By Jeffrey P Carpenter
Stroke is a devastating complication associated with thoracic endovascular aneurysm repair (TEVAR) and transcatheter aortic valve implantation (TAVI). The majority of these events take place within 24 hours of the procedure and are embolic in nature. Embolic showers result from the manipulation of large delivery systems, inserted remotely, traversing the aortic arch and disturbing calcific and atherosclerotic lesions in the aorta or heart.
Stroke is the most common major complication after TAVI. With early generation devices, clinically evident stroke was noted in up to 11% of patients. With TEVAR, the incidence of stroke rises in accordance with the proximity of the device placement to the carotid arteries. Very proximal device placement can be associated with a clinical stroke rate as high as 25%.
With recent improvements in TAVI device delivery systems, the rate of clinical stroke has been noted to decrease. A recent meta-analysis yielded a major stroke rate of 2.8%, which is comparable to that observed for traditional surgical aortic valve repair. Even with the new generation of valves, however, in studies employing routine detailed examination by neurologists, clinically evident neurological deficits can be identified in 15–28% of patients in association with new findings of brain injury on imaging studies.
In addition to clinical stroke, much attention is now being paid to the danger of “silent stroke”, the appearance of new lesions on diffusion weighted MRI (DWMRI) studies, which are not clinically apparent as neurological deficits. These findings are observed in 68–100% of patients and are associated with a 2–4 fold increase in stroke risk for later events, cognitive decline, dementia and a >3 fold increase in mortality.
Given these concerns, embolic protection devices have been developed to mitigate the risk of stroke and embolic lesions associated with these procedures. Three such devices have achieved CE marking: the Edwards Lifesciences’ Embrella, Claret Medical’s Sentinel and Keystone Heart’s TriGuard. Two of these devices rely upon deflection of embolic particles away from the cerebrovascular circulation (Embrella and TriGuard) whereas the Sentinel device functions as a filter/collection type embolic protection device as is familiar from carotid angioplasty applications.
Edwards’ Embrella is a 6F radial insertion device that covers the innominate and left common carotid origins in the aortic arch with a porous polyurethane membrane mounted on a nitinol wire frame, deflecting embolic particles downstream. The device is inserted through a 6F sheath, the tip of which is positioned at the innominate artery origin. As the device emerges from the sheath into the aortic arch, it takes its preformed shape and hugs the greater curve of the aortic arch. It does not interfere with passage of catheters and wires during TEVAR/TAVI procedures. At the completion of the procedure, the device is retracted back into the sheath for removal.
In clinical studies, the Embrella device has been demonstrated to reduce the number and volume of embolic lesions detected by DWMRI.
Keystone Heart TriGuard is also a deflection device, but it is inserted via femoral access through a 9F sheath, guided into the proximal thoracic aorta. The device employs a nitinol wire frame and porous membrane covering which covers the great vessels. The device is attached to a catheter that emerges from the sheath and is pushed against the greater curve of the arch by a contralateral stabiliser bar which pushes off of the lesser curvature. An additional stabiliser bar is deployed into the innominate artery to assist in maintenance of position. The index TAVI/TEVAR procedure is performed by working through the arch stabiliser bar that spans the aorta.
In clinical studies (DEFLECT III), the device has been demonstrated to be safe and to cover all three great vessels in 89% of cases. Imaging demonstrated reduced volume of lesions on DWMRI. A randomised controlled trial (REFLECT) has been designed to further study the efficacy of this device and will include imaging, neurological and neurocognitive assessments.
Claret Medical’s Sentinel is a dual independent filter device, inserted via a 6F radial access. Filters are placed in the innominate and left common carotid arteries via a single catheter, and are re-sheathed at the conclusion of the procedure in a manner similar to that performed with currently employed carotid embolic protection devices. The filters remain out of the path of catheters and wires involved in the index TAVI/TEVAR procedure.
Debris is found in the filters in 88% of cases. The device has been demonstrated in a clinical study (CLEAN-TAVI) to reduce the number and volume of new lesions on DWMRI.
None of these devices has been demonstrated to reduce the clinical stroke rate. All of these devices have been demonstrated to reduce the number and volume of ischaemic lesions seen on DWMRI. The latter endpoint is much easier to achieve, given the relatively low rate of clinically evident stroke and the resulting requirement for very large numbers of randomised patients to demonstrate efficacy for a clinical stroke endpoint. The place of embolic protection devices in TAVI and TEVAR remains unclear, but data are accumulating that they can decrease ischaemic brain injury, which may have long-term neurocognitive benefits. Further large-scale studies are necessary to determine their ultimate utility and place in clinical practice.
Jeffrey P Carpenter is professor and chairman, Department of Surgery, Cooper Medical School of Rowan University and vice president of Surgical Services Cooper University Health Care, Camden, USA