(Circulation. 1995;92:348-356.)
© 1995 American Heart Association, Inc.
Articles |
Early and Late Quantitative Angiographic Results of Vein Graft Lesions Treated by Excimer Laser With Adjunctive Balloon Angioplasty
From the Division of Cardiology, St Michael's Hospital, University of Toronto, Ontario, Canada (B.H.S., M.K.N., W.B.B., R.J.C.); St Anthony's Medical Center, Rockford, Ill (D.E.Y.); Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Mass (J.A.B.); Department of Medicine, Cornell–New York Hospital, New York, NY (T.A.S.); Department of Medicine, St Francis Hospital, Pittsburgh, Pa (J.A.P.); Scott and White Hospital, Temple, Tex (L.E.W.); Penrose Hospital, Colorado Springs, Colo (R.M.); and Department of Medicine, Duke University Medical Center, Durham, NC (J.E.T.).
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Abstract |
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 Top Abstract IntroductionMethods Results Discussion References |
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Background Percutaneous excimer laser coronary angioplasty (PELCA) has been approved for treatment of diseased saphenous vein bypass grafts. However, detailed and complete quantitative angiographic analysis of immediate procedural and late follow-up results has not been performed.
Methods and Results PELCA using the CVX-300 excimer laser system
was performed in 125 bypass lesions (mean graft age, 96±53 months;
range, 2 to 240 months) in 106 consecutive patients at eight centers.
Quantitative analyses of the procedural and follow-up angiograms were
done with the Cardiac Measurement System. Stand-alone PELCA was done in
21 lesions (17%). Lesions were located at the ostium (20%), body
(67%), or distal anastomosis (13%). The graft reference diameter was
3.26±0.79 mm (mean±SD). Minimal lumen diameter increased from
1.09±0.52 mm before treatment to 1.61±0.69 mm after laser and
2.18±0.63 mm after adjunctive balloon dilation (P<.001)
but had declined at follow-up to 1.40±1.17 mm. Dissections were
evident in 45% of lesions after laser treatment (types A and B, 27%;
types C through F, 18%), including 7% occlusions. Angiographic
success (
50% diameter stenosis [% DS]) was 54% after laser and
91% after adjunctive PTCA, with an overall clinical success rate of
89%. In-hospital complications were death, 0.9%; myocardial
infarction (Q-wave and non–Q-wave), 4.5%; and bypass surgery, 0.9%.
Independent predictors of % DS after laser were reference diameter,
lesion length, and minimal lumen diameter before laser. At angiographic
follow-up in 83% of eligible patients, the restenosis rate per lesion
(DS >50%) was 52%, including 23 occlusions (24%). The only
independent predictor of increased % DS at follow-up was lesion
symmetry. Logistic regression indicated that smaller reference diameter
was an independent predictor of late occlusion. Overall 1-year
mortality was 8.6%. Actuarial event-free survival (freedom from death,
myocardial infarction, bypass surgery, or target vessel percutaneous
transluminal coronary angioplasty) was 48.2% at 1 year.
Conclusions Excimer laser angioplasty with adjunctive balloon angioplasty can be safely and successfully performed in diseased, old saphenous vein bypass graft lesions considered at high risk for reintervention. The extent of laser ablation remains limited by the diameter and effectiveness of the catheters. Late restenosis and, in particular, total occlusion mitigate the early benefits of the procedure. Other approaches such as the routine use of additional anticoagulation (eg, warfarin) should be considered to reduce the risk of late occlusions and restenosis after laser angioplasty of bypass grafts.
Key Words: bypass • lasers • angioplasty • restenosis • coronary disease
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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Patients presenting with recurrence of anginal symptoms after saphenous vein bypass surgery pose a difficult and increasingly frequent challenge. In general, they are older and have more extensive and diffuse disease of both the native circulation and venous bypass grafts than patients who have not undergone bypass surgery. Repeat coronary bypass surgery is an option but is technically more demanding and is associated with a higher mortality and morbidity and less-optimal long-term clinical results compared with a first bypass operation.1 2 3 4 Although internal mammary arteries are being used more often, almost all cases require one or more additional saphenous vein bypass grafts, conduits that typically have a shorter life span.
