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Circulation. 1995;92:348-356

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(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

Bradley H. Strauss, MD, PhD; Madhu K. Natarajan, MD; Wayne B. Batchelor, MD; David E. Yardley, MD; John A. Bittl, MD; Timothy A. Sanborn, MD; John A. Power, MD; Linley E. Watson, MD; Richard Moothart, MD; James E. Tcheng, MD; Robert J. Chisholm, MD

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.).


*    Abstract
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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


*    Introduction
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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.


*    Methods
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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 {chi}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.


*    Results
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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 1Down. 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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  		Table 1. Baseline Morphology of Saphenous Vein Graft Lesions

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 2Down). 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 3Down). Only lesion length (P<.02) remained significant in the multivariate logistic regression analysis.


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  		Table 2. Dissection Grades During Procedure


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  		Table 3. Univariate Predictors of Dissections

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 1Down. 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 2Down.



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  		Figure 1. Curves showing cumulative distribution of the effect of three different laser catheter sizes (1.4 [solid line], 1.7 [dotted line], and 2.0 [dashed line] mm) on minimal lumen diameter immediately after laser (but before adjunct percutaneous transluminal coronary angioplasty). The median lumen diameters were 1.37, 1.53, and 1.74 mm for 1.4-, 1.7-, and 2.0-mm laser catheters, respectively.



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  		Figure 2. Curves showing cumulative distribution of minimal lumen diameters before procedure (light solid line), immediately after laser (dotted line), immediately after adjunct percutaneous transluminal coronary angioplasty (heavy solid line), and at follow-up (dashed line).

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 4Down). 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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  		Table 4. Univariate Predictors of Laser Success (Diameter Stenosis <=50% After Laser)

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 5Down). 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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  		Table 5. Univariate Predictors of Restenosis (Diameter Stenosis >=50% at Follow-up)

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 6Down). 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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  		Table 6. Univariate Predictors of Occlusion (Diameter Stenosis=100%) at Follow-up

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 3Down). 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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  		Figure 3. Photomicrograph of bypass graft lesion in patient who died of intractable ventricular arrhythmias 5 days after uncomplicated successful laser angioplasty. Patient had chronic ventricular arrhythmias and congestive heart failure before angioplasty associated with left ventricular dysfunction. At autopsy, the vein graft was widely patent, although there was evidence of a dissection (*). Original magnification x25, HOPS (hematoxylin, orcein, phloxine, safranin) stain.

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 4Down).



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  		Figure 4. Kaplan-Meier curve of initial clinical events during 1-year follow-up after excimer laser angioplasty. Events are death (light solid line), death/myocardial infarction (MI) (dotted line), death/MI/redo bypass surgery (CABG) (heavy solid line), and death/MI/CABG/target vessel repeat percutaneous transluminal coronary angioplasty. Pts indicates patients.


*    Discussion
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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.


*    Acknowledgments
 
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 3Up.


*    Footnotes
 
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.


*    References
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*References
 

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