Direct stenting

Emanuele Barbatoa, Jean Marcob and William Wijnsa,*

a The Cardiovascular Center, Onze-Lieve Vrouw Ziekenhuis, Aalst, Belgium
b The Clinique Pasteur, Toulouse, France

* Corresponding author. Tel.: +32-53-72-44-39; fax: +32-53-72-41-85
E-mail address: william.wijns{at}olvz-aalst.be

Received 21 October 2002; accepted 23 October 2002

Abstract

Stents have ameliorated the outcome of percutaneous coronary interventions. Improved design, profile and flexibility of the currently available stents now permit to deliver the stent without pre-dilatation. In western European countries, stent implantation now occurs in up to 80% of all percutaneous revascularization procedures. In selected cases the safety and feasibility of direct stenting over conventional balloon-predilatation stenting has been demonstrated, in association with slightly superior outcome. This likely results from reduced vessel wall damage—dissections are sealed at the moment they are created—and distal embolization is reduced. In addition, a significant reduction in terms of costs and duration of procedures was demonstrated, while restenosis rate is not reduced with direct stenting.

Key Words: Direct stenting • PTCA • Stent

1. Introduction

Since their introduction in 1986, stents have been used increasingly often during percutaneous coronary interventions (PCI) such that stent implantation now occurs in up to 80% of all procedures.1,2 This is because stented angioplasty provides a more effective dilatation and a more predictable in-hospital outcome than balloon angioplasty. Dissections are now tagged against the wall; the risk of subacute stent thrombosis and bleeding complications is reduced with the use of effective antiplatelet treatment.3–5

The deliverability of the devices available in the 1980s was poor because these stents were bulky and stiff, and their implantation required the use of large size guiding catheters. The need for hand crimping was problematic because of potential stent or balloon damage during crimping and stent loss during attempted delivery. But in the last few years, most of these issues have been addressed by the industry, which resulted in an increase in the use of stents and an improvement in procedural success even for lesions that could not be approached by PCI in the past. It is estimated that nearly 1,700,000 stents have been implanted worldwide in 2001 (Fig. 1). Despite the savings accrued by the avoidance of subsequent revascularization procedures, this trend has major financial implications for health care expenditures because stent implantation results in an incremental procedural cost of 1500 over balloon angioplasty.6,7 One potential means to contain costs is to modify the procedural technique. The conventional technique of stent implantation requires pre-dilatation with the balloon, as to allow swift stent delivery. With the improvement in the design, profile, flexibility and trackability of currently available stents and delivery balloons (Fig. 2), the possibility to deliver the stent without pre-dilatation was soon explored.



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Fig. 1 Worldwide PCI patients growth (courtesy Herbreteau T., Guidant). Black bars indicate the increasing fraction of stented patients, white bars indicate the decreasing fraction of balloon-PTCA treated patients.

 


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Fig. 2 Different stent profiles as compared with some of the commonly used balloon catheters. Black bars indicate stents. White bars indicate balloons. The stent profile has been decreasing progressively since the early days, and now nearly reaches the diameter of the smaller balloon catheters that are presently available.

 
2. Definition

Direct stenting refers to stent positioning and deployment without prior balloon dilatation of the stenosis. Direct stenting should not be confounded with primary stenting, which refers to stent implantation as the first choice to revascularize patients presenting with acute myocardial infarction.

3. Rationale: experimental data

Experimental data support the concept of reduced wall damage when stent deployment is performed without balloon pre-dilatation. A significant reduction in the inflammatory response of the vessel wall was demonstrated in a rabbit model reproducing the conditions of direct versus conventional stenting (Fig. 3). In these normal vessels, complete endothelial denudation occurred after balloon pre-dilatation, while a substantial amount of endothelium was preserved after direct stenting.8 It was hypothesized that residual endothelium promotes re-endothelialization of the stented vessel segment, which will reduce the risk of stent thrombosis as well as neointimal growth (Fig. 3). From post-mortem studies, it was shown that complete coronary re-endothelialization will only take place 3 months after stenting.9 An intravascular ultrasound (IVUS) study in humans has demonstrated that plaque compression/embolization and vessel expansion were similar with direct stenting and conventional stenting, the former resulting in a better longitudinal centering of the stent on the lesion and a more uniform axial redistribution of the plaque.10 These observations entertained the hope that direct stenting might reduce restenosis rates.



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Fig. 3 Comparison between direct stenting (DS) and conventional stenting (CS) with respect to: (A) number of adherent monocytes 3 days after the procedure; (B) percentage of intimal macrophages, at 14 days after the procedure; (C) minimal lumen diameter (MLD) loss.8 versus CS.

 
4. Observational clinical studies

Several studies have been conducted in humans to demonstrate the feasibility and safety of direct stenting (Table 1).


