Compared to occlusions of other major coronary arteries, patients presenting with acute left circumflex (LCx) occlusion usually have ST-segment elevation on the electrocardiogram <50% of the time, potentially delaying treatment and resulting in worse outcomes. In contemporary practice, little is known about the clinical outcomes of patients with LCx territory occlusion without ST-segment elevation myocardial infarction (STEMI). We identified patients with myocardial infarction from April 2004 to June 2009 in the CathPCI Registry treated with percutaneous coronary intervention for culprit LCx territory occlusion, excluding those with previous coronary artery bypass grafting. Logistic generalized estimating equation modeling was used to compare the outcomes, including in-hospital mortality between patients with STEMI and non-STEMI (NSTEMI) adjusting for differences in the baseline characteristics. Of the 27,711 patients with myocardial infarction and acute LCx territory occlusion, 18,548 (67%) presented with STEMI and 9,163 (33%) with NSTEMI. With the exception of a greater proportion of cardiac risk factors and cardiac history in the NSTEMI group, the demographic and baseline characteristics were clinically similar between the 2 groups, despite the statistical significance resulting from the large population. The patients with STEMI were more likely to have a proximal LCx culprit lesion (63% vs 27%, p <0.0001) and had greater risk-adjusted in-hospital mortality (odds ratio 1.36, 95% confidence interval 1.12 to 1.65, p = 0.002) compared to patients with NSTEMI. In conclusion, acute LCx territory occlusion often presents as NSTEMI, but patients with NSTEMI and occlusion have a lower mortality risk than those with STEMI, possibly because of factors such as the amount of myocardium involved, the lesion location along the vessel, and/or a dual blood supply.
A 12-lead electrocardiogram (ECG) detects acute occlusions of the left anterior descending artery and right coronary artery in 70% to 92% of cases; however, the sensitivity for acute left circumflex artery (LCx) occlusion ranges from 32% to 48%, likely because of its posterolateral location, which is farther from the chest wall, with a lack of corresponding electrocardiographic leads. Patients presenting with non–ST-segment elevation myocardial infarction (NSTEMI) have better short-term outcomes because these infarcts are typically smaller. However, a subset of patients with NSTEMI might in fact be “STEMI-equivalents,” with worse outcomes compared to patients presenting with ST-segment elevation due to delayed reperfusion in the NSTEMI group. In the present study, we assessed the incidence of acute occlusions in the LCx territory of patients who presented with NSTEMI and compared the outcomes between patients with STEMI and NSTEMI with acute LCx territory occlusion to determine whether acute occlusions of this territory in patients presenting with NSTEMI should be considered “STEMI-equivalents.”
Methods
The present study was supported by the American College of Cardiology Foundation’s National Cardiovascular Data Registry. The CathPCI Registry is a voluntary registry that receives data from >1,000 participating hospitals, including community, government, and university hospitals from rural, suburban, and urban areas throughout the United States. This is a standard data set with uniform data definitions, data entry and transmission requirements, and data quality checks. The details of the data collection process can be found at the National Cardiovascular Data Registry Web site ( www.ncdr.com ). For the purposes of the present study, we identified all patients with myocardial infarction who presented from April 2004 through June 2009 and underwent percutaneous coronary intervention (PCI) for culprit LCx territory occlusion. Because the acuity of the occluded lesions is not as well defined for patients with previous coronary artery bypass grafting (n = 2,951), these patients were excluded from the analysis, yielding a final study population of 27,711 patients treated.
The patients with STEMI included those who presented within 24 hours of symptom onset with ST-segment elevation on the ECG and admission symptoms consistent with acute coronary syndrome. The patients with NSTEMI presented with admission symptoms consistent with acute coronary syndrome, symptom onset of ≤24 hours, and cardiac biomarkers of myonecrosis greater than the institutional upper limit of normal. Occlusion was defined as 100% preprocedure stenosis and Thrombolysis In Myocardial Infarction 0 or 1 flow in a LCx territory (defined as LCx or obtuse marginal artery) index lesion. The patients with STEMI who had undergone rescue or facilitated PCI with index lesions in the LCx territory and <100% stenosis or Thrombolysis In Myocardial Infarction flow >1 were also included. Because the data collection form for National Cardiovascular Data Registry did not capture the culprit lesion, for patients with multivessel PCI, the first lesion treated was assumed to be the infarct culprit lesion.
