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(Radiology. 2001;219:153-156.)
© RSNA, 2001

Experimental Studies

Comparison of Three Mechanical Thrombus Removal Devices in Thrombosed Canine Iliac Arteries1

Flavio Castañeda, MD, Ruizong Li, MD, Jitendra Patel, MD, James R. DeBord, MD and James L. Swischuk, MD

1 From the Departments of Radiology (F.C., R.L., J.L.S.), Pathology (J.P.), and Surgery (J.R.D.), University of Illinois College of Medicine at Peoria, 1 Illini Dr, PO Box 1649, Peoria, IL 61656. Received March 16, 2000; revision requested May 2; revision received August 14; accepted September 12. Address correspondence to F.C. (e-mail: fcastaneda@peorad.com).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To assess and compare intimal and medial vascular damage caused by three mechanical wall-contact thrombectomy devices: Fogarty embolectomy catheter, Arrow-Trerotola peripheral thrombectomy device, and MTI-Castañeda over-the-wire brush.

MATERIALS AND METHODS: Bilateral external iliac arteries of 15 canines were thrombosed before mechanical thrombolysis. Ten thrombosed arteries were randomly assigned to receive each device. Animals were sacrificed immediately, and histologic assessment of endothelial and medial damage in the vessels was performed.

RESULTS: The vascular damage found with all devices extended into the tunica media. The Fogarty embolectomy catheter and the Arrow-Trerotola device caused significantly more damage than the Castañeda brush.

CONCLUSION: All devices caused lesions extending into the media. Previous research has shown that the extent and depth of the vascular lesion may be contributing factors in promoting early atherosclerotic and accelerated hyperplastic intimal and medial changes. These findings warrant further study of these devices in an atherosclerotic model with longer follow-up.

Index terms: Animals • Arteries, iliac, 986.442 • Arteries, thrombosis, 986.442 • Thrombolysis, 986.1269 • Thrombosis, experimental studies, 986.1269


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In 1963, Fogarty et al (1) reported their experience with an inflatable balloon catheter used to avoid extensive vascular dissection during embolectomies performed with local anesthesia. This has become the standard of therapy for removing occlusive in situ thrombi or emboli. Multiple types of vascular injuries with this device have been described. Arterial rupture and dissection account for almost 60% of acute complications (2), and delayed ones include accelerated atherosclerosis and intimal and medial hyperplasia (3–11). However, these vascular injuries are accepted as unavoidable and as part of the procedural morbidity. Because of its continuous and extensive use for nearly 40 years, the Fogarty embolectomy catheter has become the standard against which newer thrombectomy devices are compared.

More recently, pharmacomechanical thrombolysis has been gaining acceptance for the treatment of some thrombotic vascular diseases, such as in postoperative vascular reconstructions (12–14), extensive deep venous thrombosis (15,16), and thrombosed vascular dialysis access (17–20). Technologic advances have resulted in the introduction of several other mechanical thrombectomy devices (21–24). All existing devices may be classified into two groups: those that make contact with the vascular wall for fragmentation or mechanical removal and those that do not contact the wall but depend solely on aspiration.

The purpose of this study was to compare the endothelial damage caused by two of the newer and most commonly used wall-contact mechanical thrombus removal devices, the Arrow-Trerotola peripheral thrombectomy device (Arrow, Reading, Pa) and the Micro Therapeutics–Castañeda over-the-wire brush (Micro Therapeutics, Irvine, Calif), both indicated for use only in dialysis grafts, with that caused by the standard wall-contact device, the Fogarty embolectomy catheter (Baxter, Irvine, Calif).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
All institutional research and U.S. Department of Agriculture rules and regulations were strictly followed throughout the study. Fifteen laboratory-bred foxhound dogs (Marshal Farms, North Rose, NY), weighing 20–30 kg, were used. The study consisted of two stages, each performed with the animal under general halothane gas anesthesia and with strict sterile technique.

