Updated at 3:35 p.m. ET
The Food and Drug Administration is warning physicians that patients implanted with the nation's only approved dissolvable heart stent may be having more cardiac issues than those with a traditional stent.
The FDA wrote in a letter on Saturday that it is investigating an increased rate of adverse cardiac events in patients who received Absorb, a bioresorbable vascular scaffold manufactured by suburban Chicago-based Abbott Laboratories. The heightened rate was observed in patients two years after implantation and was more likely to happen when the device was placed in small heart vessels, according to the letter.
After two years, 11% of the patients implanted with the Absorb stent had a major adverse cardiac event such as death, heart attack, or the need for an additional procedure to re-open the treated heart vessel, as compared to 7.9% of patients with Abbott's metallic Xience stent. Absorb patients also showed a 1.9% rate of developing blood clots, known as thrombosis, as opposed to 0.8% of Xience patients.
As a condition of approval, Abbott has been required to follow patients in a clinical study for five years. The heightened rates weren't observed in the patients after just one year.
The FDA says it is working with Abbott to better understand the cause of the adverse events, and asks physicians to report any adverse events. The agency encouraged physicians to follow the device's label instructions when it comes to selecting a target heart vessel.
In a statement, Abbott said that the FDA's letter “emphasized the importance of following instructions for use when implanting Absorb.” As Absorb's instructions have been updated, Abbott has warned physicians to take into account the size of the vessel in which the device will be implanted. Results of studies involving the most current techniques and vessel sizing instructions are expected early next year.
“When implanted in appropriately sized vessel sizes and following current instructions for use, the results for Absorb are comparable to the leading metallic drug-eluting stent--with the added feature of leaving no metal behind once it dissolves,” according to the company.
When asked whether the dissolving of the stent could be the cause of the adverse outcomes, an Abbott spokeswoman said the company believes the higher rates of thrombosis are due to the same causes of device-related thrombosis in metallic stents, along with adverse effects when the device is placed in smaller vessels. Thrombosis can lead to adverse cardiac events.
Some critics have argued that there's no significant medical benefit to the device over traditional stents, at a time when some researchers believe stents may be overused in treating patients with coronary artery disease.
There could be any number of causes for the heightened rate of adverse events, which won't be clear until the issue is thoroughly investigated, said Diane Robertson, director of health technology assessment for the ECRI Institute, a not-for-profit that evaluates medical devices. It could be because of the device's bioresorbing nature, but it might also be because of the anti-platelet therapy regimen that is being prescribed to patients after they've been implanted with the device, she said. Part of the promise of the device is that it would reduce the need for long-term anti-platelet therapy.
"These differences are not only statistically significant, but when you think of them in terms of real numbers of people affected, a lot of people could be affected," Robertson said. ECRI issued a brief to its members on this issue in February.
Abbott seems to place some blame on physicians, noting that the adverse outcomes may be more limited when physicians are properly following instructions. This isn't an unreasonable assertion, especially given that off-label use of stents contributed to issues with some of the first drug-eluting stents on the market, but it needs to be investigated thoroughly, Robertson said.
“I don't think you can take Abbott's word for it at this point,” she said.
If hospitals intend to continue to offer the Absorb stent, they should be informing patients of the newly discovered risks, Robertson said, especially if they recommend the bioresorbable stent over a traditional metallic device.
Even though there's no evidence that dissolvability serves any medical purpose, that feature has been the subject of marketing campaigns created by several providers implanting Absorb. The stent is one of several new, high-tech devices that hospitals have featured in their ad campaigns that are more expensive but don't seem to offer any additional benefit over existing products.