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(Circulation. 1995;91:1676-1688.)
© 1995 American Heart Association, Inc.
Articles |
Intracoronary Stenting Without Anticoagulation Accomplished With Intravascular Ultrasound Guidance
Presented in part at the 66th Scientific Sessions of the American Heart Association, Atlanta, Ga, November 8-11, 1993, and the American College of Cardiology Meeting, March 1994.
From the Centro Cuore Columbus, Milan, Italy (A.C., P.H., S.N., Y.A., L.M., G.M., S.L.G.); the Villa Bianca, Bari, Italy (A.G.); and the University of California at Irvine, Orange, Calif (J.M.T.).
Correspondence to Antonio Colombo, MD, Centro Coure Columbus, Via M. Buonarotti 48, 20145 Milan, Italy.
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Abstract |
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 Top Abstract IntroductionMethods Results Discussion References |
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Background The placement of stents in coronary arteries has been shown to reduce restenosis in comparison to balloon angioplasty. However, clinical use of intracoronary stents is impeded by the risk of subacute stent thrombosis and complications associated with the anticoagulant regimen. To reduce these complications, the hypothesis that systemic anticoagulation is not necessary when adequate stent expansion is achieved was prospectively evaluated on a consecutive series of patients who received intracoronary stents.
Methods and Results From March 1993 to January 1994, 359 patients underwent Palmaz-Schatz coronary stent insertion. After an initial successful angiographic result with <20% stenosis by visual estimation had been achieved, intravascular ultrasound imaging was performed. Further balloon dilatation of the stent was guided by observation of the intravascular ultrasound images. All patients with adequate stent expansion confirmed by ultrasound were treated only with antiplatelet therapy (either ticlopidine for 1 month with short-term aspirin for 5 days or only aspirin) after the procedure. Clinical success (procedure success without early postprocedural events) at 2 months was achieved in 338 patients (94%). With an inflation pressure of 14.9±3.0 atm and a balloon-to-vessel ratio of 1.17±0.19, optimal stent expansion was achieved in 321 of the 334 patients (96%) who underwent intravascular ultrasound evaluation, with these patients receiving only antiplatelet therapy after the procedure. Despite the absence of anticoagulation, there were only two acute stent thromboses (0.6%) and one subacute stent thrombosis (0.3%) at 2-month clinical follow-up. Follow-up angiography at 3 to 6 months documented two additional occlusions (0.6%) at the stent site. At 6-month clinical follow-up, angiographically documented stent occlusion had occurred in 5 patients (1.6%). At 6-month clinical follow-up, there was a 5.7% incidence of myocardial infarction, a 6.4% rate of coronary bypass surgery, and a 1.9% incidence of death. Emergency intervention (emergency angioplasty or bailout stent) for a stent thrombosis event was performed in 3 patients (0.8%). The overall event rate was relatively high because of intraprocedural complications that occurred in 16 patients (4.5%). Intraprocedural complications, however, decreased to 1% when angiographically appropriately sized balloons were used for final stent dilations. There was one ischemic vascular complication that occurred at the time of the procedure and one ischemic vascular complication that occurred at the time of angiographic follow-up. By 6 months, repeat angioplasty for symptomatic restenosis was performed in 47 patients (13.1%).
Conclusions The Palmaz-Schatz stent can be safely inserted in coronary arteries without subsequent anticoagulation provided that stent expansion is adequate and there are no other flow-limiting lesions present. The use of high-pressure final balloon dilatations and confirmation of adequate stent expansion by intravascular ultrasound provide assurance that anticoagulation therapy can be safely omitted. This technique significantly reduces hospital time and vascular complications and has a low stent thrombosis rate.
Key Words: stents • ultrasonics • balloon • platelets
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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The placement of intracoronary stents decreases the morbidity of acute closure1 2 and reduces the restenosis rate in de novo lesions3 4 5 6 and vein grafts3 5 compared with historical angioplasty results.7 8 9 10 11 12 13 14 More recently, the Benestent and STRESS randomized trials compared stents and angioplasty in treating de novo native coronary artery lesions.15 16 Both studies demonstrated a significant reduction in the restenosis rate in the group treated with stents. In addition, in the Benestent trial, the reduction in restenosis rate was associated with a significant reduction in major clinical events in the group randomized to stents.16 Increased clinical use of stents may be justified on the basis of these investigations but is impeded by two major limitations: the risk of stent thrombosis and the complications associated with an aggressive anticoagulation regimen. A stringent anticoagulation regimen has been advocated to inhibit the incidence of subacute stent thrombosis but is associated with bleeding and vascular complications without eliminating subacute stent thrombosis.1 2 5 6 15 16 17 18 19 20
Prior studies with intravascular ultrasound imaging of deployed stents reveal that >80% of stents may be insufficiently dilated despite an apparently angiographically successful deployment.21 22 These observations suggest that stent thrombosis may be caused in part by incomplete stent dilation rather than the inherent thrombgenicity of the metallic stent.
The hypothesis of this study is that systemic anticoagulation is not necessary after stent insertion when adequate stent expansion is achieved. This hypothesis was prospectively evaluated in a consecutive series of 359 patients who received Palmaz-Schatz intracoronary stents. All patients with adequate stent expansion as confirmed by intravascular ultrasound were treated only with antiplatelet therapy and did not receive anticoagulation after the procedure.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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Between March 30, 1993, and January 1, 1994, 359 consecutive patients with 452 lesions were treated with insertion of a Palmaz-Schatz intracoronary stent. During the first 3 months of this investigation, patients were informed of the potential risks and benefits of intracoronary stents and of the novelty of the approach used in this investigation and consented to participate in the study. After the first 3 months, consent was obtained after patients were informed of the risk and benefit of intracoronary stents and of the interim results of this protocol compared with the outcome of stenting with standard anticoagulation regimens. The first 10 patients enrolled in the study were selected on the basis of having lesions that were at low risk of causing major ischemic complications in the event of a stent occlusion (eg, total occlusion lesions, non–left anterior descending lesions, or lesions supplying a small or modest amount of myocardium). Subsequent to this selection, there was no attempt to limit enrollment in patients who consented and met inclusion criteria. The entry criteria included (1) coronary artery disease manifested by clinical symptoms or objective evidence of myocardial ischemia either on exercise test or by nuclear scintigraphy and (2) angiographic evidence of single- or multiple-vessel coronary disease with target lesion stenosis >70% by visual estimate. The exclusion criteria included (1) small vessels <2.5 mm by visual estimate and (2) angiographically diffuse distal disease that might compromise outflow after stent insertion. There were no specific age or ejection fraction limitations for study entry. Patients were not excluded on the basis of indication for stent implantation, lesion location, or complex lesion morphology. Thus, patients with ostial lesions, tortuous vessels, diffuse disease, long lesions, tandem lesions, and lesions with thrombus or severe calcification were eligible for study entry.