In the first stage, both iliac arteries were occluded to promote thrombosis so that the model would mimic the clinical situation in which the studied wall-contact thrombectomy devices are commonly used. To accomplish this, bilateral common femoral arterial dissections were made, followed by the placement of bilateral 6-F vascular sheaths (Argon, Athens, Tex) by using standard Seldinger technique. Through one side, a 5-F measuring pigtail catheter (Cook, Bloomington, Ind) was advanced to the distal abdominal aorta, and a baseline pelvic arteriogram was obtained.

Then, bilateral iliac occlusion balloons were placed at the origins of both iliac arteries (Fig 1). At this point, both 6-F vascular sheaths were removed, since they were required only for the advancement of the pigtail catheter and bilateral non–over-the-wire Fogarty embolectomy catheters. The occlusion balloon catheters consisted of Fogarty embolectomy catheters that were inflated to gently occlude the inflow. These were clamped just outside the puncture site and were cut to leave 1–2 cm of the shaft outside the vessel. The end was cauterized to occlude the lumen, then folded over itself, and tightly wrapped with suture material. This prevented leakage of contrast material (iopamidol [Isovue-300]; Bracco Diagnostics, Princeton, NJ) from the balloons. The femoral artery was ligated just distal to the puncture site to prevent retrograde filling of the iliac arteries. The folded and occluded ends of the inflated occlusion balloons were covered by overlying soft tissues, and the cut downs were closed. The animals were allowed to recover and were returned to their pens. Most of the vessels (26 of 30 vessels) were allowed to remain occluded for 24 hours. The remaining four vessels continued to be occluded for 72 hours, due to the scheduled availability of the research laboratory for the second and final stage of the procedure.



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  		Figure 1. Radiograph shows bilateral iliac occlusion balloons placed to promote vascular thrombosis.

 
In the second stage, both previous surgical closures were released, and the femoral arteries were again dissected and exposed. The femoral ligatures were released, and the iliac occluding balloons were deflated and removed, leaving the 6-F vascular sheaths at the arterial puncture sites. Through one of the sheaths, a 5-F pigtail catheter was carefully advanced to the distal aorta over a guide wire so that the thrombus would not be disturbed. Then, a pelvic arteriogram was obtained before thrombolysis (Fig 2).



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  		Figure 2. Arteriogram obtained immediately after deflation and removal of the occlusion balloons shows complete bilateral thrombosis of the external iliac arteries with persistent patency of the bilateral internal iliac (large arrows) and sacral (small arrows) arteries.

 
After complete bilateral vascular thrombosis was documented, each iliac vessel was randomly assigned to one of the three studied devices; 10 thrombosed vessels were studied with each device. Of the four vessels that remained thrombosed for 72 hours, one was randomized to the Fogarty embolectomy catheter group, one to the Arrow-Trerotola device group, and two to the Castañeda brush group. Before mechanical thrombolysis, 50 U of heparin per kilogram of body weight was intravenously administered to each animal.

All devices used were commercially available and were obtained by means of standard purchasing channels. Their properties are summarized in Table 1.


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  		TABLE 1. Motorized Devices
 
In the vessels randomly assigned to the 5-F Fogarty embolectomy catheter group, the device was used as recommended (5) and as is customarily done in a clinical setting. Withdrawal of the catheter was begun before the balloon was inflated. The balloon started to fill with air within the first few millimeters of catheter motion, and after the balloon was inflated sufficiently to produce resistance, the volume in the balloon was reduced slightly. This minimized the lateral wall pressures and shear forces. Each time, the catheter was withdrawn through the entire iliac artery. This maneuver was repeated a total of four times with each vessel. We did not use a spring scale or electronic transducer because these are not used clinically. We polled 10 surgeons experienced in Fogarty embolectomy as to the number of passes required in an average procedure, and their response was four or five. We opted to use the lower number.

