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| Dr Peter Barlis is Chief
Interventional Fellow at the
Royal Brompton Hospital,
London, UK, under the
mentorship of Professor Carlo
Di Mario. He completed his
cardiology training in Melbourne,
Australia, receiving a Fellowship
of the Royal Australasian
College of Physicians in 2004.
Following this, he undertook
training in clinical epidemiology,
biostatistics and trial design
culminating in a Master of
Public Health degree in 2005.
Dr Barlis has undergone
training in general and invasive
cardiology in addition to
undertaking substantive research
with specialised areas of interest
including the recanalisation of
chronic total occlusions and
intravascular imaging with
optical coherence tomography |
The use of drug eluting stents for coronary artery disease
Peter Barlis, MBBS, MPH,
FRACP
Jun Tanigawa, MD,
Carlo Di Mario, MD, PhD
Department of Invasive Cardiology,
Royal Brompton Hospital, London, UK
Address for correspondence:
Peter Barlis
Department of Invasive Cardiology
Royal Brompton Hospital, Sydney Street
London SW3 6NP, UK.
Tel: +44-20-7351-8616 Fax: +44-20-7351-8614
Email: P.Barlis@rbht.nhs.uk
Abstract
The growth in the availability and use of drug eluting
stents has seen the interventional cardiologist tackle
more lesions with increasing complexity and in higherrisk
patients. The single digit rates of restenosis observed
have helped propel these novel devices well ahead
of their bare metal counterparts, with applications
in bifurcation lesions, chronic total occlusions and
unprotected left main disease. Not all has come
without cost, however, and the problem of late stent
thrombosis has cast a cloud on long-term outcomes and
the optimal duration of dual anti-platelet therapy. This
review will describe the role drug eluting stents have in
contemporary interventional cardiology with a focus on
their shortcomings and possible future refinements.
Introduction
Since the introduction of drug eluting stents (DES),
interventional cardiology has witnessed tremendous
growth in the types and numbers of coronary
lesions treated percutaneously. The advent of these
novel devices has propelled percutaneous coronary
intervention to the forefront of the management of
patients with coronary artery disease. Globally, the DES
market, and in particular the two leading manufacturers
(Cordis Corp. [Johnson & Johnson] and Boston Scientific,
both USA), have found their way into almost all modern
catheterisation laboratories and provided opportunities
for interventional cardiologists to safely tackle complex
coronary lesions even in high-risk patients.
More than 20 million DES have been implanted
worldwide to date and these novel devices continue to
dominate the interventional literature. More recently,
evidence is mounting to support their use in complex
coronary lesions including unprotected left main
stenosis1-6 where a percutaneous strategy may be an
alternative to coronary artery bypass grafting (CABG),
although results of current randomised trials are eagerly
awaited. DES have furthermore become a vital part of
the armamentarium in treating chronic total occlusions
and bifurcation lesions. The only limitation to more
widespread use has been their direct and indirect costs.
These stents remain in the vicinity of three to four
times more expensive than bare metal stents (BMS), and
concerns about the risk of late stent thrombosis have
prolonged the duration of dual anti-platelet therapy
including 75 mg of clopidogrel to an average of 9 to 12
months. This review will provide a practical framework
for the role of DES in contemporary practice and give
a glimpse into what the future may hold for these
innovative devices.
DES for de novo coronary lesions
A number of studies7-11 have convincingly
demonstrated a reduction in the need for target vessel
revascularisation (TVR) with DES, but the benefits in
reducing myocardial infarction (MI) and death remain
blurred (see Table 1). A meta-analysis of 10 randomised
trials concluded that both sirolimus- and paclitaxeleluting
stents were equivalent to BMS in terms of
mortality and overall MI risk for the first year of followup.12 Still, these trials deal with single-vessel, singlelesion
treatment in a super-selected patient population;
results can be different when complex-lesion and multivessel
disease is treated in high-risk patients.
DES for the treatment of bare metal in-stent restenosis
Studies such as ISAR-DESIRE13 and TROPICAL14 have
confirmed significantly improved angiographic outcomes,
led primarily by reductions in the need for TVR with
restenosis rates less than 10% using DES for BMS
in-stent restenosis (ISR).