Stent Implantation Procedure
Patients received aspirin 325 mg
and calcium channel antagonists
before stent deployment. A bolus of 10 000 U heparin was given after
sheath insertion, with a repeat bolus of 5000 U given as needed to
maintain the activated clotting time >250 seconds. Patients were not
given dextran or dipyridamole before, during, or after the stent
procedure. Ticlopidine was not administered before or during the stent
procedure. Five different types of Johnson and Johnson tubular slotted
stents were used during the course of this study: the Palmaz-Schatz
stent, a short stent composed of one 7-mm tubular slotted segment, a
10-mm-long biliary stent, a 20-mm renal stent composed of two 10-mm
segments with a central articulation, and a short (disarticulated)
renal stent. A premounted stent delivery system was used sparingly
during the study (n=7). After predilation, stents were hand crimped on
balloons and implanted under fluoroscopic guidance. Further dilatations
(angiographic optimization) were performed to achieve an acceptable
angiographic result with <20% residual stenosis by visual estimates.
After the angiographic result was considered acceptable and the
procedure would ordinarily be terminated, intravascular ultrasound was
performed. All subsequent treatment decisions were based on the
ultrasound results in conjunction with angiographic assessment. The
initial intravascular ultrasound was the first ultrasound examination
performed when initial angiographic success (<20% residual stenosis
by visual estimate) was achieved. The final intravascular
ultrasound was the last intravascular ultrasound evaluation, which
documented that the criteria for stent expansion were achieved. Further
balloon dilatation or stent implantation that was performed after the
initial intravascular ultrasound imaging was called intravascular
ultrasound–guided stent optimization.
The indications for placement of stents were defined as follows: Acute occlusion stenting was undertaken to relieve ischemia associated with complete vessel closure (100%) after angioplasty with no or markedly delayed grade 0 or 1 Thrombolysis in Acute Myocardial Infarction (TIMI) flow; threatened closure stenting was performed when the angioplasty was complicated by a longitudinal or spiral dissection associated with >50% luminal encroachment (with or without compromised flow) and evidence of ischemia; suboptimal result stenting was defined as insertion of a stent for a focal dissection or significant vascular recoil after angioplasty that resulted in >50% luminal narrowing but was not associated with ischemia; restenosis stenting was performed for lesions with a history of restenosis after one or more previous angioplasty procedures; chronic occlusion stenting was performed after a vessel that had been occluded for more than 2 months was reopened; and elective stenting was performed when the operator believed a better result would be obtained with a stent instead of balloon angioplasty. Multiple stenting was defined as the use of more than one Palmaz-Schatz (15-mm) stent. Short stents were counted as a half stent. Biliary, disarticulated renal, and renal stents were counted as one stent each.
Intravascular Ultrasound Equipment and Measurements
The
majority of coronary arteries were imaged with a 3.9F
monorail system with a 25-MHz transducer-tipped catheter (Interpret
Catheter, InterTherapy/CVIS). A Cardiovascular Imaging System (CVIS)
with a 2.9F catheter was used during the last 3 months of the study.
Validation of quantitative measurements and pathological correlation
with ultrasound measurements has been reported.23 24
All
images were obtained with a manual pullback system. The position of the
catheter on fluoroscopy was used to correlate the ultrasound image with
the angiogram. Data were stored on 0.5-in super VHS videotape. On-line
quantitative measurements were performed during the procedure. The
ultrasound catheter was advanced distal to the stent, and images were
recorded while the imaging catheter was slowly pulled through the
stented segment. The following measurements were made at the proximal
or distal reference sites, generally within 5 to 10 mm of the stented
segment: vessel cross-sectional area (CSA), vessel minimal and maximal
diameters, lumen CSA, and lumen minimal and maximal diameters. The
reference site measurements were made at sites that did not appear
severely diseased on intravascular ultrasound image and that had a
minimum of balloon trauma from prior balloon dilatation. Thus, these
measurements were thought to be a reasonable and practical reflection
of the true lumen or vessel size by intravascular ultrasound. The
border of the vessel (as distinguished from the lumen) was defined on
the ultrasound image as the outer boundary of the echolucent medium
surrounding the plaque. Lumen measurements were made at the inner
border of the echo-dense plaque. Intrastent lumen CSA and diameter
measurements were made at the tightest position within the stent. The
average of the proximal and distal vessel CSAs was used to estimate the
vessel dimensions of the stented segment because intense echo
reverberations from the metallic struts frequently prevented
measurements of the vessel boundary beyond the stent. Intravascular
ultrasound imaging was performed in the reference sites and in the
stented segment at the initial intravascular ultrasound evaluation and
after each series of balloon dilations. Measurements were made at the
tightest point within the stented segment after each series of balloon
dilations. The measurements at the reference site were done on the
initial intravascular ultrasound evaluation to minimize the potential
balloon dilation effect that might increase the dimensions of the
reference site.
Interobserver and intraobserver reproducibility of minimum lumen diameter and lumen CSA measurements was retrospectively evaluated by linear regression analysis. Interobserver reproducibility was assessed by two ultrasound reviewers (S.N. and P.H.) performing blinded measurements of randomly selected stent sites (n=30) and reference segments (n=30). Intraobserver reproducibility was based on blinded measurements performed at a different time. The reproducibility of the measurements was reported as correlation coefficients±SEE. Interobserver correlation coefficients for the minimum lumen diameter and lumen CSA measurements at the stent site were 0.94±0.14 mm and 0.97±0.50 mm2, and intraobserver correlation coefficients were 0.96±0.13 mm and 0.98±0.43 mm2. In reference segments, interobserver correlation coefficients of the minimum lumen diameter and lumen CSA measurements were 0.93±0.23 mm and 0.98±0.64 mm2, and intraobserver correlation coefficients were 0.93±0.23 mm and 0.99±0.38 mm2. Interobserver correlation coefficients for the reference minimum vessel diameter and vessel CSA were 0.98±0.16 mm and 0.99±0.46 mm2, and intraobserver correlation coefficients were 0.98±0.15 mm and 0.99±0.38 mm2. All probability values were significant to <.0001.
Intravascular Ultrasound Criteria for Optimal Stent Expansion
The criteria for optimal stent expansion were governed by the
principles of optimizing stent expansion and covering the full extent
of the lesion so as to minimize any potential impairment to flow that
could contribute to stent thrombosis. The first criterion was a
qualitative evaluation of the stent site involving the achievement of
good stent apposition to the vessel wall with good plaque compression.
