STATE-OF-THE-ART PAPERS
Distal Myocardial Protection During Percutaneous Coronary Intervention
When and Where?
Diana A. Gorog, MD, PhD, MRCP*,
Rodney A. Foale, MD, FRCP and
Iqbal Malik, PhD, MRCP
Waller Cardiac Department, St. Mary’s Hospital, London, United Kingdom
Manuscript received February 5, 2005;
revised manuscript received April 12, 2005,
accepted April 15, 2005.
* Reprint requests and correspondence: Dr. Diana A. Gorog, Waller Cardiac Department, St. Mary’s Hospital, Praed Street, London W2 1NY, United Kingdom (Email: dgorog{at}aol.com).
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Abstract
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The discrepancy between angiographic success and microvascular perfusion has been recognized for some time. In the face of an open artery, the degree of microvascular perfusion determines post-infarct prognosis. Despite successful epicardial recanalization, tissue perfusion may be absent in up to 25% patients with acute myocardial infarction. Historically associated with saphenous vein graft intervention, embolization is increasingly recognized in native coronary arteries, particularly in patients undergoing primary percutaneous coronary intervention (PCI). With more than two million PCI procedures performed worldwide each year, there is enormous interest in protecting the left ventricular myocardium from embolization during PCI. This article reviews the evidence for distal myocardial protection and discusses the relative merits of the different available techniques.
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Abbreviations and Acronyms
| | AMI = acute myocardial infarction | | ACS = acute coronary syndromes | | CAPTIVE = CardioShield Application Protects During Transluminal Intervention of Vein Grafts by Reducing Emboli | | CAS = carotid artery stenting | | DPD = distal protection device | | GP = glycoprotein | | MACE = major adverse cardiac event | | MBG = myocardial blush grade | | MMP9 = matrix metalloproteinase 9 | | PCI = percutaneous coronary intervention | | PRIDE = PRotection During Saphenous Vein Graft Intervention to Prevent Distal Embolization | | SAFE = Saphenous Vein Graft Angioplasty Free of Emboli trial | | SAFER = Saphenous Vein Graft Angioplasty Free of Emboli Randomized trial | | SVG = saphenous vein graft |
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Distal protection devices (DPDs) were first introduced for cerebral protection during carotid artery stenting (CAS) (1). In this setting, registries have demonstrated that use of DPDs may halve the combined end point of stroke or death (2,3).
Although angiographic evidence represents only the tip of the embolization iceberg during percutaneous coronary intervention (PCI), even this occurs in up to 15% patients undergoing primary PCI (4). Angiographic indicators of embolization such as corrected Thrombolysis In Myocardial Infarction (TIMI) frame count and myocardial blush grade (MBG), as well as rapidity of ST-segment resolution, are highly predictive of clinical and functional outcome (5,6).
That these phenomena are a manifestation of embolization, rather than de novo thrombus formation, is borne out by histological data showing, during elective PCI, emboli comprised of mucopolysaccharide components and necrotic cores (6–11). Vulnerable plaque morphology, namely disruption or thinning of the fibrous cap, overlying thrombus, and increased lipid content are associated with complications from endovascular procedures (12,13). High plaque macrophage content and plasma matrix metalloproteinase 9 (MMP9) levels may predict embolization during PCI, possibly due to thinning of the fibrous cap by MMP9 secreted by plaque macrophages (14). In addition to mechanical obstruction, the local response to embolization may contribute to myonecrosis (15–19).
It is thus not surprising that emboli are resistant to antiplatelet medication. Although use of glycoprotein (GP) IIb/IIIa inhibitors has contributed to improved success rates with PCI, intervention in saphenous vein grafts (SVG) and in native vessels with high intraluminal thrombus burden continues to be hampered by thromboembolic events.
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Types of devices
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Available devices fall into four categories (Table 1):
- Distal filtration devices
- Distal occlusion devices
- Proximal occlusion devices
- Thrombus extraction devices
The devices with widest evidence base in each category are the EZ-FilterWire (Boston Scientific, Natick, Massachusetts), the GuardWire (Medtronic AVE, Santa Rosa, California), Proxis (Velocimed, Maple Grove, Minnesota), and X-Sizer (EndiCOR Medical, San Clemente, California) systems, respectively. This review will therefore concentrate predominantly on these systems.
