Cardiology

Embolic Protection Devices

General description of procedure, equipment, technique

Introduction

  • Sustained freedom from angina and ischemic events after coronary artery bypass graft (CABG) surgery using saphenous vein grafts (SVGs) is limited by the development of atherosclerotic disease within the grafts, as only about 80% of SVGs remain patent 5 years status postsurgery, decreasing to 60% at 10 years.

  • Percutaneous coronary intervention (PCI) with stent placement is the most widely used revascularization strategy for SVG lesions. According to the American College of Cardiology National Cardiovascular Data Registry, there were over 90,000 patients (5.7% of all PCIs) who underwent SVG PCI between 2004 and 2009.

  • However, SVG PCI is associated with a high risk of periprocedural myocardial infarction (MI), which complicates 15% to 28% of all SVG PCI, and is associated with higher late morbidity and mortality.

  • The higher risk of periprocedural MI during SVG PCI is thought to be related to unique features of atherosclerotic disease in SVGs. The plaques tend to be more diffuse, softer, more friable, to contain more inflammatory cells, and to have absent or small fibrous caps. These features predispose SVGs to have more extensive thrombotic burden and distal embolization during percutaneous interventions, resulting in microvascular dysfunction, the no-reflow phenomenon, and periprocedural MI.

  • Embolic protection devices (EPDs) trap blood and luminal debris within the SVG during stenting, thereby preventing distal embolization.

  • EPDs offer the most reliable evidence-based strategy for reducing periprocedural MI and major adverse cardiovascular events (MACE) during SVG interventions.

  • In contrast to their clearly established efficacy in SVG interventions, studies of EPDs in primary PCI in native coronary arteries have had disappointing results and suggest that current EPDs do not improve outcomes and should not be used routinely during native coronary PCI.

Indications and patient selection

  • Historically, operators have used clinical and angiographic information to determine the need for embolic protection.

  • This clinical intuition was systematized in a SVG degeneration score, developed as a metric of the extent of lumen irregularity and ectasia. The cumulative length (in millimeters) of SVG luminal irregularities or ectasia is divided by the length of the entire SVG and presented as a percent. Scores range from 0 to 3, with 0 corresponding to minimal disease and 3 corresponding to extensive disease. Along with plaque volume, the degeneration score has been shown to be the strongest predictor of 30-day MACE following an SVG PCI.

  • The clinical benefit of EPD use is maintained across all categories of degeneration scores, which suggests that angiographic assessment of SVG lesions may not be a reliable predictor of no-reflow, and should not be used to guide the decision as to whether to use EPDs during a procedure.

  • The American College of Cardiology gives a Class I recommendation for use of EPDs when technically feasible, irrespective of the angiographic appearance of the lesions.

Types of Lesions

  • The majority of SVG lesions are located in the midbody of the graft (38%), followed by proximal (30%) and distal (23%) graft locations.

  • Ostial and anastomotic SVG lesions account for <7% of SVG lesions.

  • Ostial lesions often represent the biggest challenge to embolic protection due to the suboptimal guide engagement and difficulty in crossing the lesion.

Contraindications

  • There are no absolute contraindications to the use of EPDs, though the location of a lesion dictates which devices can safely be used in a given lesion, as discussed below under types of devices.

  • Certain anatomic features of a graft can make all of the devices unfavorable or even prohibitively difficult to use, such as aorto-ostial disease, very large SVG diameter, severe tortuosity, distal anastomotic disease, and the absence of an adequate nondiseased landing zone.

  • EPD use may also be limited by higher procedural cost, longer procedural time, greater radiation exposure, and lack of operator comfort and familiarity with use of the various devices.

  • Although not contraindicated, the efficacy of EPDs has not been demonstrated for SVG in-stent restenotic lesions. It is thought that this is because such lesions result from neointimal proliferation and thus may be less likely to cause distal embolization.

