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Asymptomatic carotid artery stenting: Filter or no filter?

Distal protection filters (DPFs) have been an accepted standard of care for the carotid artery stenting (CAS) procedures. Despite the continued discussions about the beneficial effects of the DPFs, the Centers for Medicare and Medicaid Services issued a statement requiring successful filter deployment to receive reimbursement for CAS. [1] In this issue of CCI, Van der Heyden et al. reports lack of atherosclerotic debris capture by DPFs in the high-risk asymptomatic severe carotid artery stenosis patients who underwent a staged procedure of CAS and coronary artery bypass surgery. There are several important points regarding this interesting study. First of all, considering the small sample size in these asymptomatic patients, empty filters were not necessarily a surprising observation. On the other hand, in a recent similar prospective study by Giannakopoulos et al., [2] visible debris were detected in 15% of filters in 51 consecutive patients (mostly asymptomatic) and furthermore using the Thin-Prep liquid-based cytology technique, embolic particles were detected in 56.6% of filters. In this study, echolucent plaques were associated with increased presence of embolic material. Second, significant variability exists for capture efficiency for different DPF devices. Recently, Siewiorek et al. [3] evaluated the capture efficiency between different DPFs in transient flow conditions. Wire mesh filter had the lowest capture efficacy when compared with the perforated membrane filter. Third, considering the presence of platelet aggregates in most of the captured debris, use of antiplatelet agents could stabilize the plaque and thus may also explain the empty filters as authors pointed out in their discussion. Finally, probably the biggest challenge of CAS is not knowing which lesions may lead to distal embolization due to the lack of optimal imaging modalities that will define carotid plaque characteristics in situ. Recently with introduction of novel imaging modalities such as optical coherence tomography, we may be able to better characterize the lesions that are at high-risk of embolization (thin cap fibroatheroma, ulcerated, etc), and these patients with vulnerable plaque might best be referred for carotid endarderectomy. The literature has clearly established in essentially all clinical trails the value of distal protection. Upside far outweighs any downside. There are few if any established investigators who are willing to proceed with CAS in the absence of embolic protection. Even more advanced is the use of proximal flow and flow reversal systems that now have the ability to capture particles that are 100 microns. What the authors are proposing is a randomized trial with and without distal protection, which is basically considered unethical. Thus, clinicians should be discouraged from performing CAS without the use of DPFs.