Author + information
- Antonio Colombo, MD∗ ( and )
- Lorenzo Azzalini, MD, PhD, MSc
- Division of Interventional Cardiology, Cardio-Thoracic-Vascular Department, San Raffaele Scientific Institute, Milan, Italy
- ↵∗Address for correspondence:
Dr. Antonio Colombo, Division of Interventional Cardiology, Cardio-Thoracic-Vascular Department, San Raffaele Scientific Institute, Via Olgettina 60, 20132, Milan, Italy.
On September 14, 2017, Abbott Vascular (Santa Clara, California) halted the commercialization of Absorb bioresorbable vascular scaffold, attributing the decision to “low commercial sales.” This measure marked the official end date of the first generation of bioresorbable scaffolds (BRS). But let us have a brief look at the events that led to such a development.
Balloon angioplasty gave the patient the possibility to avoid open-heart surgery. Coronary stents lowered recurrences (restenosis), and made emergency bypass surgery less likely to be needed by treating dissections, with a lower incidence of myocardial infarction and death. Drug-eluting stents (DES) lowered restenosis to a greater extent than bare-metal stents, with less of a need for a repeat procedure. The common denominators of these advantages were: 1) the gain was relatively easy to be perceived; and 2) the time to the reward was almost immediate or relatively early (restenosis). These advantages gave an easy perception of the risk-benefit ratio and simplified the implementation of randomized trials demonstrating the occurrence of endpoints within a reasonable time frame.
The situation of BRS is different. Let us first concentrate on the benefits: 1) avoidance of a permanent implant; 2) restoration of vasomotion; 3) possibility of positive vessel remodeling; 4) possibility to make the treatment of restenosis easier; 5) possibility to perform bypass surgery of the vessel treated with very long stents; and 6) possible lower incidence of late atherosclerotic lesions possibly caused by a permanent metallic implant. These are very attractive promises; nevertheless, the word possible is very present, and the rewards will come at a later time (2 years at the best, if not later). This situation puts BRS in an uncertain frame: a promise not so clear cut, and occurring at a late time.
Now, let us go to the device itself. Current BRS have wide and thick struts with less radial force and higher recoil compared with new metallic DES. These features make the implantation technique more complex and increase the risk of scaffold thrombosis (ST), unless optimal implantation has been performed. In summary, “BRS have well-defined problems, offering ill-defined benefits”!
To be completely fair, we should add that these remarks mainly apply to the Absorb BRS. Regarding other BRS, such as new thin-strut plastic devices or BRS made of magnesium, their area of use is limited, and the lack of large trials does not allow drawing strong conclusions.
Following these remarks, we could state the case is closed. The truth of the matter is that possibilities may become realities, and problems can be solved. Recognizing problems is the initial and key step toward their solution. The major shortcoming in the BRS story, and more specifically in the Absorb registries and trials, has been the lack of the early recognition of problems with the device. This situation gave the perception and confidence to the operators that they were dealing with a device (BRS) similar, if not equal, to current best-in-class DES. When you drive a truck having been told that it is a sport car, a feeling of uneasiness and possible problems are there to come.
The important value of the “state-of-the-art review” by Bangalore et al. (1), published in this issue of JACC: Cardiovascular Interventions, is to underline a number of possible problems and to positively propose solutions for this field. The most important points to be highlighted are:
1. BRS design. Bangalore et al. (1) correctly stress the importance of decreasing strut thickness in future generations of BRS (because thick struts are associated with both restenosis and thrombosis), while maintaining sufficient radial strength. Additionally, further progress shall be made regarding polymer composition, which can greatly influence not only mechanical properties, but also degradation kinetics and resorption time. In particular, Absorb PLLA polymer undergoes very slow degradation (up to 36 months), which appears to be too long, and poses problems with regard to dual antiplatelet therapy (DAPT) prescription (see later in the text).
