Stent Compression Research Articles

Contemporary Endovascular Treatment for Disease of the Superficial Femoral and Popliteal Arteries:An Integrated Device-Based Strategy

Endovascular therapy for disease of the superficial femoral artery (SFA) and the popliteal artery remains controversial. Percutaneous treatment of this arterial segment presents a particular technical challenge, as the extent of disease varies from short, focal, and stenotic to long, diffuse, and occluded lesions. Over the last 2 decades, multiple therapies have been evaluated, including simple balloon angioplasty, directional atherectomy, stenting (both balloon-expandable and self-expanding), and more recently, intra-arterial radiation, laser, and cryotherapy. Regardless of which modality is used, however, endovascular therapy as a revascularization strategy has the potential to improve symptoms and quality of life and, in selected patients, to avoid limb amputation. While percutaneous endovascular treatment has been historically associated with high procedural success and favorable short and intermediate-term patency rates, long-term clinical results have proven disappointing. Conventional balloon angioplasty is limited by elastic recoil, dissection, and restenosis. Balloon-expandable stents (particularly in the distal SFA) are associated with late stent deformation and mechanical compression, with resultant late clinical failure. Newer self-expanding stents have shown improved initial results but have been limited by late mechanical fatigue and associated restenosis. With the development of several newer endovascular techniques in recent years, the possibilities for treating this condition have increased dramatically. Currently, no long-term comparative data exist regarding the role of these alternative technologies. This article summarizes and compares important data about new endovascular options for intervention therapy in SFA and popliteal disease. In addition, based on this analysis, we propose a contemporary treatment strategy, integrating older and newer technologies into a real-world algorithm.

A PROSPECTIVE RANDOMIZED SINGLE-BLIND COMPARISON OF URETERAL STENTS COMPOSED OF FIRM AND SOFT POLYMER

Ureteral stents are composed of different polymers and it is unclear if stent composition influences patient comfort. We compared the impact of stents composed of firm and soft polymer on patient health related quality of life. A total of 130 patients requiring insertion of ureteral stents during the treatment of urinary calculi were randomized to receive a stent composed of firm (Percuflex, group 1) or soft (Contour, group 2) polymer. Patients were asked to complete the Ureteric Stent Symptoms Questionnaire, a validated instrument, at weeks 1 and 4 with the stent in situ and 4 weeks after its removal, this served as the main outcome measure. Additional assessments included difficulty in stent insertion and the need for early stent removal. There were 78 men and 38 women in total (61 in group 1 and 55 in group 2) with a mean age of 51 years (range 22 to 79) and no difference in age between the 2 groups (p = 0.9). Comparison of the results of the Ureteric Stent Symptoms Questionnaire survey at weeks 1 and 4 with stent in situ revealed no significant differences in the domain scores of urinary symptoms (p = 0.9 and p = 0.8), pain (p = 0.8 and p = 0.6) and general health (p = 0.6 and p = 0.4). Similarly, there were no differences in the number of days with reduced activities, work performance (p = 0.7) and sexual dysfunction between the 2 groups. A similar number of patients (8 and 7 in groups 1 and 2, respectively) required stent removal earlier than planned due to stent related symptoms. This randomized study showed no difference in the impact on patient quality of life between ureteral stents composed of firm or soft polymer.