The patients were grouped according to the myocardial infarction type (STEMI vs NSTEMI). We compared the baseline demographic and patient characteristics, admission medications, cardiac status on admission, and catheterization laboratory data between the 2 groups. The Pearson chi-square test was used to compare categorical variables, and the Wilcoxon test was used for continuous variables. Logistic generalized estimating equation modeling was used to compare the in-hospital mortality between the patients with STEMI and NSTEMI, adjusting for differences in the baseline characteristics and variables in the National Cardiovascular Data Registry mortality model.
We performed a secondary analysis of the patients with NSTEMI in an attempt to determine whether the prognosis associated with LCx occlusion is truly different from that associated with other coronary occlusions. We sampled all NSTEMI cases with 100% occlusions or Thrombolysis In Myocardial Infarction 0/1 flow as the culprit lesion during the same period and used logistic generalized estimating equation modeling to compare the in-hospital mortality for an occluded LCx culprit (n = 9,163) to occlusions in the left anterior descending artery (n = 7,093) and right coronary artery (n = 8,836) territories among patients with NSTEMI. All data analysis was performed by the National Cardiovascular Data Registry statistical analysis center at Duke Clinical Research Institute. A 2-tailed p value of ≤0.05 was considered significant.
Results
Of 27,711 consecutive patients without coronary artery bypass grafting who presented with STEMI or NSTEMI and underwent PCI for culprit LCx territory occlusion, 18,548 (67%) presented with STEMI and 9,163 (33%) with NSTEMI. Differences in the baseline and demographic characteristics between the 2 groups are listed in Table 1 . The patients who presented with NSTEMI were more likely to have cardiac risk factors (ie, diabetes, dyslipidemia, and hypertension) and a history of coronary artery disease (previous myocardial infarction or PCI) than were the patients with STEMI.
| Characteristic | STEMI (n = 18,548) | NSTEMI (n = 9,163) |
|---|---|---|
| Age (years) | ||
| Median | 58 | 58 |
| Interquartile range | 50–67 | 50–67 |
| Men | 13,916 (75.0%) | 6,786 (74.1%) |
| Race | ||
| White | 15,236 (82.1%) | 7,392 (80.7%) |
| Black | 1,407 (7.6%) | 856 (9.3%) |
| Hispanic | 667 (3.6%) | 308 (3.4%) |
| Other | 1,200 (6.5%) | 591 (6.5%) |
| Body mass index (kg/m 2 ) | ||
| Median | 28.3 | 28.9 |
| Interquartile range | 25.3–32.0 | 25.7–32.9 |
| Previous myocardial infarction (>7 days) | 2,472 (13.3%) | 1,337 (14.6%) |
| Previous congestive heart failure | 548 (3.0%) | 414 (4.5%) |
| Diabetes mellitus | 3,535 (19.1%) | 2,011 (22.0%) |
| Previous renal failure | 473 (2.6%) | 232 (2.5%) |
| Cerebrovascular disease | 995 (5.4%) | 547 (6.0%) |
| Peripheral vascular disease | 962 (5.2%) | 526 (5.7%) |
| Hypertension | 11,002 (59.3%) | 5,936 (64.8%) |
| Smoker | ||
| Former | 3,715 (20.0%) | 2,144 (23.4%) |
| Current | 9,062 (48.9%) | 4,111 (44.9%) |
| Dyslipidemia ⁎ | 10,485 (56.5%) | 5,735 (62.6%) |
| Previous percutaneous coronary intervention | 2,536 (13.7%) | 1,444 (15.8%) |
⁎ Documentation of total cholesterol >200 mg/dl, low-density lipoprotein ≥130 mg/dl, high-density lipoprotein <30 mg/dl, admission cholesterol >200 mg/dl, triglycerides >150 mg/dl, or initiation of treatment because of low-density lipoprotein level >100 mg/dl in patients with known coronary artery disease.
