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Original Contribution
Titanium and Nitride Oxide-Coated Stents and Paclitaxel-Eluting Stents for Coronary Revascularization in an Unselected Populatio
October 2006
Coronary stents have reduced the risk of periprocedural complications and restenosis compared to balloon angioplasty alone.1,2 In spite of this progress, restenosis is still a clinical problem of bare metal stents, particularly in certain high-risk patient subsets.3,4 Widespread use of drug-eluting stents (DES) is the most effective way to reduce restenosis according to randomized, controlled trials in selected patient groups5–9 and in everyday clinical practice.10–12 Paclitaxel, a lipophilic molecule derived from the Pacific yew tree Taxus brevifolia, is capable of inhibiting cellular division, motility, activation, secretory processes and signal transduction.13,14 A polymer-based, paclitaxel-eluting stent (PES) consistently reduced the rate of restenosis and the need for repeated revascularization procedures, as compared with bare metal stents.6,7,15 Modifications in stent geometry,16 strut thickness17 and surface material18 have been shown to influence the restenosis rate after bare metal stent implantation. Recently, patients with nickel allergy have been reported to be at an increased risk for restenosis after bare metal stent implantation.19 Attempts to reduce restenosis after angioplasty with the use of various stent coatings have been largely unsuccessful.20,21 Some studies have suggested that titanium features superior biocompatibility compared with stainless steel, gold or other surface coatings.22,23 In vitro titanium nitride oxide shows diminished platelet adhesion and fibrinogen binding compared with stainless steel.24 The Titan® stent (Hexacath, France) is a thin-strut (0.07–0.09 mm), balloon-expandable stent made of stainless steel and coated with titanium and nitride oxide (TITANOX) that completely prevents discharge of nickel, chromium and molybdenum. Stents coated with titanium nitride oxide reduced angiographic and ultrasonic measures of restenosis compared with stainless steel control stents in a prospective, randomized, multicenter trial (The TiNOX Trial).25
The aim of this study was to report one-year clinical outcome of unrestricted use of TITANOX stents and PES.
Methods
Patients and study design. The Titan PORI Registry is a prospective, single-center registry with the main purpose of evaluating the safety and efficacy of TITANOX stent implantation for consecutive unselected patients treated in daily practice. Since May 2003, PES (Taxus®; Boston Scientific, Calway, Ireland) have been used in our hospital as the default stent for all patients selected for DES implantation. The Taxus PORI Registry is a prospective, single-center registry designed with the purpose of evaluating the safety and efficacy of PES implantation for patients treated in daily practice. Between May 2003 and November 2004, all consecutive patients with symptoms or signs of myocardial ischemia and de novo coronary lesion(s) scheduled for stent implantation were considered for these registries. A total of 405 patients fulfilled the criteria and entered this study. A total of 201 patients received only 1 or more TITANOX stents, and 204 received only 1 or more PES. The study material comprised 63% of all patients who underwent percutaneous coronary intervention (PCI) during the study period. The choice of a particular stent was at the discretion of the operator, with no exclusion criteria.
The study was conducted according to the declaration of Helsinki, and written informed consent was obtained from all patients. This protocol was approved by the Ethics Committee of Satakunta Central Hospital.
Coronary stent procedure. All patients were pretreated with aspirin (100 mg daily) and received intravenous enoxaparin (1 mg/kg) during the procedure. Oral clopidogrel was administered as a loading dose of 300 mg before or immediately after the procedure. Patients treated with PES were prescribed clopidogrel (75 mg/day) for a minimum of 6 months, based on data from randomized, controlled trials.6 For patients treated with a TITANOX stent, clopidogrel was prescribed for a minimum of 3 months. Lesions were treated according to current standard interventional techniques, with the final strategy (direct stenting, post-dilatation, periprocedural glycoprotein IIb/IIIa inhibitor, intravascular ultrasound) left entirely to the operator’s discretion. Angiographic success was defined as a residual stenosis Endpoint definitions and clinical follow up. The primary endpoint was major adverse cardiac events (MACE), defined as the occurrence of any of the following within 12 months after the index procedure: death from cardiac causes, Q-wave or non-Q-wave myocardial infarction, or revascularization of the target vessel (emergency or elective coronary artery bypass grafting or repeated coronary angioplasty).
Q-wave myocardial infarction was defined as either (1) the presence of chest pain or other acute symptoms consistent with myocardial ischemia and new pathologic Q-waves in >/= 2 continuous electrocardiographic leads, or (2) elevated cardiac enzyme levels > 2 times the upper limit of normal associated with any elevation above the upper limit of normal in creatine kinase-MB levels in the presence of new pathologic Q-waves. Non-Q-wave myocardial infarction was defined as an elevated creatine kinase > 2 times the upper limit of normal associated with any elevation above the upper limit of normal in creatine kinase-MB levels.