The FilterWire system (Fig. 1) incorporates a nonocclusive filter (pore size 110 µm) in the shape of a windsock, mounted on a nitinol loop, and fixed on its own guidewire, which is deployed through a 3.2-F delivery sheath. The nitinol loop self-expands to fit vessels 3.5 to 5.5 mm in diameter, and intervention performed over the wire. Finally, the device is captured using a 4-F retrieval sheath. Other filtration devices work similarly.
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Figure 1 The FilterWire system. (Panel 1) The polyurethane porous membrane filter attached to a nitinol loop. (Panel 2) The filter is deployed distal to the lesion, and the nitinol loop self-expands to fit the vessel upon retraction of the delivery sheath. (Panel 3) Saphenous vein graft containing thrombus, seen as intraluminal filling defect (A), treated with percutaneous coronary intervention using FilterWire protection (B), achieving a good result after stenting (C).
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The GuardWire temporary occlusion-aspiration system (Fig. 2) consists of a guidewire incorporating a central inflation lumen, to which an elastomeric balloon is attached. This has a 2.8-F crossing profile, and injection of diluted contrast results in balloon inflation (2.5- to 5.0-mm or 3.0- to 6.0-mm diameter), arresting anterograde flow. Intervention is performed over the wire, and liberated debris trapped proximal to the balloon aspirated through a 5-F monorail Export Aspiration catheter. The balloon is then deflated and flow restored.
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Figure 2 The GuardWire system. Upper panel corresponds to lower panel: the GuardWire, used to cross the lesion, is inserted into the MicroSeal Adapter (A), connected to the EZ Flator, which is inflated to occlude the vessel (B). Debris is aspirated using the Export Aspiration catheter (C). SVG = saphenous vein graft.
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The Proxis system incorporates a sealing balloon that is deployed upstream of the stenosis to create a stagnant column of blood in which intervention is performed (Fig. 3). Protection is thus in place before any device crosses the lesion. The device is 7- or 8-F guide compatible, and protects vessels 2.5 to 5 mm in diameter. The stent is delivered through the Proxis system, and flow is reversed, aspirating debris, before the sealing balloon is deflated, restoring flow.
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Figure 3 The Proxis system is delivered through a guiding catheter, and the sealing balloon (A) is inflated proximal to the stenosis, arresting flow, and debris aspirated through the Proxis system (B).
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The X-Sizer system (Fig. 4) consists of a 1.5- or 2.0-mm stainless steel helical cutter in a protective housing connected to a 4.5- or 5.5-F dual-bore catheter shaft containing the guidewire and vacuum/extraction lumens. The catheter shaft is linked to a handheld control module and vacuum bottle in which debris is collected. Activating the control unit simultaneously activates the helical cutter, which extends 1 mm beyond the protective housing, rotating at  2,100 rpm and initiates the vacuum, resulting in tissue maceration, excision, and aspiration.
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Figure 4 The X-Sizer thrombectomy system comes ready to assemble in a tray (panel 1). Schematic of mechanism of action (panel 2). Panel 3 shows angiogram of right coronary artery proximally occluded by thrombus (A), X-sizer thrombectomy device in situ (B), and angiographic appearance after thrombectomy (C).
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Use in acute coronary syndromes (ACS)
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Table 2 shows the trials employing DPD in ACS (trial acronyms explained in Table 3). There have been concerns that DPD use during primary PCI might delay reperfusion. The first study using the FilterWire in primary PCI showed that successful DPD positioning was achieved in 89% of patients in  10 min (6). Compared to historical controls, FilterWire use improved final angiographic characteristics and left ventricular performance. Among the several limitations of this study, final TIMI flow grade <3 in 85% of patients in the control group may have lead to overestimation of the benefit of the DPD.
A small study using the GuardWire in patients with angiographic "high-burden thrombus" undergoing primary PCI showed improved flow and MBG, but this did not translate into a reduction in 30-day major adverse cardiac events (MACE) (20). The EMERALD study was the first large randomized trial to evaluate the GuardWire in patients with acute myocardial infarction (AMI). Although the device markedly reduced the incidence of angiographic slow/no-reflow, there was no significant overall effect on ST-segment resolution or infarct size. Preliminary results from the first 188 patients undergoing PCI using the GuardWire in the RUBY registry have suggested that direct device delivery was possible in 87% cases, with favorable angiographic and electrocardiogram characteristics and low clinical event rates. In the PROMISE study, use of the FilterWire-EX in patients undergoing primary PCI did not improve reperfusion and did not reduce infarct size compared with usual care.
There are no data on the safety or efficacy of proximal occlusion systems in AMI.
