Resorbable coronary scaffolds require ‘leap of faith’

Results reported earlier this month at the Transcatheter Cardiovascular Therapeutics annual meeting for the Absorb bioresorbable vascular scaffold made by Abbott Vascular showed the device was statistically noninferior for treating selected coronary stenoses, compared with Xience, a standard of care drug-eluting metallic stent, in the ABSORB III trial, designed as the study to get Absorb onto the U.S. market.

Given the way such trials develop now, after consultation with the Food and Drug Administration, it seems very likely that proving noninferiority against the best metallic-stent competitor will mean that, sometime in 2016, the Absorb bioresorbable scaffold will become the first U.S. routinely available coronary device built to dissolve away after a period of time, about 3 years in this case.

^{Mitchel L. Zoler/Frontline Medical News}

Dr. Gregg W. Stone

That means that sometime in the next year, U.S. interventional cardiologists, patients, other collaborating physicians, and payers will have to start deciding whether the potential advantages of using a stentlike device that eventually disappears is worth a probable uptick in price as well as certain other limitations. One of the key variables is that for the moment the advantages remain mostly hypothetical.

Dr. Gregg W. Stone, chairman of the ABSORB III trial and one of the leading advocates for U.S. development of bioresorbable vascular scaffolds (BVS) told me about some of the hoped-for benefits that BVS could provide by leaving the coronaries. Imaging data have already suggested that it improves vasomotion, and other possible benefits include restored vascular adaptability, stimulated plaque regression, and reduced late polymer reactions and neoatherosclerosis. “This is all hypothetical, and we won’t know whether the promise is a reality until we have the 5-year results from ABSORB IV, which won’t be until 6-7 years from now,” Dr. Stone said.

Of course, he added, other, more modest benefits are already real: It’s been proven that the BVS really goes away after about 3 years, which makes noninvasive imaging of coronaries where a BVS was placed easier; and it also frees side-branch arteries, as well as the treated segment itself, from the metal jacket of a stent. And some patients like the idea of a disappearing stent for “personal, religious, or cultural reasons,” he said.

Balancing this are the device’s very real limitations. Because a BVS is stiffer and less maneuverable than is a metallic stent, it isn’t appropriate for heavily calcified lesions, tortuous arteries, chronic total occlusions, true bifurcations, or bypass grafts. Also, the width of the struts on the Absorb BVS make it unsuitable for use in coronary arteries less than 2.5 mm in diameter, a limitation borne out by the ABSORB III results, which showed a much higher rate of target-lesion failure and stent thrombosis, compared with the Xience stent in the 19% of lesions that sneaked into the study in coronaries narrower than 2.5 mm. Also, for the time being, BVS is targeted only for patients with stable coronary disease or patients who have stabilized following an acute coronary syndrome event and not for patients with an acute MI or unstable acute coronary syndrome.

Dr. Stone estimated that, collectively, these clinical and anatomic limitations exclude roughly half the patients who undergo percutaneous interventions today. “The sweet spot may be young patients with relatively noncomplex lesions.”

There are more restrictions, based on what using a BVS means for the operator. Not only is the device harder to deliver to a specific coronary site, but it requires “more lesion preparation, more accurate sizing, and more frequent postdilitation.” Operators “need to realize that if they use a BVS, they can’t get away with as much as they can with state-of-the-art metallic stents,” Dr. Stone said. In fact, he felt that the ABSORB III results showed “we could do better with more training and more attention to detail.” In the future, operators “will need to work harder and pay attention to procedural factors.”

The increased technical demands posed by a BVS and the possibility that not all of the devices were placed optimally in the trial may have led to another source of doubt about Absorb: its performance relative to Xience.

At the meeting, Dr. Stone reported results from a meta-analysis of the four randomized controlled trials that have now reported 1-year outcomes data for the Absorb BVS compared with Xience: ABSORB III (with 2,008 patients), ABSORB II (502 patients), ABSORB Japan (400 patients), and ABSORB China (480 patients).

^{Mitchel L. Zoler/Frontline Medical News}

Dr. Dean J. Kereiakes

The meta-analysis confirmed two concerning trends also seen in the results from ABSORB III by itself: a strong trend toward an increased risk of 1-year stent thrombosis with Absorb, at 1.3%, compared with a 0.6% risk with Xience (P = .08); and a statistically significant excess of target-vessel MI with Absorb, at 5.1%, compared with 3.3% with Xience (P = .04). Results from both the meta-analysis and from ABSORB III by itself also showed numerically higher rates of target-lesion failure – the primary efficacy endpoint – with Absorb, although not enough of a difference to undermine fulfilling the prespecified definition of noninferiority in ABSORB III.