Fallopian tube occlusion with use of a small intestine submucosa device: evaluation in a rabbit model.

PURPOSE: The present study evaluates the short- and midterm efficacy of a small intestinal submucosa (SIS) device for fallopian tube occlusion in rabbits. MATERIALS AND METHODS: In a pilot study, several SIS device designs were tested for positional stability (absence of migration). The design selected for further testing consisted of a center of spongy SIS surrounded by an SIS sheet and held together by a 0.006-inch wire helix with two barbs. It was delivered on the tip of a short coaxial 3-F/5-F catheter set. Using this design, bilateral transuterine fallopian tube occlusion was performed in eight New Zealand White rabbits. Follow-up consisted of plain radiography at 2 weeks and hysterosalpingography at 6 weeks (n = 4 animals; eight tubes), 12 weeks (n = 2 animals; four tubes), or 24 weeks (n = 2 animals; four tubes). Thereafter, the animals were killed and the fallopian tubes were harvested for histologic evaluation. RESULTS: A single device was placed successfully in each fallopian tube. Fifteen of 16 devices (94%) remained in place throughout follow-up. One device migrated into the vagina at 2-week follow-up. Hysterosalpingography of the 15 tubes with occluders in place showed occlusion in seven of seven (100%) at 6 weeks, three of four (75%) at 12 weeks, and two of four (50%) at 24 weeks. Histologic evaluation revealed luminal occlusion by reorganized SIS containing macrophages, fibrocytes, and scant foreign-body giant cells. Only a mild inflammatory reaction was observed around the tube. In the animals with recanalization at 12 and 24 weeks, new channels were found alongside the original still-occluded fallopian tube lumen. CONCLUSIONS: The original lumen of the fallopian tube was effectively occluded by the SIS occluder, which was remodeled within the fallopian tubes of rabbits. Partial peripheral recanalization was observed over time.

Digital subtraction fluoroscopy to enhance visualization during uterine fibroid embolization.

We describe a simple but underutilized technique for improving visualization during transcatheter embolization using particulate agents. The technique is of distinct utility in uterine fibroid embolization, during which non-target embolization can be of particular clinical significance.

A canine model for studying endoleak after endovascular aneurysm repair.

PURPOSE: The aim of this study was to create an animal model of endoleak after stent-graft placement for abdominal aortic aneurysm (AAA) in which a large aneurysmal sac would be preserved for the testing of techniques for its percutaneous occlusion. MATERIALS AND METHODS: Infrarenal AAAs were created in nine dogs by anastomosis of an isolated segment of the inferior vena cava to the right side of the abdominal aorta in combination with a large anterior patch from the external jugular vein. One hour later, animals underwent percutaneous implantation of polytetrafluoroethylene-covered Z stent endografts with three 3-mm-diameter holes through the fabric. Aortograms were obtained before and after surgery, after endograft placement, and at the time of animal sacrifice at 1 week or 1, 2, 3, or 6 months. Pressures within the aorta and the aneurysm sac were recorded before animal sacrifice. Gross and histologic evaluations of the specimens were then carried out. RESULTS: Immediately after endograft placement, all nine animals had artificial type III endoleaks with angiographic filling of lumbar arteries and veins. One animal died of surgical complications within 2 days of surgery and is not included in our data analysis. One aneurysm ruptured at 1 week. At completion of the study, six endografts were patent and two were occluded. The aneurysm sac had enlarged by approximately 50% in seven animals. At follow-up, type I endoleak was present in three animals, type II endoleak was present in three, and the artificial type III endoleak was present in all six animals with patent endografts. The pressure differential between aorta and aneurysm sac was 36 mm Hg, with a mean aortic pressure of 87 mm Hg +/- 13.3 and a mean aneurysmal sac pressure of 51 mm Hg +/- 28.1. The aneurysmal sac exhibited early thrombus formation at 1 week, which progressed to complete thrombosis in 1-6 months. CONCLUSIONS: The model is technically feasible but would be useful in testing occlusive techniques for residual aneurysm sacs only in the acute phase after endograft placement. It would be not reliable for chronic evaluation because of rapidly progressive thrombosis in most aneurysm sacs and occasional complete thrombosis of the AAA and endograft.

