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Biomedical subjects

M W Webster

Publications and source records attributed to M W Webster.

At least 19 recordsLinked to original sources
PubMed2001

Clinical and angiographic factors associated with asymptomatic restenosis after percutaneous coronary intervention.

BACKGROUND: Angiographic restenosis after percutaneous coronary interventional procedures is more common than recurrent angina. Clinical and angiographic factors associated with asymptomatic versus symptomatic restenosis after percutaneous coronary intervention were compared. METHODS AND RESULTS: All patients with angiographic restenosis from the BENESTENT I, BENESTENT II pilot, BENESTENT II, MUSIC, WEST 1, DUET, FINESS 2, FLARE, SOPHOS, and ROSE studies were analyzed. Multivariate analysis evaluated 46 clinical and angiographic variables, comparing those with and without angina. The 10 studies recruited 2690 patients who underwent percutaneous revascularization and 6-month follow-up angiography (86% of those eligible). Restenosis (>/=50% diameter stenosis) occurred in 607 patients and was clinically silent in 335 (55%). Male sex (P=0.008), absence of antianginal therapy with nitrates (P=0.0002) and calcium channel blockers (P=0.02) at 6 months, greater reference diameter after the procedure (P=0.04), greater reference diameter at follow-up (P=0.004), and lesser lesion severity (percent stenosis) at 6 months (P=0.0004) were univariate predictors of asymptomatic restenosis. By multivariate analysis, only male sex (P=0.04), greater reference diameter at follow-up (P=0.002), and lesser lesion severity at 6 months (P=0.0001) were associated with restenosis without angina. CONCLUSIONS: Approximately half of patients with angiographic restenosis have no symptoms. The only multivariate predictors of silent restenosis at 6 months were male sex, greater reference diameter at follow-up, and lesser lesion severity on follow-up angiography.

Angioplasty, Balloon, Coronary↗
PubMed2001

5 French guide catheters for percutaneous coronary intervention: a feasibility study in 100 consecutive patients.

Percutaneous coronary intervention using smaller-diameter guide catheters may have a favorable impact on groin complications, mobilization time, hospital stay, and contrast use. This prospective registry study assessed the feasibility of routine stent delivery through 5 Fr guide catheters. Of the 100 consecutive patients, 5 Fr guided intervention was attempted in 84 and was successful in all but 2 patients who had chronic complete occlusions. Reasons for not selecting a 5 Fr guide were planned kissing balloons (eight), directional coronary atherectomy (one), and no suitable 5 Fr guide in stock (seven). There was no stent dislodgment, need to change to a larger-caliber guide, or inadequate contrast opacification. When necessary, guide support was achieved by deep-vessel intubation, which was not associated with vascular damage. The only adverse sequelae were non-Q-wave myocardial infarctions in two patients. Coronary artery stenting using 5 Fr guide catheters is feasible and applicable to most patients.

Adult↗
PubMed2001

Outcome events in patients with claudication: a 15-year study in 2777 patients.

OBJECTIVE: The purpose of this study was to delineate the natural history of claudication and determine risk factors for death. METHODS: We reviewed the key outcomes (death, revascularization, amputation) in 2777 male patients with claudication identified over 15 years at a Veterans Administration hospital with both clinical and noninvasive criteria. Patients with rest pain or ulcers were excluded. Data were analyzed with life-table and Cox hazard models. RESULTS: The mean follow-up was 47 months. The cohort exhibited a mortality rate of 12% per year, which was significantly (P <.05) more than the age-adjusted US male population. Among the deaths in which the cause was known, 66% were due to heart disease. We examined several baseline risk factors in a multivariate Cox model. Four were significant (P <.01) independent predictors of death: older age (relative risk [RR] = 1.3 per decade), lower ankle-brachial index (RR = 1.2 for 0.2 change), diabetes requiring medication (RR = 1.4), and stroke (RR = 1.4). The model can be used to estimate the mortality rate for specific patients. Surprisingly, a history of angina and myocardial infarction was not a significant predictor. Major and minor amputations had a 10-year cumulative rate less than 10%. Revascularization procedures occurred with a 10-year cumulative rate of 18%. CONCLUSIONS: We found a high mortality rate in this large cohort and four independent risk factors that have a large impact on survival. Risk stratification with our model may be useful in determining an overall therapeutic plan for claudicants. A history of angina and myocardial infarction was not a useful predictor of death, suggesting that many patients in our cohort presented with claudication before having coronary artery symptoms. Our data also indicate that claudicants have a low risk of major amputation at 10-year follow-up.

