In vitro comparison of the spiral Z stent and the Gianturco Z stent

Chronic Venous Disease of the Lower Extremities: A State-of-the Art Review

Chronic venous disease is a common disease, the prevalence of which increases with age, and can cause debilitating symptoms that adversely affect the quality of life. The risk factors include family history, female sex, obesity, pregnancy, parity, and history of deep vein thrombosis. Moreover, it is associated with venous obstruction, reflux, or both, which, in turn, leads to ambulatory venous hypertension. Chronic venous disease is the leading cause of leg ulcers, which place a significant cost burden on the health care system. Compression therapy remains the cornerstone of treatment, particularly for more advanced disease. Superficial saphenous vein reflux can be associated with significant symptoms. Catheter techniques, both thermal and nonthermal, have demonstrated efficacy and safety in successful closure and symptom improvement. Deep vein obstruction can be broadly divided into thrombotic and nonthrombotic and can lead to symptomatic chronic venous disease. Recanalization using balloons and stents has been increasingly used and studied in such patients. It is critical to develop training opportunities and guidelines to improve evidence-based and appropriate care for cardiologists treating chronic venous disease.

Follow-up Results of 71 Patients Undergoing Metallic Stent Placement for the Treatment of a Malignant Obstruction of the Superior Vena Cava

PURPOSE

To retrospectively clarify the utility of metallic stent placement for the treatment of the malignant obstruction of the superior vena cava (SVC) in 71 patients with VC syndrome (SVCS) on the basis of long-term follow-up data.

MATERIALS AND METHODS

Seventy-one patients underwent stent placement and were followed until death. The applicability of the spiral Z-stent (S-Z-stent) mainly used the initial and follow-up results, stent placement for bilateral BCV obstruction and the value of concurrent anticancer therapy were studied.

RESULTS

The technical success rate was 100%, the initial clinical success rate was 87% (62/71), the primary clinical patency rate was 88% (57/65), and the secondary clinical patency rate was 95% (62/65). The obstruction rate of the stent was 12% (8/65), and an additional stent was useful for relief of recurrent SVCS. Survival of 57 patients in whom there was no recurrence of SVCS until death ranged from 1 week to 29 months (mean, 5.4 months and the S-Z-stent appeared to be suitable for the treatment of the malignant obstruction of SVC. Unilateral stent placement was effective for relief of SVCS with bilateral BCV obstruction. Patients who received concurrent anticancer therapy survived 2 months longer than those who did not.

CONCLUSION

Stent placement is an effective treatment for SVCS. Further, the utility of S-Z-stent for SVCS, an additional stent for recurrence, unilateral stent for patients with bilateral BCV obstruction, and anticancer therapy after stent placement were verified.

Infrarenal Abdominal Aortic Aneurysm Complicated by Persistent Endotension After Endovascular Repair: Report of a Case

Endoleak and endotension may prevent the successful exclusion of an aneurysm after endovascular aortic aneurysm repair (EVAR). The pressurization in the excluded aneurysm sac caused by endotension may lead to rupture of the aneurysm; however, the cause of endotension and its underlying mechanisms remain unclear. We report a case of infrarenal abdominal aortic aneurysm (AAA) complicated by persistent endotension after EVAR. Although no endoleaks were found on conventional double-phase computed tomographic scans, a thrombosed endoleak existed in the side branch and attachment site of the endograft. After treating the undetectable thrombosed endoleaks, physical examination revealed that the pressure of the excluded aneurysm had diminished, with shrinkage of the aneurysm. This case report suggests that a high-pressure undetectable type I or type II endoleak could be a major cause of endotension. Thus, postoperative evaluation of the attachment site of an endograft is important after EVAR.

Mechanical properties of various z-stent designs: an endovascular stent-grafting perspective

PURPOSE

To comparatively assess the mechani-cal behavior of various clinically relevant Z-stent designs.

METHODS

A total of 16 Z-stents of original, biliary, spiral, and double-skirted designs (n=4 for each) were constructed using similar specifications for all. Stents were then evaluated for stiffness, snap opening force (SOF), flexibility, and displacement force using a novel tensiometer. Differences among the stents were determined using statistical methods. Stents explanted from dog aorta after a mean follow-up of 13 months were examined under a scanning electron microscope for surface defects.

