Original Contribution

Significance of left circumflex artery-related acute myocardial infarction without ST-T changes

Su-Kiat Chua MD^a, Kou-Gi Shyu MD^a,b, Jun-Jack Cheng MD^a,c, Jer-Young Liou MD^a, Sheng-Chang Lin MD^a, Huei-Fong Hung MD^a, Shih-Huang Lee MD^a,c,

Chiung-Zuan Chiu MD^a,c, Huey-Ming Lo MD^a,c,?

^aSection of Cardiology, Department of Internal Medicine, Shin Kong Wu Ho-Su Memorial Hospital, Taipei 111, Taiwan

^bGraduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan

^cFu-Jen Catholic University School of Medicine, Taipei County, Taiwan

Received 26 August 2008; revised 6 October 2008; accepted 7 November 2008

Abstract

Introduction: Left circumflex (LC)-related acute myocardial infarction (AMI) presenting without ST-T changes has been underdiagnosed in the emergency department. There is little information on its clinical features and significance.

Aims: The aims of the study were to investigate the clinical characteristics and outcomes of LC-related AMI without ST-T changes.

Population and Methods: Ninety-six patients were admitted for LC-related AMI. Comparisons between those with and without ST-T changes were analyzed.

Results: Twenty-two patients (23%) did not have ST-T changes, whereas 74 patients (77%) had them. Patients without ST-T changes had younger age (55.6 +- 16.8 vs 62.6 +- 12.0 years, P = .03), fewer presented as Killip III/IV (4.5% vs 27.4%, P = .02) and with lower creatine kinase (1647.3 +- 1602.2 vs 2778.2 +- 2343.3 IU/L, P = .037) and creatine kinase-MB (136.8 +- 130.3 vs 247.7 +- 200.0 IU/L, P =

.017), and more were with concurrent culprit lesion in the middle or distal LC and right- or balanced- dominant coronary circulation (86.4% vs 44.6%, P b .001). During follow-up, the need for repeat percutaneous coronary intervention (48.6% vs 45.5%, P = .40) and recurrent infarction (13.5% vs 13.6%, P = .62) were similar between the 2 groups. The 30-day mortality (0% vs 5.4%, P = .35) and overall mortality rate (4.5% vs 12.2%, P = .28) between them were not different statistically.

Conclusion: The relatively lower prevalence of LC-related AMI without ST-T changes in the study might be underestimated. These patients have smaller infarct size than patients with ST-T changes without differences in the short- and long-term outcomes between them.

(C) 2010

* Corresponding author. Section of Cardiology, Department of Internal Medicine, Shin Kong Wu Ho-Su Memorial Hospital, Taipei 111, Taiwan. Tel.: +886 2 2833 2211; fax: +886 2 2838 9335.

E-mail address: [email protected] (H.-M. Lo).

Introduction

Patients with acute myocardial infarction (AMI) may present without ST-T changes, limiting the sensitivity of the electrocardiogram (ECG) in diagnosis of AMI [1].

0735-6757/$ – see front matter (C) 2010 doi:10.1016/j.ajem.2008.11.010

The presentation of the ECG varies depending on the coronary artery involved [2]. Patients with left anterior descending coronary artery or right coronary artery occlusion commonly result in electrocardiographic ST-T changes [3]. In contrast, fewer patients with acute complete left circumflex (LC) occlusion have diagnostic ST- T changes [3,4]. In addition, elevation of cardiac biomarkers can be delayed for up to 8 to 12 hours, so that LC-related patients with AMI presenting without ST-T changes could be diagnosed as having unstable angina or, even, misdiagnosed in the emergency department (ED). Accordingly, LC-related AMI has been underpresented and undertreated in clinical practice [5]. To date, clinical outcomes of LC-related AMI without ST-T changes have not been reported. This study sought to investigate the significance of LC-related AMI without ST-T changes by comparing patients who had nondiagnostic ST-T changes to those whose ECGs were highly suggestive of infarction in terms of presenting characteristics, coronary angiographic analysis, cardiac biomarkers changes, and clinical outcome.

