Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3955_Библиотеки_им_академика_М_И_Перельмана.pdf
Carotid Stenting and Angioplasty 171
b
Recurrent carotid stenosis after CEA
b
Contralateral nerve palsy
b
Spinal immobility
b
Tracheostomy
• Clinical factors conferring higher risk for CAS:
b
Symptomatic patients
b
Renal failure − not on dialysis
b
Severe contrast allergies
b
Extreme aortic arch/carotid artery tortuosity/angulation
Laboratory
• Laboratory analysis similar to that performed in the setting of atherosclerotic
disease anywhere:
b
Risk-factor evaluation:
Lipid profile
Diabetics − blood glucose, hemoglobin A1C
C reactive protein, homocysteine levels
b
Preparation for angiography, contrast administration:
Serum creatinine and calculated glomerular filtration ratio (GFR)
Coagulation parameters (PT, PTT, CBC with platelet count) − if clinically
necessary:
• Liver disease
• Recent history of anticoagulation therapy
• Other coagulopathies − inherited or acquired
Imaging
• Digital subtraction angiography (DSA) remains the gold standard for the mea-
surement of carotid artery stenosis.
• The NASCET criteria are commonly used for the measurement of percentage
stenosis:
b
100 − (narrowest luminal diameter/diameter of the normal distal cervical
internal carotid artery).
b
DSA provides no information about plaque morphology.
• Ultrasound with color Doppler, spectral analysis, and grayscale imaging is easy
to use, relatively inexpensive, and avoids the use of contrast agents and radiation:
172 G. Wyse and K.J. Murphy
b
Can be used for longitudinal follow-up.
b
Disputed role as primary test prior to CEA but can be correlated with
angiography at the time of CAS.
• Non-invasive cross-sectional imaging techniques:
b
Contrast-enhanced MRA of the neck correlates well with DSA
b
CTA gives superb anatomic detail but as a sole modality is limited especially
in heavily calcified lesions were it can overestimate the degree of stenosis.
• Imaging of the brain prior to CAS is essential. It helps to visualize recent ischemia
and hemorrhage. Brain imaging also rules out other lesions such as tumors. In
addition, imaging acts as a comparison for post-procedural studies.
Indications for Carotid Artery Stenting
• Who will definitely benefit from CAS?
b
The current role of medical management, CEA, and CAS in relation to carotid
artery disease is not always clear. There is no agreed consensus and practices
vary widely.
b
The North America Symptomatic Carotid Endarterectomy Trial (NASCET)
and the European Carotid Surgery Trial (ECST) showed that patients benefit
from surgery as opposed to medical treatment in the setting of symptomatic
carotid stenosis greater than 70 and 50%, respectively.
• The indications for CAS have been generally adopted from the surgical trials.
CAS is generally performed on
b
Patients at high risk for surgery with a symptomatic carotid stenosis of greater
than 70%. Surgical high-risk patients include
A prior history of CEA and recurrent stenosis
Contra-lateral carotid occlusion
Previous radiation therapy
Previous radical neck dissection
High or low surgically inaccessible lesions
Significant medical co-morbidities.
b
High-risk status is not a contraindication to CEA. It depends on the individual
surgeon and the skills available. The importance of institutional audit and a
multidisciplinary approach when selecting patients for either CAS or CEA is
critical.
b
Since most embolic strokes occur in patients with a stenosis less than 70%, is
there an indication for stenting such lesions?
Ongoing investigation into this area with multiple trials and registries.
Currently the role of CAS in symptomatic lesions below 70% is unclear.
Carotid Stenting and Angioplasty 173
b
Is there any evidence to support CAS in the setting of asymptomatic carotid
artery disease?
Little solid evidence exists. However, CAS is infrequently offered to
asymptomatic patients with a carotid artery stenosis of greater than 80%.
b
Other, less common indications for carotid stent placement:
Covered stents have been successfully used for carotid “blowouts” (perfo-
ration) from tumor infiltration or traumatic carotid injury.
