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Chapter 19
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Dedicated Thrombus-Containing Stent
Platforms
Arthur Shiyovich
1
Institute of Interventional Cardiology, Petach Tikva, Israel;2Tel Aviv University, Tel Aviv-Yafo, Israel
1,2
and Ran Kornowski
1,2
INTRODUCTION
Coronary atherosclerosis is the main underlying cause of ischemic heart disease, while plaque disruption with superimposed throm bosis is the main cause of acute coronary syndrome (ACS) [1]. Non-ST-segment elevation myocardial
infarction (non-STEMI) and unstable angina are most commonly associated with a nonocclusive or transiently occlusive
thrombus (“white” thrombus), whereas STEMI is characterized by stable and occlusive thrombus (“red” thrombus) [2,3].
Thrombus burden can be evaluated using published classification scores (see Chapter 12), with the most widely used being
the thrombolysis in myocardial infarction (TIMI) thrombus grade [2,4,5]. The presence of an intracoronary thrombus is
associated with increased incidence of percutaneous coronary intervention (PCI)-related complications, in-hospital major
adverse cardiac events (MACEs) [6,7], and long-term mortality [8]. Furthermore, such a thrombus poses a great technical
challenge for interventional cardiologists [9], because it hampers the estimation of the vessel size and hence may result in
implantation of an undersized stent and late stent malposition, a known risk factor for stent thrombosis [10,11]. Moreover,
distal microembolization of thrombus debris or micromaterial from fissured and ruptured atheromatous plaques from the
infarct-related artery can compromise reperfusion at the microcirculatory level [12], even with a fully patent epicar dial
artery, and result in the “ no-reflow” phenomenon [13,14]. This often occurs throughout balloon dilatation or stent implantation due to thrombus fragmentation and protrusion by the stent struts [15] and is evident by continuing or recurrence
of symptoms such as chest pain, ischemic ECG changes such as persistent ST-segment elevation despite coronary
revascularization, or suboptimal myocardial blush score. The incidence of no-reflow has been reported to be as high as
50% [16], according to various angiographic definition criteria, with patients at highest risk being those with ACS or
undergoing PCI of saphenous vein grafts (SVGs). SVGs are commonly used conduits for surgical coronary revascularization but are associated with poor long-term patency rates due to accelerated atherosclerosis and intimal fibrosis [17].
Because repeat surgical revascularization is often associated with increased morbidity and mortality, PCI of a diseased
SVG is often the preferred strategy. However, owing to the distinct characteristics of the atherosclerotic plaque s in SVG
(longer, softer, more friable, and containing more embolic material) compared with native artery plaques, PCI of SVGs
comprises a high risk for distal embolization, no reflow, and periprocedural myocardial infarction (MI) [18]. Poor outcomes seen with no-reflow are probably related to reduced myocardial salvage and increased infarct size, and hence
increased rate of complications, including heart failure, arrhythmias, and reinfarction, is reported with this phenomenon
[13]. Furthermore, once no-reflow is established treatment is unlikely to be highly efficacious, thus various therapeutic
approaches, including pharmacologic and mechanical measures, focusing on prevention of embolization were introduced
[19]. The former typically include glycoprotein IIb/IIIa platelet inhibitors, while the latter include embolic protection
devices (filters and distal balloon occlusion with aspiration), mechanical thrombectomy, and manual or aspiration
thrombectomy catheters. Pharmacological measures showed conflicting results tending toward some benefit in this setting
[20,21]. Catheter-based thrombus aspiration showed signals of some benefit in earlier small studies [22], yet no beneficial
impact on outcomes and even increase in the incidence of stroke in more recent extensive randomized controlled studies
[23e25]
. Embolic protection devices have been shown to effectively retrieve debris and reduce the incidence of MACE
Cardiovascular Thrombus. https://doi.org/10.1016/B978-0-12-812615-8.00019-3
Copyright © 2018 Elsevier Inc. All rights reserved.
