Endovascular Therapies in Peripheral Arterial Disease




IN THE BEGINNING



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In 1929, a 25-year-old intern named Werner Forssman was dissatisfied with the available methods of evaluating cardiac function at his hospital in Berlin. His appeals to his supervising physicians for permission to test a cardiac catheterization technique he had envisioned were flatly denied. Secretly, Forssman enlisted the help of a nurse and conducted the experiment on himself. Threading a rubber catheter through a vein in his left arm to the level of his heart and injecting dye, Forssman completed the first successful cardiac catheterization. Upon discovery of his experiment, he was promptly fired from his job and ostracized by the medical community. It was not until 27 years later, in 1956, that Forssman was awarded the Nobel Prize in physiology and medicine for his achievement.



Several other great medical inventions made their debut around the time Forssman received the Nobel Prize. John Gibbons revealed his heart–lung machine, and Michael Debaky successfully performed open heart surgery and created the artificial arterial conduit Dacron. The field of cardiovascular surgery was at the forefront of new medical technologies. During the same period, when the medical community was enchanted with open surgery, minimally invasive techniques were quietly being developed.



In 1953, a 32-year-old Swedish radiologist named Sven Seldinger developed a percutaneous technique in which a wire, threaded through a needle into a vessel, is exchanged for a catheter. The “Seldinger technique” is ubiquitous in medicine today and makes a surgical incision unnecessary for catheter-based therapies. Another important, although less well-known, contribution of Seldinger’s was the design of a U-shaped catheter tip for selective catheterizations. By placing a wire through a straight catheter and bending both together over the steam of a coffee pot before cooling them rapidly, Seldinger fabricated a bent tipped catheter that could be straightened by advancing the wire through the lumen. This model, common today, makes selective arterial catheterization feasible for physicians of average dexterity. The Seldinger technique was widely practiced in Sweden soon after its description, but it took more than a decade and the endorsement by radiologist Charles Dotter from the University Of Oregon Health Sciences for the technique to catch on in the United States.




A SWITCH TO INTERVENTIONS



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In 1958, Mason Sones, a pediatric cardiologist at the Cleveland Clinic, made a landmark discovery. At that time, the current practice for obtaining coronary angiograms involved a large-volume contrast injection into the aortic arch to opacify the coronary arteries. It was thought that selectively coronary cannulation would cause fatal arrhythmias. While attempting a left ventricular image, Sones inadvertently cannulated the right coronary and produced a selective arteriogram with 30 cc of Hypaque contrast. Initially horrified, when the patient suffered only a transient rhythm disturbance and recovered quickly, Sones realized that selective coronary angiography could be tolerated. In 1962, he published his technique of slowly hand injecting 3 to 6 cc of contrast and using an image intensifier to obtain high-quality coronary angiograms with high success and minimal contrast.



The ability to selectively cannulate vessels along with improvements in fluoroscopy and the development of rapid film changers and power injectors greatly improved the quality of arteriographic images. Using the Seldinger technique and shaped catheters, it became possible to accurately visualize almost any named vessel without making an incision. As the quality of images improved, radiologists became increasingly valuable diagnosticians to the medical community and their prestige grew accordingly.



In 1964, the same year Debakey successfully completed the world’s first coronary artery bypass graft, Charles Dotter was the first nonsurgeon to cross into the realm of arterial remodeling. He used catheters of increasing diameter to open the iliac artery of an 82-year-old woman with an ischemic foot to complete the first percutaneous arterial angioplasty.1 Time Life Magazine chronicled this achievement with a series of vivid intraoperative photographs in August 1964. Dotter’s toothy grin and elated facial expressions shown in these pictures earned him the nickname “Crazy Charlie.” Dotter built his own guidewires using anything from a guitar string to a Volkswagon speedometer cable and catheters using Teflon tubing and a blow torch. He is considered by many to be the founding father of interventional radiology.



Europeans coined the phrase “dottering” to describe the opening of a stenosis by passing serial coaxial dilating catheters of increasing diameter. Dotter’s technique was the method of choice worldwide until the 1970s. There were limitations to this method, including a limitation to small-diameter lesions, because the largest dilating catheter had to fit through the access arteriotomy and the fact that the stiff catheters could not be maneuvered to branch vessels. Even in his original publication, Dotter foresaw the development of radially expanding dialating catheters.



A collaborative effort between Dotter, Forssman, and others to develop a balloon dialating catheter became a primary focus of their efforts. Their models were based on the concept of an inflatable balloon-tipped catheter pioneered by a cardiovascular surgeon, Thomas Fogarty, nearly a decade earlier. Fogarty, using his boyhood Fly-tying kit and the fingertip of a latex glove, had designed an inflatable balloon-tipped catheter capable of removing intravascular thrombus by passing it through an open artery. Fogarty’s balloon catheter made its debut as an embolectomy catheter but had been used for balloon angioplasty as early as 1965, making it the first successful technology of this type.



Early models of angioplasty balloons by Dotter and Forssman were “caged” or “corseted” balloons made of Teflon. The outer size-restricting component was used to ensure that the balloon would not overinflate and rupture the vessel being treated. Despite early success, these catheters were not highly successful because of problems with inflexibility and thrombogenicity. It was not until a young German physician, Andreas Gruentzig, used polyvinyl chloride to build a balloon-tipped, double-lumen catheter that had the handling characteristics of modern-day catheters. Gruentzig presented his initial animal research results at the American Heart Association meeting in 1976 and was largely met with skepticism. One year later in 1977, when he presented the results of his first four human coronary angioplasties at the American Heart Association meeting, the audience burst into applause and provided him with a standing ovation. It was clear that a medical revolution had taken place.




