Benefits of the Novel Transcarotid Artery Revascularization (TCAR) Technique for the Treatment of Carotid Artery Stenosis
By: Devorah Chasen
Cerebrovascular diseases consist of a group of cerebral blood vessel disorders which affect blood flow to the brain. Consequences of cerebrovascular disease include cell death and stroke due to cerebral hypoxia. Unfortunately, stroke is the fifth leading cause of death in the United States and the number one leading cause of disability. Carotid Artery Stenosis (CAS) is one of the most common cerebrovascular diseases that often leads to ischemic stroke. CAS is typically caused by the buildup of atherosclerotic plaque, which consists of fatty substances, cholesterol, cellular waste products, calcium, and fibrin, along the inner lining of the carotid artery. As the plaque grows, it protrudes into the lumen of the artery causing stenosis; subsequently, the plaque may rupture and promote the formation of a blood clot that further occludes the artery. Medical management is effective at controlling the effects of Carotid Artery Stenosis and preventing future strokes. However, in certain cases of severe stenosis, surgical intervention is often recommended. The Carotid Endarterectomy (CEA) was the standard surgical intervention for revascularization for almost seventy years. Until recently, no other intervention compared to it in its effectiveness and safety. However, with the introduction of the Transcarotid Arterial Revascularization (TCAR) technique in 2015, a new standard for interventional cardiology was born. Studies over the past seven years have shown promising results for this novel procedure, which combines the methods of traditional stenting with a blood flow reversal neuroprotection system to create a quick, efficient, and minimally invasive revascularization option. Future studies hope to further prove its effectiveness as it becomes a more mainstream procedure to treat CAS.
Cerebrovascular disease is a group of disorders characterized by bleeding in or restricted blood flow to a part of the brain that causes temporary or permanent effects and involves one or more cerebral blood vessel.1 It is essential that the heart pumps enough blood to the brain so that oxygen and important nutrients can also be transported to the brain and circulated throughout. When cerebral ischemia occurs, or blood flow to the brain is reduced or restricted, it puts the patient at an increased risk of developing a stroke.
Possible causes of ischemia to areas of the brain are due to vessel stenosis (narrowing), thrombosis (blood clot formation), embolism (foreign clot or debris blockage), or hemorrhage (rupture).1 Carotid artery stenosis, also known as carotid artery disease, is one of the primary forms of cerebrovascular disease.1 The carotid arteries, along with the vertebral arteries, are the main vessels that supply the brain with oxygen and essential nutrients.2 Therefore, damage to the carotid arteries, such as stenosis, can cause cerebral hypoxia, or a decrease of oxygen supply to the brain, which leads to the death of the affected tissue and an ischemic stroke. Unfortunately, in the United States, strokes are the fifth leading cause of death, and about 3% of adults will experience a stroke in their lifetime.3 Strokes are the leading cause of long-term disability, as those who suffer a stroke are often left with reduced mobility. Furthermore, one-third of people who suffer a stroke are left permanently disabled.
Carotid Artery Stenosis
Carotid artery stenosis is almost always caused by atherosclerosis, which is the buildup of fatty substances, cholesterol, cellular waste products, calcium, and fibrin into the plaque along the inner lining of the carotid artery, the intima layer. As seen in Figure 1, the carotid artery is made up of three layers: the intima, the smooth innermost layer; the media, the muscular middle layer; and the adventitia, the protective outer layer. As the buildup of plaque increases, the lumen of the artery narrows (stenosis), and the walls of the artery become thickened and stiff. Through various mechanisms, the atherosclerotic plaque can cause significant stenosis over time, which may lead to an ischemic stroke. Therefore, it is important to be proactive at managing risk factors even from a young age, which is when the atherosclerotic plaque begins building up.4
Figure 1. Layers of the Carotid Artery19
Mechanism of Stroke Due to Atherosclerosis
As a fibrous plaque grows, it accumulates more fatty lipids and cholesterol. Once the plaque has reached a certain size, it begins to protrude into the lumen of the artery. This causes partial occlusion of the vessel, or stenosis, and it may reduce the amount of blood that can flow through the artery.5
Thrombosis and embolization, which are other complications from atherosclerosis that result in blood clots, can occur and contribute to a carotid stenosis-related stroke. As the atherosclerotic plaque grows and becomes unstable , it also becomes increasingly likely to rupture.6 When plaque ruptures, the cholesterol and collagen become exposed, and the body recognizes this occurrence as an injury. This injury stimulates the release of pro-coagulants and activates thrombosis or the clotting cascade to create a blood clot (Figure 2).5 Occlusion of any portion of the carotid artery, whether from a thrombus or embolized thrombus, may result in cell death and subsequent ischemic stroke.
