Arthur B. Fontaine

Angiographic description of blunt traumatic injuries to the thoracic aorta with specific relevance to endograft repair.

Purpose: To describe the precise anatomical location and extent of injury (based on angiography) in a series of patients with blunt thoracic aortic injury (BTAI) and evaluate the findings relative to the potential for endograft repair. Methods: Thoracic aortograms from 50 trauma patients (37 men; mean age 37 years, range 13–87) with BTAI were retrospectively reviewed. Parameters important for endograft repair were recorded, including the length of the pseudoaneurysm, the distance between the origin of the most distal arch vessel and the pseudoaneurysm, the diameter of the aorta both above and below the pseudoaneurysm, and finally, the curvature of the aorta in the vicinity of the pseudoaneurysm. Results: The mean distance from the left subclavian artery to the superior aspect of the injury measured 5.8 mm along the lesser curve and 14.9 mm along the greater curve. The mean length of the injury was 17.0 mm and 26.0 mm along the lesser and greater curves, respectively. The mean aortic diameter adjacent to the injury measured 19.3 mm. The mean degree of curvature of the aorta over the length of the injury was 27.2°, with a mean radius of curvature of 32.6 mm at the superior aspect of the injury and 39.3 mm inferiorly. Conclusions: In most cases of BTAI, the location of the injury will necessitate covering the origin of the left subclavian artery if endovascular repair is to be performed. The curvature of the aorta in the region predisposed to these injuries requires that the endograft be very flexible and/or precurved.

Stent-induced Intimal Hyperplasia: Are There Fundamental Differences between Flexible and Rigid Stent Designs?

PURPOSE To evaluate possible differences in neointimal development resulting from overdilation of rigid versus flexible vascular stents. MATERIALS AND METHODS Twelve vascular sheaths were placed bilaterally through femoral arteries in six swine. After angiographic measurement, 12 stents (six flexible and six rigid) were balloon expanded to 8-mm diameters in 12 6-mm iliac arteries (approximately 30% overdilation). All stents were similar in surface area, gauge, and type of wire (tantalum). The primary difference was longitudinal flexibility (low hoop strength) versus rigidity (high hoop strength). Stents were studied with angiography and intravascular ultrasound 5 weeks after implantation. The animals were killed, and the stented segments were removed and examined histologically. RESULTS Rigid stents maintained larger diameters than flexible stents: mean, 6.52 mm versus 5.82 mm (mean difference, 0.70; standard deviation [SD], 0.47; confidence interval [CI], +/- 0.49; P < .05). In addition, rigid stents developed a thicker, eccentric neointimal reaction relative to flexible stents: mean 1.08 mm versus 0.74 mm (mean difference, 0.338; SD, 0.315; CI, +/- 0.331; P < .05). CONCLUSION Rigid stents maintain larger diameters over the long term relative to flexible stents when overdilated in normal swine arteries. However, a thicker neointima develops within the lumen of rigid stents at follow-up (greater late loss).

UPDATE ON THE USE OF PERCUTANEOUS NEPHROSTOMY/BALLOON DILATION FOR THE TREATMENT OF RENAL TRANSPLANT LEAK/OBSTRUCTION

PURPOSE Retrospective evaluation of the efficacy of percutaneous nephrostomy and nephroureteral stent placement for treatment of post-transplant ureteral leak, and percutaneous nephrostomy and balloon dilation for treatment of post-transplant ureteral obstruction. PATIENTS AND METHODS Data were reviewed for all patients who underwent percutaneous therapy for complications after renal transplantation between January 1985 and June 1995. A total of 61 patients with complications (leak, n = 17; obstruction, n = 44) had been treated. Patients underwent percutaneous nephrostomy followed by antegrade placement of a nephroureteral stent. In addition, all patients with obstruction also underwent ureteral balloon dilation. Follow-up ranged from 9 weeks to 24 months. Positive outcome was defined as nonsurgical closure of leak, significant improvement in renal function, and removal of the nephroureteral stent with maintenance of stable renal function. RESULTS Regarding ureteral leak, 10 of 17 patients (59%) healed after treatment. Seven patients (41%) did not respond and went on to surgical repair. All patients with early (n = 13) ureteral obstruction (< 3 months after transplantation), had improved renal function (P < .025). Sixty-two percent of patients with early obstruction were cured (tube out with stable renal function) and 38% went to surgery for ureteral repair. In patients with late (n = 31) obstruction (> 3 months after transplantation), renal function improved in only 58% (P < .01). Only 16% of patients with late obstruction were cured (tube out with stable renal function). Ureteral obstruction was persistent in the remaining patients and did not respond to multiple balloon dilations. All complications were minor and included 23 of 61 (38%) patients with urinary tract infections and nine of 61 (14%) patients with limited hematuria. CONCLUSION Percutaneous nephrostomy is very effective in improving renal function in patients with early obstruction. It is moderately successful in treating ureteral leak. Ureteral balloon dilatation is moderately effective for treatment of obstruction in the early (< 3 months) postoperative period. However, balloon dilation is minimally successful in curing ureteric obstruction occurring more than 3 months after transplantation.

