Protection Devices and Thrombectomy for Native Coronary
Artery ST-Elevation Myocardial Infarction

Primary percutaneous coronary intervention (PCI) is established as optimal therapy for patients with ST-elevation myocardial infarction (STEMI).¹ The goal of primary PCI is to achieve a thrombolysis in myocardial infarction (TIMI) 3 flow and also to restore adequate perfusion at the myocardial level. However, visible thrombus embolization to the distal circulation during primary PCI occurs in up to 14% of patients, and outcomes in these patients are compromised.² Furthermore, even in patients without such macroembolization, myocardial reperfusion is often suboptimal, with patients showing persistent ST-segment elevation and abnormal myocardial blush grades (MBG).^3,4 The wellrecognized “slow/no reflow” phenomenon results when there is failure to achieve myocardial reperfusion despite the presence of a patent epicardial coronary artery, and this too has been associated with adverse long-term outcomes.^5–8 Subsequently, great interest has been shown in various techniques aimed at either reducing the amount of thrombus present or preventing its distal migration.
Apart from pharmacological agents such as glycoprotein (GP) IIb/IIIa antagonists, several mechanical devices have been proposed to prevent distal embolization. These can be divided into: 1) distal embolic filters; 2) occlusive devices: (a) proximal or (b) distal; 3) intracoronary aspiration thrombectomy; 4) thrombectomy with the X-Sizer system (ev3, Inc., Plymouth, Minnesota); and 5) laser debulking. However, despite their intuitive appeal, their application remains uncertain given the results of emerging randomized trials. The purpose of this review is to summarize the current clinical evidence and provide guidelines for their use.

Distal Embolic Filters
Distal embolic filters have proven to be of significant clinical benefit for PCI of saphenous vein bypass graft (SVG) lesions.⁹ The theoretical advantage of such devices lies in their ability to maintain distal perfusion while trapping most particulate debris before it becomes lodged in the distal circulation. Other strengths include the ability to inject contrast during the procedure. In view of their popularity and benefit in SVG PCI, early reports suggested a beneficial effect in patients with native coronary acute myocardial infarction (AMI).^10–12 Limbruno et al showed improved TIMI frame counts, higher occurrence of MBG 3, more frequent ST-segment resolution, lower peak creatine kinase MB (CKMB) release and greater improvement in left ventricular ejection fraction (LVEF). However, data from randomized trials have thus far not shown any convincing benefits (Table 1).

The PROMISE trial (Protection Devices in PCI-Treatment of Myocardial Infarction for Salvage of Endangered Myocardium) using the FilterWire EZ^™ system (Boston Scientific, Natick, Massachusetts) randomized 200 patients undergoing primary PCI, but also included patients with non-ST-elevation AMI. No differences were found in the two groups in terms of maximal adenosine-induced flow velocity (primary endpoint), infarct size, incidence of distal embolization or 30-day mortality.¹³
The recently published UPFLOW study (MI Use of Protective FilterWire to improve Flow in Acute Myocardial Infarction) assessed whether the capture of embolic particles during PCI would improve myocardial reperfusion outcomes.¹⁴ This multicenter prospective trial of 100 patients with STEMI and thrombotic vessel occlusion randomized patients to the FilterWire EZ or no distal protection. Although captured debris were noted in 52% of those treated with the device, the primary efficacy endpoints, including markers of epicardial and myocardial reperfusion, did not differ between the two study groups (TIMI flow, MBG and ST-segment resolution).
The PREMIAR (Protection of Distal Embolization in High-Risk Patients with Acute ST-Segment Elevation Myocardial Infarction) trial was a prospective, randomized, controlled study of a filter distal protection device during PCI in patients with acute STEMI at high risk of embolic events.¹⁵ Only patients with TIMI grade flow between 0–2 were included. A new, novel, low-profile filter was used (SpideRX, ev3), which allows standard 0.014 inch guidewires to be used to cross the target lesion. The filter size can be chosen depending on vessel size (3–5 mm). The study randomized 150 patients, and visible macroscopic atherothrombotic debris was noted in the filters in 48% of patients from the filter arm (by visual assessment). Similar to the other randomized trials, however, the filter device did not improve myocardial reperfusion as demonstrated by quantitative biomarkers such as ST-segment resolution or MBG. Left ventricular function, CKMB release and clinical outcomes were also essentially similar in the two arms. The study was unable to identify any specific STEMI subgroup that might benefit from adjunctive distal protection.
Possible explanations for the lack of benefit of distal filters may include: (a) the risk of distal embolization during passage of the relatively high-profile devices; (b) filters do not protect against embolization into sidebranches proximal to the filter basket; (c) increased procedure time; (d) frequent need to predilate the lesion to allow passage of the filter device; and (e) distal filters require pore sizes of ~100 μm to allow distal blood flow, while most liberated particles during PCI are < 100 μm.¹⁶
On current evidence, distal protection filters cannot be recommended for routine use in patients undergoing PCI for STEMI in native coronary arteries.

