Safety of AngioJet Thrombectomy in Acute ST-Segment Elevation Myocardial Infarction: A Large, Single-Center Experience

Embolization of thrombus and atherosclerotic plaque occurs frequently during mechanical reperfusion for acute myocardial infarction (MI), especially in vessels with a large clot burden.^1,2 Plugging of the distal microvasculature causes mechanical obstruction of flow and also induces a secondary inflammatory response in the injured myocardium.^3,4 This phenomenon can occur even with attainment of Thrombolysis in myocardial Infarction (TIMI) grade 3 flow, and may occur in as many as one-third of patients undergoing interventional treatment for ST-segment elevation myocardial infarction (STEMI).^5–7 Accordingly, several techniques have been developed to limit the effects of distal embolization, including the use of thrombectomy devices and distal protection systems. Rheolytic thrombectomy is a catheter-based system that employs high-velocity water jets to produce a vacuum at the catheter tip for effective thrombus aspiration and removal. Initial studies demonstrated superior procedural and clinical outcomes in patients treated with AngioJet thrombectomy (AT, Possis Medical Inc, Minneapolis, Minnesota).^8–10 However, in a recent randomized trial, patients with STEMI treated with AT followed by stent implantation had a larger mean final infarct size and higher mortality compared with control patients.¹¹ The purpose of the present study was to further evaluate whether use of AT increases the risk of adverse angiographic or clinical outcomes in patients undergoing primary or rescue percutaneous coronary intervention (PCI) for STEMI.

Methods

Study population. All patients with acute STEMI undergoing primary or rescue PCI at our institution between January 2000 and December 2005 were included in this retrospective analysis (Figure 1). All patients had symptoms consistent with acute MI lasting < 24 hours and ST-segment elevation ≥ 1 mm in two contiguous leads. Patients with a saphenous vein graft culprit or stent thrombosis were excluded. Patients with cardiogenic shock were included in the study.
Cardiac catheterization and coronary intervention. Coronary intervention was performed using standard equipment and techniques. Heparin was administered to maintain the activated clotting time > 250 seconds. Use of AT, stents and glycoprotein IIb/IIIa receptor inhibitors was at the attending cardiologist’s discretion. Generally, AT was performed for angiographically visible thrombus, or if the operator considered there was a high risk of distal embolization. AT was performed with either the AngioJet XMI or XVG catheter (Possis Medical Inc.).
Study endpoints and definitions. The primary study endpoint was the incidence of in-hospital major adverse cardiac events (MACE) including death, reinfarction, target vessel revascularization and stroke. Secondary endpoints included the incidence of TIMI 3 flow after PCI, in-laboratory complications (ventricular tachycardia [VT]/ventricular fibrillation [VF], coronary perforation), vascular complications (pseudoaneurysm, retroperitoneal hemorrhage) and transfusion. Outcomes were examined according to whether the patient was treated with or without AT. Re-infarction was defined as the recurrence of clinical symptoms or new electrocardiographic changes accompanied by a rise in creatine kinase-MB levels > 2 times baseline. Target vessel revascularization was defined as urgent revascularization of the target vessel by either PCI or coronary artery bypass surgery.
Statistical analysis. All analyses were performed using SAS^® software (version 9.1, Cary, North Carolina). Continuous variables are expressed as mean ± SD and were examined using a Wilcoxon rank test. Categorical variables are expressed as counts or percentage and were examined using a Chi-square test, or where appropriate (expected frequency < 5) a Fisher’s Exact test. A multivariate step-down logistic regression analysis of in-hospital MACE and in-hospital mortality was performed including all univariate variables with a p-value < 0.10. A p-value < 0.05 was considered to indicate statistical significance.

Results

Clinical data. Between January 2000 and December 2005, a total of 1,388 patients underwent primary or rescue PCI for STEMI (Figure 1). Of these, 114 patients had a saphenous vein graft culprit and 14 had stent thrombosis and were excluded from the analysis. Of the remaining 1,260 patients, 239 underwent PCI with adjunctive AT device and 1,021 underwent PCI without thrombectomy. The baseline clinical characteristics of the two study groups are shown in Table 1. Patients in the AT group were more likely to be male, smokers and have a shorter time to hospital presentation. A higher peak creatine kinase level was observed in the AT group.
Angiographic and procedural data. Patients treated with AT were more likely to have a right coronary artery culprit compared with patients who did not undergo AT (61.5% vs. 34.8%, p < 0.0001) (Figure 2). There was no difference in the incidence of initial TIMI 3 flow or baseline diameter stenosis between the study groups (Table 2). A temporary venous pacemaker was used in 95% patients in the AT group and 5% of the control group. There was no difference in the use of an intra-aortic balloon pump between the study groups. Patients in the AT group had a larger stent diameter used. After PCI, there was a slightly lower incidence of TIMI 3 flow in the AT group compared with the control group (86% vs. 90%, p = 0.04).
In-hospital outcomes. The incidence of in-hospital MACE was 7.5% in the AT group and 9.0% in the control group (p = 0.47) (Figure 3). There was a trend toward a lower in-hospital mortality in the AT group (2.9% vs. 5.4%, p = 0.11), but there was a higher rate of re-infarction in the AT group compared with the control group. A higher peak creatine kinase level was observed in the AT group (Table 3). There was no significant difference in the incidence of in-lab VT/VF, cardiogenic shock, vascular complications or transfusion between the study groups. After adjustment for imbalances in baseline clinical and angiographic characteristics, age, history of renal failure, ejection fraction < 45%, low hematocrit and cardiogenic shock were found to be independent predictors of in-hospital MACE (Table 4). Use of adjunctive AT was not a predictor of either in-hospital MACE or death (Tables 4 & 5).