Details of how the procedure is performed

Types of Devices

  • There are three basic classes of EPDs, categorized according to their mechanism of operation: distal occlusion systems, distal filter systems, and proximal occlusion systems.

    • Distal occlusion systems :

      • Concept: In these systems, a balloon is advanced past the target lesion and inflated, occluding the distal vessel. The concept is that this prevents plaque disrupted during the procedure from embolizing past the device. After the intervention, the stagnant blood and debris is aspirated prior to deflation of the balloon and restoration of antegrade flow.

      • Devices: The PercuSurge Guardwire system was the first device in its class. It was studied in the Saphenous Vein Graft Angioplasty Free of Emboli Randomized (SAFER) trial, which showed a significant reduction in the incidence of no-reflow and 30-day MACE with use of this EPD. More recently the FDA approved the TriActiv system after it was found to be noninferior to Guardwire in the Prolonging Remission in Depressed Elderly (PRIDE) trial.

      • Advantages: The advantages are the low crossing profile of these devices; and theoretically, the occlusion mechanism blocks transmission of both particles and soluble mediators rather than just particles (unlike filter membrane systems).

      • Disadvantages: The disadvantages include the risk of end-organ ischemia caused by balloon occlusion, and limited contrast opacification of the target lesion during occlusion.

    • Distal filter systems :

      • Concept: These systems rely on deployment of a filter membrane distal to the target lesion prior to intervention. The filter stays in place during the intervention and traps particulate debris liberated during the procedure. Antegrade flow is maintained throughout the procedure. At the end of the intervention, a sheath is advanced to retrieve the wire and filter.

      • Devices: The Filterwire EZ device (the second generation Filterwire) was studied successfully in the BLAZE trials. Another distal filter system, the Spider Rx, demonstrated noninferiority to Guardwire and Filterwire in the Saphenous Vein Graft Protection In a Distal Embolic Protection Randomized (SPIDER) study. Finally, another filter system, the Interceptor PLUS, was shown to be noninferior to the other systems in the AMEthyst trial.

      • Advantages: The advantages of these systems include maintenance of distal perfusion, normal contrast opacification of the target lesion during operation, and ease of use.

      • Disadvantages: The disadvantages include the large diameter sheath generally required, the potential for distal emboli or vasoactive substances to pass through filter pores, and occasional difficulties retrieving the filter.

    • Proximal occlusion systems

      • Concept: Proximal occlusion devices occlude the vessel proximal to the target lesion, suspending antegrade flow during the intervention. Subsequently, the debris-laden blood is then aspirated prior to restoring flow down the vessel.

      • Devices: The only FDA-approved proximal occlusion device is the Proxis system, which demonstrated noninferiority to the other EPDs in the Proximal Protection During Saphenous Vein Graft Intervention (PROXIMAL) trial. However, it appears that this device is no longer available in the United States.

      • Advantages: The advantages include the establishment of protection prior to any device being passed across the target lesion, potential for complete recovery of particles and substances, compatibility with any conventional guidewire, and the superior support the device provides after anchoring, which can facilitate stent delivery during subsequent PCI.

      • Disadvantages: The disadvantages of this system include the necessity of vessel occlusion during the procedure, and a smaller internal working diameter of the short sheath.

  • It is important to note that none of the existing devices can be used for all SVG lesions, and an operator must choose the appropriate device based on lesion characteristics. For instance, ostial lesions require a distal EPD, lesions in the body of the graft can be approached with either a proximal or distal device, and distal lesions can only be undertaken with a proximal device.

  • The salient features, applications, and limitations of the most commonly used SVG EPDs available in the U.S. are summarized for ease of reference in Table 1. However, it must be underscored that the familiarity of the primary operator and catheterization laboratory staff with one or more of these EPDs is crucial for technical success and procedural safety.

Table I.

Embolic Protection Devices

Outcomes (applies only to therapeutic procedures)

  • The use of EPDs has reduced the 30-day MACE rate in multiple clinical trials by between 40% and 50%.

