex coronary artery disease on thallium myocardial perfusion scanning. Am J Cardiol 51:1052-1056, 1983.

18. Berry C, Zalewski A, Kovach R, et al: Surface electrocardiogram in the detection of transmural myocardial ischemia during coronary artery occlusion. Am J Cardiol 63:21-26, 1989.

19. Cooksey JD, Dunn M, Massie E: Inferoposterior myocardial infarction. In: Clinical Vectorcardiography and Electrocardiography, ed. by Cooksey JD, Dunn M, Massie E. Chicago: Year Book Medical Publishers, 1977, pp 391-427.

Osman Bolca, MD, Mehmet Eren, MD, Osman Akdemir, MD,* Aydm Yildirim, MD, Bahadir Dagdeviren, MD, and Tuna Tezel, MD, Istanbul and Edirne, Turkey

Angiology 55:679-683, 2004

From the Siyami Ersek Thoracic and Cardiovascular Surgery Center, Department of Cardiology, Istanbul; and the *Trakya University, School of Medicine, Cardiology Department, Edirne, Turkey

Presented at the XXIst Congress of the European Society of Cardiology, Barcelona, Spain, 1999

Correspondence: Osman Bolca, MD, Liderkent Sit. 3A Blk.K: 2, D: 6, Yeni Camlica Mh, Yukan Dudullu, 81260, Istanbul, Turkey

E-mail: Bolca@superonline.com

2004 Westminster Publications, Inc., 708 Glen Cove Avenue, Glen Head, NY 11545, USA

Copyright Westminster Publications, Inc. Nov/Dec 2004

Source: Angiology

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