X-Sizer thrombectomy was first assessed in a small randomized study of patients with suspected intracoronary thrombus (21). Although the study failed to show a benefit on final angiographic characteristics, creatine kinase-MB, or 30-day MACE, X-sizer pretreatment was associated with more rapid normalization of epicardial flow and, in patients with ST-segment elevation myocardial infarction, more rapid ST-segment resolution. The study was underpowered to detect a benefit in clinical parameters. In AMI patients with angiographic evidence of thrombus (22), thrombectomy significantly improved pre-PCI flow, post-procedural MBG, and ST-segment resolution, but this was not reflected in hard clinical end points, and the device failed to traverse the lesion in 9% of patients.
In the VeGAS-2 study, the AngioJet thrombectomy device (Possis, Minneapolis, Minnesota) was compared with intracoronary urokinase infusion (23). Although thrombectomy was technically successful and reduced in-hospital MACE, the results were clouded by subsequent studies demonstrating worse outcomes with urokinase than with placebo in patients with thrombotic lesions undergoing PCI (24). The disappointing results of the AIMI study, presented at Transcatheter Cardiovascular Therapeutics (TCT) 2004, showed that AngioJet use paradoxically increased infarct size.
There seem to be no data to suggest that routine use of any DPD system is beneficial in patients with ACS undergoing PCI. However, it may be hard to show the benefit of protection against embolization that undoubtedly happens during angioplasty for AMI. In a prothrombotic milieu, thrombi may form on the downstream (low pressure) side of the protection device and embolize. Furthermore, fragmentation of large thrombi by GP IIb/IIIa inhibitors or thrombolysis may result in small particles that pass through the filter. Lastly, in contrast to the cholesterol emboli released in SVG intervention, the consequence of embolization during AMI is not a fait accompli, because thrombotic platelet emboli may subsequently be lysed in the distal myocardial bed, without sequelae. Thus, the significance of embolization during AMI may depend on the nature of the embolic material and integrity of endogenous thrombolytic response.
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Use in SVG
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Pathophysiology.
Saphenous vein graft interventions carry a 20% risk of MACE, predominantly AMI, and significant risk of no-reflow (25). The protection offered by GP IIb/IIIa inhibitors during native vessel PCI has not been mirrored in SVG intervention (26,27), reflecting the differing composition of plaque in these settings; SVG plaques tend to be cholesterol-rich, with relatively low calcium content and less intimal proliferation than plaques in native coronaries (28). Accordingly, debris embolized from SVG largely consists of fibrin and necrotic core (29).
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Clinical studies
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The SAFE registry was the first to report on use of DPD in SVG intervention (Table 4) (29). Patients had relatively low-grade thrombus burden and good pre-procedural flow (TIMI flow grade 3, 84%). GuardWire balloon inflation (mean 5.4 min) was well-tolerated. Final angiographic appearances were excellent, and post-procedural creatine kinase-MB release compared favorably with historical controls (30). These results spawned the larger SAFER trial, which confirmed the favorable effects on angiographic/myonecrotic markers and clinical end points (31). Thrombus burden was higher than in SAFE.
Use of the FilterWire was first reported in a registry which, like SAFE and SAFER, excluded patients with AMI or severe left ventricular failure (32). Pre-procedure TIMI flow grade 3 was present in 85% cases, with a higher thrombus burden (65%) than in the GuardWire trials. Analysis of phase I results identified several correctable factors that led to improved results in phase 2 (see technical concerns in the following text). The trial highlighted the difficulty in predicting embolic risk during SVG intervention and the need for DPD deployment from the outset of intervention.
A comparison of the GuardWire and FilterWire (FIRE) in patients with low thrombus burden and good pre-procedural flow revealed similar rates of successful device deployment, angiographic and myonecrotic end points, and 30-day MACE (33). Subgroup analysis suggested an advantage of the FilterWire over the GuardWire in smaller vessels and eccentric lesions.
In an early safety and feasibility study in 40 patients undergoing mainly SVG PCI (FASTER) (34), the Proxis system was successfully deployed in 95% of cases and appeared safe (MACE 5%). The first clinical trial with this device (PROXIMAL) is now under way (Table 5).
In the X-TRACT trial (35), use of the X-Sizer system (70% SVG) was not associated with reductions in MACE. Although the overall incidence of procedural AMI was unchanged, the incidence of large infarcts was significantly reduced in the X-Sizer arm.
