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INTRODUCTION:
Intravascular ultrasound (IVUS) provides an objective assessment of vessel dimensions, characterizes plaque composition, identifies disease distribution and has been shown to improve the clinical results of angioplasty (PTA) and stenting. This study evaluates carotid artery stenting (CAS) with and without intravascular ultrasound (IVUS) interrogation assessing the region of stent deployment and angioplasty.
METHODS:
Retrospective review of a prospective carotid stent registry from 2003 to 2012 identified 412 consecutive CAS procedures (399 patients) to treat de novo atherosclerosis or recurrent stenosis of the carotid bulb and internal carotid artery. Asymptomatic carotid disease was treated for >75% diameter reduction (DR) with an ICA/CCA ratio of > 4 and symptomatic lesions were treated per NASCET criteria. Exclusion criteria were carotid occlusion (n=2) or diffusely diseased ICA (“string sign”) with adequate collateralization on cerebral angiogram (n=2). A cerebral protection device was used in all cases. Imaging with IVUS was performed in selected cases prior to and following stent-angioplasty. Residual stent stenosis was defined as > 30% diameter reduction on angiography or IVUS and was treated with additional PTA. Surveillance duplex ultrasound was performed in an ICAVL accredited vascular laboratory with validated criteria at 30 days followed by 6 month intervals. Outcome measures included procedure time, final balloon diameter for PTA, contrast volume, hemodynamic parameters on duplex surveillance, cardiac events, neurologic outcome, and mortality. Statistical level of significance was calculated with Pearson Χ² and student t-test (p=< 0.05).
RESULTS:
CAS was performed using either digital C-arm angiography alone (AA) (n=167) or in conjunction with IVUS (AI) (n=241). The two groups were comparable with regard to indication, stenosis severity, and atherosclerotic risk factors; 77% (n=314) of patients were asymptomatic. Using AA or AI, accurate single carotid stent deployment was achieved in all patients. Mean procedure times were similar between AA and AI groups (63.0 min; 63.4 min, p= 0.87). As compared to AA, AI altered procedural conduct by using lower contrast volumes (mean 50 cc; range 5-120cc) as compared to AA (mean 90 cc; range 40-170cc) due to fewer angiogram runs for stent sizing and verification of adequate stent deployment. AI directed use of larger diameter balloons ranging in size from 5.5 to-7mm (median 6mm) for final stent PTA based on assessment of normal luminal diameter while AA balloons ranged from 4.5 to 6 mm (median 5mm, p=<0.0001). AI also detected more residual stent abnormalities (n=24, 10%) versus CAS using AA (n=3, 2 % p= 0.002). Eighty-nine percent of stents (24/27) receiving adjunctive PTA for residual stent stenosis demonstrated <50% DR on the early (30 day) surveillance duplex scan. Early neurologic event rates were low and there was no different between groups (AA 1.2%, AI 1.2%). Duplex ultrasound surveillance at 30-days and last surveillance interval is recorded in Table I.

Table I. Hemodynamic Parameters

	30-day Duplex Scan			Most Recent Duplex Scan
	<50% DR	50-75% DR	>75% DR	<50% DR	50-75% DR	>75% DR
Angio Alone	152	15(9%)	0	141	21 (13%)	5 (3%)
Mean PSV (cm/s)	98 +46	198+47	-	106 +38	204 +51	422+45
Angio+IVUS	233	8 (3%)	0	232	8 (3%)	1 (0.4%)
Mean PSV (cm/s)	84 +50	182 +31	-	82 +40	186+28	347

Mean follow-up was 54 months. (range 6-120 mos.) Duplex surveillance at 30-days showed DR 50-75% was more likely in the AA group (p=0.02). At last duplex surveillance DR > 50% were recorded for 26 (16%) AA and 9 (4%) AI CAS (p=<.0001). Six CAS sites (5 AA, 1 AI, p=<.0001) developed >75% asymptomatic re-stenosis and underwent secondary percutaneous intervention with PTA with one AA stent later developing an asymptomatic thrombosis. Each group had one late neurologic event, one stroke (AA) and one TIA (AI) (0.6%, 0.4% respectively). A single early cardiac death was recorded in an AI patient.
CONCLUSION:
IVUS guidance allows operators to accurately define disease distribution, vessel size, and target stent landing zones without adding independent risk or increasing procedural time. IVUS affords a measure of quality control that directs optimal stent and balloon selection. Adjunctive use of IVUS can improve both early and late carotid stent hemodynamics which may enhance outcomes and reduce secondary interventions for recurrent stenosis.