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and no-reflow phenom enon in patients undergoing PCI of degenerated SVGs [26,27], yet no improvements in thrombus
size or mortality were found in patients undergoing primary PCI [28]. In addition, these devices have multiple technical
deficiencies, as they often prolong the procedure, adding complexity to the PCI procedure. Among the recognized limitations of the embolic protection devices are the requirement of a distal “ landing zone,” device clogging, inability to protect
side branches, lack of postprocedural protection, and device-related vessel spasm [29e31]. Thus, novel thrombuscontaining stent platforms, designed as “built-in” and permanent embolic prote ction devices, have been introduced into
clinical trials and practice. Accordingly, the most prominent and widely investigated stents are the MGuard (InspireMD,
Boston, MA, USA), a balloon-expandable stent whose outer surface is covered by an ultrathin flexible mesh of the polymer
polyethylene terephthalate, and the STENTYS stent (STENTYS, Paris, France), a self-expanding and self-apposing nitinol
stent. Both dedicated stent platforms have shown promising results in high-thrombus-burden settings, especially primary
PCI in patients with STEMI and revascularization of SVGs. This chapter reviews thrombus-containing stent platforms,
describing their design, technical characteristics, and pathophysiological rationale. The chapter presents up-to-date clinical
evidence suggesting their potential role in contemporary interventional cardiology.
MESH-COVERED STENTS: RATIONALE AND TECHNICAL CHARACTERISTICS
The MGuard stent was conceived to both trap the thromboembolic debris underneath the fiber net and isolate the prothrombotic intima from the bloodstream [15]. It has also been hypothesized that the outer mesh of the MGuard stent could
enable a more uniform distribution of the radial force of the scaffold of the vessel wall [31]. Before the introduction of the
MGuard, several studies tested polytetrafluoroethylene covered stents in the revascularization of SVGs with rathe r
disappointing results, mostly due to postdilatation squeezing of embolic material (“toothpaste effect”) resulting in distal
embolization and high rates of restenosis [31e35]. Hence the MGuard was designed to be more flexible, with the outer
mesh looser and not completely sealing bifurcation branches [31].
The MGuard consists of a balloon-expandable bare metal stent (BMS) platform whose outer surface is covered by an
ultrathin flexible mesh of the polymer polyethylene terephthalate anchored to the external surface of the struts [15]
(Fig. 19.1).
The metallic frame of the first-generation stent used stainless steel with a strut thickness of 100 mm, whereas the new
MGuard Prime platform is manufactured of a cobalt chromium alloy (strut thickness 80 mm). The MicroNet is identical on
both stents, with a fiber width of 20 mm and an expanded aperture size of 150 180 mm [36]. Thus, during stent
deployment, the net stretches and slides over the expanding stent struts, creating custom-designed pores of z200 mmin
diameter (pores created by stent struts have 5- to 40-fold larger diameter, translating into 25- to 1600-fold larger crosssectional area) [30]. MGuard and MGuard Prime diameters range from 2.5 to 4.0 mm, while lengths range from 11 to
39 and 13 to 38 mm, respectively [15]. Both stents are compatible with 0.014-inch guidewires and 6-Fr guiding catheters.
The crossing profile is slightly higher than that of newer-generation BMSs (1.1e1.3 mm for the stainless steel platform and
1.0e1.2 mm for the cobalt chromium platform), which together with the close-cell design may impair to some extent the
deliverability [15].
STUDIES EVALUATING THE MGUARD STENT
MGuard in ST-Segment Elevation Myocardial Infarction
Nonrandomized Trials
Following successful preliminary deliverability and safety studies that evaluated the MGuard in a porcine model [37] and
in acute myocardial infarction patients with coronary lesions that were highly prone to embolization [38], MGuard was
successfully tested in the acute setting of primary PCI for STEMI in a small case series (n ¼ 5) [39]. Subsequently, the
MGuard was evaluated in STEMI involving native coronary arteries in four uncontrolled single- and multicenter studies
that included altogether more than 300 patients (Table 19.1) [40e 44].
Patients with large side branches, cardiogenic shock, or chronic kidney disease were often excluded. These studies
demonstrated high rates of successful implantation of the MGuard, with relatively low rates of di stal embolization or
procedure-related complications. Furthermore, good procedural outcomes (which were the primary outcomes of these
studies), expressed mainly as achievement of myocardial blush gr ade (MBG) 3, complete (70%) ST-segment resolution (STR), and TIMI flow 3 were reported in 55%e90%, 59%e90%, and 82%e 97% of patients, respectively
(Fig. 19.2).
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FIGURE 19.1 The MGuard is a mesh-covered stent
designed to trap atherothrombotic debris.
