Author + information
- Received April 20, 1998
- Revision received March 19, 1999
- Accepted June 3, 1999
- Published online September 1, 1999.
- Yoshio Kobayashi, MDa,
- Joseph De Gregorio, MDa,
- Nobuyuki Kobayashi, MDa,
- Tatsuro Akiyama, MDa,
- Bernhard Reimers, MDa,
- Leo Finci, MD, FACCa,
- Carlo Di Mario, MD, FACCa and
- Antonio Colombo, MD, FACCa,* ()
- ↵*Reprint requests and correspondence: Dr. Antonio Colombo, Centro Cuore Columbus, Via Buonarroti 48, 20145 Milan, Italy
We sought to evaluate the relation between stented segment length and restenosis.
Multiple or long coronary stents are now being implanted in long lesions or in tandem lesions. A longer stented segment might result in a higher probability of restenosis. However, there is little information available on the relation between stented segment length and restenosis.
Between April 1995 and December 1996, 725 patients with 1,090 lesions underwent stenting. Lesions were divided into three groups according to the length of the stented segment: 1) group I (n = 565): stented segment length ≤20 mm; 2) group II (n = 278): stented segment length >20 but ≤35 mm; and 3) group III (n = 247): stented segment length >35 mm.
There was no significant difference in the incidence of subacute stent thrombosis among the three groups (0.4% in group I, 0.4% in group II, 1.2% in group III; p = NS). The minimal lumen diameter (MLD) after stenting was greater in group I than in group III (3.04 ± 0.60 mm in group I, 3.01 ± 0.54 mm in group II, 2.91 ± 0.58 mm in group III; p < 0.05). At follow up, a smaller MLD was observed in group III as compared with group I and group II (2.04 ± 0.93 mm in group I, 1.92 ± 1.00 mm in group II, 1.47 ± 0.97 mm in group III; p < 0.01). The restenosis rates were 23.9% in group I, 34.6% in group II and 47.2% in group III (p < 0.01). Using multivariate analysis, the longer stented segment, the angiographic reference vessel diameter and the percent diameter stenosis after stenting were independent predictors of restenosis.
The present study shows that a longer stented segment is an independent predictor of restenosis without an influence on the risk of subacute thrombosis.
Coronary stenting has been shown to decrease the morbidity of acute vessel closure (1). Although clinical and angiographic restenosis rates in selected lesions are reduced with coronary stenting as compared with angioplasty (2,3), it is not known whether this benefit extends to other types of lesions. Multiple or long coronary stents are now being
implanted in long lesions or in tandem lesions. Previous studies (4–7)have shown higher restenosis rates with multiple overlapping stents. However, it is difficult to assess the relative importance of increased metal exposure with multiple partial overlapping stents versus a long lesion or a long stented segment. A longer stented segment might result in a higher probability of restenosis. However, there is little information on the relation between stented segment length and restenosis.
Between April 1995 and December 1996, 754 consecutive patients with 1,119 lesions underwent intracoronary stenting at Centro Cuore Columbus in Milan, Italy. In 29 lesions, another stent was deployed in the first stent because of plaque prolapse. These lesions with almost completely overlapping stents were excluded from further analysis. A total of 1,090 lesions in 725 patients were included in this study. Lesions were divided into three groups according to the length of the stented segment: 1) group I (n = 565): stented segment length ≤20 mm; 2) group II (n = 278): stented segment length >20 but ≤35 mm; and 3) group III (n = 247): stented segment length >35 mm. Of 1,090 lesions, 277 were treated with multiple stents. Because the operator tried to deploy multiple stents with minimal or no overlap, the length of the stented segment for these lesions was considered as the sum of the length of implanted stents.
Stent implantation procedure
Procedural details of stent placement have been described previously (8–10). Indications for stenting were defined as follows: elective stenting was performed when the operator elected to use stenting before starting the procedure. Suboptimal result stenting was defined as insertion of a stent for a focal dissection or significant vascular recoil after percutaneous transluminal coronary angioplasty (PTCA) associated with >30% lumen narrowing without ischemia. Threatened closure stenting was performed when PTCA was complicated by a longitudinal or a spiral dissection associated with >50% lumen encroachment (ischemia was not always present in the setting of threatened closure). Acute occlusion stenting was undertaken to relieve ischemia associated with total or subtotal vessel closure after angioplasty with no or markedly delayed distal flow (Thrombolysis in Myocardial Infarction [TIMI] flow grade 0 or 1). Total occlusion stenting was performed after reopening a vessel that had been occluded before the procedure had begun. Restenosis stenting was performed for lesions with a history of restenosis after one or more previous angioplasty procedures.