Aged↗
PubMed2001

Association of intraluminal thrombus in abdominal aortic aneurysm with local hypoxia and wall weakening.

PURPOSE: Our previous computer models suggested that intraluminal thrombus (ILT) within an abdominal aortic aneurysm (AAA) attenuates oxygen diffusion to the AAA wall, possibly causing localized hypoxia and contributing to wall weakening. The purpose of this work was to investigate this possibility. METHODS: In one arm of this study, patients with AAA were placed in one of two groups: (1) those with an ILT of 4-mm or greater thickness on the anterior surface or (2) those with little (< 4 mm) or no ILT at this site. During surgical resection but before aortic cross-clamping, a needle-type polarographic partial pressure of oxygen (PO2) electrode was inserted into the wall of the exposed AAA, and the PO2 was measured. The probe was advanced, and measurements were made midway through the thrombus and in the lumen. Mural and mid-ILT PO2 measurements were normalized by the intraluminal PO2 measurement to account for patient variability. In the second arm of this study, two AAA wall specimens were obtained from two different sites of the same aneurysm at the time of surgical resection: group I specimens had thick adherent ILT, and group II specimens had thinner or no adherent ILT. Nonaneurysmal tissue was also obtained from the infrarenal aorta of organ donors. Specimens were subjected to histologic, immunohistochemical, and tensile strength analyses to provide data on degree of inflammation (% area inflammatory cells), neovascularization (number of capillaries per high-power field), and tensile strength (peak attainable load). Additional specimens were subjected to Western blotting and immunohistochemistry for qualitative evaluation of expression of the cellular hypoxia marker oxygen-regulated protein. RESULTS: The PO2 measured within the AAA wall in group I (n = 4) and group II (n = 7) patients was 18% +/- 9% luminal value versus 60% +/- 6% (mean +/- SEM; P <.01). The normalized PO2 within the ILT of group I patients was 39% +/- 10% (P =.08 with respect to the group I wall value). Group I tissue specimens showed greater inflammation (P <.05) compared with both group II specimens and nonaneurysmal tissue: 2.9% +/- 0.6% area (n = 7) versus 1.7% +/- 0.3% area (n = 7) versus 0.2% +/- 0.1% area (n = 3), respectively. We found similar differences for neovascularization (number of vessels/high-power field), but only group I versus control was significantly different (P <.05): 16.9 +/- 1.6 (n = 7) vs 13.0 +/- 2.3 (n = 7) vs 8.7 +/- 2.0 (n = 3), respectively. Both Western blotting and immunohistochemistry results suggest that oxygen-regulated protein is more abundantly expressed in group I versus group II specimens. Tensile strength of group I specimens was significantly less (P <.05) than that for group II specimens: 138 +/- 19 N/cm2 (n = 7) versus 216 +/- 34 N/cm2 (n = 7), respectively. CONCLUSION: Our results suggest that localized hypoxia occurs in regions of thicker ILT in AAA. This may lead to increased, localized mural neovascularization and inflammation, as well as regional wall weakening. We conclude that ILT may play an important role in the pathology and natural history of AAA.

Aged↗
PubMed2001

Mechanical properties and microstructure of intraluminal thrombus from abdominal aortic aneurysm.

