Vascular Disease Management

Plaque type for 34 patients is presented in Table 2. PIT was the most common plaque type, TCFA least common, and there were no cases of FC (p < 0.0001). A non-significant association was observed with higher NC in patients with hyperlipidemia and preprocedure TIA/amaurosis fugax (p = 0.105 and p = 0.134, respectively), presented in Table 3. Analysis of individual plaque types again revealed an insignificant association between less hyperlipidemia and TIA/amaurosis in patients with PIT (p = 0.105 and 0.088, respectively). Periprocedural TIA/stroke was significantly associated with FA by VH IVUS (p = 0.016), presented in Table 4. Lesion characteristics, arch anatomy, and VH IVUS plaque type for the 3 periprocedural neurological events are presented in Table 5. A type III aortic arch was present in 2 of the 3 patients with periprocedural TIA/stroke, whereas only a single type III arch was present among the remaining patients (p = 0.031). Interobserver agreement for VH IVUS plaque classification was Κ = 0.743.

Discussion

We found a trend towards higher NC content in patients with hyperlipidemia or prior TIA/amaurosis driven mainly by lower NC content and PIT in patients without hyperlipidemia or prior TIA/amaurosis fugax. These findings parallel the coronary literature showing a positive association between unstable symptoms, hyperlipidemia, and high NC content plaques.^21,22,29 Only 5 of the 6 plaque types described in the CAPITAL study (n = 30) were present in this series of 34 patients (PIT, FA, CaFA, CaTCFA, and TCFA).¹⁷ The absence of FC from our series and our moderately strong agreement between observers raises the question whether this plaque type, as defined in CAPITAL, warrants distinction from the others.

The patient and angiographic characteristics we examined have been included in prior CAS trials and registries, and identified as either contributing to carotid occlusive disease or conveying higher procedural risk with CAS.^6,7,9,37 The characteristics of our patients undergoing CAS are similar to those reported previously. Our incidence of periprocedural TIA and major stroke compares well to prior trials comparing CAS and CEA.^8,9

We found a trend towards higher NC and periprocedural TIA and major stroke, and a statistically significant association of FA with this important periprocedural outcome. This suggests the potential for distal embolization may be greater with higher NC. This finding parallels the PCI literature indicating a higher risk of periprocedural myocardial ischemia and necrosis with higher NC in both stable and unstable coronary artery disease.^{26–28,30–34} Sampling of embolic debris during CAS in one study demonstrated an association between plaque fibrofatty content by VH IVUS and the mass of debris retrieved.¹³

Our determination of VH IVUS plaque type was based on mutually blinded assessment of plaque and periprocedural outcomes whereby each observer established their own luminal and vessel borders from the provisional images. When observations differed, the plaque type with the higher NC content was used for one TIA case, and the plaque with lower NC was used for the non-stroke cases. This assumption was justified on the basis of the aforementioned studies revealing the association of NC content and high NC plaque types with adverse events during PCI. The substantial interobserver agreement for our series argues against a systematic under or over classification with respect to NC. These findings illustrate the need for defining plaque type with VH IVUS in occlusive carotid disease in a larger series or registry.

Presence of a type III aortic arch, whereby the innominate arises from the ascending aorta, was the sole angiographic and clinical variable significantly associated with periprocedural stroke risk in this small series. We included a number of angiographic features associated with higher periprocedural stroke in our analysis in an attempt to explain these periprocedural events. A type III arch requires longer procedure time and more catheter manipulations which may result in ipsilateral or contralateral embolic events.³⁷ This may justify direct carotid puncture as a viable means of access in selected cases with a type III or IV aortic arch, as has been reported elsewhere.³⁸    

Strengths and limitations