Journal of the American College of Cardiology
What is the risk of stent thrombosis associated with the use of paclitaxel-eluting stents for percutaneous coronary intervention?A meta-analysis
Author + information
- Received August 3, 2004
- Revision received November 11, 2004
- Accepted November 29, 2004
- Published online March 15, 2005.
Author Information
- Anthony A. Bavry, MD, MPH*,
- Dharam J. Kumbhani, MD, SM†,
- Thomas J. Helton, DO* and
- Deepak L. Bhatt, MD*,* (bhattd{at}ccf.org)
- ↵*Reprint requests and correspondence:
Dr. Deepak L. Bhatt, Interventional Cardiology and Cardiovascular Fellowships, Cleveland Clinic Foundation, Department of Cardiovascular Medicine, 9500 Euclid Avenue, Desk F25, Cleveland, Ohio 44195
Abstract
Objectives This study investigated the risk of stent thrombosis associated with the use of paclitaxel-eluting stents (PES) compared to bare-metal stents (BMS).
Background Clinical experience with coronary drug-eluting stents (DES) is relatively limited. There is concern that DES used for percutaneous coronary intervention may result in subsequent thrombosis.
Methods We conducted a meta-analysis on eight trials (total of 13 study arms) in 3,817 patients with coronary artery disease who were randomized to either PES or BMS.
Results As compared with BMS, PES do not increase the hazard for thrombosis up to 12 months (risk ratio [RR] = 1.06, 95% confidence interval [CI] 0.55 to 2.04, p = 0.86]). There was no evidence of heterogeneity among the studies (chi-square value for Q-statistic = 5.90 [10 degrees of freedom], p = 0.82). Similar results were obtained when the analysis was restricted to trials with a polymeric stent platform (Treatment of de novo coronary disease using a single pAclitaXel elUting Stent [TAXUS]-I, -II, -IV, and -VI) (RR = 1.01, 95% CI 0.40 to 2.53, p = 0.99), trials with longer lesions (TAXUS-IV and -VI) (RR = 0.62, 95% CI 0.2 to 1.91, p = 0.41), and trials that used a higher dose of paclitaxel (ASian Paclitaxel-Eluting Stent Clinical trial [ASPECT], European evaLUaTion of paclitaxel Eluting Stents [ELUTES], and DELIVER-I) (RR = 1.87, 95% CI 0.52 to 6.81, p = 0.34).
Conclusions Current evidence suggests that standard dose PES do not increase the hazard of stent thrombosis compared to BMS.
Percutaneous coronary intervention (PCI) is often limited by restenosis. The advent of drug-eluting stents (DES) generated excitement by dramatically reducing restenosis (1,2). A pooled analysis documented a 74% reduction in the risk of target-lesion revascularization from the use of sirolimus-eluting stents (Cypher, Johnson & Johnson, Miami Lakes, Florida) or paclitaxel-eluting stents (PES) (TAXUS, Boston Scientific Corp., Natick, Massachusetts) compared to bare-metal stents (BMS) (3).
Based on a number of clinical case reports, concerns have been raised about an increased risk of stent thrombosis with DES. This prompted the release of an advisory concerning a potential risk of subacute thrombosis and hypersensitivity reactions with the use of sirolimus-eluting stents (4). It is possible that with increased use and experience with PES, similar concerns may surface. Accordingly, we conducted a systematic review of the literature specific to PES to study the association between this stent and the risk of thrombosis after PCI.
Methods
Literature review
We searched the MEDLINE, EMBASE, CRISP, metaRegister of Controlled Trials, and Cochrane databases for randomized clinical trials from 2001 to 2004 using the medical subject heading terms “angioplasty, transluminal, percutaneous coronary,” “stents,” “paclitaxel,” and “thrombosis.” We also hand-searched relevant journals, obtained recently presented data from national cardiology and interventional cardiology conferences, corresponded with authors and experts in the field, and used the Science Citation Index to cross-reference any articles that met our selection criteria.
Our inclusion criteria were as follows: 1) a randomized clinical trial that assigned patients to either a PES or BMS; and 2) angiographically documented thrombosis data were available for at least 30 days of follow-up. Stent thrombosis was defined as either an angiographically documented thrombosis or an event where angiographic data were not available, although the study investigators clinically presumed that a stent thrombosis occurred. Studies were excluded from analysis if both groups received DES, if sirolimus (rapamycin) was used, if paclitaxel was given orally, if other analogues of paclitaxel such as QP-2 were employed, or if reliable data could not be obtained.
We identified eight studies that compared PES to BMS (Treatment of de novo coronary disease using a single pAclitaXel elUting Stent [TAXUS]-I, -II, -IV, and -VI, ASian Paclitaxel-Eluting Stent Clinical trial [ASPECT], European evaLUaTion of paclitaxel Eluting Stents [ELUTES], DELIVER-I, and PAclitaxel-Coated logicsTENt for the CYtostatic prevention of restenosis [PATENCY]) (5–16). This represents 13 study arms as TAXUS-II had two DES arms, ASPECT had two arms, and ELUTES had four arms.