RESULTS

Forces required for about 50% reduction in diameter were 1.88 +/- 0.16 N, 3.81 +/- 0.21 N, 2.76 +/- 0.22 N, and 3.35 +/- 0.19 N for original, biliary, spiral, and skirted designs, respectively. Differences among the four designs were statistically significant at almost all points of measurement (P < 0.0001). Biliary and skirted designs showed higher SOF values in the early measurements. Stents explanted from dog aorta after a mean duration of 13 months showed no obvious corrosion or breakage in the wire struts.

CONCLUSIONS

Significant differences exist among the various Z-stent designs in terms of their mechanical properties. Understanding them should help to select the appropriate stent for a given lesion. 316L stainless steel shows a favorable long-term tissue interaction.

Aortic stent-grafting with transrenal fixation: use of newly designed spiral Z-stent endograft

PURPOSE

To evaluate the feasibility and efficacy of a newly designed stent-graft placed across the renal arteries for exclusion of abdominal aortic aneurysms (AAAs) with short or tortuous proximal necks.

METHODS

Among a group of AAA patients treated with endovascular grafting, 5 had tortuous proximal necks and 13 had necks <20 mm (mean 13 mm). In these 18 cases, a 2- to 3-cm uncovered segment of the stent-graft was placed transrenally using a catheter inserted into the renal artery as a guide for graft margin positioning. A newly designed stent-graft was constructed from a custom-made spiral Z-stent covered with a thin-walled Dacron material; the endografts were deployed through 16-F (aortoaortic model) or 18-F sheaths (bifurcated devices). Renal function was assessed by preoperative and postoperative measurement of urea nitrogen and creatinine. Aneurysm exclusion and renal artery patency were evaluated during follow-up using spiral computed tomography and angiography.

RESULTS

The stent-grafts were correctly placed at the intended site in all 18 patients. Renal function was not affected except transiently in 1 patient who developed bilateral renal artery stenoses 24 hours after the procedure; Palmaz stents were deployed in each renal artery to reestablish satisfactory blood flow. Of the 33 renal arteries crossed by the bare stent-graft segment, all were patent over a mean 14-month follow-up (range 7-24), including the patient with Palmaz stents implanted for postprocedural renal stenosis. Complete aneurysm exclusion was maintained in 15 (83%) of 18 patients; proximal leaks persisted in 3 patients, including 2 with severely angled proximal necks.

CONCLUSIONS

Transrenal placement of the uncovered leading edge of custom-made spiral Z-stent-based endografts appears feasible and clinically effective in the treatment of AAAs with short or tortuous proximal necks.

Stent longitudinal flexibility: a comparison of 13 stent designs before and after balloon expansion

Longitudinal flexibility is an important property of coronary stents, facilitating delivery and allowing the expanded stent to conform to vessel contour. Subjective descriptions of flexibility abound, but there are few independent quantitative data to aid stent selection. A three-point bend test was employed to measure stiffness, the reciprocal of flexibility, for 13 stent designs in the unexpanded (bare) state, then after expansion with a 3.5-mm balloon. For eight of the designs, stiffness of the proprietary stent/balloon delivery system was also measured. In the unexpanded state, there was a wide spread of stiffness, which ranged from 0.5+/-0.2 to 91.5+/-10.0 g force/mm, depending on design. Stiffness was least for the coil (Wiktor and Crossflex) and hybrid (AVE GFX and Bard XT) designs. The MultiLink was the most flexible and the Crown the stiffest of the slotted tube designs. All stents became stiffer upon expansion. For most manufacturer-mounted stents, the delivery balloon was the main determinant of stent/balloon delivery system stiffness. Manufacturer-mounted stent profile ranged from 1.15+/-0.11 mm for the Jostent to 1.53 +/- 0.05 mm for the MultiLink system. Independent quantitative assessment of characteristics such as flexibility and profile should aid rational comparison of stent designs.

CT appearance of implanted esophageal stents

Three different types of esophageal stents, the Z-stent, Ultraflex, and Wall-stent, exhibit different shapes on CT, which may suggest a difference in the radial forces applied by each of the stents. CT is useful for displaying the relationship between an esophageal stent and adjacent structures and complications.

Long-term results of treatment of benign central venous obstructions unrelated to dialysis with expandable Z stents

PURPOSE

To evaluate long-term patency of self-expanding Z stents for treatment of benign central venous obstructions unrelated to dialysis.