In evaluating the feasibility of DES compared with
vascular brachytherapy (VBT), Barlis et al15 identified
a rate of major adverse cardiac events (MACE)
significantly lower in the DES group (n=29) compared
with the VBT group (n=25) (14% versus 40%, p=0.03).
More recently, two randomised controlled trials
comparing the use of DES with VBT confirmed superior
results out to 9 months of follow-up for a strategy of
repeat stenting with a DES.16,17 The TAXUS V ISR (instent
restenosis) study17 enrolled 396 patients and
showed that, compared with VBT, implantation of
paclitaxel-eluting stents (PES) reduced the 9-month
rate of TVR from 17.5% to 10.5% (p=0.046) and target
lesion revascularisation (TLR) rate from 13.9% to 6.3%
(p=0.01). The study also demonstrated an 11.5% rate of
MACE for the PES group, compared with 20.1% for VBT.
The SISR trial16 randomised 384 patients with ISR to
receive either VBT (n=125) or a sirolimus-eluting stent
(SES, n=259). In this trial target vessel failure occurred
in 22% patients who underwent VBT and 12% of those
who received a SES. Overall, the TLR rate was 19% in
the VBT group compared with 8.5% in the SES group
(relative risk for VBT versus SES, 2.3, 95% CI, 1.3-3.9
p=0.004). The rate of MACE was 19% in the VBT group
versus 10% in the SES group (p=0.015).
DES for complex coronary interventions:
unprotected left main stenosis
Restenosis in an unprotected left main (ULM) may mean
sudden death and this sword of Damocles has prevented widespread diffusion of percutaneous treatment with
conventional BMS despite immediate results being
better than surgery. Improvements in stent deployment
techniques using high balloon pressures, IVUS guidance
and glycoprotein IIb/IIIa receptor antagonists have
dramatically reduced complications such as sub-acute
stent thrombosis.18-21 Now, a number of registries
and non-randomised studies (Table 2) have emerged
suggesting the effectiveness of DES for ULM treatment.
 |
MACE Major adverse cardiac events; DES Drug eluting stent; BMS Bare metal stent; TLR Target lesion revascularisation
Table 1. An overview of four randomised trials of drug eluting stents (DES) in de novo coronary lesions. |
In a series of 102 patients with ULM, Park et al2 reported
excellent clinical and angiographic outcomes with elective
SES implantation. Six-month angiographic follow-up
was completed in 84.3% of patients, with an overall
restenosis rate of 7.0% and 2.0% requiring TLR. Oneyear
mortality was 0% and MACE-free survival 98%. In
looking at a more representative population, Chieffo et
al5 enrolled 85 patients with ULM with high mortality risk
scores (EuroSCORE >6 and/or Parsonnet >15) present
in 45%. The 6-month cardiac mortality and MACE-free
survival rates were 3.5% and 80%, respectively. With the
inclusion of emergency procedures due to ST-elevation
MI (STEMI) and cardiogenic shock, Valgimigli et al4 reported a mortality rate of 11% at 12 months. Notably,
all deaths within 30 days occurred in patients with
STEMI and cardiogenic shock.
On multivariate analysis, the authors identified use of
DES, Parsonnet classification, troponin elevation at entry,
distal left main location and reference vessel diameter as
independent predictors of MACE.4
Recently two groups have published non-randomised
studies of DES for ULM compared with consecutive
patients undergoing CABG during the same time
period. Lee et al1 compared 50 patients having DES
percutaneous coronary intervention (PCI) for ULM with
123 CABG patients. High-risk patients (Parsonnet score
>15) comprised 46% of the CABG group and 64%
of the PCI group (p=0.04). Thirty-day mortality was
lower in the PCI group (2% versus 5% for CABG) with
6-month follow-up demonstrating a non-significant
survival advantage in the PCI group (96% versus 87% for
CABG). Price et al3 studied 50 patients with surveillance
angiography performed at 3 and 9 months follow-up.
