Durably Biocompatible? New-Generation DES Show Superior Long-Term Outcome Irrespective of Polymer Degradability

Introduction
From the first procedure performed by Andreas Grützing in 1977 until today, percutaneous coronary intervention (PCI) has become the treatment of choice for millions of patients suffering from occlusive coronary artery disease. Owing to their high antirestenotic efficacy and safety, drug-eluting stents (DES) have become a cornerstone of percutaneous treatment strategies and are largely responsible for their broad application today.

The importance of long-term follow-up in clinical trials became particularly evident after the introduction of first-generation DES. Although a significantly improved antirestenotic efficacy had led to the replacement of bare-metal stents and implantation of millions of early-generation DES between 2003 and 2011, long-term data revealed a sustained accrual of late adverse events.1,2 Preclinical research focusing on the underlying mechanisms attributed a main part of these observations to persistent inflammatory reaction to permanent polymer coating.3,4 That resulted in the development of a second generation of DES with improved long-term antithrombotic properties. An important target concerning this enhancement of DES technology is biocompatibility, in particular regarding the drug-eluting polymer coating.5 With that in mind, biodegradable stent components are associated with the hope of superior biocompatibility and late clinical outcome, although trials are failing to provide convincing evidence to date.6,7 It has therefore been hypothesized that this lack of evidence is owed to the lack of trials with follow-up durations long enough to be able to detect the favorable effects of biodegradable polymer on arterial healing and thus very late adverse events.

The unique long-term outcome analysis of the ISAR-TEST 4 trial (Intracoronary Stenting and Angiographic Results: Test Efficacy of 3 Limus-Eluting Stents-4), first presented at the American Heart Association Scientific Sessions in 2018 as a late-breaking trial, now closed this notable scientific gap.8 The ISAR-TEST 4 trial was designed to compare two new-generation DES—a permanent polymer-based everolimus-eluting stent (PP-EES), Xience (Abbott Vascular; Green Oaks, IL), and a biodegradable polymer-based sirolimus-eluting stent (BP-SES), Yukon Choice PC (Translumina Therapeutics; New Delhi, India)—as well as an early-generation permanent polymer sirolimus-eluting stent (PP-SES), Cypher (Cordis Corporation; Baar, Switzerland). In light of the lessons drawn from the introduction of early-generation DES, where randomized controlled trials had initially shown excellent results before subsequent meta-analysis, and registries revealed a concerning incidence of very late adverse events,1,5 patients in this study were followed up out to 10 years after the index procedure. The ISAR-TEST 4 trial revealed a significant reduction of major adverse cardiac events (MACE) after new-generation DES compared with early-generation DES, mainly driven by a significantly lower all-cause mortality, while showing no significant difference between PP-EES and BP-SES.

The Trial
Between September 2007 and August 2008, a total of 2,603 patients with ischemic symptoms or evidence of myocardial ischemia in the presence of ≥50% de novo stenosis located in native coronary vessels was enrolled at 2 centers in Munich, Germany. Patient were randomly assigned in a 2:1:1 fashion to receive a new-generation BP-SES (Yukon Choice PC), a new-generation PP-EES (Xience), or an early-generation PP-SES (Cypher). Patients were systematically evaluated at 1 and 12 months and annually out to 120 months thereafter.

Ten-year follow-up was acquired of 2,153 patients (83%, no difference among the groups). In patients without complete follow-up out to 10 years, median follow-up duration was 5.9 years. Both new-generation DES showed superior clinical outcome compared with the early-generation DES, irrespective of differences in polymer characteristics. Significant differences among the 3 treatment groups were observed for MACE (p = 0.003), all-cause death (p = 0.02), and definite stent thrombosis (p = 0.03). Furthermore, hazard ratios (HR) showed significantly lower mortality, incidence of MACE, and definite stent thrombosis after implantation of either one of the two studied new-generation DES, in each case compared with the early-generation comparator DES. Definite or probable stent thrombosis, target lesion revascularization (TLR), myocardial infarction (MI), and cardiac death occurred numerically lower with both new-generation DES compared with the early-generation DES but demonstrated no significant difference among the groups. Event rates of patients receiving new-generation DP-EES and PP-SES were similar for all studied endpoints and throughout all prespecified subgroups.

Table 1: Clinical Outcomes Out to 10 Years, HR, by Treatment Group

Event

BP-SES (n = 1299)

PP-EES (n = 652)

PP-SES (n = 652)

Overall P Value

BP-SES vs. PP-SES

PP-EES vs. PP-SES

BP-SES vs. PP-EES

MACE

575 (47.7)

279 (46.0)

336 (54.9)

0.003

0.82 (0.69–0.96)

0.79 (0.65–0.96)

1.04 (0.87–1.24)

All-Cause Death

374 (31.8)

179 (30.3)

223 (37.2)

0.02

0.82 (0.70–0.97)

0.78 (0.64–0.95)

1.05 (0.88–1.26)

MI

88 (7.7)

45 (7.9)

49 (9.1)

0.85

0.90 (0.64–1.28)

0.92 (0.62–1.38)

0.98 (0.69–1.41)

TLR

225 (20.3)

103 (18.2)

129 (22.5)

0.15

0.85 (0.69–1.06)