Favorable results have been achieved with balloon angioplasty in
discrete, short lesions in relatively young bypass grafts but have been
discouraging in older, diffusely diseased, ulcerated, or thrombosed
venous
grafts.5 6 7 8 9 10 11 12
Distal emboli are also more common in
bypass grafts5 6 13 (2% to 13%) than in
native arteries
(1.0%).14 15 16 17
Furthermore, it appears that the
restenosis rate is high, varying from 30% to 70%, depending on the
site of the lesions in the graft and the overall extent of disease in
the graft.
Recently, several new devices have been evaluated as alternatives or adjuncts to conventional balloon angioplasty in saphenous vein bypass grafts, including coronary stents (Wallstent18 19 20 and Palmaz-Schatz stents21 22 23 ), directional coronary atherectomy,22 24 and transluminal extraction coronary (TEC) atherectomy.25 Percutaneous excimer laser angioplasty (PELCA) has been approved by the FDA for treatment of saphenous vein bypass grafts. Industry-sponsored registries of approximately 1000 patients with saphenous vein bypass graft lesions have demonstrated that excimer laser angioplasty can be performed successfully with acceptable complication rates.26 27 28 However, these registry reports on bypass graft lesions have been limited by lack of a central core laboratory performing quantitative coronary angiography (QCA) and low rates of angiographic follow-up (<50%). Although the late angiographic outcome of excimer laser angioplasty in bypass graft lesions remains uncertain, Bittl et al29 reported an encouraging restenosis rate of 30% in a small number of graft lesions (n=27).
The purpose of the present study was to provide an in-depth analysis of excimer laser treatment of saphenous vein bypass graft lesions. In a central core laboratory, QCA was performed in 125 consecutive saphenous vein bypass graft lesions from eight centers, and angiographic follow-up in 83% of eligible patients ensured minimal bias in the analysis of follow-up results. The objectives of this study were twofold. First, a detailed qualitative and quantitative analysis of the laser contribution of the procedure was done to assess the acute effects of the excimer laser. Second, the overall immediate and late angiographic and clinical outcomes of excimer laser-assisted angioplasty for saphenous vein graft lesions were evaluated to determine whether lesion- or laser-related variables were associated with outcome.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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Study Patients
The study population consisted of 106 patients who underwent laser treatment of 125 saphenous vein bypass graft lesions. Five additional patients were excluded from the study because of missing angiograms (n=1) or technically inadequate angiograms for analysis (n=4; no guiding catheters filmed for calibration). The study patients were treated consecutively at the respective centers but were enrolled at different times (December 1989 through March 1993), since some centers started at later dates. The study protocol was approved by the individual hospital institutional review boards, and patients were enrolled after informed consent was obtained. Entry criteria included a history of angina or evidence of provocable ischemia associated with lesions that appeared to be amenable to laser therapy. Exclusion criteria included total occlusions, filling defects (although 10 lesions [8%] had angiographic evidence), evolving myocardial infarction, and left ventricular ejection fraction <30%. Patients were asked to return for repeat angiography at 6 months, but this was performed earlier if necessary for recurrence of symptoms.
Excimer Laser Angioplasty Procedure
All patients were treated
with the CVX-300 excimer laser
(Spectranetics Corp) by use of over-the-wire concentric catheters (with
diameters of 1.4, 1.7, or 2.0 mm) and techniques previously
described.26 30 The energy fluence ranged from 40 to
60
mJ/mm2 and ablation time from 5 to 64 seconds. At the
discretion of the investigator, adjunctive balloon angioplasty and, in
two cases, directional atherectomy were used. Stand-alone laser
angioplasty (without adjunctive percutaneous transluminal coronary
angioplasty [PTCA]) was performed in 17% of the lesions. Multilesion
laser angioplasty was attempted in 11%. All patients were routinely
pretreated with aspirin 325 mg. During the procedure, patients received
an initial bolus injection of heparin (10 000 to 15 000 U)
supplemented as needed to maintain an activated clotting time of at
least 300 seconds (350 in two centers). Heparin was continued as an
infusion after the procedure at the discretion of the operator
(overnight [ie, 10 to 18 hours] in 78%; 15% for 
48 hours).