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Table 1 Observational clinical studies demonstrating the safety and the feasibility of direct stenting, provided appropriate lesion selection

 
4.1. Procedural and in-hospital results
Pentousis et al.11 demonstrated in 94 patients a comparable crossing rate between direct stenting and pre-dilatation in carefully selected lesions, without major complications in-hospital and at 1 month follow-up. The feasibility and safety of direct stenting have also been demonstrated in 122 patients with acute coronary syndromes (ACS), with a success rate of 96% and a low 2.5% incidence of no-reflow.12,13 Direct stenting in ACS has been associated with significant improvement in ST-segment resolution (used as a marker of myocardial reperfusion), and a reduction in post-procedural increase in TnI.14 In patients with myocardial infarction, a higher rate of TIMI III flow and an overall improvement in TIMI frame count has been reported with direct stenting rather than pre-dilatation.15,16

In another 130 patients with ACS, there was no difference in the rate of no-reflow and in the corrected TIMI frame count between direct stenting and pre-dilatation.17 In the study by Wilson et al.18 TIMI flow was lower after direct stenting, probably due to the inclusion of a higher number of thrombus containing lesions and degenerated vein grafts (SVG) in their study. He reported fewer dissections after direct stenting than with pre-dilatation but the long-term outcome was similar between the two groups.18

On the other hand, direct stenting was demonstrated to have a positive impact on procedure duration, radiation exposure time and amount of contrast dye used.19–21 As a consequence, direct stenting may reduce the procedural costs by as much as 41%.21 Finally, direct stenting, whenever feasible, had been proposed as the strategy of choice in the treatment of SVG lesions. In fact, IVUS-guided direct stenting of degenerated SVG resulted in a reduction in non-Q wave periprocedural myocardial infarctions and lower target lesion revascularization as compared to balloon pre-dilatation.22

4.2. Impact on late restenosis
Most data on restenosis rate that are presently available do not support any superiority of direct stenting over the conventional procedure. Two observational studies have shown discrepant results: comparable restenosis rates after direct stenting versus pre-dilatation in the study by Hammer et al.23 but significantly lower angiographic restenosis rate (DS, 20.3% versus CS, 30.5%, ), and target lesion revascularization (DS, 17.5% versus CS, 28.0%, ) after direct stenting in the study by Brueck et al.24 Recently, a direct stenting strategy comparing IVUS with QCA has demonstrated a reduction in restenosis rate from 24 to 9%, and a trend to oversizing the stent used.25

5. Randomized clinical trials

Following the encouraging and perhaps optimistic results from single-center, observational studies, a number of multicenter, prospective and randomized clinical trials have been initiated, many of which are still ongoing (Tables 2 and 3). The available data so far support the concept that direct stenting is both feasible and safe, provided appropriate case selection. The procedural outcome seems to be superior in the absence of pre-dilatation due to a reduced incidence of dissections at the stent edges.26 Although dissections are unlikely to be completely avoided during direct stenting, it is conceivable that they occur in a more controlled way and are covered by stent deployment at the moment they are created. With the use of square-shouldered balloons, which reduce the ‘dog-boning’ effect, damage to the vessel segments immediately adjacent to the stent edges is likely reduced. With balloon pre-dilatation, the dissection may extend beyond the stenotic segment, may not be visible at angiography and eventually fail to be entirely covered by the stent. Another major advantage of direct stenting could be the reduction of distal embolization during PCI on thrombus containing lesions or SVG disease. However, no randomized data have been published so far. No difference in restenosis rates between the two approaches has been observed in four randomized trials.27–30 Clinical outcome seems to be equivalent with or without pre-dilatation.26,31–39 The reduction in procedural and equipment costs, as well as in the exposure time to radiation, which had been reported by observational studies, has been confirmed in randomized trials (Table 4).


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Table 2 Prospective, randomized clinical trials

 

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Table 3 Available results from the randomized clinical trials

 

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Table 4 Head to head comparison of the economical implications of direct stenting (DS) versus conventional stenting (CS)

 
6. Provisional stenting versus ‘Stentomania’

According to the provisional stenting strategy, stent implantation is needed only when the immediate result after plain balloon angioplasty is poor or when the risk for restenosis following balloon angioplasty is high.40,41 In contrast with direct stenting, all technically eligible stenoses receive a stent, by primary criterion. Randomized trials comparing direct stenting with provisional stenting are ongoing. Other studies have evaluated the value of IVUS and Doppler flow measurements to identify patients who would be unlikely to benefit from stent implantation after successful balloon angioplasty.42,43 Balloon-treated vessels that meet the QCA, IVUS or Doppler criteria of an ‘optimal stent-like’ result, range from 22 to 52% of all attempted cases and were shown to have very low restenosis rates.42,44–46 The avoidance of stent implantation in this subset of patients might reduce procedural costs without compromising the clinical outcome. However, the DEBATE II trial demonstrated no significant difference in outcome between the ‘per principle’ and provisional stenting approach, but the costs of the latter strategy at 1 year were significantly higher.44 Furthermore, in the DEBATE II study, stent implantation despite achieving a ‘stent-like’ result following balloon dilatation, incrementally reduced the event rate at 1 year from 16 to 6.5%.44 The OPUS trial has shown a significantly higher MACE rate (death, myocardial infarction and target lesion revascularization) in the provisional stenting group than in the elective stenting group, demonstrating that angiography alone is not sensitive enough to identify patients who do not require stent implantation.47 Thus, it appears that the clinical applicability of provisional stenting is limited because this strategy requires detailed physiologic and morphologic (IVUS) assessment of the angioplasty result, which will jeopardize potential savings.

