#10 CAROTID DUPLEX WITH CONTRALATERAL DISEASE:
THE INFLUENCE OF VERTEBRAL ARTERY BLOOD FLOW.
Harold J. Welch, MD, Mary Claire Murphy, BS, Kevin B. Raftery,
MD, and Edward R. Jewell, MD
Lahey Clinic, Burlington, MA
Purpose: It is widely believed that severe carotid stenosis
or occlusion will increase blood flow in the contralateral carotid
causing an overestimation of duplex ultrasound (DU) measured stenosis
in the "less diseased" internal carotid artery (ICA). This study
examines the role of the vertebral artery system (VAS) on duplex
results in patients with severe carotid disease.
Methods: Retrospective study of 110 patients who underwent
carotid endarterectomy between 1/1/95 and 1/31/98. All study
patients had a preoperative and postoperative carotid duplex within
6.5 months of each other, and a magnetic resonance angiogram (MRA) or
conventional angiogram (CA) preoperatively that correlated with the
preoperative duplex on the severely diseased carotid. Duplex
criteria for stenosis were determined by University of Washington
standards in and ICAVL accredited vascular lab. Angiograms were
reviewed for degree of stenosis calculated by NASCET criteria and
vertebral artery status. Vertebral arteries were considered abnormal
if they were hypoplastic, had slow or retrograde flow, had >50%
stenosis or occlusion, or ended in a posterior inferior cerebellar
artery. Pre- and post-operative values for ICA Peak Systolic
Velocity (PSV), ICA End Diastolic Velocity (EDV), and ICA/CCA PSV
ratios were recorded. An additional 19 patients had an occluded
carotid contralateral to a severely diseased carotid artery, with
comparison of preoperative DU and MRA or CA. Paired t-tests were
used to assess significant improvement from preoperative to
postoperative values within groups and independent t-tests compared
changes between groups.
Results: 67 patients had normal VAS, 43 had an abnormal VAS.
Normal VAS patients had a significant decrease in their PSV (mean
change 11.46 cm/s, p=0.04) and EDV (mean change 6.73 cm/s, p<0.01)
in the contralateral ICA after endarterectomy, as did the abnormal
VAS group (mean change PSV 27.7 cm/s, p<0.001, mean change EDV
17.7 cm/s, p<0.001). Comparing the changes between these two
groups, the EDV change in the abnormal VAS group was significantly
greater than the normal VAS group (p=0.01). The 110 patients were
also divided into those who underwent endarterectomy for a 50-79%
stenosis (n=33) versus those with an 80-99% stenosis (n=77). There
was minimal change in postoperative velocities after contralateral
endarterectomy for moderate stenosis, but significant changes (PSV
mean change 23.8 cm/s, p=0.03, EDV mean change 14.4 cm/s, p=0.001)
after endarterectomy for severe stenosis. When comparing the 77
patients with severe stenosis, 49 patients with normal VAS had mean
decreases in their postoperative PSV and EDV of 18.0 cm/s and 8.9
cm/s, respectively. 28 patients with abnormal VAS had a mean PSV
decrease of 34.0 cm/s and mean EDV decrease of 24.0 cm/s. The
difference in the EDV change was significantly greater for the
abnormal VAS group (p=0.03). Of the additional 19 patients with an
occluded ICA by DU and MRA and/or CA, the contralateral DU
interpretation agreed with the additional imaging modality in 16
patients. 2 patients had overestimation of the stenosis by DU, they
both had tandem ICA stenoses of 50% or greater and one had abnormal
VAS. One patient had discordance between DU, MRA, and CA.
Conclusions: Vertebral artery blood flow significantly contributes
to the "hemodynamic effect" of carotid disease identified by duplex.
There is a greater decrease in postoperative ICA EDV after
contralateral endarterectomy in patients with abnormal VAS,
especially in those with severe contralateral ICA stenosis. These
changes in EDV play a role in the DU categorization of stenosis and
the possible overestimation of stenosis. DU is more accurate in
assessing carotid stenosis in the presence of severe contralateral
disease in patients with normal vertebrobasilar arteries.
