Changes in arterial wall compliance after endovascular stenting

PURPOSE

The response of arterial wall to endovascular stenting after angioplasty is not well understood. Additionally, changes in the elastic properties of stented vessels are unknown in situ. Vascular compliance was measured in normal canine iliac arteries (n = 11) before and after intravascular ultrasound-guided deployment of self-expandable metallic stents.

METHODS

Nine animals were restudied and killed 1, 2, and 4 weeks after initial deployment, and two dogs were studied at deployment only. An absolute induction angiometer was used to make in situ measurements of vessel compliance via catheter-based delivery. The angiometer consists of a wire loop probe, which conforms to the diameter of the vessel in which it is placed. Systolic/diastolic changes in loop diameter are translated into measureable changes of induced voltage.

RESULTS

Mean compliance of the artery before and immediately after stenting was 4.4 +/- 2.1 and 1.9 +/- 2.0 (x 10(-2) diameter %/mm Hg), respectively. As early as 1 week after deployment, stented arteries began to lose expansile properties, and some were noncompliant. At explantation diminished compliance was accompanied by a periadventitial fibrous reaction around stented vessels. A thin, unobstructing layer of neointimal hyperplasia covered the iliac stents at all intervals, and all vessels remained patent and free of thrombus.

CONCLUSIONS

The potential advantages provided by a flexible, radially compliant stent are lost within a relatively short time after implantation in nonatherosclerotic canine arteries.

Eccentric iliac artery stenosis: a canine model for angioplasty

A canine model was developed to induce eccentric iliac artery stenosis. Lesions were induced by exposing the medial aspect of the right and left common iliac arteries in four animals to direct argon laser energy (LA). A 2.5-mm diameter side-firing laser probe was used to deliver 10 W of power in 5-s intervals. Twenty-five pulses were delivered over a 5-cm length of artery with an approximate spot size of 0.8 mm2. Selected arteries (n = 2, LA + Ca) were injected in the same laser injury site with calcium chloride (10% solution). Injections were accurately accomplished using an angioscopically guided guidewire/needle device. In all cases, the internal elastic lamina was broken with focal disruptions of the media. At 9 and 14 days, the LA (n = 3) and LA + Ca vessels (n = 1) had minimal stenoses (< 5% area reduction). These vessels contained edematous media with replacement of necrotic smooth muscle by fibrous tissue. At 23 days, the LA (n = 1) and LA + Ca (n = 1) vessels contained 22% and 33% luminal reductions, respectively, with moderate neointimal proliferation and no evidence of calcification. At 56 days the LA vessels (n = 2) contained 30 and 42% luminal area stenoses with marked neointimal hyperplasia. This preliminary data suggests that controlled arterial wall injury with LA irradiation can induce eccentric fibrointimal lesions in a canine model.

Laser-fused biologic vascular graft anastomoses

Tissue fusion using laser energy is a promising new technology that may improve the healing of anastomoses. This study evaluated the feasibility of using argon laser energy to fuse vascular tissue and biologic vascular prostheses (St. Jude Medical, Inc.) in a canine arteriovenous (A-V) fistula model. Five animals had 4-cm length, 3-mm internal diameter grafts (n; eq 10) placed bilaterally as side-to-side A-V interpositions from the femoral artery to femoral vein. One A-V graft was placed using argon laser energy with the vessel edges aligned by 6-0 polypropylene traction sutures at 3 to 4 mm intervals. The contralateral graft was sutured using running 6-0 polypropylene suture. Anastomoses were successfully fashioned in all animals except for episodes of delayed bleeding at two laser-fused segments (15 min and 2 hrs) and one segment in a suture control (6 days). The implants were removed to evaluate the integrity and healing of the anastomoses at 2 hrs, 8 days, and at 7, 9, and 11 weeks. In all instances, there was no evidence of anastomotic dehissance or enlargement. Histologic examination of the anastomoses revealed coapted vessel and prosthetic edges in laser-fused specimens and a limited foreign-body response to the permanent sutures in the suture controls. In the longer term specimens there was marked intimal proliferation at the venous anastomosis in all implants, with recent bilateral occlusions of the 7 and 11 week implants at the venous connection. We conclude that laser fusion of biologic vascular prostheses to autogenous vessel is possible with healing and no evidence of anastomotic dehissance.(ABSTRACT TRUNCATED AT 250 WORDS)

A canine iliac artery occlusion model

This report describes an occlusive canine iliac artery model for use in experimental angioplasty procedures. Lesions were induced by overdistending and breaking the internal elastic lamina of the artery and implanting a 2-cm long occlusive collagen plug. The collagen plug diameter was varied to fit the iliac artery and caused immediate bilateral iliac occlusions. Histology of the lesions at 9 and 14 days (n = 2) showed that the lumen was filled with a mixture of fresh thrombus and collagen pad material (more collagen than thrombus) with focal disruptions of the internal elastic lamina. At 36 days (n = 2) the lumen was obliterated with a mixture of organizing thrombus and collagen pad material (more organizing thrombus than collagen). At 60 (n = 4) and 80 (n = 8) days the collagen pad had been completely replaced with organizing thrombus consisting of collagen fibers and hemosiderin-laden macrophages with persistent focal disruptions of the internal elastic lamina. These initial data demonstrate the ability to create fibrotic arterial occlusions in as short a time as 60 days and to provide a practical model to study methods for treating localized peripheral vascular occlusive disease.

