|Abbott's Absorb bioresorbable stent--Courtesy of Abbott|
GAITHERSBURG, MD--Questionable data among patients with small vessels is the dominant issue at hand during the FDA panel's consideration of Abbott's ($ABT) Absorb bioresorbable scaffold.
Working in Abbott's favor, subjects with a reference vessel diameter of less than 2.5 millimeters are not recommended for the device under the indication for use. But 375 patients in the pivotal trial (or almost 20%) had a reference vessel diameter of less than 2.25 millimeters, reflecting the challenges of accurately estimating the metric.
Those Absorb patients with vessels smaller than 2.25 millimeters had a one-year rate of stent thrombosis of 4.6%, compared to 1.5% for the comparator device, Abbott's permanent drug-eluting Xience. The difference was not statistically significant, but Dr. Gregg Stone of the Columbia University Medical Center said it is mechanistically and biologically plausible that the one-year event rate is higher among Absorb patients with small vessels, in part because the device's struts are thicker than those of the Xience.
Abbott has proposed labeling that recommends quantitative coronary angiography or intravascular imaging in patients with visually assessed diameters estimated to be less than 2.75 millimeters. That's because visual assessment routinely results in an overestimate of vessel size, Abbott and the FDA say.
It also proposed a warning stating implantation in device in vessels less than 2.5 millimeters "may lead to an increased risk of adverse events such as myocardial infarction and scaffold thrombosis."
More discussion of patient selection, usage among patients with small vessels and the role of imaging to determine vessel size will surely occur during the upcoming panel deliberation. The device appears comparable to Xience among all other patients, and met its noninferiority endpoint.
The FDA also has questions about the data among patients with diabetes, which are scheduled be discussed by the panelists. Abbott said during its presentation that the questionable data among those with diabetes was restricted to diabetics who also had small vessel sizes.
- read the March 15 meeting's literature