Figure 2. Aseptic loosening in patient with hyperparathyroidism.5
Clinical Presentation of Carotid Artery Stenosis
Patients can have symptomatic or asymptomatic carotid artery stenosis. Symptomatic carotid artery disease is defined as neurologic symptoms that are sudden in onset and ipsilateral to significant carotid atherosclerosis. It also includes a TIA, characterized by focal neurological dysfunction or transient monocular blindness, a minor, non-disabling ischemic stroke).7 In addition, in order to be considered “symptomatic,” a patient must have had carotid symptoms within the past six months.8 Management of symptomatic carotid artery stenosis is important because atherosclerotic plaques are usually embologic and pose an increased risk of causing another stroke.
Asymptomatic carotid artery stenosis refers to stenosis of the carotid artery without accompanying neurological symptoms or stroke. Many randomized and controlled studies have shown that there is only a small risk of stroke (1-2%) in asymptomatic cases of carotid stenosis for mild (<50% stenosis) or moderate (50-69% stenosis). Because of these findings, medical management and longitudinal monitoring is typically the recommended course of treatment for patients with asymptomatic carotid stenosis. However, surgical intervention is sometimes recommended in cases of asymptomatic patients with a greater degree of stenosis (>80% stenosis).9
The risk factors for carotid artery stenosis can be divided into two categories: non-modifiable and modifiable risk factors. Non-modifiable risk factors are those that cannot be controlled by a person, like age, sex, race and ethnicity, and family history. Modifiable risk factors are those that can be controlled by a person to minimize the risk associated with them and include hypertension, smoking, high cholesterol, hyperglycemia, diet, weight, alcohol consumption, and drug use. Oftentimes, nonmodifiable risk factors are linked to or exacerbated because of modifiable risk factors.10
Many factors impact treatment options for carotid artery stenosis, and it is important to balance the risk of stroke vs. risk of intervention for the patient. Many forms of carotid artery stenosis can be managed with medical therapies so that the disease won’t progress to the point of risking a stroke. Common medications given are antihypertensives to reduce blood pressure, statins to control LDL cholesterol levels, and antiplatelets to prevent clot formation. Carotid revascularization is also an option for certain individuals who could benefit from additional interventional help. These types of surgical interventions are oftentimes used for more extreme cases of stenosis but have been effective in preventing strokes or other symptoms of carotid artery stenosis.11
There are three main surgical procedures to treat carotid artery stenosis that have been instituted over the past seventy years: the carotid endarterectomy (CEA), transfemoral carotid artery stenting (TFCAS), and transcarotid artery revascularization (TCAR).12
Carotid Endarterectomy (CEA)
The carotid endarterectomy (CEA) has been the gold standard for carotid revascularization procedures since the mid-1900s. Many randomized controlled trials show that this method is safe and effective at minimizing the risk of stroke in symptomatic patients with moderate to severe stenosis.13 During the procedure, found in Figure 3, the surgeon performs an arteriotomy, in which he makes an incision in the neck and carotid artery at the carotid bifurcation or location of the plaque. The surgeon then removes the plaque, and the artery is repaired using sutures or a patch which widens the lumen of the artery. While this method is invasive, it produces promising results for those affected by moderate to severe symptomatic carotid artery stenosis.12
Figure 3. Carotid Endarterectomy (CEA) Procedure21
Transfemoral Carotid Artery Stenting (TFCAS)
The transfemoral carotid artery stenting (TFCAS) intervention was introduced in 1996 as an alternative, minimally invasive technique to the CEA procedure.14 During the procedure, a sheath and catheter are placed in the femoral artery in the groin followed by a carotid stent. The stent is advanced until it reaches the carotid artery and then expanded. An angioplasty balloon is used to ensure the stent is positioned properly against the arterial wall and stabilizes the plaque. The surgeon will use an embolic protection device to filter and catch any debris that may break off during the procedure, and intraoperative imaging and contrast material is used to visualize the vessels.14
Many studies have been conducted to compare the outcomes of CEA vs. TFCAS. The Carotid Revascularization Endarterectomy Versus Stenting Trial (CREST) determined that composite outcomes (stroke/death/MI) are similar between the two procedures. Unfortunately, the CREST trial also found that the TFCAS method has an increased risk of 30-day perioperative stroke compared to the CEA, likely due to aortic arch manipulation resulting in embolization. In fact, a meta-analysis done in 2012 found that the 30-day risk of perioperative stroke or death was 8.2% for TFCAS vs. 5.0% for CEA.14 Because the CEA is still the ideal method of choice for revascularization, the TFCAS is typically only used when the patient is at high risk for the CEA due to it being an open surgery.