When the Arrow-Trerotola device was used, it was advanced to the distal aorta, retracted inside its catheter, then extruded and pulled back into the iliac artery, where it was activated and withdrawn, during 60 seconds, through the entire vessel. A solution of nonionic contrast material and normal saline with 2,000 U of heparin was infused through the side arm of its motorized device for visualization. No thrombolytic agent was used.

When the Castañeda brush was used, it was advanced to the distal abdominal aorta over a guide wire while it was retracted into its housing. It was then extruded and pulled back into the iliac artery, where it was activated and withdrawn, during 60 seconds, through the entire vessel. The same mixture of nonionic contrast material, normal saline, and heparin was used. No thrombolytic agent was used with this device, despite recommendations, to avoid the introduction of other variables.

Shortly after completion of this portion of the procedure, a 5-F pigtail catheter was advanced to the distal aorta, and a completion pelvic arteriogram was obtained (Fig 3). The animals were sacrificed while under general anesthesia. By means of midline laparotomy, the distal abdominal aorta and the entire iliac vessel were carefully removed en bloc and fixed in formaldehyde. Histologic assessment of the vessels for endothelial and medial damage was performed. We adopted a previously published (25) endothelial and medial damage grading scale for this study (Table 2). The most proximal and distal 2 cm of iliac arteries were excluded to avoid ligature sites and the site of extended Fogarty balloon inflation at the location of the occluding balloons.



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  		Figure 3. Final pelvic arteriogram obtained after mechanical thrombectomy of the external iliac arteries (arrows) shows no angiographically evident vascular injuries.

 

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  		TABLE 2. Histologic Grades of Arterial Damage in the Device Groups
 
The pathologist (J.P.) was blinded as to which device was used with each vessel. The statistical differences in arterial damage grades among these three device groups were analyzed by using the Kruskal-Wallis and Nemenyi tests. The protocol was strictly designed to assess the degree of vascular damage. Distal embolization was not evaluated, and no preventative means were used.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
All iliac arterial diameters measured 5.5–6.0 mm. All vessels were successfully thrombosed with the method used. Each device successfully recanalized all vessels in which it was used and left no angiographically detectable residual thrombus within the segment that was studied. No vascular or intraluminal abnormalities, such as dissection of intimal flaps, were found at angiography.

At histologic examination, there were differences among the three devices (Table 2). The Fogarty embolectomy catheter produced a mean depth damage of 4.4 in the grading scale used, with approximately 80% of vessels in the grades IV and V. The Arrow-Trerotola device followed with a mean depth of 3.9. This corresponded to 80% of vessels in the grades III and IV. The Castañeda brush followed with a mean depth damage of 2.4. This corresponded to 90% of vessels in the grades I, II, and III.

There were statistically significant differences in the grades of arterial damage among the three device groups (P < .005). These are summarized in Table 3 and are as follows: further analysis showed that the difference between the Arrow-Trerotola device and Fogarty embolectomy catheter groups were not statistically different (P > .05). However, the differences in arterial damage grades between the Castañeda brush group and the Arrow-Trerotola device (P < .05) and Fogarty embolectomy catheter groups (P < .01) were statistically significant.


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  		TABLE 3. Comparison of Arterial Damage Grades in the Device Groups
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
All devices were equally effective in removing the thrombus from the treated iliac arteries. The protocol provided a standardized means of testing the different devices in thrombosed vessels as they are used clinically. All Fogarty embolectomies were performed by an experienced vascular surgeon (J.R.D.), who performs this procedure daily in patients, and the motorized mechanical thrombectomies were performed by experienced interventional radiologists (J.L.S., F.C.) who have performed hundreds of these clinical procedures. Mechanical spring scales or electronic transducers were not used because we believed that their use did not replicate the clinical setting. Within these parameters, the Castañeda brush caused significantly less damage when compared with the Arrow-Trerotola device and Fogarty embolectomy catheter.