The following stents were used: the Palmaz-Schatz stent (Johnson & Johnson Interventional Systems, Warren, New Jersey), the Gianturco-Roubin stent (Cook, Bloomington, Indiana), the Wiktor stent (Medtronic Interventional Vascular, Kerkrade, The Netherlands), the AVE Micro stent (Arterial Vascular Engineering, Santa Rosa, California), the Cordis stent (Cordis, Miami, Florida), the Wallstent (Schneider-Europe, Bulach, Switzerland), the Angiostent (AngioDynamics, Glens Falls, New York), the NIR stent (Medinol, Tel Aviv, Israel), the Multi Link stent (Advanced Cardiovascular Systems, Santa Clara, California), the Crown stent (Johnson & Johnson Interventional Systems), the beStent (Medtronic In Stent, Minneapolis, Minnesota), the ACT-One nitinol stent (Progressive Angioplasty Systems, Menlo Park, California), the Tensum Biotronik stent (Biotronik, Berlin, Germany), the Div Ysio stent (Biocompatibles, Galway, Ireland), the PURA VARIO stent (DEVON Medical, Hamburg, Germany) and the IRIS stent (UNI-CATH, Saddle Brook, New Jersey). Stenting of a lesion with two or more kinds of stents was defined as combination of stents.
After stent implantation, angiographic optimization was performed using high pressure balloon dilation to achieve an acceptable angiographic result with <20% residual stenosis by visual estimate. In some of the lesions intravascular ultrasound (IVUS) was used at the operator’s discretion. Subsequent treatment decisions were based on IVUS results in conjunction with angiographic assessment. The final IVUS evaluation was the IVUS study after the last balloon inflation that documented achievement of optimal stent expansion criteria (8).
Before stent implantation, patients received aspirin (325 mg/day), which was continued indefinitely. After stent implantation, ticlopidine (250 mg two times a day) was added for one month. In rare situations oral anticoagulation was added without the use of ticlopidine.
Procedure success was defined as a final angiographic residual diameter stenosis <30% by quantitative analysis without a major complication (death, Q wave myocardial infarction or coronary artery bypass graft surgery) during the hospital period. Q wave myocardial infarction was documented by the presence of new Q waves of at least 0.04 in duration and a creatine kinase level or MB fraction at least twice the upper limit of normal. Acute thrombosis events were defined as angiographically documented occlusion with TIMI flow grade 0 or 1 at the stent site occurring within 24 h of the stent procedure. Subacute thrombosis events were angiographically documented occlusions with TIMI flow grade 0 or 1 at the stent site occurring beyond 24 h and within the first month of the stent procedure.
Quantitative coronary angiography
Patients received intracoronary nitroglycerin before initial, final and follow-up angiograms to achieve maximal vasodilation. Quantitative analysis was performed as previously described using an automated computer-based system by experienced angiographers not involved in the stenting procedure (11). Image calibration was performed with a contrast-filled catheter. The external diameter of the catheter was used as the calibration standard. Coronary end-diastolic frames from matched views obtained on initial, final and follow-up angiograms were analyzed using a contour detection minimal cost algorithm (QCA-CMS version 3.0, MEDIS, Leiden, The Netherlands). Reference and minimal lumen diameters (MLD) were determined from the single worst view. In some of the lesions with total occlusion, lesion length could not be measured before the intervention, and it was therefore measured after dilation with a small (1.5 or 2 mm) balloon catheter. Lesions were characterized according to the modified American College of Cardiology/American Heart Association (ACC/AHA) classification (12). Acute lumen gain was defined as the difference between the MLD before and after the intervention. Late lumen loss was defined as the difference between the MLD immediately after the intervention and at follow-up angiography. The loss index was calculated as the ratio of the late lumen loss to the acute lumen gain. Restenosis was defined as diameter stenosis ≥50% at follow-up angiography.