15-YEAR EXPERIENCE WITH THE MANAGEMENT OF EXTRINSIC URETERAL OBSTRUCTION WITH INDWELLING URETERAL STENTS

We assessed the success of retrograde placement of indwelling ureteral stents in the management of ureteral obstruction due to extrinsic compression. Between July 1987 and December 2002 adequate followup was available for 101 patients who underwent primary retrograde ureteral stenting for extrinsic ureteral obstruction. Mean age at presentation was 61.4 years (range 33 to 90). Chart review was performed on all patients for primary diagnosis, symptomatology, degree of hydronephrosis, creatinine levels (baseline, treatment and posttreatment), location of compression, size and number of stents used, progression to percutaneous nephrostomy tube (PNT), stent failure, days to stent failure, post-stent therapy and status at last followup. Mean length of followup was 11 months (range 1 to 127). In 101 patients 138 ureteral units (UU) were stented. Total stent failure occurred in 41 (40.6%) patients and 58 (42.0%) UU. A total of 40 (29.0%) UU required PNTs at a mean of 40.3 days (range 0 to 330) with 18 PNTs placed in less than 1 week. Cases of stent failure that did not undergo PNT placement included 18 (13.0%) UU at a mean of 52.4 days (range 3 to 128). A total of 90 (89.1%) patients had metastatic cancer at stenting with 32.2% dead at 5.8 months (range 1 to 32). Univariate and multivariate analyses identified cancer diagnosis, baseline creatinine greater than 1.3 mg/dl and post-stent systemic treatment as predictors of stent failure. Proximal location of compression and treatment creatinine greater than 3.11 mg/dl were marginal predictors of failure on univariate analysis, while proximal location of obstruction was also marginally significant on multivariate analysis. No predictors were identified for early stent failure (less than 1 week). At almost 1 year followup stent failure due to extrinsic compression occurred in nearly half of treated patients. Analysis of data revealed a diagnosis of cancer, baseline mild renal insufficiency and metastatic disease requiring chemotherapy or radiation as predictors of stent failure. Managing extrinsic compression by retrograde stenting continues to be a practical but guarded decision and should be tailored to each patient.

Redilation of endovascular stents in congenital heart disease: factors implicated in the development of restenosis and neointimal proliferation

OBJECTIVES We sought to determine the incidence of and risk factors for the development of restenosis and neointimal proliferation after endovascular stent implantation for congenital heart disease (CHD). BACKGROUND Risk factors for the development of restenosis and neointimal proliferation are poorly understood. METHODS This was a retrospective review of patients who underwent endovascular stent redilation between September 1989 and February 2000. RESULTS Of 368 patients who had 752 stents implanted, 220 were recatheterized. Of those 220 patients, 103 underwent stent redilation. Patients were classified into three groups: 1) those with pulmonary artery stenosis (n = 94), tetralogy of Fallot/pulmonary atresia (n = 72), congenital branch pulmonary stenosis (n = 9), status post-Fontan operation (n = 6), status post-arterial switch operation (n = 7); 2) those with iliofemoral venous obstruction (n = 6); and 3) those with miscellaneous disorders (n = 3). The patients’ median age was 9.9 years (range 0.5 to 39.8); their mean follow-up duration was 3.8 years (range 0.1 to 10). Indications for stent redilation included somatic growth (n = 67), serial dilation (n = 27) and development of neointimal proliferation or restenosis, or both (n = 9). There was a low incidence of neointimal proliferation (1.8%) and restenosis (2%). There were no deaths. Complications included pulmonary edema (n = 1), hemoptysis (n = 1) and contralateral stent compression (n = 2). CONCLUSIONS Redilation or further dilation of endovascular stents for CHD is effective as late as 10 years. The risk of neointimal proliferation (1.8%) and restenosis (2%) is low and possibly avoidable. Awareness of specific risk factors and modification of the stent implantation technique, including avoidance of minimal stent overlap and sharp angulation of the stent to the vessel wall and avoidance of overdilation, have helped to reduce the incidence of restenosis.

Propensity and mechanisms of restenosis in different coronary stent designs: Complementary value of the analysis of the luminal gain-loss relationship

OBJECTIVESThis study sought to investigate the influence of stent design on the long-term angiographic outcome.BACKGROUNDThe proportional relationship between vessel injury and late luminal loss in percutaneous revascularization should be best appreciated in coronary stenting, where recoil and shrinkage are theoretically minimal. It is unclear whether all stent designs can counterbalance this reactive loss by achieving a large initial luminal gain (bigger is better).METHODSIn 523 lesions successfully stented, the long-term angiographic results of slotted-tube (n = 331), coil (n = 85), multicellular (n = 70) and self-expandable mesh (n = 37) stent designs were compared using the angiographic gain-loss relationship (GLR).RESULTSRestenosis rate was 10% for multicellular, 20% for slotted-tube, 46% for coil and 49% for self-expandable designs (p = 0.001). At a difference with other designs, no significant GLR was found in coil stents, suggesting additional mechanisms of luminal loss (i.e., plaque protrusion, stent compression) to neointimal proliferation. Significant differences in late loss between stents were found within each quartile of luminal gain, suggesting a specific role of design in luminal loss. Multivariate analysis identified use of coil and self-expandable stents, vessel size, minimal luminal diameter preintervention, luminal gain and stent length as variables with independent predictive value for several indices of angiographic long-term outcome.CONCLUSIONSThe analysis of GLR: 1) demonstrates that stent design influences late luminal loss; 2) challenges the applicability of the widely accepted “bigger is better” approach to all stent designs; and 3) appears as a valuable tool in assessing long-term stent performance.

