(Circulation. 1996;93:412-422.)
© 1996 American Heart Association, Inc.
Articles |
From the Thoraxcenter, Department of Interventional Cardiology, Erasmus University, Rotterdam, Netherlands.
Correspondence to Prof P.W. Serruys, MD, PhD, Thoraxcenter, Department of Interventional Cardiology, Erasmus University, Dr Molewaterplein 40, 3015 GD Rotterdam, Netherlands.
| Abstract |
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Methods and Results The study consisted of three initial phases (I, II, III) during which resumption of heparin therapy after sheath removal was progressively deferred by 6, 12, and 36 hours. In phase IV, coumadin and heparin were replaced by 250 mg ticlopidine and 100 mg aspirin. Of the 207 patients with stable angina pectoris and a de novo lesion in whom heparin-coated stent implantation was attempted, implantation was successful in 202 patients (98%). Stent thrombosis did not occur during all four phases, and the overall clinical success rate at discharge was 99%. Bleeding complications requiring blood transfusion or surgery fell from 7.9% in phase I to 5.9%, 4%, and 0% in the three following phases. Hospital stay was 7.4, 6.1, 7.2, and 3.1 days for the consecutive phases. The restenosis rate for the combined four phases was 13% (15% in phase I, 20% in phase II, 11% in phase III, and 6% in phase IV). The overall rate of reintervention for the four phases was 8.9%. At 6 months, 84%, 75%, 94%, and 92% of the patients of phases I to IV, respectively, were event free. For the four phases, the event-free rate was 86%, which compares favorably with the rate observed in the Benestent-I study (80%; relative risk, 0.68 [0.45 to 1.04]).
Conclusions The implantation of stents coated with polyamine and end-pointattached heparin in stable patients with one significant de novo coronary lesion is well tolerated, is associated with no (sub)acute stent thrombosis, and results in a favorable event-free survival after 6 months.
Key Words: heparin stents anticoagulants angina coating
| Introduction |
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The Benestent-I trial, a multicenter randomized study comparing the safety and efficacy of primary Palmaz-Schatz stent implantation with PTCA in patients with stable angina pectoris and a single de novo lesion in a native coronary artery demonstrated that event-free survival was higher at 6 months' follow-up in patients who received a stent compared with patients treated with PTCA (80% versus 70%).3 This was largely due to a reduction in repeat revascularization in patients treated with a stent, associated with a significantly lower RR in this group (22% versus 32%).
However, the incidence of bleeding complications (13.5%, bleeding episodes or peripheral vascular complications at the puncture site) and subacute coronary thrombosis (3.5%) reflects the difficult balance between the thrombogenicity of the stent and the need for an intensive anticoagulation regimen.4 In addition, the hospital stay was considerably longer (8.3 days) in the stent group because of the need to monitor anticoagulation. Thus, the positive effects in terms of event-free survival were partly negated by a prolonged hospital stay and bleeding complications. To further improve the clinical results of coronary stenting, attention was directed to coating the stent with material that would minimize the risk of abrupt stent closure and thereby allow a reduction in anticoagulant therapy. With this objective in mind, a heparin-coated stent has been developed.5 6 7 8
Covalent binding of heparin onto solid surfaces by end-point attachment has become technically possible, allowing heparin to interact freely with plasma components and enzymes, thereby expressing its biological activities and resulting in a highly biocompatible surface. The compatibility of this bioactive surface with circulating blood is achieved by at least three mechanisms: inhibition of the activation of coagulation, potentiation of the inhibition of the activated coagulation enzymes, and prevention of platelet adhesion to the surface.
Data from animal studies indicate that Palmaz-Schatz stents with this heparin coating are associated with a significant reduction in acute thrombus formation. In stented rabbit iliac arteries a reduction in angiographically detected thrombus was observed at 4 and 24 hours.5 6 In a baboon extracorporeal arteriovenous shunt (N. Chronos, MD, private communication, 1995) and in an in vitro circulation loop with bovine blood, indium-labeled platelet attachment to the same stents was reduced by 95% or more by the heparin coating compared with uncoated stents.
In a porcine coronary model, heparin-coated and uncoated Palmaz-Schatz stents were implanted in the LAD. In pigs that received a coated stent, no thrombotic events were recorded compared with a 30% to 40% occlusion rate with uncoated stents.8 These data formed the basis of the present study investigating this heparin-coated version of the Palmaz-Schatz stent in clinical practice.
| Methods |
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The secondary objectives were the determination of the efficacy of heparin-coated stent implantation (symptom and event-free survival at 6 monthsfreedom from death, MI, repeat intervention, or CABG) and the evaluation of the changes in stenosis geometry immediately after stent implantation and at 6 months by quantitative coronary angiography.
Definitions
(Sub)acute thrombotic stent occlusion was defined
as either the
angiographic documentation of a complete occlusion (TIMI flow 0 or 1)
or the angiographic documentation of a flow-limiting thrombus (TIMI
flow 1 or 2). Intracoronary thrombus was defined as the
presence of a filling defect within the lumen, surrounded by contrast
material seen in multiple projections in the absence of calcium
within the filling defect, or the persistence of contrast material
within the lumen or a visible embolization of intraluminal material
downstream. Acute occlusion was defined as occurring in the
interventional suite when the guiding catheter was still in place;
subacute occlusion was defined as occurring after removal of the
guiding catheter and outside the interventional suite.
Bleeding complications included any clinical (ie, direct) or biological (ie, indirect) evidence of bleeding. Bleeding was classified as major if it was overt and produced a fall in hemoglobin of at least 5 g/dL or 3.1 mmol/L, if it led to transfusion of 2 or more units of whole blood or packed cells, if it was retroperitoneal, or if it occurred into a major prosthetic joint space. Bleeding was classified as minor if it was overt but did not meet the criteria of major bleeding. Hematuria was classified as follows: macroscopic (ie, clinically evident), microscopic (more than four erythrocytes per high-power field in the urine sediment obtained from fresh, concentrated, clean voided urine specimen), or absent (absence of red cells or presence of less than four erythrocytes per high-power field). Intracranial hemorrhage: All cerebrovascular accidents occurring in patients receiving anticoagulant drug therapy were considered as intracranial hemorrhage unless CT scan of the brain unequivocally demonstrated an ischemic stroke.
False aneurysms and arteriovenous fistula necessitating transfusion and/or surgical treatment were reported as adverse events and bleeding complications.