The group predominantly consisted of patients with
distal bifurcation lesions (94%). TLR occurred in 19
patients (38%) over a mean follow-up of 276 ฑ 57 days.
There were two acute stent thromboses and five deaths
at 1 year. Angiographic follow-up at both 3 and
9 months revealed angiographic restenosis in 23% of left
main to left anterior descending (LAD) stents and 35%
in the left circumflex (LCx) with an overall angiographic restenosis rate of 42% in any vessel. Although alarming,
this study confirms the need for meticulous surveillance
of patients receiving DES for ULM even if they remain
asymptomatic. Results from multicentre randomised
trials (e.g. SYNTAX) comparing the percutaneous
approach with CABG are eagerly awaited.
 |
DM Diabetes mellitus; EF Ejection fraction; LM Left main; MI Myocardial infarction; TLR Target lesion revascularisation;
MACE Major adverse cardiac events
Table 2. Clinical and procedural characteristics and outcome of drug eluting stent (DES) implantation for left main stenosis in five registries. |
DES for complex coronary interventions:
bifurcation lesions
The use of DES for bifurcation lesions has seen improved
angiographic and clinical outcomes compared with
previous attempts using BMS. Still, restenosis of the side
branch ostium and late thrombosis22,23 following DES
implantation continue to hamper the treatment of this
lesion subset while casting doubts on the best long-term
strategy. In fact, the problem of focal restenosis at the
side branch ostium has not been overcome by the use
of DES and the best treatment for bifurcation lesions
remains a subject of controversy.
In deciding on an appropriate strategy for PCI to a
bifurcation lesion, the operator will chose between a
simple (DES implantation only at the main vessel with
optional balloon angioplasty or stenting at the side branch) or complex (DES implantation at the main
vessel and the side branch) technique.
In one of only a few randomised trials looking at these
bifurcation strategies, Colombo et al enrolled 85 patients
(86 lesions) to assess the feasibility and safety of two
SES using a T technique at true bifurcation lesions
(>50% stenosis in both main vessel and ostium of side
branch) versus the implantation of a single SES in the
main vessel with balloon dilatation across the stent
struts for the side branch.24 There was an extremely
high crossover rate (22/43, 51%) in the provisional
stent group who received two stents. At 6-month
follow-up, the total restenosis rate was 25.7%, and it
was not significantly different between the doublestenting
(28.0%) and the provisional side branchstenting
(18.7%) groups. In another study, Pan et al25 randomised 91 patients to stenting of the main branch
and balloon dilatation for the side branch (n=47) and
compared this group to a technique of stenting both
branches (n=44). At 6-month follow-up, there were
no differences in clinical outcomes between the two
groups: restenosis of the main vessel was observed in
one (2%) patient from the single stent arm and four (10%) from the double stent group (p=ns). Restenosis
of the side branch developed in two (5%) patients from
the single stent group and six (15%) of those receiving
two stents. Although the optimal strategy for bifurcation
stenting remains undetermined, stenting in the DES era
must ensure complete lesion coverage, especially at the
side branch ostium with well apposed stents to limit
complications such as restenosis or thrombosis.20
DES for complex coronary interventions: chronic
total occlusions
Chronic total occlusions (CTO) are identified in up to
30% of patients with significant coronary artery disease
on angiography26,27 and represent 1015% of cases
treated by PCI.28,29 The primary success rate remains
relatively low, mainly due to inability to cross the
occlusion with the guide wire,26 while the recurrence rate
is higher than that of subtotal stenoses particularly with
BMS.27 Moreover, the overall procedure and fluoroscopy
times are longer and equipment use higher than with
PCI of non-occluded vessels.28 A successfully recanalised
CTO can improve anginal status, left ventricular (LV)
function and survival, but this is hindered by the high
rate of restenosis or reocclusion.30
Recently, reports comparing DES with BMS have shown a
dramatic decrease in restenosis rate after CTO treatment
with relatively low complexity.31,32 In the PRISON II
study32 the binary restenosis rate (in-stent) for the BMS
group was 41% versus 11% for the sirolimus group at
6-month angiographic follow up (p<0.0001). The MACE
rate was also significantly reduced in the sirolimus group
(4% versus 20% for the BMS group; p<0.001). Despite
the significant advantage of DES in reducing ISR, this
is not eliminated completely with predictors of ISR
post-CTO treatment similar to those seen with BMS
including smaller reference vessel diameter and longer
stent length.6,33 There is no doubt, however, that when
available DES should be the first-line treatment following
recanalisation of a CTO.