Stents may be used as flow diverters in the setting of post-dissection carotid
pseudoaneurysm.
• In the US, the Center for Medicare Services (CMSs) will reimburse CAS only
for symtomatic patients with high surgical risk (see above criteria) and carotid
stenosis greater than or equal to 70%:
b
Symptomatic patients with 50–70% stenosis or asymptomatic patients with
80% or more stenosis are reimbursed but only for patients enrolled in FDA-
approved clinical trials.
• The Society of Vascular Surgery recommends the following treatment guidelines
for carotid stenosis:
b
Asymptomatic
<60% stenosis − medical management
>60% stenosis − CEA
>80% stenosis and anatomic risks for CEA − consider CAS
b
Symptomatic
<50% stenosis − medical management
>50% stenosis − CEA
>50% stenosis with high perioperative risks − CAS
Contraindications
• Absolute contraindications: (uncommon):
b
Previous history of anaphylaxis to contrast agents
b
Uncontrolled coagulation problems
• Relative contraindications:
b
Renal impairment:
Treat with intravenous hydration and bicarbonate therapy plus oral dosing
of N-Acetyl cyteine
b
Inability to tolerate anti-platelet therapy
174 G. Wyse and K.J. Murphy
b
Aneurysm or vascular malformation downstream from stented lesion:
Aneurysms or vascular malformation should be addressed prior to CAS to
prevent the increased intracranial flow possibly resulting in hemorrhage.
b
Many physicians consider near total carotid occlusion a relative contraindi-
cation, especially in the present of good collateral flow in the Circle of
Willis:
There is an increased risk of peri-procedural stroke with increasing carotid
artery stenosis but this risk decreases at near total occlusion.
A careful consideration of the risks and benefits must be made prior to
CAS in the setting of total or near carotid occlusion.
b
Evidence of higher complication rates in octogenarians who undergo CAS
suggests that age is a relative contraindication.
No gender difference has been demonstrated with CAS.
b
Visible luminal clot is also an important consideration (Fig. 3). Crossing such
a lesion with a wire or embolic protection device is hazardous and may lead
to inadvertent distal embolism:
CEA with back bleeding of the carotid or a proximal EPD is advantageous.
Observation and anticoagulation for luminal clot with deferred treatment
should also be considered.
b
Severe cognitive impairment:
Fig. 3 Lateral digital
subtraction angiogram
showing visible luminal clot,
a relative contraindication to
carotid angioplasty and
stenting
Carotid Stenting and Angioplasty 175
There is no evidence of improved quality of life with CAS for the
cognitively impaired.
b
Short life expectancy:
The statistical benefit of CAS is based on a reasonable life expectancy.
Surgical experience suggests that patients should have a life expectancy
of at least 3 years for symptomatic disease and 5 years for asymptomatic
disease to benefit from CAS.
b
Severe tortuosity and heavily calcified lesions:
CAS can be dangerous with significant risks of iatrogenic vessel rupture
or dissection or cerebral emboli.
Such cases may be better treated by a surgical or medical approach.
Patient Preparation and Selection
• Proper patient selection is mandatory to improve clinical outcomes after CAS.
The reliance on measurements of vascular luminal narrowing to predict future
ischemic events is somewhat limited. This is certainly an imprecise method:
b
There is significant compensatory enlargement of a vessel in response to
plaque.
b
The majority of culprit lesions causing myocardial infarction in retrospective
studies showed luminal narrowing of less than 50%.
• Identification of the “at risk” patient is crucial. Newer imaging techniques will
help to more clearly identify patients who will benefit from CAS:
b
Hemodynamics − Paired flow studies:
Test the ability of the cerebral vessels to increase blood flow in the setting
of a vasodilatory stimulus (Fig. 4). If flow does not increase pre-existing
vasodilation is inferred.
Existing hemodynamic impairment has a strong association with stroke
risk and paired flow studies may be used in the future as a means of patient
selection for CAS.
b
Plaque examination
Plaque which contains an extracellular lipid core, active inflammation and
a thin fibrous cap is at the highest risk of rupture.