The occurrence of all cardiac and noncardiac clinical events over an observational period of 7 months (death, MI, repeat interventionpercutaneous reintervention or CABG) was assessed. Death was defined as all deaths, regardless of cause. MI was diagnosed if there were new pathological Q waves according to the Minnesota Code9 or if there was an increase in serum creatine kinase to more than twice the normal value, together with a pathological increase in myocardial isoenzymes. Bypass surgery was defined to include emergency or elective bypass surgery involving the previously treated segment. Emergency bypass surgery was defined as involving an immediate transfer from the interventional suite to the operating room during the initial phase of treatment. Repeat interventions were those involving the target lesion that followed the initial procedure. Revascularization (surgical or percutaneous) involving other coronary arteries did not constitute an end point.
Study Design
After stent implantation, heparin was
reinstituted in a stepwise
fashion. The study consisted of four phases in which a total of 203
patients were treated with a single stent (51, 51, 51, and 50 patients
in each of the four phases). One attempt to implant a stent failed and
resulted in the death of the patient; the remaining 202 patients
successfully received a heparin-coated stent. Heparin infusion was
started 6, 12, and 36 hours after sheath removal in the first three
phases, respectively. In phase IV, no heparin or coumadin was given,
but patients were treated with aspirin (>100 mg/d) and ticlopidine
(250 mg/d).
The decision to proceed with the study from one phase to the next was based on a predetermined incidence of (sub)acute thrombotic stent occlusion. If three or more incidents of subacute stent thrombosis occurred in any phase (based on a 3.5% angiographically demonstrated subacute thrombosis rate in Benestent-I), the study had to be terminated.
Selection of Patients
Patients scheduled to undergo
angioplasty because of stable
angina due to a single de novo lesion in a coronary artery were
eligible if they had no contraindication to anticoagulation or
antiplatelet therapy and if they were suitable candidates for
CABG. The target lesion was required to be less than 15 mm long and
located in a vessel
3.0 mm supplying normally functioning
myocardium. Patients having an ostial lesion or a lesion at
a bifurcation or in a previously grafted vessel were excluded as well
as patients in whom an intracoronary thrombus was
suspected.
The study was carried out according to the Declaration of Helsinki. Written or witnessed oral informed consent according to the local practice was obtained for every patient.
Stent Coating
Palmaz-Schatz PS 153 coronary stents, 15 mm
long with a
central articulation, were coated with a modified version of the
Carmeda Bioactive Surface (Carmeda AB).10 The stainless
steel stent was coated with base layers of polyethylene imine and
dextran sulfate (Fig 1
). Aldehyde-terminated heparin
(porcine mucosal origin) was covalently bonded to the polyethylene
imine surface layer.11 After coating, the stents were
washed in borate buffer and deionized water to remove unbound heparin.
The efficacy of this coating is based on the continuous and repeated
interaction between the active site of the immobilized
heparin and circulating antithrombin III. The coated stents were
mounted on 3.0-, 3.5-, and 4.0-mm polyethylene balloon delivery
catheters with integral sheath (Johnson & Johnson Interventional
Systems Co) and sterilized with ethylene oxide gas. The coating was
optimized to provide a high level of antithrombin-III binding-site
bioavailability, as measured by antithrombin-binding assay and
expressed as picomoles (antithrombin III binding activity) per
stent.
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Medical Regimen
Beginning the day before the procedure, all
patients received
250 to 500 mg of aspirin daily. This medication was continued for 6
months. Diltiazem 120 mg BID was continued until hospital discharge. In
the first three phases, coumadin was given from the day of stent
implantation for a period of 3 months. Heparin was administered as a
bolus dose of 10 000 IU at the start of the procedure and reinstituted
as a continuous infusion 6 hours (phase I), 12 hours (phase II), and 36
hours (phase III) after removal of the arterial sheath.
Sheath removal took place when the activated partial
thromboplastin time had fallen to below twice the normal value (normal
range, 30 to 40 seconds). Heparinization was gradually decreased when
the international normalized ratio was within the therapeutic range
(2.5 to 3.5) for at least 36 hours. In phase IV, patients received
ticlopidine (250 mg/d) for 1 month starting the day before the
procedure. In this phase coumadin was not given and heparin 10 000 IU
was administered only during the procedure. No heparin was administered
after removal of the sheath. An additional outpatient visit at day 15
was planned for the patients recruited in phase IV to detect any
abnormality in white blood cell count or liver enzyme elevation induced
by ticlopidine. None was documented at 15 or 30 days in the 50 patients
of phase IV.
Clinical and Angiographic Follow-up
Patients were seen at the
outpatient clinic at 1, 3, and 6
months for an interview, physical examination, exercise testing, and
ECG. One of the major drawbacks of studies on the prevention of
coronary restenosis is that at follow-up the
angiographic knowledge of coronary anatomy may
influence the physician's therapeutic decision and artificially
increase (or decrease) the number of repeat interventions. To
circumvent this possible source of bias, a second intervention was
considered an end point only when it was substantiated on the basis of
anginal symptoms or objective evidence of ischemia. For that
purpose, exercise testing was performed before the 6-month repeat
catheterization. The objective signs of
ischemia as well as the exercise protocols followed in the
different participating centers were left to the discretion and
judgment of the respective exercise testing laboratories.
Three angiograms were obtained for each patientone immediately before the intervention, one immediately after, and one at follow-up. If a revascularization procedure involving the treated segment had been performed before the 6-month repeat angiography, the last angiogram obtained before this intervention was used as the follow-up angiogram irrespective of the timing of repeat intervention. If the time to follow-up angiography was less than 3 months and no repeat intervention was performed, the patient was asked to undergo another angiogram at 6 months. In the absence of a 6-month repeat angiogram, the last angiogram obtained within the previous 3 months, if available, was used provided that no end point had occurred.
All angiograms were analyzed by the Cardiovascular Angiography Analysis System and sent to the core laboratory (Cardialysis, Rotterdam, the Netherlands). To standardize the method of data acquisition and to ensure exact reproducibility of postintervention and follow-up angiograms, methodology was standardized as described previously.12
The quantitative analysis was applied to two different segment lengths of the treated coronary artery: the vessel analysis was applied to the segment located between two sizeable side branches that were used as landmarks to determine the length of the segment to be analyzed. If a lesion overlapped a side branch, the next side branch was taken as a landmark. The stent analysis was applied to the part of the vessel (stenotic and nonstenotic) actually stented. This dual type of analysis was deemed necessary because most of the vessels taper, and frequently after stenting the MLD is found to be outside the stented area. In each analyzed segment, a mean diameter, an MLD, and a reference interpolated diameter were determined. The stent/artery ratio was defined as the ratio between the mean diameter of the stent (stent analysis) and the RD (vessel analysis) predilatation. It quantifies correct stent deployment more appropriately than the measurement of the DS within the stent.