No difference was found in the proportion of patients who presented with congestive heart failure between the 2 groups. However, patients with STEMI presented to the hospital earlier and were more likely to have cardiogenic shock and be in New York Heart Association class IV congestive heart failure on admission ( Table 2 ). Comparisons of the initial admission medical therapy among the groups are listed in Table 3 . The patients with STEMI were more likely to receive glycoprotein IIb/IIIa inhibitors and unfractionated heparin (p <0.001). The patients with NSTEMI were more likely to receive β blockers, statins, low-molecular-weight heparin, and thrombin inhibitors on admission (p <0.001). The patients with STEMI were more likely to require insertion of an intra-aortic balloon pump during their hospitalization and were more likely to have a proximal lesion (lesion in the proximal portion of the LCx, obtuse marginal-1, or ramus arteries) than were patients with NSTEMI (62.8% vs 37.2%, p <0.0001). The patients with NSTEMI were more likely to have multivessel disease and more frequently had a drug-eluting stent or no stent placed for their culprit lesion ( Table 4 ). The success of the intervention was not different between the 2 groups. A small percentage (9.9%) of patients in the STEMI group had culprit lesions with stenosis <100%. This group represented those patients with STEMI who had undergone rescue or facilitated PCI.
| Cardiac Status | STEMI (n = 18,548) | NSTEMI (n = 9,163) | p Value |
|---|---|---|---|
| Symptom onset to admission (hours) | NA | ||
| ≤6 | 15,354 (82.8%) | 4,955 (54.1%) | |
| 6–≤12 | 2,098 (11.3%) | 2,077 (22.7%) | |
| 12–≤24 | 1,096 (5.9%) | 2,131 (23.3%) | |
| Congestive heart failure | 1,756 (9.5%) | 805 (8.8%) | 0.0654 |
| New York Heart Association class | <0.0001 | ||
| I | 4,063 (21.9%) | 2,069 (22.6%) | |
| II | 1,387 (7.5%) | 908 (9.9%) | |
| III | 2,911 (15.7%) | 2,410 (26.3%) | |
| IV | 10,185 (54.9%) | 3,775 (41.2%) | |
| Cardiogenic shock | 1,884 (10.2%) | 377 (4.1%) | <0.0001 |
| Medication | STEMI (n = 18,548) | NSTEMI (n = 9,163) |
|---|---|---|
| Aspirin | 16,759 (91.3%) | 8,435 (92.8%) |
| β Blocker | 12,295 (70.0%) | 6,465 (73.2%) |
| Any glycoprotein IIb/IIIa inhibitor | 14,036 (75.8%) | 6,609 (72.2%) |
| Any low-molecular-weight heparin | 2,045 (11.0%) | 2,336 (25.5%) |
| Unfractionated heparin | 13,481 (73.2%) | 6,741 (74.2%) |
| Clopidogrel | 13,507 (73.1%) | 6,750 (74.1%) |
| Statins | 5,544 (30.1%) | 3,594 (39.5%) |
| Bivalirudin | 3,066 (16.5%) | 1,974 (21.6%) |
| Any thrombin inhibitor ⁎ | 3,096 (16.7%) | 1,982 (21.6%) |
⁎ Other than heparin products (i.e., bivalirudin, argatroban, lepirudin).
| Catheterization Laboratory Data | STEMI (n = 18,548) | NSTEMI (n = 9,163) | p Value |
|---|---|---|---|
| Intra-aortic balloon pump | 1,912 (10.3%) | 513 (5.6%) | <0.0001 |
| Multivessel disease | 10,435 (56.3%) | 5,307 (57.9%) | 0.0049 |
| Any drug-eluting stent | 9,873 (53.2%) | 5,230 (57.1%) | <0.0001 |
| No stent | 2,080 (11.2%) | 1,296 (14.1%) | <0.0001 |
| Preprocedure stenosis 100% | 16,708 (90.1%) | 9,163 (100%) | <0.0001 |
| Previously treated lesion | 865 (4.7%) | 422 (4.6%) | 0.8267 |
| Percutaneous coronary intervention procedure success | 16,937 (92.3%) | 8,258 (90.6%) | 0.3910 |
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