Journal of Vascular Surgery
Volume 46, Issue 6 , Pages 1155-1159, December 2007

Incidence and clinical significance of distal embolization during percutaneous interventions involving the superficial femoral artery

Presented at the Thirty-fifth Annual Society for Clinical Vascular Surgery Symposium, Orlando, Fla, Mar 21-24, 2007.

Division of Vascular Surgery, Columbia University College of Physicians, Weill Medical College of Cornell University New York Presbyterian Hospital, New York, NY.

Received 15 May 2007; accepted 30 July 2007.

Article Outline

Objective

Distal embolization of plaque or thrombus may cause organ ischemia following percutaneous peripheral interventions. The purpose of this study was to evaluate the incidence and clinical significance of particulate embolization during percutaneous superficial femoral artery (SFA) intervention by monitoring with continuous Doppler ultrasound. The rate and timing of embolization at various phases of intervention such as guidewire crossing, balloon angioplasty, stent deployment, and directional atherectomy were analyzed and compared.

Methods

Sixty patients underwent SFA intervention. Of these 60 patients, 10 patients underwent percutaneous transluminal angioplasty (PTA) alone, 40 patients underwent PTA with stenting, and 10 patients underwent plaque excision with the SilverHawk atherectomy device (8) or Spectranetics excimer laser (2) with or without additional PTA or stent placement. A 4-MHz Doppler probe was used for continuous monitoring in the ipsilateral popliteal artery. Distal embolization was registered as embolic signals (ES). ES were quantitatively assessed during critical portions of the procedure including guidewire crossing, balloon angioplasty, stent deployment and/or atherectomy. ES during different phases of intervention were compared using analysis of variance (ANOVA).

Results

ES was noted in every patient during wire crossing, angioplasty, stent deployment and atherectomy. The average number of ES noted during guidewire crossing was 8, PTA was 12, stent deployment was 28, SiverHawk atherectomy was 49, and Spectranetics excimer laser was 51. The frequency of ES was statistically higher during stent deployment vs wire crossing or balloon angioplasty but equivalent to that generated by plaque excision. ES was observed more frequent during balloon angioplasty than during wire crossing. In one patient who was treated with the excimer laser, a single runoff vessel was occluded with embolic debris but patency was restored angiographically after thrombolysis. The patient went on to require below knee amputation. During follow-up, all patients with claudication reported improved symptoms and those with ulcers or gangrene demonstrated healing. The average increase in ankle-brachial index following intervention was 0.31.

Conclusion

While ES were recorded at each step of SFA intervention, the frequency was greatest during stent deployment. Despite the frequency of these events, only one patient developed angiographically and clinically significant embolization. Thus, our findings do not support the routine use of protection devices during percutaneous SFA intervention.

 

Endovascular therapy for occlusive disease of the superficial femoral artery (SFA) has gained acceptance as a primary treatment modality for peripheral arterial disease (PAD).1, 2 Surgery remained the gold standard for complete SFA occlusion or concomitant common femoral artery involvement. Percutaneous interventions have a number of potential advantages, including a shorter hospitalization, ability to use local anesthesia, and less perioperative morbidity.3 Endovascular treatment of this arterial segment presents a particular technical challenge, as the extent of disease varies from lesions that are short, focal, and stenotic to long, diffuse, and occluded. Over the past two decades, numerous modalities have been evaluated, including simple balloon angioplasty, subintimal angioplasty, cryoplasty, stenting, and directional atherectomy.

While there is considerable debate about the optimal percutaneous treatment modality for peripheral arterial disease, embolization of the distal arteries is a potential complication that may produce worsening ischemia or limb loss. The incidence of distal embolization as determined by angiographic or clinical manifestations has been estimated to range from 4% to 5% for peripheral interventions. however, the true incidence of asymptomatic embolization is likely higher.3, 4, 5, 6, 7, 8 Thus far, attempts at measuring embolization during peripheral arterial interventions have been few and with small numbers of patients.9, 10, 11 The purpose of this prospective study was to evaluate the incidence of distal embolization during percutaneous SFA intervention using continuous transcutaneous Doppler ultrasound. We quantified the rate of embolization at various phases of intervention, such as during guidewire crossing, balloon angioplasty, stent deployment, and directional atherectomy with either the SilverHawk (FoxHollow Technologies, Redwood City, Calif) device or the Spectranetics excimer laser device (Spectranetics Corporations, Colorado Springs, Colo), and analyzed angiographic and clinical sequelae of these events. Finally, rates of embolization for lesions of different anatomic severity as outlined by the Transatlantic Inter-Society Consensus (TASC) classification or calcification were compared.

