Emerging Technologies in Peripheral Vascular Interventions
Recent studies suggest the staggering clinical and economic costs of critical limb ischemia can be reduced by utilizing newer treatment technologies
At the 2008 New Cardiovascular Horizons conference held in New Orleans, we created several visionary sessions titled Ã?Â¢??Treating the Infrapops Like the LADÃ?Â¢?? and Ã?Â¢??Treating PAD Like CAD.Ã?Â¢?? We designed these sessions to focus on the emerging interventional strategies and technologies to treat peripheral arterial disease (PAD) and, especially, critical limb ischemia (CLI), the end-stage of lower extremity PAD.
The costs in morbidity, mortality and dollars are astonishing regarding CLI. In the last two decades, the amputation rate has increased from 19 to 30 per 100,000 persons, with diabetics most at risk. Annual costs of treating CLI in the U.S. could top $20 billion. Follow-up, long-term care and treatment for one homebound amputee is about $49,000 per year compared with $600 per year after limb salvage. A 25 percent reduction of amputations could save more than $3 billion yearly in U.S. healthcare costs. These significant clinical and economic costs are staggering, especially with multiple published experiences appearing over the last three to four years reporting 85 percent to 95 percent limb salvage rates at 12 and 24 months utilizing contemporary peripheral vascular interventional (PVI) technologies.
I believe it is time we Ã?Â¢??treat PAD like CADÃ?Â¢?? and Ã?Â¢??treat infrapops like the LADÃ?Â¢?? with both refined PVI technologies and strategies that will indeed improve outcomes. I will review some of the emerging PVI strategies and technologies I have found clinically promising and have the potential to improve outcomes, especially in CLI.
Vessel imaging and sizing
Multidetector CT angiography (CTA) has been revolutionary in our PVI practice, not only in diagnosing but also in the overall interventional management of the PAD patient. We have found that CTA helps with accurate diagnosis, safer access site identification/management, procedural and device choice planning, as well as understanding vessel morphology and size. It also helps to lessen overall case time, as well as fluoroscopy time and contrast use. CTA identifies unknown anatomic challenges (tortuosity, ulcerative plaques, thrombus, etc.), facilitates PVI follow-up and potentially decreases vascular access complications.
For these reasons, peripheral CTA has totally replaced traditional diagnostic catheter peripheral angiography in our practice and most PVIs today are preceded by CTA. This strategy has optimized preprocedural planning, periprocedural case execution and improved our overall PVI outcomes.
Optimal vessel sizing is a prerequisite for percutaneous coronary intervention (PCI) and minimal lumen diameters are associated with improved short and long-term PCI outcomes. Intravascular ultrasound (IVUS) during PCI is commonplace, reimbursed and associated with improved PCI outcomes. Minimal lumen diameters are rarely mentioned during PVI and peripheral vascular IVUS is not reimbursed, therefore rarely used during PVIs. Little attention is given to precise/optimal vessel sizing during PVI, especially when treating infrapopliteal artery disease. Precise infrapopliteal artery sizing is complex, challenging and, unfortunately, Ã?Â¢??guess workÃ?Â¢?? is often used in PVI device decision-making, certainly much more so than during PCI. It only stands to reason that if we had a simple, cost-effective, accurate technology to precisely size infrapopliteal arteries, outcomes would similarly improve as PCI outcomes have. This is especially important now that we have small profile PVI technologies and dedicated infrapopliteal stents.
As a peripheral IVUS equivalent, we have utilized the Metricath Libra balloon (Neovasc) as a vessel-sizing balloon to precisely measure vessels, especially infrapopliteal arteries, to the hundredth millimeter. The Libra balloon inflates to 1/3 atm and uses a small computerized console to simply and quickly inflate in the reference vessel of interest and calculate the diameter of the vessel. We recently reported our experience in approximately 100 infrapopliteal arteries where about 50 percent of the vessels were oversized or undersized by &amp;gt; 0.50 mm as predicted by the operator before Libra vessel sizing. In our experience, this additional accurate vessel sizing has facilitated our choices of all of our definitive treatments during PVI including atherectomy devices, PTA, specialty balloons and, especially, infrapopliteal stents.
Atherectomy in PAD and CLI
Several atherectomy technologies are now available for PVI, as interventionalists appear to have lowered their threshold for atherectomy in treating PAD. The Spectranetics TURBO Elite line of excimer laser catheters is available in 0.9 mm to 2.5 mm lengths. The Elite catheters have achieved optimal laser efficiency with 30 percent more fibers and an advanced hydrophilic coating. The Booster laser catheter allows directional 360Ã??Ã?Â° rotational laser atherectomy, which can improve the athero- and thrombo-ablation capacity of the laser by increasing the atherectomy diameter by 50 percent to 60 percent. We have found laser therapy to be especially helpful in long, diffuse, minimally calcified atherosclerotic disease, including chronic total occlusions (CTOs), along with in-stent restenosis and any lesion harboring a moderate to large thrombus burden.
