Peripheral Plaque Volume Changes Pre- and Post-Rotational Atherectomy followed by Directional Plaque Excision: Assessment by Intravascular Ultrasound and Virtual Histology
ABSTRACT: Atherectomy in the infra-inguinal peripheral vascular bed may be an effective alternative to the balloon and stent-based approach. The change in plaque volume and composition with rotational atherectomy and directional plaque excision has not been studied. We performed rotational atherectomy (RA) followed by adjunctive plaque excision (PE) in 8 patients with infra-inguinal lesions. Lesions were assessed by quantitative angiography and intravascular ultrasound (IVUS) with virtual histology (VH) pretreatment, post-RA, and post-PE. Paired t-tests were used to assess the change in plaque volume, luminal area and dimensions and overall vessel size. Total plaque volume decreased by 24% (347 ± 118 to 264 ± 85 mm3; p = 0.03), which resulted in a lumen increase of 66% (7.08 ± 3 to 11.7 ± 2.8 mm2; p = 0.006). This was mainly due to PE compared to RA. This was achieved without any significant increase in the overall vessel area (27.4 ± 6.3 to 28 ± 6.7 mm2; p = 0.42). The effect on minimal and maximal luminal diameters was synergistic between RA and PE. Fibrotic and fibrofatty plaque were amenable to PE, whereas necrotic core and dense calcium were less responsive to either atherectomy technique. In conclusion, RA followed by PE result in significant improvements in plaque volume and luminal area and diameter primarily by removing plaque rather than vessel expansion. This is mainly attributable to the removal of fibrotic and fibrofatty plaque.
J INVASIVE CARDIOL 2009;21:501–505
Peripheral arterial disease (PAD) is a major cause of medical morbidity in the United States. Clinical manifestations vary from intermittent claudication to gangrene and critical limb ischemia. The primary risk factors for PAD are diabetes mellitus, dyslipidemia, hypertension and advanced age.1
Conservative treatment of PAD consists primarily of an exercise regimen and administration of antiplatelet and lipid-lowering agents. As disease manifests itself, more invasive treatments are common including surgical bypass or amputation. Less invasive percutaneous approaches for resistant symptoms and limb salvage are gaining popularity.
For the past decade, percutaneous interventions for PAD have relied on balloon- and stent-based technologies, which increase the lumen size by expanding the vessel (Dotter effect). Atherectomy, or plaque removal, is an alternative to balloon-based interventions. By alteration or removal of the plaque burden, a larger lumen can be obtained without using a balloon.
Several forms of atherectomy have been studied in the coronary and peripheral beds, the first of which was directional coronary atherectomy (DCA). The results were disappointing perhaps because it elicited a “Dotter effect,” that is, a vessel expansion of up to an 18% cross-sectional area rather than the intended plaque removal.2
High-speed rotational atherectomy (RA) was then introduced and has been shown to change the morphology of the superficially calcified lesion to one more amenable to plaque removal via DCA.3
Plaque excision (PE) is the third and most recent development of tissue retrieval. It features a novel approach of performing extensive longitudinal plaque removal despite the absence of an appositional balloon due to the fact it self-apposes with a hinge system. It is conceivable that this could minimize excessive stretching of the vessel, reducing the stimulus for overwhelming neointimal proliferation.4 An early study has shown minimal increases in vessel diameter post PE, thus producing a smaller “Dotter effect” than traditional DCA.5
Despite the usefulness of intravascular ultrasound (IVUS) in coronary artery intervention, it is less commonly used for peripheral angioplasty and stenting, even though it has been shown to provide useful perspectives for the interventionalist.6,7 IVUS was more accurate than angiography alone to assess the residual plaque burden after coronary atherectomy,8,9 but its use in studying such treatment in the peripheral arterial bed has been limited.
We used IVUS and virtual histology (VH) to study changes in plaque volume and composition and vessel size after treating peripheral stenoses with RA followed by PE. RA was performed first in the hopes of maximizing the efficacy of PE, which is less effective in superficially calcified lesions.10,11
Materials and Methods
Patient population. Eight patients with PAD requiring intervention (severe claudication despite medical treatment or critical limb ischemia) were treated with RA followed by PE (7 had superficial femoral artery lesions and 1 had a tibioperoneal trunk lesion). Target lesions were highly stenotic, but not completely occlusive. The index lesion was studied with IVUS and VH at baseline, after RA and after PE. The study was approved by the institutional review board at St. John Hospital and Medical Center.