Relative rates of blood flow reduction during transcatheter arterial embolization with tris-acryl gelatin microspheres or polyvinyl alcohol: quantitative comparison in a swine model.

PURPOSE: To determine whether two commonly used embolic agents have differing rates of blood flow reduction during transcatheter embolization of the renal arteries in an animal model. MATERIALS AND METHODS: The renal arteries of 10 pigs were embolized with either polyvinyl alcohol (300-500 or 500-700- micro m) or tris-acryl gelatin microspheres (300-500 or 700-900- micro m). Equivalent unit doses of each agent were suspended in 40 mL of fluid and injected in 1-mL aliquots for 20 mL and then in 5-mL aliquots for 20 mL. Blood flow was measured after each aliquot with an intraarterial Doppler flow wire placed through the embolization catheter. RESULTS: Renal arterial blood flow was most rapidly and reliably decreased by 300-500- and 700-900- micro m microspheres, both of which had achieved >90% reduction from baseline flow after the injection of 6 mL of suspension. An equivalent reduction in flow required 25 mL of 300-500- micro m PVA suspension and 30 mL of 500-700- micro m PVA suspension. The reduction in blood flow with microspheres was significantly greater (P <.05) than that with PVA between 5 and 19 mL of suspension delivered. Differences between larger and smaller particle sizes of the same agent were not statistically significant. CONCLUSIONS: Tris-acryl gelatin microspheres reduced renal blood flow more quickly and reliably than did PVA. The type of agent used in embolization had a greater impact on the rate of flow reduction than did particle size in the range of sizes tested.

An evaluation of commonly employed central venous catheter kits and their potential risk for complications of excess guidewire introduction.

STUDY OBJECTIVE: To evaluate the components of commonly used central venous catheter kits with respect to the potential for guidewire-mediated complications during catheter placement.Prospective, nonrandomized, observational study. SETTING: Six academic hospitals across the United States. PATIENTS: None. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: 30 commercially manufactured catheter kits (15 tunneled, 15 nontunneled) were opened and evaluated. The catheter or sheath to be introduced was measured and a corresponding ideal guidewire length was calculated. The ideal length was then compared to the actual length, and differences were tabulated. Wire tip configuration and the presence and pattern of distance markings were recorded and, in conjunction with the catheter and wire length discrepancies, were used to grade the relative risk of introducing excess guidewire during catheter placement. Of 30 kits evaluated, 14 (46.7%) had guidewires more than 20 cm longer than necessary. The mean excess wire length was 15 cm (range: 8 to 55 cm) and did not differ significantly between tunneled and nontunneled catheter kits. Only 10 kits (33.3%) had distance markings of any type, and there was no standardization among them; none corresponded to previously published recommendations. There was potential risk of excess wire introduction in 18 catheter kits, of which seven were nontunneled devices designed for bedside placement. CONCLUSIONS: The design of commonly employed central venous access catheter kits is such that there is a mismatch between guidewire and catheter length and a general lack of guidewire markings. We believe that these designs may predispose to the introduction of excess guidewire and result in guidewire-mediated complications during catheter placement. This risk can likely be reduced by matching the guidewires to the devices placed over them and by standardizing guidewire distance markings.

I. Uterine fibroid embolization: preprocedure assessment.

Increasing clinical experience with uterine fibroid embolization (UFE) has improved the ability of interventionalist radiologists to discern who is and who is not an appropriate candidate for this procedure. Initial evaluation should be directed at obtaining answers to the following key questions: (1) Does the patient have uterine fibroids that account for her symptoms and are they severe enough to require invasive treatment? (2) Does she desire future childbearing? (3) Are there any clinical indications or imaging signs of uterine malignancy? (4) Are there any medical or anatomic features that would favor a particular therapeutic modality? (5) What are her own preferences regarding treatment? Ultrasound and magnetic resonance imaging are vital elements to the assessment and planning of the appropriate course of action. Given the lack of prospective comparative trials between UFE and surgical treatment, recommendations are often highly influenced by patient preference.

