Cerebral protection system
Cerebral protection systems are used in the catheter-supported treatment of narrowed carotid arteries ( stent angioplasty of the carotid artery) in order to prevent atherosclerotic vascular wall deposits from being carried over into the brain (cerebral embolism) with neurological deficits during the procedure. Systems are available for this purpose that filter (distal filter protection) or interrupt (distal and proximal balloon occlusion) the blood flow to the brain.
Distal filter protection
First, a guiding sheath or a guiding catheter is advanced from the artery of a leg ( arteria femoralis ) of an arm ( arteria brachialis ) or a wrist (arteria radialis) to the carotid artery ( common carotid artery , ACC). The filter system is placed about 4 cm behind the carotid stenosis via a fine guide wire using a thin-lumen application catheter and unfolded by withdrawing the same. The filter consists either of a basket-shaped mesh made of nitinol wire or of a nitinol framework coated with a polyurethane membrane with a pore size between 100 and 150 μm. The balloon expansion of the carotid stenosis and the implantation of a self-expanding stent then take place one after the other via the guide wire. This is usually modeled onto the vessel wall with a 5-6 mm x 20-30 mm balloon. Finally, the filter is recovered with an export catheter and the treatment result is documented angiographically.
Distal balloon occlusion
Instead of a filter, the guide wire contains a low-pressure balloon with a diameter of approx. 6 mm, which is carefully filled with a mixture of X-ray contrast medium and physiological saline solution behind (distal) the carotid stenosis via the lumen of the wire. This obstructs the internal carotid artery (ACI) and prevents blood flow to the brain on the same side. Only then can the stent angioplasty be performed. The blood column below the occlusion balloon is then sucked out several times and injected through a microfilter. If thromboembolic material is no longer detectable, the flow blockade is lifted and the protection system is removed. In contrast to filter protection, angiographic control recordings are not possible during the flow blockage, but are carried out comparatively before and after the procedure.
Proximal balloon occlusion with flow arrest
A protection set with 2 low-pressure balloons is brought into the carotid artery. The first balloon is deployed in the external carotid artery (ACE) to prevent retrograde flow into the internal carotid artery. The second occlusion balloon blocks the antegrade flow into the internal carotid artery in the common carotid artery. The complete blockage of blood flow is documented with a few ml of contrast medium. Then the carotid stenosis can be passed through the working channel of the protection kit with a guide wire and the stent angioplasty can be performed. As with distal balloon occlusion, blood is aspirated after angioplasty until no more embolic particles can be detected. At the end of the procedure, the flow blockage is lifted, the protection system is removed and the success of the therapy is shown angiographically.
Proximal balloon occlusion with flow reversal
A flow reversal in the internal carotid artery to be treated is achieved by creating an additional arteriovenous shunt between the protection equipment and the femoral vein. The blood, which may contain thromboembolic plaque material (debris) released by the stent angioplasty, is continuously diverted via the protection system and, after being filtered through an extracorporeal microfilter (pore size approx. 180 μm), returned to the bloodstream via the arteriovenous connection to the femoral vein.
Advantages and disadvantages
In everyday clinical practice, the filter systems are preferred because of their easy handling. Both distal protection systems have the decisive disadvantage that they have to pass through the stenosis. A cerebral embolism can be triggered by the protection system, especially in the case of a very high degree of very vulnerable stenosis with thrombus appendage. On the other hand, with the more complex proximal balloon occlusion, there is complete embolic protection even before the first wire passage. In the case of an incomplete cerebral arterial circle, the balloon occlusion systems are generally not tolerated by the patient; they are contraindicated in the case of occlusion of the contralateral carotid artery. Large prospective randomized clinical studies that prove the advantage of a specific protection system are not yet available.
Clinical Evidence
Although carotid tangioplasties are routinely performed around the world with cerebral protection systems, their benefit has not yet been scientifically proven, due to the lack of a randomized comparative study on stent angioplasty without cerebral protection. Large therapy registers (carotid PTA register of the Arbeitsgemeinschaft Leitende Kardiologische Krankenhausärzte e.V., Global Carotid Artery Stent Registry), a meta-analysis of 134 published studies on carotid tangioplasty with and without embolic protection, as well as numerous reports from larger therapy centers showed a lower death and stroke rate Using an embolic protection system. The lead-in phase of the CREST study (Carotid Revascularization Endarterectomy versus Stenting Trial) also showed a tendency towards advantages of carotid tentangioplasty with cerebral protection. In contrast, the Pro-CAS register managed by the German Radiological Society and the German Angiological Society, pooled data from the EVA-3S study (Endarterectomy versus Angioplasty in Patients with Symptomatic Severe Carotid Stenosis Trial) and the SPACE study (European Stent-Supported Percutaneous Angioplasty of the Carotid Artery versus Endarterectomy Trial) and subgroup analyzes of the ICSS study (International Carotid Stent Study) did not show any significant difference. The use of cerebral protection systems in the endovascular treatment of high-grade carotid stenoses is still the subject of controversy.
literature
- Rainer Knur: Cerebral Protection in Carotid Tangioplasty: Technique, Use and Necessity. In: cardiologist. Volume 3, 2009, pp. 220-227, doi: 10.1007 / s12181-009-0169-2 .
- Rainer Knur: Technique and clinical evidence of neuroprotection in carotid artery stenting. In: Vasa. Volume 43, No. 2, 2014, pp. 100-112, doi: 10.1024 / 0301-1526 / a000336 .
- Rainer Knur: Carotid artery stenting: A systematic review of randomized clinical trials. In: Vasa. Volume 38, No. 4, 2009, pp. 281-291, doi: 10.1024 / 0301-1526.38.4.281 .