The second criterion was the achievement of a quantitative assessment
of optimal stent expansion. During the course of the investigation, two
quantitative criteria for stent expansion were used. For the majority
of the lesions (n=339), 60% of the average of the proximal and distal
CSAs was the target for defining intravascular ultrasound
success.25 This target criterion was initially chosen to
accommodate the compensatory dilation that occurs with early atheroma
deposition, an observation that has been made in both morphology and
intravascular ultrasound investigations even in the angiographically
normal reference site.23 26 27 The
quantitative criterion
for optimal stent expansion was altered in the last 113 lesions so that
the goal was to achieve an intrastent lumen CSA equal to or greater
than the distal reference lumen CSA. The quantitative criterion for
assessing optimal stent expansion was adjusted during the course of the
investigation to simplify the criterion and because of the perceived
overriding importance of not leaving the stent with a stenosis relative
to the distal lumen rather than achieving a specified percent dilation
relative to the reference vessel. A third (and equally important)
ultrasound criterion was that the nonstented segments immediately
adjacent to the stent (proximal or distal) did not reveal evidence of a
significant lesion defined as a CSA stenosis >60% relative to the
adjacent reference lumen. This criterion was established in an attempt
to apply a simple and consistent quantitative measurement that could be
used to judge and treat lesions that were occasionally seen at the
stent margin or in adjacent unstented segments. When a significant
lesion was observed in these segments, angioplasty or, more commonly,
stent implantation was performed. These lesions were categorized as
residual plaque or fractured plaque. A final criterion involving the
achievement of symmetrical stent expansion was also one of the initial
criteria as previously reported but was never used independently of CSA
measurements and was shown in previous intravascular ultrasound studies
to not change significantly during stent
optimization.22 25 Thus, the use of this criterion
was
abandoned.
Balloon Dilatation and Stent Implantation Strategy
The
approach to stent expansion evolved during the study.
In the initial 339 lesions, the balloon for final dilatations was sized
close to the intravascular ultrasound vessel major diameter. The final
stent balloon dilatations were performed with minimally compliant short
balloons (generally the 9-mm Chubby, Schneider). This strategy
translated into performing final balloon dilatations with balloons
oversized by visual estimate of the angiogram. Moderate maximal
inflation pressures (8 to 14 atm) were used in the first 40 lesions,
and subsequently, high maximal inflation pressures (>14 atm) were used
for the final balloon dilatation. In the final 113 lesions, final stent
dilatations were performed with a balloon more appropriately sized to
the angiographic vessel diameter by visual estimate when inflated to
high maximal pressures. In this phase, final balloon dilatations were
performed with noncompliant balloons (NC Shadow, SCIMED Life Systems)
inflated to pressures up to 20 atm.
Angiographic Analysis
Coronary angiograms were analyzed
without knowledge of the
intravascular ultrasound data by experienced angiographers not involved
in the stenting procedure. Patients received intracoronary
nitroglycerin before baseline and final angiograms to achieve maximal
vasodilation. To optimize reproducibility, the position of the x-ray
gantry was recorded in all views at the time of the baseline
angiograms, and final angiograms were done in matching views.
Angiographic measurements were made during diastole. The lesions were
measured with digital calipers (Brown and Sharp) from an optically
magnified image in a single, matched "worst" view. The guiding
catheter was used as the reference object for magnification
calibration. Previous studies have shown that digital calipers
correlate closely with computer-assisted methods, with a low
interobserver and intraobserver variability.28 29
Minimal
lumen diameter and percent diameter stenosis were obtained on the
baseline and final angiograms. The diameters of the proximal and distal
lumen reference sites were averaged to obtain a mean reference
diameter. The average reference diameter was used to calculate the
percent diameter stenosis at baseline and final angiogram. The average
reference diameter was used for these calculations to have a
correlation with the proximal and distal measurements performed on
intravascular ultrasound and also because the average reference vessel
was thought to be a better reflection of the vessel size when multiple
stents were placed in long segments that were of varying diameter.
Lesion length was measured on baseline angiography from the point at
which the lumen was compromised by 50% at the proximal or distal
reference vessel site. Lesions were characterized according to the
modified American College of Cardiology-American Heart Association
(ACC/AHA) score.30 The distance between lesions in the
same vessel was measured. Tandem lesions were defined as lesions in the
same vessel that were separated by <15 mm. Long lesions were defined
as a single continuous narrowing >15 mm. The presence of large filling
defects was noted at baseline or during the procedure. Thrombus was
defined as a filling defect seen in multiple projections surrounded by
contrast in the absence of calcification. TIMI grade flow was recorded
at the time of the initial procedure to characterize the indication for
stenting as previously described.31 Angiographic findings
such as the occurrence of dissection, vessel rupture, or side branch
compromise were recorded and analyzed.
Events
Major clinical events were considered death, emergency
bypass
surgery, elective bypass surgery, myocardial infarction (Q-wave or
non–Q-wave), emergency repeat intervention (bail-out stenting or
repeat angioplasty), and vascular complications. Specific major event
definitions were as follows: Death was defined as any death
irrespective of cause. A diagnosis of Q-wave myocardial infarction was
made when there was documentation of new pathological Q waves (
0.14
seconds) on an ECG in conjunction with elevation of creatine kinase to
greater than twice the upper limit of normal. A diagnosis of
non–Q-wave myocardial infarction was defined as elevation of the
cardiac enzymes to greater than twice the upper limit of normal without
the development of new pathological Q waves. Emergency coronary bypass
surgery was defined as bypass surgery involving immediate transfer of
the patient from the catheterization laboratory to the operating room.
Elective coronary bypass surgery was defined as nonemergent bypass
surgery performed more than 24 hours after a stent procedure for
procedural failure in the absence of ischemia or evolving myocardial
infarction. Acute thrombosis events were defined as angiographically
documented occlusion with TIMI grade 0 flow at the stent site occurring
within 24 hours of the stent procedure. Subacute thrombosis events were
angiographically documented occlusions with TIMI grade 0 flow at the
stent site occurring beyond 24 hours of the stent procedure. Emergency
intervention was bail-out stenting or emergency angioplasty performed
for ongoing acute ischemia or evolving myocardial infarction in the
setting of an angiographically documented stent thrombosis event.
Repeat angioplasty was nonemergency angioplasty performed for
symptomatic restenosis. Vascular complications were defined as the
occurrence of bleeding or hematoma formation at the access site
requiring transfusion, vascular repair, or external compression.
Events were categorized as intraprocedural complications, postprocedure events that occurred during hospitalization (hospital events), events that occurred after hospital discharge up to 2 months (short-term posthospitalization events), and late events that occurred between 2 and 6 months of clinical follow-up. Cumulative events were reported at 6-month clinical follow-up. Intraprocedural and early postprocedural events were separated to evaluate the safety of the intravascular ultrasound–guided stent implantation procedure and to assess the efficacy of antiplatelet therapy without anticoagulation after a successful stent procedure.
Postprocedure Medication Protocol
If the intravascular
ultrasound criteria for optimal stent
expansion were met and the angiographic result was also acceptable, no
further heparin was administered and sheaths were removed in 4 to 6
hours. When procedures were performed in the evening, heparin was
infused overnight and the sheaths were removed the following morning.
The first 252 patients to complete a successful Palmaz-Schatz stent
procedure received ticlopidine 250 mg PO BID for 2 months (the first
150 patients) or 1 month (subsequent 102 patients). Patients who had
not received ticlopidine before the stent procedure also received
aspirin 325 mg/d for 3 to 5 days. The last 69 consecutive patients in
this cohort were treated only with aspirin 325 mg BID.