Intravascular ultrasound equipment and measurements
Intravascular ultrasound studies were performed using the Cardiovascular Imaging System (CVIS, Sunnyvale, California). This system uses a single-element 30-MHz beveled transducer within either a 2.9F long or a 3.2F short monorail imaging catheter. The transducer was withdrawn automatically at 0.5 mm/s to perform the imaging sequence. The position of the catheter on fluoroscopy was used to correlate the ultrasound image with the angiogram. The ultrasound catheter was advanced distal to the stent, and images were recorded while the imaging catheter was pulled back. On-line quantitative measurements were performed during the procedure. Intravascular ultrasound studies were recorded on 1/2-in. high resolution s-VHS tape for off-line analysis.
The major and minor diameters of the lumen and vessel were measured. Lumen and vessel cross-sectional areas were planimetered at the lumen–intima interface and the media–adventitia interface, respectively. The part of the lesion with the smallest lumen area was selected for measurements for each pass of the IVUS catheter. Reference lumen cross-sectional areas were measured proximal and distal to the stented segments in the closest most normal-appearing segments.
Data were expressed as proportions or mean value ± SD. Differences in categoric variables were analyzed using the chi-square test, and differences in continuous variables were analyzed using analysis of variance. The Scheffé F test was used as a post hoc test when analysis of variance was done. Statistical significance was defined as p < 0.05.
Univariate analysis consisted of the chi-square test for categoric variables and an unpaired, two-tailed ttest for continuous data. The variables that were found to be significant by univariate analysis were entered into multivariate analysis. The independent association of several variables with restenosis was evaluated using forward stepwise logistic regression analysis with the statistical computer package SPSS (SPSS, Inc., Chicago, Illinois). Forward stepwise procedures were used with a cutoff p value of 0.05 for inclusion of variables in the model, maintaining those variables with a Wald Static significance <0.1.
The clinical characteristics of the patients are shown in Table 1. There were no differences in terms of age; gender; incidences of risk factors, previous angioplasty, unstable angina and multivessel disease; left ventricular ejection fraction; and use of anticoagulation or antiplatelet therapy among the three groups. Group III had a higher incidence of previous myocardial infarction and a lower incidence of previous coronary artery bypass graft surgery than the other groups.
Angiographic and procedural characteristics
The indication for stenting and angiographic characteristics are shown in Table 2. Group III had a lower frequency of elective stenting and a higher frequency of total occlusion stenting than groups I and II. Stent implantation was performed more frequently in the left circumflex artery and less frequently in the left anterior descending coronary artery or the right coronary artery in group I as compared with groups II and III. The proximal location site and type B2 lesion (according to the modified AHA/ACC classification) were most frequent in groups I and II, whereas the mid-lesion site and type C lesion were most frequent in group III.
The procedural characteristics are shown in Table 3. The implanted stents were different among the three groups. The Palmaz-Schatz stent and the NIR stent were deployed more frequently in groups I and II. In contrast, a combination of different stents, the Wallstent and the Gianturco-Roubin stent were used more frequently in group III. The number of stents used was higher in groups II and III than in group I. A single stent was implanted in almost all lesions in group I, whereas multiple stents were deployed in almost half of the lesions in groups II and III. By definition, there was a significant difference in the length of the stented segment among the three groups. The final balloon size was greater in group III than in group I. The balloon vessel ratio was higher in groups II and III than in group I. There was no significant difference in maximal inflation pressure among the three groups.
The procedural outcomes are shown in Table 4. There were no significant differences in the incidences of angiographic success, procedural myocardial infarction and procedural death. The incidence of procedural coronary artery bypass graft surgery was higher in group III than in groups I and II. Procedural success was lower in group III than in groups I and II.
Acute stent thrombosis occurred more frequently in group III than in groups I and II. However, in lesions without acute or threatened closure, it was not different among the three groups (0.2% in group I, 0% in group II, 0.5% in group III). There was no significant difference in the incidence of subacute stent thrombosis among the three groups.
Quantitative angiographic analysis
Table 5shows the results of quantitative angiographic analysis. There were no significant differences in the reference vessel diameter at baseline, after stenting and at follow up among the three groups. Group III had a smaller MLD and a higher percent diameter stenosis at baseline than did groups I and II. The lesion length was longer in groups II and III than in group I. The MLD after stenting was greater in group I than in group III. After stenting group III had a greater residual percent diameter stenosis than did groups I and II.