Data abstraction
Two independent reviewers abstracted the following outcomes by intention-to-treat analysis: 1) angiographically documented or presumed coronary thrombosis; and 2) length of follow-up from deployment of the index stent procedure. We also abstracted baseline information such as patient demographics as well as angiographic and procedural characteristics of the coronary artery revascularization. Discrepancies were resolved through a third reviewer. Because all eight studies were double-blind randomized clinical trials, a formal quality assessment was not used.
End points
In order to utilize data from all available studies, and thereby increase the statistical power of our meta-analysis, we considered stent-associated thrombosis at any point in time (up to one year) after the index procedure as the primary end point. In trials that examined various doses or release kinetics of paclitaxel, each DES arm was treated as a separate study for analysis. We also conducted a number of subanalyses by analyzing groups that shared various similarities. The four TAXUS trials were analyzed together because they used clopidogrel for six months in addition to aspirin, while the other four trials used a shorter duration of dual antiplatelet therapy. Similarly TAXUS-IV and -VI trials studied patients with longer lesions (mean length >12 mm), while ASPECT, ELUTES, and DELIVER-I trials examined higher doses of paclitaxel (2.7 to 3.1 μg/mm2) and were analyzed together.
Statistical methods
We tabulated the number of thromboses and persons at risk for thrombosis in each arm of a study and calculated the risk ratio (RR) (PES vs. BMS). In order to determine if the studies were similar enough to be comparable for analysis, the Cochran's Q statistic for heterogeneity was employed. To evaluate if the studies were published with a certain bias (i.e., only studies with positive results were published), the Egger's funnel plot for publication bias was constructed. We utilized the automatic “zero cell” correction so that studies with no events in a single arm would still be included for analysis. We obtained a summary estimate of the RR and 95% confidence interval (CI) for PES compared to BMS. A fixed effects model was used to calculate the summary statistic. All p values were two-tailed, with statistical significance set at 0.05. All CIs were calculated at the 95% level. All analyses were performed using STATA software v8.0. (STATA Corp., College Station, Texas).
Results
Baseline characteristics
The eight studies that met our inclusion criteria were TAXUS-I, -II, -V, and -VI, ASPECT, ELUTES, DELIVER-I, and PATENCY (5–16). The characteristics of these studies are listed in Table 1.A total of 3,817 patients were enrolled; 1,995 were randomized to PES and 1,822 to BMS. All trials were multicentered studies. The baseline characteristics of patients randomized to PES and to BMS were similar within each study. The median ages of participants ranged from 58 to 66 years. The percentage of enrolled females ranged from 6% to 38%. Approximately one-quarter to one-third of the patients had a history of previous myocardial infarction.
Baseline Characteristics of Eight Paclitaxel-Eluting Stent Studies
Heterogeneity/publication bias
There was no evidence for heterogeneity among the studies (chi-square value for Q-statistic = 5.90 [10 degrees of freedom], p = 0.82). Similarly the p value for publication bias was nonsignificant (p = 0.86).
Risk of stent-associated thrombosis
Length of follow-up, event data, and RRs (with 95% CI) for the development of stent-associated thrombosis are listed in Table 2.Six study arms revealed a nonsignificant decrease in the risk of stent-associated thrombosis (TAXUS-IV, TAXUS-VI, ELUTES: 0.2, 0.7, and 1.4 μg paclitaxel/mm2of stent arms; and DELIVER-I), five study arms revealed a nonsignificant increase in risk (TAXUS-II SR and MR arms and ASPECT: 1.3 and 3.1 μg paclitaxel/mm2of stent arms, and ELUTES 2.7 μg paclitaxel/mm2of stent arm), and in two studies there were no events (TAXUS-I and PATENCY).
Event Data and Outcome Measures
In the ASPECT trial, all cases of thrombosis occurred in individuals randomized to PES who received nontraditional antiplatelet therapy (i.e., aspirin without the use of a thienopyridine). Aspirin and cilostazol was used in these individuals for one month (n = 29) or six months (n = 8) as this was considered standard antiplatelet therapy at the participating centers. The remaining individuals in this trial received aspirin with ticlopidine (n = 120) or clopidogrel (n = 18) for one or six months. The duration of therapy for those that received clopidogrel was one month, while the duration of therapy for 78% of the individuals given ticlopidine was six months (one month of therapy for the remaining individuals on ticlopidine).
The plot of stent-associated thrombosis and the pooled RR estimate is shown in Figure 1.The hazard of stent thrombosis for PES versus BMS was not increased up to 12 months after the index stent deployment (RR = 1.06, 95% CI 0.55 to 2.04, p = 0.86).
In trials with varying doses of paclitaxel, a = 1.3, b = 3.1, A = 0.2, B = 0.7, C = 1.4, and D = 2.7 μg paclitaxel/mm2of stent. BMS = bare-metal stent; CI = confidence interval; DES = drug-eluting stent; MR = moderate-release; SR = slow-release.