Quantitative Coronary Analysis
All cineangiograms were
analyzed at the Core Laboratory by use
of the Cardiac Measurement System (Medical Imaging Systems), which has
been described in detail.31 Measurements of minimal lumen
diameter (MLD), reference diameter (RD), and lesion length were
obtained from the known diameter of the nontapered section of the
guiding catheter tip used as a calibration factor. In some cases of
ostial lesions, user-defined RDs were determined when the proximal
vessel was inadequate for the computer to calculate the interpolated
RD. The percentage diameter stenosis (% DS) of the narrowed segment
was derived by comparing the observed stenosis dimensions with the
reference values. The area between the actual and reconstructed
contours at the obstruction site was a measure of the amount of
"atherosclerotic plaque" and was expressed in square millimeters
(plaque area). Using the reconstructed borders of the vessel, the
computer calculated a symmetry coefficient for the stenosis.
Differences in distance between the actual and reconstructed vessel
contours on both sides of the lesion were measured. Symmetry was
determined by the ratio of these two differences, with the largest
distance between the actual and reconstructed contours becoming the
denominator. Values for symmetry range from 0 for extreme eccentricity
to 1 for maximal symmetry (that is, equal distance on both sides
between reconstructed and actual contours). Relative (laser or
procedural) gain relates the increase in MLD normalized for the RD (ie,
relative laser
gain=MLDpostlaser-MLDpreprocedure/RD).
The ratio of the diameter of the final device to the RD, called the D/A
ratio, was a measure of relative device sizing.25 Two
parameters could be determined only by manual methods performed on
photographs of the lesions. Lesion bend was measured with a protractor,
using the angle of the artery subtending the stenosis, and was
considered severe if 45°.32 For focal lesions, the
angle used was that formed by the vessel centerline proximal and distal
to the stenosis. For long lesions, the measured angle was that formed
by the most angulated region of the stenosis. Face angle is a measure
of the abruptness of the proximal aspect of the lesion. This parameter
was defined as the angle between the proximal face of the stenosis and
the contiguous proximal lumen and was considered "abrupt" if
45°.32 33 Three parameters were determined by
visual
inspection of the angiogram. Diffuse disease was defined as irregular
or ulcerated lumen surface occupying 50% of the length of a bypass
graft. Thrombus was considered present if a discrete intralumen
filling defect was visible. Dissections were defined according to the
modified National Heart, Lung, and Blood Institute
criteria,34 based on the consensus of two experienced
observers at the core laboratory (B.H.S., R.J.C.).
The angiographic analyses were done before and after laser, after angioplasty, and at follow-up in all patients and used the average of multiple matched views with orthogonal projections wherever possible. Validation studies on this particular quantitative system have demonstrated an intraobserver MLD variability of 0.07 mm on immediate reanalysis and of 0.20 mm on 25 paired angiograms analyzed 6 months apart.35
Angiographic Outcomes
Laser success and procedural success
were defined as DS 50%
immediately after PELCA and after procedure (either stand-alone or with
adjunctive PTCA). Although device success has been defined in some
laser and TEC reports as 20% improvement in stenotic
diameter,25 27 30 36 we chose
a 50% DS criterion to be
consistent with other device reporting, including the New Approaches to
Coronary Intervention registry,37 and because, in
practice, clinicians continue to assess the success of a device or a
procedure according to this definition. Distal embolization was defined
as filling defects distal to the treated graft with or without evidence
of "no-reflow" or myocardial infarction. Graft perforation was
defined by a persistent extravascular collection of contrast medium
beyond the graft wall with a well-defined exit port. Restenosis was
defined as follow-up DS >50% in a lesion that had been initially
successfully (ie, DS 50%) treated.
Clinical Outcomes
Clinical success was defined as procedure
success without
in-hospital complications (death, myocardial infarction [Q-wave and
non–Q-wave], bypass surgery, or PTCA). Q-wave myocardial infarction
was documented by the presence of new Q waves of at least 0.04
second's duration and an increase in serum creatine kinase to more
than twice the normal value together with a pathological increase in
myocardial isoenzymes. Non–Q-wave infarctions required the cardiac
enzyme elevations without the presence of new pathological Q waves.
Cardiac enzymes were measured in 73% of the patients and were done
routinely at five of the eight centers. At the other centers, cardiac
enzymes were drawn only if there was a clinical indication such as
chest pain during or after the procedure or angiographic evidence of
distal embolization.
Statistical Methods
The data obtained by QCA analysis are
given as mean±SD. The
means for each angiographic variable before laser, after laser, after
balloon, and at follow-up were compared by ANOVA. If significant
differences were found, two-tailed t tests were applied to
pairs of data. A probability of <.05 was considered significant.