Statistical Analysis
The main clinical analysis consisted of
the
determination of the primary clinical end points in the time period
between stent implantation and 30 days after the implantation; this
analysis included all patients except those in whom no stent
implantation had taken place.
The secondary clinical end point was evaluated by performing a total count of all clinical events (nonmutually exclusive) and by ranking these clinical events according to the highest category on a scale ranging from (1) death, (2) MI, (3) emergency CABG, (4) elective CABG, and (5) repeat PTCA.
The main angiographic analysis consisted of the determination of the MLD at follow-up of all patients in whom a stent had been implanted and whose angiogram was suitable for quantitative coronary angiography.
Discrete variables were expressed as counts and
percentages. The
2 test with Yates' correction was used to
compare proportions. Comparison of proportions was expressed as
relative risks (for stenting compared with the historical series of
Benestent-I), with 95% CIs calculated by the formula of Greenland and
Robins.13 Continuous variables were expressed as
mean±SD and compared by the unpaired Student's t test.
All
statistical tests were two-tailed. A value of P<.05 was
considered statistically significant.
| Results |
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In phases I, III, and IV all the
implantation procedures were
successful. In one phase II patient, the ostium of a right
coronary artery was dissected, mandating acute surgery. This
patient died postoperatively from intractable arrhythmias and
is included in the report. Four other patients from phase II were
excluded from further analysis as they did not receive a stent.
In 3 patients, the Stent Delivery System could not cross the lesion;
they underwent an uneventful balloon angioplasty and were
asymptomatic at follow-up. In 2 other patients
there was a problem with removal of the Stent Delivery System sheath.
One of these patients could not be stented, was dilated, and had an
uneventful long-term outcome, and in the other a "bare"
heparin-coated stent was implanted by removing the protective
sheath prior to crossing of the lesion. This latter patient has been
included in the evaluable population. Baseline clinical characteristics
and lesion characteristics are displayed in Tables 1
and
2
,
respectively. For comparison, data on
stented patients participating in the Benestent-I study are included in
the tables (Tables 1
and 2
).
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Procedural Data
During the course of the study, on-line
quantitative
coronary angiography became increasingly used, in 53%, 63%,
59%, and 68% of cases analyzed during the four phases,
respectively. In 12%, 8%, 20%, and 8% (phases I to IV) of the
enrolled patients, intravascular ultrasound was used to guide the stent
procedure. Dilatation after stenting to optimize final results was
applied in 82%, 86%, 84%, and 92% of the patients in the four
phases, respectively. Inflation pressure inferior to 12 atm
was used in 57%, 29%, 33%, and 18%, whereas pressures greater than
12 atm were applied in 43%, 71%, 67%, and 82%, respectively. In all
groups, a mean of 2.8 devices (stent included) were used to achieve an
acceptable final result. Maximal balloon diameter (nominal size)
increased from 3.56±0.40 mm to 3.55±0.36, 3.62±0.43, and
3.62±0.42
mm in the four respective phases. For comparison, in Benestent-I the
mean maximal balloon diameter was 3.40±0.40 mm, which is significantly
different from the overall balloon diameter used in Benestent-I
(3.59±0.40 mm, P<.0001).
Acute Angiographic Results
In Table 3
, data on
preprocedural and
postprocedural RD, MLD, and DS are given. When compared with
Benestent-I (RD of 3.00 mm), a trend toward selecting patients with a
larger RD was seen (3.17, 3.05, 3.22, and 3.19 mm in phases I to IV,
respectively) as well as an increase in MLD after stenting (2.51 mm in
Benestent-I versus 2.77, 2.76, 2.78, and 2.77 mm in the four
consecutive phases of the present study). In phases I to IV a
preprocedural RD of <3.0 mm was encountered in 40% of the 203
patients, an RD<2.75 mm in 15%, and an RD<2.5 mm in 3%. In Fig
2
cumulative frequency curves of MLD and DS are
represented for Benestent-I and the four pooled phases of
Benestent-II. As mentioned in "Methods," the stent/vessel size
ratio (0%±9%, mean±SD) describes the appropriateness of stent
deployment more adequately than the DS measured within the stent
(18%±6%, mean±SD), which is presumably related to the small
unscaffolded vessel area located at the site of the stent
articulation.
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Clinical Outcome in Hospital and at 30 Days
Stent thrombosis,
clinically or angiographically demonstrated, did
not occur in the hospital or during the first 30 days (primary
objective). In phase II, 1 patient described above died after a failed
attempt to deploy a stent. A cardiac enzyme rise (CPK: 349 IU [normal
upper limit=190 IU]) was detected in 1 phase I patient as the
result
of a transient occlusion of a side branch. An additional stent had to
be implanted in 7 patients (two coated and five noncoated stents) to
cover a distal or proximal dissection. All the remaining patients were
free of cardiac events during hospitalization and at 30 days. Bleeding
complications requiring therapy fell from 7.9% in phase I to 5.9%,
4.0%, and 0% in the following three phases of the pilot study. Fig
3
details the type of bleeding complications encountered
in the four phases of the pilot study as well as during the course of
Benestent-I. Hospital stay was 7.4, 6.1, and 7.2 days in the first
three phases when anticoagulation and heparin were still used and was
reduced to 3.1 days once the anticoagulation regimen was replaced by an
antiplatelet regimen.
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6-Month Follow-up
Clinical Events
At the
6-month follow-up visit, 3 patients had died. In
phase I, 1 patient (No. 17) anticoagulated with antivitamin K
(coumadin) died at 75 days from intracranial bleeding documented by a
CT scan; another asymptomatic patient (No. 35) no
longer anticoagulated with coumadin died at 6 months from intracranial
bleeding also documented by CT scan while waiting for his repeat
catheterization. In phase III, a
symptomatic patient (No. 30) scheduled for a
catheterization at 4 months died suddenly at home. In
phase III, 1 patient (No. 23) still on anticoagulant treatment
presented with a reversible ischemic neurological
deficit diagnosed as an intracranial bleed by CT scan. Fortunately, he
recovered without sequelae.