Vascular wall injury associated with the use of the Fogarty embolectomy catheter has been studied extensively, both clinically and experimentally. The most cited study, which has resulted in several publications, is that of Jorgensen and Dobrin (5). This elegant laboratory experiment showed the correlation of the shear forces with the histologic injuries found in pristine carotid and iliac arteries. The study examined shear forces ranging from 30 to 200 g. The findings ranged from no appreciable intimal changes at 30 g, to severe intimal damage with fracturing of the internal elastoma lamina that persisted after 6 months. They estimated that an approximate shear force of 60 g corresponds to the usual clinical surgical experience. This amount of shear force would be expected to produce primarily minimal intimal injury. Contrary to this study, our study showed that, throughout the entire vessel, the depth of the lesions produced by the Fogarty embolectomy catheter extended into the tunica media, with 80% involving three-fourths of the whole depth of this layer.

Multiple clinical studies and case reports by experienced operators (3–11) showed that the findings of Jorgensen and Dobrin (5) might have caused under estimation of the damage caused by what was perceived as the usual clinical surgical experience. More recently, Dobrin (26), in referring to the previous study, expands on other possible variables—such as lateral wall pressure, catheter size, catheter manufacturer, catheter tip sharpness, balloon eccentricity, fluid- versus gas-filled balloons, syringe size, velocity of catheter motion, presence of blood in the vascular lumen, and inflating balloons at rest versus during catheter motion—all of which appear to play a role in the degree of vascular injuries. Furthermore, other experimental findings (9,27,28) corroborate our findings of substantial vessel wall injury with the Fogarty embolectomy catheter.

The Arrow-Trerotola device had a mean depth damage with a value of 3.9 in the scale used, and statistical analysis showed no difference in the amount of vessel wall injury seen with this device and with the Fogarty embolectomy catheter (P > .05). This correlates well with findings of a previous study (28) in which the Arrow-Trerotola device and Fogarty embolectomy catheter were compared in a rabbit model; venous injury was similar for both devices. Although the study was done in the inferior vena cava rather than an arterial vessel, the vascular damage compares well with the results of our study.

The Castañeda brush produced the least damage, with a mean of 2.4 on the scale used. When compared with the other two devices, the results were statistically significant (Table 3). Although it was the least damaging, vascular disruption still extended beyond the intima in all but two instances.

Studies (4,29) have shown that large areas of endothelial denudation without substantial medial trauma cause only mild intimal thickening, whereas focal endothelial denudation with substantial medial trauma produces marked intimal thickening. These results are also substantiated by those of other studies (30) that have shown that smooth muscle cells are normally quiescent with respect to proliferation but that deep injuries result in the expression of a proliferative phenotype of vascular smooth muscle cells that exhibits a high proliferative response to other mitogens. Although both motorized devices are approved for use only within synthetic hemodialysis grafts, there is always the potential for inadvertent protrusion into the native vascular segments close to the anastomotic regions. In this circumstance, endothelial damage can occur. If the conclusions of these studies are correct, there may be some benefit in using the least damaging device, even when mechanical thrombolysis in a synthetic graft is performed.

Practical application: There are noticeable differences in vascular endothelial damage with different wall-contact thrombectomy devices. Therefore, this should be taken into consideration in clinical use and might warrant further follow-up.


   FOOTNOTES
 
F.C. is a member of the medical advisory board of and has a royalty agreement with Micro Therapeutics.

Author contributions: Guarantor of integrity of entire study, F.C.; study concepts and design, F.C.; literature research, R.L.; experimental studies, F.C.; data acquisition, F.C.; data analysis/interpretation, J.P., F.C.; statistical analysis, R.L.; manuscript preparation, F.C.; manuscript definition of intellectual content, J.R.D., J.L.S., F.C.; manuscript editing, J.L.S.; manuscript revision/review, J.R.D., J.L.S.; manuscript final version approval, F.C.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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