The results of two noninferiority studies, PRIDE (TriActiv, Kensey Nash, Exton, Pennsylvania) and CAPTIVE (CardioShield, MedNova, Galway, Ireland), using new DPD in SVGs were presented at TCT 2004. The TriActiv system has three components: a distal protection balloon, a 3-F flushing catheter, and a peristaltic pump extraction system, which allow constant flushing and aspiration of debris. The PRIDE trial demonstrated noninferiority to established DPD with respect to 30-day MACE. The CAPTIVE trial, which assessed the CardioShield filter device, failed to demonstrate both superiority to no embolic protection, and noninferiority to the GuardWire.
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Technical concerns
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Failure to cross the lesion.
The relatively large crossing profile and lack of torquability may make it technically challenging to advance these devices beyond a tight stenosis or in a tortuous vessel. Some devices come loaded on their own delivery wire, the handling characteristics of which will clearly be better suited to crossing some vessels than others. Pre-dilatation can overcome this problem, at the risk of distal embolization before protection is in place. The importance of such early embolization should not be underestimated; significant embolization has been documented in ex vivo studies (36), and in patients undergoing CAS with transcranial Doppler monitoring (37,38).
Positioning.
In AMI with TIMI flow grade 0, it may be difficult to know where to position the DPD, in order to be far enough away from the lesion to allow unimpeded stenting, yet in a part of the artery large enough to accommodate the device, and proximal to major side branches.
Sizing the device.
Some devices, such as the FilterWire, expand to fit a range of vessel diameters. However, with other systems, the size of the distal vessel may be underestimated if flow is reduced, and device malapposition due to undersizing may allow distal embolization.
Side-branch protection.
In Y anastomotic grafts or distal graft lesions where the native vessel run-off gives off early major side-branches, it may be difficult to position the DPD such that side-branches are protected. To overcome this, two similar devices may be used in each branch ("kissing" filters), assuming that the caliber of both branches is commensurate with use of a DPD. Alternatively, a filter-type device may be deployed in one branch and an occlusion-aspiration or thrombectomy device used in the other. Importantly, these techniques will be feasible for balloon angioplasty but may make stenting challenging, in order to avoid jailing the wires of either DPD during stent deployment.
Persistent embolization.
Using balloon occlusion systems, embolization may occur due to gradual balloon deflation during the procedure. Minor deflation may be difficult to detect without frequent injections of contrast to ensure a tight seal, but this itself may cause embolization with an inadequate seal. Furthermore, debris may fail to be aspirated by the suction catheter, either because of resistance to aspiration or because the catheter cannot approach sufficiently close, leaving a "suction shadow" of embolic material behind (39). With filter-based devices, incomplete apposition is a significant concern and has been found to correlate with periprocedural AMI (32). This may be easily missed without orthogonal views to assess the filter both en face and in profile. The most common cause of malapposition is lifting of the nitinol frame away from one side of the vessel wall due to wire bias (32), and may be corrected by repositioning the filter.
The benefit of filter devices over balloon occlusion systems is the preservation of flow. This is a two-edged sword because it also allows the passage of smaller microemboli. The SAFE registry revealed that 80% of particles collected were smaller than 100 µm diameter, although it is impossible to know how much suction/aspiration contributed to particle break up (29).
Embolization may also occur during device retrieval. Filters may become full, and may spill their contents when collapsed during retrieval. Newer devices will incorporate a built-in shutter mechanism to close the mouth of the filter before retrieval.
Retrieval.
The relatively large-profile aspiration catheter or the retrieval catheter of the filter devices may become caught in stent struts.
Use in small vessels.
Use of either DPD or thrombectomy is generally recommended for vessels >3.0 to 3.5 mm in diameter. Recently, the first small study employing the FilterWire in small native vessels (2.6 ± 0.5 mm diameter) with moderate-complex lesions has revealed high rates of procedural success, no device-related vessel dissection, and distal embolization in only 4% patients (40). Although vasospasm (50%) and reduction in coronary flow (45%) were frequent, these universally resolved after device retrieval.
Use in large vessels.
Degenerative SVGs can become markedly ectatic, and the risk of no reflow during PCI is particularly high. Although DPD do not generally expand to >6 mm in diameter, a larger range of devices is expected to become available soon.
Uncertain clinical scenarios.