Percutaneous Stenting of the Internal Carotid Artery: The European CAST I Study

To report the results of a multicenter safety trial of percutaneous carotid stenting performed by vascular surgeons. Symptomatic or asymptomatic patients > or = 65 years of age with internal carotid artery (ICA) stenoses > or = 70% and < or = 2-cm long were eligible for enrollment. The procedures were performed in an operating room with the choice of anesthesia and the percutaneous access site at the discretion of the surgeon. Only Palmaz stents were used. From January 1, 1996 to December 31, 1997, 99 patients (74 men, mean age 70 years, range 51 to 94) were enrolled in the study. More than half (57 of 99 patients) were asymptomatic. The direct cervical approach was used predominantly (97%). Three (3%) cases were converted to surgery for inability to access the artery or deploy the stent (technical success 97%). No perioperative death or myocardial infarction was reported. Six (6%) procedural complications included 1 reversible arterial spasm, 2 dissections, 1 cervical hematoma, and 2 residual stenoses. One neurological event reversed within 7 days (1% minor stroke rate) and 4 (4%) transient ischemic attacks resolved within 24 hours. One (1%) asymptomatic early occlusion occurred 2 days postoperatively. No neurological event was observed in the 1- to 24-month follow-up (mean 13 months). Two (2%) patients died of nonprocedurally related causes. No stent compression was seen, but 1 asymptomatic occlusion and 3 asymptomatic, non-flow-limiting restenoses (2 < 40%, 1 at 60%) were found within 1 year (3% restenosis rate on an intention-to-treat basis). Patency was 98% at 1 year. The results of this trial support the contention that carotid stenting of short ICA lesions can be performed with a low neurological complication rate.

Percutaneous Stenting of the Internal Carotid Artery: The European CAST I Study

Purpose: To report the results of a multicenter safety trial of percutaneous carotid stenting performed by vascular surgeons. Methods: Symptomatic or asymptomatic patients ≥ 65 years of age with internal carotid artery (ICA) stenoses ≥ 70% and ≤ 2-cm long were eligible for enrollment. The procedures were performed in an operating room with the choice of anesthesia and the percutaneous access site at the discretion of the surgeon. Only Palmaz stents were used. Results: From January 1, 1996 to December 31, 1997, 99 patients (74 men, mean age 70 years, range 51 to 94) were enrolled in the study. More than half (57 of 99 patients) were asymptomatic. The direct cervical approach was used predominantly (97%). Three (3%) cases were converted to surgery for inability to access the artery or deploy the stent (technical success 97%). No perioperative death or myocardial infarction was reported. Six (6%) procedural complications included 1 reversible arterial spasm, 2 dissections, 1 cervical hematoma, and 2 residual stenoses. One neurological event reversed within 7 days(1% minor stroke rate) and 4 (4%) transient ischemic attacks resolved within 24 hours. One (1%) asymptomatic early occlusion occurred 2 days postoperatively. No neurological event was observed in the 1- to 24-month follow-up (mean 13 months). Two (2%) patients died of nonprocedurally related causes. No stent compression was seen, but 1 asymptomatic occlusion and 3 asymptomatic, non-flow-limiting restenoses (2 &lt; 40%, 1 at 60%) were found within 1 year (3% restenosis rate on an intention-to-treat basis). Patency was 98% at 1 year. Conclusions: The results of this trial support the contention that carotid stenting of short ICA lesions can be performed with a low neurological complication rate.

Elastic deformation properties of implanted endobronchial wire stents in benign and malignant bronchial disease: A radiographic in vivo evaluation.

