In total, 342 consecutive CAS procedures performed at a single institution between January 2009 and December 2017 were examined in this retrospective review. All lesions were associated with atherosclerotic ICA and/or common carotid artery (CCA) stenosis. Our institutional guidelines call for CAS of stenotic ICAs in the following scenarios: severe stenosis (> 75% based on North American Symptomatic Carotid Endarterectomy Trial [NASCET] criteria) regardless of symptoms; symptomatic moderate stenosis (> 50 and ≤ 75%); or symptomatic patients with ≤ 50% lesion ulceration. CAS procedures performed for arterial dissections were excluded from this study. The primary study endpoint was RAO within 3 days after CAS. RAO was confirmed by photography and fluorescent angiography of the fundus, performed by an ophthalmologist immediately after onset of visual symptoms.

The following baseline patient parameters were examined: age, gender, hypertension, diabetes, hyperlipidemia, prior stroke or transient ischemic attack (TIA), coronary artery disease, atrial fibrillation, chronic renal failure, and smoking. The following angiographic variables were also assessed: symptomatic stenosis, degree of ipsilateral stenosis (based on NASCET criteria), CCA plaque involvement, ECA stenosis, ulcerative or calcific plaques, ipsilateral basal perfusion status on a single-photon emission computed tomography (SPECT) scan of the brain, ipsilateral vascular reservoir on a SPECT scan, and OA supply source (ECA-dominant vs. ICA-dominant group) prior to CAS. Among procedure-related variables, we analyzed external pacing, intra-procedural flow compromise, stent type (closed, open, or mixed-cell), type of cerebral protection device (CPD), and post-balloon angioplasty. In all patients treated during the study period, various types of distal filtering systems were used exclusively. Clinical outcomes were assessed in terms of peri-procedural ischemia (TIA, infarction, or RAO) and hemorrhage. This study was approved by our Institutional Review Board.

All stenotic lesions were detected using computed tomography angiography, magnetic resonance angiography, or carotid sonography. All patients underwent cerebral angiography and rotational angiography with three-dimensional image reconstruction via Innova IGS 630 (GE Healthcare, Chicago, IL, USA) or another system (Integris V or AlluraClarity; Philips Medical Systems, Amsterdam, The Netherlands) to assess the degree and configuration of stenosis with precision and to determine the therapeutic plans.

ECA- or ICA-dominant OA flow was confirmed by ipsilateral carotid angiography prior to CAS by assessing whether the OA was supplied chiefly and more expeditiously by the ICA or ECA. Retinochoroidal blushing from ECA collaterals (Fig. 1) or the ICA was also assessed.

Most CAS procedures were performed under local anesthesia. Patients were pre-treated with aspirin (100 mg/d) and clopidogrel (75 mg/d) at least 3 days before each procedure. All interventions were carried out via puncture of the femoral artery, followed by administration of heparin (70–100 U/kg) to achieve activated clotting times of 250 seconds. Long 6- or 7-Fr carotid sheaths (Flexor Shuttle-SL; Cook Medical, Bloomington, IN, USA) were advanced into the CCA and angiograms were recorded. Cerebral protection was attempted using various types of distal filtering systems at the operator's discretion and based on device availability. Once a filter was placed in the straightest possible segment, device flow status was routinely tested by contrast injection. Thereafter, pre-stent angioplasty was performed using a full-size balloon. Predilation using a 2- to 3-mm coronary balloon catheter was performed before filter placement only if angiography showed that the narrowest vessel diameter was insufficient for passage of the filter device. Self-expanding stents were delivered over the 0.014-inch filter guidewire and deployed in relatively straight arterial segments. Stent delivery and catheter retrieval after deployment were executed with caution under continuous fluoroscopic monitoring to maintain the filter's position. Various types of self-expandable stents (closed, open, or mixed-cell) were chosen according to the operator's preference or the stented arterial course. Post-deployment angiography was routinely performed to evaluate any complications or residual stenosis. If significant residual stenosis (> 30%) persisted without neurologic events or complications after stent deployment, postdilation procedures were performed using a larger balloon catheter under continuous fluoroscopic monitoring of the filter position. A retrieval catheter was then introduced over the filter wire for filter collapse and withdrawal, again using continuous fluoroscopic monitoring to avoid potential problems when crossing the stented segment. After the procedures, completion angiography was performed to confirm either distal embolic occlusion or ample perfusion. The patients continued the clopidogrel regimen for at least 90 days and the aspirin regimen indefinitely.