To
determine parameters associated with laser-induced dissections,
acute laser success (DS 50% after laser), late restenosis (DS >50%
at follow-up), and late occlusions (DS=100%), comparisons were made
with unpaired t tests for continuous variables. For discrete
variables, a likelihood-ratio 
2 was used. To
determine the independent predictors of postlaser DS and follow-up DS,
linear regression analysis was used. Independent predictors of
laser dissection and occlusion were determined by a logistic regression
analysis. All analyses were carried out on a computerized
statistical package (SAS PC version 6.04).
The late clinical follow-up was assessed according to a life table format by the Kaplan-Meier method.38 The following events were considered clinical end points: death, myocardial infarction, bypass surgery, or nonsurgical target vessel revascularization (PTCA with or without repeat laser). The life table was constructed according to the initial clinical event and included both procedural and follow-up events. All patients had clinical follow-up to at least 170 days (unless an earlier event occurred), with the exception of one patient who was lost to follow-up after hospital discharge following successful laser angioplasty.
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Results |
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The mean age (±SD) of the group was 65±8 years. The majority (76%) of the patients were male. Anginal symptoms were classified as I (5%), II (6%), III (30%), or IV (59%) according to the Canadian Cardiovascular Society classification. Unstable angina was present in 65% of the patients. The mean graft age was 96±53 months (range, 2 to 240 months). Prior PTCA had been performed in 17% of the lesions.
Angiographic Results
The baseline morphology of the vein
graft lesions is given in
Table 1
. Only 33% of the lesions were classified as low
risk (concentric, short lesions). The remaining lesions were assessed
to have increased risk due to several parameters, including ostial
position, lesion length >10 mm, diffusely diseased grafts, location on
severe bend, or complex morphology (thrombus, ulceration).
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Acute
angiographic success (DS 50%) was achieved in 54% of lesions
after PELCA and in 91% after adjunctive balloon angioplasty. Distal
emboli were apparent angiographically in six grafts after laser (4.8%)
and in three after PTCA (2.4%). There were two localized perforations
(1.6%), which both sealed with balloon angioplasty. The overall
dissection rate was 45% after PELCA and 48% after adjunct PTCA (Table
2). The dissections were predominantly mild in severity
(types A and B). Moderate to severe dissections (types C through F)
were identified in 18% of lesions after PELCA and 16% after PTCA,
including occlusions in 9 lesions (7%) after laser and 5 lesions (5%)
after balloon. In the univariate analysis of postlaser dissections,
longer lesions and lesion location (ie, body of the graft) were
significantly associated with dissections (Table 3).
Only lesion length (P<.02) remained significant in the
multivariate logistic regression analysis.
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The mean RD for the overall
group was 3.26±0.79 mm. The cumulative
curves of the effects of individual laser diameters on MLD are shown in
Fig 1. The mean (and median) lumen diameters after laser
were 1.43±0.38 mm (1.37 mm), 1.60±0.62 mm (1.53 mm), and
1.67±0.75
mm (1.74 mm) for 1.4-, 1.7-, and 2.0-mm laser catheters, respectively.
There was an increase in MLD from 1.09±0.52 to 1.61±0.69 mm
after
PELCA and then further to 2.18±0.63 mm immediately after adjunctive
PTCA (P<.001). At follow-up, the MLD was found to have
decreased to 1.40±1.17 mm (P<.001). The % DS changed
similarly, with an initial decrease from 66±15% to 50±21% after
PELCA and a further decrease to 34±15% after PTCA
(P<.001). The mean DS at follow-up was 61±29%. The
cumulative distribution curves for MLD before procedure, after PELCA,
after PTCA, and at follow-up are shown in Fig 2.
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Laser
success (DS 50% after laser) was significantly associated with
less severe stenoses, smaller plaque area, smaller RDs, shorter
lesions, and increased D/A ratio (Table 4). Linear
regression analysis indicated that lesion length (F=14.796,
P<.001), DS before procedure (F=4.98, P<.03),
and RD (F=3.62, P<.06) were independent predictors of
postlaser DS.
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Angiographic follow-up was obtained at 178±119
days (range, 30 to 700
days) in 79 patients (93 lesions) discharged from hospital without
complications, which represented 83% of eligible patients.
Four patients who had follow-up angiograms performed 2 months after
PELCA without evidence of restenosis did not undergo a later angiogram.
The restenosis rate per lesion using the DS 50% criterion was 52%.