Accurate estimation of the wall stress distribution in an abdominal aortic aneurysm (AAA) may prove clinically useful by predicting when a particular aneurysm will rupture. Appropriate constitutive models for both the wall and the intraluminal thrombus (ILT) found in most AAA are necessary for this task. The purpose of this work was to determine the mechanical properties of ILT within AAA and to derive a more suitable constitutive model for this material. Uniaxial tensile testing was carried out on 50 specimens, including 14 longitudinally oriented and 14 circumferentially oriented specimens from the luminal region of the ILT, and 11 longitudinally oriented and 11 circumferentially oriented specimens from the medial region. A two-parameter, large-strain, hyperelastic constitutive model was developed and used to fit the uniaxial tensile testing data for determination of the material parameters. Maximum stiffness and strength were also determined from the data for each specimen. Scanning electron microscopy (SEM) was conducted to study the regional microstructural difference. Our results indicate that the microstructure of ILT differs between the luminal, medial, and abluminal regions, with the luminal region stronger and stiffer than the medial region. In all cases, the constitutive model fit the experimental data very well (R2>0.98). No significant difference was found for either of the two material parameters between longitudinal and circumferential directions, but a significant difference in material parameters, stiffness, and strength between the laminal and medial regions was determined (p<0.01). Therefore, our results suggest that ILT is an inhomogeneous and possibly isotropic material. The two-parameter, hyperelastic, isotropic, incompressible material model derived here for ILT can be easily incorporated into finite element models for simulation of wall stress distribution in AAA.

Aged↗
PubMed2000

Flavone-8-acetic acid (Flavonoid) profoundly reduces platelet-dependent thrombosis and vasoconstriction after deep arterial injury In vivo.

BACKGROUND: Flavone-8-acetic acid (FAA; [Flavonoid]), an adjuvant antitumor drug, inhibits ristocetin-induced aggregation of human platelets. The effect of FAA on platelet-dependent thrombosis was studied in vivo in the porcine carotid artery after deep arterial injury by balloon angioplasty. METHODS AND RESULTS: (111)In-labeled autologous platelet and (125)I-labeled porcine fibrin(ogen) deposition, and the incidence of macroscopic mural thrombosis onto deeply injured artery (tunica media) were compared in 20 pigs (40+/-1 kg [mean+/-SEM], body surface area=1.0+/-0.1 m(2)), randomized to FAA bolus (n=10) of 5.5g/m(2), followed by an infusion at 0.14g. m(-2). min(-1) or placebo (n=10). Vasoconstriction was measured immediately beyond the dilated segment using quantitative angiography. Platelet deposition (x10(6)/cm(2) of carotid artery) was reduced over 12-fold in pigs treated with FAA (13+/-3 versus 164+/-51, P=0.001) compared with placebo. Fibrin(ogen) deposition (x10(12) molecules/cm(2) of carotid artery) did not significantly differ in FAA-treated pigs versus placebo (40+/-8 versus 140+/-69, P=0.08). Large mural thrombi were present in 100% of placebo-treated pigs versus very small thrombi in 40% of FAA-treated pigs (P=0.005). Vasoconstriction was reduced from 46+/-6% in the placebo group to 15+/-3% in the FAA group (P<0.001). Plasma level of FAA before angioplasty was 515+/-23 microgram/mL. The activated partial thromboplastin time was unchanged. The bleeding time was >2SD above the normal mean in 4 of 5 treated pigs (increased from 157+/-29 to 522+/-123 s). CONCLUSIONS: FAA markedly reduced platelet deposition, mural thrombi, and injury-induced vasoconstriction after deep arterial injury, suggesting that a major inhibition of platelet glycoprotein Ibalpha may be beneficial therapy.

Animals↗
PubMed2000

Gelfoam embolization of a distal coronary artery guidewire perforation.

A guidewire-induced distal coronary artery perforation presenting with cardiac tamponade was occluded by distal Gelfoam embolization via an infusion catheter. This extends the treatment options for this rare complication of coronary interventional procedures. Cathet. Cardiovasc. Intervent. 49:214-217, 2000.

Aged↗
PubMed2000

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.

Equipment Design↗
PubMed2000

A randomized study of direct coronary stent delivery compared with stenting after predilatation: the NIR future trial. On behalf of the NIR Future Trial Investigators.

