Cardiologists at UAB Hospital are the first in Alabama to treat coronary artery disease patients with a new dissolving heart stent. The Abbott's Absorb bioresorbable vascular scaffold (BVS), FDA approved for use in July, gradually dissolves and may be a safer option for patients in the future.
"Metal stents are an excellent option, but the problem is that the metal stays in the coronary artery forever," says Mark F. Sasse, MD, an interventional cardiologist at UAB. "As the coronary arteries age, the metal cannot adapt to the inevitable physiologic changes that occur with aging. Researchers in the field of interventional cardiology hypothesize that if the stent disappears, the artery will regain its vasomotor reactivity without the metal embedded in the wall.
"Also, if someone has a number of stents in their coronary arteries and develop new lesions later, the rigid metal could prevent surgeons from performing potentially lifesaving bypass surgery. That's where this new stent comes in, potentially providing us with a device that we can put in an artery that will treat the plaque and then dissolve over time."
Unlike the current metallic stents, the BVS is made of naturally dissolving polylactic acid, similar to dissolving sutures. It disappears completely in about three years while permanent metal stents can restrict vessel motion for the life of the patient. Clinical studies of the Absorb BVS show that treated arteries return to natural vasoconstriction and vasodilation after the stent is reabsorbed, and no metal may mean reduction of future blockages and could allow easier access to other treatment options should the patient need them.
While the bioresorbable vascular scaffold offers a promising therapy, there are a few disadvantages with this new technology. "The BVS is not as strong as the metal stents, and it is not good for patients with moderate and severe calcific arteries," Sasse says. "The scaffold must be placed meticulously and sized appropriately, because the scaffold does not stretch and can fracture if it is too aggressively post dilated."
Researchers have identified other limits of this first-generation BVS, including size limitations. "The Absorb BVS has a maximal diameter of 3.5mm and cannot be sized over 4mm. Also, it cannot be used in arteries less than 2.5mm. Therefore, this limits use to medium-sized arteries only," Sasse says. Higher costs also may be associated with BVS implantation since the device has a slightly higher price and will require adjunct imaging techniques for proper implantation.
As with other technologies, first-generation products will continue to be improved, leading to the evolution of subsequent generations. To address some of the unanswered questions, UAB is still conducting the Absorb IV trial. This randomized trial includes 5,000 patients and will show late superiority of Absorb compared to Abbott's Xience drug eluting stent. "The Absorb BVS has been approved based on multiple trials in different countries, and based on that data, they approved this study," Sasse says. "We are going to complete this trial, but the BVS has been approved by the FDA so it can be placed in patients based on the operator's judgement."
Sasse believes there will still be a market for metal stents in the future regardless of the success of the Absorb BVS. "With the aging population, more patients will present with calcified and fibrotic arteries in which case the BVS is not the ideal choice," he says. "Also, in patients with hypertension, the arteries develop tortuosity. The BVS is not easily delivered through curves or extremely rigid arteries. Nonetheless, as updates are made, we can expect improvements in deliverability and radial strength that will allow the BVS to be used in a wider patient population."
Sasse cautions cardiologists to be sure they are comfortable with all the imaging technologies because of the need for proper sizing of the BVS. "The main reason UAB was selected to do the first BVS implantation was because of our expertise with all the imaging technologies necessary for optimal placement," Sasse says. "We have great experience using intravascular ultrasound and optimal coherence tomography for stent implantation, both of which are mandatory tools for making sure the BVS is optimally implanted. Patients who have image-guided stent implantation do better because we know the stent is well expanded, is well opposed, and is properly sized. As a result, blood flow is maximized which lessens the risk for stent thrombosis in the future."
He also encourages cardiologists to be conservative in their use of this new technology. "Some cardiologists in the US and Europe are putting BVS in all subsets of patients. I don't necessarily agree with treatment of all of the patient populations when we have an excellent alternative therapy, our third-generation metallic stents. The BVS has not been studied in all types of patients, so we have no idea how the stent will react in these subpopulations," he says. "I think in the beginning, American cardiologists should be judicious in their use of this new therapy, because we don't have long-term data for other patient subsets."