To evaluate the long-term mechanical behavior in vivo of expandable endobronchial wire stents, we imaged three different prostheses in the treatment of tracheobronchial disease. Six patients with bronchial stenoses (three benign, three malignant) underwent insertion of metallic stents. Two self-expandable Wallstents, two balloon-expandable tantalum Strecker stents and two self-expandable nitinol Accuflex stents were used. Measurements of deformation properties were performed during voluntary cough by means of fluoroscopy, at 1 month and 7-10 months after implantation. The procedures were videotaped, their images digitized and the narrowing of stent diameters calculated at intervals of 20 msec. After stent implantation all patients improved with respect to ventilatory function. Radial stent narrowing during cough reached 53% (Wallstent), 59% (tantalum Strecker stent), and 52% (nitinol Accuflex stent) of the relaxed post-implantation diameter. Stent compression was more marked in benign compared with malignant stenoses. In the long term permanent deformation occurred with the tantalum Strecker stents; the other stents were unchanged. Endobronchial wire stents can be helpful in the treatment of major airway collapse and obstructing bronchial lesions. However, evidence of material fatigue as a possible effect of exposure to recurrent mechanical stress on the flexible mesh tube may limit their long-term use. This seems to be predominantly important in benign bronchial collapse.

Angioplasty and Stenting of the Extracranial Carotid Arteries

Purpose: To study the feasibility and safety of stent-supported angioplasty in the treatment of atherosclerotic stenoses of the extracranial carotid arteries. Methods: Carotid angioplasty was attempted in 174 arteries (163 patients: 126 males; mean age: 71 ± 10 years, range 47 to 93). Mean lesion length was 15.1 ± 4.1 mm, and mean percent stenosis was 83.8% ± 7.3% (reference diameter 5.8 ± 0.7 mm). The majority (106, 65%) were asymptomatic (51% of all patients had severe coronary disease, 32% had peripheral vascular diseases). Patients underwent independent neurological examination, computed tomography, duplex ultrasonography, and angiography preprocedurally, 24 hours after the procedure, and at 6-month follow-up intervals. Most (142, 82%) carotid arteries were treated without cerebral protection, but a protective triple coaxial catheter was used in 32 (18%) patients. Stents (primarily Palmaz and Wallstent) were deployed routinely in all cases; 18% were implanted without predilation. Results: Immediate technical success was 173 of 174 (99.4%) (1 access failure referred electively to surgery). Eight (4.6%) neurological complications occurred in the periprocedural period: 3 transient ischemic attacks, 2 minor strokes, and 3 major strokes (1 amaurosis and 2 hemiplegias). Two major complications developed despite cerebral protection. There were no deaths or myocardial infarctions and only 3 cervical access site hematomas. Over a mean 12.7 ± 9.2 month follow-up (range 1 to 36), no ipsilateral neurological complications have been seen. There were 4 (2.3%) restenoses (3 redilated, 1 treated medically) and 1 mild Palmaz stent compression, all found within the first 6 months. Primary and secondary patencies at 3 years are 96% and 99%, respectively. Conclusions: Angioplasty with routine stenting seems feasible and safe for treating certain types of carotid stenoses even in high-surgical risk patients; however, randomized trials are necessary before this treatment can be offered as an alternative to endarterectomy.

New endoureteral double-J stent resists extrinsic ureteral compression.

The disadvantages of highly flexible endoureteral (double J) stents in the face of tumor-induced extrinsic ureteral compression are a consequence of insufficient cross-sectional stability, leading to stent compression and thus to hydronephrosis or pyonephrosis. The newly developed tumor stent, which is used in cases of tumor-induced ureteral compression, is available in sizes from 6F to 8F in diameter and 24 to 32 cm in length. The shaft consists of a combination of high-stability plastics that presents sufficient elasticity in length. Both ends are made of extremely elastic J parts, guaranteeing stable fixation. Compared with common double-J stents with the same outside diameter, the tumor stent possesses a comparable interior diameter and compared with available stents promises sufficient interior flow in the face of extrinsic diseases. The application can be undertaken using well-known endoscopic techniques, needs no special instrumentation, and entails no learning curve. To date, 49 stents were placed at our urologic departments without any problems, the latest stent remaining for 15 months. Tumor-induced compression or a higher rate of encrustation were not seen. All patients tolerated these stents well. In our opinion, the new stabilized endoureteral stent can be seen as a better solution than percutaneous nephrostomy or frequent stent changing to tumor-induced extrinsic ureteral compression.

