Methods

The study design and primary results of the INFUSE AMI trial have previously been reported in detail. Briefly, INFUSE AMI was a prospective, 2 × 2 factorial, multicenter, single-blinded randomized trial evaluating the impact of intracoronary bolus of abciximab delivered at lesion site through the ClearWay RX Local Therapeutic Infusion Catheter (Atrium Medical, Hudson, New Hampshire) and the impact of manual aspiration on final infarct size in patients with anterior STEMI undergoing primary PCI. Patients aged ≥18 years with symptoms consistent with STEMI >30 minutes and ST-segment elevation of ≥1 mm in ≥2 contiguous leads in V ₁ to V ₄ or new left bundle branch block, with symptom-to-presentation time of ≤3.5 to 4 hours were eligible for enrollment. The study was approved by the institutional review board or ethics committee at each participating center, and all patients provided written informed consent. Blood samples were obtained after a median of 2.0 hours (interquartile range 1.5 to 3.0) from hospital admission at each participating center and recorded in the electronic case report form. WBCc was measured in ethylenediamine-tetra acetic acid-anticoagulated whole-blood specimen. cMRI acquisition and analysis as well as angiographic and ST-segment resolution analysis were previously described.

In this study, we included only the patients treated with primary PCI who had a baseline WBCc. The primary objective was to evaluate the impact of WBCc on final infarct size (percentage of total left ventricular mass) determined by late-enhancement cMRI 30 days after primary PCI. Secondary objectives were absolute infarct size (in grams), left ventricular end-systolic and diastolic volumes, left ventricular ejection fraction (LVEF), and total abnormal wall motion score. We also investigated the association between WBCc and 30-day death, cardiac death, reinfarction, target vessel revascularization, stent thrombosis defined according to the Academic Research Consortium definition, and major bleeding not related to coronary artery bypass graft surgery.

All analyses were stratified by tertiles of WBCc. Categorical variables were compared by chi-square or Fisher’s exact test. Continuous data are presented as mean ± SD or median and interquartile range and were compared using the Student t test or the Mann-Whitney rank sum test, as appropriate. Independent predictors of final infarct size (percentage of total left ventricular mass) were examined using a multivariate stepwise linear regression analysis with entry and exit criteria set at p = 0.1. The variables entered in the model were WBCc as a continuous variable, thrombus aspiration randomization, abciximab infusion randomization, age, gender, diabetes mellitus, insulin-dependent diabetes mellitus, hypertension, hyperlipidemia, current smoker, body mass index, creatinine clearance, symptom onset to first device, proximal left anterior descending (LAD) location, number of diseased vessels, baseline TIMI 0/1 flow, collaterals present, final TIMI 3 flow, jeopardy score of LAD, and β blocker, angiotensin-converting enzyme inhibitor, or angiotensin receptor blocker therapy at hospital discharge. All outcomes were expressed using the Kaplan-Meier method and compared using the log-rank test. Statistical analyses were performed using SAS, version 9.2 (SAS Institute, Cary, North Carolina). p Values <0.05 were considered statistically significant.

Results

Among the 452 patients enrolled in the trial, WBCc was available in 407 patients (90.0%), representing the present study cohort. Clinical characteristics of patients stratified by WBCc tertiles are listed in Table 1 . Patients in the upper tertile of WBCc (WBCc ≥13,200/mm ³ ) were younger, more likely to be smokers, had a longer ischemic time, and a lower LVEF determined at hospital admission compared with patients in the mid (9,700/mm ³ ≤ WBCc < 13,200/mm ³ ) or lower (WBCc <9,700/mm ³ ) WBCc tertile. Anatomical, procedural, and electrocardiographic variables stratified by tertiles of WBCc are listed in Table 2 . Patients in the upper tertile of WBCc were more likely to present with preprocedural TIMI 0 flow, thrombus containing lesions, greater thrombus area, and greater extent of ST-segment elevation. Other baseline variables were independent of WBCc. Similarly, no significant differences were apparent in main postprocedural variables across tertiles of WBC ( Table 2 ).

cMRI 30 days after primary PCI was available in 335 patients. As listed in Table 3 and Figure 1 , a significant stepwise increase in infarct size (percentage of total left ventricular mass) was apparent across tertiles of WBCc. Specifically, median infarct size (interquartile range) determined as the percentage of total ventricular mass was 11.2% (3.8% to 19.6%) in the lower WBCc tertile, 17.5% (10.5% to 22.9%) in the midtertile, and 19.1% (13.7% to 26.0%) in the upper tertile (p <0.0001). Similarly, significant differences were apparent across tertiles of WBCc in absolute infarct mass ( Table 3 and Figure 1 ), left ventricular end-systolic and diastolic volumes ( Table 3 and Figure 2 ), and total abnormal wall motion score ( Table 3 ). Moreover, LVEF determined by cMRI at 30 days was significantly lower in patients in the upper tertile of WBCc compared with those in the mid or lower tertile ( Table 3 ). As listed in Table 4 , after adjusting for possible confounders, WBCc was an independent predictor of infarct size along with age, intracoronary abciximab randomization, total ischemic time, proximal LAD location, and baseline TIMI 0/1 flow. No significant interaction between WBCc and abciximab was apparent for the extent of infarct size (p = 0.30).

Table 3

Infarct size determined at 30 days by cardiac magnetic resonance imaging in patients stratified by tertiles of white blood cell count (WBCc)

Variable	WBCc/mm 3			p
	<9,700 (n = 105)	≥9,700 and <13,200 (n = 112)	≥13,200 (n = 106)
Infarct size ∗ (%)	11.2 (3.8–19.6)	17.5 (10.5–22.9)	19.1 (13.7–26.0)	<0.0001
Total infarct mass (g)	13.7 (4.2–29.7)	21.4 (13.9–32.0)	25.6 (17.6–36.1)	<0.0001
Total abnormal wall motion score	5.0 (0.0–10.0)	8.0 (2.0–10.0)	8.0 (4.0–11.0)	0.0003
Left ventricular end-systolic volume (ml)	80.2 (64.8–110.2)	84.3 (63.6–113.4)	94.6 (71.1–122.7)	0.02
Left ventricular end-diastolic volume (ml)	169.3 (141.9–207.9)	172.6 (144.8–201.8)	181.3 (151.6–217.8)	0.09
LVEF (%)	52.9 (44.1–58.3)	49.7 (43.1–57.3)	47.9 (40.0–53.9)	0.03

All values are reported as median (interquartile range).

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