Although these studies were inadequately designed for drawing conclusions regarding clinical outcomes, strong
consistent signals of an overall safe and efficacious device were reported: in-hospital deaths were generally not high
(except when cardiogenic shock patients were included), MACE rates were in the range of 0%e10.6% at 1e38.7 months
(mean) follow-up in these studies, with stent thrombosis rates approximating 2%. A multicenter Polish study showed that
the early safety and efficacy of angiographic and clinical outcomes of the MGuard stent were excellent and stayed so for
1 year following STEMI [41,42]. The study of Romaguera et al. [43] is of particular interest for showing the MGuard
device to be highly efficacious and relatively safe in thrombus containment in STEMI patients with high thrombus burden
(TIMI score 4e5), which was present despite initial application of mechanical aspiration.
Randomized Trials
Following rather successful preliminary and uncontrolled trials with the MGuard stent, subsequent randomized multicenter
studies emerged (Table 19.1). These studies, with the MASTER study as the largest and most important completed study as
of this writing, included almost 800 patients altogether and further substantiated the angiographic merits of the MGuard
device in patients with STEMI. Yet, the randomized studies were still underpowered to discern statistically significant
differences in the hardest and most critical clinical end points. Nevertheless the MASTER trial reported a trend toward
reduced mortality with the MGuard stent that became significant after pooling the results of the MAS TER I and II trials. On
TABLE 19.1 Clinical Trials Evaluating MGuard Stent for Treatment of ST-Segment Elevation Myocardial Infarction
https://t.me/med1917
Procedural Outcomes (MGuard vs. Control)
Study Name/Year Study Type n
Nonrandomized Studies
Piscione et al. (2010) [40] Multicenter
MAGICAL (2010) [41,42] Multicenter
Romaguera et al. (2013)
[43]
Cerrato et al. (2015) [44] Single cen-
Randomized Studies
MICAMI-MGUARD
(2013) [48]
single arm
single arm
Single center, single
arm
ter, single
arm
Multicenter
randomized
Stents
Evaluated Follow-Up
100 MGuard 30 days Distal edge dissection 1% Complete STR 90%
60 MGuard 38.7 months
56 MGuard 9 months Failed implantation 1.8%
104 MGuard 455 days
40 MGuard vs.
BMS
(mean)
(mean)
6 months NA TIMI flow 3 90% vs.
Distal edge dissection 3.3%
Distal embolization 5%
Coronary spasm 3.3%
Edge dissection 1.8%
Side-branch occlusion 3.5%
Side-branch embolization 8.9%
No reflow 4.1%
NA Complete STR 64%
Reperfusion
Outcomes
TIMI flow grade
cTFC (mean) 17.2
10.5
MBG 3 90%
Complete STR 61%
TIMI flow 3 90%
MBG 3 73%
Complete STR 59%
TIMI flow 3 82%
MBG 3 55%
TIMI flow 3 97%
MBG 3 57%
80%, P ¼ NS
MBG 3 90% vs. 50%,
P [ .0006
cTFC £23 85% vs. 30,
P < .001
Clinical End PointsTechnical Complications
In-hospital mortality 7%
ST 2%
MACE (postdischarge) 0%
6 months
MACCE 1.7%
MACE 0%
TLR 0
Mortality 0
38.7 months (mean)
MACCE 8.8%
MACE 8.8%
TLR 1.8%
Mortality 8.8%
MACE 3.6%
ST 1.8%
Mortality 0
In-hospital mortality 2.9%
MACE 10.6%
Cardiac mortality 4.9%
ST 1.9%
ST 5% vs. 5%, P ¼ NS
MACE 0% vs. 0%, P ¼ NS
288 Cardiovascular Thrombus
a
MASTER (2012)
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[45,46,49,50]
MASTER II (2014) [47] Multicenter
MASTER I þ II pooled
analysis (2014) [47]
GUARDIAN
b
[51] Multicenter
Multicenter
randomized
randomized
Multicenter
randomized
randomized
433 MGuard vs.
BMS/DES
310 MGuard vs.
BMS/DES
743 MGuard vs.
BMS/DES
556 MGuard vs.
BMS
1 year Failure to cross lesion 4.1%
Stent dislodgment 0.9%
30 days MGuard arm
Failure to cross lesion 2.6%
Stent dislodgment 3.2%
Failure to deploy 3.2%
Control arm
Failure to cross lesion 0.6%
Other 0.6%
30 days Any device failure 5.6% vs.
