Microembolization is the Achilles‰Ûª heel of carotid artery stenting


Recent trials have shown carotid artery stenting to be equivalent to endarterectomy. However, stenting is linked to a higher microembolic burden. Sumaira Macdonald’s presentation examining the burden of microembolic signals for endarterectomy, carotid stenting with flow reversal and carotid stenting with filter protection showed interesting results.


“Carotid artery stenting is associated with a higher microembolic burden than carotid endarterectomy. The rate and procedural stage of highest risk depends on the embolic protection device used,” said Sumaira Macdonald, consultant vascular radiologist and honorary clinical senior lecturer, Newcastle, UK, at the annual iCON meeting in Phoenix, USA, in February.


She presented the results of a recent non-randomised comparison of carotid endarterectomy, filter-protected carotid artery stenting and carotid artery stenting with flow reversal utilising microembolic signals on transcranial Doppler as primary outcome event.


Results from the study (Gupta N, Corriere MA, Dodson TF et al. JVS Dec 1st 2010 [Epub]) showed that carotid endarterectomy had the fewest microembolic signals (largely in the post-protection phase). This was followed by flow reversal carotid artery stenting; in this case, signals detected were mostly in the pre-protection phase. Of the three procedures, filter-protected carotid artery stenting had the highest number of signals and these were mostly recorded during the protection phase.


“Clearly, there is room for improvement for carotid artery stenting,” Macdonald said. She told delegates that the patient is vulnerable pre-protection for proximal embolic protection devices and even during the protection phase when filters are used.


Does filter-protected carotid artery stenting have more microembolic signals than unprotected carotid artery stenting?


Filters are associated with significantly more microemboli compared with unprotected carotid artery stenting, said Macdonald based on DWMRI findings and procedural transcranial Doppler.


“Small randomised controlled trials (Macdonald S, Evans DH, Griffiths PD et al. Cerebrovascular Diseases 2010;29:282–289; and  Horowitz MB et al. J Vasc Surg. 2008 Apr;47(4):760–5. Epub 2008) demonstrate a significant increase in microembolic signals for filter-protected carotid artery stenting compared with unprotected carotid artery stenting and a substantial increase in hyperintensities on diffusion-weighted imaging for filter-protected compared with unprotected carotid artery stenting. In the trial evaluating both surrogate markers, periods of contrast injection were excluded from the final analysis as gaseous microemboli introduced during angiography would have constituted a major confounding variable. In a substudy of the International Carotid Stenting Study (Bonati L, Jongen LM, Haller S et al) comprising 231 patients, two of seven participating centres performed unprotected carotid stenting and the remaining five largely filter-protected carotid stenting. Sixty eight per cent of filter-protected cases and 35% of unprotected cases had new diffusion-weighted imaging lesions (odds ratio 3.28 [1.50–7.20], p=0.003),” Macdonald noted.


She also referred to a small randomised controlled trial (Montorsi P, Caouti L, Galli S et al, presented at TCT 2010) which reported a substantial reduction in diffusion-weighted imaging and a significant reduction in microembolic signals on transcranial Doppler for proximal protection compared with filters and a non-randomised evaluation of filters versus proximal protection (Schmidt A, Diederich KW, Scheinert S et al. J Am Coll Cardiol 2004;44:1966–9) showing significant reduction in microembolic signals during emboligenic stages (lesion crossing, stent deployment, post-dilatation). However, “establishment and retrieval of protection devices (both filter-type and proximal) are universally emboligenic stages,” Macdonald said, and catheterisation of the aortic arch and great vessel origins necessary for establishment of proximal protection explains the pre-protection microembolic penalty incurred during use of proximal protection systems.


Proximal embolic protection devices represent a significant improvement in the management of the microembolic burden associated with carotid stenting and there is the potential for important advances in terms of both access and stent design.


Are closed-cell stents better than open-cell stents?


Macdonald told delegates that a systematic review (Schnaudigel S, Gröshel K, Pilgram SM et al. Stroke 2008;39:1911–1919) comprising 32 studies (1,363 carotid stenting procedures) demonstrated that closed cell stents significantly reduced diffusion-weighted imaging hyperintensities compared with open cell stents. A small randomised controlled trial (Schillinger M, Dick P, Wiest G et al. J Endovasc Ther 2006;13:312–319) comparing the Wallstent and the ePTFE covered Symbiot stent (stopped early due to excessive restenosis in the covered stent limb) demonstrated significantly fewer microembolic signals on transcranial Doppler with the covered compared with the bare metal stent.


No level one evidence for benefit from embolic protection devices

Jos C van den Berg, Lugano, Switzerland, told delegates at iCON 2011 that currently there is no level one evidence establishing the benefit of embolic protection devices.


He suggested that carotid artery stenting can be performed at least as safely without distal embolic protection devices. “Carotid artery stenting without embolic protection has similar results to the procedure with protection. However, the use of embolic protection devices still does not protect from adverse events post-procedure, and they do not prevent hyperperfusion,” he said.


“A randomised comparison of protected and non-protected carotid stenting would require several thousands of patients. As such, there is no level one evidence. Several studies indicate that stenting can be performed without distal embolic with a risk comparable to protected stenting. “Importantly, carotid stenting with distal filter-type embolic protection devices lead to more embolic events (as demonstrated with transcranial Doppler and diffusion-weighted MRI), a large part of the procedure is unprotected anyway and adverse events related to embolic protection devices do occur,” noted van den Berg. “Experience with proximal protection devices is currently growing, and shows great promise,” he said.