At follow-up, 2 patients were readmitted with persisting signs of acute ischemia. One patient in phase I (No. 4) sustained an acute anterior MI at 4 months with a CPK rise of 537 IU and later developed a Q-wave MI; the patient was acutely treated with a thrombolytic agent and urgently catheterized; coronary angiography revealed a patent stent with an intrastent defect suspected to be a thrombus. One patient in phase IV (No. 38) presented at 2 months with signs of acute anterior infarction; thrombolytics were administered and the maximal rise in CPK was 271 IU (normal upper limit=110 IU); no Q wave developed, and catheterization did not disclose any angiographic abnormality within the stent or in the stented vessel.
Finally, at the time of the 6-month angiographic follow-up, an iatrogenic dissection of the left main stem occurred with subsequent occlusion of the vessel. The dissection was successfully stented and the patient was referred for emergency surgery. In the postoperative phase, elevation of the creatine kinase enzyme to 2700 IU was observed, but no Q wave developed on a 12-lead ECG.
At the 6-month follow-up, 21
reinterventions for
revascularization (19 percutaneous,
2 surgical) were performed. Table 4
summarizes clinical
events ranked in the following order: death, intracranial
hemorrhage or cerebrovascular accident, Q-wave and nonQ-wave
MI, urgent CABG, elective CABG, and repeat PTCA.
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Quantitative Angiography at Follow-up and Exercise
Testing
At the 6-month follow-up, repeat
catheterization and quantitative angiography were
obtained in 192 patients, 97% of the eligible population. Two
additional patients had their repeat angiography at 9 and 12 months,
outside the time window (6 months±4 weeks) allotted by the protocol
for the angiographic follow-up; their angiographic results were
therefore not included in the results although both had a DS<50% with
an MLD of 2.75 and 2.51 mm, respectively. The actual angiographic
follow-up is thus 98% of the eligible cases. The results of the
angiographic follow-up are tabulated in Table 3
; the overall RR
for
the pooled patients of the four phases is 13%, which is statistically
lower (relative risk, 0.65 [0.42 to 1.02]) than the RR of 20%
observed in the stent group of the Benestent-I trial, which has similar
inclusion criteria.
Although the preprocedural MLD, the acute gain, and
the MLD after
stenting were almost identical in each phase, important variations of
the RRs between the four phases were observed with a recurrence
of 15% in phase I, 20% in phase II, 11% in phase III, and 6% in
phase IV. Accordingly, similar variations from phase to phase in loss,
net gain, and loss index are shown in Table 3
.
Prior to the repeat catheterization, 172 of 192 eligible patients (90%) performed an exercise test. This exercise test was required by the protocol to justify prospectively any intervention that might otherwise have been driven primarily by the angiographic findings. Only 2 patients (with a DS of 52% and 55%, respectively) among the 21 patients who underwent either a surgical (n=3) or a percutaneous (n=18) reintervention for revascularization might possibly have been redilated unnecessarily.
Conversely, "treatment denial" can be suspected in 3 patients who had a positive exercise test and a DS>50% and did not undergo a reintervention.
The overall rate of percutaneous reintervention on the target lesion for the four phases was 8.9% (n=18 patients).
At 6
months, 84%, 75%, 94%, and 92% of the patients of phases I to
IV were event free. When pooled, 86% of the patients were event free,
which compares favorably with the event-free survival (80%) of the
patients enrolled in the stent group (n=259) of the Benestent-I trial
(relative risk, 0.68 [0.45 to 1.04]) (Table 4
, Fig
4
).
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| Discussion |
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It has been shown that heparin-like molecules with anticoagulant activity are synthesized on the luminal surface of endothelial cells.16 17 Indeed, the endothelium plays an important part in the inactivation of thrombin and possibly other coagulation factors. Not unexpectedly, therefore, heparin has been one of the most extensively explored substances for absorption or binding to the surface of biomaterials. Heparin-coated surfaces have been evaluated in various types of devices where thromboresistance might be of particular clinical value, eg, arteriovenous shunts, catheters, arterial filters, oxygenators, cardiopulmonary bypass circuits, and vascular endoprostheses.18 19 20 21 22
The principal anticoagulant mechanism of heparin is its interaction with antithrombin-III, accelerating the inactivation of thrombin and other coagulation factors. It has been shown that the active site of heparin contains a specific carbohydrate sequence.23 24 25 When the heparin molecule is modified by the process of surface coating, it is essential that the active sequence responsible for anticoagulation remains unaltered. The simplest solution for binding heparin to a surface is adsorbing a heparin solution to the biomaterial surface.26 A problem with this type of coating is the lack of control of the rate of release; the heparin molecule contains a large number of negatively charged groups and may therefore be ionically or electrostatically bound to surfaces with positive charges.27 28 29 Another principle is to incorporate heparin molecules into a polymer, either to make heparin a permanent component of the polymer ("surface-grafted" heparin)30 or to provide a controlled release of heparin upon introduction into the bloodstream.31 32 Since heparin is a highly charged and hydrophillic polymer, the binding has to be prepared by pretreatment of the surface to be coated with reactive groups ("functionalizing"). In the early development of heparin coatings, a reduction of heparin activity was frequently observed when the molecules were covalently attached to the surface, probably due to alteration of the active carbohydrate sequence during the linking process.33 It was found that this problem was circumvented if heparin was coupled by end-point attachment.34 35 The first step in this procedure is partial degradation of heparin with nitrous acid, creating reactive terminal aldehyde groups. In 1983 it was shown by Larm et al33 that heparin fragments could be immobilized by end-point attachment on materials coated with polyethylenemine. The aldehyde group was subsequently coupled to the aminated surface by reductive amination. By this method, the active carbohydrate sequence of the heparin molecule could be preserved functionally intact throughout the coupling reaction.
In addition to being compatible with the plasma coagulation system, a thromboresistant surface should not promote adhesion and activation of platelets and leukocytes. Because heparin has been reported to induce platelet activation,35 this consequence might be expected with surface-immobilized heparin as well. However, it has been shown that in comparison with uncoated material, the surface with end-pointattached heparin on a high-molecular-weight polyamine stabilized with glutaraldehyde is highly compatible with platelets as well as granulocytes and macrophages.9 36
The principle of perpendicularly oriented, end-attached, covalently bound, and immobilized heparin molecules on a polymer surface (Carmeda Bioactive Surface, Carmeda AB) was considered to be the best technique for coating of coronary stents. A new "CH5" coating, a special form of the Carmeda Bioactive Surface, was developed, allowing higher heparin activity on the stent surface.