A word of caution applies to the case of small vessels and long lesions. Clinical data have clearly demonstrated increasing restenosis rates with decreasing vessel size.48 On the other hand, the results of the trials comparing stent implantation versus balloon-PTCA in small vessels have demonstrated substantial equivalent results in terms of long-term outcome.48 In long lesions, procedural success rate was not different between stent implantation and balloon-PTCA.49 Additional stenting, following successful balloon angioplasty, was associated with a modest reduction in angiographic restenosis at 9 months. However, no difference in freedom from major adverse cardiac events was observed between the two strategies. In the setting of small vessels and long lesions, a strategy of provisional stenting remains advisable, at least with the use of bare metal stents.

7. Direct stenting in clinical practice

7.1. Predictors of failure
Univariate analysis by Chevalier et al.15 identified the following predictors of failure of direct stenting: pre-PTCA MLD, circumflex location, distal location, use of GFX stent, calcified vessel and age >70 years. By multivariate analysis, circumflex location was the strongest predictor of failure.14 Figulla et al.50 recorded the presence of angiographically visible calcification and age older than 70 years to be predictors of direct stenting failure. In the BET trial using the Tenax stent, predictors of failure were: stent length greater than 10mm, stent diameter of 3mm and complex lesion (type C).31

7.2. Case selection
While direct stenting was attempted liberally in single-center experiences, most of the randomized multicenter prospective studies have defined strict inclusion criteria (Tables 2 and 3). Eligible cases included single lesion PCI in a suitable vessel (no major calcification, no angulation proximal to the lesion, vessel size greater than 2.5 or even 3.0mm and lesion length no more than 25mm). Totally occluded vessels were excluded as well. There are limited data on the safety and efficacy of direct stenting in unselected cases. In the study by Voigt et al.35 which included moderately and heavily calcified vessels, the success rate was only 83%. Pre-dilatation was required in 17% and in-stent post-dilatation in 19% of cases.35

7.3. Practical tips
Stent delivery anyhow requires adequate support from the guiding catheter and the guide wire; this is particularly true for direct stenting, in general and for the left circumflex artery location, in particular. Precise positioning becomes difficult when the device is occlusive. Side-branches can be used as landmarks; another approach is to advance the stent distally beyond the stenosis to restore flow and opacification of the lesion. Stent loss has not been reported. Although theoretically still present, the risk of stent loss seems quite low in the hands of experienced and trained operators, also considering the greatly improved crimping technology. A different balloon design (with two conical radiopaque markers) specially suited for direct stenting has been proposed.50 However, its use requires hand crimping of the stent, which is not desirable. Most companies are now proposing low-profile devices that are labelled for use with the direct stenting approach.

The possibility exists that the stent will not expand or will do so suboptimally. In 50 patients undergoing direct stenting, stent under-deployment was detected by IVUS in 38% of cases, despite good angiographic result by QCA.51 This could be the result of any of the following: underestimation of vessel size and selection of an undersized stent, insufficient stent deployment, lack of vessel expansion in the absence of plaque splitting by prior balloon angioplasty. Such a situation requires the use of additional in-stent dilatation with short balloons, annihilating the effort to reduce the costs. One should also keep in mind that stent under-deployment is known to occur quite often with the conventional pre-dilatation deployment strategy.5 The stent pre-mounted on a combined IVUS and balloon cathether (Josonics stent) is a promising tool, which will potentially allow to verify proper stent deployment immediately after delivery.

With the increasing use of drug-eluting stents,52 additional concerns were raised about the safety of direct stenting. Issues such as medication leak or stent loss will have to be addressed when these stents eventually become available in routine practice. So far, pre-dilatation was required in all trials using drug-eluting stents, with the exception of the E-Sirius, which is yet to be reported.

8. Summary and conclusions

Direct stenting has a number of potential advantages with respect to procedural success, outcome and costs, as listed in Table 5. Direct stenting is feasible and safe in selected cases and cheaper than stent implantation following prior balloon dilatation by 20–40%. Direct stenting may be preferable for thrombus containing lesions and SVG intervention but is contra-indicated in heavily calcified vessels. Circumflex artery lesions with a sharp take-off and older patients (>70 years) represent a relative contra-indication.


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Table 5 Potential advantages and disadvantages of direct stenting

 
At times when the health care systems are forced to constrain their budget, direct stenting appears as a useful contribution to cost containment. Since the clinical results of direct stenting are equivalent or perhaps slightly superior to those obtainable with pre-dilatation, this strategy should be applied in all appropriate situations when stent implantation is required. Additional results from ongoing randomized clinical trials will become available in the near future. These statements will need to be reassessed when drug-eluting stents eventually become standard practice.

Acknowledgments

We acknowledge Mr Frank Staelens for his technical help.

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