Angiographic restenosis was significantly associated with smaller MLD
and more severe diameter stenoses before procedure and in more
concentric lesions (ie, increased symmetry) (Table 5).
In the linear regression model, the only independent predictor of
follow-up DS was symmetry (F=6.10, P<.02), although MLD
before procedure approached significance (F=2.80,
P<.10).
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Occlusions were observed in 23 lesions (24%) at
follow-up and
accounted for 46% of the restenosis lesions. Occlusions at follow-up
were significantly associated with smaller vessels, more concentric
lesions, smaller obstruction diameter before procedure, and increased
D/A ratio (Table 6). In the logistic regression
analysis, RD (P=.05) was the only independent predictor
of follow-up occlusion, whereas symmetry approached significance
(P<.07).
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Clinical Results
In Hospital
Clinical success,
defined as DS 50% and no in-hospital clinical
event (death, non–Q-wave or Q-wave myocardial infarction, CABG, or
PTCA) was achieved in 95 patients (89%). Five patients had
postprocedural DS >50% (but not occluded), without a clinical event.
Three patients (five lesions) had total occlusions at the end of the
procedure, with a Q-wave and a non–Q-wave infarct documented in two of
these patients. One patient had evidence of severe distal embolization
with reduced flow after procedure that was associated with marked chest
pain and a non–Q-wave myocardial infarction. Another patient with TIMI
grade 2 flow immediately after the procedure had an occluded graft at
repeat angiography before hospital discharge but no creatine kinase
rise. One patient developed chest pain several hours after a successful
procedure and was sent for urgent bypass surgery. Postoperatively, this
patient had evidence of a Q-wave myocardial infarction. One patient
died 5 days after an uncomplicated procedure due to intractable
arrhythmias associated with left ventricular dysfunction. There was no
evidence of periprocedural myocardial infarction, and autopsy revealed
a widely patent bypass graft at the site of laser angioplasty (Fig
3). Overall, the incidence of in-hospital complications
was death, 0.9%; myocardial infarction, 4.5% (Q-wave, 1.9%;
non–Q-wave, 2.6%); and bypass surgery, 0.9%.
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Follow-up
The 1-year mortality was 8.6% (9 deaths).
Three of the late
deaths occurred after repeat procedures (1 patient died after failed
PTCA and urgent coronary artery bypass graft surgery [CABG], 1
patient during elective PTCA, and 1 patient after elective CABG). Four
deaths were sudden, and one death was due to chronic renal failure.
After the initial hospitalization, revascularization (either target
lesion PTCA or CABG) was required in 31 patients, including both
procedures in 4 patients, and 1 patient had a documented Q-wave
infarction. The 1-year event-free survival (freedom from death,
myocardial infarction, CABG, or PTCA) was 48.2% (Fig 4).
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Discussion |
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Acute Procedural Results
This study indicates that excimer laser angioplasty in conjunction with adjunct balloon angioplasty can achieve a success rate of 89% in symptomatic patients with diseased saphenous vein bypass graft lesions with low complication rates. The non–Q-wave myocardial infarction rate (2.6%) is based on the 77 patients who had cardiac enzymes measured after the procedure. However, this may be an overestimation, because cardiac enzymes were not drawn in 27% of the group, since it was not thought to be clinically indicated. It should be stressed that the grafts in this study in general were at increased risk (particularly for distal embolization)33 because of advanced graft age, diffuse disease, large plaque volume, and prominent number of ostial stenoses. Only 33% of the lesions were considered low risk, and a significant number of the higher-risk cases would not have been considered for balloon angioplasty as primary therapy. Furthermore, the mean age of the patients was 65 years, which is 9 years older than several other reported angioplasty studies.39 40 41
However, several shortcomings of the use of excimer laser in old saphenous vein bypass grafts are evident. Distal embolization occurred in 7.2% of lesions, with 33% related to adjunctive balloon angioplasty. Despite a high dissection rate of 45% after laser, the majority of dissections were mild. Increasing lesion length was the only lesional or procedural variable significantly associated with laser-induced dissections. Although 10 lesions were type E or F at the conclusion of the procedure, 2 of these cases were multilesion angioplasty (5 lesions in 2 grafts). Other excimer laser studies, predominantly in native coronary arteries, have reported dissection rates in the range of 12% to 30%.27 32 37 It is unclear whether our dissection rates are higher because of the method of analysis (core laboratory versus individual investigators in registry reports) or a particular feature of laser angioplasty in bypass grafts. A report by Safian et al25 described a similar rate of dissection (34.5%) with the use of TEC in bypass grafts. Several recent studies have made investigators aware of undesirable laser effects, such as gas bubble formation, cavitation, and shock waves, that can result in dissection.42 43 Recent data have shown that saline infused directly into the coronary vessel at the time of laser activation significantly decreases the incidence and severity of acute dissections.44 However, this technique was not used by the investigators in the trial and could be an important maneuver to improve acute results.