Subanalyses
When the four TAXUS trials that used aspirin and clopidogrel for six months were analyzed together, the summary RR obtained was similar to the overall effect estimate (RR = 1.01, 95% CI 0.40 to 2.53, p = 0.99). Analyzing TAXUS-IV and -VI, which enrolled patients with longer lesions (mean length >12 mm) resulted in a similar association (RR = 0.62, 95% CI 0.20 to 1.91, p = 0.41). Analyzing ASPECT, ELUTES, and DELIVER-1, which used a higher dose of paclitaxel (approximately 3.0 μg/mm2) revealed the same overall association (RR = 1.87, 95% CI 0.52 to 6.81, p = 0.34).
Discussion
Our meta-analysis suggests that stent-associated thrombosis is not increased by standard-dose PES compared to BMS. In fact, the risk of stent-associated thrombosis up to 12 months after the index procedure was equivalent with PES compared to BMS. This information is derived from systematically analyzing eight worldwide clinical trials that have been published or presented at prominent cardiology conferences to date.
We performed various subanalyses. These examined the effect of longer duration of dual antiplatelet therapy (in contrast to shorter duration of therapy), longer versus shorter lesion lengths, and higher versus lower doses of paclitaxel (around 3 μg/mm2). The subanalyses confirmed the same overall association of no increased (or decreased) risk of stent-associated thrombosis. It should be noted that although there was a nonsignificant increased risk of stent-associated thrombosis with higher doses of paclitaxel, this association was driven by a high rate of stent thrombosis in the ASPECT trial.
It is interesting that all thrombotic events in the ASPECT trial occurred in participants randomized to PES who were on aspirin and cilostazol. No events occurred in either stent group when standard antiplatelet therapy (aspirin with a thienopyridine) was employed. The TAXUS studies used clopidogrel for six months after the index stent deployment, while ELUTES, DELIVER-I, and PATENCY used clopidogrel for three months. This suggests that a nonthienopyridine-based antiplatelet regimen is not sufficient in preventing thrombosis, and this issue may be especially important for DES (17).
We did not formally analyze the Stent Comparative REstenosis (SCORE) trial because this study used a paclitaxel analogue (7-hexanoyltaxol) that could not be directly compared to PES (18). This trial was terminated early secondary to a high rate of stent thrombosis (9.4%) and myocardial infarction (14.5%). This event rate occurred despite the use of aspirin plus a thienopyridine for 1 month in the BMS arm and for 12 months in the DES arm.
The current study is limited in that some of the analyzed trials had small sample size, with relatively short duration of follow-up. We also included data that have only been reported in conference presentations or in abstract form and so have not undergone peer review. This was necessary, however, to maximize the utilization of all available data on this rapidly evolving topic. Experience with coronary stents has elucidated several predictors of stent thrombosis including residual dissection, underexpansion of the stent, combining/overlapping different stents, and longer total stent length (19–22). Based on the randomized nature of the studies included in the present meta-analysis, any known and unknown confounders of stent thrombosis should be divided equivalently between both arms of the study.
A large percentage of enrolled participants eventually underwent angiographic follow-up. In six of the studies, repeat angiography was performed in approximately 80% to nearly 100% of participants. Angiographic follow-up was lower in the DELIVER-I and TAXUS-IV trials, where only 42% and 56% of participants, respectively, underwent follow-up angiography. It remains possible that these angiographic subsets are not representative of the entire group of participants, although there was no indication of increased mortality or myocardial infarction in either group during longer periods of clinical follow-up. This is supported by a recent meta-analysis that analyzed sirolimus-eluting stents and PES compared to BMS. This analysis found that all-cause mortality and myocardial infarction were not increased by the use of DES, (odds ratiomortality= 1.11, 95% CI 0.61 to 2.06; odds ratiomyocardial infarction= 0.92, 95% CI 0.65 to 1.25) (23). Additionally, none of the analyzed trials commented upon discovering a clinically silent occluded target vessel at the time of protocol-driven angiography. Because it is unclear if these events occurred (and if they did, whether or not they were tabulated as a thrombotic event), then another source of potential bias exists.
We also included any occurrence of thrombosis during follow-up including periprocedural thrombotic events. Periprocedural myocardial infarctions were not included for analysis unless the investigators felt that the event was secondary to stent thrombosis. It is possible that periprocedural thrombi are more influenced by technical aspects of the stent-based PCI (such as coronary dissection or underdeployment of the stent), rather than effects of the drug itself. While this might be true, there were only three occurrences of periprocedural stent-associated thrombi (one in the PES arm and two in the BMS arms), thus minimizing the importance of this potential effect.
So although there is some anecdotal concern that DES may increase the hazard of stent thrombosis, the current study supplements available experimental and clinical evidence to suggest that thrombosis does not occur more (or less) frequently than with BMS. Additionally, it remains possible that in real word practice, if adequate oral antiplatelet therapy is not used or prematurely discontinued after revascularization, the hazard of stent thrombosis with DES may be greater than with BMS.
- Abbreviations and acronyms
- BMS
- bare-metal stents
- CI
- confidence interval
- DES
- drug-eluting stents
- PCI
- percutaneous coronary intervention
- PES
- paclitaxel-eluting stents
- RR
- risk ratio
- Received August 3, 2004.
- Revision received November 11, 2004.
- Accepted November 29, 2004.
- American College of Cardiology Foundation
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