Patients who did not have intravascular ultrasound performed, patients who had an attempted but unsuccessful intravascular ultrasound evaluation, and patients who had a final suboptimal intravascular ultrasound performed were treated with a standard postprocedure anticoagulation and antiplatelet regimen. In these patients, at the completion of the stent procedure, the heparin was discontinued briefly to allow for sheath removal, then reinstituted within 4 to 6 hours. Warfarin was initiated on the day of the procedure, and both heparin and warfarin were continued until the prothrombin time was >16 (international normalized ratio, 2.0 to 3.5), after which the heparin was stopped. Starting on the day of the procedure, these patients received aspirin 325 mg/d indefinitely but did not receive dextran or dipyridamole.
Follow-up
In the first 2 months of this protocol (first 60
patients),
patients were observed in the hospital for 7 to 10 days. Subsequently,
patients were discharged from the hospital within 2 days. This was done
so that an evaluation of the safety and efficacy of short
hospitalizations after stent implantation could also be performed. The
short-term complications (stent thrombosis) continued to be carefully
assessed with regular and uniform contact of all patients within 4
weeks of hospital discharge and at 2 months. Late clinical follow-up
was performed at 6 months.
Statistics
Normally distributed data are expressed as
mean±SD. Data that
are not normally distributed are expressed as a median with a range of
values. Comparisons between equivalent groups were performed by paired
Student's t test. Subgroup comparisons of discrete
variables were made by 
2 analysis.
Differences were considered statistically significant at
P<.05. Intraobserver and interobserver reproducibility of
minimum lumen diameter and lumen CSA measurements were evaluated by
linear regression analysis.
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Results |
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TopAbstractIntroductionMethods Results Discussion References |
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Patient, Angiographic, and Procedural Characteristics
The clinical characteristics and indications for use of a stent in the 359 patients undergoing Palmaz-Schatz stent implantation are shown in Table 1
. The majority of stent procedures were
performed electively (67%). Angiographic and procedural
characteristics are presented in Table 2. A total of
452 lesions were treated in 398 vessels. A total of 864 stents were
implanted. Multiple stents were implanted in 180 of 452 lesions (40%),
in 196 of 398 vessels (49%), and in 199 of 359 patients (55%). The
mean number of stents per lesion was 1.51±0.98 (range, 0.5 to 9 stents
per lesion), per vessel 1.72±1.14, and per patient 1.8±1.17. A
single
short stent was placed in 36 lesions (8%). A single Palmaz-Schatz
stent (one Palmaz-Schatz or two short stents) was placed in 234 lesions
(52%). One Palmaz-Schatz stent and one short stent were deployed in 50
lesions (11%). Two or more Palmaz-Schatz stents were implanted in 132
lesions (29%).
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Procedural Success
Between March 30, 1993, and January 1,
1994, a total of 359
consecutive patients with 452 lesions underwent intracoronary stent
implantation. After stent deployment and angiographic optimization,
initial stent implantation was successful in 347 patients (96.6%) and
in 438 lesions (96.9%), as shown in Fig 1. Before
intravascular ultrasound imaging, stent implantation was unsuccessful
in 12 patients (3.3%) with 14 lesions (3.1%). After initial stent
implantation success, there were 9 patients (2.6%) with 13 lesions
(2.9%) that did not have intravascular ultrasound performed for
technical reasons, and intravascular ultrasound was unsuccessful in 3
patients (0.8%) with 5 lesions (1.1%). Of the 420 lesions in 335
patients that were imaged by intravascular ultrasound, optimal stent
expansion was observed in 127 lesions (30%) on the initial ultrasound
evaluation. After intravascular ultrasound–guided stent site
optimization, a final optimal ultrasound result was achieved at the
stent site on 402 lesions (96%) in 321 patients (96%). With increased
experience and the change in the criteria for success, the percent of
lesions in which there was adequate stent expansion at the initial
intravascular ultrasound increased from 12% in the first 100 lesions
to 60% in the last 113 lesions. During the process of intravascular
ultrasound–guided optimization, stent failure with
major complications occurred in an additional 6 patients (1.7%) with 8
lesions (1.7%). There were 8 patients (2.2%) with 10 lesions (2.2%)
who had a suboptimal stent result at the final intravascular ultrasound
evaluation. The 321 patients who had adequate stent expansion by
intravascular ultrasound criteria were treated with antiplatelet
medications and did not receive additional anticoagulation (heparin or
warfarin). During the 2-month short-term clinical follow-up, there were
three stent thrombosis events in the 321 patients (0.9%) with 399
lesions (0.7%) treated only with antiplatelet therapy and no
anticoagulation. The short-term clinical follow-up was done in all
patients at 2 months. An additional two stent occlusions (0.6%) were
documented at angiographic follow-up at 3 and 4 months. These
occlusions were associated with angina recurrence but not clinical
events.
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A total of 20 patients (5.6%) were treated with a standard anticoagulation regimen consisting of short-term heparin, warfarin for 2 months, and aspirin indefinitely. This group included the 9 patients who did not have intravascular ultrasound guidance, the 3 patients who had an attempted but unsuccessful intravascular ultrasound procedure, and the 8 patients who had a final intravascular ultrasound that revealed suboptimal stent expansion. These patients did not have any clinical or angiographically documented stent thrombosis events.
Unsuccessful Stent Implantation and Intraprocedural Events
The stent implantation procedure was unsuccessful in 18 patients
(5.0%). Two of the procedures were unsuccessful without clinical
events. Unsuccessful stent implantation associated with a major event
occurred in 16 patients (4.5%), as shown in Table 3. In
these 16 patients, myocardial infarction occurred in 11 patients
(3.1%), only 5 of whom had Q-wave myocardial infarctions (1.4%).
Emergency bypass was necessary in 11 patients (3.1%) and elective
bypass in 2 patients (0.6%). Three patients (0.8%) died during the
procedure. The timing of the 18 unsuccessful stent implantation
procedures relative to the intravascular ultrasound imaging is
illustrated in Fig 1
. Unsuccessful stent implantations
associated with
major clinical events were due to unsuccessful stent delivery in 5
patients (1.4%) and occurred after successful stent delivery to the
lesion site in 11 patients (3.1%), as shown in Fig 2.
Unsuccessful stent delivery was due to incomplete lesion coverage in 3
patients, left main dissection from guiding catheter trauma before
stent delivery in 1 patient, and left anterior descending artery
dissection that occurred during stent delivery into an angulated
circumflex in 1 patient. Causes of complications after successful stent
delivery included distal embolization in a degenerated vein graft in 1
patient and dissection from the intravascular ultrasound catheter in
one patient. After successful stent delivery, stent site optimization
complications were nonocclusive dissections in 4 patients (1.1%),
coronary vessel rupture in 4 patients, and side branch compromise
during stent optimization in 1 patient.