Continuous variables are expressed as mean ± standard deviation. Chi-squared and Fisher's exact tests or unpaired t tests were used to assess categorical or continuous variables, respectively. To evaluate the risk factors predisposing patients to symptomatic RAO after CAS, univariate analysis was applied. Multivariate analysis was then conducted by incorporating variables with p values < 0.10 in univariate analysis. In multivariate analysis, if the sample size was small, Firth's method was used. The results of a binary logistic regression model were reported as odds ratios (ORs) with 95% confidence intervals (95% CIs) and p values. A two-tailed p value < 0.05 was considered statistically significant. All computations relied on standard software (STATA v15.0; StataCorp LP, College Station, TX, USA).

In total, 342 stenotic carotid lesions (men: 302/342, 88.4%) were selected for this study (Table 1). The mean age of the patients was 70.0 ± 7.3 years (range, 49–87 years). Symptomatic stenosis was present in 133 (38.9%) patients, and the mean degree of stenosis was 75.5% ± 14.7% based on the NASCET criteria. Prior to CAS, OA was supplied by ECA collaterals (ECA-dominant group) in 74 patients (21.6%). Bilateral CAS was performed in 30 patients, and staged stenting was performed in 36. During CAS procedures, flow arrest developed in seven patients who remained deficit-free. In terms of stent type, an open-cell stent (254/342, 74.3%) was the most commonly applied, followed by closed-cell (85/342, 24.8%) and mixed-type (3/342, 0.9%) stents. Among CPDs, FilterWire (218/342, 63.7%; Boston Scientific, Marlborough, MA, USA) was the most commonly used, followed by Emboshield (72/342, 21.1%; Abbott Vascular, Santa Clara, CA, USA), SpiderFX (32/342, 9.4%; Medtronic, Minneapolis, MN, USA), and AngioGuard (20/342, 5.8%; Cordis Corp., Milpitas, CA, USA). Post-stent angioplasty was performed for 101 lesions (29.5%). After CAS, none of the patients exhibited reperfusion hemorrhage, but procedure-related ischemia developed in 27 patients (TIA, 4; infarction, 17; RAO, 6).

Prior to CAS, the OA was supplied by the ICA in 268 patients (78.4%) and by the ECA in 74 (21.6%). In the latter group (n = 74), the OA was supplied from the orbital branch of the MMA in 53 patients, the sphenopalatine branch of the internal maxillary artery in 15 patients, the angular branch of the facial artery in four patients, and the zygomatico-orbital branch of the STA in two patients. The characteristics of the patient population are summarized by OA subsets in Table 1. In multivariate analysis, OA was mainly supplied via the ECA collaterals in patients with more advanced stenosis of the ipsilateral ICA (p = 0.001) and ulcerative plaques (p = 0.021). Although there were no intergroup differences in terms of postprocedural hemorrhage or ischemia, symptomatic RAO was more common in the OA subset with ECA (vs. ICA) dominance (p = 0.002). After CAS, OA flow in the ECA-dominant group reverted to the ICA supply in 42 patients (56.8%).

After CAS procedures, six patients (1.8%) developed symptomatic RAO (central RAO, 4; branch RAO, 2), for which older age, ulcerative plaque, and ECA-dominant OA emerged as significant risk factors in univariate analysis. In the binary logistic regression analysis, ECA-dominant OA (OR, 9.705; 95% CI, 1.519–62.017; p = 0.016) and older age (OR, 1.159; 95% CI, 1.005–1.336; p = 0.041) were independently correlated with RAO (Table 2). Among the six patients with RAO, five showed an OA supplied via ECA collaterals (orbital branch of the MMA in all 5). Baseline characteristics of these six patients with RAO are summarized in Supplementary Table 1.

Intra-arterial thrombolysis was performed in one of the six cases of RAO. Visual symptoms improved in three patients (one after intra-arterial thrombolysis and two after medical management), although minor deficits persisted; the other three patients failed to show improvement.