The Renaissance of Directional Coronary Atherectomy: A Second Look From the Inside

The dawn of atherectomy. The concept of transcatheter atherectomy — removing obstructive tissue by a catheter-based excision technique — was first introduced by Simpson to overcome several unsolved limitations of the conventional “forced-dilation or plaque-displacement” approach by balloon angioplasty (PTCA).1–3 The first directional atherectomy of human vessels was performed in a superficial femoral artery in 1985,2 with an initial experience in human coronary arteries following the next year.3 The safety of the peripheral and coronary devices was confirmed by subsequent large multicenter experience; the peripheral device was approved by the Food and Drug Administration (FDA) in 1987 and the coronary device in 1990. Despite the initial enthusiasm for this first non-balloon percutaneous coronary interventional device, the early randomized clinical trials of directional coronary atherectomy (DCA) in 1993, CAVEAT (Coronary Angioplasty Versus Excisional Atherectomy Trial) and CCAT (Canadian Coronary Atherectomy Trial), failed to demonstrate a clinically significant reduction in late angiographic or clinical restenosis after DCA versus PTCA.4,5 These negative findings for DCA, combined with the approval of the Palmaz-Schatz coronary stent (Cordis Corporation, Miami Lakes, Florida) in 1994, resulted in a rapid decrease in the usage of this unique technology. However, questions remained about whether the potential benefits of DCA might have been underestimated because of the way in which DCA was performed in these early trials. Initial concern over deep vessel wall injury, which might cause unfavorable acute or long-term outcomes, biased the technique toward limited acute gain with relatively small cutter sizes as well as avoidance of post-dilation by adjunctive PTCA. Accordingly, quantitative coronary angiography (QCA) demonstrated large residual stenosis with only a small advantage for DCA: the final diameter stenoses were 29% versus 36% in CAVEAT, and 25% versus 33% in CCAT for DCA versus PTCA, respectively.4,5 Although few centers in the two trials used intravascular ultrasound (IVUS), contemporary IVUS studies suggested that with this degree of angiographic result, more than 60–70% of the vessel area was presumably occupied by residual plaque. Over the following several years, it had been shown that late lumen diameter and the probability of restenosis after interventions are influenced strongly by the lumen diameter immediately after the procedure, rather than by the specific device used.6,7 In addition, several IVUS trials, including Phase II of GUIDE (Guidance by Ultrasound Imaging for Decision Endpoints), suggested that the residual plaque burden (plaque area/vessel area at the lesion site) assessed by IVUS was a significant predictor of restenosis following non-stent coronary interventions.8–10 These concepts led to a great emphasis on aggressive plaque removal and on the use of adjunctive PTCA to achieve “optimal” atherectomy results. “Optimal” atherectomy era. The safety and efficacy of the optimal atherectomy strategy were evaluated by three additional multicenter trials initiated in 1994. OARS (Optimal Atherectomy Restenosis Study) was a prospective, 200 patient registry designed to test the theory that an aggressive DCA strategy achieving a 3x normal was more common with DCA (16% vs. 6%; p Device improvement. Despite these encouraging results, the recent exponential evolution of current-generation coronary stents has further attenuated the use of stand-alone DCA. This is primarily due to several inherent limitations associated with the conventional DCA catheters as well as its high technical demand for operators to achieve optimal results. Despite improvements in the design, safe placement of the relatively large and rigid metal housing of the conventional DCA catheter is a challenge to the operator, and is also dependent on vessel dimensions, degree of tortuosity, and vessel compliance. In addition, calcification of the target or proximal vessel segments is another critical factor determining the outcome of DCA.15 Furthermore, this device requires the use of significantly larger guiding catheters compared to current-generation stents. In the past issue of the Journal, however, O’Brien et al. report their initial experience with a new 8 French guiding catheter compatible DCA device (Flexicut, Guidant Corporation, Santa Clara, California) for the treatment of in-stent restenosis.16 This new atherectomy system offers: 1) improved flexibility due to a 17% reduction in the rigid housing length; 2) improved cutting efficiency due to a titanium nitrite-coated cutter; and 3) a wider window with a circumferential arc of 127 degrees (117 for the GTO AtheroCath). In their preliminary series, successful insertion of the Flexicut catheter was achieved in 15 of 17 in-stent restenosis lesions, despite the relatively small reference diameter of 2.62 ± 0.63 mm. Interestingly, no patient had elevated CPK levels 6–12 hours post-procedure. A revival? One potential new role for DCA in this stent era is debulking neointimal tissue within the stents to maximize