In vitro and in vivo studies of thromboresistance of the heparin-coated stent, as summarized at the beginning of this article, formed the basis for implantation in humans in this Benestent-II pilot study.
Rationale for the Trial Design
The primary goal of this
registry was to demonstrate the
feasibility and the safety of implantation of a heparin-coated
stent. The design and the objectives of this trial reflect the state of
the art in stenting in 1993. At that time, the Benestent-I trial was
close to completion and it was already recognized that the rate of
subacute occlusion (3.5%) was not negligible, that the incidence
of bleeding complications (13.9%) was substantial, and that the length
of in-hospital stay (8.3 days) was not acceptable.
It was evident that these three major drawbacks of the treatment had to be eliminated to render this new modality of angioplasty widely applicable. A thromboresistant, or at least a less-thrombogenic stent, was conceptually an appealing solution to the above-mentioned limitations. On the other hand, around the same period a pharmacological regimen after stenting different from the conventional approach was introduced by French practitioners37 : the use of intravenous heparin and oral antivitamin K was progressively replaced by subcutaneous low-molecular-weight heparin and administration of ticlopidine. Subsequently, registries demonstrated a favorable impact of this regimen on subacute thrombosis and bleeding.38 Around the same period, Colombo and his colleagues39 also reported their experience with ultrasound-guided stent deployment without anticoagulation; they attributed subacute thrombotic occlusion of the stent to inappropriate and incomplete deployment, emphasizing the need for almost perfect normalization of the intrastent rheology to prevent subacute occlusion.4 Ticlopidine was nevertheless also incorporated in their treatment after stenting. It is therefore understandable that the investigators in the Benestent-II Pilot Study agreed to test the new heparin-coated stent provided the anticoagulant was replaced by an antiplatelet drug such as ticlopidine. The dosage of ticlopidine (250 mg/d) and the timing of administration (within 12 hours of the procedure) selected for this trial are based on the favorable clinical experience of the French registry and are at variance with the recommendations of the pharmaceutical industry, which, on the basis of their pharmacokinetic studies, would advise a BID administration (500 mg/d) preceding the stent procedure by 72 hours.40
In addition to this safety issue, concerns also were expressed about potential inflammatory reactions that might be induced by the polymeric coating of the stent, although animal experiments had been most reassuring on that point.7 For all these reasons, the trial was cautiously phased with a stepwise postponement of the heparin infusion and replacement of the anticoagulation by antiplatelet regimen combining ticlopidine and aspirin to prevent subacute occlusion while reducing the bleeding complications and the length of the in-hospital stay. In designing the pilot study as well as the randomized trial (currently underway), we have adopted a very practical and pragmatic approach: a presumably thromboresistant stent is used in conjunction with two antiplatelet drugs. Our goal was clearly not to demonstrate the intrinsic value of the thromboresistance of the heparin-coated stent but rather to evaluate from a cost-effectiveness point of view a combined therapy of device and drugs by comparison with a strategy of conventional balloon angioplasty.
A specific demonstration of the thromboresistant properties of the heparin-coated stent might require either a large double-blind randomized trial or the evaluation of the coated stent versus an uncoated version in a very thrombogenic environment such as unstable angina, impending infarction, or even evolving MI, so that the beneficial thromboresistant properties of the heparin-coated stent may become manifest. These latter trials are currently in the planning stage.
Have the Thromboresistant Properties of the
Heparin-Coated Stent Been Demonstrated?
We have to emphasize that the
favorable short- and long-term
outcome observed in the pilot study is multifactorial: careful
selection of the patient with vessel size slightly larger than in the
Benestent trial, better techniques of implantation partially guided by
either on-line quantitative angiography or intravascular ultrasound
resulting in a large postprocedure MLD, and use of two
antiplatelet drugs of which the synergic action is presumably
beneficial.41 42
We are therefore not entitled to make any scientific statement on the specific merits of this thromboresistant stent. Currently our knowledge on the thromboresistant properties of this stent mainly originates from in vitro, ex vivo, and animal experiments, and it can only be assumed that these thromboresistant properties are "operational" in our patients. Although it is tempting to compare the overall results of the four phases of the Benestent-II pilot with the outcome of the stent group in Benestent-I, we must bear in mind that this type of comparison is a post hoc analysis, partially invalidated by small differences in baseline characteristics and in procedural treatment. In particular it must be pointed out that the vessel sizes of the selected patients in the Benestent-II pilot were slightly but statistically larger than in Benestent-I; we have previously demonstrated that larger vessel size in itself is an independent determinant of reduction in loss in MLD at follow-up.43
Obviously, a significantly higher procedural gain due to better techniques of deployment resulted in a larger postprocedural MLD, which is known to be a major determinant of the MLD at follow-up. Identification of the major determinants of the MLD at follow-up have been derived from multivariate analysis performed on the stent population of the Benestent-I trial.44 If the current vessel size (VS=3.16 mm) recorded in the pilot study and the MLD postprocedure (2.77 mm) as well as the nature of the treated vessel (LAD 56%) are incorporated in the multivariate analysis derived from Benestent-I (MLD at follow-up=-0.26+0.47xMLD post+0.35xVS (pre)-0.11xLAD), then it appears that the predicted MLD at follow-up (2.08 mm) is in fact identical to the MLD at follow-up observed in the pilot study of Benestent-II (2.08 mm).
In other words, presently there is no compelling evidence indicating that the heparin coating is actively affecting the neointimal hyperplasia within the stent. However, it should be pointed out that the low RR and loss index observed in this series at least indicate that the polymeric coating used in the clinical trial does not induce an excess of intimal hyperplasia, a reaction frequently observed in animal experiments with a variety of biodegradable or nonbiodegradable polymers previously tested.45
Conversely, the variation in RR from phase to phase does not necessarily have to be interpreted in biological terms. From a purely statistical point of view, these variations may be simply explained in probabilistic terms: sequential statistical analyses of RRs in four cohorts of 50 patients are compatible with a range of RRs varying between 8.3% and 17.8% (95% CIs) in the case of an overall RR of 13%. Interestingly, however, the RR of phase IV (6%) falls outside the 95% CIs.