Occlusive Devices
Proximal occlusion. Proximal occlusion devices work on the principle of occluding the vessel proximal to the target lesion, thus suspending antegrade flow during target vessel intervention. The intent is to stop the distal release of both particulate matter and humoral mediators. Protection is established before any device is passed across the target lesion, thus reducing the risk of mechanical distal embolization. It holds the theoretical advantage of protecting sidebranches originating distal to the target lesion. The stagnant blood containing suspended debris particles must be evacuated before antegrade flow is restored at the end of the intervention.
The Proxis system (St. Jude Medical, Minneapolis, Minnesota) is the most studied device and was evaluated in the FASTER (Feasibility And Safety Trial for its embolic protection device during transluminal intervention in coronary vessels: a European Registry) trial. This showed that retrograde blood flow can be achieved during proximal occlusion and that the device can be safely used in both SVG and native-vessel PCI.
At the present time, no randomized, controlled trials have assessed the Proxis or other proximal occlusion devices in STEMI.

Distal occlusion. Unlike proximal occlusion devices, various randomized, controlled trials have evaluated distal occlusion (Table 2). The principle is to stop plaque and other liberated debris from flowing distal to the target lesion by blocking distal blood flow in the vessel. The column of blood needs to be completely aspirated prior to the relief of distal occlusion and restoration of antegrade flow. Such devices include the PercuSurge GuardWire (Medtronic, Inc., Minneapolis, Minnesota) and the TriActiv system (Kensey Nash, Exton, Pennsylvania). Conceptual advantages to such systems include the ability to stop both large and small particles as well as soluble mediators and relatively low crossing profiles (typically 0.026–0.033 inches), which minimize distal embolization during the first crossing (prior to distal balloon inflation). Disadvantages include poor vessel opacification by contrast during the procedure, no protection of sidebranches and distal ischemia while occlusion is maintained.
Although such systems have shown clear benefits in SVG PCI, the benefits in STEMI have been much less convincing.^17–19 Although early pilot studies and small randomized trials did suggest frequent retrieval of embolic debris, greater rates of normal or improved TIMI flow and MBG, improved left ventricular function and enhanced event-free survival compared to historical controls, the large randomized EMERALD (Enhanced Myocardial Efficacy and Recovery by Aspiration of Liberated Debris) trial showed no benefit.^11,20–23 The EMERALD trial randomized 501 patients who presented within 6 hours for primary (81%) or rescue PCI (19%) to receive PCI with the GuardWire Plus (Medtronic) distal balloon occlusion system compared to angioplasty without distal protection. Although visible debris were retrieved from 73% of patients randomized to the device, this did not result in improved microvascular flow, reperfusion success, reduced infarct size or enhanced eventfree survival. Furthermore and paradoxically, infarct size with distal protection was increased in several highrisk groups in which embolization would be most expected, such as those with angiographically-confirmed thrombus (13.0% vs. 9.0%; p = 0.04) and totally occluded vessels (17.5% vs. 11.0%; p = 0.04). The recently-published ASPARAGUS trial also assessed the GuideWire Plus system.24 In this trial of 341 AMI patients, those treated with the device had less slow/no-reflow (5.3% vs. 11.4%; p = 0.05), but showed no improvements in MBG, creatine kinase levels or clinical outcomes. Possible explanations include insufficient efficiency in aspirating liberated debris, embolization to sidebranches, embolization during device crossing and added injury caused by the several minutes of balloon occlusion. Another limitation of the GuideWire system is that material aspiration is performed without thrombus fragmentation such as in the Angiojet or X-sizer systems, which may have resulted in larger thrombotic fragments not being adequately removed from the vessel. On the basis of these results, routine use of distal occlusion during STEMI cannot be recommended.