Renal artery dissection causing renal infarction in otherwise healthy men

Arterial dissection is usually associated with pathological states such as malignant hypertension, severe atherosclerosis, severe trauma, Marfan syndrome, or Ehlers-Danlos syndrome. However, we report three cases in which renal artery dissection occurred in otherwise healthy, normotensive men. In two cases, the onset of symptoms of renal artery dissection was coincident with an unusual degree of physical activity. In the third case, the symptoms occurred while the patient was sitting but during a stressful business meeting. In each case, the patient experienced severe unilateral flank pain. Urolithiasis was suspected, but intravenous pyelography showed only ipsilateral impaired renal cortical perfusion, and the urinalyses showed no hematuria. The diagnosis of renal artery dissection was established by arteriography in two cases and by nephrectomy in one case. The latter case showed fibromuscular dysplasia by arteriography performed after the nephrectomy. The other two cases showed no evidence of fibromuscular dysplasia. We conclude that spontaneous renal artery dissection can occur in otherwise healthy individuals. Our experience and the reports of others indicate that this condition occurs mainly in men, conservative (nonsurgical) management is generally indicated, and the long-term prognosis is generally excellent. In some patients, an unusual degree of physical exertion might be the cause of renal artery dissection.

Polymeric Surface Modifications of Tantalum Stents

Purpose: To compare two kinds of polymer-coated tantalum stents with bare tantalum stents (control) to determine if the coatings can improve thromboresistance. Methods: Twenty-seven Fontaine-Dake stents were balloon expanded in three 8-mm × 80-cm.polytetrafluoroethylene (PTFE) grafts; 9 stents were bare tantalum (T); 9 were coated with polyetherurethane (PL); and 9 were coated with parylene (PA). There were 9 stents placed in each graft as follows: 3 tantalum, 3 polyetherurethane, and 3 parylene. In swine whose platelets had been radiolabeled with indium 111, the ends of each stented graft were connected to 14F femoral and venous sheaths to create an ex vivo fistula. Each graft was exposed to blood for 30, 60, and 120 minutes. At the end of each test period, the stented grafts were disconnected from the sheaths, flushed with saline until clear, and then flushed with formalin. The stents were removed from the grafts, and a radionuclide well counter recorded radionuclide counts from each stent type at each period of blood contact. These values were converted to platelet density per 1000 mUm2. Stents were then photographed and scanned with electron microscopy (EM) for qualitative analysis. Possible significant differences in platelet adhesion with the three types of stents (both between stent groups and within stent groups) were examined using a two-tailed Students f-test. Results: There were significantly fewer platelets adsorbed on PA versus T at all time periods (p < 0.005); on PL versus T at 60 and 120 minutes (p < 0.005); and on PA versus PL at 30 and 120 minutes (p < 0.0005). There was no significant difference in platelet density within each stent group (p = 0.1). Mean platelet density (number of platelets per 1000 mUm2 ± SD) was as follows: at 30 minutes: T = 1891 ± 965; PL = 373 ± 193; and PA = 27 ± 3; at 60 minutes: T = 6226 ± 1621; PL = 1573 ± 793; and PA = 1185 ± 710; at 120 minutes: T = 5307 ± 591; PL = 3164 ± 318; and PA = 180 ± 100. Gross inspection of the 120-minute groups demonstrated focal areas of thrombus on T, less on PL, and none on PA. Scanning EM demonstrated extensive platelet accumulation covering T at all time periods, less on PL, and even less on PA. Conclusions: Polymeric surface modification of tantalum stents with parylene and/or polyetherurethane can improve the acute thromboresistance of these devices; parylene appears to be the more thromboresistant of the two coatings.

Decreased Platelet Adherence of Polymer-coated Tantalum Stents☆

PURPOSE To compare the acute thrombogenicity of polyurethane-coated stents with that of bare tantalum stents. MATERIALS AND METHODS Thirty stents (15 coated with polyurethane) were balloon expanded in 8-mm x 80-cm sections of polytetrafluoroethylene grafts (six stents per graft). Under sterile conditions, 8- and 10-F vascular sheaths were placed percutaneously in the femoral artery and vein of a 100-lb (45-kg) swine. Platelets were labeled with indium-111 and reinjected for quantitative assay. The stented grafts were connected to the arterial and venous sheaths to create an ex vivo fistula. Each fistula was opened for 5, 10, 30, 60, or 120 minutes, exposing heparinized blood to fully expanded stents. The fistulas were closed, flushed with saline until clear, and fixed with formalin. Stents were explanted, placed in a radionuclide well counter, and scanned with electron microscopy. RESULTS Quantitatively, there were considerably fewer platelets on coated versus uncoated stents. At 60 minutes, coated stents averaged 12.93 platelets per 1,000 microns 2 compared with 75.88 platelets per 1,000 microns 2 for bare metallic stents. At 120 minutes, there were 23.22 platelets/1,000 microns 2 versus 102.31 platelets/1,000 microns 2, respectively. Electron microscopy of coated stents demonstrated few scattered platelets at 5, 10, and 30 minutes. There was a uniform layer of platelets at 60 and 120 minutes. Uncoated stents demonstrated random areas of platelet clumping at 5, 10, and 30 minutes. At 60 and 120 minutes, uncoated stents showed extensive layering of platelets and fibrin. CONCLUSION Polyurethane coating decreases platelet adhesion, relative to bare tantalum, at all time intervals tested.

