Duplex ultrasound velocity criteria for the stented carotid artery

Abstract

Ultrasound velocity criteria for the diagnosis of in-stent restenosis in patients undergoing carotid artery stenting (CAS) are not well established. In the present study, we test whether ultrasound velocity measurements correlate with increasing degrees of in-stent restenosis in patients undergoing CAS and develop customized velocity criteria to identify residual stenosis > or =20%, in-stent restenosis > or =50%, and high-grade in-stent restenosis > or =80%. Carotid angiograms performed at the completion of CAS were compared with duplex ultrasound (DUS) imaging performed immediately after the procedure. Patients were followed up with annual DUS imaging and underwent both ultrasound scans and computed tomography angiography (CTA) at their most recent follow-up visit. Patients with suspected high-grade in-stent restenosis on DUS imaging underwent diagnostic carotid angiograms. DUS findings were therefore available for comparison with luminal stenosis measured by carotid angiograms or CTA in all these patients. The DUS protocol included peak-systolic (PSV) and end-diastolic velocity (EDV) measurements in the native common carotid artery (CCA), proximal stent, mid stent, distal stent, and distal internal carotid artery (ICA). Of 255 CAS procedures that were reviewed, 39 had contralateral ICA stenosis and were excluded from the study. During a mean follow-up of 4.6 years (range, 1 to 10 years), 23 patients died and 64 were lost. Available for analysis were 189 pairs of ultrasound and procedural carotid angiogram measurements; 99 pairs of ultrasound and CTA measurements during routine follow-up; and 29 pairs of ultrasound and carotid angiograms measurements during follow-up for suspected high-grade in-stent restenosis > or =80% (n = 310 pairs of observations, ultrasound vs carotid angiograms/CTA). The accuracy of CTA vs carotid angiograms was confirmed (r(2) = 0.88) in a subset of 19 patients. Post-CAS PSV (r(2) = .85) and ICA/CCA ratios (r(2) = 0.76) correlated most with the degree of stenosis. Receiver operating characteristic analysis demonstrated the following optimal threshold criteria: residual stenosis > or =20% (PSV >or =150 cm/s and ICA/CCA ratio > or =2.15), in-stent restenosis > or =50% (PSV > or =220 cm/s and ICA/CCA ratio > or =2.7), and in-stent restenosis > or =80% (PSV 340 cm/s and ICA/CCA ratio > or =4.15). Progressively increasing PSV and ICA/CCA ratios correlate with evolving restenosis within the stented carotid artery. Ultrasound velocity criteria developed for native arteries overestimate the degree of in-stent restenosis encountered. These changes persist during long-term follow-up and across all grades of in-stent restenosis after CAS. The proposed new velocity criteria accurately define residual stenosis >or =20%, in-stent restenosis >or =50%, and high-grade in-stent restenosis > or =80% in the stented carotid artery.