The SilverHawk plaque excisional (ev3) line of treatment includes the RockHawk, which allows for atherectomy in more calcified vessels. Likewise, a lower profile MiniHawk will allow plaque excision in vessels between 1.5 mm to 2 mm. The CSI Diamondback 360Ã??Ã?Â° orbital atherectomy device is now available and provides excellent atherectomy in highly calcified vessels. This device uses a series of diamond-coated crowns that spin at up to 200,000 rpms to Ã?Â¢??sandÃ?Â¢?? or perform differential plaque atherectomy. The CSI system is particularly useful in patients with both localized and diffused highly calcified lesions. Pathway Medical Technologies recently released the Jetstream atherectomy catheter, which provides simultaneous atherectomy with aspiration to remove thrombotic, atherosclerotic and atherectomized debris. Atherectomy is accomplished utilizing a unique proprietary device tip with small cutting blades. There has been limited U.S. experience with this device, but promising results have been reported from Europe.
One of the significant advances in the last five years with PVI technology has occurred with the development of multiple specialty balloons designed for PVI. These include the PolarCath (Boston Scientific), AngioSculpt (AngioScore), VascuTRAK2 system (IDev), traditional Cutting Balloon (Boston Scientific), drug-eluting balloons and the release of several long, low-profile PTA balloons specifically designed for CLI and treating infrapopliteal arteries (Invatec). Several reports describe adequate early and mid-term results in treating CLI with PTA only. This group of specialty balloons has been developed and advocated to improve upon the PTA-only results.
The PolarCath uses -10Ã??Ã?Â°C cryotherapy and theoretically apoptosis to decrease intimal hyperplasia and dissections. Multicenter data have not proven statistical significance versus PTA, but we continue to find cryotherapy useful in recurrent lesions, discrete lesions, in-stent restenosis and vessels in which avoiding a stent is important such as the common femoral and infrapopliteal arteries. The Cutting Balloon utilizes straight stainless steel blades and has data supporting its benefits in treating PAD and CLI. We have found this technology to be useful in larger vessels with discrete refractory lesions to other PTA technologies. Cost, profile and less deliverability are somewhat of a disadvantage, but we continue to find usefulness, especially in the larger vessels.
The AngioSculpt is a lower-profile cutting-balloon technology utilizing multiple nitinol-based cutting blades placed on the balloon shaft in a circumferential fashion. Supportive data are also available and this technology is easily delivered in vessels as small as 2 mm. We have found it especially useful in localized non- or minimally-calcified discreet superficial femoral arteries, infrapopliteal arteries or graft anastomotic lesions. A limiting factor with this technology is its maximum length at 40 cm.
The VascuTRAK2 is a recently commercially available PTA system that is highly deliverable and available in diameters from 2 mm to 6 mm and lengths from 20 mm up to 200 mm. A 300 mm system will soon be available. This balloon is delivered by two wires along the longitudinal axis, which allows for maximal Ã?Â¢??focal pressureÃ?Â¢?? PTA, or FPP. Slower balloon inflation is advocated to allow for optimal FPP, which, in concept, may decrease intimal hyperplasia and decrease the incidence and severity of intimal hyperplasia. Our initial results have been excellent, especially in delivering this long catheter-based technology into the infrapopliteal vessels down to the ankle that will allow a single inflation to cover the entire infrapopliteal and, occasionally, popliteal artery systems.
We will soon embark upon treatments in the U.S. with drug-eluting balloons. The European-based THUNDER Trial was published comparing a paclitaxel-coated balloon with PTA. Encouraging results were reported and a similar balloon should be available in the U.S. within the next 12 months. An interesting balloon-based technology combined with radiofrequency (RF) and thermal energy is being developed by Minnow Medical, but is not commercially available. This balloon-based technology will deliver a series of RF microfilaments arranged on the balloon that can be individually calibrated and controlled. This potentially would afford highly selective delivery of RF thermal energy within the target vessel in hopes to deliver positive tract modification and improve non-stent results.
In summary, there are multiple emerging PVI strategies and technologies available today that are increasingly being performed in the contemporary cath lab with the potential to significantly improve PVI outcomes, even in the most complex cases.
Dr. Allie is director of Louisiana Cardiovascular and Limb Salvage Center, APMC, Lafayette, La.