DES for ST-elevation myocardial infarction (STEMI)
The use of DES in STEMI remains a controversial area
with limited data currently available to definitively
support the widespread use in such cases. In the
STRATEGY trial,4 the first randomised trial looking at
DES and acute MI (AMI), 175 patients were assigned to
receive single high-dose bolus tirofiban plus SES versus
abciximab plus BMS. The primary composite endpoint
of death, re-infarction, stroke, and angiographic binary
restenosis at 8 months occurred more frequently
in patients allocated to receive abciximab plus BMS
(50% versus 19%, p<0.001). The main driver was a higher restenosis rate in the BMS group (36% versus
9%, p=0.002). There were no differences in death,
re-infarction or stroke at 8 months, and no episodes
of stent thrombosis in the SES group. Similarly, the
RESEARCH registry34 compared the outcomes of 186
consecutive patients with STEMI treated with DES
against those of 183 patients treated with BMS. The
composite rate of death and re-infarction was 9% at
10 months with a long-term TVR rate of 5%.
A recent randomised study by Lee et al35 using the two
commercially available DES (Cypher® [SES] and Taxus® [PES]) enrolled 217 patients randomly assigned to PES
(n=108) or SES (n=109). The PES group showed higher
angiographic in-segment restenosis (16% versus 4%,
p=0.04) and higher in-segment late loss (0.35 ฑ 0.69 mm
versus 0.05 ฑ 0.42 mm, p<0.001) than the SES group.
Ten-month MACE rates were also significantly higher in
the PES group (92 ฑ 3% versus 82 ฑ 4%, p=0.04). The
PASSION trial36 randomised 619 patients with STEMI to
receive either a PES or a BMS. The use of PES was not
associated with a difference in the primary composite
endpoint of death, MI or TLR when compared with BMS
at 1 year.36 The TYPHOON trial37 compared the SES with
BMS in STEMI and showed it to be associated with a
significant reduction in target vessel failure compared
with BMS (3.7% versus 12.6% p<0.0001).37 This was
largely driven by a reduction in TLR with no difference in
death or MI between the two groups.37
Drug eluting stent thrombosis
Drug eluting stent thrombosis rates as high as 3.6% have
been reported in patients with complex lesions including
bifurcations.23 Such complications have also cast a cloud
on the appropriate duration of dual anti-platelet therapy,
particularly given the increased bleeding risks of longterm
therapy.38 Ong et al39 studied 2,006 patients treated
with DES and identified an early (<30 day) incidence of
stent thrombosis of 1%. At a mean follow-up of 1.5 years,
there were eight angiographically confirmed cases of late
stent thrombosis, three with SES (at 2, 25 and 26 months)
and five with PES (at 6, 7, 8, 11 and 14.5 months). Three
cases were related to complete cessation of anti-platelet
therapy, two cases occurred while patients were on
aspirin therapy within 1 month of cessation of clopidogrel
and three cases occurred at a time when patients were
apparently clinically stable on aspirin monotherapy.39
There were no cases of late stent thrombosis in patients
who were on dual anti-platelet therapy.