Thrombectomy
The use of thrombectomy devices avoids the need to cross the lesion and can be performed prior to the intervention to reduce thrombus burden. Several thrombectomy devices have been assessed for use during STEMI, with some significant differences in both construction and operational principles. The best studied and most widely-used devices include the Export Catheter (Medtronic), Diver CE (Invatec), Rescue catheter (Boston Scientific), Pronto catheter (Vascular Solutions, Inc., Minneapolis, Minnesota), X-Sizer , and rheolytic thrombectomy with the AngioJet Rheolytic device (Possis Medical, Inc., Minneapolis, Minnesota). As shown in the following summaries of the randomized data, despite conceptual appeal and benefits in various reperfusion markers, no benefit of routine use with these devices has yet been demonstrated in clinical endpoints.
Aspiration thrombectomy. The REMEDIA (Randomized evaluation of the effect of MEchanical reduction of DIstal embolization by thrombus aspiration in primary and rescue Angioplasty) trial tested the Diver CE device in 100 unselected patients with STEMI and showed that those treated with thrombectomy had better MBG ≥ 2 frequency (68% vs. 58%; p = 0.02) and better ST-segment resolution. There were no differences in clinical outcomes.²⁵ In a study using the same catheter by De Luca et al, 76 patients with anterior STEMI showed more frequent MBG-3, better ST-segment resolution and LV remodeling at 6 months, but no differences in cumulative MACE rates.²⁶
The Export catheter, which is one component of the Guard- Wire distal occlusion device, was assessed in a nonrandomized trial by Margheri et al in which 129 consecutive patients with STEMI were treated and compared to a historical group treated previously without thrombectomy. The trial showed improved reperfusion parameters with thrombectomy (TIMI frame counts, TIMI flow, thrombus grade and myocardial perfusion), although clinical outcome data and rates of GP IIb/IIIa use in the historical group were not reported.²⁷ The same catheter was assessed in a small series of 64 patients by Cohen et al and also showed improvement in flow with thrombectomy prior to PCI, but no comparison was made to a group not using the device.²⁸ Another feasibility study by Varbella et al showed that patients undergoing PCI (selected according to angiographic features) achieved high rates of restoration of TIMI 3 flow with aspiration thrombectomy alone (86.2%).²⁹ A recent retrospective nonrandomized study assessed whether the Export catheter may be beneficial in selected high-risk patients — those with visible thrombus or severely reduced flow (TIMI 0/1).30 Thrombectomy was associated with less residual thrombus (7.5% vs. 19.2%; p = 0.03), more frequent TIMI 3 flow (91.3% vs. 67.9%; p = 0.005) and improved 1-year mortality (7.7% vs. 26.2%; p = 0.005). These results need confirmation in a large, prospective, randomized trial.
The Pronto extraction catheter was evaluated in the DEARMI (Dethrombosis to Enhance Acute Reperfusion in Myocardial Infarction) study, randomizing 148 patients to PCI with or without routine thrombectomy prior to further intervention.³¹ The results showed improved myocardial reperfusion with more ST-segment resolution (68% vs. 50%; p < 0.05), improved rates of optimal MBG (88% vs. 44%; p < 0.0001), less angiographic embolization, less no-reflow and less CKMB release. Inhospital clinical events were no different.
In a recent randomized study of routine thrombectomy in 215 patients in whom the Rescue catheter was used, thrombectomy was found to have no benefit on the primary endpoint of nuclear imaging-assessed myocardial salvage.³² In fact, final infarct size was increased in the thrombectomy group (15% vs. 8%; p = 0.004). This result was independent of the presence of visible thrombus. The device also failed to show a benefit on echocardiographically-determined left ventricular systolic or diastolic function. Patients who underwent thrombectomy did not experience any improvement of LVEF.³³ Table 3 summarizes these current major randomized trials.

Rheolytic thrombectomy. The Angiojet Rheolytic Thrombectomy System creates a low-pressure zone at its distal tip by high-velocity saline jets that are directed back into the catheter, resulting in breakup and removal of thrombus by suction through the outflow lumen. Its use was evaluated in the large multicenter AiMI (AngioJet Rheolytic Thrombectomy in Patients Undergoing Primary Angioplasty for Acute MI) trial, randomizing 480 patients with STEMI for routine adjunctive thrombectomy including those without visible thrombus.³⁴ Final infarct size was significantly higher with thrombectomy compared to PCI alone (12.5% vs. 9.8%; p = 0.03), and final TIMI flow grades, blush scores or ST-segment resolution were not improved. Regarding the presence or absence of thrombus, in those with large or moderate baseline thrombus (but excluding total occlusions), no significant differences were noted in the two groups — although the PCI-alone group had higher baseline TIMI grade flow. The 30-day major adverse cardiac event (MACE) rate was higher in the thrombectomy group (6.7% vs. 1.7%; p = 0.01), driven by surprisingly very low mortality rates in the control group (4.6% vs. 0.8%; p = 0.02), lower than those in other contemporary acute MI reperfusion trials.^35–37 Noteworthy is the fact that the data safety and monitoring committee found no indication that any of the incidents of mortality in the AngioJet group were related specifically to the device.
Thrombectomy summary. Many unanswered questions remain as to the role of thrombectomy in STEMI. The results of the above randomized trials are mixed, with multiple small trials suggesting improved myocardial reperfusion, but the largest trial (AiMI) showing larger infarct sizes and worse clinical outcomes in patients treated with thrombectomy. Based on current evidence, routine thrombectomy as adjunctive therapy cannot be recommended in patients with STEMI in the native circulation. However, thrombectomy devices are effective in removing thrombus, thus selective use may still provide benefit in such circumstances.