  • However, despite their use, there remains an approximately 10%, 30-day MACE rate. This may reflect the limitations of current EPDs, and/or suggest an alternate mechanism of SVG disease.

  • At this point, SVG interventions continue to be higher risk procedures than routine native coronary interventions and call for consistent use of mechanical EPDs while additional therapies aimed at decreasing the rate of periprocedural MI are being developed.

Clinical implementation

  • Despite the success of EPDs in clinical trials, clinical adoption is lagging at many centers.

  • Studies have reported a dismal rate of use of EPDs ranging from 19% to 22% of procedures, even in centers where up to half of the lesions were deemed suitable for embolic protection and the devices were available.

  • It appears that the most common reason an EPD is not used in a given case where it is technically feasible is operator preference.

Alternative and/or additional procedures to consider

Alternative therapies

  • Aggressive secondary prevention measures, including use of antiplatelet therapies and statins, have been shown to be effective in the prevention of the development of occlusive SVG disease; control of comorbidities (blood pressure, diabetes, smoking cessation) is recommended in all patients with coronary artery disease.

  • Once SVG stenosis is present, however, only EPDs have consistently been shown to be effective in attenuating the risk of periprocedural MI, though a host of pharmacologic and alternative mechanical strategies have been proposed and tested over the last two decades to address this problem.

  • Pharmacologic strategies to prevent or attenuate no-reflow have included calcium-channel blockers, nitrates, adenosine, thrombolytics, and glycoprotein IIb/IIIa agents. None of these measures has consistently been shown to be effective in decreasing 30-day MACE.

  • The proposed mechanical alternatives to EPD's have included direct stenting, and use of minimally undersized stents, but these have not been shown to have comparable efficacy to the use of EPDs.

Complications and their management

  • EPDs are generally safe, however they can be associated with procedural complications. The potential complications vary by device:

    • Any balloon-occlusive device (proximal or distal) may cause ischemia, and can result in significant patient discomfort, and associated hemodynamic and electrical instability. Note, however, that with operator experience the ischemic time can be reduced to <90 seconds in most cases.

    • EPDs using a distal filter system have the potential risk of becoming trapped within the SVG stented segment during device retrieval, rarely requiring surgery to remove.

    • With the exception of the proximal occlusion system, delivery of any of the EPDs can be challenging across severely stenotic lesions, and can cause distal embolization prior to the embolic protection device being in place, which may itself cause a periprocedural MI.

    • Any of the EPDs can potentially cause vessel trauma or damage at the landing zone.

Use of embolic protection devices in native coronary arteries

Although atherosclerotic debris is almost certainly released during native coronary interventions, the link between such embolization and clinical events (and thus the rationale for embolic protection) has been more difficult to establish. In fact, a number of randomized clinical trials of the various distal EPDs have been performed in native coronary PCI and have consistently demonstrated a lack of efficacy in improving microvascular perfusion or clinical outcomes.

Several explanations have been advanced for the lack of efficacy in native coronaries. First, unlike in SVG interventions, in native coronaries there are side branches that are not protected by the devices and may be compromised by their use.

Second, the devices themselves may promote distal embolization while initially crossing the lesion, especially in situations where the lesion must be predilated prior to delivery of the EPD. Finally, the devices may not allow sufficient removal of debris in native coronaries as opposed to SVG lesions.

Proximal embolic protection devices have not been adequately investigated in native coronary interventions; however, preliminary experience is not suggestive of a routine role in primary PCI in native coronaries.

What's the evidence?

Smith, SC, Feldman, TE, Hirshfeld, JW. "ACC/AHA/SCAI 2005 guideline update for percutaneous coronary intervention: a report of the American College of Cardiology/American Heart Association task force on practice guidelines". Circulation. vol. 113. 2006. pp. E166-E286.

(Issued a Class I recommendation that distal embolic protection devices be considered in all PCI for SVG stenosis where technically feasible.)