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Methods 

Patients 

From December 2005 to December 2006, 60 patients who underwent percutaneous SFA interventions provided informed consent and were enrolled in this study under institutional IRB approval. Inclusion criteria were a primary SFA stenosis or occlusion and a minimum of one vessel runoff. Patients undergoing concomitant tibial intervention were not excluded; however, embolic detection was valid only for SFA or above knee popliteal lesions, given the location of our probe. Patients needed to have a patent popliteal segment at the level of the knee in order for there to be successful insonation at that level. Data were accumulated prospectively for analysis. Preoperative imaging consisted of lower extremity arterial pressures, ankle-brachial index (ABI) measurements and pulse volume recordings in all cases. Arterial duplex and magnetic resonance angiography were performed in selective cases based on the surgeon’s preference. No patient was excluded based upon anatomic characteristics that were noted on preoperative imaging. Choice of intervention was performed at the discretion of the operating surgeon. There was no specific protocol defining the use of predilation, routine stenting, No patients were lost to follow-up. All patients were interviewed and examined postoperatively and at 30 days postintervention. ABIs were repeated at 30-days postintervention and were compared with preintervention values.

Anatomic evaluation 

Digital subtraction angiograms of all 60 patients were available for evaluation. SFA calcification was assessed on orthogonal views and evaluated as absent or mild if there was no or a trace calcium shadow, moderate if there was a calcium shadow on < or = 50% of the vessel diameter, and severe if the calcium shadow outlined 51% to 100% of the vessel. Lesions were classified according to the TASC criteria23 as follows:

TASC A: Single stenosis < or = 3 cm. not at the origin of the superficial femoral or distal popliteal artery.

TASC B: Single stenosis or occlusion 3 to 5 cm, not involving the distal popliteal or multiple stenoses or occlusions each < 3 cm long.

TASC C: Single stenosis > 5 cm or multiple lesions each 3 to 5 cm long.

TASC D: Complete common femoral or superficial femoral artery occlusions.

Doppler evaluation 

Intraoperative monitoring was continuous and all critical portions of the procedure were recorded. All evaluations were performed by the same ultrasonographer and the senior author (NJM). A 4 -MHz pulse wave transcranial Doppler (TCD) system (Multigon Industries, Yonkers, NY) was used to insonate the ipsilateral popliteal artery. The probe was secured in place in the posterior popliteal fossa. The presence of the probe did not interfere with or necessitate modification of standard endovascular techniques. Instrument power and gain settings were adjusted to provide an optimal signal-to-noise ratio and achieve a constant analog signal recording level. The Doppler signal was recorded continuously on digital audio tape (Sony TCD-D10 ProII, Sony Corporation, New York, NY). A 6 decibel (dB) intensity threshold above peak background intensity was considered indicative of an embolic signal (ES).24 Differentiation between air and particulate embolism based on ES intensity measurements was not attempted because the sensitivity of the TCD device in this study does not permit such differentiation. Number of ES were calculated at each procedure and the total number for each intervention type (wire crossing, angioplasty, tent deployment, atherectomy) determined per patient. Comparison between different types of angioplasty (predilation, post-stent deployment) did not reveal significant difference in ES between these subtypes and further analysis based on this was not performed.

Statistical analysis 

ES counts were not normally distributed and were represented as averages. The rate of ES during different phases of intervention were quantified and compared using analysis of variance (ANOVA) with statistical significance achieved at P < .05. In addition, we compared ES between different TASC and calcification categories using ANOVA. SAS statistical software was used.

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Results 

Sixty patients were enrolled in the present study. Thirty-eight patients (63%) were men and 22 patients (37%) were women. The average age was 70 years (range 45 to 82 years). The technical success rate in this study was 100%. The indications for SFA intervention included disabling claudication in 34 patients (56.7%), rest pain in 10 patients (16.7%), ischemic ulceration in 8 patients (13.3), and gangrene in 8 patients (13.3%) (Table I). Of these 60 patients, 10 patients underwent percutaneous transluminal angioplasty (PTA) alone, 40 patients underwent PTA with stenting, and 10 patients underwent plaque excision with the SilverHawk atherectomy device (8) or Spectranetics excimer laser (2) with or without additional PTA or stent placement. Anatomic evaluation revealed that 41 patients had severe, 17 patients had moderate, and 2 patients had mild calcification at the site of arterial treatment. These lesions were characterized anatomically by TASC classification (Table II) and the number of runoff vessels was recorded from the preintervention angiography runs (Table III).

Table I. Clinical indications for percutaneous SFA intervention
Indications for SFA interventionn = number of patients
Disabling claudication34
Rest pain10
Ischemic ulcers8
Gangrene8

SFA, Superficial femoral artery.

