“Let me go over the reasons why we think the carotid arteriogram is the gold standard for evaluating patients,” said Dr Mark H Wholey, Pittsburgh Vascular Institute, UPMC-Shadyside Hospital, PA, speaking at the ISES meeting. Despite some of the risks involved with the imaging procedure, the detailed information available from intracranial angiography makes it a necessity, he told delegates.
Wholey started by reassuring the audience. “Criticizing the non-invasive technology in this area is like criticizing motherhood. I don’t intend to do that.” He pointed out that there are various imaging modalities currently available: magnetic resonance angiography, computered tomography angiography with maximum intensity projection reconstruction in combination with color-flow duplex, magnetic resonance angiography, which he predicted may replace digital subtraction angiography as a screening procedure.
“There is no question that [these technologies are] glamorous and exciting… But this is not the issue. The issue is using carotid arteriography in stenting procedures. The carotid arteriogram is a gold standard. Not as a screen – we already know the patient has some type of carotid artery occlusive disease. But we don’t know the status of the stenting procedure. We’re aware that the definitive procedure for stenting is to get some idea of the intracranial circulation, and that is best determined by angiography.”Isolated magnetic resonance angiography, color-flow duplex, magnetic resonance angiography or computered tomography angiography alone have obvious limitations,” Wholey explained. These include drop-out artifacts, low specificity (70%) and the technical variables such as over-estimating the degree of stenosis at the time of the angiogram. He elaborated on the difficulty in determining the total occlusions versus pre-occlusive disease, “and the vertebral-basilar junction limitations in the non-invasive modalities are quite significant”. He added: “We’re tired of surprises.”
Carotid angiography is done as a staged procedure to provide information prior to stenting. The risk of stroke from angiograms is 1.2% according to Asymptomatic Carotid Atherosclerosis Study figures. “I think by today’s standards, most investigators are seeing 0.3% in the experienced centers,” Wholey explained. “The value of the angiogram, and I can’t stress this strongly enough, is that we need it as a staging procedure prior to the stenting. It is basically a rehearsal to give you some idea of the difficulty you may encounter in the manipulation of your catheters when it comes to the priority that is the stenting procedure itself. So it provides an insight to both the extra- and intracranial circulation that simply isn’t provided by the other technology.”
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Wholey explained that at his center, the approach is a four-vessel angiogram with a Volcano intravascular ultrasound system, a plaque analysis, an idea of the virtual histology of the plaque as a stroke predictor, and the territory at risk. “Basically we’re using this angiogram as a guideline for the stent.” He continued: “At this time we’re also interested in gaining some understanding of the vulnerability of the plaque in the carotid as we think there’s some similarity to the coronary circulation. So basically we’re looking at the angiogram and intravascular ultrasound as an analysis of the block prior to the stenting.”
Wholey gave examples where this approach has helped. “This is a high-grade lesion in a patient who’s had aortic coronary bypass twice who absolutely refused surgery. We analyzed this [Volcano output] and said ‘This is a very high risk situation’. The fibrous activity was minimal but on the other hand you can see that the distal calcification and the necrotic core make this patient much more subject to a peri-procedural event.” Stenting the patient was not satisfactory. “Obviously this patient with a previous volcano intravascular ultrasound has to be monitored very carefully for plaque rupture.”
Intravascular ultrasound information on a second patient showed that they could tolerate stenting and should not experience stroke, but the angiogram revealed that the carotid artery had a redundant loop that would create access difficulties. Knowing this was the case, Wholey said they could modify their procedure slightly to allow for it, using a JR4 guide positioned at the ostium. “If we hadn’t had that pre-op evaluation we would have spent endless time with guide-sheaths etc. just prolonging the procedure.” Most importantly, he continued, it is extremely difficult for non-invasive imaging modalities to separate pre-occlusive from total-occlusive lesions.
“The value of the angiogram is seeing the intracranial circulation in detail and understanding your territories at risk, therefore coming up with some strategic idea of what you can anticipate with a stent,” Wholey opined. Non-invasive imaging technologies will simply not show retrograde flow in the basilar artery or retrograde dynamic activity in the superior cerebellar that would indicate basilar artery occlusive disease. Similarly, primitive hypoglossal is not as clearly seen with magnetic resonance angiography /computered tomography angiography as it is with the angiogram. “This highlights the risk of stenting in a patient who may have stenosis in the absence of a detailed angiogram. We’re clearly trying to avoid extensive basilar infarction,” he said. “Although the resolution in computered tomography angiography is impressive and getting better it is still not going to define pericallosal disease in the intracerebral circulation. The resolution is just not there.”
Wholey admitted that physicians are still trying to understand some of the stroke predictors. “We need more information, not less,” he said. “That type of definitive information for stenting we need requires, as a gold standard, a carefully done angiogram without question. Carotid stenting without angiography is dead.”