Methods

Patients

Between April 1992 and October 2007, 1200 patients were admitted for AMI in this institution. Ninety-six consecutive LC-related patients with AMI (77 men and 19 women; mean age, 61 +- 13.5 years) were retrospectively included by the following criteria: (1) a typical chest pain lasting at least 20 minutes; (2) elevated serum cardiac biomarkers at least twice the Upper limit of normal; (3) complete occlusion or critical stenosis of LC, including obtuse marginal branches, without concomitant occlusion or critical stenosis of RCA or LAD confirmed by coronary angiography; (4) no history of prior myocardial infarction or coronary artery bypass graft operation; (5) no bundle branch block or intraventricular conduction disturbance and pace- maker-dependent rhythm. For evaluation of the peak serum cardiac biomarkers activity, blood samples were obtained every 6 hours for 48 hours or until the activity returned to normal. The reference values for creatine kinase (CK) and CK-MB were 26 to 192 and 7 to 25 IU/L, respectively. Repeat percutaneous coronary intervention (PCI) was defined as repeated revascularization during follow-up. Clinical follow-up variables, including 30-day mortality, unstable angina that required repeat PCI, recurrent myocar- dial infarction, and overall mortality, were obtained at clinic visits and by telephone conversation and chart review.

Standard 12-lead surface ECG

The presence of significant ST-T changes by standard 12- lead surface ECG was determined at the time of visiting ED

or during admission. Typical evolutional ECG changes of AMI were defined as ST-segment elevation or depression of 1 mm or more with subsequent evolution of Negative T waves with a depth of 1 mm or more and development of new Q waves with at least 0.04 seconds or longer or deeper than one fourth of the following R wave in voltage. Diagnostic ST-T changes and lead groups in LC-related AMI were (1) inferior lead (II, III, aVF) ST-segment elevation 1 mm or greater; (2) lateral precordial lead (V₅ through V₆) and lateral limb lead (I, aVL) ST-segment elevation 1 mm or greater; (3) anterior precordial lead (V₁ through V₃) ST-segment depression 1 mm or greater; or (4) left lateral precordial and limb lead T-wave inversion 1 mm or greater and 5 mm or less, respectively. Patients with concomitant anterior ST-segment elevation were excluded. Patients were classified into 2 groups according to the ECG presentation: group with ST-T changes, whose ECG showed diagnostic ST-T changes as mentioned above, and group without any ST-T changes. Comparisons of clinical features and coronary angiographic analysis between the LC-related patients with AMI with and without diagnostic ST-T changes were analyzed.

Coronary angiography

After providing written-informed consent, all the study patients received PCI for AMI. Judgment of vessel flow was according to the Thrombolysis in Myocardial Infarction flow grade. Angiographic stenosis was defined as a diameter reduction of 50% or greater. Critical stenosis was defined as 70% or greater narrowing of the coronary artery luminal diameter. Complete coronary occlusion was defined as the total absence of anterograde flow of contrast media or TIMI flow grade 0 in the infarct-related coronary artery. The infarct-related lesion was identified based on morphology, including complete occlusion, thrombus, and ulcerative stenosis, or assumed to be the tightest stenosis if these features were absent. Only patients with critical stenosis or complete occlusion in isolated LC were included. Successful PCI was defined as a target vessel at the treatment site with less than 20% residual stenosis and TIMI 3 flow. Standard coronary anatomical angiogram was measured at 60? left anterior oblique and 30? right anterior oblique projections. Coronary artery dominance, including right-dominant, left- dominant, and balanced-dominant circulation, referred to the origin of blood flow to the inferolateral wall of the left ventricle [6]. Right-dominant circulation was defined as the RCA forming the AV nodal artery, the posterior descending, and the posterolateral left ventricular branches that supplied the inferior aspect of the interventricular septum. The left- dominant circulation was that the posterolateral left ven- tricular, posterior descending, and AV nodal arteries were all supplied by the terminal portion of the LC. Balanced- dominant circulation was defined as the RCA giving rise to the posterior descending artery and then terminating, and the LC giving rise to all the posterior left ventricular branches