MATERIALS AND METHODS

Z stents were placed in 19 patients, (ages 26-72 years) with severe symptomatic obstructions of the superior or inferior venae cavae and their large branches and portal vein caused by surgical or catheter injury (n = 8), fibrosis (n = 5), cirrhosis (n = 3), Budd-Chiari syndrome (n = 2), and extrinsic compression (n = 1). Fourteen patients underwent stent placement primarily, five after local urokinase infusion for superimposed thrombosis. Follow-up was performed with ultrasound and venography.

RESULTS

Venous congestive symptoms quickly resolved in all patients after stent placement. The follow-up period was from 1 to 94 months. Twelve patients have died during follow-up from 1 to 37 months although all remained asymptomatic until death. Six patients remain alive, asymptomatic, with patent stents, and with follow-up from 24 to 94 months. Primary patency was 83%, and secondary patency was 100%. One patient with a patent stent at 12 months was lost to follow-up. No stent migrations, perforations, infections, or significant complications occurred.

CONCLUSION

Benign central venous obstructions are effectively treated by the placement of self-expandable Z stents. Placed percutaneously into obstructive lesions with a minimum risk, these stents offer long-term durability and patency.

Effect of antithrombotic agents on the patency of PTFE-covered stents in the inferior vena cava: an experimental study

PURPOSE

To evaluate the efficacy of antithrombotic agents in the prevention of stenosis of polytetrafluoroethylene (PTFE)-covered stents in the venous system.

METHODS

Spiral Z stents covered with PTFE (PTFE-covered stents) were placed in the inferior vena cava (IVC) of 34 dogs. Nineteen dogs, used as a control group, were sacrificed at 2, 4, and 12 weeks. Fifteen dogs, previously given antithrombotic agents [cilostazol (n = 5), warfarin potassium (n = 5), cilostazol plus warfarin potassium (n = 5)] were sacrificed at 4 weeks, and then examined angiographically and histopathologically. The effect of the antithrombotic agents was compared between groups.

RESULTS

The patency rate of the antithrombotic agent group was 93% (14/15), which was higher than the control group rate of 63% (12/19). The mean stenosis rate of the patent stent at both ends and at the midportion was lower at 4 weeks in the antithrombotic agent group than in the control group. In particular, the mean stenosis rate in the cilostazol plus warfarin potassium group was significantly lower than the control group (Tukey's test, p < 0.05). The mean neointimal thickness of the patent stent at both ends and at the midportion was thinner at 4 weeks in the antithrombotic agent group than in the control group. In particular, the thickness of the neointima in the cilostazol plus warfarin potassium group was significantly decreased when compared with the control group (Tukey's test p < 0.05). At 4 weeks, endothelialization in the antithrombotic agent group tended to be almost identical to that in the control group.

CONCLUSION

The present study suggests that administration of an antithrombotic agent is an effective way of preventing the stenosis induced by a neointimal thickening of PTFE-covered stents in the venous system.

Covered gianturco stents for malignant biliary obstruction: preliminary clinical evaluation

PURPOSE

To evaluate the effectiveness of covered Gianturco stents in patients with malignant biliary obstruction.

MATERIALS AND METHODS

Three types of partially polyurethane-covered stents were implanted in 19 patients with malignant biliary obstruction located distal to the hilar confluence. A transhepatic approach was employed in all but one patient, in whom the stent was placed through a T-tube tract.

RESULTS

Stent placement was possible in all patients. In 15 patients, the implanted stents were expanded to a mean of 81% of their original diameter. In the remaining four patients, the stents expanded to less than 40% of the original diameter, and balloon dilation and additional bare stent placement were required. All patients except one, who had impairment of liver function due to multiple liver metastases, showed relief of jaundice after stent placement. At follow-up, which ranged from 5 to 57 weeks (mean, 24.7 weeks), one stent (5%) was occluded after 26 weeks due to tumor growth above the upper stent edge, and required secondary intervention. Complications in three patients included stent migration in one (5%) and cholangitis in two (11%).

CONCLUSION

Preliminary results suggest that placement of covered Gianturco stents is feasible, the complication rate is acceptable, and short-term patency appears promising.

Experimental TIPS with spiral Z-stents in swine with and without induced portal hypertension

PURPOSE

To assess the suitability of spiral Z-stents for transjugular intrahepatic portosystemic shunt (TIPS) and the influence of portal hypertension on shunt patency in young swine.