IVUS analysis. The Eagle Eye® Gold Catheter (Volcano Corp., San Diego, California) is a 5 French (Fr) compatible catheter that performs intravascular analysis of the culprit lesion measuring both gray-scale images and VH over a 0.014 inch guidewire. Automated pullback (1.0 mm/second) was implemented by using the Track Back® II disposable pullback device. Images were recorded on DICOM format and stored on the s5i™ Imaging System (Volcano) hard drive for later analysis. All pullbacks were performed at a set and sufficiently distal point using an external ruler to mark the precise starting point. All pullbacks were precisely 60 seconds or 60 mm in length in order to assure adequate assessment of possible longitudinal displacement of plaque. All images were assessed independently by two experienced reviewers who were blinded to the treatment status.
VH is a new and more novel approach to lesion assessment. It uses the backscatter information obtained during IVUS to further delineate the composition of the plaque into four specific histologic composition categories: fibrotic, fibrofatty, necrotic core and dense calcium.12 VH also provides a useful plaque volume tool with automatic border detection. In our experience, Results
IVUS analysis of plaque volume and vessel size. Patient and lesion characteristics are summarized in Table 1. Overall, mean total plaque volume decreased by 24% (347 ± 118 to 264 ± 85 mm3; p = 0.03), which resulted in a luminal increase of 66% (7.08 ± 3 to 11.7 ± 2.8 mm2; p = 0.006) (Table 2). RA alone had a small effect on plaque volume and luminal area, whereas plaque excision significantly reduced plaque volume (330 ± 114 to 264 ± 85 mm3; p = .005) and increased the luminal area (8.6 ± 3.3 to 11.7 ± 2.8 mm2; p = 0.005) (Figure 1). This was achieved without a significant Dottering effect with either technique, evidenced by the virtually unchanged vessel area before and after treatment (27.4 to 28 mm2; p = 0.42).
The effect on luminal diameter was synergistic and almost equal between the two techniques, leading to a significant overall increase in both minimal (1.86 ± 0.49 to 2.45 ± 0.42 mm; p = 0.001) and maximal (4.5 ± 0.99 to 5.3 ± 0.74 mm; p = 0.016) luminal diameters.
VH analysis of plaque composition. The lesions were primarily fibrotic in nature, ranging from a low of 49.2% of total plaque volume to a high of 84%, with an average of 64% (Figure 2). Fibrofatty plaque formed 9% of the total plaque volume on average, whereas necrotic core and dense calcium formed 15% and 12%, respectively.
RA had no significant effect on fibrotic plaque volume. In contrast, plaque excision removed fibrotic plaque effectively (209 to 153 mm3; p = 0.001). This represented a 26% decrease in fibrotic plaque volume and 80% of the plaque volume removed. Post treatment, the overall percent of fibrotic plaque burden remained at 59% of the total plaque (Table 3).
The percent of fibrofatty plaque ranged from 5–12% of the total plaque volume, with an average of 9%. Fibrofatty plaque also seemed amenable to atherectomy. Again, no significant fibrofatty volume change occurred post RA, but PE significantly reduced this volume (24 to 16 mm3; p = 0.004). There was a total removal of 47% of all fibrofatty tissue, which represents 16% of all plaque removed.
Necrotic core plaque was not as amenable to atherectomy. The percent of necrotic core plaque ranged from 9–21% of the total plaque volume, with an average of 15%. Post RA and PE, only 6% of all necrotic core was removed, which actually raised the necrotic core percent from 15% to 19%. Overall, 4% of all plaque removed was necrotic core.
Dense calcium volume was not affected by either type of atherectomy. The percentage of dense calcium plaque ranged from 6–20% of the total plaque volume, with an average of 12%. Post RA and PE, no appreciable volume was removed, while the percentage of dense calcium to total plaque volume increased to 18%.