and also a parallel posterior descending branch that supplied part of the interventricular septum. The major segments and branches of LC were each assigned a numerical identifica- tion according to the Bypass Angioplasty Revascularization Investigation modification of the Coronary Artery Surgery Study nomenclature: segments 18, 19, and 19a referred to the proximal, middle, and distal portions of the LC, respectively; and segments 20, 21, and 22 referred to the first, second, and third obtuse marginal branch segments, respectively [7-9].

Statistics

Statistics were performed with SPSS version 13.0 (SPSS, Chicago, Ill). Quantitative data are expressed as mean +- SD. The ?2 test with Yates correction or Fisher exact test was used to analyze the nonparametric data. If the frequency of any cell was less than 5, then a Fisher exact test was used. Multivariate analysis was performed with logistic regression to determine the independent factors of the patients with LC- related AMI without ST-segment changes. Variables selected for testing in the multivariate analysis were those with a P value less than .05 in the univariate model. P value less than

.05 was considered statistically significant.

Results

Ninety-six consecutive patients underwent PCI for LC- related AMI in this institution. The mean age of the patients was 61 +- 14 years (range, 35-92 years). Seventy-seven patients (80%) were men. The average maximal CK and CK- MB levels were 2516.3 +- 2238.3 and 221.7 +- 191.3 IU/L, respectively. Seventy-four patients (77%) had, and the remaining 22 patients (23%) did not have, diagnostic ST-T changes (ie, ST-segment deviation or T-wave inversion). Among the 74 patients with diagnostic ST-T changes, 61 (82%) had inferior (II, III, AVF) or lateral lead (V₅ through V₆, I, aVL) ST-segment elevation, 8 (11%) had isolated anterior precordial lead (V₁ through V₃) ST-segment depression, and 5 (7%) had isolated lateral lead T-wave inversion. Seventy-four patients (77%) received primary coronary intervention, and the remaining 22 patients (23%) received elective PCI. Coronary angiography revealed that 44 patients (46%) had right-dominant circulation, 28 (29%)

left-dominant circulation, and 24 (25%) balanced-dominant circulation. Sixty-nine (72%) patients had more than one diseased vessel; 32% were double-vessel disease and 40% triple-vessel disease. None had significant left main disease. Also, 76 patients (79%) had total angiographic occlusion of the LC.

The clinical and angiographic characteristics of the groups with and without diagnostic ST-T changes are summarized in Tables 1 and 2, respectively. There were no significant

ST-T changes No ST-T changes P (n = 74) (n = 22)

Male 58 (78.4) 19 (86.4) .31 Age 62.6 +- 12.0 55.6 +- 16.8 .03 Diabetes mellitus 23 (31.1) 3 (13.6) .86 Hypertension 34 (45.9) 11 (50.0) .37 Dyslipidemia 14 (21.2) 6 (30.0) .21 Smoking 24 (32.4) 8 (36.4) .37 Heart failure 4 (5.4) 0 (0) .35 COPD 4 (5.4) 1 (4.5) .68 CVA 2 (2.7) 1 (4.5) .55 Presentation Typical angina 67 (90.5) 22 (100) .15 Killip III/IV 20 (27.4) 1 (4.5) .02 SBP 125.4 +- 37.6 136.7 +- 27.9 .21 DBP 75.3 +- 25.0 68.5 +- 24.4 .29 Heart rate 77.7 +- 22.3 71.7 +- 20.8 .28 Respiratory rate 20.0 +- 11.1 19.5 +- 11.3 .86 Primary PCI 69 (93.2) 5 (23.8) b.0001 Laboratory analysis Anemia 3 (4.2) 0 (0) .44 Leukocytosis 23 (32.9) 9 (40.9) .25 BUN 19.5 +- 7.8 16.4 +- 4.9 .08 Cre N1.3 14 (19.2) 2 (9.1) .22 CK (IU/L) 2778.2 +- 2343.3 1647.3 +- 1602.7 .037 CK-MB (IU/L) 247.7 +- 200.0 136.8 +- 130.3 .017