Of the 1,040 lesions eligible for follow up, 743 (71%) had follow-up angiography at 5.4 ± 1.9 months after stent implantation. At follow up, a smaller MLD and a higher percent diameter stenosis were observed in group III than in groups I and II. Groups II and III had a longer lesion length at follow up than did group I. Although there was no significant difference in acute lumen gain among the three groups, group III had greater late lumen loss than did groups I and II. The loss index was greater in group III than in group I. The restenosis rates were 23.9% in group I, 34.6% in group II and 47.2% in group III (p < 0.01, Fig. 1A). To exclude the potential effect of multiple overlapping stents, the restenosis rates in the lesions with a single stent were also investigated (24.3% in group I, 41.8% in group II and 41.4% in group III [p < 0.01]) (Fig. 1B). The restenosis rates in the lesions with slotted tube stents were evaluated because the effect on restenosis may be different between slotted tube stents and coil stents (21.8% in group I, 35.5% in group II and 45.0% in group III [p < 0.01]) (Fig. 1C). Because stenting for total occlusion was frequent in group III, the restenosis rates in the lesions without total or subtotal occlusion before the procedure were evaluated (22.7% in group I, 33.9% in group II and 49.3% in group III [p < 0.01]) (Fig. 1D). To exclude the potential effect of acute or threatened closure, restenosis rates in lesions without acute or threatened closure after PTCA were evaluated (23.9% in group I, 33.3% in group II and 45.1% in group III [p < 0.01]) (Fig. 1E). The restenosis rates in lesions with IVUS optimization were evaluated because IVUS optimization may affect restenosis (19.9% in group I, 27.4% in group II and 41.2% in group III [p < 0.01]) (Fig. 1F).
Intravascular ultrasound analysis
Intravascular ultrasound measurements after stenting are shown in Table 6. These measurements after the stent procedure were available in 546 (50%) of the 1,090 lesions. There were no significant differences in the proximal reference vessel diameter and cross-sectional area among the three groups. Group III had a smaller MLD in the stented segment than did group I. The minimal lumen cross-sectional area in the stented segment was smaller in group III than in groups I and II. The distal reference vessel diameter and lumen cross-sectional area were smaller in group III than in groups I and II.
Table 7shows the results of univariate and multivariate analysis. When the variables that were significant by univariate analysis were entered into forward stepwise logistic regression analysis, three factors were independent predictors of restenosis: length of the stented segment, angiographic reference vessel diameter and percent diameter stenosis after stenting.
The present study shows that a progressively longer stented segment is associated with an increased risk of restenosis, but does not influence the risk of subacute thrombosis. Multivariate analysis shows that a longer stented segment, as well as the angiographic reference vessel diameter and percent diameter stenosis after stenting, are independent predictors of restenosis.
Restenosis in the lesion with a long stented segment
The influence of lesion length on restenosis after stenting is controversial. Schomig et al. (13)showed that lesion length was an independent correlate of the amount of late lumen loss. In contrast, other studies (4,5)did not demonstrate the relation between lesion length and restenosis. However, previous studies (4–7)have shown higher rates of restenosis with multiple stents as compared with a single stent. After implantation of Palmaz-Schatz stents, Ellis et al. (4)found a 64% incidence of restenosis at sites where multiple overlapping stents were placed. The higher restenosis rate was explained by greater metal density with multiple overlapping stents, which results in more pronounced neointimal hyperplasia (14–17). However, most of the previous studies (4,6,7)that investigated the relation between lesion length, multiple overlapping stents and restenosis were performed with multiple Palmaz-Schatz stents. Because the length of a Palmaz-Schatz stent is 15 mm, it is difficult to assess the relative importance of increased metal exposure with multiple partial overlapping stents versus a long lesion or a long stented segment. The availability of long stents enables one to evaluate outcome without the confounding factors of stent overlapping or stent gaps. The present study shows a persistently higher restenosis rate for the lesions treated with a single long stent as compared with a single short stent (Fig. 1B). The results of multivariate analysis demonstrate that the length of the stented segment is an independent predictor of restenosis, although multiple stents are not predictive. Strauss et al. (5)showed that after implantation of Wallstents, there was no relation between stent length and restenosis, although multiple overlapping stents was a predictor of restenosis. However, the specific nature of self-expanding stents may be unique and not comparable with other experiences.