1.3%, P [ .03
NA NA NA
Complete STR 57.8%
vs. 44.7%, P [ .008
TIMI flow 3 91.7%
vs. 82.9%, P [ .006
MBG 2/3 83.9% vs.
84.7%, P ¼ NS
cTFC 17 vs. 18
P ¼ NS
Complete STR 56.9%
vs. 59.3%, P ¼ NS
TIMI flow 3 91.4%
vs. 89%, P ¼ NS
Complete STR 57.5%
vs. 50.7%, P ¼ .07
TIMI flow 3 91.6%
vs. 85.4%, P [ .008
cTFC 18 vs. 18,
P ¼ NS
30 days
1 year
MACE 2.6% vs. 4.5%,
P ¼ NS
Mortality 0.6% vs. 1.9%,
P ¼ NS
ST 2.6% vs. 3.2%, P ¼ NS
TLR 2.6% vs. 2.6%,
P ¼ NS
MACE 2.2% vs. 3.2%,
P ¼ NS
Mortality 0.3% vs. 1.9%,
P [ .04
ST 1.9% vs. 1.9%, P ¼ NS
TLR 2.2% vs. 1.3%,
P ¼ NS
MACE 1.8% vs. 2.3%,
P ¼ NS
Mortality 0% vs. 1.9%,
P ¼ .06
TLR 1.8% vs. 0.5%,
P ¼ NS
ST 1.4% vs. 0.9%,
P ¼ NS
MACE 9.1% vs. 3.3%,
P [ .02
Mortality 1% vs. 3.3%,
P ¼ .09
TLR 8.6% vs. 0.9%, P
[ .0003
ST 2.3% vs. 0.9%,
P ¼ .26
Dedicated Thrombus-Containing Stent Platforms Chapter | 19 289
Continued
TABLE 19.1 Clinical Trials Evaluating MGuard Stent for Treatment of ST-Segment Elevation Myocardial Infarctiondcont’d
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Procedural Outcomes (MGuard vs. Control)
Study Name/Year Study Type n
Stents
Evaluated Follow-Up
Reperfusion
Outcomes
“Real-world” Postmarketing Studies
IMOS Prime (2015) [52] Multicenter,
single arm
97 MGuard
prime
12 months Complications 0% Complete STR 76%
TIMI flow 3 92%
MBG 3 74%
REWARD-MI (2015) [53] Single cen-
ter, double
158 MGuard vs.
BMS
10 months No reflow 3.8% vs. 3.8%,
P ¼ NS
TIMI flow 3 97.5% vs.
94.9%, P ¼ NS
arm
Vaknin-Assa et al. (2017)
[54]
Single center, single
MGuard 1 year Delivery failure 1.9%
45
Slow/no reflow 9%
TIMI flow 3 99% MACE 11%
c
arm
290 Cardiovascular Thrombus
Clinical End PointsTechnical Complications
30 days
MACE 2.2%
TLR 1.1%
ST 1.1%
MACE 20.3% vs. 12.7%,
P ¼ NS
Mortality 7.6% vs. 7.6%,
P ¼ NS
ST 2.4% vs. 1.3%, P ¼ NS
TLR 11.4% vs. 1.3%, P
[ .009
Mortality 1.9%
MI 1.9%
ST 1.9%
TVR 7.4%
TLR 5.6%
Bold results indicate statistically significant findings.
BMS, bare metal stent; cTFC, corrected TIMI frame count; DES, drug-eluting stent; MACCE, major adverse cardiac and cerebrovascular events; MACE, major adverse cardiac events; MBG, myocardial
blush grade; MI , myocardial infarction; NA, not available; NS, not significant; ST, stent thrombosis; STR, ST-segment resolution; TIMI, thrombolysis in myocardial infarction; TLR, target-lesion revascularization; TVR, target-vessel revascularization.
a
Most deaths (5/7) occurred in patients presenting with cardiogenic shock.
b
Not yet completed or published.
c
Includes 83% STEMI and 17% non-ST-segment elevation acute coronary syndrome.