Values are presented as number (%) and mean +- SD. BUN indicates blood urea nitrogen; COPD, chronic obstructive pulmonary disease; Cre, creatinine; CVA, cerebral vascular accident; DBP, diastolic blood pressure; SBP, systolic blood pressure.

differences between the 2 groups in sex, history of under- lying disease, presentation of symptoms, initial vital signs, anemia, leukocytosis and impaired renal function, or clinically relevant concomitant stenosis of the LAD or RCA. However, the group without ST-T changes had a younger age (55.6 +- 16.8 vs 62.6 +- 12.0 years, P = .03), and fewer presented with Killip III/IV (4.5% vs 27.4%, P = .02). Also, the peak CK activity (1647.3 +- 1602.2 vs 2778.2 +- 2343.3 IU/L, P = .037) and CK-MB activity (136.8 +- 130.3

vs 247.7 +- 200.0 IU/L, P = .017) were both significantly lower in those patients without diagnostic ST-T changes. The culprit lesion in the group without ST-T changes was more likely in the middle or distal portion of the LC (95.5% vs 62.2%, P = .0015, Table 2). In addition, right- or balanced- dominant circulation was also found more frequently in the group without ST-T changes (86.4% vs 66.2%, P = .05). The group without ST-T changes had higher rate of middle or distal lesion with right-dominant circulation (54.5% vs 29.7%, P = .02). Furthermore, the rate of combination of middle or distal lesions with a right- or balanced-dominant circulation was significantly higher in the group without ST- T changes (86.4% vs 44.6%, P b .001). Patients with diagnostic ST-T changes had higher rate of receiving primary PCI (93.2% vs 23.8%, P b .0001) and having complete LC

Table 1 Comparisons of patients’ characteristics between groups with and without ST-T changes

ST-T No ST-T P changes changes (n =74) (n = 22)

No. of diseased vessels SVD 18 (24.3) 9 (40.9) DVD 24 (32.4) 7 (31.8) .25 TVD 32 (43.2) 6 (27.3) Location of culprit lesion, site Proximal 28 (37.8) 1 (4.5) .0015 Middle or distal 46 (62.2) 21 (95.5) Coronary anatomy Right dominant 32 (43.2) 12 (54.5) .18 Right or balanced dominant 49 (66.2) 19 (86.4) .05 Right dominant with 22 (29.7) 12 (54.5) .02 culprit lesion in the middle or distal segment of LC Right or balanced 33 (44.6) 19 (86.4) b.001 dominant with culprit lesion in the middle or distal segment of LC Complete LC occlusion 64 (87.7) 14 (63.6) .009 Clinical outcomes 30-d mortality 4 (5.4) 0 (0) .35 Repeat PCI 36 (48.6) 10 (45.5) .40 recurrent MI 10 (13.5) 3 (13.6) .62 Overall mortality 9 (12.2) 1 (4.5) .28 Follow-up (mo) 48.5 +- 40.9 31.4 +- 34.1 .078

Values are presented as number (%) and mean +- SD. MI indicates myocardial infarction; DVD, double-vessel disease; SVD, single-vessel disease; TVD, triple-vessel disease.

occlusion confirmed by coronary angiography (87.7% vs 63.6%, P = .009). After multivariable analysis, the peak CK- MB activity was significantly lower in the group without diagnostic ST-T changes.

Table 2 Comparisons of coronary angiography and clinical outcomes between the group with and without ST-T changes

In comparison with the group with ST-T changes, those patients without them tended to have lower 30-day mortality (0% vs 5.4%, P = .35); however, this was statistically insignificant. During the mean follow-up periods of 48.5 +-

40.9 and 31.4 +- 34.1 months (P = .078) in groups with and without ST-T changes, respectively, there were no differ- ences in rates of unstable angina that required repeat PCI (48.6% vs 45.5%, P = .40) and recurrent myocardial

infarction (13.5% vs 13.6%, P = .62) between the 2 groups. Also, the group without diagnostic ST-T changes tended to have lower overall mortality (4.5% vs 12.2%, P = .28), but the difference was statistically insignificant.