X-Sizer System
The X-Sizer catheter system contains a helicalshaped cutter distally that rotates at 2100 rpm, with the catheter lumen connected to a vacuum bottle to collect aspirated debris. Two small randomized trials have assessed reperfusion outcomes.
The X AMINE (X-Sizer in AMI for Negligible Embolization and Optimal ST Resolution) trial showed improved STsegment resolution and reduced risk of distal embolization, but no difference in MBG.³⁸ There were no differences in 6-month clinical endpoints. In another trial by Napodano et al, 92 patients with STEMI and evidence of intraluminal thrombus were randomized.³⁹ More MBG 3 (71.7% vs. 36.9%; p = 0.006) and better ST-segment resolution were noted with thrombectomy, although similar TIMI 3 flow post PCI was seen. No differences in clinical endpoints at 30 days were seen, including no difference in LVEF. Table 4 summarizes the major current randomized trials evaluating the X-Sizer device and rheolytic thrombectomy.

Excimer Laser
The Excimer laser (Spectranetics CVX-300, Spectranetics, Inc., Colorado Springs, Colorado) works on the principle that ultraviolet laser light of mid-ultraviolet wavelength is well absorbed by thrombus,⁴⁰ induces thrombolysis, inhibits platelet aggregation and may ablate the atherosclerotic plaque.⁴¹ The CARMEL (Excimer Laser Angioplasty in Acute Myocardial Infarction) multicenter trial, a nonrandomized, observational study, documented the feasibility and safety of its use in 151 patients undergoing PCI for AMI with high-risk target lesions (thrombus and complex underlying plaque morphology).⁴² Use of the excimer laser resulted in increases in TIMI flow (1.2–2.8 ± 0.5; p < 0.001), increased minimal lumen diameter from 0.5 ± 0.5 to 1.6 ± 0.5 mm (p < 0.001) and decreased target stenosis from 83 ± 17% to 52 ± 15% (p < 0.001) prior to further dilatation.
The only randomized data evaluating the use of the excimer laser emanate from the small LaserAMI study in which 27 patients with STEMI were randomized.⁴³ The device crossed the target lesion and decreased the diameter stenosis by > 20% in all patients. The trial suggests that the procedure is feasible and safe, with results largely on par with conventional treatment. Further randomized, controlled trials are required to assess whether any superiority exists with the laser debulking device before recommendations for its use can be made.

Conclusions and Recommendations

A multitude of adjunctive mechanical devices are available aiming to improve the outcomes of patients undergoing primary PCI for STEMI (Table 5). Data presently available show a significant discrepancy between softer clinical endpoints such as reperfusion and hard clinical outcomes. Despite suggestion of greater restoration of TIMI 3 flow, better myocardial perfusion and less distal embolization, there are currently no data showing a mortality benefit, and in fact, some studies suggest adverse patient outcomes.
Numerous explanations may account for the lack of demonstrable benefit. The effect on microvascular reperfusion, if any, may be too small to be clinically relevant. Distal embolization during the PCI itself may be negligible compared to spontaneous distal embolization during evolving MI. There may be potential mobilization of plaque material by the adjunctive devices themselves. Vessel occlusion while aspirating material may be incomplete. Finally, incomplete sidebranch protection may be present, depending on the device used.
Two recent metaanalyses of adjunctive device treatment have also been published. Kunadian et al analyzed 14 studies including thrombectomy and distal protection devices.⁴⁴ The pooled results suggest that the use of antiembolic devices does not decrease early mortality, recurrent AMI or overall MACE. In the second analysis by De Luca et al, a total of 21 trials with 3721 patients were included.⁴⁵ The results showed that adjunctive devices were associated with higher postprocedural MBG 3 (48.8% vs. 36.5%; p < 0.001), higher rates of postprocedural TIMI 3 flow (89.4% vs. 87.1%; p = 0.03) and less distal embolization (6.0% vs. 9.3%; p = 0.008), without any benefit on 30-day mortality (2.5% vs. 2.6%; p = 0.88).
Major limitations in currently available trials stem from inclusion of all patients regardless of the presence or absence of angiographicallyvisible thrombus and the inclusion of lower-risk lesions and patient populations. As such, benefits in high-risk subgroups may be diluted out. Current trials have not been adequately powered to detect significant differences in higher-risk subgroups, and most have a short follow-up period (only 30 days).
Potential specific clinical scenarios in which there may be significant benefit include large vessels with a large thrombus burden (e.g., right coronary artery), initial TIMI 0 or 1 flow, and vessels that supply collaterals to other jeopardized myocardium.
Whether a benefit exists for very selective use in specific patient populations remains to be defined in adequately powered randomized clinical trials. Pending results from these studies, the routine use of adjunctive mechanical devices during primary PCI cannot be universally recommended, although these devices may be helpful for selective groups of patients.

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