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FIGURE 19.2 Inferior STEMI in a thrombotic right coronary artery (RCA) culprit vessel (left image) with a focal thrombotic aneurysmal dilatation
(arrow), treated using initial coronary aspiration (top middle image), followed by predilatation with a 1.5 20-mm balloon (bottom middle image,
arrows) and implantation of the MGuard stent (right image, arrows). Final TIMI 3 flow and optimal myocardial blush were established in this case. STEMI,
ST-segment elevation myocardial infarction; TIMI, thrombolysis in myocardial infarction.
the other hand, technical difficulties that resulted in a reduced rate of successful stent implantation, increased stent
dislodgment, and especially an increased rate of ischemia-driven target-lesion revasc ularization were reported for the
MGuard mesh-covered BMS compared with control stents [45e47].
The MICAMI-MGUARD trial was a small randomized study that included 40 patients with STEMI referred for primary PCI and randomized 1:1 for MGuard stent or a BMS [48] and showed better angiographic results in the MGuard
group compared with the control arm, with no differences in clinical outcomes at 6-month follow-up.
The MASTER trial reported by Stone et al. [45] was the largest prospective, randomized multicenter evaluation of the
MGuard stent in patients with STEMI. A total of 433 patients presenting with STEMI within 12 h of symptom onset and
undergoing PCI at 50 international sites in nine countries were randomized 1:1 to the MGuard (n ¼ 217) or commercially
available stents (either BMS or drug-eluting stent [DES]) (n ¼ 216). Successful implantation rates were somewhat better in
the control arm (95.9% for MGuard vs. 99.1% for control, P ¼ .003) and two cases of MGuard dislodgment were reported.
However, superior reperfusion indices (complete STR and TIMI 3 flow) were reported for the MGuard arm. Thirty-day
mortality for the MGuard arm tended to be lower, with borderline statistical significance (MGuard 0% vs. control
1.9%, P ¼ .06), while the rate of MACE at 30 days did not significantly differ between the groups. Clinical outcomes at
12-month follow-up were overall similar, with a mildly weaker trend toward reduced mortality in the MGuard group (1%
vs. 3.3%, P ¼ .09, respectively) [46]. However, a significantly incre ased rate of MACE at 12 months was observed
(MGuard 9.1% vs. control 3.3%, P ¼ .02), attributed mainly to increased rate of ischemia-driven target-lesion revascularization (8.6% vs. 0.9%, P ¼ .0003) in the MGuard arm compared with the control arm, respectively. Stent thrombosis
rates did not significantly differ between the two arms [46] . Subsequent two-subgroup analyses showed that differences
toward better outcomes with MGuard are most prominent with large thrombus burden [49] or long delay time [50].A
substudy of 59 patients who underwent cardiac magnetic resonance, which was performed 3e5 days following the index
procedure, did not demonstrate significant differences in infarct size or microvascular obstruction between the groups.
Since the MASTER trial was underpowered for long-term hard clinical outcomes, the subsequent MASTER II trial [47]
was an international, multicenter, randomized trial designed to enroll 1114 patients to show superiority of the MGuard
Prime stent versus conventional PCI, especially in all-cause mortality and target-vessel MI. However, the MASTER II trial
was voluntarily suspended in April 2014 because of a higher than expected frequency of MGuard Prime stent dislodgment
(3.2%). A total of 310 patients were enrolled, with no statistically significant differences in the analyzed outcomes. A
pooled analysis of the MASTER I and II trials (n ¼ 743) [47] showed increased rate of any device failure for the MGuard
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compared with the control stents (5.6% vs. 1.3%, P ¼ .03). Furthermore, angiographic success was superior only for the
rate of TIMI 3 flow in the MGuard stent. Considering clinical outcomes, the rate of MACE at 30 days was also similar in
both groups (2.2% MGuard vs. 3.2% control, P ¼ .36). However, a statistically significant mortality benefit at 30 days was
observed with the MGuard stent compared with control stents (0.3% vs. 1.9%, P ¼ .03). Nevertheless, these findings
should be interpreted carefully considering the inherent limitations of pooling analyses from different studies and premature termination of the pivotal MASTER II trial.
The GUARDIAN trial [51] was planned as a multicenter, prospective, randomized, open-label noninferiority study, to
investigate whether the use of the MGuard stent without manual thrombus aspiration is noninferior to thrombus aspiration
followed by BMS implantation in patients with STEMI. However, results have not been reported as of this writing.