Discussion

The major findings of the present study are that 23% of the LC-related patients with AMI did not have, whereas the

remaining 77% had, electrocardiographic ST-T changes. Those patients without ST-T changes had significantly higher rate of middle or distal lesion in LC with right- or balanced- dominant circulation. Also, the group without ST-T changes had significantly fewer patients presented as Killip III/IVand a lower peak of serum cardiac biomarkers. However, during follow-up, there was no difference in reinfarction and unstable angina that subsequently required repeat PCI for control of symptoms. There were trends toward lower 30-day and overall mortality in the group without ST-T changes, but they were statistically insignificant.

Previous studies had demonstrated that only 40% of patients with complete occlusion of the LC had diagnostic ST-segment elevation in standard leads [3]. In a comprehen- sive analysis of myocardial infarction due to LC occlusion, Huey et al [10] reported that about 40% of patients had no significant ST changes, whereas about 45% and 15% of patients had ST-segment elevation and depression, respec- tively. Also, in some studies in which surface ECGs were performed during coronary angioplasty, about one third of patients with LC occlusion had ST-segment elevation, whereas one third had isolated ST-segment depression, and the remaining one third had no ST-segment deviation in any lead [4,11]. Nevertheless, approximately one fifth of the LC- related patients with AMI in the present study did not have diagnostic ST-T changes, whereas four fifths had them. The prevalence of LC-related AMI without diagnostic ST-T changes in the present study is relatively lower as compared with former studies. The study methods between the present and the former studies were different. None of the patients in the study of Huey et al received coronary angiography in the acute period. Furthermore, by using surface ECG, the relationship between the pattern of ST-segment deviation during acute occlusion caused by AMI and transient myocardial ischemia caused by coronary angioplasty is still inconclusive [12-14]. In contrast, most of the patients in the present study received emergent coronary angiography for AMI, and the location of the culprit lesion in the LC and morphology of coronary anatomy were analyzed. Also, the group without ST-T changes in the present study had excluded those with isolated ischemic T-wave inversion, which may contribute a possible cause of the lower prevalence. Despite the different study methods, the relatively lower prevalence in the present study could also be explained by those without ST-T changes being under- recognized in the ED of our institution.

The lack of ECG presentation in patients with LC-related infarct is multifactorial. One possible reason is that the LC usually supplies the lateral and posterior walls of the left ventricle, which are areas not well detected by the standard 12-lead ECG [4,15]. Besides, there were some trials suggesting that patients without ST-segment deviation were likely because of incomplete coronary occlusion due to thrombus or vasospasm [5,16]. However, there were about three fifths of patients in the group without ST-T changes in the present study who had complete LC occlusion during