Table II. Distribution of lesions based on TASC classification
TASC ClassificationTASC ATASC BTASC CTASC D
Number of lesions816279
Table III. Status of runoff vessels in patients undergoing percutaneous SFA intervention
Number of runoff vessels
123
Number of patients83220

SFA, Superficial femoral artery.

ES was noted in each patient while crossing of the lesion with a guidewire, as well as during balloon angioplasty, stent deployment, and/or plaque excision (Fig). The frequency of ES was significantly higher during stent deployment than during wire crossing or balloon angioplasty. When more than one stent was deployed, there were no significant differences in ES detected during the first stent deployment vs subsequent stents. The number of ES was significantly higher during balloon angioplasty than wire crossing. The number of ES during stent-deployment was not significantly different than that seen during SilverHawk plaque excision or during laser atherectomy (Table IV). There were no significant differences in ES seen between TASC classifications (Table V). Moreover, severity of calcification did not predict the frequency of ES, although more cases in each category of calcification are needed to conclusively state the effect of vessel calcificaton on ES frequency. During plaque excision with the SilverHawk device, ES occurred during device passage but also during the quiescent periods between passages while the device was outside of the patient. We did not note any difference in the rate of ES for predilation angioplasty vs postdilation of an implanted stent. Postdilation of one patient had angiographic evidence of loss of a solitary anterior tibial runoff artery (1.7%). This patient had been treated with laser atherectomy and the anterior tibial artery was reopened after infusion of TPA. The number of ES in this patient was statistically identical to number observed with the other laser atherectomy and SilverHawk patients in this series. The patient presented initially with a severely ischemic foot which had already suffered sensory loss and some motor compromise. In spite of angiographic evidence for restoration of flow in the anterior tibial artery and an increase in ABI, the patient eventually underwent a below the knee amputation. There was no clinical evidence of digital embolization in this patient or in any of the patients evaluated in this series.

Table IV. Results of analysis of variance (ANOVA) for embolic signals (ES) during various phases of SFA intervention
Average ESP value
Stent deployment30.9<.001
Balloon angioplasty16.38
Average ESP value
Stent deployment30.9<.001
Guidewire8.9
Average ESP value
Balloon angioplasty16.38<.001
Guidewire8.9

SFA, Superficial femoral artery.

Table V. Difference in ES frequency based on TASC classification, analyzed with ANOVA
Summary GroupsAverageP value between groups
A63.965
B65
C61
D69

ANOVA, Analysis of variance.

Patients were followed for an average 12 months (range 6 to 18 months). All patients suffering from claudication reported an improvement in symptoms at the time of follow-up visit. The average ABI preintervention was 0.62 and postintervention increased to 0.93 for an average improvement in ABI of the treated limb of 0.31 ± 0.2. All patients with gangrenous digits healed toe amputations and all ulcers demonstrated some degree of healing following intervention, although, perhaps due to short follow-up in some cases, some wounds remain open.

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Discussion 

Distal protection systems are becoming standard practice for carotid15 and coronary artery interventions and, consequently, interest in these devices for peripheral interventions has increased. However, no evidence exists to support the routine use of protection devices for percutaneous treatment of peripheral vascular disease, and there are currently no data available that define which patients might be at high risk for embolization. Nonetheless, articles in non-peer reviewed publications have raised the question of whether distal protection might be useful during SFA angioplasty.12 Conversely, embolic protection devices are expensive and they may cause arterial injury. In order to address this issue, we felt as a first step that it would be useful to quantify the incidence and significance of embolization during SFA angioplasty.

Previous reports of percutaneous carotid interventions revealed that multiple embolic particles often classified on Doppler ultrasound as embolic signals were generated from plaques and that these particles were associated with each phase of endovascular intervention.13, 14, 15, 16 Rates of detection of ES varied during the phases of carotid intervention and occurred less frequently in the presence of distal protection.15 We used methods similar to those employed in these carotid studies to define ES in patients treated with percutaneous peripheral vascular interventions. Based on the routine use of TCD for ES detection in the carotid literature, we felt comfortable that our methodology was satisfactory and that ES could be reliably reported.

In all 60 patients studied in our series, ES were detected in the ipsilateral popliteal artery during all critical phases of the SFA and proximal popliteal interventions. We found clear differences in ES rates between different phases of intervention with stent deployment and plaque excision resulting in the highest number of ES followed by angioplasty followed by wire crossing. We did not find differences in ES rates related to lesion type. Surprisingly, neither TASC classification nor the degree of calcification influenced the frequency of embolic events. These findings suggest that lesion characteristics may not predict embolization or their clinical sequelae after percutaneous intervention. The data with respect to calcification may be misleading since there were only a few patients with mild calcification for comparison. It is possible that if this study included a larger number of patients with mild or no calcification, a difference might have been realized.