Almost all available clinical data are in men, with very limited data in diabetics. There are no data on the tolerability of the balloon occlusion systems in patients with poor left ventricular function or AMI and cardiogenic shock. Studies are needed to determine whether combined treatment with both thrombectomy and DPD will confer additional advantages. Whether use of GP IIb/IIIa inhibitors or lytic therapy combined with DPD will offer additional benefit, or whether it reduces the size of embolizing particles such that these pass through filters unhindered, remains to be determined. In the X-Sizer AMI registry, where 43% of patients received abciximab (22), no difference in TIMI flow grade 3 or MBG was found according to abciximab use.
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Filter, balloon-occlusion, and aspiration, or thrombectomy?
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In deciding on the best protection strategy, it is important to consider specific lesion and vessel characteristics, as well as thrombus burden. Electron microscopy of material aspirated with the GuardWire system showed particles ranging from 3.6 to 5,262 µm in diameter, 50% of which were <100 µm (29,41). Filter devices have 80- to 150-µm pores, and may therefore allow significantly more debris to pass through. Although smaller pore sizes might appear advantageous, these also cause more frequent filter thrombosis (42) with a size of 100 µm representing a reasonable compromise. Why then do filters with 100-µm pores appear to offer equal benefit to balloon occlusion systems when half the particles are under that size? Although it is possible that the cardiac end points examined thus far have been too crude to assess the effects of "trashing" by smaller microemboli, it is equally possible that, unlike the brain, a shower of smaller emboli that is not reflected in a troponin rise or decline in left ventricular function is of no clinical significance.
The important benefit of filter devices over occlusion balloon systems is flow preservation. The occlusion-aspiration systems require a period of balloon inflation of several minutes. There may be situations in which this is unacceptable, for example when a large volume of uncollateralized myocardium is subtended by the target vessel, or in cases of severe left ventricular dysfunction, where even a brief period of ischemia may be poorly tolerated. In these instances, filter-based protection would intuitively seem preferable. Generally, the left anterior descending coronary artery and the right coronary artery lend themselves well to DPDs, whereas the anatomy of the circumflex is less accommodating. The X-Sizer lends itself best to SVG and right coronary artery lesions, with a relatively straight "run." Although the benefit of thrombectomy on clinical end points is unproven, there may be a niche for such devices in clinical situations where DPDs cannot be used, such as in very distal SVGs and bifurcation points, or where thrombus burden is overwhelming for filter protection.
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Newer devices
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Table 1 lists some of the newer devices, many of which are not yet commercially available. Table 5 shows some of the ongoing clinical trials. Filters include the Spider and TRAP cardiovascular filtration systems, the AngioGuard, and the Interceptor (Medtronic AVE). The coaxial actuating wire design of the Rubicon wire (Rubicon Medical Corp., Salt Lake City, Utah) eliminates the need for a delivery catheter, allowing a stent to be preloaded onto the wire, and both devices delivered in one step.
The Parodi Anti-Embolic (ArteriA, San Francisco, California) and the MO.MA systems consist of a guiding catheter through which an elastomeric balloon is inflated proximal to the stenosis in the common carotid, and a second balloon inflated in the external carotid, causing retrograde flow in the internal carotid artery during intervention. Experience with both systems remains confined to CAS due to the requirement for 10- to 11-F sheaths.
Hydrodynamic thrombectomy systems employ saline jets emanating from the catheter to create a vacuum via the Venturi effect and fragment the thrombus, which is sucked into the catheter. These include the AngioJet, the Hydro-lyser (Cordis, Miami, Florida), and the Kerberos Rinspirato (Kerberos, Cupertino, California). The Pronto (Vascular Solutions, Minneapolis, Minnesota) and the Rescue (Boston Scientific) catheters use vacuum aspiration.
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Conclusions
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The efficacy of DPDs should be balanced against high initial costs, the risk of device-related vessel dissection, increased procedural time, and the learning curve associated with their use.
In SVG intervention, both balloon occlusion/aspiration and filter-based DPDs have reduced the incidence of AMI and should remain the treatment of choice. In contrast, the benefit of the X-Sizer device remains unproven and should only be considered where DPD cannot be used.
The jury is out regarding the usefulness of DPDs in ACS. Although histological studies have shown that filters contain embolic debris in virtually all cases (6) and angiographic results are improved, this benefit has not been reflected in reduced infarct volume or hard clinical end points.
Finally, with increasing intervention in thrombus-rich milieux, as occurs during primary PCI, further studies are needed to establish the usefulness of DPDs in combination with GPIIb/IIIa inhibitors, with direct thrombin inhibitors, and in patients at highest risk, such as those with multivessel disease or significant left ventricular impairment, who are likely to benefit most.
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Abstract
Types of devices