Target lesion revascularization (TLR) was defined as a repeat intervention to treat a stenosis within the stent or in the segments 5 mm distal or proximal to the stent. Target vessel revascularization (TVR) was defined as a reintervention driven by any lesion located in the stented vessel. Stent thrombosis was diagnosed in the presence of an acute coronary syndrome with angiographic evidence of either vessel occlusion or thrombus within the study stent, or in autopsy.
All MACE were reviewed by two cardiologists (P.K, A.Y). All patients underwent clinical follow up. Adverse events were monitored at hospital discharge and by office visits or telephone interviews by the cardiologist at 1, 6 and 12 months. In addition, all data available from hospital records, the institutional electronic clinical database and the referring physicians were checked at the end of the follow-up period (February 2006) and entered into the computer database.
In both groups, follow-up coronary angiography was clinically driven by symptoms or signs suggestive of myocardial ischemia. Indication for repeat revascularization was a significant luminal stenosis (> 50% diameter stenosis) in the presence of anginal symptoms and/or proven myocardial ischemia in the target vessel territory.
Statistical analysis. Continuous variables are presented as mean (SD) and were compared by Student’s unpaired t-test. Categorical variables are presented as counts and percentages and were compared by the chi square or Fisher’s exact test. The associations between variables were evaluated by univariate technique (Spearman’s correlation coefficient). After the univariate analyses (p p-value Results
Baseline and procedural characteristics. Between May 2003 and November 2004, 405 patients (462 lesions/468 stents) were enrolled; 201 patients (218 lesions/21 stents) were treated with TITANOX coated stent(s), and 204 patients (244 lesions/247 stents) with PES. Table 1 shows the baseline clinical characteristics of the study population. The procedural characteristics are shown in Table 2. The TITANOX stent patients (p = 0.011) had acute myocardial infarction more often as their presenting symptom and more (p = 0.004) complex B- and C- type lesions treated. The total stent length was longer (p One- and twelve-month follow up. MACE during follow up are listed in Table 3. Complete follow up at 12 months was achieved in all 405 patients. At 30 days, the rate of MACE was 0% and 4.9% for the TITANOX stent and PES groups, respectively (p = 0.001). A significant difference in TVR was also seen in favor of the TITANOX stent patients (0% vs. 2.9%; p = 0.014). This was mainly driven by stent thrombosis (n = 7). At 12 months, the rate of myocardial infarction was higher in the PES group (p = 0.025), but the TLR rate was similar in both groups (Figure 1). The rate of clinical restenosis was 5% for TITANOX and 2.5% for PES (p = 0.18). At 1 year, 2.5% of patients in the TITANOX stent group and 3.9% in the PES group had died (p = 0.41). Event-free survival was 89.1% in the TITANOX stent group, as compared with 86.3% in the PES group (Figure 2). Clinically-driven control angiography was performed in 20% of the patients in the TITANOX stent group and 19% of the patients in the PES group during the 12-month follow-up period.
Late follow up. At the end of follow-up period (February 2006), the mean follow up based on hospital records was 17 +/- 4 months (median 20) for the TITANOX stent patients, and 20 +/- 6 months (median 25) for the PES patients. The main finding in the late follow-up data was that there were 6 cases of late (after 1 year) stent thrombosis documented angiographically, and all of them were in the PES group. Characteristics of individual cases of PES stent thrombosis are shown in Table 4. In addition, there were 4 myocardial infarctions, 2 noncardiac deaths and 1 cardiovascular death in the PES group, and 1 myocardial infarction and 1 noncardiac death in the TITANOX stent group.
Predictors of stent thrombosis and MACE. In the PES group, the patients with stent thrombosis had myocardial infarction more often as their presenting symptom before the index procedure (11% vs. 3%; p = 0.02), but there were no other significant predictors of stent thrombosis. MACE at 12 months was predicted by older age (70 vs. 63 years; p = 0.001), previous PCI (p = 0.002), previous CABG (p = 0.006) and multivessel disease (p = 0.020). Multivariate analysis showed that patient age (p = 0.014,) and previous PCI (p = 0.012) were the only independent predictors of MACE. In the TITANOX group, we found no significant predictors of MACE. When both registries were taken together, multivariate analysis revealed that total stent length (p = 0.042) was the only independent predictor of subacute, late and cumulative stent thrombosis.