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2 Months), Late (2 to 6 Months), and Cumulative Events at
6-Month Follow-up
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Early Postprocedural Events
Early postprocedural hospital
events occurred in 4 patients (Table 3). Two patients had acute
thrombosis events at the stent site 3 hours
and 12 hours after the stent procedure. Both of these events were
associated with Q-wave myocardial infarctions. One of the acute
occlusions occurred in the vessel with slow flow related to a prestent
coronary Rotablator procedure. The second acute thrombosis event was
the result of a vessel closure distal to a patent stent that had
preserved flow into a large side branch. While not strictly a stent
thrombosis, the occlusion was counted as an acute thrombosis event
because the distal dissection was a result of the stent implantation
procedure. This patient underwent bailout stent implantation, which
restored vessel patency and hemodynamic stability before emergency
coronary bypass surgery. One other non–Q-wave myocardial infarction
occurred in the postprocedure hospitalization period that was not due
to stent thrombosis. This patient had undergone a combined Rotablator
and stent procedure and returned to the catheterization laboratory for
angiographic evaluation of an asymptomatic cardiac enzyme elevation.
Angiographic and intravascular ultrasound evaluations revealed a patent
stent site and no evidence of thrombus. This non–Q-wave myocardial
infarction event was considered an embolic event related to a prestent
Rotablator procedure.
After the procedure, there were one vascular complication and one death, in the same patient. This patient underwent multiple percutanous interventions and vascular surgical repairs for lower-extremity ischemia, developed rhabdomyolysis and renal failure, and died 17 days after the stent procedure of multiorgan failure and sepsis.
Short-term
clinical follow-up was obtained in all patients at 2 months.
During the 2-month short-term clinical follow-up period after hospital
discharge, there was one subacute stent thrombosis event (Table
3). The
event occurred 8 days after the stent procedure and was associated with
a non–Q-wave myocardial infarction. The occlusion was reopened, an
additional bailout stent was placed at the site of a distal dissection,
and the patient continued on antiplatelet therapy.
Late Events
Long-term follow-up was obtained in 351 patients
(98%). Late
events between 2 and 6 months occurred in 57 patients (16%), as shown
in Table 3. The majority of these events were repeat
angioplasty,
performed in 47 patients (13.1%) for symptomatic restenosis. A total
of 8 patients (2.2%) underwent nonemergency coronary bypass during the
late follow-up period. Myocardial infarction during the late follow-up
was observed in 5 patients (1.4%). There were 3 deaths during the late
follow-up period, and all were cardiac related. One death occurred
after a large inferior myocardial infarction in a patient 5.5 months
after stent implantation in the left anterior descending artery. An
angiogram performed 3 weeks before the death revealed a patent left
anterior descending artery stent and moderate diffuse disease in the
right coronary artery but no evidence of a critical lesion. A second
late death was a witnessed in-hospital ventricular fibrillation event 4
months after the procedure. The patient had a history of ischemic
cardiomyopathy and refractory ventricular arrhythmias. The third late
death also occurred in a patient with ischemic cardiomyopathy due to
refractory congestive heart failure without evidence of ischemia.
Angiographic Analysis
As shown in Table 4, the
baseline proximal
reference vessel diameter was 3.3±0.53 mm. The baseline distal
reference vessel was 3.06±0.56 mm. The baseline average (of proximal
and distal) reference vessel diameter was 3.18±0.53 mm. The reference
vessel diameter after the stent procedure was not significantly
different. Baseline minimum lumen diameter was 0.94±0.57 mm, with a
baseline percent diameter stenosis of 71±16%. The final stent
diameter was 3.39±0.53 mm, with a mean final percent stenosis of
-7±16%. Mean lesion length was 9.5±6.7 mm. The median
length of the
lesions was 7.6 mm (range, 1.2 to 39 mm). The results were achieved
with a mean pressure of 14.9±3.0 atm and a balloon-to-vessel ratio of
1.17±0.19.
|
Qualitative angiographic assessment revealed other information on the effect of high-pressure balloon dilatation. Transient side branch occlusion during the stent procedure occurred in 15 lesions (3.3%). These transient occlusions usually resolved with the administration of intracoronary nitroglycerin but sometimes required balloon dilatation. All had resolved at the end of the stent procedure and were not associated with major events. Vasospasm was noted more prominently during the procedure when high pressures, >15 atm, were used for final balloon dilation. This phenomenon was self-limiting, always resolved with time or after high doses of intracoronary nitroglycerin, and was not associated with any unfavorable clinical events.
Intravascular Ultrasound Analysis
Table 5
shows the intravascular ultrasound
measurements. The mean lumen CSA at the tightest point within the stent
increased 26%, from 6.5±2.0 mm2 at the initial
intravascular ultrasound to 8.8±2.5 mm2 at the final
intravascular ultrasound (P<.0001). The tightest
intrastent lumen area relative to the reference area expanded from
49±13% at the initial intravascular ultrasound to 66±13% at the
final intravascular ultrasound (P<.0001). The minor stent
lumen diameter increased from 2.7±0.5 to 3.1±0.5 mm
(P<.0001), and the major stent diameter increased from
3.1±0.5 to 3.5±0.5 mm between the initial and final
intravascular
ultrasound (P<.0001). A mean of 2.4±1.2 ultrasound
evaluations were performed per lesion. Examples of suboptimal stent
expansion with subsequent intravascular ultrasound–guided
stent optimization are shown in Figs 3 and 4.
|
|
|
Intravascular ultrasound evaluation of the artery segments adjacent to the stent revealed that 73 of the 419 lesions (17%) had significant luminal encroachment of >60% relative to the reference lumen. The lumen CSA of these lesions was 3.8±1.9 mm2. Additional stents were inserted at these stenoses to reduce potential flow limitations in the stented artery. These lesions at the stent margins were identified as residual plaque (57 lesions) or, less commonly, fractured plaque (16 lesions).
Effect of Balloon Dilatation Strategy
The oversize and
appropriate-size final balloon dilatation
strategies that were used sequentially during the study are summarized
in Table 6. The reference artery diameters were similar
with the two balloon dilatation strategies. The use of larger balloons
in the oversize dilatation strategy is reflected by the
balloon-to-vessel ratio of 1.20±0.19, in contrast to the
balloon-to-vessel ratio of 1.05±0.14 when appropriate-size balloons
were used for final dilatation (P<.0001). The maximal
balloon inflation pressure (in atmospheres) when final dilatations were
performed with oversize balloons was 14.7±2.9, compared with a maximal
pressure of 15.7±3.1 when appropriate-size balloons were used for
final dilatations (P<.0001). The effect that the different
balloon dilatation strategies had on stent expansion is demonstrated by
both the final stent minimum lumen diameter and the final percent
diameter stenosis. The final stent minimum lumen diameter decreased
from 3.44±0.54 mm when the oversize balloon dilatation strategy was
used to 3.2±0.47 mm in the final phase (P<.0001). The mean
final percent stenosis of -9±15% when oversize balloons were
used for final dilatations is a clear reflection of the overdilatation
effect with the oversize balloon dilatation strategy and was in
contrast to the final percent stent stenosis of 1±10% when
appropriate-size balloon were used for final stent dilatations. With
the change in dilatation strategy, there was a reduction of
intraprocedural complications from 5.7% to 1% (P=.04).
