Methods

We performed a retrospective, single-center study at the Tel-Aviv Sourasky Medical Center, a tertiary referral hospital with a 24/7 PPCI service. Included were all 546 consecutive patients admitted from January 2006 and April 2012 to the cardiac intensive care unit (CICU) with the diagnosis of acute anterior STEMI. Excluded were 7 patients who were treated either conservatively or with thrombolysis and another 20 whose final diagnoses on discharge were other than anterior wall STEMI (e.g., myocarditis or takotsubo cardiomyopathy). All patients in the CICU undergo echocardiography 24 to 48 hours after admission, and all of those with evidence of anterior MIs and LV ejection fractions (EF) <50% undergo repeat echocardiography 5 to 7 days after admission. We excluded another 90 patients with anterior STEMIs who had undergone only 1 echocardiographic examination at admission (these 90 patients had LV EFs >50%, and none demonstrated LV thrombus). The final study population included 429 patients whose baseline demographics, cardiovascular histories, clinical risk factors, and treatment characteristics were retrieved from their medical files.

The diagnosis of STEMI was established by a typical history of chest pain, diagnostic electrocardiographic changes, and serial elevations of serum cardiac biomarkers. The electrocardiographic criterion for the diagnosis of ST-segment elevation was an ST-segment elevation ≥1 mm in >2 adjacent leads.

Patients were treated according to the discretion of the senior attending physician in the CICU. All patients received dual-antiplatelet therapy consisting of aspirin (a loading dose of 300 mg followed by 100 mg/day) and clopidogrel (a loading dose of 300 to 600 mg followed by 75 mg/day), as well as a heparin bolus (4,000 U) in the emergency department. Those who arrived to the hospital by ambulance were administered aspirin and heparin while being transported. If not contraindicated, patients with symptoms ≤12 hours in duration underwent PPCI, as did patients with symptoms of 12 to 24 hours in duration if they continued to be symptomatic on admission. All patients were treated with heparin boluses during angioplasty, aiming to obtain an activated clotting time of 250 to 300 seconds in those treated with glycoprotein IIb/IIIa antagonists and an activated clotting time >300 seconds in the others. Glycoprotein IIb/IIIa antagonists were administered during PPCI at the discretion of the senior operator. Post-PPCI anticoagulation treatment was deferred unless the echocardiographic examination demonstrated an LV thrombus.

All patients admitted to the CICU with diagnoses of STEMI underwent screening echocardiographic examinations 24 to 48 hours after admission. Repeat echocardiography was performed during days 5 to 7. Echocardiography was performed using Philips iE33 (Philips Medical Systems, Andover, Massachusetts) and GE Vivid 3 (GE Healthcare, Waukesha, Wisconsin) models equipped with S5-1 transducers. Parasternal long- and short-axis, apical, and 2- and 4-chamber views were obtained using standard transducer positions. Special considerations were given to apical and low parasternal echocardiographic windows. Echocardiograms were interpreted independently by 2 expert investigators. An LV thrombus was defined as an echo-dense mass adjacent to an abnormally contracting myocardial segment. It had to be distinguishable from the underlying myocardium, have a clear thrombus-blood interface, and be visible in ≥2 transducer positions.

The 16-segment model was used for scoring the severity of segmental wall motion abnormalities, according to the American Society of Echocardiography. LV wall motion was graded on a scale ranging from 1 to 5 (1 = normal motion, 2 = hypokinesia, 3 = akinesia, 4 = dyskinesia, 5 = signs of an LV apical aneurysm). The first echocardiographic study was technically difficult in 47 patients, while the second echocardiographic study was technically difficult in another 37 patients.

Analysis was performed retrospectively using the institution’s electronic records and database, and the study was approved by the institutional review board, which waived the requirement for informed consent. All data were summarized and are displayed as mean ± SD for continuous variables and as numbers and percentages of patients in each group for categorical variables. The p values for the chi-square test were calculated using Fisher’s exact test. The p value for the Student’s t test is reported following Levene’s test for equality of variance. Binary logistic regression models were performed at the enter mode for LV thrombus as the dependent variable and adjusted for age, gender, diabetes mellitus, hypertension, hyperlipidemia, smoking history, previous MI, long-term use of aspirin or clopidogrel, periprocedural use of glycoprotein IIb/IIIa antagonists, a low EF (referenced to >40%) on the first echocardiogram, coronary artery disease severity (referenced to 1-vessel disease), a proximal left anterior descending coronary artery lesion (referenced to middle and distal lesions), a Thrombolysis In Myocardial Infarction (TIMI) score ≤1 (referenced to a TIMI score ≥2), and time from symptom onset to PPCI (higher than the median time referenced to lower than median time). All analyses were considered significant at a 2-tailed p value <0.05. SPSS was used to perform all statistical evaluation (SSPS, Inc., Chicago, Illinois).

Results

Data from 429 consecutive patients with anterior STEMIs who underwent serial echocardiography were analyzed. LV thrombus was diagnosed before hospital discharge in 18 of the 429 evaluated patients (4%), with the first echocardiogram diagnosing 11 of them. The baseline characteristics of the patients with and without LV thrombus are listed in Table 1 . Patients with diagnosed LV thrombi had significantly lower LV EFs than those without LV thrombi on both echocardiograms, longer time to reperfusion, and higher than the median time from symptom onset to PPCI ( Table 1 ). In addition, preangioplasty TIMI flow grade ≤1 was significantly more frequent in patients with LV thrombi compared to those without. The multivariate binary logistic regression model ( Table 2 ) revealed that an admission LV EF <40%, TIMI flow grade ≤1 before angioplasty, and being higher than the median time from symptom onset to PPCI were all independent predictors of early LV thrombus formation. Surprisingly, only 1 of the 18 patients with LV thrombi had severe LV dysfunction (LV EF ≤30%).

Table 2

Binary logistic regression models results

Correlates	β	p Value ∗
Age	1.002	0.93
Male gender	1.336	0.671
Diabetes mellitus	0.282	0.142
Hyperlipidemia	2.009	0.21
Hypertension	2.230	0.167
Smoker	2.659	0.104
Personal history of MI	0.001	0.997
Long-term aspirin use	2.269	0.36
Long-term clopidogrel use	8.402	0.224
Use of glycoprotein IIb/IIIa inhibitors	1.507	0.439
1-vessel disease (reference)
2-vessel disease	0.476	0.25
3-vessel disease	0.274	0.084
Proximal left anterior descending coronary artery lesion	1.405	0.543
Preangioplasty TIMI flow grade ≤1	0.141	0.018
First documented EF <40%	0.156	0.027
Total time to balloon >150 minutes	3.022	0.05

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