In our single case of angiographically evident embolization, most likely a subacute thrombus from a chronic severe plaque was dislodged. Although the TCD is an instrument that primarily quantifies microembolization, it is important to realize that during peripheral vascular interventions thrombus or a large piece of atherosclerotic plaque can also pass downstream. This patient’s presenting symptoms were acute and severe, likely related to that fact that he had only single vessel runoff. Embolization most likely occurred during repeated passages of the laser catheter for treatment. Our ability to treat the embolus with thrombolysis suggests it was largely thrombus. It is possible in this one case, that a distal protection device would have prevented this untoward complication. This patient was treated with an excimer laser atherectomy device. However, stent placement and atherectomy were also associated with rates of ES that were equivalent to laser atherectomy. Unfortunately, we were not able with this study to determine factors that would predict which patients should be treated with filter devices.

Konig and colleagues used a distal protection device in 11 cases of SFA intervention.11 They collected debris in the filter but typically this was fibrin and red cells. The authors also typically observed macroemboli around and distal to the filter, which were not retrieved by the filter. In all of their cases, there was a significant decrease in flow through the filter related to debris obliterating its pores. Interestingly, they did not heparinize their patients until PTA was performed. Most of the debris they collected appeared to be thrombotic and may have been related to a lack of anticoagulation prior to intervention.11 Other investigators have evaluated the incidence of embolization associated with peripheral interventions. Kudo et al used Doppler techniques to analyze the incidence of ES during different facets of iliac artery intervention; comparing the different phases such as passage of the guidewire, balloon angioplasty, and stent deployment.9 In their series of 10 cases, the authors reported the incidence of ES was greatest during stent deployment vs guidewire passage or balloon angioplasty a finding that was similar to ours.

Studies have demonstrated that disruption of plaque after carotid angioplasty sets in motion a cascade of events, including the release of plaque debris, the deposition of platelets, and the formation of thrombus.4, 5, 15 The emboli detected after angioplasty of mature plaques is typically a combination of atherosclerotic debris, cholesterol, calcified material, and platelet emboli.18, 19 We made no attempt in this study to determine size of particles although methods and devices exist that can provide semiquantitative assessment of ES properties.17 With only one clinically significant case of embolization, it is unlikely that analysis of particle characteristics would provide insight into the risk of clinically relevant events in a series of this size.

Plaque excision with the SilverHawk atherectomy device is currently employed as an alternative or adjunct to angioplasty and stenting in endovascular SFA interventions. To avoid distal embolization, these devices have a built in chamber for the collection of the excised plaque for later removal. However, Suri et al21 and Zeller et al22 also noted the presence of distal emboli during femoropoliteal plaque excision with the SilverHawk atherectomy device in their series.19, 20 We similarly detected emboli during our SilverHawk cases. Interestingly, numerous emboli were detected during the period between passes of the plaque excision catheter, while the device was quiescent. Such a finding may reflect embolization of debris from a traumatized, disrupted surface. In spite of these findings, we saw no clinically or angiographically significant embolization during SilverHawk treatment. Since we enrolled only eight patients undergoing plaque excision, our number may be too low to make any definitive conclusions.

This study has several limitations. A theoretical limitation of this study was the lack of an objective correlation between what was observed as embolization on Doppler ultrasound and actual proof of embolization since distal protection devices were not employed in this study for reasons discussed. Although we did enroll 60 patients, the sample population was relatively small considering the variables present in these types of patients. Although an attempt was made to include in this series all patients undergoing intervention, some patients were excluded because of patient refusal or scheduling problems. In spite of these limitations, the fact remains that we consistently detected emboli in all patients undergoing SFA intervention with only one case of clinically significant embolization. These results indicate that although embolization occurs routinely during percutaneous SFA intervention, clinical sequelae are rare. It seems at least in the absence of further data, routine use of embolic protection in these patients is not warranted.

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Author contributions 


Conception and design: NM, KK

Analysis and interpretation: NM, JM, SS, RL

Data collection: RL, NM, SS

Writing the article: RL, KK, NM, SS

Critical revision of the article: KK, RL, NM, JM, SS

Final approval of the article: NM, KK

Statistical analysis: SS, NM

Obtained funding: Not applicable

Overall responsibility: NM

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References 

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 Competition of interest: none.

PII: S0741-5214(07)01291-8

doi:10.1016/j.jvs.2007.07.058

Journal of Vascular Surgery
Volume 46, Issue 6 , Pages 1155-1159, December 2007

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