Methods

This prospective CMR study was a predefined substudy of the Abciximab Intracoronary versus intravenously Drug Application in STEMI (AIDA STEMI) trial, which compared intravenous versus intracoronary abciximab application in patients with STEMI and did not show a difference in infarct size, reperfusion injury, and clinical outcome between the treatment groups. The detailed design and main results of the trial have previously been published. The study was approved by national regulatory authorities and ethics committees of participating centers. All patients provided written informed consent.

Consecutive patients enrolled in the AIDA STEMI trial at 8 sites were included in the CMR substudy. The sites were chosen on the basis of proven expertise in performing CMR examinations in patients with MI. By protocol, CMR was performed on days 1 to 10 after the index event. Exclusion criteria were the typical contraindications for CMR as described previously together with the detailed scan protocol. CMR images were sent to the CMR core laboratory for blinded assessment. Certified CMR evaluation software was used (cmr ⁴² ; Circle Cardiovascular Imaging Inc, Calgary, Alberta, Canada), and all analyses were done according to standard definitions as previously described.

A moderate-to-large PE was defined as a collection of fluid of ≥5 mm in the end-diastolic phase in the short-axis and corresponding 2- and 4-chamber views of the cine steady state free precision sequences ( Figure 1 ). The CMR core laboratory is highly experienced in CMR postinfarction acquisition and postprocessing with excellent reproducibility and low interobserver and intraobserver variability.

Patient example. Patient with transmural anterior MI with circumferential pericardial effusion with a maximal diameter of 14.7 mm next to the right ventricle. (A) Steady state free precision (SSFP) 4-chamber view, (B) SSFP 4-chamber view with measurements, (C) SSFP 2-chamber view, and (D) SSFP short-axis view.

The primary clinical end point major adverse cardiovascular event (MACE) was a composite of all-cause death, reinfarction, and new congestive heart failure within 1 year after infarction, using outcome definitions described previously. All components of the combined clinical end point were adjudicated by a clinical end point committee, blinded to the patient’s assigned treatment, on the basis of data provided by the clinical trial sites. To avoid double counting of patients with more than 1 event, every patient could be counted only once for the primary clinical end point. Consequently, for those subjects who had more than 1 type of event at the same time, the more severe event was counted according to a hierarchical order (death > reinfarction > congestive heart failure).

Baseline patient characteristics, procedural details, and CMR findings are described according to the presence or absence of a moderate-to-large PE. Data for continuous variables are presented as medians with interquartile range (IQR). Categorical variables are presented as frequencies and percentages. Differences between groups were assessed by Fisher’s exact and by the Wilcoxon rank-sum test for categorical and continuous data, respectively. To identify predictors for a moderate-to-large PE and MACE, stepwise multivariate logistic and Cox regression analyses were performed, respectively, after univariate preselection of candidate predictors. The inclusion criterion for stepwise multivariate analysis was a p <0.05 in univariate analysis. For univariate preselection, all variables of Tables 1 and 2 were considered. To improve the ratio of events per variable, the Thrombolysis in Myocardial Infarction (TIMI) risk score and not its single variables was considered for Cox regression analysis. Because the myocardial salvage index accounts for infarct size by its inclusion in the formula for calculation of myocardial salvage, we also discarded the myocardial salvage index. Hazard ratios (HR) and odds ratios (OR) with 95% confidence intervals (CI) were calculated for univariate and multivariate analyses as appropriate. Rates for MACE and all-cause mortality were plotted and compared by means of Kaplan–Meier curves and log-rank test, respectively. A 2-tailed p value <0.05 was defined as statistically significant. SPSS version 20.0 was used for statistical analyses.

Table 2

Cardiovascular magnetic resonance results

Characteristic	Total study	Pericardial effusion		P
	(n=780)	<5 mm (n=597)	≥5 mm (n=183)
Area at risk (%LV)	35 (25-48)	34 (24-47)	39 (28-49)	0.01
Infarct size (%LV)	17 (8-25)	15 (7-24)	21 (15-29)	<0.001
Myocardial salvage index	51 (33-69)	54 (35-75)	44 (23-59)	<0.001
Late MO (%LV)	0.0 (0.0-1.7)	0.0 (0.0-1.4)	0.9 (0.0-2.9)	<0.001
Hypointense core (%LV)	0.0 (0.0-1.7)	0.0 (0.0-1.2)	0.0 (0.0-3.4)	<0.001
Hypointense core present	238/689 (35%)	167/528 (32%)	71/161 (44%)	0.004
LV ejection fraction (%)	50 (43-58)	51 (44-58)	48 (41-55)	<0.001
LV enddiastolic volume (ml)	146 (120-173)	146 (120-173)	146 (123-172)	0.79
LV endsystolic volume (ml)	72 (54-91)	72 (54-89)	75 (56-99)	0.03

 

Continuous and categorical data are presented as median (interquartile range) and frequency (percentage), respectively.

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