Discussion

In acute MI, the presence of visible thrombus is an important predictor of PCI-related complications, including distal embolization and the no-reflow phenomenon.^1,12–16 Furthermore, even in patients who achieve TIMI grade 3 flow after angioplasty, residual thrombus has been associated with worse outcomes.¹⁷ Therefore, a number of adjunctive devices, including the AT catheter, have been developed to mechanically remove thrombus during the angioplasty procedure to improve angiographic and clinical outcomes.
Several studies have demonstrated the safety and feasibility of adjunctive rheolytic thrombectomy in patients with acute MI. In the Vein Graft AngioJet Study (VeGAS)-I trial and the VeGAS-2 acute MI registry, rheolytic thrombectomy significantly reduced thrombus burden in acute myocardial infarction patients before definitive treatment (73.2 ± 64.6 vs. 15.5 ± 30.1 mm²) and was associated with a high rate of final TIMI 3 flow.⁹ Subsequently, Antoniucci et al. performed a randomized trial comparing rheolytic thrombectomy before stenting with direct stenting alone.¹⁰ Patients randomized to thrombectomy had a significantly higher rate of early ST-segment resolution and improved corrected TIMI frame count. In addition, patients treated with thrombectomy had a significantly smaller infarct size measured with sestamibi scintigraphy at 1-month (13.0% vs. 21.2%, p = 0.01). In aggregate, these data suggested that adjunctive thrombectomy improved early angiographic outcomes, myocardial perfusion and also limited the extent of infarction.
On the basis of these promising results, a larger multicenter randomized trial was designed. In the AngioJet Rheolytic™ Thrombectomy In Patients Undergoing Primary Angioplasty for Acute Myocardial Infarction (AiMI) trial, 480 patients were randomized to primary PCI with or without rheolytic thrombectomy before stent implantation.¹¹ In contrast to the Antoniucci trial, the primary endpoint (infarct size by single photon emission computerized tomography imaging) was higher in the thrombectomy group (12.1% vs. 10.9%, p < 0.02), and there was no difference in myocardial blush, TIMI frame count or ST-segment resolution between study groups. A lower incidence of TIMI 3 grade flow post PCI was also observed in the AT group (92% vs. 97%, p = 0.02). Moreover, there was a significantly higher mortality at 30-days in the thrombectomy arm (4.6% vs. 0.8%, p < 0.02). Although this mortality difference was most likely related to the unexpectedly good outcomes in the control arm, results of the trial raised questions about the safety of AT in STEMI patients.
In the present study, we examined the clinical outcomes of 239 patients with acute MI who were treated with adjunctive AT during mechanical reperfusion. The most important finding of our study was that in-hospital mortality and MACE were not significantly different in patients treated with AT. Although there was a higher proportion of patients with inferior infarction in the AT group, after adjustment for the imbalance in baseline characteristics, thrombectomy was not independently associated with in-hospital MACE or death. Moreover, there was no difference in the incidence of other complications such as in-lab VT/VF, cardiogenic shock or transfusion between the study groups. Overall, our data suggest that in a large, high-volume center with experienced operators, use of adjunctive AT is safe and does not increase the risk of adverse clinical outcomes.
Several other observations from the study deserve mention. We believe that careful patient selection probably played an important role in achieving the good outcomes observed in the AT group. As noted above, there was a much higher use of AT in patients with inferior infarction. Although the reasons for the difference in device utilization are unclear, we believe that operators selected AT for patients with larger thrombus burden or higher perceived risk of embolization. Additionally, the larger stent size observed in the AT group also suggests that operators chose to use the AngioJet catheter with larger, technically suitable infarct vessels.
Study limitations. This was a retrospective, non-randomized comparison. There were several significant imbalances between the study groups, such as gender and infarct location, which may have influenced the clinical results. The study was also underpowered to detect a difference in mortality. Notably, our results represent experience in a single, high-volume center and it may not be possible to extrapolate our findings to other centers. Nevertheless, our study represents one of the largest series of patients treated with AT for STEMI. Additionally, no significant difference in clinical outcomes was observed in the AT group after adjustment for the baseline imbalances. Quantitative angiographic analysis was not employed in the study, and therefore we were unable to stratify clinical and angiographic results based on the baseline thrombus burden in the infarct vessel. Finally, we did not have systematic 30-day or 6-month outcomes available for the study population.

Conclusions

In this large, single-center experience, use of AT during mechanical reperfusion for STEMI was not associated with an increased risk of adverse outcomes. Importantly, there was no apparent difference in in-hospital mortality among patients treated with or without AT. Our data suggest that AT may be performed safely in selected patients with STEMI.

References

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