acute luminal gain for the treatment of in-stent restenosis. In the U.S., it is estimated that over 50,000 patients per year require the revascularization of restenosed stents. Early clinical experience with stand-alone PTCA to treat in-stent restenosis showed excellent acute results, optimistically suggesting that this old, but least technically demanding technique might be able to cost-effectively treat this lesion subset.17 However, several subsequent studies revealed significantly high rates of recurrent restenosis following plain balloon dilation of in-stent restenosis, particularly in lesions with diffuse in-stent morphology.18–21 The studies also confirmed smaller minimum lumen diameter immediately post-procedure as a strong predictor of target vessel revascularization following the treatment of in-stent restenosis as well. Moreover, detailed serial IVUS examination by Shiran et al. uncovered several interesting morphologic findings that had not been previously detected by conventional angiography.22 In their study, both planar and volumetric IVUS analyses demonstrated a significant and consistent tissue reintrusion back into the stent, resulting in early lumen loss shortly after successful treatment of in-stent restenosis — a testimony to conservation of mass. This phenomenon was more prominent in longer lesions and those with greater in-stent tissue burden, which may partially account for the worse long-term outcomes in diffuse versus focal in-stent restenosis. These observations, in combination, have significantly prompted the use of tissue debulking techniques before dilating diffuse in-stent restenosis. In doing so, direct tissue removal, rather than tissue compression/extrusion through the stent struts, would achieve greater acute lumen gain, presumably by minimizing early lumen loss due to tissue reintrusion. Accordingly, several investigators have reported a considerable reduction in angiographic and/or clinical recurrence of in-stent restenosis in patients with diffuse in-stent restenosis treated with debulking devices (DCA, rotational atherectomy, or laser angioplasty) compared with PTCA alone.23–29 Despite these promising results observed with debulking of in-stent restenosis, clinical recurrence rates of over 20–30% across a broad range of lesion characteristics continue to represent a therapeutic challenge in the “real world” of in-stent restenosis. Although several new biological approaches, including intracoronary radiation therapy and drug-eluting stents, have recently shown favorable outcomes as adjunctive breakthrough technologies for the treatment of those “malignant’ in-stent restenosis cases,30–34 strategies to optimize initial stent deployment should be considered the first priority for interventional cardiologists. Over the past few years, several IVUS studies have suggested that the paradigm linking pre-interventional or residual plaque burden and long-term outcomes, as observed in both PTCA and DCA trials, also applies to stent implantation as well.35–39 In a study of 382 lesions treated with 476 stents, Hoffman et al. demonstrated that pre-interventional plaque burden was a consistent predictor of angiographic late lumen loss and restenosis.36 Recent IVUS work by Prati et al. also showed that late in-stent neointimal hyperplasia correlates with the amount of plaque burden outside the stent.37 Debulking plaque prior to stenting is, therefore, another potentially important new role for DCA in the current interventional laboratory. Recently, several investigators have demonstrated that DCA plus stenting is a safe procedure, with both good clinical success rates and a low incidence of restenosis.40,41 Accordingly, several large multicenter prospective randomized trials, including AMIGO (Atherectomy before Multilink Improves lumen Gain Outcome) and DESIRE (DEbulking and Stenting In Restenosis Elimination), are currently underway to confirm their relatively small number experiences (Figure 1). Of note, this combined strategy requires greater procedural time as well as technical demands, thereby affecting direct and indirect costs. Therefore, this approach may be limited to those clinical conditions in which stent implantation alone is likely to fail. Although a large number of patients may be required to determine the optimal threshold, pre-intervention IVUS may be useful to identify those lesions with large plaque burden, providing triage information for increased risk of subsequent in-stent restenosis and possibly the need for debulking prior to stenting. Improvements in the latest DCA device may translate to greater success rates, not only for in-stent restenosis lesions, but for small target vessels, diffuse disease, or complex bifurcation lesions, all of which may derive clinical benefit from the “mass removal” plus scaffolding strategy as well. So we are faced with an old concept in a new environment; as medieval art transitioned to a modern form in the 14th century, today, DCA may experience a Renaissance revival in this stent-focused era. Acknowledgment. The authors thank Heidi N. Bonneau, RN, MS, for her expert review of the manuscript.

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