II. Uterine fibroid embolization: technical aspects.

Successful superselective catheterization of the uterine artery requires familiarity with female pelvic arterial anatomy, knowledge of effective catheter and guidewire combinations, and a few tricks. A learning curve can be expected for each of these elements, although it is assumed that the operator will already have experience in basic catheter techniques. Safe transcatheter delivery, understanding of embolization end points, and avoidance of nontarget embolization are essential. Equally important are knowledge of the properties of the embolic agents currently available and their indications for use. Uterine fibroid embolization unavoidably results in radiation exposure to the uterus and ovaries, and adherence to meticulous fluoroscopic technique is crucial to keep the absorbed dose as low as possible.

V. Uterine fibroid embolization: management of complications.

Fortunately, the number of complications reported after uterine fibroid embolization (UFE) is extremely low. Angiographic mishap or drug reaction are probably more common than purely UFE-related complications. However, the possibility of infection or necrosis of the uterus, with their significant attendant morbidity, is a sobering reminder that embolotherapy can have a powerful impact on the target organ(s). Knowledge of the expected time course for symptom resolution and the often confusing imaging findings shortly after UFE are critical for avoiding unnecessary delay in surgical intervention or, perhaps more important, an inappropriate rush to surgery when antibiotics alone will suffice. Other complications include alteration of uterine physiology, which may disrupt sexual function, and menstrual irregularity and even premature menopause.

III. Uterine fibroid embolization: pain management.

Conscious sedation and analgesia are integral components of successful uterine fibroid embolization (UFE), both in providing comfort to the anxious patient undergoing an elective procedure and for providing relief of the severe pelvic pain, cramps, and nausea that may result from acute uterine ischemia and the postembolization syndrome that may follow. The agents used are typically those with which interventional radiologists already have extensive experience in the performance of a variety of invasive procedures. Immediate postprocedure care benefits greatly from the use of narcotic delivered via PCA (patient-controlled analgesia) pump. Nonsteroidal anti-inflammatory drugs (NSAIDs) are also particularly useful for treating the pain and cramping caused by UFE and help reduce the amount of narcotic necessary for pain relief during the recovery period. Detailed instructions for the first week of convalescence are necessary to insure comfort and avoid complications.

VI. Uterine fibroid embolization: developing a clinical service.

Building a uterine fibroid embolization (UFE) practice can be a complex process. Choices must be made regarding whether to align oneself with a gynecologist or to accept direct referrals. For the interventional radiologist, the responsibilities of evaluation and patient care pose unique and time-consuming administrative and clinical challenges. Physician extenders, either nurse practitioners or physician's assistants, play key roles as clinical coordinators by guiding the patient through the medical system and making certain that she is cleared for the procedure medically and logistically. In some settings, they may also assist in many of the technical aspects of the procedure and postoperative care. Interventional radiologists must be prepared for battles with insurance companies and be willing to go through the appeals process. Business officers must also be trained to properly code for the procedures to insure optimal reimbursement. The success of building a UFE practice may also be bolstered by directly marketing to patients and by providing them with access via the Internet.

Lack of suitability of the rabbit model for particulate uterine artery embolization.

PURPOSE: The goal of this study was to evaluate the rabbit model for studies of particulate uterine artery embolization (UAE). Rabbits were chosen because it was believed that their year-round breeding time and short duration of pregnancy would be useful in studies of fertility and pregnancy after UAE. MATERIALS AND METHODS: Bilateral UAE was performed in 12 adult female New Zealand White rabbits weighing 4-5.2 kg. All animals were proven to be breeders before treatment. Each uterine artery was embolized to stasis with use of 180-300- microm polyvinyl alcohol (PVA) particles (n = 9 animals), 500-710- microm PVA particles (n = 1), or tris-acryl 500-700- microm gelatin microspheres (n = 2). RESULTS: Two rabbits died 7 days after embolization and the other 10 rabbits had to be killed because of malaise and weight loss 4-8 d after embolization. In all animals, necropsy demonstrated extensive uterine necrosis sparing only the tip of the uterine horn. CONCLUSION: Rabbits are an unsuitable model for studies of UAE with the embolic agents in clinical use.