Transbronchial Palmaz Stent Placement for Tracheo-bronchial Stenosis

Evaluation of the efficacy of transbronchial Palmaz stent placement in the treatment of tracheo-bronchial narrowing. Twelve patients with stenoses of the tracheo-bronchial tree were treated with balloon-expandable Palmaz stents. Etiology was anastomotic stenosis after lung transplantation (n = 3), bronchogenic carcinoma (n = 2), external compression from thoracic aortic aneurysm (n = 2), Mycobacterium tuberculosis (n = 1), esophageal carcinoma (n = 1), after lobectomy (n = 1), after lobectomy and endobronchial radiation (n = 1), and lye ingestion (n = 1). All patients had respiratory symptoms, radiologic findings of persistent atelectasis, or worsening pulmonary function tests. Bronchoscopy was used to delineate the stenosis prior to intervention. With use of fluoroscopic guidance, stents were placed in the mainstem bronchus (n = 11), lower lobe bronchus (n = 5), bronchus intermedius (n = 5), trachea (n = 3), and middle lobe bronchus (n = 1). Initial technical success was achieved in all patients. Ten of the 12 patients (83%) had improvement of clinical pulmonary signs or symptoms. During follow-up, five patients died. One was lost to follow-up and was presumed dead. The 30-day mortality rate was 17% (two of 12 patients). The two complications were superficial laceration of the bronchial mucosa during balloon dilation in one patient and compression of stents by a thoracic aortic aneurysm in another patient. Initial results suggest that transbronchial Palmaz stent placement is a feasible and effective method of treating tracheo-bronchial stenosis.

Endovascular Stents for Carotid Artery Occlusive Disease

To study the feasibility and safety of endovascular stenting of cervical carotid artery stenosis. Between April 1994 and May 1997, 108 consecutive patients (58 men; mean age 70.1 years) with > or = 70% carotid stenosis were treated with percutaneous stent implantation under a protocol that featured independent neurological review. Forty-four percent were asymptomatic. Over half the lesions (59%) were in the internal carotid artery; the mean stenosis was 86%. Palmaz stents were implanted without cerebral protection following preliminary balloon dilation; two Wallstents were used in long lesions. Carotid stents were successfully placed in 108 of 114 (95%) lesions. Of the 6 technical failures, 5 were access related and 1 was due to seizures during balloon dilation. Two major (1.8%) and 2 minor (1.8%) strokes occurred (3.7% stroke rate for 108 patients; 3.5% in 114 procedures), all in symptomatic patients, one of whom died. There were 5 (4.4%) transient ischemic attacks and 2 (1.8%) brief seizure episodes during dilation. One patient died of a cardiac event on day 20. The all stroke or death rate was 5.3% based on 114 arteries at risk (5.6% in 108 patients). In the mean 6-month follow-up (range 1 to 36) of 97 eligible patients, 3 (3.1%) died from unrelated causes. There was 1 restenosis (1.0%) from a stent compression, which was successfully redilated. There were no neurological sequelae, cranial palsies, or cases of stent or vessel thrombosis in follow-up. The use of stents in the treatment of cervical carotid occlusive disease appears feasible, effective in the short term, and without excessive risk of periprocedural stroke.

Palmaz stent compression in patients following carotid artery stenting.

Carotid artery stenting is being investigated as a therapeutic strategy for the management of bifurcation stenosis. Palmaz stents were deployed successfully in the carotid arteries of 112 patients using high-pressure balloon inflations. In 11 out of 70 patients who came for 6-mo follow-up angiography, a stent collapse was noted. Carotid ultrasound was able to detect stent collapse in only two patients at follow-up. Only one patient who had collapse of stent along its entire length was symptomatic at follow-up. Repeat balloon angioplasty was performed in 5 patients, 3 of whom had a Wallstents deployed within the Palmaz stent. Stent collapse was observed in a significant number of Palmaz stents within 6 mo of placement in the carotid arteries. These observations should influence the choice of stents for the treatment of extracranial carotid disease.

Restenosis of Endovascular Stents From Stent Compression

Objectives. We sought to determine the basis for restenosis within superficial femoral arteries (SFAs) and hemodialysis conduits treated with balloon-expandable stents.Background. Use of stents within coronary and peripheral vessels continues to increase exponentially. The mechanism of restenosis within stents placed at various vascular sites is not well understood. In particular, the implications of deploying a balloon-expandable stent in a compressible site are not well understood.Methods. After the serendipitous detection of stent deformation during intravascular ultrasound (IVUS) examination of a restenosed dialysis fistula, we evaluated a consecutive series of patients with stents placed in compressible vascular sites, including the SFA (six patients) and hemodialysis fistulae (five patients). Clinical, angiographic and IVUS examinations were performed to evaluate mechanisms of restenosis.Results. Stent compression was identified as the principal cause of restenosis in all dialysis conduits and SFAs. Stent deformity was not reliably identified by angiography; however, IVUS identified compression of two forms: eccentric deformation, implicating two-point compressive force, and complete circumferential encroachment of stent struts around the catheter, suggesting multidirectional compressive force. Despite redilation, secondary restenosis resulting from recurrent compression recurred in most sites.Conclusions. Restenosis within balloon-expandable endovascular stents may occur as a result of stent compression, a phenomenon readily detected by IVUS, but often not by angiography. These findings have significant implications for the use of balloon-expandable stents within vascular sites subject to extrinsic compression, such as hemodialysis conduits, the adductor canal segment of the SFA and carotid arteries.(J Am Coll Cardiol 1997;29:328–38)

