Analysis of Particulate Debris after Superficial Femoral Artery Atherectomy

ABSTRACT: Purpose. To evaluate the occurrence, size and composition of embolized debris captured during routine directional atherectomy using the SilverHawk device. Methods. 15 consecutive eligible patients with a nonocclusive superficial femoral artery (SFA) were enrolled. Patients were included if they were > 18 years of age and had ≥ 70% stenosis in the SFA. All lesions underwent plaque excision with the SilverHawk atherectomy device. A FilterWire EZ was used for distal protection and retrieval of embolized material. Specimens were collected separately from the filter basket and the SilverHawk atherectomy device’s nosecone and were studied by a pathologist for number, size and composition. Results. Visible debris captured in the filter was found in the majority of patients 14/15 (93%). Clinically-significant debris was found in 7/15 (47%) patients. The proportion of captured debris ranged from 0.1–0.4 cm. Microscopy revealed that the shaved particles consisted predominantly of collagen, fibrin, lipid-laden macrophages, cholesterol and calcium. Analysis of the embolized material revealed a different composition, mostly consisting of collagen with fibrosis, cholesterol and macrophages. Conclusion. In this single-center comparative study we have shown that during SilverHawk atherectomy of SFA lesions, distal embolization is universal. The debris captured in the filter is different in overall composition from the captured material in the nosecone of the SilverHawk device. Debris large enough to cause clinically-significant embolization, no-reflow and ischemia following SFA interventions occurred in nearly 50% of cases. J INVASIVE CARDIOL 2009;21:7–10 Femoral artery atherosclerotic disease is reported to occur in up to 40% of patients with peripheral arterial disease (PAD).1 In recent years, the number of patients treated with endovascular interventions as a method of revascularization has been increasing. Distal embolization has frequently complicated otherwise successful interventions and is reported to occur in different vascular beds.2–4 The use of embolic protection devices (EPD) has become the standard of care in both carotid and saphenous vein graft interventions, and has improved outcomes in these vascular territories.5–8 Up to 5% of all endovascular treatments of the superficial femoral artery (SFA) are complicated by clinically-significant distal embolization.2,3 Moreover, certain interventions, particularly directional atherectomy, have been associated with a higher risk of embolic complications.6 The current role of EPD during SFA interventions has not been clearly established. Furthermore, little information is available about the occurrence and composition of embolized material during SFA interventions. Goal. In this study, we set out to evaluate the occurrence, size and composition of embolized debris captured during routine directional atherectomy using the SilverHawk device (ev3 Inc., Plymouth, Minnesota). Methods Between January 2008 and June 2008, 15 consecutive eligible patients with nonocclusive SFA were enrolled. The study was approved by the institutional review board at our center. Patients were included if they were > 18 years of age, able to provide informed consent and had ≥ 70% stenosis in the SFA. All lesions underwent plaque excision with the SilverHawk atherectomy device. A FilterWire EZ (Boston Scientific Corp., Natick, Massachusetts) was used for distal protection and retrieval of embolized material. Specimens were collected separately from the filter basket and the SilverHawk atherectomy device’s nosecone and were studied by a pathologist for number, size and composition. Interventions. All patients were preloaded with 600 mg of clopidogrel and 325 mg of aspirin orally. Intravenous unfractionated heparin was utilized to achieve an activated clotting time (ACT) goal of 250–300 seconds. All patients underwent SilverHawk atherectomy. One FilterWire EZ was used per patient for distal protection and retrieval of embolized material. The FilterWire EZ was successfully delivered distal to the lesion in 100% of the patients. All interventions were performed by cardiologists experienced in peripheral interventions. Debris and histological analysis. All excised and retrieved debris was safely and carefully removed from the SilverHawk atherectomy device and the FilterWire EZ, respectively. The material was placed in sterile saline and immediately analyzed. The saline solutions were then centrifuged, prepared for cytology evaluation and stained with papanicolaou stain (ThinPrep, Cytyc Corporation, Boxborough, Massachusetts). The material was then fixed in 10% formalin, embedded in paraffin and stained with hematoxylin and eosin (H&E) for light microscopy. Results A total of 15 patients were enrolled. The mean age 68.5 years of which 40% were male (6/15) and 60% were diabetic. All patients had multiple risk factors for