Discussion
Percutaneous transluminal angioplasty (PTA) alone and PTA plus stenting to treat infra-inguinal peripheral arterial disease have poor long-term results.16–19 This led to increased interest in alternative endovascular approaches, especially atherectomy. The SilverHawk plaque excision system is one such approach that showed promising results in prospective registries.20–22 It has become the dominant DCA device on the market despite the lack of randomized data. The Diamondback 360° orbital atherectomy system is a new atherectomy device that showed effectiveness in the OASIS prospective, multicenter, nonrandomized study, which resulted in the Food and Drug Administration approval in 2007.
IVUS has consistently provided insights into the mechanisms and pitfalls of both balloon-based technologies and atherectomy.2,3 Ikeno et al used IVUS and histological data to study the mechanism of luminal gain with plaque excision in coronary and peripheral arteries.5 They reported a predominant reduction in plaque volume rather than mechanical vessel expansion or “the Dotter effect.” No similar data are available to compare the effects of different atherectomy devices on the plaque volume, luminal area and dimensions and plaque composition by VH.
This study confirms that plaque excision with the SilverHawk system increased the luminal area and dimensions primarily by plaque removal with virtually no “Dottering effect.” Meanwhile, the Diamondback 360° orbital atherectomy system appears to have a modest effect on the total plaque volume and luminal area. It has a synergistic effect with PE on minimal and maximal luminal diameters. The orbital atherectomy system may be particularly useful in bulky lesions causing severe stenosis, with or without calcification, to alter plaque compliance and allow the passage of the more definitive treatment with plaque excision.
We can also state that while the luminal gain was impressive with the combined approach, it was even more impressive that so much plaque remained after aggressive debulking. Larger-sized devices and repeated runs may bring even greater plaque reduction than we currently obtain. IVUS may be a very useful complementary tool to accurately assess the success of the atherectomy procedure, since angiographic appearance may be misleading in this regard.
Our study also sheds light on the effect of atherectomy on different plaque components. Fibrotic and fibrofatty plaque were amenable to removal by PE, whereas necrotic core and dense calcium were not effectively removed by either technique. While the mechanism of high-speed rotational ablation centers on the alteration of plaque compliance, we did not observe a substantial benefit in the ability of PE to remove dense calcium after alteration. Newer PE devices that specialize in addressing this pitfall exist, but this was not the focus of our study.
Study limitations. The major limitation of this study was the small sample size. However, the results were still highly statistically significant. This actually attests to the significant changes in plaque volume and luminal area in all the subjects. Another limitation was the use of the coronary IVUS catheter in this study in order to have VH capability. Consequently, the field of examination was fixed at 10 mm. There were a few cases in which we could not proceed due to the large size of the superficial femoral artery. In addition, VH can underestimate the extent of deep-wall calcium in the presence of superficial calcium. While this was a very small percentage of the total plaque volume, it is arguable that more calcium was removed than can be appreciated by VH. Finally, although there were no major clinical complications during the procedure or the index hospitalization, we did not follow the clinical outcomes of these patients.
Conclusion
Atherectomy with the SilverHawk PE system results in substantial plaque reduction, namely in the form of fibrotic and fibrofatty plaques. This typically results in a dramatic increase in luminal area, which averaged 66% in our study when synergistically used with the Diamondback OAS™ system to pretreat the lesion for maximum efficacy. With further evidence showing a minimal “Dotter effect” and a possible reduction in barotrauma, future studies seem warranted to examine clinical outcomes and anatomic endpoints for these promising technologies.
From the Division of Cardiovascular Diseases, Department of Internal Medicine, St. John Hospital and Medical Center, Detroit, Michigan.
Disclosure: Dr. Thomas Davis is on the advisory board of both ev3, Inc. and Cardiovascular Systems, Inc. (CSI). He also owns stock in CSI. The other authors have no conflicts to report.
Manuscript submitted March 12, 2009 and accepted June 4, 2009.
Address for correspondence: Thomas Davis, MD, St. John Hospital, 22101 Moross Road, Cardiac Cath Lab, 2nd Floor, VEP, Detroit, MI, 48236.
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