Benestent-II Pilot Study as a Preamble to the Benestent-II
Trial
The ultimate goal of the substantive Benestent-II trial will be
to
investigate the efficacy and cost-effectiveness of a strategy of
elective stenting versus a treatment with conventional balloon
angioplasty; the use of a heparin-coated stent in combination with
two antiplatelet drugs as adjunctive therapy represents
a pragmatic approach that has apparently eliminated the risk of
subacute occlusion and bleeding complications as well as the need
for a prolonged stay in the hospital; thus, the heparin-coated
stent should be viewed as a safety net for the interventional
cardiologist. In other words, the pilot study must be viewed strictly
as a preamble to the randomized Benestent-II trial, the goal of which
will be mainly economic: the cost-effectiveness assessment of
stenting versus balloon angioplasty.
Conclusions
The postponement of heparin treatment to 6, 12,
and 36 hours after
sheath removal has not resulted in (sub)acute occlusions in these
patients treated with antivitamin K (coumadin). A trend toward less
bleeding and fewer peripheral vascular complications was
observed. Heparin-coated stents are well tolerated. No
thrombogenic, allergic, toxic, or immunologic side effects were
observed.
The absence of (sub)acute occlusion as well as the virtual disappearance of bleeding and peripheral vascular complications in phase IV (ticlopidine and aspirin only) confirm the feasibility of conducting a randomized trial testing the clinical value of this new stent coating, as well as the innocuous nature of the new posttreatment regimen.
The very low rate of restenosis observed in phase IV seems promising and needs confirmation in a larger randomized approach.
| Appendix |
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Erasmus University, Thoraxcenter, Rotterdam, the Netherlands (16): P.W. Serruys, P. de Jaegere, P. Ruygrok; Sahlgrenska Hospital, Goteborg, Sweden (14): H. Emanuelsson, P. Albertsson; University Hospital San Carlos, Madrid, Spain (13): C. Macaya, F. Alfonso, J. Goicolea, R. Hernandez, A. Iniguez; Rudolph Virchow, Berlin, Germany (12): W. Rutsch; OLVZ, Aalst, Belgium (11): G. Heyndrickx, B. de Bruyne, W. Wijns; Ziekenhuis De Weezenlanden, Zwolle, the Netherlands (10): H. Suryapranata, J. Hoorntje; Sart Tilman, Liège, Belgium (10): V. Legrand; CHUV, Lausanne, Switzerland (9): J. Goy, E. Eeckhout; La Citadelle, Liège, Belgium (9): P. Materne, J. Boland; Catharina Ziekenhuis, Eindhoven, the Netherlands (9): H. Bonnier, J. Koolen; CCN, Paris, France (8): M.C. Morice; Clinique Pasteur, Toulouse, France (8): J. Marco, J. Fajadet, P. Brunell; Instituto Cardiovascular, Buenos Aires, Argentina (7): J. Berlardi, R. Piraino; Centro Cuore Columbus, Milan, Italy (7): A. Colombo; Gregorio Marañon, Madrid, Spain (7): E. Garcia, J. Delcan; Ospedale Maggiore, Trieste, Italy (6): S. Klugmann, E. Della Grazia, A. Salvi; St. James, Dublin, Ireland (6): P. Crean; Middelheim, Antwerp, Belgium (6): P. van den Heuvel, F. van den Brande; St. Luc, Brussels, Belgium (5): C. Hanet; RBNHBLI, London, United Kingdom (5): U. Sigwart; Christian-Albrecht University, Kiel, Germany (5): R. Simon, M. Lins; OLVG, Amsterdam, the Netherlands (4): F. Kiemeneij, G.J. Laarman; CHUR, Nancy, France (4): N. Danchin; St. Antonius, Nieuwegein, the Netherlands (4): G. Mast, T. Plokker; Hopital Kantonal, Geneva, Switzerland (3): P. Urban; Academic Hospital, Groningen, the Netherlands (3): P. den Heijer; Instituto Dante Pazzanese, Sao Paulo, Brazil (3): E. Sousa; Ziekenhuis De Klokkenberg, Breda, the Netherlands (3): H. te Riele; Polyclinique Volney, Rennes, France (2): C. Bourdonnec; AMC, Amsterdam, the Netherlands (1): K. Koch, J. Piek; Franz-Volhard Klinik, Berlin, Germany (1): D. Gulba; Hopital Cochin, Paris, France (1): C. Spaulding; University Essen, Essen, Germany (1): M. Haude.
Steering Committee: Patrick W. Serruys (Chairman), Håkan Emanuelsson, Stan Rowe. Critical Event Committee: Pim de Feyter, Paul van den Heuvel. Coordinating Center, Cardialysis BV, Rotterdam, the Netherlands: Aida Azar, Gerrit-Anne van Es, Linda Goderie, Marie-Angèle Morel. Angiographic Core Laboratory, Cardialysis BV, Rotterdam, the Netherlands: Diny Amo, Marcel van den Brand, David Foley, Ina Hoekman. Safety Committee: Jan Tijssen, Freek Verheugt.
| Selected Abbreviations and Acronyms |
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Received November 28, 1995; revision received December 13, 1995; accepted December 13, 1995.
