Methods

The Korean Acute Myocardial Infarction Registry (KAMIR) is a prospective, observational, multicenter registry to reflect real-world practice for Korean patients with AMI. Fifty highly experienced hospitals in primary PCI participated and registered online consecutive patients with AMI. The ethics committee of each hospital approved the study protocol. From November 2005 to June 2008, 11,872 patients with AMI were registered in the KAMIR database. Of these, 248 patients with AMI of the ULMCA as the culprit vessel were enrolled in this study. These patients were divided in 2 groups according to the absence (shock−, n = 206) or presence (shock+, n = 42) of shock at initial presentation.

PCI was performed using standard techniques. All patients received aspirin 325 mg orally and a loading dose of clopidogrel 300 mg before coronary angiography or after PCI for emergency cases. After PCI patients were routinely treated with aspirin 100 mg/day, clopidogrel 75 mg/day, and/or cilostazol 200 mg/day at the operator’s discretion. Patients were advised to maintain lifelong aspirin therapy. Duration of clopidogrel therapy was left to the operator’s discretion depending on the complexity of the lesion and procedure.

Study outcome was a composite of major adverse cardiac events including cardiac death, MI, and ischemia-driven target vessel revascularization for 1 year. Stent thrombosis was also evaluated. Cardiogenic shock was defined as sustained hypotension with systolic blood pressure <90 mm Hg for ≥30 minutes. MI was defined as typical ischemic chest pain and/or ST-segment and/or T-wave abnormalities with an increased creatine kinase-MB level ≥2 times reference values without any new pathologic Q waves. ST-segment elevation MI was defined as electrocardiographic findings of ST-segment elevation of ≥2 mm in 2 contiguous precordial leads or >1 mm in 2 limb leads or presumably new-onset left bundle branch block. All other electrocardiographic patterns including ST-segment depression or T-wave inversion, were diagnosed as non–ST-segment elevation MI. Ischemia-driven target vessel revascularization was defined as emergency or elective coronary artery bypass grafting or repeat PCI in the target vessel for chest pain or a positive test result for ischemia (exercise stress test, stress echocardiogram, 24-hour Holter monitor, evidence of ST-segment depression or increase in >1 lead on echocardiogram at rest, or radionuclide study showing a reversible defect). Stent thrombosis was defined as previously described by the Academic Research Consortium. Cumulative rates of event-free survival and major adverse cardiac events were analyzed over a 1-year follow-up.

All results in this study are expressed as mean ± SD or number (percentage). Comparisons of categorical variables were performed using chi-square test. Student’s t test was used to compare continuous variables. Multiple logistic regression analysis was performed to determine independent predictors of in-hospital mortality associated with AMI of the ULMCA. The following variables were tested: use of intra-aortic balloon pump, initial ST-segment elevation MI, Thrombolysis In Myocardial Infarction score before the procedure, initial shock at presentation, left ventricular ejection fraction <30%, and diabetes mellitus. Major adverse cardiac event-free survival distributions were estimated according to Kaplan–Meier methods. Log-rank test was used to compare major adverse cardiac event-free survival between the 2 groups. A p value <0.05 was considered statistically significant. Data were analyzed using SPSS 12.0 for Windows (SPSS, Inc., Chicago, Illinois).

Results

Baseline characteristics between the 2 groups were found to be similar ( Table 1 ). However, the number of patients with ST-segment elevation MI was larger in the shock+ than in the shock− group (12.1% vs 80.9%, respectively, p = 0.001); however, all patients without ST-segment elevation were acutely ill. Table 2 presents angiographic and procedural results. Most lesions were type B2/C (75.7% in shock− group vs 76.2% in shock+ group, p = 0.543). Thrombolysis In Myocardial Infarction score before the procedure was higher in the shock− than in the shock+ group (1.9 ± 1.1 vs 1.2 ± 1.1, respectively, p = 0.001), however, Thrombolysis In Myocardial Infarction score after the procedure was not different between the 2 groups (2.8 ± 0.5 in shock− group vs 2.8 ± 0.4 in shock+ group, p = 0.582). PCI was performed in 134 patients in the shock− group (65%) and in 36 patients in the shock+ group (85.7%). Drug-eluting stenting was used in 126 patients in the shock− group and in 34 patients in the shock+ group (94.0% vs 94.4%, p = 0.476). Mean stent length and diameter did not differ between the 2 groups ( Table 2 ). Treatment in hospital is presented in Table 3 . Conservative treatment by medical therapy was performed in 24.7% of patients in the shock− group and in 11.9% of patients in the shock+ group (p = 0.137). Thrombolytics were given in 3.8% of patients in the shock− group and in 9.5% of patients in the shock+ group (p = 0.134). Revascularization by PCI and/or coronary artery bypass grafting was performed in 75.3% of patients in the shock− group and in 88.1% of patients in the shock+ group. Overall in-hospital mortality was 14.9% (38 of 248), which was broken down as 8.7% in the shock− group and 47.6% in the shock+ group (p = 0.001). By multivariate analysis, initial shock at presentation (odds ratio 8.9, 95% confidence interval 4.1 to 19.2, p = 0.004) and left ventricular ejection fraction <30% (odds ratio 7.6, 95% confidence interval 2.7 to 21.1, p = 0.001) were independent risk factors for in-hospital mortality associated with ULMCA-related AMI. Use of medical therapy or revascularization was associated with a statistically similar in-hospital mortality (19.6% in medical therapy vs 14.1% in revascularization, p = 0.308).

Table 3

Treatment and in-hospital mortality

Variables	Cardiogenic Shock		p Value
	No	Yes
	(n = 206)	(n = 42)
Conservative treatment	51 (24.7%)	5 (11.9%)	0.137
Use of thrombolytics	8 (3.8%)	4 (9.5%)	0.134
Revascularization	155 (75.3%)	37 (88.1%)
Percutaneous coronary intervention	134 (65.0%)	36 (85.7%)	0.476
Bare-metal stent	8 (6.0%)	2 (5.6%)
Drug-eluting stent	126 (94.0%)	34 (64.4%)
Coronary artery bypass grafting	26 (12.3%)	2 (4.5%)	0.133
In-hospital mortality	18 (8.7%)	20 (47.6%)	0.001

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