Baim, DS, Wahr, D, George, B. "Randomized trial of a distal embolic protection device during percutaneous intervention of saphenous vein aortocoronary bypass grafts". Circulation. vol. 105. 2002. pp. 1285-90.

(This is the pivotal trial that led to Food and Drug Administration approval of the first EPD. The trial reported a remarkable 42% reduction in 30-day MACE and a marked decrease in no-reflow with the use of the PercuSurge Guardwire system.)

Carrozza, JP, Mumma, M, Breall, JA, Fernandez, A, Heyman, E, Metzger, C. "Randomized evaluation of the TriActiv balloon-protection flush and extraction system for the treatment of saphenous vein graft disease". J Am Coll Cardiol. vol. 46. 2005. pp. 1677-83.

Stone, G, Rogers, C, Hermiller, J. "Randomized comparison of distal protection with a filter-based catheter and a balloon occlusion and aspiration system during percutaneous bypass grafts". Circulation. vol. 108. 2003. pp. 548-53.

Cox, DA. "Stenting in saphenous vein grafts with distal protection using a second generation filter-based catheter: the combined BLAZE I and II registries".

Dixon, SR. "Saphenous vein graft protection in a distal embolic protection randomized trial".

Kereiakes, DJ, Turco, MA, Breall, J. "A novel filter-based embolic protection device for percutaneous intervention of saphenous vein graft lesions: results of the AMEthyst randomized controlled trial". JACC Cardiovasc Interv. vol. 1. 2008. pp. 248-57.

Mauri, L, Cox, DA, Hermiller, J. "The PROXIMAL trial: proximal protection during saphenous vein graft intervention using the Proxis embolic protection system: a randomized, prospective, multicenter trial". J Am Coll Cardiol. vol. 50. 2007. pp. 1442-9.

(The six above trials demonstrated the safety and noninferiority of each of the EPDs that subsequently came on to the market.)

Mehta, SK, Frutkin, AD, Milford-Beland, S. "Utilization of distal embolic protection in saphenous vein graft interventions (an analysis of 19.546 patients in the American College of Cardiology-National Cardiovascular Data Registry)". Am J Cardiol. vol. 100. 2007. pp. 1114-8.

(Reports a mere 22% use of EPDs during SVG PCI in the American College of Cardiology-National Cardiovascular Data Registry, despite nearly half of the lesions being deemed suitable for embolic protection. )

Badhey, N, Lichtenwalter, C, de Lemos, JA. "Contemporary use of embolic protection devices in saphenous vein graft interventions: Insights from the stenting of saphenous vein graft trials". Catheter Cardiovasc Interv. vol. 76. 2010. pp. 263-9.

Banerjee, S, Brilakis, ES. "Embolic protection during saphenous vein graft intervention". J Invasive Cardiol. vol. 21. 2009. pp. 415-417.

Mauri, L, Rogers, C, Baim, DS. "Devices for distal protection during percutaneous coronary revascularization". Circulation. vol. 113. 2006. pp. 2651-2656.

(Examined the use of EPDs in the SOS trial, and characterized the reasons for underuse of the devices; concluded that operator discretion [rather than technical feasibility] is the main determinant of EPD use.)

Hindnavis, V, Cho, SH, Goldberg, S. "Saphenous vein graft intervention: a review". J Invasive Cardiol. vol. 24. 2012. pp. 64-71.

(This article offers a nice overview of the challenges of saphenous vein graft intervention in general, as well as a review of the embolic protection device strategies.)

Srinivasan, M, Rihal, C, Holmes, DR, Prasad, A. "Adjunctive thrombectomy and distal protection in primary percutaneous coronary intervention: impact on microvascular perfusion and outcomes". Circulation. vol. 119. 2009. pp. 1311-9.

(This article contains a description of the various randomized controlled trials demonstrating the lackluster outcomes of the use of embolic protection devices in native coronary arteries.)
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