Transcarotid Artery Revascularization (TCAR)
A novel stenting method was introduced in 2015 called the transcarotid artery revascularization (TCAR) procedure. It combines carotid bifurcation stenting with an advanced reversal of blood flow, so the risk of plaque embolization is minimized. In preparation for the procedure, patients are prescribed the DAPT (dual antiplatelet) regimen statins. During the procedure, the surgeon makes a small incision (2 to 4 cm) just above the collarbone ipsilateral to the atherosclerotic plaque. A sheath is placed inside the carotid artery as well as a neuroprotection system. This system provides CEA-like neuroprotection for the patient through high-rate temporary flow reversal; any blood flowing to the brain is reversed and redirected outside the body where it gets filtered through a device before it is returned to the body via a sheath in the femoral vein (Figure 4).
Figure 4. TCAR Neuroprotection System Providing Flow Reversal22
Once the flow reversal system is in place, a stent is placed inside the carotid artery to stabilize the plaque and prevent future stroke (Figure 5) and fluoroscopy is used to monitor the procedure.15
Figure 5. TCAR Stent Insertion23
The primary study conducted evaluating the TCAR procedure is the Safety and Efficacy Study for Reverse Flow Used During Carotid Artery Stenting Procedure (ROADSTER). The initial results of the TCAR procedure as described by the ROADSTER multicenter trial show that TCAR with ENROUTE neuroprotection system is a safe and effective method for preventing a stroke. The 30-day perioperative stroke rate was only 1.4% in surgical high-risk patients, which is lower than in patients who had the TFCAS procedure. Additionally, 1.4% of patients died, and 0.7% of patients suffered an MI, thus resulting in a 30-day stroke/death/MI rate of 3.5%.16 The ROADSTER 2 trial had a 30-day stroke/death/MI rate of just 1.7%.17 These low rates of stroke, death, and MI with the TCAR are most likely due to avoidance of aortic arch manipulation and the advanced neuroprotection system. With TFCAS, it is often difficult to avoid aortic arch manipulation which results in embolization and subsequent stroke, death, or MI. With the TCAR procedure, the flow reversal system also protects against embolization by plaque that breaks free during the procedure.16
The results of TCAR were also comparable to CEA results, as the Transcarotid Artery Revascularization Surveillance Project showed no significant differences in 30-day perioperative stroke or death outcomes between TCAR and CEA. In fact, the results for the TCAR procedure were obtained using a high-risk patient population, which shows the similar effectiveness of the TCAR compared to CEA. The main difference in outcomes between the TCAR and CEA was the significantly lower rates of cranial nerve damage with the TCAR procedure. This is because there is only one vulnerable cranial nerve that can be injured in the TCAR procedure vs. four in the CEA.18 Additionally, positive results were obtained from surgeons with little to no experience in the TCAR procedure, which speaks to the safety of the procedure.17 There is also reduced operative time with the TCAR procedure, which is beneficial to both the surgeon and patient. The preliminary results of TCAR studies are promising because no other method to date has had comparative results in outcomes to CEA. Because of the introduction of the TCAR and emerging data on its effectiveness, it is likely that the TCAR will become the standard of care in the future for revascularization.14
Carotid artery stenosis and associated strokes have been of concern as they are one of the leading causes of death and disability worldwide. Fortunately, there are many types of treatments to manage carotid artery stenosis. Medical treatment and surgical intervention have shown promising results, and the introduction of the TCAR procedure is a significant contribution to the field of vascular surgery. The implementation of this new minimally invasive procedure has already benefited many patients and will hopefully continue to do so in the future.
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