ANGIOPLASTY TODAY



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In the 1980s, public awareness of percutaneous arterial interventions soared. Patients who wanted their coronary vessels treated without a sternotomy embraced PTCA, and celebrity patients increased awareness of alternatives to open surgery. Johnny Carson, after choosing peripheral angioplasty over surgery for claudication, joked with Ed Mcman on the Tonight Show about his “balloon job.” Meanwhile, in the medical community, the reality of restenosis became evident.



From the beginning, studies have documented the increased rate of restenosis of angioplasty compared to surgery, but this has not slowed the progression of catheter-based interventions. The battle against restenosis is a primary focus of physicians and industries today.



Multiple techniques from atherectomy to stenting have been used, but none are as durable as surgery. Currently, dozens of stents with various materials and sizes are available from a number of manufacturers. Balloon expandable drug-eluting stents have been the most effective in intermediate-length trials. Industry-sponsored trials of the first coronary drug-eluting stents showed a reduction of restenosis rates into the single digits for the first time (33% of the bare metal stents restenosed), but recent analysis suggests that these are more predisposed to late thrombosis than their bare metal counterparts and may be overused. Other emerging technologies such as cryoplasty, cutting balloon angioplasty, and stent brachytherapy are also areas of active research.



What started as a cottage industry, with catheters being developed by physicians in their basements and attics, grew into a multibillion dollar industry dominated by major corporations. One emerging dilemma is that the physicians who are most qualified to evaluate new products often have financial interests in the results. In addition, concerns about the economic impact on our health care system are rising as the use of expensive technology increases. Drug-eluting stents, in particular, because of their high price, have been criticized in a “societal cost–benefit analysis” through multiple studies. The sudden emergence of endovascular therapy into medicine has magnified philosophical dilemmas within our field. Issues such as “cost containment vs. individual benefit” and the emerging partnerships between physicians and industry with their inherent conflict of interest are two such examples.




ABDOMINAL AORTIC ANEURYSM



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The historically standard method for the surgical repair of abdominal aortic aneurysms involves a transperitoneal approach, clamping the aorta proximally and distally, incising the aneurysm anteriorly, sewing in an interposition graft, and finally closing the aneurysm sac around the graft to prevent an aortoenteric fistula. This method replaced nonresective approaches such as ligation, thrombosis, and aneurysm wrapping, which produced unacceptable rates of rupture and mortality. A shortcoming of the open repair is the detrimental impact of a transperitoneal operation and aortic cross-clamping in patients with significant comorbidities. These high-risk patients were the original candidates for endovascular repair because the less invasive nature of endovascular abdominal aortic aneurysm repair (EVAR) shifted the risk–benefit ratio in their favor.



In 1987, J.C. Palmaz, inventor of the Plamaz stent, revealed that he and Jaun Parodi, an Argentinean vascular surgeon, had conceptualized the use of a covered stent to exclude an abdominal aortic aneurysm. Three years later, Parodi used a Dacron graft handsewn into a Palmaz stent to complete the first successful EVAR via a common femoral artery approach. Soon afterward, in November 1991, Parodi, Palmaz, and Barone published a series of five high-risk patients treated successfully with EVAR in The Annals of Vascular Surgery and brought to international attention the feasibility of a catheter-based repair. One year after Parodi’s benchmark paper, Frank Veith, with Parodi and a team of coworkers from Buenos Aires, performed the first EVAR in the United States at Montefiore medical center in New York, on November 23, 1992.



During the next decade, multiple studies showed both the limitations and the benefits of EVAR. Parodi himself published an 80% initial failure rate in his first 15 patients. But as devices and techniques become more refined, the data are being accumulated in support of EVAR. The first FDA-approved trials of the Ancure endograft showed an equivalent perioperative mortality between open and endovascular repair, but, by 2004, there was growing level 1 data showing benefit to EVAR. Well-designed trials published in the Lancet and The New England Journal of Medicine show that patients with EVAR suffer significantly fewer perioperative complications and lower rates of 30-day mortality.2,3 Stent-graft patients do, however, have an increased need for secondary interventions and require lifelong surveillance to screen for graft migration and, more commonly, continued aneurysm expansion owing to endoleaks.



While critics of EVAR cite the necessary surveillance and the lack of long-term data as justification for open surgery, the trend toward EVAR predominance is clearly underway. The proportion of patients who are considered eligible for EVAR has risen from approximately 20% to 80% in recent years. Current indications for EVAR are the same as those for open repair, size >5.5 cm in asymptomatic patients, but in future years the lower morbidity and mortality of EVAR may make the repair of smaller aneurysms a safe option. As technology continues to expand and devices become more advanced, it is inevitable that many of the current hurdles will be crossed. One example is a recently developed pressure-sensing device that can be deployed into the aneurysm sac at the time of graft deployment and monitored easily in the clinical setting, potentially minimizing the need for serial contrast-based imaging. Other horizons include the ability to repair currently prohibitive anatomy, such as juxtarenal aneurysms, with fenestrated grafts that allow simultaneous stetting of major aortic branches.

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Jan 13, 2019 | Posted by in CARDIOLOGY | Comments Off on Endovascular Therapies in Peripheral Arterial Disease

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