Discussion
To our knowledge this is the first prospective comparison of titanium nitride oxide-coated stent with paclitaxel-eluting stent in routine clinical practice. The major finding of this study was that the unrestricted use of TITANOX stents and PES in de novo lesions leads to favorable and comparable outcomes after clinical decision making, even in high-risk patients with complex coronary lesions. Secondly, although the overall risk of stent thrombosis was low, it was concentrated in the use of PES in the setting of acute myocardial infarction.
Currently, the use of DES is considered to be the most effective tool to prevent restenosis.5–9 There is no evidence that DES could influence mortality or prevent myocardial infarction after stent implantation. PES have been shown to reduce the risk of restenosis in a broad range of lesions and patients undergoing PCI.6,7 In the present study, the rates of clinical restenosis were low for both stent groups, substantiating the results of previous DES studies.5–7 The three principal determinants of restenosis after coronary stent implantation are diabetes, vessel size and lesion length.3–7 In the present study, there was no difference in the vessel size or prevalence of diabetes between the TITANOX stent- and PES-treated patients (Tables 1 and 2). The total stent length was, however, significantly longer in the PES group, although the actual stenosis length was comparable between the two groups.
Clinically, the most alarming and unexpected finding was the high rate of stent thrombosis in the PES group. The overall rate of stent thrombosis in the PES group was higher in the present study than in previous DES studies.27–30 The higher rate may have been due to the inclusion of patients with more complex conditions and lesions and a higher prevalence of acute coronary syndromes, since acute myocardial infarction and stent length were the significant predictors of stent thrombosis. In everyday clinical practice, late stent thrombosis may be an underestimated problem for DES, and the operators may not become aware of all late complications. Secondly, our findings underscore the importance of long-term follow up, particularly in the DES studies.
The mechanisms of late stent thrombosis are unknown, but may be related to malapposition, inadequate endothelial coverage of DES, thrombogenic surface,31 polymer coatings32 and drugs in high doses.33 In the present study all cases of late stent thrombosis occurred quite shortly (range 1–13 months) after clopidogrel withdrawal, stressing the importance of adequate long-term antiplatelet therapy after PES implantation.28 Earlier studies28,31,34 have shown that longer stented segments may predispose patients to stent thrombosis after DES implantation. In our patient cohort, stent length was a significant predictor only when both registries were taken together.
The rate of restenosis was acceptable and there were no cases of stent thrombosis in the TITANOX group. Our current practice is to try to cover the entire plaque area with the PES, compared with a spotlike approach with bare metal stents in similar lesions. This difference in approach may reduce the risk of restenosis and thrombotic events in the TITANOX group.28,31,35 Stent coating may also contribute to the findings, since an in vitro study has suggested that titanium nitride oxide reduces platelet adhesion and fibrinogen binding compared with stainless steel.24 Similarly, a recent study compared the behavior of endothelial cells cultured on different stent materials. Metallic sheaths coated with titanium nitride (TiN) or titanium oxide (TiO2) exhibited higher cell density values on their surface compared to those without coating, supporting the view that deployment of stents coated with TiN or TiO2 may achieve earlier complete endothelial coverage.36
Study strengths and limitations. The strength of our single-center registry is the fact that Satakunta Central Hospital is the only center with coronary angiography capacity in the referral area. In this rural area, the population is stationary, enabling complete and sufficiently long follow up of an all-inclusive, unrestricted PCI population reflecting daily clinical practice. One of the limitations of our study is the limited size of the patient groups for subgroup analysis. This study also carries the general problems of registry-based observational studies with nonblinded outcome assessment. The fact that this is a single-center, low-patient-number registry may also give rise to unrecognized selection and performance bias. Angiographic control was performed in a minority of patients, and we may have underestimated the incidence of angiographic restenosis and silent stent thrombosis. However, there is no evidence that they were more frequent in either of the groups because the clinical outcomes were similar. On the other hand, by relying on clinical follow up only, we avoided the chance of unnecessary target lesion revascularization procedures due to the oculostenotic reflex or the patient’s unjustified anxiety. In addition to the characteristics listed in the Tables, the patients in the registries may have other unrecognized differences, e.g., we observed a less frequent use of PES in the setting of acute myocardial infarction during the latter part of the study period, and it is conceivable that patients at the highest risk of restenosis were more likely to be treated with PES.
Conclusions
In conclusion, both TITANOX coated stent and PES resulted in good clinical outcomes with infrequent need for repeat interventions in the real-world setting of high-risk patients and complex coronary lesions. Secondly, although the overall risk of stent thrombosis was low, it was concentrated in the use of PES in the setting of acute myocardial infarction. Further studies are warranted to randomly compare the TITANOX stent (to other passive and active coated stents) as an alternative to current DES, particularly in patients with acute myocardial infarction.
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