Percutaneous laser discectomy

Percutaneous discectomy, for treatment of lumbar disc herniation, was first described in 1975 by Hijikta. Since its inception, a variety of instruments including rongeurs, augers, automated mechanical devices, and more recently, lasers have been developed to remove tissue from the herniated disc. The advantages of lasers include miniaturized, safe, and efficient energy delivery for percutaneous tissue removal. This article reviews the development of lasers for percutaneous discectomy.

Holmium:YAG laser ablation of human intervertebral disc: preliminary evaluation

Percutaneous discetomy has become a viable alternative in the treatment of herniated intervertebral disc. This study determined the effectiveness of holmium: YAG laser for ablation of human disc tissue. Human cadaveric intervertebral disc was harvested and stored in cold saline-soaked gauze for evaluation within 24 hr of removal. Using a specially designed apparatus, a 600 microns diameter fiber was advanced perpendicular through the annulus fibrosis at a controlled force of 0.098 Newtons (10 g). Samples were lased in air (n = 17) and in room temperature saline (n = 32). The laser energy was delivered at 5 Hz, 250 microseconds pulsewidth, and from 50 mJ/mm2 to 1,100 mJ/mm2 fluence. Three to six holes were lased using identical parameters in each tissue specimen and were evaluated histologically and by morphometric analysis. The maximum zone of thermal necrosis and thermal denaturation occurred at 700-1,100 mJ/mm2; 140 microns and 590 microns in air and 80 microns and 730 microns in saline, respectively. At fluences between 200 and 700 mJ/mm2, the thermal necrosis ranged from 20 to 60 microns in air and from 10 to 50 microns in saline, the zone of denaturation also being less. The holes created with the 600 microns fiber were circular in shape, with a mean diameter of 500 microns (n = 3). The etch rates (penetration/pulse) appeared to increase with increasing fluences. In saline, the etch rate ranged from 7 to 53 microns/pulse (r = 0.57, P less than or equal to 0.10), and, in air, the values ranged from 7 to 65 microns/pulse (r = 0.79, P less than or equal to 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo human comparison of intravascular ultrasonography and angiography

This study evaluates the in vivo correlation of intravascular ultrasonography and uniplanar angiography in determining the luminal dimensions of normal and moderately atherosclerotic human arteries. Five French and 8F rotating A scan intravascular ultrasound catheters were used to obtain 48 images in four superficial femoral arteries, five iliac arteries, and one aorta in eight patients undergoing vascular surgery. Cross-sectional areas measured by intravascular ultrasonography were compared to cross-sectional areas calculated by uniplanar angiography of the same location in the vessel. Maximum and minimum luminal diameters were also measured from intravascular ultrasound images. An ellipticity index was defined as the maximum/minimum diameter ratio (max/min) and ranged from 1.0 to 1.8 (mean, 1.2). Comparison of the cross-sectional areas measured from intravascular ultrasound images and those calculated from uniplanar angiography showed no significant difference at any level of ellipticity studied. However, when the values of cross-sectional areas were analyzed in groups corresponding to the diameter of the vessel, that is, aortic, iliac, and femoral, the values for the iliac arteries calculated from uniplanar angiography were significantly greater by 9.8% +/- 0.7% (n = 29, p = 0.03) when compared to those measured by intravascular ultrasonography. In addition to providing accurate luminal determinations, intravascular ultrasound images displayed transmural morphology, the location and character of the atherosclerotic lesions, and the thickness of the vessel wall. We conclude that intravascular ultrasound imaging provides accurate, novel information regarding human vessels and that this technology may play a significant role in future diagnostic and interventional therapies.

Duplex ultrasound diagnosis of lower limb deep venous thrombosis

To compare a non-invasive technique with contrast venography in the diagnosis of lower limb deep venous thrombosis (DVT), 355 patients (380 limbs) were examined over 15 months, using Duplex ultrasound. During this period, ascending venograms were performed in 53 of these patients (56 limbs) and the results were compared. Duplex detection of intraluminal thrombus was based on venous compressibility, Doppler-derived flow spectra, and visualization of thrombus within the lumen. Venography was designated the 'gold standard'. Duplex scanning had a sensitivity of 90.9%, and specificity of 91.3% in diagnosing DVT anywhere in the lower limb. Sensitivity, specificity, and accuracy were best in the femoral segment (95.2%, 100%, 98.2%, respectively), and fell slightly in the more distal limb: popliteal segment (90.4%, 97.1% and 94.6%), and calf veins (88.8%, 92.0% and 90.4%). These results indicate that duplex scanning produces sufficiently accurate data in the diagnosis of lower limb DVT to warrant its clinical use. It provides both the facility for diagnosis without the risks of contrast venography, and permits repeated imaging to follow the immediate progression of disease and efficacy of treatment.

Results of early excision and grafting in hand burns

A total of 658 admissions to the Burns Unit at the Royal Brisbane Hospital were reviewed over a 4-year period. During this time, 73 hand burns were treated. The policies of the Burns Unit regarding hand burns are detailed; and, where possible, early excision and grafting is performed. The results of these hand burns are discussed and indicate minimal requirements for reconstructive surgery. The most common reconstructive surgery needed was for web space release in 10 patients and excision of hypertrophic scar in 2 patients. It is concluded that early excision and grafting of hand burns is safe and practical, and combined with adequate splinting, exercise and pressure garments, gives good results and lessens hospital stay in patients with relatively small injuries. The duration of stay in hospital in patients with large burns is not due to the treatment of their hand burns, but to their overall large body surface area burnt.