2D Perfusion Angiography: A Useful Tool for CLI Treatment
Does this method have the potential to help predict clinical outcome and reduce revascularization time?
Endovascular therapy has become the first-choice option for patients with critical limb ischemia (CLI). Development of dedicated guidewires, crossing catheters, angioplasty balloons, and the use of distal access has made it possible to treat complex below-the-knee lesions with a high technical success rate. Most interventionists adopt an approach that aims for direct revascularization according to the angiosome concept. However, this concept remains controversial, and two recent studies came to equivocal conclusions.1,2 For this reason, indirect revascularization may have a place from a theoretical perspective, but perhaps even more so from a practical point of view, because it is not always possible to achieve direct revascularization.
Although outcomes may improve as more vessels are opened, extensive three-vessel revascularization may be very time consuming and induce higher cost. In addition, restoring the macrocirculation may not be sufficient, especially in diabetic patients, in whom microcirculatory problems play a significant role.3 Currently, there are no methods for periprocedurally determining whether partial (one- or two-vessel) recanalization will be sufficient to resolve rest pain or achieve wound healing. Having the ability to predict the clinical outcome in the interventional suite could potentially reduce procedure time and associated contrast medium and radiation exposure.
TWO-DIMENSIONAL PERFUSION ANGIOGRAPHY
Two-dimensional (2D) perfusion angiography is used in the assessment of the penumbra and has been applied in evaluating foot perfusion in CLI patients.4 The technique is based on standard digital subtraction angiography (DSA), with an injection rate of 3 mL/sec of 12 mL of (1:1 diluted) iodinated contrast medium (iodine 150 mg/mL) and a frame rate of three images/sec. Two-dimensional perfusion images are automatically reconstructed with postprocessing software on a dedicated workstation (Allura Xper FD20 and Interventional Workspot, Philips Medical Systems).
Images are obtained before and after the revascularization procedure. Care should be taken to fully immobilize the foot. The reconstructed images can be evaluated for arrival time, time to peak, wash-in rate, width, area under the curve, and mean transit time. An operator-defined, freehand region of interest can be selected to determine a time-to-density curve, which is typically done at the level of the ulcer/wound.
A 77-year-old woman was referred for necrosis of the fourth toe of the right foot. Duplex ultrasound revealed a hemodynamically significant stenosis of the popliteal artery and suspicion of below-the-knee disease (the ankle-brachial index was not measurable). The patient was scheduled for an outpatient endovascular procedure.
After an antegrade puncture of the right common femoral artery, a 4-F introducer sheath (Ultimum EV Hemostasis Introducer, St. Jude Medical) was placed. Diagnostic angiography confirmed the presence of a 75% stenosis of the P2 segment of the popliteal artery as well as multiple stenoses of the anterior tibial artery (Figure 1A). The tibioperoneal trunk was patent, but the posterior tibial artery was occluded. The fibular artery had an occlusion at the level of the mid-calf. On the level of the foot, a patent dorsalis pedis artery was seen (Figure 1B). No filling of the plantar arteries was noted.
Angioplasty of the popliteal artery stenosis was performed using a 5- X 40-mm angioplasty balloon (Pacific Plus, Medtronic, Inc.). Subsequently, the stenoses of the anterior tibial artery were crossed with a 0.014-inch guidewire (Glidewire Advantage, Terumo Interventional Systems), the proximal stenosis was dilated with a 2.5- X 40-mm angioplasty balloon (Tercross, Terumo Interventional Systems), and the distal segment was dilated with a 2- X 200-mm balloon (Armada 14, Abbott Vascular). Control angiography showed an improvement of the flow toward the foot (Figure 1C and 1D). The 2D perfusion angiography, reconstructed from the lateral DSA of the foot, showed a significant improvement in arrival time and perfusion of the forefoot (Figures 2 and 3). Further recanalization of the posterior tibial artery and fibular artery was deemed unnecessary. The clinical course was uneventful, with progressive healing of the ulcer.
Endovascular treatment of CLI has been shown to be effective in preventing amputation.5 The goal of revascularization is not only to recanalize the vessels to the foot, but also to obtain a better wound perfusion. One of the problems interventionists face during the procedure is determining when an adequate level of revascularization has been achieved. To choose the optimal strategy, oftentimes the angiosome concept is used, but there are variations in infrapopliteal vessel anatomy, the presence of collateral connections, and changes in microcirculation that are not related to angiosomes. Therefore, the advantage of direct revascularization versus indirect flow restoration may not be evident in all cases.
The presence of previously absent or improvement of wound blush after endovascular therapy is associated with higher skin perfusion pressure and can be a predictor of limb salvage in patients with CLI.6 The wound blush concept is independent from the angiosome concept but is only a qualitative parameter; a method to quantify the blush is not yet available. The same drawback applies to current, commercially available 2D perfusion angiography, but it is likely that quantification of the perfusion will be possible in the near future.4 Other methods can evaluate local perfusion, such as indocyanine green fluorescence imaging and tissue oxygen saturation foot mapping.7-9 These methods have been demonstrated to be reliable, but all have the drawback of not being easily implemented in the interventional suite with the patient still on the angiographic table completely draped.
The initial experience with 2D perfusion angiography in the endovascular treatment of patients with CLI is promising. The technique requires additional software acquisition but does not induce additional radiation exposure or an increase in contrast dose.
See 2D Perfusion in Motion
Marco Manzi, MD, is with the Interventional Radiology Unit, Foot & Ankle Clinic, Abano Terme Clinic, in Abano Terme, Italy. He has stated that he has no financial interest related to any of the products or companies mentioned herein. He can be reached at email@example.com.
Jos C. van den Berg, MD, PhD, is Head of Service of Interventional Radiology, Ospedale Regionale di Lugano, cede Civico, Lugano, Switzerland, and Associate Professor of Radiology, University of Bern, Switzerland. He has stated that he has no financial interests related to this article.
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