The high restenosis rate seen with multiple stents as well as with long stents supports the view that the problem may be difficult to solve with a mechanical approach. When stenting a long lesion with a long stent, a number of variables that are likely to affect the outcome come into play. The two most important ones are the higher probability for an unfavorable metal to artery interaction as more artery is exposed to metal, and the natural vessel tapering invariably associated with stenting a long segment. The latter factor adds a smaller reference vessel size and a smaller achievable final stent lumen, which are known factors associated with increased risk of restenosis (2,18).
Subacute thrombosis in the lesion with a long stented segment
Subacute stent thrombosis is one of the most feared complications after stenting, resulting in ischemic complications such as death and myocardial infarction. A low incidence of subacute thrombosis has been reported after high pressure final balloon dilation and the use of antiplatelet therapy with ticlopidine and aspirin without anticoagulation (8,19,20). However, there have been fears that the risk of thrombosis might increase with exposure of more metal after longer or multiple stent implantation. In fact, a previous study (21)showed that the use of multiple stents was one of the predictors of subacute thrombosis. In contrast, other studies demonstrated low incidences of subacute thrombosis with multiple stents (7,22). The present study supports the view that a long stented segment is not associated with an increased risk of subacute thrombosis when a good initial result is obtained. Most of the patients underwent optimization of stent deployment with high pressure balloon dilation, had dissection sites appropriately covered and received antiplatelet therapy with ticlopidine and aspirin without anticoagulation. These factors probably played a significant role in maintaining a low incidence of subacute thrombosis in the present study.
In contrast to subacute thrombosis, the incidence of acute thrombosis was higher in patients with a longer stented segment. However, in lesions without acute or threatened closure, it was not different among the three groups. Patients with a longer stented segment should be observed carefully for a period of 24 h after the procedure if stenting was performed in lesions with acute or threatened closure after PTCA.
This is a retrospective study, which accounts for the differences in patient backgrounds among the three groups. During the study period (1995–1996), there was some evolution of the stenting procedure, and changes in decision-making occurred. Although we tried to deploy multiple stents with minimal or no overlap, the length of a stented segment with multiple stents may be slightly overestimated. However, the restenosis rate was higher in the lesions with a longer single stent. Another possible limitation is that many different types of stents were used in the study. Restenosis rates in the lesions with different types of stents may vary, however. In the subgroup analysis using only slotted tube stents, for example, restenosis rates were still higher in lesions with a longer stented segment. The next possible confounding variable was stenting for total occlusions, which was more frequent in group III than in groups I or II. Subanalysis eliminating this group from the calculations showed that restenosis rates continued to be higher in the lesions with a longer stented segment.
There was a discrepancy between lesion length and stented segment length. In most of the lesions, stented segment length was longer than lesion length (Fig. 2), although there was a significant correlation between lesion length and stented segment length (p < 0.01). In the present study, IVUS was used in half of all the lesions included in all three groups. Using IVUS, Mintz et al. (23)showed that atherosclerosis was ubiquitous in angiographically normal coronary artery reference segments. If lesion length was measured with IVUS, it would be longer than that measured by angiography. Therefore, stented segment length might be much longer than lesion length as measured by angiography, especially in cases where IVUS was used. In the First International New Intravascular Rigid-Flex Endovascular Stent Study (FINESS) (24), although only 6% of lesions were assessed to be >15 mm in length by quantitative angiography, experienced operators chose a long (32 mm) NIR stent for 26% of the NIR stents that were deployed. They explained that this choice might reflect a desire by the interventionalist to more completely cover visible vessel narrowing beyond the area of significant stenosis or to treat consecutive lesions with a single stent. We believe that is an issue that also played some significant role in the present study. In addition, in lesions with dissection after PTCA, stented segment length might be longer than lesion length.
This study represents a relatively large, nonselected, single-center experience, which provides some insight into the difficulties associated with use of long stent lengths, and how this is a strong independent predictor of restenosis.
Even when possible confounding variables are removed, a longer stented segment remains a strong independent predictor of restenosis without influencing the risk of subacute thrombosis. Therefore, when stenting is performed, the shortest possible stent length should be used.
- American College of Cardiology/American Heart Association
- intravascular ultrasound
- minimal lumen diameter
- percutaneous transluminal coronary angioplasty
- Thrombolysis in Myocardial Infarction
- Received April 20, 1998.
- Revision received March 19, 1999.
- Accepted June 3, 1999.
- American College of Cardiology
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