METHODS

TIPS were established using spiral Z-stents in 14 domestic swine. In 7 animals, the portal venous pressure was normal; in the other 7, acute portal hypertension was induced by embolization of portal vein branches. Follow-up portal venography and histologic evaluations were done from 1 hr to 12 weeks after TIPS.

RESULTS

Follow-up transhepatic portal venograms showed progressive narrowing of the shunt, most prominent in the midportion of the tract. Ingrowth of liver parenchyma between the stent wires found after 3 weeks led to progressive shunt narrowing and shunt occlusion by 12 weeks. A pseudointima grew rapidly inside the stent, peaked in thickness around 4 weeks, and decreased later. Acutely created portal hypertension rapidly returned to normal and there was no difference in TIPS patency between the two groups of animals.

CONCLUSION

Although the spiral Z-stent can be used as a device for creation of TIPS in patients with cirrhotic livers, it is associated with extensive liver ingrowth in swine that leads to rapid shunt occlusion. Portal hypertension was only transient in this model.

Noncoronary vascular stenting

The aim of this report is to review the current state of the art with respect to noncoronary vascular stenting. A review of the literature was performed, examining the historical aspects of stent design and usage, as well as the currently available designs and their respective functions. When appropriate, we note our personal experience with stent placement in each anatomic site. Currently available stents take many forms: balloon-expandable, self-expanding, and shape-memory alloy. Varied design modifications have been made to maximize the open area, to limit the surface area of the prosthesis, to increase (or decrease) flexibility, and to increase (or decrease) stent plasticity and elasticity. Modifications to minimize thrombogenicity are also underway. The clinical uses of the currently available stents in multiple anatomic locations will be discussed. Intravascular stents are an addition to the arsenal available for prolonging blood vessel patency.

Management of malignant tracheobronchial stenosis with metal stents and Dumon stents

BACKGROUND

Tracheobronchial stenosis caused by malignancy is a life- threatening problem. Stenting is one of the treatment modalities and recently has been used widely for the management of such stenosis, but we do not have a clear guide as to which stent should be selected.

METHODS

We evaluated 25 patients (19 men, 6 women; mean age, 60.7 years; range, 34 to 77 years) received 24 metal stents (four covered with silicone rubber) and three Dumon stents. All 25 patients had severe dyspnea because of airway stenosis caused by malignant tumors.

RESULTS

Among the 25 patients, airway obstruction due to extrinsic compression by tumor developed in 11 and was treated with a bare metal stent. The airway remained patent in 10 patients. In 16 patients with intraluminal tumor invasion, nine lesions were treated with a bare metal stent, four lesions with a covered metal stent, and the remaining three lesions with a Dumon stent. Recurrent stenosis did not occur in any patient with a covered metal stent or a Dumon stent. However, restenosis occurred in 4 patients with a bare metal stent, all of whom received laser therapy. In all patients, stenting immediately relieved dyspnea. Six patients lived for 32 days to 53 months after stenting, and 19 patients died of primary malignancies with a mean survival of 131.9 days.

CONCLUSIONS

Metal stents are effective in treating malignant extrinsic tracheobronchial compression. The use of covered metal stents or Dumon stents is preferable for intraluminal stenosis due to malignant growth.

New self-expandable spiral metallic stent: preliminary clinical evaluation in malignant biliary obstruction

PURPOSE

To describe a new self-expandable spiral-shaped metallic stent and to evaluate its clinical efficacy in malignant biliary obstructions.

PATIENTS AND METHODS

The stent was made of a 0.01-inch (0.25-mm) stainless steel wire bent in a zigzag pattern and was formed into a spiral configuration by differing the length of legs on each bend. One revolution was composed of 10 bends, and the stent was longitudinally connected by hanging each bending point of abutting bends, without use of suture or silver solder. Twenty-six stents were placed to relieve malignant biliary obstruction in 18 patients. Follow-up of 5-11 months (mean, 7 months) was obtained.

RESULTS

All stents were placed in the desired location, and no procedural complications were encountered. Within 1 week after placement, all stents regained 90% or more of their original diameters. Five patients died (range, 5-36 weeks), and 13 patients are still alive (range, 20-45 weeks). Two patients experienced recurrent jaundice and underwent further treatment. The stent was easily inserted, expanded well, was flexible, could be repositioned, and did not shorten.