This randomized trial compared a strategy of direct stenting without predilatation (n = 39) with conventional stenting with predilatation (n = 42) in patients with suitable lesions in native vessels > or = 2. 5-mm diameter to be covered by either a 9- or 16-mm-length NIR Primo stent. Equipment cost [mean (median) +/- SD] was less in those with direct stenting [$1,199 (979) +/- 526] than in those with predilatation [$1,455 (1,285) +/- 401, P < 0.001]. There was no significant difference in contrast use or fluoroscopy time. Procedural time was shorter in the direct stenting group. The clinical outcome at 1 month was satisfactory in both groups. In selected patients, a strategy of direct stenting is feasible, costs less, and is quicker to perform than the conventional strategy of stenting following predilatation.

Adult↗
PubMed2000

Etiologic factors in progression of carotid stenosis: a 10-year study in 905 patients.

PURPOSE: The purpose of this study was to determine the etiologic factors in the progression of carotid stenosis. METHODS: We performed prospective serial duplex scan surveillance of 1470 carotid arteries in 905 asymptomatic patients during a 10-year period, with an average follow-up interval of 29 months and an average of 3.0 scans per carotid artery. Vascular laboratory and hospital records were used to collect risk factor information. The data were analyzed with proportional hazards modeling. RESULTS: We examined several demographic, clinical, and laboratory risk factors that were chosen because of their potential relevance to atherosclerotic disease. These factors were analyzed with univariate proportional hazards modeling, in which time to progression of stenosis was the outcome variable. The six significant predictors (P <.05) were age, sex, systolic pressure, pulse pressure (systolic pressure - diastolic pressure), total cholesterol, and high-density lipoprotein (HDL). All, except HDL, were positive predictors of time to disease progression. With multivariate modeling, only pulse pressure and HDL remained as significant independent predictors of stenosis progression. The risk ratio for a 10-mm Hg rise in pulse pressure was 1.12, and the risk ratio for a 10-mg/dL decrease in HDL was 1.20. CONCLUSION: In this large cohort of patients who were followed prospectively for carotid stenosis, pulse pressure and HDL were found to be the key risk factors for carotid stenosis progression. The fact that pulse pressure superseded systolic pressure in multivariate modeling may shed light on the biology of carotid plaque progression. Further, our identification of these modifiable risk factors may help in the design of therapeutic trials for the prevention of progression of carotid atherosclerosis.

Age Factors↗
PubMed2000

Wall stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm.

PURPOSE: Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall tissue. Therefore, knowledge of the stress distribution in an intact AAA wall could be useful in assessing its risk of rupture. We developed a methodology to noninvasively estimate the in vivo wall stress distribution for actual AAAs on a patient-to-patient basis. METHODS: Six patients with AAAs and one control patient with a nonaneurysmal aorta were the study subjects. Data from spiral computed tomography scans were used as a means of three-dimensionally reconstructing the in situ geometry of the intact AAAs and the control aorta. We used a nonlinear biomechanical model developed specifically for AAA wall tissue. By means of the finite element method, the stress distribution on the aortic wall of all subjects under systolic blood pressure was determined and studied. RESULTS: In all the AAA cases, the wall stress was complexly distributed, with distinct regions of high and low stress. Peak wall stress among AAA patients varied from 29 N/cm(2) to 45 N/cm(2) and was found on the posterior surface in all cases studied. The wall stress on the nonaneurysmal aorta in the control subject was relatively low and uniformly distributed, with a peak wall stress of 12 N/cm(2). AAA volume, rather than AAA diameter, was shown by means of statistical analysis to be a better indicator of high wall stresses and possibly rupture. CONCLUSION: The approach taken to estimate AAA wall stress distribution is completely noninvasive and does not require any additional involvement or expense by the AAA patient. We believe that this methodology may allow for the evaluation of an individual AAA's rupture risk on a more biophysically sound basis than the widely used 5-cm AAA diameter criterion.

Adult↗
PubMed2000

Is routine use of the intensive care unit after elective infrarenal abdominal aortic aneurysm repair necessary?