There were four coronary vessel ruptures (1.2%) when oversize balloons
were used for final dilatations, and this decreased to 0% when
appropriate-size balloons were used for final dilatation
(P=NS). There was no significant change in the stent
thrombosis events when oversize balloons were used (0.8%) and when
appropriate-size balloons were used (1.0%).
|
Effect of Antiplatelet Therapy
In the 252 patients treated
with ticlopidine, there were two acute
stent thromboses (0.8%). In the 69 patients treated with aspirin alone
after the stent procedure, there was one subacute stent thrombosis
(1.4%). There was no significant difference between the stent
thrombosis rates between the ticlopidine and the aspirin treatment
groups. Side effects that precipitated medication discontinuation were
more frequent with ticlopidine than with aspirin. Ticlopidine was
stopped for minor complications of skin rash or gastrointestinal
disturbances within 2 weeks of the stent insertion in 5 patients.
Neutropenia was documented in 2 patients and was reversible after the
medication was stopped. These 7 patients were continued on aspirin
after the ticlopidine was discontinued. There were no adverse
medication effects in the 69 patients treated with aspirin.
|
Discussion |
|---|
|
TopAbstractIntroductionMethods Results Discussion References |
|---|
The results of this nonrandomized study on patients undergoing intravascular ultrasound–guided intracoronary stent implantation indicate that anticoagulation can be safely withheld when adequate stent expansion is achieved and flow optimized in the stented and adjacent inflow and outflow segments. These findings represent a departure from previous doctrine regarding coronary stents and suggest an alternative approach that may eliminate the need for anticoagulation, with reduction in hospital stay and vascular complications.
Comparison With Other Studies
Large multicenter studies on
patients undergoing elective stenting
have reported an incidence of stent thrombosis of 3% to
4%.6 15 16 17 Hospital or
early complications included a 3%
incidence of Q-wave myocardial infarction, a 2% to 3% rate of
non–Q-wave myocardial infarction, and a 2% to 3% need for bypass
surgery.15 16 When stenting is performed for bailout
or
emergency indications, stent thrombosis and major complication rates
are higher.1 2 19 20 The
incidence of stent thrombosis is
8% to 16%, with a 6% to 21% rate of myocardial infarction, a 4% to
13% need for emergency bypass surgery, and a 2% to 4% incidence of
death.1 2 19 Although stents decrease
morbidity of acute
closure,1 2 lower the incidence of major hospital or
early
events, and reduce restenosis rates compared with angioplasty-treated
groups,15 16 the potential benefit of stent
implantation
is, unquestionably, lost in patients with stent thrombosis.
Vascular access complications and bleeding associated with a stringent anticoagulation regimen further increase the morbidity of the stenting procedure. The reported incidence of access site complications requiring vascular repair is 4% to 10%.2 5 6 16 19 The combined rate of vascular complications and bleeding complications at the access site or other sites that require transfusions varies considerably, from 7% to 20%.1 2 5 15 19
In the present study, stent insertion was performed for a variety of indications but was frequently performed electively. Lesion anatomy was complex in this cohort, as reflected by the 16% of lesions >15 mm, the 14% of tandem lesions, the 26% of lesions that were stented in angiographically small vessels (<3 mm), the high percentage of complex lesion morphology (modified AHA/ACC lesion types B2 or C), and the 3% of lesions with large filling defects consistent with thrombus. Despite the high complexity in this nonselected cohort of patients, the overall clinical success and complication rates compare favorably with those reported for elective or single stent deployment and those reported for the indications of acute or threatened closure.
As with prior studies, intravascular ultrasound was important in assessing adequate stent expansion, which was frequently underestimated by angiography.21 22 The most frequent site of potential flow limitation was within the stented segment. After intravascular ultrasound–guided repeat dilatations, the intrastent lumen CSA was significantly enlarged, from 6.5 to 8.8 mm2, P<.0001. With this approach, stent thrombosis was rare despite the absence of anticoagulation.
The primary focus of the present study was a short-term assessment of the safety of stent implantation without subsequent anticoagulation after intravascular ultrasound confirmation. The novelty of the approach that combines both improved stent expansion and the use of multiple stents for full lesion coverage also warranted a long-term assessment of outcome. Despite the complexity of the patients in this cohort, the 6-month event rate is only slightly higher than the event rates reported in multicenter trials on single stent implantation.15 16 The procedural complications in the early experience and the inclusions of patients with low ejection fraction contribute to the cumulative high death rate reported at 6 months.
Intravascular Ultrasound–Guided Stenting
By study
design, intravascular ultrasound imaging was first
performed after an initially successful angiographic result with <20%
residual stenosis by visual analysis was obtained. Despite the
angiographic appearance, measurements at the initial intravascular
ultrasound study suggested that further dilatation was necessary in the
majority of cases. The diameter and CSA of the stent lumen were
enlarged significantly after repeat dilatation. Analysis of the
intravascular ultrasound data provided other important information in
evaluating the effect of various balloon dilatation strategies. The
intravascular ultrasound data illustrated the overdilation effect from
the oversize balloon strategy. Balloons that were sized to the
intravascular ultrasound vessel diameter (angiographically oversized)
were used for final balloon dilatations in the majority of the stent
implantation procedures. This strategy was initially used to maximize
protection against stent thrombosis in a large, unselected, and
consecutive series of patients who were undergoing stent implantation
without subsequent anticoagulation for the first time. Although
protective against stent thrombosis, this strategy came with the price
of a high procedural complication rate and an unacceptable incidence of
intracoronary vessel rupture. The experience gained from intravascular
ultrasound imaging together with an evaluation of clinical results
affected the choice of balloon size and inflation pressures. As the
study progressed, balloons selected on the basis of angiographic vessel
size and higher pressures were used to provide adequate expansion
within the stented segment. With the adjustment in the balloon
dilatation strategy, the final stent expansion was more appropriate
relative to the reference vessel measurements. This resulted in a lower
intraprocedural complication rate but did not increase the incidence of
stent thrombosis.
Full Lesion Coverage and Use of Multiple Stents
Intravascular
ultrasound identified lesions in the adjacent
unstented segments that were poorly visualized on angiogram. Typically,
the angiogram at the corresponding site would reveal an area of
ill-defined haziness without stenosis, a discrete stenosis <20%, and
less commonly, no evidence of a lesion. The decision to treat the
lesions at the stent margins based on a quantitative assessment of
their severity by intravascular ultrasound was in keeping with a
practice of covering the full extent of the lesion. Both intravascular
ultrasound and pathology reports have shown that angiography
underestimates the severity of coronary
disease.22 23 26 27 32
In some instances, intravascular
ultrasound imaging was also valuable in assisting in the decision not
to deploy stents to lesions at the stent margins. The lesions that were
stented tended to be in angiographically small vessels in which the
lesions were more likely to encroach on the intravascular ultrasound
catheter and in which the risk for stent thrombosis was perceived to be
higher. In the majority of these lesions, the lumen CSA was <5
mm2.