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A. J. Wardeh, I. P. Kay, M. Sabate, V. L. M. A. Coen, A. L. Gijzel, J. M. R. Ligthart, A. den Boer, P. C. Levendag, W. J. van der Giessen, and P. W. Serruys {beta}-Particle-Emitting Radioactive Stent Implantation : A Safety and Feasibility Study Circulation, October 19, 1999; 100(16): 1684 - 1689. [Abstract] [Full Text] [PDF] |
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P. W. Serruys, I. P. Kay, C. Disco, N. V. Deshpande, P. J. de Feyter, and on behalf of the BENESTENT I BENESTENT II Pilot BE Periprocedural quantitative coronary angiography after Palmaz-Schatz stent implantation predicts the restenosis rate at six months: Results of a meta-analysis of the belgian netherlands stent study (BENESTENT) I, BENESTENT II pilot, BENESTENT II and MUSIC trials J. Am. Coll. Cardiol., October 1, 1999; 34(4): 1067 - 1074. [Abstract] [Full Text] [PDF] |
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C. T. Lloyd, A. M. Calafiore, P. Wilde, R. Ascione, L. Paloscia, C. R. Monk, and G. D. Angelini Integrated left anterior small thoracotomy and angioplasty for coronary artery revascularization Ann. Thorac. Surg., September 1, 1999; 68(3): 908 - 911. [Abstract] [Full Text] [PDF] |
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C. E. Buller, V. Dzavik, R. G. Carere, G. B. J. Mancini, G. Barbeau, C. Lazzam, T. J. Anderson, M. L. Knudtson, J.-F. Marquis, T. Suzuki, et al. Primary Stenting Versus Balloon Angioplasty in Occluded Coronary Arteries : The Total Occlusion Study of Canada (TOSCA) Circulation, July 20, 1999; 100(3): 236 - 242. [Abstract] [Full Text] [PDF] |
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C. Rogers, D. Y. Tseng, J. C. Squire, and E. R. Edelman Balloon-Artery Interactions During Stent Placement : A Finite Element Analysis Approach to Pressure, Compliance, and Stent Design as Contributors to Vascular Injury Circ. Res., March 5, 1999; 84(4): 378 - 383. [Abstract] [Full Text] [PDF] |
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M. Zenati, H. A. Cohen, and B. P. Griffith ALTERNATIVE APPROACH TO MULTIVESSEL CORONARY DISEASE WITH INTEGRATED CORONARY REVASCULARIZATION J. Thorac. Cardiovasc. Surg., March 1, 1999; 117(3): 439 - 446. [Abstract] [Full Text] [PDF] |
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C. Stefanadis, K. Toutouzas, E. Tsiamis, C. Vlachopoulos, S. Vaina, D. Tsekoura, L. Haldi, E. Stefanadi, M. Gravanis, and P. Toutouzas Stents covered by an autologous arterial graft in porcine coronary arteries: feasibility, vascular injury and effect on neointimal hyperplasia Cardiovasc Res, February 1, 1999; 41(2): 433 - 442. [Abstract] [Full Text] [PDF] |
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J. K. Mickelson, M. N. Ali, N. S. Kleiman, N. M. Lakkis, T. W. Chow, B. J. Hughes, and C. W. Smith Chimeric 7e3 Fab (ReoPro) decreases detectable CD11b on neutrophils from patients undergoing coronary angioplasty J. Am. Coll. Cardiol., January 1, 1999; 33(1): 97 - 106. [Abstract] [Full Text] [PDF] |
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M. B. Leon, D. S. Baim, J. J. Popma, P. C. Gordon, D. E. Cutlip, K. K.L. Ho, A. Giambartolomei, D. J. Diver, D. M. Lasorda, D. O. Williams, et al. A Clinical Trial Comparing Three Antithrombotic-Drug Regimens after Coronary-Artery Stenting N. Engl. J. Med., December 3, 1998; 339(23): 1665 - 1671. [Abstract] [Full Text] [PDF] |
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R. Erbel, M. Haude, H. W. Hopp, D. Franzen, H. J. Rupprecht, B. Heublein, K. Fischer, P. de Jaegere, P. Serruys, W. Rutsch, et al. Coronary-Artery Stenting Compared with Balloon Angioplasty for Restenosis after Initial Balloon Angioplasty N. Engl. J. Med., December 3, 1998; 339(23): 1672 - 1678. [Abstract] [Full Text] [PDF] |
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P. Urban, C. Macaya, H.-J. Rupprecht, F. Kiemeneij, H. Emanuelsson, A. Fontanelli, M. Pieper, T. Wesseling, L. Sagnard, and f. t. M. Investigators Randomized Evaluation of Anticoagulation Versus Antiplatelet Therapy After Coronary Stent Implantation in High-Risk Patients : The Multicenter Aspirin and Ticlopidine Trial after Intracoronary Stenting (MATTIS) Circulation, November 17, 1998; 98(20): 2126 - 2132. [Abstract] [Full Text] [PDF] |
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E. J. Topol and P. W. Serruys Frontiers in Interventional Cardiology Circulation, October 27, 1998; 98(17): 1802 - 1820. [Full Text] [PDF] |
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A. Kastrati, F.-J. Neumann, and A. Schomig Operator volume and outcome of patients undergoing coronary stent placement J. Am. Coll. Cardiol., October 1, 1998; 32(4): 970 - 976. [Abstract] [Full Text] [PDF] |
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H. M. M. van Beusekom, D. M. Whelan, S. H. Hofma, S. C. Krabbendam, V. W. M. van Hinsbergh, P. D. Verdouw, and W. J. van der Giessen Long-term endothelial dysfunction is more pronounced after stenting than after balloon angioplasty in porcine coronary arteries J. Am. Coll. Cardiol., October 1, 1998; 32(4): 1109 - 1117. [Abstract] [Full Text] [PDF] |
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O. F. Bertrand, R. Sipehia, R. Mongrain, J. Rodes, J.-C. Tardif, L. Bilodeau, G. Cote, and M. G. Bourassa Biocompatibility aspects of new stent technology J. Am. Coll. Cardiol., September 1, 1998; 32(3): 562 - 571. [Abstract] [Full Text] [PDF] |
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C. R. Narins, D. R. Holmes Jr, and E. J. Topol A Call for Provisional Stenting : The Balloon Is Back! Circulation, April 7, 1998; 97(13): 1298 - 1305. [Full Text] [PDF] |
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H. K. Breddin Antiplatelet Agents in Cardiovascular and Cerebrovascular Diseases Clinical and Applied Thrombosis/Hemostasis, April 1, 1998; 4(2): 87 - 95. [Abstract] [PDF] |
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A. M. Calafiore, G. D. Giammarco, G. Teodori, S. Gallina, N. Maddestra, L. Paloscia, G. Scipioni, T. Iovino, M. Contini, and G. Vitolla Midterm results after minimally invasive coronary surgery (last operation) J. Thorac. Cardiovasc. Surg., April 1, 1998; 115(4): 763 - 771. [Abstract] [Full Text] [PDF] |
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A H Gershlick and J Baron Dealing with in-stent restenosis Heart, April 1, 1998; 79(4): 319 - 323. [Full Text] |
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H. J. Rupprecht, H. Darius, U. Borkowski, T. Voigtlander, B. Nowak, S. Genth, and J. Meyer Comparison of Antiplatelet Effects of Aspirin, Ticlopidine, or Their Combination After Stent Implantation Circulation, March 24, 1998; 97(11): 1046 - 1052. [Abstract] [Full Text] [PDF] |