More recently, a study by Joner et al40 reviewing autopsies
of 23 DES cases compared these with 25 autopsies from
matched patients with BMS implantation. Of 23 patients with DES >30 days old, 14 (61%) had evidence of late
stent thrombosis. Cypher® and Taxus® DES showed
greater delayed healing characterised by persistent fibrin
deposition and poorer endothelialisation (55.8 ฑ 26.5%)
compared with BMS (89.8 ฑ20.9%, p=0.0001). In five
of 14 patients suffering late stent thrombosis, antiplatelet
therapy had been withdrawn with procedural
and pathologic risk factors for the development of
late stent thrombosis being: 1) local hypersensitivity
reaction to the polymer; 2) ostial and/or bifurcation
stenting; 3) malapposition/incomplete apposition; 4)
restenosis; and 5) strut penetration into a necrotic
core.40 In an accompanying editorial, Colombo et al41 reflected on many of these pathological findings, which
they postulated may be a manifestation of a number
of factors including the individuals healing response
to sirolimus or paclitaxel, the drugs themselves, the
polymer or a complex interplay of all factors. Barlis et al42 have also confirmed the multi-factorial nature of stent
thrombosis with findings of poor stent expansion and
eosinophilic infiltrates in thrombotic material extracted
from a patient successfully treated for late acute stent
thrombosis, 12 months after SES implantation.
 |
| Figure 1. An example of the culotte bifurcation stenting technique
using drug eluting stents. This 74-year-old male with hypertension and
dyslipidaemia presented with exertional angina and a positive exercise
treadmill test. Coronary angiography in the AP cranial projection
demonstrated a complex left anterior descending (LAD) and diagonal
bifurcation lesion (a). The culotte technique was employed with a
2.5 x 18 mm sirolimus eluting stent deployed in the diagonal branch and
a 3.0 x 23 mm sirolimus eluting stent deployed in the LAD. The procedure
ended with final kissing inflation (b). |
Recently presented findings from the BASKET-LATE
trial,43 designed to assess the incidence of stent
thrombosis in patients treated with DES (n=502) versus
BMS (n=244) following cessation of clopidogrel therapy,
identified rates of death and MI that were higher in
the DES group. These were more frequently related to
late stent thrombosis which carried a 4-times greater
risk of cardiac death/MI compared to non-thrombosis
related events. Although the complete 18-month data
did not confirm these initial findings, anecdotal evidence
of stent thrombosis several months or years after DES implantation is worrisome and involves both Cypher and
Taxus trials. These observations have also led the FDA
to issue a statement on coronary DES in which they
support their use for approved indications but will more
stringently focus their attention on monitoring late
thrombotic risks to minimize future patient harm.44
Intravascular imaging in the DES era
Intravascular imaging has the ability to give the
operator greater detail in both lesion assessment
and in optimising stent implantation compared
with angiography alone. Many of the DES studies
incorporating intravascular ultrasound (IVUS) have
shown that intimal hyperplasia volume is reduced to
<10% of stent volume, but stent under-expansion
continues to be a consistent finding in DES failures
(restenosis and thrombosis).45 Intravascular ultrasound
also has a vital role to play in guiding the percutaneous
treatment of complex lesion subsets including left main
disease where optimal stent sizing and expansion is of
paramount importance.20,45
 |
| Figure 2. Intravascular imaging following stent implantation. Two imaging
modalities are shown: intravascular ultrasound IVUS (a) and optical
coherence tomography OCT (b). Although image resolution is superior
with OCT, where stent struts can clearly be visualised apposed to the vessel
wall (b, arrow), the limited penetration of infrared light makes assessment
of stent expansion difficult compared with IVUS, where the external elastic
membrane can clearly be seen (a, arrow). |
IVUS remains the gold standard for the assessment
of stent strut apposition but is limited by low
resolution (100150 µm) and the artefacts induced
by the stent struts. More recently, optical coherence
tomography (OCT, LightLab®: Light Lab Imaging Inc.,
Westford, MA, USA), a relatively new imaging modality
using infrared light, has been used with the distinct
advantage of greater resolution (1015 m) and less
artefact compared with IVUS.46 With the improved
image resolution, this modality can give more precise
information on stent strut apposition, which may itself
play a pivotal role in unravelling some of the reasons
behind DES failures.
Future trends
Some of the important parameters of coronary stents
include the structure, geometry and dimensions.
These play an important role in deliverability, visibility,
scaffolding performance and procedural success.
Refinements of currently available stents will come
from improvements in flexibility and handling together
with advances in polymer design, with attention to biodissolvable
stent coatings47 especially given that the stent
polymer has come under scrutiny as a possible contributor
to long-term DES failure. Polymers currently utilized for
DES are either biodegradable or non-biodegradable.