CONCLUSION

Favorable clinical results were obtained with this spiral stent in malignant biliary obstruction, and further clinical testing is warranted.

Comparison of Gianturco Z stents and Wallstents in a hemodialysis access graft animal model

PURPOSE

To compare the primary patency of two structurally different metallic stents in an animal model of hemodialysis access grafts.

MATERIAL AND METHODS

Nineteen synthetic femorofemoral arteriovenous shunts were created in 10 dogs. After a 1-month period of maturation (during which one graft thrombosed), stents were placed spanning the venous anastomosis. The grafts were divided into two treatment groups (Wallstent, n = 6, and Gianturco stent, n = 6) and a control group with no stent (n = 6). Fistulograms and pressure measurements were obtained at monthly intervals for 6 months or until thrombosis of the graft.

RESULTS

Mean graft patency in the Wallstent group (112 days +/- 30) was significantly shorter than in the control (157 days +/- 32, P < .03) or Gianturco (157 days +/- 32, P < .05) groups. Patency in the Gianturco stent group was no different from that in the control group. Stenosis due to intimal hyperplasia within the stents appeared greater in the Wallstent group but did not achieve statistical significance. One Wallstent migration, three Gianturco stents shifts, and two Gianturco stent breakages occurred. Histologic examination revealed a necrotizing vasculitis in the portion of vein containing the stent in all grafts treated with the Gianturco stent but not in any other grafts.

CONCLUSION

In an animal model of hemodialysis access grafts, the Gianturco stent had longer primary patency than the Wallstent when placed across the venous anastomosis. However, stent fractures and focal necrotizing inflammation may limit the use of the Gianturco stent in hemodialysis access.

Treatment of acute aortic dissections with expandable metallic stents: experimental study

PURPOSE

This experimental study was designed to evaluate the effectiveness of metallic stents for the treatment of acute aortic dissection.

MATERIALS AND METHODS

Thoracic aortic dissections were created in 14 mongrel dogs. Aortography performed immediately after creation of dissections showed two types of aortic dissections: rapid flow in the false lumen (group 1) and slow flow in the false lumen (group 2). Each group consisted of seven dogs. For each group, expandable metallic Gianturco stents were placed in five dogs and two dogs were used as controls.

RESULTS

A week later, false lumina were patent in all dogs in group 1 and thrombosed in all dogs in group 2. In group 1, the mean diameter of the true lumina was considerably enlarged from 5.9 mm +/- 1.6 to 9.9 mm +/- 2.8 and that of the false lumina significantly diminished from 9.1 mm +/- 1.3 to 5.2 mm +/- 2.3 (P < .05) after stent placement. In group 2, the true lumina were significantly dilated (5.2 mm +/- 2.3 vs 12.3 mm +/- 3.1, P < .05) and the false lumina disappeared completely (9.2 mm +/- 3.3 vs 0.0 mm, P < .01). Furthermore, the two control dogs in group 2 died of visceral ischemia due to the compression of the true lumen by the thrombosed false lumina, but the dogs with stents showed no symptoms of the visceral ischemia.

CONCLUSION

Expandable metallic stents are not effective in obliterating the false lumen in acute aortic dissection but may be useful in maintaining the blood flow in the true lumen and avoiding visceral ischemia.

Portal decompression after transjugular intrahepatic portosystemic shunt creation with use of a spiral Z stent

PURPOSE

An experimental swine model of acute presinusoidal portal hypertension was used to investigate the feasibility of a spiral Z stent for transjugular intrahepatic portosystemic shunt (TIPS) placement and the correlation between the shunt (stent) size and degree of portal pressure decrease.

MATERIALS AND METHODS

Twelve young swine were used. Acute portal hypertension was induced by means of selective injections of absolute alcohol, ethiodized oil, and polyvinyl alcohol sponge particles into intrahepatic portal branches.

RESULTS

TIPS was successfully created in all swine by using spiral Z stents that were 6, 8, and 10 mm in diameter; each size stent was deployed in four animals. Being sufficiently flexible, spiral Z stents accommodated for curved shunt tracts. An average of 48% portal pressure decrease was achieved with 6-mm-diameter stents, 61% with 8-mm-diameter stents, and 87% with 10-mm-diameter stents.

CONCLUSION

These results are in agreement with our clinical experience with use of Gianturco-Rösch Z stents for TIPS formation.