Imaging methods to identify high-risk plaque have included
• Ultrasound, intravascular ultrasound
• PET/CT.
•MRI
176 G. Wyse and K.J. Murphy
Fig. 4 (a) A cerebral blood flow (CBF) map at the level of the basal ganglia in an elderly male
with known, high-grade right ICA stenosis reveals significant decrease in the right hemispheric
perfusions (arrows). (b) A mean transit time (MTT) map at the same level also reveals severe
elevation of MTT in the entire right hemisphere. Values as high as 11 sec were obtained in some
regions of interest in the right MCA territory.(c) A CBF map repeated following the administration
of acetazolamide fails to reveal any augmentation in the CBF values. In fact, paradoxical response
(decreased CBF) was noted in the right MCA territory, suggesting an impaired cerebrovascular
reserve
Carotid Stenting and Angioplasty 177
Fig. 5 (a) Maximum intensity projection MRA of the carotid bifurcation revealing narrowing of
the proximal right internal carotid artery without significant luminal narrowing. (b) Post-contrast
high resolution, T1-weighted, black blood MR imaging reveals the same lesion. Noted the eccentric
posterior lipid core and enhancing cap. Plaque imaging with MR or other techniques may replace
our reliance on luminal narrowing to predict future stroke
• T2-weighted images offer good contrast to discriminate plaque com-
ponents
• Calcification is better identified on T1 imaging.
• Discrimination of the fibrous cap from a lipid core and cap thickness
can be accessed with contrast-enhanced MRI.
• These techniques can be used to assess the individual’s risk of
future cerebral ischemia rather than reliance on luminal narrowing
measurements to statically predict stroke risk (Fig. 5).
Relevant Anatomy − Normal and Variant
• Normal aortic arch anatomy is right common carotid originating from first aor-
tic arch branch, the brachiocephalic artery and a separate origin of left common
carotid artery from the arch.
b
Frequent variant is left common carotid artery arising off the origin or
proximal portion of the brachiocephalic artery (bovine arch)
Can be difficult to catheterize due to acute angle of left common carotid
artery with the aorta. A Simmons or shephard’s-hook catheter is often
needed.
• With increasing age, the brachiocephalic and right common carotid arteries may
become especially tortuous and/or calcified:
b
Requires stiffer guidewires placed more distal in the carotid circulation
(external carotid) in order to successfully catheterize
b
Increased risk of iatrogenic arterial injury or embolic events.
178 G. Wyse and K.J. Murphy
Pre-procedure Medications
• All patients are pre-treated with anti-platelet agents for 5 days prior to the pro-
cedure. The use of double anti-platelet therapy commonly using aspirin and
clopidogrel is widespread. This practice is derived from coronary artery stenting
but lacks evidence in the carotid arteries:
b
The use of various platelet assays to determine the degree of platelet inhibition
is also becoming a more common practice.
• Optimal management of blood pressure and blood glucose is critical to a
successful outcome:
b
There may be a role for statins in plaque stabilization prior to CAS.
Procedural Considerations
• A full neurological examination should be performed prior to CAS.
• The procedure can be carried out under conscience sedation:
b
Avoids general anesthesia which may be advantageous in the setting of
significant medical co-morbidities.
b
Permits neurological examination during the procedure which requires the co-
operation of the patient
• Performing the procedure under general anesthesia may be easier on the patient
and clinician. Although the ability to perform a neurological examination is
lost, intra-procedural angiography with a careful review to assess for missing
intracranial branches can be performed.
• With either technique the presence of an anesthesiologist for managing bradycar-
dia and blood pressure instability is invaluable.
• Timing of the procedure is also important:
b
To avoid the risk of hemorrhagic conversion in an infarcted area, wait 4 weeks
after an acute ischemic event before performing CAS.