The diameter of the lumen channels after one or more laser passes remains less than the diameter of the laser catheter in >50% of cases, suggesting suboptimal ablation. This was most evident with the largest (2.0-mm) laser catheter, which provided only marginally larger channels than the 1.7-mm catheter. This limitation of channel diameter after PELCA is particularly relevant to bypass grafts, which are generally of larger caliber than native coronary arteries. In this study, the mean RD is 3.26 mm, which was considerably larger than the 2.60- to 2.70-mm value measured for native arteries in several balloon angioplasty trials that used a similar system of quantitative analysis.39 40 41 The rather limited contribution of the excimer laser in these bypass graft lesions is emphasized by the observation that only approximately half of the overall increase in minimal luminal diameter was derived from the laser (mean laser gain of 0.52 mm compared with 0.55 mm by adjunctive angioplasty). Moreover, a significant mean residual DS of 34% persisted at the end of the procedure, which could have implications for late restenosis.45 These data are in contrast to the postprocedural results from a study of stents in bypass grafts that used a similar QCA system of analysis, which revealed a mean residual stenosis of 23%.20 Univariate and multivariate analyses indicated that several lesion- and procedure-related variables were associated with increased DS after the laser part of the procedure. Laser failure (DS >50% after laser), which was more frequent in long and bulky lesions and large grafts, could be attributed to both relative inefficiency of ablation (ie, channel size smaller than laser diameter) and undersizing of laser catheters relative to the diameter of these bypass grafts. It remains to be determined whether improved laser ablation or more effective adjunctive balloon angioplasty will improve the late results.
Follow-up Results
An angiographic restenosis rate of 52% and
1-year clinical event
rate of approximately 50% are disappointing but appear to be
comparable to previous studies of balloon
angioplasty,10 11 12
stent,18 20 and
TEC25 in bypass grafts (although Piana et
al23 recently described a 17% restenosis rate for
Palmaz-Schatz stenting of focal vein graft lesions). It should be
emphasized, however, that high-risk lesions predominated in this study
and may not be comparable to bypass graft lesions reported with other
devices. The restenosis rate in our study is similar to the 53%
restenosis rates in native arteries treated with excimer laser
angioplasty recently reported by Bittl et al29 but higher
than the 30% rate determined in a small number of bypass graft lesions
in that study. The only independent predictor of follow-up % DS was
symmetry, with more concentric lesions demonstrating larger-diameter
stenoses. This has never been reported in studies of balloon
angioplasty alone. One possible explanation for this observation is
that more contact may be occurring between concentric laser catheters
and concentric plaques than with eccentric plaques. The transmission of
laser energy to a larger plaque surface may be unfavorable for
restenosis, since experimental studies have indicated that excimer
laser can incite potent smooth muscle cell proliferation in the vessel
wall.46 There was also a trend toward increased restenosis
in more severe lesions, similar to several balloon angioplasty
studies.47 48 Although relatively few in number,
distal
anastomotic lesions had a lower restenosis rate (22%) than ostial and
shaft stenoses (55% in both), which is consistent with results of
several studies.5 7
The high occlusion rate at follow-up (24%) is of concern and suggests an especially important role of thrombus in the late outcome of vein graft lesions treated with excimer laser angioplasty. All patients were taking aspirin. Fifteen patients (16%) were discharged on chronic warfarin therapy, and two of the 12 patients with angiographic follow-up had a documented occlusion. Previous follow-up studies of angioplasty and stent procedures, predominantly in native coronary arteries, showed a late occlusion rate of 5.3% and 5.7% of patients, respectively.20 49 Minimal data of follow-up occlusions after PTCA in saphenous vein bypass grafts are available. In the Thoraxcenter's experience, only 3 of 53 high-risk graft patients in whom the Wallstent was implanted had occluded vessels at angiographic follow-up.18 This group received aggressive anticoagulation therapy, including warfarin and aspirin. Safian et al25 had a 29% late occlusion rate in bypass graft patients treated with TEC despite chronic coumarin and aspirin therapy in 80% of patients. However, 28% of lesions contained thrombus before the procedure, including 6% total occlusions. The high occlusion rate in our follow-up study is of particular concern, since several studies have described poor results in attempting to reopen occluded grafts.50 51
Several features unique to venous grafts could increase the thrombogenic and proliferative response after laser ablation. The endothelial cells in veins are larger, thinner, and less firmly anchored than in arteries. The tunica intima is more permeable, and the internal elastic lamina is poorly defined.52 Particularly relevant to our laser results are data suggesting that veins appear to be intrinsically more susceptible to thrombosis than arteries. This may be related to relatively less production of prostacyclin, a potent vasodilator and inhibitor of platelet aggregation.53 Furthermore, there is a tendency for vein graft lesions to accumulate lipid because of increased lipid uptake, decreased lipolysis, and increased synthesis of complex lipids.53 Grafts also may display an increased tendency for erosion and undermining of the thickened intima, which results in the formation of plaque with a fibrous cap of uneven thickness51 52 and therefore more at risk for deeper subintimal injury by laser ablation. Finally, many vein grafts are oversized relative to the distal vessel, and this size mismatch may result in sluggish flow in the graft, which could promote thrombus formation.
