Hatim Attar, MD

Müller MD, Ahlhelm FJ, von Hessling A, Doig D, Nederkoorn PJ, Macdonald S, et al. Vascular Anatomy Predicts the Risk of Cerebral Ischemia in Patients Randomized to Carotid Stenting Versus Endarterectomy. Stroke. 2017

There has been a longstanding debate on management of patients with carotid disease. In the ICSS study, patients were randomly assigned to Carotid Artery Stent (CAS) vs. Carotid Endarterectomy (CEA). CAS was related to higher peri-procedural stroke risk, but both therapies were equally effective in long-term stroke prevention. This study is a post-hoc analysis on a sub group of the ICSS study, providing the first randomized trial on vascular anatomy as an independent procedural risk factor for stroke during CAS and CEA. Studies have been completed assessing vascular anatomy for procedural risks with CAS, but none have compared the risk between CAS and CEA, making this study unique and its results invaluable.

In the ICSS MRI subgroup, brain MRI was performed before and 1-3 days after CAS or CEA; primary outcome was new diffusion restricted lesions. Patients in this study underwent Contrast Enhanced Magnetic Resonance Angiography (CE- MRA) or Computed Tomographic Angiography (CTA) to define vascular anatomy. Vascular anatomy was objectified with measurable criteria. Aortic arches were divided into three types based on origins of supra aortic arteries, and angles between all large vessels were defined, as shown below in the images.

 The authors validated the inter-rater reliability on reading these anatomic parameters. Associations were made between the laterality, stenosis length and degree, plaque ulcerations and vasculature angles.

There were 184 patients with vessel imaging; 97 were assigned to CAS, 87 to CEA. Procedural cerebral ischemia was found in 49 of the CAS group (51%), with only 14 after CEA (16%). After correcting for age, only two factors were found to be statistically significant in the CAS group—aortic arch configuration type 2 and 3, and larger ICA angulation (≥ 60 degrees). 

As described previously in the literature, greater tortuosity of ICA is associated with increased risk of stroke in CAS, which was again noted in this study. Carotid plaque characteristics did not confer any stroke risk in CAS or CEA in the ICSS MRI subgroup, but it has been implicated in prior studies based off the more specific conventional angiogram. The authors believe that this difference can be explained by the difference in vessel imaging modalities as this study used MRA and CTA. The use of these common vessel imaging modalities makes this study more relevant and easier to identify within clinical practice.

Complex vascular anatomy increases technical difficulties, especially in CAS. Catheter types and number of runs with guidewire amongst several other procedural factors have not been considered. Additionally, ICSS excluded patients with very unfavorable anatomy that would not have been suitable CAS candidates, thus limiting the full impact of this study. Yet the most relevant limitation is that this study cannot take into account the advances in modern practices in access routes, newer stent designs and even protective devices that would have significantly lowered the risk of thromboembolic complications.

It must be borne in mind that ICSS was initiated over a decade ago. Complex vascular anatomy can increase risk of stroke during CAS, but the impact can be negated to some degree by known advances in modern practices of reducing thromboembolic risk. The final verdict—vascular anatomy should be considered as an independent factor while selecting patients for different therapies for carotid disease irrespective of age.