Transcatheter arterial embolization for intractable epistaxis secondary to gunshot wounds.

PURPOSE To evaluate the efficacy of transcatheter arterial embolization for intractable epistaxis secondary to gunshot wounds. MATERIALS AND METHODS Seven patients with intractable epistaxis secondary to penetrating trauma (gunshot wounds) were studied with angiography and subsequently underwent embolization with particles (polyvinyl alcohol, gelatin sponge) and/or microcoils. Clinical follow-up included standard hemodynamic monitoring, serial hematocrit determinations, and clinical observation for recurrent bleeding. RESULTS Diagnostic angiography demonstrated evidence of acute arterial injury in all patients. All patients subsequently underwent embolization to complete angiographic stasis. Two patients had persistent bleeding following embolization. One of these patients required maintenance of his nasal packing for 7 days after embolization; no blood products were required during this time. The second patients bleeding resolved following correction of his coagulopathy. No complications occurred in any of the patients. CONCLUSIONS Transcatheter arterial embolization for epistaxis secondary to gunshot wounds is efficacious in the acute setting when conservative management fails.

Tantalum Balloon-expandable Stent: In Vivo Swine Studies

PURPOSE The authors describe the experimental use of a balloon-expandable tantalum vascular stent in normal and atherosclerotic microswine. MATERIALS AND METHODS Thirty-one stents (15 iliac, 13 aorta, two femoral, one renal) were placed in 11 animals. Stents were placed in both normal and stenotic atherosclerotic arteries. The animals were killed and the stents explanted 2-32 weeks after placement. Arteriography was performed just prior to death in all cases. RESULTS All stents were patent arteriographically and on gross inspection. Histopathologic study showed a thin, smooth, endothelial-lined neointima over the segments with stents. This covering had a mean thickness of 2.9 x 10(-5) mm and appeared maximally developed 2-5 weeks after stent placement. The stent design incorporates the following engineering and clinical considerations: minimal profile and surface area and maximal expansion ratio, hoop strength, flexibility, fluoroscopic visibility, biocompatibility, and ease of placement. When compressed and mounted on the balloon catheter, the stent is flexible. This allows it to be easily maneuvered through tortuous or diseased vessels. On expansion, the stent becomes a semirigid tubular structure composed of multiple rhomboid cells. Stents with an expanded diameter of less than 11 mm can be introduced through a 7-F vascular sheath. CONCLUSION Initial results suggest that this stent successfully incorporates a number of theoretically desirable features for a vascular prosthesis, and it may offer some advantages over previously described devices.

Prototype Stent: In Vivo Swine Studies in the Biliary System

PURPOSE To evaluate the safety of implantation and the biocompatibility of a new balloon-expandable stent in the biliary system of the swine model. MATERIALS AND METHODS Thirty stents, varying in diameter from 4 mm to 12 mm and in length from 2 cm to 6 cm, were placed in the bile ducts of 10 microswine. After implantation, one-third of the animal subjects were killed at 2 months and the rest, at 6 months. All animals underwent premorbid cholangiography. Stents were pressure fixed, harvested, and encased in methacrylate. Specimens were then sectioned with a diamond saw, prior to staining. Individual specimens were photographed for visualization of the histologic reaction. RESULTS Technical success (implantation) was 100%. All stents were widely patent at 2-month and 6-month follow-up. Histopathologic study demonstrated a very thin epithelial hyperplasia that formed between stent wires. This did not cover the stent wires. CONCLUSION This new stent is safely implantable and demonstrates minimal tissue reaction in the biliary system of the swine, when compared with other metallic biliary stents.

Use of polyetherurethane to improve the biocompatibility of vascular stents.

PURPOSE To investigate potential differential growth on neointima following overdilating arterial trauma with polyetherurethane-coated versus bare metallic stents in swine. METHODS Twelve specially constructed tantalum stents, 6 coated with polyetherurethane block copolymer and 6 uncoated, were overdilated by 25% in 12 normal renal arteries of six swine. The stents were harvested 8 weeks after implantation and prepared for histologic examination. Neointimal thickness was quantified and analyzed for significant differences between coated and uncoated prostheses. RESULTS All specimens demonstrated fractures of the internal elastic lamina consistent with vascular injury. There was significantly less neointimal formation (0.0001 < p < 0.05) in coated specimens as compared to uncoated controls in each test animal. CONCLUSIONS The vascular response to overdilating stent trauma appears to be moderated with the use of polyetherurethane block copolymer as compared to control.