Serial follow-up after optimized ultrasound-guided deployment of Palmaz-Schatz stents. In-stent neointimal proliferation without significant reference segment response.

The effects of ultrasound-guided high-pressure stenting on late stent and reference segment dimensions are unknown. In this study, we report about angiographic and ultrasound measurements to assess the amount and distribution of neointimal ingrowth within the stent and the changes of plaque burden and dimensions within the reference segments. Sixty-eight consecutive patients with 72 lesions received single or multiple Palmaz-Schatz coronary stents with a standardized protocol for stent optimization under ultrasound guidance. The residual angiographic diameter stenosis was 3 +/- 12% (reference diameter, 3.16 +/- 0.61 mm). At follow-up 4.8 +/- 2.5 months later, angiography revealed a diameter stenosis of 27 +/- 21% with a restenosis rate of 15.3% (confidence interval: 7.8% to 25.6%). Lumen renarrowing within the stent was exclusively due to neointimal ingrowth; no stent compression was observed. The neointima covered 20 +/- 20% of the stent area and was more pronounced in the midportion of the stent. Volumetric assessment performed in 26 patients resulted in 13 +/- 14% or 65 +/- 28% of the stent volume occupied by neointimal ingrowth in patients without or with restenosis, respectively. Vessel remodeling had an impact on lumen dimensions only at reference sites but not within the stent. Plaque burden of 46 +/- 11% and 48 +/- 11% at the proximal and distal reference sites, respectively, did not show a relevant progression during the follow-up. Serial ultrasound analyses did not show any evidence of stent compression or relevant vessel remodeling. Restenosis was solely due to neointimal ingrowth. Despite a considerable plaque burden within the reference segments, there was no relevant progression of the disease adjacent to the stent.

783-5 Intravascular Stents in Systemic Venous and Systemic Venous Baffle Obstructions

For the management of systemic venous and systemic venous baffle obstructions, both surgery and isolated balloon dilation of are often unrewarding. Since 1991 we have managed such obstructions with intravascular stents. Twelve pts aged 3 mths-20 yrs Imean 8.2 yrs), have had 21 stents implanted in 13 systemic venous obstructions: 9/13 in central veins and 4/13 post atrial baffles for TGA. 12/13 obstructions were acquired and 1/13 congenital. 8/13 obstructions were symptomatic (SVC syndrome 6/8) and 5/13 were asymptomatic. Obstruction was complete requiring transeptal needle perforation in 4/13. Post-stent implantation, the diameter of the obstruction increased from 2 ± 2.4 mm (range 0-8.5 mm) to 11.4 ± 3.7 mm (range 7.620 mm, p &lt; 0.001). The gradient decreased from 10.8 ± 8.1 mmHg (range 0–20 mmHg) to 0.9 ± 1.3 mmHg (range 0–4 mmHg, p &lt; 0.001). There was residual angiographic obstruction in 1/13 pts. Symptoms resolved in 6/8 and improved in 2/8 symptomatic pts. No complications were incurred. 6/13 obstructions were restudied 2–13 mths post stent implantation. All stents remain patent with no stent fracture or compression. No stents required redilation. Neointimal hyperplasia was seen in 5/6 stents. Differences between immediate post stent and follow-up lumen size (13 ± 4.7 mm vs 11 ± 4.7 mm) and gradients (1 ± 1.6 mmHg vs 0.7 ± 1.2 mmHg) were not significant. In 1 pt. with 4 serial stents, 1 stent had ‘unlocked’ and rotated, but remained unobstructed. Stent implantation in systemic venous obstructions is safe and effective. even where obstruction is complete. Longterm follow-up is required to determine if neointimal proliferation will require redilation. We postulate intravascular stents will become the treatment of choice for selected systemic venous and systemic venous baffle obstructions.