INTRODUCTION: Postoperative care after infrarenal abdominal aortic aneurysm (AAA) repair has traditionally involved admission to the intensive care unit (ICU). With the advent of endovascular AAA repair, the management of open procedures has received increased scrutiny. We recently modified our AAA clinical pathway to include selective use of the ICU. METHODS: Consecutive elective infrarenal AAA repairs performed by members of the vascular surgery division at a university medical center from 1994 to 1999 were analyzed retrospectively with a computerized database, the Medical Archival Retrieval System. Group I consisted of 245 patients who were treated in the ICU for 1 or more days, and Group II included 69 patients admitted directly to the floor. Ruptured, symptomatic, suprarenal, endovascular, and reoperative repairs were excluded. Outcome variables were compared over the 6-year period. RESULTS: Floor admissions increased over the study period with 0%, 0%, 3.3%, 16.3%, 48.6%, and 43.6% of patients admitted directly to the surgery ward from 1994 to 1999. The average ICU length of stay declined from 4.6 to 1.2 days, whereas the hospital length of stay decreased from 12.5 to 6.8 days from 1994 to 1999. The change in ICU use had no effect on death (2.4% in Group I vs 0% in Group II). Major and minor morbidity was comparable. Hospital charges were significantly lower for patients in Group II. CONCLUSION: A policy of selective utilization of the ICU after elective infrarenal AAA repair is safe. It can reduce resource use without a negative impact on the quality of care.

Aged↗
PubMed2000

Is color-flow duplex a good diagnostic test for detection of isolated calf vein thrombosis in high-risk patients?

Color-flow duplex scanning (CDS) is a good diagnostic test for lower extremity proximal deep vein thrombosis (DVT). This report aims to evaluate the diagnostic accuracy of CDS in detecting isolated calf DVT in two in-hospital populations. A total of 166 patients had routine DVT testing with both CDS and venography: 99 total joint arthroplasty patients and 67 symptomatic in-hospital patients. Isolated calf DVT was noted in 34% of arthroplasty patients and 12% of symptomatic in-hospital patients. Peroneal DVT was most common. The sensitivity, specificity, positive predictive value, and negative predictive value (with 95% confidence interval [CI]) of CDS in detecting isolated calf DVT in the symptomatic in-hospital group was 39% (16%-62%), 98% (94%-99%), 88% (65%-99%), and 81% (71%-91%), respectively. In the arthroplasty patients these values were 13% (3%-23%), 92% (85%-99%), 60% (30%-90%), and 55% (45%-65%), respectively. CDS has a low sensitivity in detecting isolated calf DVT among hospitalized patients and cannot be deemed an effective tool for identifying clots limited to only one or two tibial vessels.

Arthroplasty, Replacement, Hip↗
PubMed1999

Stent deformation following simulated side-branch dilatation: a comparison of five stent designs.

We aimed to determine the effects of simulated stent side-branch dilatation and subsequent redilatation of the central lumen. Following coronary stent implantation it may be necessary to dilate through the side of a stent to maintain branch patency. Branch dilatation through the side of 3.5-mm-diameter stents (AVE GFX, beStent, Crown, MultiLink, and NIR) was simulated in a plexiglass phantom using 2.5-, 3.0-, 3.5-, and 4.0-mm balloons. In further experiments, the main lumen was redilated with a 3.5-mm balloon after 3.0-mm side-branch dilatation. Thereafter, a 3.5-mm central and a 3.0-mm side-branch balloon were simultaneously inflated ("kissing balloons"). The larger the balloon size used for side-branch dilatation, the greater the distortion of the stent immediately distal to the side-branch, which for a 4.0-mm balloon ranged from 36% +/- 2% (Crown) to 65% +/- 6% (NIR). Central lumen redilatation or kissing balloons abolished this stenosis with little reduction of the side-lumen diameter. The main stent lumen compromise caused by side-branch dilatation can be abolished by main-lumen redilatation or by kissing balloons.

Catheterization↗