Pushing the Limits: Is there an Optimal Therapy for Very Small Vessels?

Stent placement in coronary arteries larger than 3 mm in diameter has been proven to be superior to conventional balloon angioplasty (PTCA) in reducing the risk of restenosis and major adverse cardiac events (MACE). Subsequent improvements in stenting technique and antithrombotic regimen have dramatically reduced the incidence of stent thrombosis.¹ This has resulted in an exponential rise in the number of stent-related procedures and has extensively broadened the indications for stenting. Yet, it is estimated that 30–50% of all percutaneous coronary interventions (PCI) involve small-diameter vessels. Small vessel size is one of the major predictors of restenosis after PCI for both balloon angioplasty and stenting.² Dedicated stents for small vessels with less metal coverage, appropriate expansion to the vessel size, thinner struts, fewer circumferential cells, active coating materials and less prothrombotic properties, may theoretically improve the results of stenting in this setting. Some metal coating may have a benefit in small vessels. The Titan titanium-nitride-oxide-coated stent (Hexacath, Reuil-Malmaison, France) has been proposed as having a reduced proliferative response in a recent randomized trial showing a 1-year clinical restenosis rate of 12.5%. Our experience with the use of this stent for small vessels has been favorable. Bare metal, customized stents for small vessels were used in several trials comparing stents with PTCA in the setting of small vessels. The procedural success rate was equivalent or better in the stent treatment arm compared to the PTCA treatment arm in these trials; however, a significant proportion of patients (14–37%) assigned to PTCA had to undergo stent placement for the treatment of suboptimal angiographic results or acute/threatened closures. The acute luminal gain was also significantly greater in the stent group compared to the PTCA group. Recently, a meta-analysis of stent versus PTCA trials in small coronary arteries³ demonstrated a strong relationship between the residual stenosis grade after PTCA and restenosis reduction with stenting. Drug-eluting stents (DES) have dramatically changed the paradigm of coronary stenting. Both sirolimus-eluting stent (SES) and paclitaxel-eluting stent (PES) implantation have shown to markedly decrease the incidence of in-stent restenosis and the rate of adverse outcomes. Their remarkable capacity to reduce the incidence of in-stent restenosis might be particularly beneficial in small coronary vessels, since neointimal hyperplasia is relatively constant and independent of stent size. Thus, for small vessels, the same degree of neointimal proliferation, as measured by the late loss, is associated with an increased rate of restenosis as compared to large-caliber coronary arteries. Table 1 summarizes the data from the recent trials dealing with DES.^4–10 SVELTE10 was a multicenter, nonrandomized, study that included 101 patients with de novo coronary artery lesions in small vessels (2.25–2.75 mm), with long lesions (15–30 mm) treated with the SES. Results were compared to matched subgroups from the SIRIUS trial. The results of this trial were exceptional. The 8-month in-stent binary restenosis rate was 3.2%; the in-segment binary restenosis rate was 6.3%, and an overall MACE (major adverse cardiac event) rate was 5%. Therefore, the SVELTE data have proven that SES implantation is an extremely efficient treatment modality for small vessels. However, SVELTE did not address the issue of very small vessels and the questions regarding the most appropriate type of stent for such small vessels. In this month’s issue of the Journal, a comparison of the 1-year clinical outcomes of the 2.25 mm DES coated with either SES or PES is reported by Rodriguez-Granillo et al. (see pages 409–412). The authors concluded that SES (n = 107, RESEARCH) were associated with better 12-month clinical outcomes, and the use of PES (n = 90, T-SEARCH) was identified as an independent predictor of adverse events. The results were significantly in favor of the SES, with a 5.6% overall 12-month MACE rate as compared to a 17.8% MACE rate with the PES. While the study is a nonrandomized comparison which is limited in its ability to draw firm conclusions, it is in concordance with the prior observations of a higher late loss with PES versus SES, and with some reports of increased thrombosis rates with PES. The overall impression from the cumulative data is that SES is the therapy of choice for small and very small vessels. The treatment of very small vessels needs a combined consideration of the potential clinical benefit in respect to the overall risk of restenosis. Small vessels are often of negligible clinical significance and should be approached with caution. If the overall consideration favors therapy, we developed a strategy that includes balloon angioplasty and provisional stenting only if the results are suboptimal. We do not see a major role at this stage for widespread use of DES in small vessels. While the early results¹¹ and those presented here seem promising, there is still a lack of randomized comparative data to make a determination on which is the best revascularization method for small vessels. If the vessel is judged to be of clinical importance, then DES implantation presents an efficient therapy. Email: grendier@barak-online.net

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