2. Implantation technique. Even if we do not have randomized studies demonstrating that optimal implantation technique is important to lower the risk of ST, there are a number of single-center registries supporting this concept (2,3). What is important to stress is that despite the value of simplicity in the “pre-dilatation, sizing, and post-dilatation” (PSP) concept, these actions should not be considered dichotomous. “High-pressure” post-dilatation can be high, but not sufficient to allow optimal expansion. Similarly, lesion preparation does not work by “intention to prepare.” The issue of implantation technique is particularly relevant, because a great proportion of early Absorb adopters failed to recognize the fact that BRS represent a different technology compared with metallic stents, and as such, they require a specific implantation protocol. Bangalore et al. (1) deal in detail with issues such as correct BRS sizing and avoidance of BRS implantation in small or large vessels and in specific lesion subsets. A special discussion should be dedicated to the role of intravascular imaging: although this can sometimes be avoided in simple, focal lesions, we believe that most BRS-based procedures (particularly those with overlapping scaffolds, scaffolds <3.0 mm and/or >18 mm, treatment of bifurcations or calcified lesions) with first-generation devices should rely on intravascular ultrasound or optical coherence tomography guidance. Because malapposition and underexpansion are quite frequent when BRS are used and are hardly detected on angiographic grounds, use of intravascular imaging is of utmost importance. Data from our institution indicate that if BRS implantation is performed according to an optimized strategy including intravascular imaging, long-term clinical outcomes are acceptable, despite high lesion complexity and long total scaffold length (2). It remains to be seen whether second-generation BRS can be “freed” from such a strong reliance on intravascular imaging to guarantee acceptable outcomes. The bottom line is that BRS will be accepted when the implantation technique will not be very different from the one necessary for metal stents.
3. Duration of DAPT. This topic is full of uncertainties. Initially, the idea of a bioresorbable device has been linked to the possibility of stopping DAPT. Presently, we have insufficient data to support the “reasonable” concept that optimal scaffold implantation is protective for late thrombosis and does not tie the patient to prolonged DAPT (at least until full scaffold resorption). Due to their slow resorption, polymeric material remains present within vessel architecture for up to 3 years. During this period, polymer dismantling into the lumen can trigger ST. As such, we advocate for tailoring DAPT duration depending on the specific BRS resorption kinetics (36 months for Absorb) (4). Supporting this recommendation are data from a recent Dutch study (5) in which no case of very late ST was observed in patients who continued on DAPT for >18 months, and the incidence of this dreaded event was higher after DAPT termination (particularly during the first month), compared with the incidence on DAPT.
4. The problems related to Absorb should not be automatically extended to other BRS. Despite the lack of large randomized trials and the fact that lesion selection takes place in registries, the very low risk of ST occurring with magnesium-alloy BRS (Magmaris, Biotronik, Berlin, Germany) is a fact (6). The faster resorption time for this device (12 months) is a potential added benefit. Some of these encouraging remarks can be extended to other BRS; some of them are available on the market, others are being evaluated in early studies. These considerations mean that there is room for improvement, and data are moving in that direction.
We congratulate Bangalore et al. (1) for providing such a thorough and lucid analysis of the factors that led to inferior performance of Absorb versus best-in-class metallic DES, as well as important principles on how BRS technology should evolve. We believe that if BRS is to be adopted in a significant proportion of patients undergoing percutaneous coronary intervention, future platforms should provide solid evidence of noninferiority compared with metallic DES. This is a fundamental prerequisite, given the higher costs of BRS technology. Albeit an appealing concept for patients and media, the simple slogan that “nothing is left behind” might not be sufficient for health care authorities to support reimbursement in clinical practice.
The first chapter of BRS saga has been closed. Ours is the responsibility to write the next.
↵∗ Editorials published in JACC: Cardiovascular Interventions reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Interventions or the American College of Cardiology.
Dr. Azzalini has received research support from ACIST Medical Systems; and honoraria from Guerbet. Dr. Colombo has reported that he has no relationships relevant to the contents of this paper to disclose.
- 2017 American College of Cardiology Foundation
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