PAD (Table 1). The median ACT was 300 seconds. All filters were deployed and retrieved successfully. Procedural success, defined as less than or equal to 20% residual stenosis, was achieved in 93% (14/15) of the patients. Approximately 54% of the patients had 0% residual stenosis. The average lesion length was 74.27 mm. there were zero chronic total occlusions. Visible debris captured in the filter was found in the majority of patients 14/15 (93%). Clinically-significant debris (defined as ≥ 0.2 cm [using the PROTECT registry’s definition])9 was found in 7/15 (47%) patients. The composition of this debris is shown on Figure 2. One patient (Patient #5) did not have excised material due to a mechanical failure of the atherectomy device. The proportion of captured debris ranged from 0.1–0.4 cm. Microscopy revealed that the excised particles consisted predominantly of collagen, fibrin, lipid-laden macrophages, cholesterol and calcium (Figure 1 and Table 2). Analysis of the embolized material revealed a different composition, primarily consisting of collagen with fibrosis, cholesterol and macrophages (Table 3). Discussion PAD is a systemic atherosclerotic disease that affects up to 20% of patients ≥ 65 years.10 Persons with PAD, compared to those without, have four-to-five times the risk of dying of a cardiovascular disease event, resulting in a two-to-three times higher total mortality risk.11,12 Endovascular recanalization and therapy for PAD has been accepted as a treatment modality. A favorite tool frequently utilized by interventionists has been directional atherectomy using the SilverHawk device. However, the simplicity of use may have become its hindrance, as it has been associated with a high degree of distal embolization. Moreover, the application of distal protection in SFA interventions has not been fully investigated and/or accepted. Previously, Lam et al studied the incidence and clinical significance of distal embolization during percutaneous interventions involving the SFA by continuous Doppler ultrasound monitoring of the ipsilateral popliteal artery. They studied 60 patients and found embolic signals in all phases of SFA interventions. They also found the highest embolic signals when utilizing the SilverHawk atherectomy device and during stent deployment.13 In the Preventing Lower Extremity Distal Embolization Using Embolic Filter Protection (PROTECT) registry, Shammas et al9 studied the safety and effectiveness of embolic filter protection in reducing distal embolization during percutaneous lower-extremity interventions. They found that SilverHawk atherectomy was an independent predictor of macroembolization (particle size ≥ 0.2 mm.) Moreover, it was shown to have a 31-fold chance of distal embolization. However, in their study they did not perform histopathological analysis of the debris and could not conclude as to the composition and origin of the material. To our knowledge, our study is the first to investigate and compare the characteristics of material captured in the EPD with that captured in the nosecone of the SilverHawk atherectomy device. Our study’s principal finding is that embolic atherothrombotic particulate matter is commonly liberated during SilverHawk atherectomy of the SFA. This particulate matter may play a role in the pathogenesis of distal embolization, no-reflow and ischemia following SFA interventions. Analyses of debris captured in the EPD consisted mostly of large, visible athero-thrombotic material composed of cholesterol, fibrin, collagen, macrophages and calcium. Moreover, the embolized debris differed in overall composition from that retrieved from the nosecone shavings of the atherectomy device. Although the overall composition differed, it is not unjustified to assume the debris originated from uncaptured material by the nosecone during atherectomy. Moreover, these results lead us to hypothesize that most of the embolized debris came after the initial pass with the atherectomy device. There were no identifiable angiographic or clinical predictors of embolization, as the majority of patients had emboli captured by the FilterWire. Study limitations. This single-center study is limited by its small size, no clinical or angiographic follow up, and the lack of randomization. A larger trial is needed to confirm the results. Conclusion During this single-center comparative study, we have shown that during SilverHawk atherectomy of SFA lesions, distal embolization is universal. The debris captured in the filter is different in overall composition from the captured material in the nosecone of the SilverHawk device. Debris large enough to cause clinically-significant embolization, no-reflow and ischemia following SFA interventions (especially with limited distal vessel runoff) occurred in nearly 50% of cases. Based on these results, we therefore recommend the universal use of EPD when using the SilverHawk atherectomy device.

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