Although it has been observed from in vitro studies
that the pulsed
excimer laser can create deep, smooth-edged craters in hard, calcified
atherosclerotic tissue,54 the subintimal surface exposed
by the ablation is probably highly thrombogenic. Our study adds some
support to this speculation in that several variables that may be
indicators of more aggressive ablation, such as larger laser catheters,
increased D/A ratios, and increased relative laser gain, were
significantly associated with late graft occlusion. The angiographic
appearance (complex features including ulcer or thrombus) of the lesion
either before or after procedure was not predictive for late occlusion.
According to these results, the use of more intense anticoagulation
therapy, such as warfarin, should be considered after excimer laser
angioplasty of old grafts, especially if the RD is 3.0 mm. If more
extensive ablation is observed with the newer eccentric catheters, the
argument for routine long-term anticoagulation in this patient group
would be even more compelling.
Study Limitations
This is a retrospective observational study
that was performed
during a period of changes in both the laser catheter designs and
techniques of lasing (eg, multiple versus single laser passes). All of
the cases represent the initial experience of each center, and
increased operator experience may improve the results. However, the
adverse results were not clustered around the early cases. The
restenosis rate may be underestimated, since angiographic follow-up in
this study was not performed in 17% of the patients. Furthermore, a
late restenosis could not be detected in the four patients who did not
demonstrate angiographic restenosis in angiograms performed <60 days
after procedure. Although the presence of distal native disease and the
size of the distal bed are potentially important factors in maintaining
graft patency, these factors were not assessed in this study. No direct
comparisons with balloon angioplasty can be made because of the lack of
a conventional balloon angioplasty control group in our study. Because
of the sample size, we also cannot rule out a significant ß-error.
Therefore, these data require confirmation by other studies.
Summary
Excimer laser angioplasty, with adjunctive balloon
angioplasty,
can be safely and successfully performed in diseased, old saphenous
vein bypass grafts that are at high risk for reintervention (surgical
or by PTCA alone). The extent of laser ablation remains limited by the
size and effectiveness of the laser catheters. Late restenosis and
total graft occlusion, particularly in smaller grafts, mitigate the
early benefits of the procedure.
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Acknowledgments |
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This study was supported in part from a grant from Spectranetics, Colorado Springs, Colo. Dr Strauss is a Research Scholar of the Heart and Stroke Foundation of Canada. We are grateful for the technical assistance of Hamid Keshvari, Saied Babaie, Kimberley Bowman, Debbie Andrews, and Gigi Sorenson and the statistical assistance of Lisa Thurston and Lois Adams. We also want to thank Dr Allan Adelman for helpful comments and use of the Cardiac Measurement System at the Mount Sinai Hospital Cardiac Research Laboratory, Toronto, and Dr Brian Chiu, Department of Pathology, St Michael's Hospital, for Fig 3
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Footnotes |
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Reprint requests to Bradley H. Strauss, MD, PhD, Division of Cardiology, St Michael's Hospital, 30 Bond St, Toronto, Ontario, Canada M5B 1W8.
Received October 11, 1994; revision received December 28, 1994; accepted January 9, 1995.
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