Palmaz stent in the treatment of central venous stenosis: safety and efficacy of redilation.

To assess the safety and efficacy of redilation of central venous stents in a growing animal model. Palmaz stents were placed in the inferior vena cava (IVC) in 18 newborn lambs. After 5 months, vena cavography was performed. Those animals in which growth of the IVC adjacent to the stent and/or neointimal hyperplasia had resulted in a stenosis were considered candidates for redilation. Repeat vena cavography, intravascular ultrasound, and histologic examination were performed at 2 or 6 months. A stenosis of > 20% was demonstrated in 13 animals. Redilation was performed, and a 50% mean increase in stent diameter was achieved. There were no immediate complications. Late complications included nonocclusive laminar clot (n = 2), and a bar of tissue dividing but not occluding the caval lumen (n = 1). Moderate neointimal hyperplasia occurred in all stents. Stent compression (unrelated to redilation) occurred in seven animals. Palmaz stents can be redilated safely and effectively in an animal model of growing central veins.

Mechanisms of restenosis and redilation within coronary stents—Quantitative angiographic assessment

Objectives. This study was designed to assess the relative contributions of intimal hyperplasia and stent compression to the lumen narrowing seen after intracoronary stenting and to determine whether the lumes enlargement produced by angioplasty of in-stent restenosis results primarily from compression or extrusion of intimal hyperplasia through the stent or from additional stent expansion.Background. Palmaz-Schatz stent placement outwardly displaces plaque and eliminates elastic vessel recoil to provide a large and smooth lumen. Some degree of late lumen narrowing occurs within each stent and causes significant restenosis (≥50% stenosis) in 25% to 30% of treated lesions. It has not been clear, however, whether this narrowing results from stent compression (crush) or from in-stent intimal hyperplasia. Because the Palmaz-Schatz stent has a distinct radiographic shadow, it is possible to determine the late diameter of both the stent and the enclosed vessel lumen to assess the relative contributions of these two processes.Methods. From cineangiograms, initial (after stenting) and late (follow-up) lumen and stent diameters were examined in 55 patients (59 stents, group I) who had both immediate and 6-month (192 ± 117 days) angiography. Lumen and stent diameter were also examined before and after dilation in 30 patients (30 stents, group II) who underwent angioplasty of severe in-stent restenosis.Results. Late loss in minimal lumen diameter was 0.99 ± 0.87 mm for group I despite only a slight (0.03 ± 0.23-mm) reduction in the corresponding stent diameter. After redilation for in-stent restenosis, the acute gain in minimal lumen diameter was 1.51 ± 0.82 mm for group II, again without appreciable increase (0.06 ± 0.20 mm) in stent diameter.Conclusions. Restenosis after intracoronary Palmaz-Schatz stenting appears to be due predominantly to lumen encroachment by intimal hyperplasia within the stent, with minimal contribution of stent compression. Lumen enlargement after coronary angioplasty of in-stent restenosis appears to be due primarily to compression or extrusion of intimal hyperplasia the ough the stent, or both, rather than to further stent expansion.

The Double-J Ureteral Stent: In Vivo and in Vitro Flow Studies

Although most ureters can now be stented, the rate of ureteral obstruction from extrinsic compression remains relatively high. To illuminate the mechanisms of obstruction in these patients we performed 20 in vivo pressure-flow investigations in 14 patients with indwelling ureteral Double-J††Medical Engineering Corp., New York, New York.† stents. All patients had a percutaneous nephrostomy tube in place. Our investigations revealed proper drainage to the bladder in 17 of the 20 studies at an average renal pelvic pressure of 19.9cm. water. Vesicorenal reflux was noted at an average bladder pressure of 20cm. water in 17 studies. Three stents appeared to be obstructed. They showed no drainage to the bladder but also no reflux.To evaluate the in vivo results we then performed an in vitro study of pressure-flow characteristics under conditions simulating ureteral obstruction. At physiological flow rates different ureteral stents showed no major differences in pressure-flow characteristics. With compression and kinking, flow resistance in softer stents was notably greater than in hard stents. Therefore, we believe that in patients with suspected extrinsic compression of the ureter hard Double-J stents should be used. Vesicorenal reflux appears to be a reliable predictor of stent function.