While non-biodegradable polymers reside permanently
on the stent surface, biodegradable polymers are released
together with the drug and dissolve after a certain period
of time. One such stent, the Biolimus A9 stent (Biosensors
International, Singapore) is a novel DES that incorporates
the S-Stent platform, a thin, stainless steel, laser-cut,
tubular stent with 0.0054 strut thickness.48 Biolimus, a
sirolimus analogue, is coated onto the S-Stent platform
with a bio-absorbable, polylactic acid, polymer matrix that
releases the drug (~70% eluted in 30 days); subsequently
the polymer is absorbed over time locally into cells.48
Novel gene eluting stents with plasmid encoding human
vascular endothelial growth factor (VEGF) 2 coatings
have shown promise in reducing ISR in animal models
and may be used alone or in conjunction with other DES
in the near future.47 Apart from sirolimus and paclitaxel,
Tyrphostin AGL-2043, a potent tricyclic quinoxaline
inhibitor of platelet-derived growth factor (PDGF)
B receptor tyrosine kinase, has also demonstrated
impressive results in porcine models with the ability to
significantly reduce smooth muscle cell proliferation and
migration and reduce neointimal formation.47
A further novel technology aims to eventually do away
with the stent altogether. These biodegradable stents
are based on a magnesium alloy that allows controlled
corrosion with release to the vessel wall and the blood
stream of a natural body component such as magnesium
with beneficial anti-thrombotic, anti-arrhythmic and
anti-proliferative properties.49 Recently, a forthcoming
study (ABSORB) using a fully bio-absorbable stent coated
with everolimus was announced this aims to enrol 60
patients and assess the safety profile of this technology.50
Another recent advance uses a balloon catheter coated
with paclitaxel, thereby doing away with the stent
altogether. This technology has been successfully applied
to a small series of patients with in-stent restenosis51 and
may become a viable alternative for the treatment of
de novo coronary disease in the future.
 |
| Figure 3. An example of the utility of drug eluting stents in complex coronary
interventions. Angiography in this 73-year-old man revealed a lesion in the
left main bifurcation involving the ostium of the left circumflex (LCx, white
arrow, a) with a further occlusion in the mid left anterior descending artery
(LAD, black arrow, a). Following successful recanalisation of the occluded
LAD, a 3.0 x 23 mm Cypherฎ stent was implanted (b, black arrow). In
approaching the left main bifurcation lesion, two guide wires were used in
the LAD and LCx with a single Cypherฎ 3.5 x 28 mm stent implanted from
the LM to LCx, stenting across the LAD (b, white arrow). The procedure
ended with final kissing inflation. Nine-month follow-up angiography (c)
revealed widely patent stents. |
Conclusions
Drug eluting stents have been instrumental in
broadening the complexity and type of coronary lesions
treated by interventional cardiologists. With applications
in ISR, bifurcation lesions, chronic occlusions and
unprotected left main disease these novel devices have
played a great part in giving rise to excellent clinical
and angiographic outcomes. There remain, however,
unanswered questions relating to long-term risk of stent
thrombosis and the optimal duration of therapy with
both aspirin and clopidogrel. Such complications may be
addressed by future modifications in stent design and
delivery systems that will no doubt continue to modify
the ever-changing practice of interventional cardiology
well into the future.
Key Learning
- Drug eluting stents (DES) have changed the landscape of interventional cardiology with treatment of more
complex lesions in higher-risk patients
-
DES reduce in-stent restenosis significantly compared with bare metal stents, with rates less than 10% in
randomised trials
-
DES have been shown to be efficacious in treating bare metal in-stent restenosis, chronic total occlusions,
bifurcation lesions and unprotected left main disease
-
The ongoing concern with DES is late stent thrombosis, and this has led to confusion about the optimal
duration of therapy with both aspirin and clopidogrel
-
New stent technologies and advances are in the form of dissolvable polymers or fully bio-absorbable stents
that may negate the problems related to restenosis and stent thrombosis
|
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