coronary angiography. On the other hand, the present study found that the group without diagnostic ST-T changes was significantly associated with smaller infarction size, which was determined by the assessment of the amount of serum cardiac biomarkers, location of culprit lesion, coronary artery dominance, and Killip classification. The group without diagnostic ST-T changes had a lower peak of serum cardiac biomarkers. In addition, most of the patients in the group without ST-T changes had culprit lesion in the middle or distal portion of the LC. There were differences in coronary anatomy between the groups with and without ST-T changes. Those patients without ST-T changes had significantly higher rate of right- or balanced-dominant circulation, which means most of these patients had relatively less dominant LC. Therefore, the LC in these patients supplied less myocar- dium. Furthermore, the rate of combination of culprit lesion in the middle or distal portion with right- or balanced- dominant circulation was significantly higher in the group without diagnostic ST-T changes. These findings suggest that less myocardium was supplied by the portion behind the culprit lesion in the middle or distal portion of a less dominant LC. In addition, the group without ST-T changes had fewer patients presented as Killip III/IV, which could be attributed to a smaller infarct size in these patients. All these findings demonstrated a smaller infarct size in LC-related AMI without ST-T changes. In a previous study in which myocardial perfusion imaging with sestamibi was performed in LC-related patients with AMI, the infarct size and ischemic risk areas were similar between patients with and without ST changes [17]. The design in this study, including comparison of LC-related AMI with or without ST-segment elevation, was different from that of the present study. Also, anatomy of coronary arteries and location of the culprit lesion in the LC, in which different sizes of supplied myocardium were affected, and the peak of cardiac biomarkers were not available in that study. In contrast, comparison of LC-related AMI with and without ST-T changes by coronary anatomy, location of culprit lesion, and cardiac biomarkers were used in the present study. Therefore, the present study was more specific and reliable to demonstrate the clinical character- istics of isolated LC-related patients with AMI presenting without diagnostic ST-T changes.

In one analysis of consecutive patients with AMI, those presenting with normal or nonspecific ECG had lower peak CK levels and slightly lower mortality [16]. Previous reports demonstrated that the 30-day mortality, incidence of reinfarction, repeat PCI, and overall mortality during a mean follow-up period of 39 months in LC-related AMI were 15%, 15%, 15%, and 7.5%, respectively [10,18]. In contrast to the previous reports, the present study had lower 30-day mortality and higher rate of repeat PCI but similar reinfarction and overall mortality rate. Our data found that there was no significant difference in repeat PCI and reinfarction between the groups with and without ST-T changes. However, the rate of repeat PCI was much higher as compared with previous studies, which is probably because

of more patients receiving PCI instead of Pharmacologic therapy for angina pectoris in the current stent era. In addition, 30-day mortality and overall mortality in the present study tended to be higher in the group with diagnostic ST-T changes, which had a higher rate of left- dominant circulation. However, because of the small sample size, the mortality rate between both groups was not statistically different. These results suggest that with increasing size of myocardial infarction caused by occlusion of a dominant LC, the risk of arrhythmia, left ventricular dysfunction, and death is proportionally increased [15].

Implications

The present study found that the prevalence of LC-related AMI without ST-T changes was relatively lower compared with those in previous studies, and that could be explained by the prevalence being underestimated, because these patients might be misdiagnosed by the physician in the ED. As compared with those patients with ST-T changes, those without them had smaller infarct size and similar rate of repeat PCI or reinfarction but similar short- and long-term outcome between them. Also, the present study found that fewer patients in the group without ST-T changes received primary PCI, which may salvage more myocardium in transmural myocardial infarction. Therefore, clinical physi- cians in the ED should be aware of this information, and LC- related AMI should not be excluded in patients presenting with acute chest pain but apparently normal ECG. Previous studies had reported that use of additional ECG leads, such as leads (V₇ through V₉) placed on the left posterior thorax [3,15], and possibly imaging, such as multidetector com- puted tomography and myocardial perfusion image with sestamibi, may assist the clinician in identifying these patients [19-22]. When the image findings are suggestive or the clinical suspicion of acute ischemic syndrome is high, early coronary angiography should be performed to confirm the presence of LC occlusion without delayed therapeutic interventions while awaiting cardiac biomarker results.

Study limitations

This was a retrospective analysis, which may have inherent shortcomings. Second, the number of patients in the present study was small; we may not have had enough power to determine the difference of outcomes between the 2 groups. Finally, patients were treated according to the experiences and judgments of their clinical physicians, such that some of the LC-related AMI without ST-T changes were treated with primary PCI, which may have influenced the outcome of the patients.

Conclusion

The relatively lower prevalence of LC-related AMI without ST-T changes in the present study might be

underestimated because these patients could be misdiag- nosed in the ED. The lack of ECG finding in these patients was correlated with smaller infarct size than in those with ST- T changes. However, there were no differences in the short- and long-term clinical outcomes between them.

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