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Duplex Ultrasound Velocity Criteria For The Stented Carotid Artery

Brajesh K Lal, Robert W Hobson, II, Babak Tofighi, Indu Kapadia, Salvador Cuadra, Zafar Jamil.
UMDNJ-New Jersey Medical School, Newark, NJ.

OBJECTIVES: We have demonstrated that carotid artery stenting (CAS) alters arterial compliance, necessitating new velocity criteria defining a normal luminal diameter early after the procedure. In the present study we: 1) test whether duplex US velocity measurements correlate with increasing degrees of ISR after CAS, and 2) develop customized velocity criteria to identify in-stent restenosis (ISR ≥50%) and high-grade ISR (≥80%).

METHODS: We compared post-procedural US with cervical angiography (CA) performed on completion of CAS. Patients were also followed with US, and the results compared with concurrent CT angiography (CTA). Patients suspected of high-grade ISR underwent diagnostic CA and reintervention at a threshold stenosis of ≥80%. The US protocol included peak-systolic (PSV) and end-diastolic velocity (EDV) measurements in the native common carotid (CCA) and distal internal carotid arteries (ICA), and in the proximal, mid and distal parts of the stent. PSV/EDV and ICA/CCA ratios were recorded. Receiver operator characteristic (ROC) curves were developed to obtain threshold velocities for diagnosing increasing degrees of ISR.

RESULTS: 213 CAS procedures were reviewed, of which 32 had contralateral ICA stenosis ≥60% and were excluded. 53 patients underwent follow-up US and CTA/CA between 1-10 years post-procedure. Therefore 234 pairs of observations (US vs. CA/CTA) were available for comparison. Accuracy of CTA was confirmed with CA (r2=0.88). Post-CAS PSV (r2=0.79) and ICA/CCA ratio (r2=0.7) correlated with degree of ISR. The threshold PSV≥230 cm/sec for native arteries categorized 22 stented arteries with ISR≥80% of which only 13 were confirmed by imaging. ROC analysis identified optimal thresholds for ISR (≥50%) and for high-grade ISR (≥80%) as: PSV≥226 cm/s, ICA/CCA ratio≥2.7; and PSV≥343 cm/s, ICA/CCA ratio≥4.1; respectively. % sensitivity and specificity for the thresholds were: 95, 86 and 100, 93 respectively.

CONCLUSIONS: Increasing degrees of restenosis after CAS correlate with increasing PSV and ICA/CCA ratios. However, US velocity criteria developed for native ICAs over-estimate the degree of ISR encountered during long-term follow-up of patients after CAS. The proposed new velocity criteria accurately define ISR≥50% and high-grade ISR≥80% in the stented carotid artery.