Optimizing Acute Success in Lower-Extremity CTOs
As the field matures and we approach increasingly complex lesions, technologies such as the CrossPoint catheter will be critical to the technical success of endovascular interventions.
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TEndovascular attempts to recanalize chronic total occlusions of the lower extremities have gained increasing acceptance during the past decade. Although newer technologies have been developed to facilitate lesion crossing, the basic approach remains the same. Virtually all such procedures have relied on a subintimal approach to the distal target vessel. First described in 1990 by Bolia et al,1 this technique involves passing a hydrophilic wire from the proximal aspect of the occlusion, through a subintimal plane, and then re-entering the true lumen distally. The transit of the wire is typically performed with a loop that is nonsteerable and its success is primarily related to various plaque and vessel wall characteristics at the distal most extent of the lesion. Although experience and technique do make an impact, the technical success in crossing lesions in this manner has been reported to be approximately 80%;1-8 leaving a significant number of patients with an aborted or failed endovascular approach. A novel device has been developed to facilitate re-entry into the true lumen distally with a precise combination of intravascular imaging and steerable, directable catheter technology.
CrossPoint TransAccess CATHETER
The CrossPoint TransAccess Catheter facilitates the accurate targeting necessary to safely return a guidewire to the true lumen of a target vessel from a subintimal position. The catheter (Figure 1) contains a precisely constrained needle oriented in a fixed relationship with an integrated intravascular ultrasound (IVUS) guidance system, and facilitates delivery of a 0.014-inch guidewire into the true lumen. The device is compatible with the EndoSonics In-Vision IVUS platform (Volcano Therapeutics, Inc., San Diego, CA), which allows for two-dimensional as well as color Doppler imaging of the target vessel.
SAFE RETURN TECHNIQUE
In lower-extremity cases in which the subintimal approach “dead-ends” in a blind pouch, the subintimal wire is exchanged over a catheter for a 0.014-inch peripheral wire and the wire is advanced to a position 2 cm to 3 cm distal to the known segment of collateral reconstitution. The CrossPoint catheter houses two guidewire lumina. The first is a monorail lumen that simply permits delivery of the catheter to the distal target; the second is an over-the-wire lumen that exits distally through an orifice at the tip of the nitinol hypotube re-entry needle.
After advancing the catheter to the desired vascular segment, the catheter is connected to the IVUS console. The catheter can then be rotated until the true lumen is visualized; a maneuver that is greatly assisted by color-flow imaging. The true lumen is then aligned at the 12-o’clock position on the IVUS monitor screen. The operator can then set the desired depth of needle penetration depending on distance from the target vessel and its diameter. The needle is then fired into the lumen with a simple manual technique, and the 0.014-inch guidewire is advanced through the needle and back into the true lumen. At this point, the needle is withdrawn back into its housing, the monorail wire is removed, and the CrossPoint catheter is backed out over the remaining exchange-length wire. Dilation of the re-entry site with an appropriately sized coronary balloon will then facilitate catheter exchange for a larger wire system, and the intervention can be successfully completed using standard angioplasty and stent techniques.
Subintimal techniques have been utilized in countless vascular beds and, as a result, the potential applications of the CrossPoint technology are numerous. Significant clinical experience has been gained in iliac, femoral, popliteal, and tibial interventions, and new applications are being explored. Aside from the obvious advantage of being able to complete the intended intervention, the ability of the device to minimize the extent of the subintimal path may have importance to the long-term integrity of collateral channels. Also, in iliac and popliteal procedures, the accuracy provided by the catheter may help to protect patients from arterial perforation complications, such as retroperitoneal bleeding and compartment syndromes.
The baseline angiogram shown in Figure 2 reveals a long, chronic occlusion of the left superficial femoral artery with typical geniculate reconstitution at the level of the proximal popliteal artery. A hydrophilic wire was advanced the length of the occlusion using a subintimal approach, but it failed to re-enter the true lumen distally (Figure 3). After advancing a CrossPoint catheter to the distal extent of the subintimal plane, IVUS images were obtained (Figure 4). Using IVUS-guided placement of the re-entry needle, the lumen was accurately and safely accessed (Figure 5). Successful angioplasty and stenting of the occlusion was then performed, and normal distal flow was restored (Figure 6).
THE NEXT FRONTIER:
The ability to safely and predictably move from one vascular plane to another may create other opportunities for treating patients with peripheral arterial occlusive disease. Previous studies by Oesterle et al with the CrossPoint catheter in coronary applications have sought to create bypass channels using a percutaneous approach.9 This background experience makes it possible to conceive of a method to provide for percutaneous bypass of the lower extremities. There is a significant number of patients who are not ideal surgical bypass candidates due to comorbid conditions and a lack of native conduits. There are also patients in whom a subintimal approach is not achievable because of dense vascular calcification or the sequelae of radiation therapy.
The ease with which one can now re-enter the true lumen from an entrapped subintimal position raises the possibility of safely exiting the true lumen proximally. In doing so, one may traverse the length of occlusion by either tunneling in the extravascular space or by entering venous structures adjacent to the occluded artery, and using such conduits as a means of reaching the distal target. Following significant cadaveric and animal modeling of such a technique, three human procedures have now been performed.
The first human percutaneous bypass was performed in a patient who had exhausted his venous conduits undergoing a coronary bypass procedure and a femoral-tibial bypass for limb salvage of the left lower extremity. He had a densely calcified midsuperficial femoral artery occlusion with reconstitution of the popliteal artery and well-preserved distal runoff (Figure 7).
Previous attempts to cross the lesion had failed from both a contralateral and retrograde popliteal approach. Using the CrossPoint catheter, we were able to safely exit the artery above the level of occlusion and re-enter the true lumen distally after tunneling through the extravascular space between with a guidewire and support catheter. Using a pair of Viabahn endoprostheses, we then created a bypass graft of the right superficial femoral artery and restored normal antegrade flow to the popliteal artery and tibial arteries (Figure 8). A feasibility study is underway to evaluate the long-term safety and efficacy of such an approach.
True lumen return in patients with chronic total occlusions that are hampered by subintimal entrapment is now a reliable expectation. As newer antirestenosis technologies such as cryoplasty and drug-eluting stents continue to develop, the validity of pursuing long occlusions with an endovascular approach will gain wider acceptance. As the field matures and we approach increasingly complex lesions, technologies such as the CrossPoint catheter will be critical to the technical success of endovascular interventions. Should the concept of percutaneous bypass prove to be viable in clinical trials, we will bear witness to yet another advance in the field of minimally invasive vascular medicine. n
James D. Joye, DO, is Director, Cardiac Catheterization Labs, El Camino Hospital, Director, Peripheral Vascular Interventions, The Cardiovascular Institute, Mountain View, California. He holds no financial interest in any product or company mentioned herein. Dr. Joye may be reached at (650) 969-8600; firstname.lastname@example.org.
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