• Detailed review of all imaging is essential for procedural planning. Anatomical
considerations, tortuosity, aneurysmal vessels, arch configuration, and heavy
calcification can result in a difficult or even dangerous procedure:
b
Access and equipment selection depend on these anatomical factors.
b
Femoral access is commonly used, alternatively brachial or radial access may
have advantages for certain lesions.
b
Direct carotid puncture i s another option although surgical closure of the
puncture is required.
• An arch aortogram will display the anatomy and will often save time by
influencing equipment choices:
Carotid Stenting and Angioplasty 179
b
Prior to stenting, biplanar views of the intracranial circulation distal to the
stenosis are crucial. These angiograms are compared to procedural angiogram
to assess for distal emboli.
• Placement of a secure and stable guiding catheter in the common carotid artery is
the opening critical step of the procedure. In the setting of challenging anatomy
this can be difficult.
b
Cannulation of an external carotid branch and exchange over a stiff wire can
be performed.
Intra-procedural Medications and Devices
Embolic Protection Devices
• The use of embolic protection devices (EPDs) is widespread although there is no
randomized trial comparing stenting with an EPD and without an EPD.
• EPD rationale:
b
Crossing a tight stenosis or angioplasty and stenting may cause ischemic
events by embolization of plaque material or clot into a distal intracranial
vessel.
b
Doppler studies confirm emboli occur at the time of CAS.
• EPD may itself cause problems:
b
The distal devices which consist of a filter (Fig. 2) or a balloon that is mounted
on a wire still have to cross the stenosis as a first step, there can be incomplete
wall apposition, vessel occlusion with debris, vessel spasm or wall damage.
b
There are multiple devices available with a learning curve for each one.
Operator inexperience and unfamiliarity can cause significant problems.
• Embolic protection devices are of two main types:
b
Distal-types including occlusive balloons
b
Umbrella-type embolic filters.
• Excessive angulation and heavy calcification can make device deployment
hazardous. Crossing profile and capturing efficiency vary with different products.
• Over-sizing of distal filters can ensure luminal adherence and contrast injection
will ensure the vessel is patent and not occluded with debris.
• A second type of device is a proximal protection device. These Parodi-type
devices avoid the unprotected crossing of a stenosis with a distal filter or balloon:
b
Consists of a large balloon-tipped guiding catheter for aspiration, which
occludes the common carotid and a smaller coaxial balloon catheter occluding
the external carotid.
180 G. Wyse and K.J. Murphy
b
Reversed flow in the internal carotid artery is induced and the stenosis is
crossed for the first time with protection in place. The aspirate is filtered and
returned to the femoral vein.
Unfortunately not all patients can tolerate reversal of ICA flow.
Intra-procedural Medications
• Atropine 0.5–1.0 mg IV for bradycardia
b
Glycopyrrolate IV (alternate) 0.1 mg IV q 2–3 min
• Heparin 5,000 u IV before crossing lesion
b
1,000 u bolus IV every hour
b
Maintain ACT near 250
• Heparin alternative is direct thrombin inhibition
b
Bivalirudin 0.75 mg/kg IV bolus (about 50 mg)
• GIIbIIIa inhibitors:
b
Abciximab 0.25 mg/kg IV bolus, then 0.125 mg/kg/min ×12 h
b
Inhibits platelet accumulation on newly placed stents
• Local preference dictates choice of procedural medications
Crossing a Stenotic Lesion
• The aim is to cross the lesion in a non-traumatic fashion without causing distal
embolic events.
b
An EPD is carefully advanced
b
A micro-catheter and a micro-wire may give better control for crossing a
tightly narrowed lesion. Once the lesion is crossed the microwire is then
exchanged for an EPD.
b
Pre-dilation may be necessary to allow an EPD or stent to pass through the
stenosis. In addition, many operators like to perform a definitive angioplasty
prior to stent deployment.
b
A wide variety of rapid exchange and over the wire systems are available:
Rapid exchange systems (monorail) allow a single operator to control the
wire and advance the device.
Over the wire devices (OTWs) allow for greater stability and better control.