0.78 (0.60–1.00)

1.10 (0.87–1.38)

Definite/Probable Stent Thrombosis

20 (1.8)

14 (2.5)

20 (3.7)

0.09

0.50 (0.27–0.93)

0.70 (0.35–1.39)

0.71 (0.36–1.41)

Definite Stent Thrombosis

12 (1.1)

5 (0.8)

14 (2.4)

0.03

0.43 (0.20–0.92)

0.36 (0.13–0.99)

1.20 (0.42–3.42)

Probable Stent Thrombosis

8 (0.7)

9 (1.6)

6 (1.3)

0.23

0.67 (0.23–1.90)

1.52 (0.54–4.26)

0.44 (0.17–1.15)

Data are shown as number (Kaplan–Meier estimates as percentages), HR (98.3% confidence interval for MACE analysis and 95% confidence interval for the analysis of other events) are derived from Cox proportional hazard models, and P values are derived from Cox proportional hazard models. In the analysis of MI, TLR, and stent thrombosis, the competing risk of death was also accounted for.

Figure 1: Comparison of Clinical Outcomes at 10 years in Patients Treated with New-Generation BP-SES Versus New-Generation PP-EES Versus Early-Generation SES.

Figure 1
Kaplan–Meier curves for (A) primary end point, (B) all-cause mortality, (C) definite/probable stent thrombosis, and (D) TLR. The primary end point is the composite of all-cause death, MI, or TLR.

Conclusions and Implications
Four main conclusions can be drawn from the results of the 10-year clinical outcomes from the ISAR-TEST 4 trial.

First, new-generation DES are superior to early-generation DES in terms of clinical outcomes. As stated initially, new-generation DES development was prompted by an excess of late thrombotic complications after early-generation DES implantation. Although undoubtedly multifactorial, this phenomenon was partly attributed to impaired arterial healing and thus incomplete and incompetent reendothelialization potentially caused by poor biocompatibility.3,4 New-generation stent designs focused on minimizing these effects by thinner struts, optimized drug delivery, and release kinetics as well as more biocompatible polymers.3,9 Although these enhancements had translated into improved clinical efficacy and safety,1,10 the ISAR-TEST 4 trial is the first trial to show a sustained and significant effect of these technical improvements in terms of clinical events out to 10 years.

Second, both new-generation DES, BP-SES and PP-EES, show comparable clinical outcomes out to 10 years. Although the study compared two new-generation DES with differing characteristics beyond polymer coating, similar event rates suggest no relevant influence of whether polymer is permanent or biodegradable in nature. These results are in line with a number of clinical trials that failed to show superior outcomes for biodegradable polymer DES compared with permanent polymer DES.7 Still, whether "leave nothing behind" is just not the right approach to tackle late adverse events after coronary stent implantation, or whether further refinement of this technology will eventually lead to improved clinical results, cannot be decided yet. Clinical trials investigating the newest-generation DES, with further optimized polymer biocompatibility as well as ultra-thin strut designs with the potential to minimize vascular injury and benefit arterial healing, are already in progress. So far, results seem promising.11,12 However, the long-term results of the ISAR-TEST 4 trial do not indicate any advantage in clinical performance of biodegradable polymer DES over permanent polymer DES.

Third, the increase of event rates over time is significantly greater in early-generation DES than in new-generation DES. Nevertheless, new-generation DES event rates don't plateau within 10 years but continue to accrue with what seems like a constant rate after the first year. This observation is true for both investigated new-generation DES irrespective of polymer degradability; the observation is true not only for mortality but also for TLR rates and definite and/or probable stent thrombosis. This course of event rates on the one hand and the overall low incidence of late thrombotic adverse events on the other demonstrate the importance of long-term follow-up in randomized controlled trials with the purpose of detecting significant differences among different DES types. Although recommended for a comprehensive clinical assessment of coronary stents,13 extended long-term follow-up is not yet a well-established standard throughout these trials.

Fourth, as opposed to the overall low incidence of definite and/or probable stent thrombosis, new-generation DES absolute 10-year event rates of approximately 45% MACE and 35% all-cause mortality still seem alarmingly high. The high incidence of MACE and mortality after coronary stenting is attributable to the index procedure but not exclusively; it is also largely due to age, progress of the primary disease, and co-morbidity. Nevertheless, owing to the world-wide disease burden, high number of PCIs, and high mortality of (late) stent thrombosis, continued preclinical and clinical research remain crucial to better understand vascular response to stent implantation and to further improve coronary stent technology. Special motivation should be drawn from the fact that improvements in stent technology from early- to new-generation DES have been proven to significantly impact hard clinical endpoints. Data regarding the impact of latest device innovations on extended long-term clinical outcome are eagerly awaited.

References

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Clinical Topics: Invasive Cardiovascular Angiography and Intervention, Stable Ischemic Heart Disease, Atherosclerotic Disease (CAD/PAD), Interventions and Coronary Artery Disease, Chronic Angina

Keywords: Drug-Eluting Stents, Coronary Artery Disease, Sirolimus, American Heart Association, Polymers, Follow-Up Studies, Constriction, Pathologic, Percutaneous Coronary Intervention, Myocardial Infarction, Coronary Occlusion, Registries, Thrombosis, Angina, Stable


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