Previous stent investigations have identified residual lesions and dissections after stent implantation as a major cause of subsequent early thrombotic events.2 33 34 35 36 37 38 Residual lesions (or dissections) after stent implantation are due either to a failure to cover the distal extent of a lesion or to the balloon dilatation process after successful stent deployment to the appropriate lesion site. In the present study, the use of more than one stent, when necessary, to achieve full lesion coverage may also be an important reason for the low incidence of stent thrombosis. The low incidence of stent thrombosis also demonstrates that the use of multiple stents for full lesion coverage is a safe strategy to use despite the lack of anticoagulation after the stent procedure.
Angiographic Versus Ultrasound Assessment
Well-defined
angiographic criteria for successful stent expansion
that alleviates the risk of stent thrombosis and the need for
anticoagulation have not been developed. There is a limit to visual
interpretation of small percent stenosis differences on the angiogram.
It is arguable that careful on-line quantitative angiographic
measurements could better determine angiographic success similar to the
results achieved with intravascular ultrasound. The experience of this
study showed that indentations in the balloon profile or angiographic
mismatch between the measured and chosen balloon diameters correspond
to inadequate stent expansion as documented by intravascular
ultrasound. Empirical high-pressure balloon inflations with an
appropriate-size noncompliant balloon may increase the number of
patients who will have acceptable stent expansion. In the present
study, high-pressure balloon inflations have increased the
percentage of patients who achieved adequate stent expansion at the
initial intravascular ultrasound evaluation from 12% to 60%. Despite
this aggressive inflation approach, 40% of the stents with an
acceptable angiographic result still required additional dilatation
with higher pressures or, less commonly, a dilatation with a larger
balloon. The angiographic method of determining stent expansion has
inherent limitations of a one-dimensional assessment of percent
diameter stenosis. In contrast, intravascular ultrasound
cross-sectional imaging from within the lumen of the stent is a
reliable method of confirming adequate stent expansion with a degree of
security that allows anticoagulation to be eliminated from the
poststent medical regimen.
Antiplatelet Therapy
In this study, the majority of patients
were treated with
ticlopidine after stent insertion. In this group, there were two stent
thrombosis events (0.8%). In the group treated with aspirin, there was
one stent thrombosis event (1.4%) (P=NS). The two late
stent occlusions occurred with the patients on aspirin (started after 1
to 2 months of ticlopidine therapy). The lack of difference in the
stent thrombosis rates suggests that the achievement of adequate stent
expansion and good flow in adjacent segments is a more important
variable in the prevention of stent thrombosis than the specific
antiplatelet agent. A randomized comparison may better determine
whether small differences in efficacy exist between the two
antiplatelet agents.
Study Limitations
One limitation was the absence of
computerized quantitative
coronary angiographic analysis. Another important methodological
weakness was the lack of a consistent intravascular ultrasound
criterion and balloon dilatation strategy. The change in the
quantitative intravascular ultrasound criterion was based on knowledge
gained during the course of the investigation and reflects an
adjustment to a simplified criterion that is easier to achieve and may
have more physiological meaning in terms of the prevention of stent
thrombosis. After the initial experience showed a low stent thrombosis
rate, balloon dilatation strategies were also adapted in an attempt to
reduce intraprocedural complications, which were unacceptably high. The
evolving balloon dilatation strategy, however, significantly decreases
the sample size for each phase and creates difficulties in discerning
differences for low event rate complications such as stent thrombosis
and coronary vessel rupture. Postprocedure complications associated
with prestent rotational atherectomy contributed to two of the early
postprocedural events. Although the Rotablator has utility in the
treatment of lesions that resist dilatation, cautious use of this
device may be warranted in the patient in whom stent implantation is
anticipated. Short-term heparin for 24 hours may also be appropriate in
this select situation.
One drawback to the technique of using intravascular ultrasound to assess the adequacy of stent expansion and lesion coverage is the increased number of stents and balloons and a longer procedure time. A more accurate analysis of the overall cost of the technique, however, should weigh the expense of increased procedural resources together with an evaluation of the savings from a decrease in postprocedural complications, a reduction in hospital stay, and the elimination of laboratory costs associated with monitoring anticoagulation regimens. The use of balloon delivery systems that incorporate a high-pressure balloon for the initial stent deployment would further reduce procedural costs and might also decrease dissections at stent margins that are due to balloon misplacement when stents are not visible.
The results of the study apply primarily to patients undergoing elective stent implantation, since the majority of patients underwent stent insertion for nonemergent indications. It is encouraging, however, that there were no stent thromboses in 21 consecutive patients who underwent emergency Palmaz-Schatz stent implantation despite not having postprocedural anticoagulation. Whether there is an absolute requirement of intravascular ultrasound to confirm stent expansion before treatment only with antiplatelet therapy was not addressed in the present investigation. A randomized, multicenter trial would perhaps best answer this issue in view of the important clinical and economic ramifications.
Conclusions and Future Directions
On the basis of these
observations, it is reasonable to conclude
that the Palmaz-Schatz stent can be deployed in coronary arteries with
a low rate of thrombosis provided that stent expansion is adequate and
there are no other flow-limiting lesions present. If high-pressure
stent dilatation, treatment of the entire lesion, and intravascular
ultrasound documentation of optimal stent expansion and lesion coverage
are used, anticoagulation can be safely omitted after the procedure.
This strategy should facilitate the expanded use of stents to provide
the benefit of decreased restenosis while simultaneously reducing the
cost and complications associated with stent insertion.
|
Acknowledgments |
|---|
This study was supported in part by National Institutes of Health grant 5-RO1-HL-45077-03.
Received August 2, 1994; revision received October 3, 1994; accepted October 24, 1994.