Real-World Experience
Several “real-world” reports evaluated the MGuard device in STEMI patients undergoing primary PCI (Table 19.1). These
studies are largely from Europe since the MGuard received European regulatory approval (C E Mark), yet as of this writing
it is not approved for clinical use the United States. Although relatively small, including a few hundred patients, these
studies, as well as our experience, show that real-world results are consistent with those of clinical trials [52e54].Successful stent delivery and implantation rates were high, though some failures were reported. Most patients achieved good
procedural reperfusion outcomes and when no reflow existed it usually resolved with pharmacologic therapy. Clinical
outcomes and real-world comparison did not show a consistent advantage of the MGuard stent over BMS, but rather a
significant increase in target-lesion revascularization rates as was already seen in the MASTER trial [45e47].
MGuard for Revascularization of Saphenous Vein Grafts
The implantation of the MGuard stent in SVGs was evaluated in small nonrandomized trials with overall promising
outcomes. The first-in-man study [38] included 17 patients that underwent SVG PCI. Device success was 100% and TIMI
3 flow was observed in all cases. One patient experienced periprocedural MI, while no MACEs were reported at 30-day
follow-up. However, the subsequent extension of the study with 23 SVG interventions and follow-up of up to 20 months
showed a MACE rate of 23%. No stent thrombosis or cardiac deaths were reported. The INSPIRE trial [55] included 16
patients with de novo SVG lesions undergoing PCI. The MGuard stent was successful ly implant ed in all cases with no
procedural complications. Final TIMI 3 flow and MBG 3 were achieved in all cases with no MACEs up to 30 days
following the procedure (Fig. 19.3).
FIGURE 19.3 MGuard stents deployed in a degenerated and thrombotic SVG with multiple stenotic lesions (arrows, left), with excellent PCI result
following implantation of four MGuard stents (right), with favorable clinical durability at 3 years of follow-up. PCI, percutaneous coronary intervention;
SVG, saphenous vein graft.
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The experience of our academic medical center [54] includes more than 100 cases of SVG PCI (about 80% with ACS),
with a mean graft age of 14 years. There were two cases of delivery failure. Transient no reflow or slow flow complicated
8% of the patients, most of which resolved following pharmacologic treatment, and final TIMI 3 was observed in 98% of
the cases. One-year mortality was 10% (4% cardiac death), with a MACE rate of 29%, mainly driven by respective targetlesion or -vessel revascularization (11% and 15%, respectively). The rate of stent thrombosis was 1.8%.
MGuard in Other Coronary Pathologies
Coronary Aneurysm
Coronary aneurysms are rare localized dilatations exceeding the diameter of adjacent normal segments by 50% or more,
with a reported incidence of 0.3%e4.9% [56], and can result in rupture, thrombus formation, and distal embolization
[15,57]. The therapeutic approach toward coronary aneurysms is controversial and includes surgical approach, percuta-
neous covering stent, and medical management (e.g., antiplatelet, anticoagulation therapy) [58]. Previous attempts at
treatment of coronary aneurysm with the polytetrafluoroethylene-covered stents were limited by their dimension, their low
flexibility, the lack of access of side branches, and the inherent risk of restenosis [59,60]. Considering its increased
flexibility and low profile, the MGuard stent was also evaluated for the treatment of anecdotal coronary aneurysms in
several reported cases with partial success: three case reports showed complete exclusion of the aneurysm, while another
two cases did not achieve such total exclusion [61e63].
Coronary Perforation
When coronary perforation, an uncommon but potentially catastrophic complication of PCI, occurs, the initial approach
usually comprises prolonged balloon inflation and anticoagulation reversal. When the latter fails, implantation of a covered
stent is considered. A previous report showed successful implantation of the MGuard stent in two patients with coronary
perforation [64]. In both patients the perforation was sealed successfully by the MGuard stent in a bailout situation without
significant procedure-related complications; however, they developed symptomatic in-stent restenosis 9e12 months after
the perforation. It has been postulated that in addition to the mechanical compression and stretching of the perforated
vessel, the net, although pored, appears to be an effective mechanical barrier, preventing leakage to the pericardial cavity,
while allowing endothelization of the stent [15].
SELF-EXPANDING AND SELF-APPOSING STENTS: RATIONALE
Self-expanding means that the stent deploys and increases in volume because of its inherent temperature-dependent elasticity
without the need for balloon dilatation. It is different from self-apposing, which refers to the ability of a stent to adapt to
changes in shape and inward or outward vessel wall defect [65]. The concept of self-expanding coronar y stents is not new;
actually the first coronary stent reported to be implanted in humans was a self-expandable stent made of the nitinol alloy [66].
