Tomography, Optical Coherence Clinical Trial
Official title:
Mechanisms of Very Late Bioresorbable Scaffold Thrombosis Assessed by Optical Coherence Tomography: Insights From the International INVEST Registry
Bioresorbable vascular scaffold (BVS, ABSORB BVS1.1, Abbott Vascular) has been approved (CE
mark) and is used in daily clinical practice. While recent randomized controlled trials
comparing BVS versus metallic drug-eluting stent showed higher risk of definite or probable
device thrombosis after BVS implantation, the causes underlying thrombotic events occurring
beyond one year after scaffold implantation remain unclear and require investigation in an
independent manner.
The INVEST registry is a world-wide, multi-center, observational, retrospective,
investigator-initiated registry, which will include any patients who suffered from very late
(>1 year) scaffold thrombosis, underwent optical coherence tomography (OCT) at the time of
thrombosis and provided informed consent for the further use of their health related data for
this registry.
Background: The 3-year clinical outcome data of ABSORB II study failed to reach the two
co-primary endpoints of vasomotion and late loss, but also reported a higher risk of definite
or probable stent thrombosis throughout 3 years (3% vs 0%, p=0.03) with the Absorb BVS
compared with the metallic EES as well as myocardial infarction.(1) In addition, a
numerically higher rate of definite very late device thrombosis (2% vs 0%, p=0.19) was
observed. In ABSORB Japan study, malapposition and late strut discontinuities were observed
at the timepoint of very late scaffold thrombosis in all the 4 cases of definite very late
scaffold thrombosis.(2,3) There is mounting evidence from other studies with extended
follow-up supporting the notion of an increased risk of very late scaffold thrombosis. While
the causes of acute scaffold thrombosis are explained at least in part (i.e. underexpansion,
increased strut thickness), the causes underlying thrombotic events occurring beyond one year
after scaffold implantation remain unclear and require investigation in an independent
manner.
The investigators have previously reported that scaffold discontinuity and restenosis during
the resorption process may provide mechanistic explanations for very late scaffold
thrombosis.(4) As this report was based on a limited number of cases, the investigators
extend the OCT database to comprehensively study the phenomenon very late scaffold
thrombosis.
Rationale: The investigators consider the establishment of an independent OCT registry of
paramount important as more than 150 000 patients have been implanted with Absorb BVS
worldwide. The findings may provide important insights to identify patients at increased risk
in addition to considerations regarding long-term antiplatelet therapy.
Objectives: The specific aim is to systematically analyse scaffold thrombosis occurring
beyond 1 year after implantation of a Absorb BVS 1.1 investigated by OCT at the timepoint of
thrombosis (either prior or after thrombus aspiration).
Primary and secondary endpoint/outcome(s): The primary endpoint is the underlying main reason
for stent thrombosis as per quantitative and qualitative analysis and per expert panel
consensus. To investigate the underlying mechanisms of very late scaffold thrombosis, the
investigators will systematically assess the following parameters:
- Distal and proximal reference area, mm2
- Scaffold area, mm2
- Lumen area, mm2
- Incomplete scaffold apposition area, mm2
- Neointimal area, mm2
- Intracoronary thrombus area, mm2
- Percent area stenosis, %
- Scaffold expansion, %
- Eccentricity index
- Presence of macrophage accumulations, %
- Uncovered struts, %
- Malapposed struts, %
- Neointimal thickness, µm
- Incomplete scaffold apposition distance, µm
- Thrombus area, mm2
Other study variables: Retrospective data about clinical and drugs history of patients,
procedural features and any intracoronary imaging information will be collected and analysed.
This will include data for any imaging information between index implantation and very late
scaffold thrombosis, when available, in order to investigate the underlying mechanisms of
very late scaffold thrombosis.
Inclusion Criteria:
1. Any patients who suffered from scaffold thrombosis occurring beyond 1 year after
implantation of a Absorb BVS 1.1 and investigated by OCT at the timepoint of thrombosis.
2. Sufficient quality of the OCT recording allowing for CoreLab analysis.
Exclusion Criteria: No exclusion criteria will be applied.
OCT assessment: Commercially available ILUMIEN (St. Jude Medical) or OFDI (Terumo) system are
used. The analysis will be conducted at the Core laboratory at Bern University Hospital,
Bern, Switzerland using a systematic and validated approach.
The lumen contour is drawn by semi-automated detection using QCU-CMS software, following the
endoluminal contour of the neointima with manual correction wherever required. In case of
thrombus with low attenuation, the lumen contour can still be drawn. In case of high
attenuation, the lumen contour was extrapolated when the lumen contour was visible in at
least three quadrants. The scaffold area was measured by joining the middle points of the
signal poor core of the abluminal side of the struts if at least one strut was clearly
visible in every quadrant. Distal and proximal reference area and scaffold expansion were
calculated as previously reported by the MUSIC (Multicenter Ultrasound Stenting in
Coronaries) investigators.(5) The neointimal thickness is measured from the abluminal border
of the black strut core to the lumen. Uncovered struts are defined in the absence of a
homogenous coverage by neointima. If the apposed struts is not covered by neointima but
rather by irregular tissue, struts are categorized as "apposed uncovered with superimposed
thrombus". If the coverage of apposed struts cannot be assessed owing to the presence of
attenuating thrombus precluding the evaluation of neointima, the struts were categorized as
"apposed possibly uncovered". Malapposed struts were defined as struts where the abluminal
surface was clearly separated from the vessel wall. Incomplete scaffold apposition (ISA)
distance was measured from the abluminal border of the strut core to the vessel wall. If
malapposed struts are partially or completely surrounded by thrombus, struts were regarded as
malapposed with thrombus. The area between the backside of the struts and the vessel wall was
measured as ISA area, while the neointimal area is measured as scaffold area - (lumen area -
ISA area). Intracoronary thrombus was identified as any irregular mass inside the lumen, with
a sharp border and various degrees of attenuation.
Angiography assessment: The analysis will be conducted at the Core laboratory at Bern
University Hospital, Bern, Switzerland using a conventional quantitative coronary angiography
software (Qangio XA).
Determination of sample size: Up a total number of 30 patients who suffered from very late
scaffold thrombosis and underwent OCT will be analysed retrospectively. This sample size is
justified by the need to have precise estimates of event rates in terms of narrow 95%
confidence intervals.
Planned analysis: Descriptive statistics will be provided. The investigators will assess
geographic association between distribution of thrombus within scaffold and abnormal findings
assessed by OCT. Statistical analyses will be performed with R (R Foundation for Statistical
Computing, Vienna, Austria). Continuous variables will be summarized as mean ± standard
deviation or median ± 95% confidence interval, depending on normality of distribution. The
investigators will assess underlying reasons for scaffold thrombosis based on the same
methodology with previous publication.(6)
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