|
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J. L. Orford, A. Lerman, and D. R. Holmes Routine intravascular ultrasound guidance of percutaneous coronary intervention: A critical reappraisal J. Am. Coll. Cardiol., April 21, 2004; 43(8): 1335 - 1342. [Abstract] [Full Text] [PDF]
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P.W Radke, A Kaiser, C Frost, and U Sigwart Outcome after treatment of coronary in-stent restenosis: Results from a systematic review using meta-analysis techniques Eur. Heart J., February 1, 2003; 24(3): 266 - 273. [Abstract] [Full Text] [PDF]
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W. C. Lau, L. A. Waskell, P. B. Watkins, C. J. Neer, K. Horowitz, A. S. Hopp, A. R. Tait, D. G.M. Carville, K. E. Guyer, and E. R. Bates Atorvastatin Reduces the Ability of Clopidogrel to Inhibit Platelet Aggregation: A New Drug-Drug Interaction Circulation, January 7, 2003; 107(1): 32 - 37. [Abstract] [Full Text] [PDF]
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I.-M. o Chung, H. K. Gold, S. M. Schwartz, Y. Ikari, M. A. Reidy, and T. N. Wight Enhanced extracellular matrix accumulation in restenosis of coronary arteries after stent deployment J. Am. Coll. Cardiol., December 18, 2002; 40(12): 2072 - 2081. [Abstract] [Full Text] [PDF]
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J. L. Orford, R. Lennon, S. Melby, P. Fasseas, M. R. Bell, C. S. Rihal, D. R. Holmes, and P. B. Berger Frequency and correlates of coronary stent thrombosis in the modern era: Analysis of a single center registry J. Am. Coll. Cardiol., November 6, 2002; 40(9): 1567 - 1572. [Abstract] [Full Text] [PDF]
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A. Colombo, G. Stankovic, and J. W. Moses Selection of coronary stents J. Am. Coll. Cardiol., September 18, 2002; 40(6): 1021 - 1033. [Abstract] [Full Text] [PDF]
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D. L. Bhatt, M. E. Bertrand, P. B. Berger, P. L. L'Allier, I. Moussa, J. W. Moses, G. Dangas, M. Taniuchi, J. M. Lasala, D. R. Holmes, et al. Meta-analysis of randomized and registry comparisons of ticlopidine with clopidogrel after stenting J. Am. Coll. Cardiol., January 2, 2002; 39(1): 9 - 14. [Abstract] [Full Text] [PDF]
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H. Schuhlen, A. Kastrati, J.u. Pache, J. Dirschinger, and A. Schomig Incidence of thrombotic occlusion and major adverse cardiac events between two and four weeks after coronary stent placement: analysis of 5,678 patients with a four-week ticlopidine regimen J. Am. Coll. Cardiol., June 15, 2001; 37(8): 2066 - 2073. [Abstract] [Full Text] [PDF]
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P. H. Grewe, T. Deneke, A. Machraoui, J.u. Barmeyer, and K.-M. Muller Acute and chronic tissue response to coronary stent implantation: pathologic findings in human specimen J. Am. Coll. Cardiol., January 1, 2000; 35(1): 157 - 163. [Abstract] [Full Text] [PDF]
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J. M. Rankin, J. J. Spinelli, R. G. Carere, D. R. Ricci, I. M. Penn, J. D. Hilton, M. A. Henderson, R. I. Hayden, and C. E. Buller Improved Clinical Outcome after Widespread Use of Coronary-Artery Stenting in Canada N. Engl. J. Med., December 23, 1999; 341(26): 1957 - 1965. [Abstract] [Full Text] [PDF]
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R. A. M. van Liebergen, J. J. Piek, K. T. Koch, R. J. G. Peters, R. J. de Winter, C. E. Schotborgh, and K. I. Lie Hyperemic coronary flow after optimized intravascular ultrasound-guided balloon angioplasty and stent implantation J. Am. Coll. Cardiol., December 1, 1999; 34(7): 1899 - 1906. [Abstract] [Full Text] [PDF]
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C. Briguori, I. Sheiban, J. De Gregorio, A. Anzuini, M. Montorfano, P. Pagnotta, F. Marsico, F. Leonardo, C. Di Mario, and A. Colombo Direct coronary stenting without predilation J. Am. Coll. Cardiol., December 1, 1999; 34(7): 1910 - 1915. [Abstract] [Full Text] [PDF]
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A. Cappelletti, A. Margonato, G. Rosano, A. Mailhac, F. Veglia, A. Colombo, and S. L. Chierchia Short- and long-term evolution of unstented nonocclusive coronary dissection after coronary angioplasty J. Am. Coll. Cardiol., November 1, 1999; 34(5): 1484 - 1488. [Abstract] [Full Text] [PDF]
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P. J. de Feyter, P. Kay, C. Disco, and P. W. Serruys Reference Chart Derived From Post-Stent-Implantation Intravascular Ultrasound Predictors of 6-Month Expected Restenosis on Quantitative Coronary Angiography Circulation, October 26, 1999; 100(17): 1777 - 1783. [Abstract] [Full Text] [PDF]
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E. Tsuchikane, S. Sumitsuji, N. Awata, T. Nakamura, T. Kobayashi, M. Izumi, S. Otsuji, H. Tateyama, M. Sakurai, and T. Kobayashi Final results of the STent versus directional coronary Atherectomy Randomized Trial (START) J. Am. Coll. Cardiol., October 1, 1999; 34(4): 1050 - 1057. [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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Y. Kobayashi, J. De Gregorio, N. Kobayashi, T. Akiyama, B. Reimers, L. Finci, C. Di Mario, and A. Colombo Stented segment length as an independent predictor of restenosis J. Am. Coll. Cardiol., September 1, 1999; 34(3): 651 - 659. [Abstract] [Full Text] [PDF]
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D. E. Cutlip, M. B. Leon, K. K. L. Ho, P. C. Gordon, A. Giambartolomei, D. J. Diver, D. M. Lasorda, D. O. Williams, M. M. Fitzpatrick, A. Desjardin, et al. Acute and nine-month clinical outcomes after "suboptimal" coronary stenting: Results from the STent anti-thrombotic regimen study (STARS) registry J. Am. Coll. Cardiol., September 1, 1999; 34(3): 698 - 706. [Abstract] [Full Text] [PDF]
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J. Dirschinger, A. Kastrati, F.-J. Neumann, P. Boekstegers, S. Elezi, J. Mehilli, H. Schuhlen, J. Pache, E. Alt, R. Blasini, et al. Influence of Balloon Pressure During Stent Placement in Native Coronary Arteries on Early and Late Angiographic and Clinical Outcome : A Randomized Evaluation of High-Pressure Inflation Circulation, August 31, 1999; 100(9): 918 - 923. [Abstract] [Full Text] [PDF]
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R. Waksman Late Thrombosis After Radiation : Sitting on a Time Bomb Circulation, August 24, 1999; 100(8): 780 - 782. [Full Text] [PDF]
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M. A. Costa, M. Sabate, W. J. van der Giessen, I. P. Kay, P. Cervinka, J. M. R. Ligthart, P. Serrano, V. L. M. A. Coen, P. C. Levendag, and P. W. Serruys Late Coronary Occlusion After Intracoronary Brachytherapy Circulation, August 24, 1999; 100(8): 789 - 792. [Abstract] [Full Text] [PDF]
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J. P. Carrozza Jr, S. E. Hosley, D. J. C. MD, and D. S. Baim In Vivo Assessment of Stent Expansion and Recoil in Normal Porcine Coronary Arteries : Differential Outcome by Stent Design Circulation, August 17, 1999; 100(7): 756 - 760. [Abstract] [Full Text] [PDF]
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I. Moussa, M. Oetgen, G. Roubin, A. Colombo, X. Wang, S. Iyer, R. Maida, M. Collins, E. Kreps, and J. W. Moses Effectiveness of Clopidogrel and Aspirin Versus Ticlopidine and Aspirin in Preventing Stent Thrombosis After Coronary Stent Implantation Circulation, May 11, 1999; 99(18): 2364 - 2366. [Abstract] [Full Text] [PDF]
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E. D. Peterson, P. A. Cowper, E. R. DeLong, J. P. Zidar, R. S. Stack, and D. B. Mark Acute and long-term cost implications of coronary stenting J. Am. Coll. Cardiol., May 1, 1999; 33(6): 1610 - 1618. [Abstract] [Full Text] [PDF]
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