However, because of significant technical limitations and high rates of restenosis with the use of these self-expandable stents,
balloon-expandable stents have predominated since the 1990s. Stent malapposition, or incomplete stent apposition, is a
morphological description defined by the lack of contact between at least one stent strut and the underlying intimal surface of
the arterial wall in a segment not overlying a side branch [67,68]. This phenomenon is often identified by intravascular
imaging tools such as intravascu lar ultrasound and optical coherence tomography [67e69] and can be classified as acute
(detected at the time of the stent implantation) or late (detected during subsequent follow-up). The risk factors for stent
malapposition are clinical (e.g., ACS, especially STEMI; younger age; large vessels) as well as periprocedural parameters
(e.g., DES, longer stent length, an ectatic small-caliber vessel). Stent malapposition is of great importance because of the
association with increased risk for stent thrombosis [65,68,70,71]. Although the pathophysiological mechanisms explaining
this association are not utterly clear, the plausible belief is that stent malapposition serves as a nidus for clotting factors, fibrin,
and platelet deposition, hence creating a prothrombotic vascular milieu with increased risk for thrombus formation [68].
Optimizing stent choice and implantation techniques is considered pivotal for reducing incomplete stent apposition
[68]. The self-expanding, self-apposing nitinol stent (STENTYS, Paris, France) was designed to overcome the pathological
mechanisms related to incomplete stent apposition [65] and to spare the potentially traumatic balloon expansion.
STENTYS STENT: DESIGN AND TECHNICAL CHARACTERISTICS
The STENTYS frame comprises several important features providing anatomical and functional advantages (Fig. 19.4).
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FIGURE 19.4 Schematic representation of the STENTYS self-expanding, self-apposing stent within a thrombotic vessel (left) and as imaged during
coronary angiography (right).
First, it has a highly biocompatible nitinol coronary scaffold. Nitinol is a metallic alloy of nickel and titanium that has
two important traits: superelasticity and shape memory. The latter enables self-expansion following heat absorption
throughout the release from the delivery system in the coronary artery and adaptation to vessel size and shape in a way that
ensures full strut apposition during the procedure and thereafter (e.g., following vessel remodeling or thrombus dissolution). Moreover, self-apposition and self-expansion can potent ially reduce restenosis by attenuating deleterious pathological components such as stent-induced vascular barotraumas, underexpansion, and residual atherosclerotic plaque
[65,71,72]. Second, a closed Z-shaped cell design potentially reduces thrombus embolization and the occurrence of no
reflow. Third, the presence of easily breakable (by low-pressure balloon inflation) small interconnectors between the cells
all along the device’s longitude (except first and last 2 mm) enables easy access to side branches in bifurcation lesions and
confers a therapeutic advantage in this setting for which the STENTYS was originally designed [73].
The STENTYS stents are commercially available in three types: STENTYS BMS, STENTYS paclitaxel-eluting stent,
and STENTYS sirolimus-eluting stent. In the STENTYS sirolimus-eluting stent, the antiproliferative drug is embedded in a
polymer that lies on the aluminal side of the stent [65]. The STENTYS DES diameters range from 2.5 to 4.5 mm, while the
available lengths are 17, 22, and 27 mm. The delivery catheter is a rapid-exchange single-wire system with hydrophilic
coating, compatible with a 6-Fr guide catheter and a 0.014-inch guidewire. The delivery of the STENTYS is considered
somewhat more intricate than that of balloon-expandable stents. The stent is deployed through a retractable sheath and the
system comprises a trigger handle and three markers: a proximal stent marker, a distal stent marker, and the outer sheath
marker. It is recommended to advance the device distal to the stenosis by at least 5 mm, then pull back the stent until it
reaches the desired position, and then implant the stent while keeping the whole system in tension during implantation [74].
Throughout the first days following deployment the stent gradually expands and adheres to the vessel.
STENTYS in ST-Segment Elevation Myocardial Infarction
The series of APPOSITION IeV clinical trial programs evaluated STENTYS implantation in patients presenting with
STEMI. The design and main findings of these trials are summarized in Table 19.2.
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