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D. J. Kereiakes, A. M. Lincoff, D. P. Miller, J. E. Tcheng, C. F. Cabot, K. M. Anderson, H. F. Weisman, R. M. Califf, and E. J. Topol Abciximab Therapy and Unplanned Coronary Stent Deployment : Favorable Effects on Stent Use, Clinical Outcomes, and Bleeding Complications Circulation, March 10, 1998; 97(9): 857 - 864. [Abstract] [Full Text] [PDF] |
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D. O. Williams and M. C. Fahrenbach Directional Coronary Atherectomy : But Wait, There's More Circulation, February 3, 1998; 97(4): 309 - 311. [Full Text] [PDF] |
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M. A Mariani, P. W Boonstra, and J. G Grandjean Minimally invasive coronary surgery: fad or future? BMJ, January 10, 1998; 316(7125): 88 - 88. [Full Text] |
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P. W. Serruys, C. di Mario, J. Piek, E. Schroeder, C. Vrints, P. Probst, B. de Bruyne, C. Hanet, E. Fleck, M. Haude, et al. Prognostic Value of Intracoronary Flow Velocity and Diameter Stenosis in Assessing the Short- and Long-term Outcomes of Coronary Balloon Angioplasty : The DEBATE Study (Doppler Endpoints Balloon Angioplasty Trial Europe) Circulation, November 18, 1997; 96(10): 3369 - 3377. [Abstract] [Full Text] |
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M. A. Mariani, P. W. Boonstra, J. G. Grandjean, J. O. J. Peels, S. H. J. Monnink, P. den Heijer, and H. J. G. M. Crijns MINIMALLY INVASIVE CORONARY ARTERY BYPASS GRAFTING VERSUS CORONARY ANGIOPLASTY FOR ISOLATED TYPE C STENOSIS OF THE LEFT ANTERIOR DESCENDING ARTERY J. Thorac. Cardiovasc. Surg., September 1, 1997; 114(3): 434 - 439. [Abstract] [Full Text] |
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D. Brieger and E. Topol Local drug delivery systems and prevention of restenosis Cardiovasc Res, September 1, 1997; 35(3): 405 - 413. [Full Text] [PDF] |
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G. Vassalli and D. A Dichek Gene therapy for arterial thrombosis Cardiovasc Res, September 1, 1997; 35(3): 459 - 469. [Abstract] [Full Text] [PDF] |
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S. P. Schwarzacher, T. T. Lim, B. Wang, R. S. Kernoff, J. Niebauer, J. P. Cooke, and A. C. Yeung Local Intramural Delivery of L-Arginine Enhances Nitric Oxide Generation and Inhibits Lesion Formation After Balloon Angioplasty Circulation, April 1, 1997; 95(7): 1863 - 1869. [Abstract] [Full Text] |
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D. S. Baim and J. P. Carrozza Jr Stent Thrombosis: Closing in on the Best Preventive Treatment Circulation, March 4, 1997; 95(5): 1098 - 1100. [Full Text] |
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R. R. Makkar, F. Litvack, N. L. Eigler, M. Nakamura, P. A. Ivey, J. S. Forrester, P. K. Shah, R. E. Jordan, and S. Kaul Effects of GP IIb/IIIa Receptor Monoclonal Antibody (7E3), Heparin, and Aspirin in an Ex Vivo Canine Arteriovenous Shunt Model of Stent Thrombosis Circulation, February 18, 1997; 95(4): 1015 - 1021. [Abstract] [Full Text] |
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E. M. Ohman and B. E. Tardiff Periprocedural Cardiac Marker Elevation After Percutaneous Coronary Artery Revascularization: Importance and Implications JAMA, February 12, 1997; 277(6): 495 - 497. [Abstract] [PDF] |
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D. B. Schneider and D. A. Dichek Intravascular Stent Endothelialization: A Goal Worth Pursuing? Circulation, January 21, 1997; 95(2): 308 - 310. [Full Text] |
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E. Van Belle, F. O. Tio, T. Couffinhal, L. Maillard, J. Passeri, and J. M. Isner Stent Endothelialization: Time Course, Impact of Local Catheter Delivery, Feasibility of Recombinant Protein Administration, and Response to Cytokine Expedition Circulation, January 21, 1997; 95(2): 438 - 448. [Abstract] [Full Text] |
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R. K. Aggarwal, D. C. Ireland, M. A. Azrin, M. D. Ezekowitz, D. P. de Bono, and A. H. Gershlick Antithrombotic Potential of Polymer-Coated Stents Eluting Platelet Glycoprotein IIb/IIIa Receptor Antibody Circulation, December 15, 1996; 94(12): 3311 - 3317. [Abstract] [Full Text] |
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W. J. van der Giessen and P. W. Serruys ß-Particle–Emitting Stents Radiate Enthusiasm in the Search for Effective Prevention of Restenosis Circulation, November 15, 1996; 94(10): 2358 - 2360. [Full Text] |
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J. A. Bittl Advances in Coronary Angioplasty N. Engl. J. Med., October 24, 1996; 335(17): 1290 - 1302. [Full Text] [PDF] |
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S. Goldberg, M. P. Savage, and D. L. Fischman The Interventional Cardiologist and the Diabetic Patient: Have We Pushed the Envelope Too Far or Not Far Enough? Circulation, October 15, 1996; 94(8): 1804 - 1806. [Full Text] |
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N. G Uren and N. A. Chronos Intracoronary stents BMJ, October 12, 1996; 313(7062): 892 - 893. [Full Text] |
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T. A. Fischell Polymer Coatings for Stents: Can We Judge a Stent by Its Cover? Circulation, October 1, 1996; 94(7): 1494 - 1495. [Full Text] |
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P. N. Ruygrok and P. W. Serruys Intracoronary Stenting: From Concept to Custom Circulation, September 1, 1996; 94(5): 882 - 890. [Full Text] |
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M. L. Simoons Myocardial Revascularization -- Bypass Surgery or Angioplasty? N. Engl. J. Med., July 25, 1996; 335(4): 275 - 277. [Full Text] |
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A. Schomig, F.-J. Neumann, A. Kastrati, H. Schuhlen, R. Blasini, M. Hadamitzky, H. Walter, E.-M. Zitzmann-Roth, G. Richardt, E. Alt, et al. A Randomized Comparison of Antiplatelet and Anticoagulant Therapy after the Placement of Coronary-Artery Stents N. Engl. J. Med., April 25, 1996; 334(17): 1084 - 1089. [Abstract] [Full Text] [PDF] |
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Heparin-Coated Stents Get Thumbs Up Journal Watch Cardiology, April 1, 1996; 1996(401): 2 - 2. [Full Text] |
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HEPARIN-COATED CORONARY STENTS: ENCOURAGING DATA Journal Watch (General), February 13, 1996; 1996(213): 6 - 6. [Full Text] |
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D. O. Williams Dressing Up the Palmaz-Schatz Stent Circulation, February 1, 1996; 93(3): 400 - 402. [Full Text] |
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