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Biomedical subjects

M W Webster

Publications and source records attributed to M W Webster.

At least 37 records · Page 2Linked to original sources
PubMed1999

Preliminary experience with the V-flex plus coronary stent: immediate and one-month clinical outcome.

Procedural and 1-month outcome data following implantation of the V-Flex Plus stent in our first 54 consecutive patients (35 male; mean age, 62 years) are described. Sixty-four stents were implanted for 60 mainly complex lesions; 48% were left anterior descending; 20%, circumflex; 27%, right coronary artery; and 5%, saphenous vein graft. The Indication for stenting was elective in half of the patients and for a suboptimal result or as a bailout procedure in the other half. The stents were deployed at a mean of 12 atm (range, 6-18) and postdilatated to a mean of 15 atm (range, 8-20). Pre- and postdilatation balloon sizes were 2.96 +/- 0.57 mm and 3.16 +/- 0.34 mm, respectively. The procedural success rate was 98%. There were no deaths or Q-wave myocardial infarctions. One patient suffered a non-Q-wave myocardial infarction and another developed a femoral false aneurysm. At 1-month follow-up, there were no additional events, in particular no revascularization procedures. Eighty-nine percent of patients were free of angina. Implantation of the V-Flex Plus stent is safe and effective with an excellent early success rate comparable to that of published randomized trials and registries of carefully selected patients.

Adult↗
PubMed1999

Oxygen-dependent chronic obstructive pulmonary disease does not prohibit aortic aneurysm repair.

BACKGROUND: Severe oxygen-dependent chronic obstructive pulmonary disease (COPD) is considered by many to be a contraindication to open abdominal aortic aneurysm (AAA) repair. We reviewed our own experience with this patient population. METHODS: From July 1995 to March 1999, 14 consecutive patients limited by home oxygen-dependent COPD underwent elective open infrarenal AAA repair. Their medical records were reviewed. RESULTS: The mean aortic aneurysm size was 6.3 cm. The mean PaO2 = 70 mm Hg, PaCO2 = 45 mm Hg, forced expiratory volume in 1 second (FEV1) = 34% of predicted, and forced vital capacity (FVC) = 67% of predicted. All 14 patients were extubated within 24 hours, mean length of hospital stay was 5.9 days, and there were no perioperative deaths. CONCLUSIONS: Severe home oxygen-dependent COPD is not a contraindication to safe elective open AAA repair.

Aged↗
PubMed1999

Progression of asymptomatic carotid stenosis: a natural history study in 1004 patients.

PURPOSE: The purpose of this study was to delineate the natural history of the progression of asymptomatic carotid stenosis. METHODS: In a 10-year period, 1701 carotid arteries in 1004 patients who were asymptomatic were studied with serial duplex scans (mean follow-up period, 28 months; mean number of scans, 2.9/patient). At each visit, stenoses of the internal carotid artery (ICA) and the external carotid artery (ECA) were categorized as none (0 to 14%), mild (15% to 49%), moderate (50% to 79%), severe (80% to 99%), preocclusive, or occluded. Progression was defined as an increase in ICA stenosis to >/=50% for carotid arteries with a baseline of <50% or as an increase to a higher category of stenosis if the baseline stenosis was >/=50%. The Cox proportional hazards model was used for data analysis. RESULTS: The risk of progression of ICA stenosis increased steadily with time (annualized risk of progression, 9.3%). With multivariate modeling, the four most important variables that affected the progression (P <.02) were baseline ipsilateral ICA stenosis >/=50% (relative risk [RR], 3.34), baseline ipsilateral ECA stenosis >/=50% (RR, 1.51), baseline contralateral ICA stenosis >/=50% (RR, 1.41), and systolic pressure more than 160 mm Hg (RR, 1. 37). Ipsilateral neurologic ischemic events (stroke/transient ischemic attack) occurred in association with 14.0% of the carotid arteries that were studied. The progression of ICA stenosis correlated with these events (P <.001), but baseline ICA stenosis was not a significant predictor. CONCLUSION: In contrast to recently published studies, we found that the risk of progression of carotid stenosis is substantial and increases steadily with time. Baseline ICA stenosis was the most important predictor of the progression, but baseline ECA stenosis also was identified as an important independent predictor. Contralateral ICA stenosis and systolic hypertension were additional significant predictors. We found further that the progression of ICA stenosis correlated with ischemic neurologic events but not baseline stenosis. The data provide justification for the use of serial duplex scans to follow carotid stenosis and suggest that different follow-up intervals may be appropriate for different patient subgroups.

Aged↗
PubMed1999

Management of splenic artery aneurysms: the significance of portal and essential hypertension.

BACKGROUND: Splenic artery aneurysm(s) (SAA) are rare. But the incidence and significance of SAA among patients with portal hypertension (PHTN), especially among those who undergo orthotopic liver transplantation (OLT), have not been clearly delineated. STUDY DESIGN: An 11-year (February 1987 to June 1998) retrospective review of our experience with treated SAA was performed. Patient characteristics, risk factors, clinical presentation, surgical management, aneurysm characteristics, and patient outcomes were assessed. Patients were separated according to a history of PHTN for analysis. Patients were also subdivided into ruptured versus elective presentations. RESULTS: Thirty-four patients (22 in the PHTN group) were treated for SAA during the study period. Sixty-two percent (21 of 34) were women; the average age was 50.6 years. In patients without a history of PHTN (n = 12), essential hypertension was a significant risk factor (p < 0.001) for development of SAA. All patients underwent surgical treatment for SAA: resection with splenectomy (n = 23), ligation with splenectomy (n = 5), ligation of SAA only (n = 4), and vascular reconstruction (n = 2). The average size of all treated SAA was 4.8 +/- 2.6 cm, ranging from 1.5 to 12cm. Operative mortality after SAA rupture (n = 15) was 40%, compared with zero mortality for elective SAA repair (n = 19, p < 0.005). Rupture of SAA was associated with a higher mortality in patients with PHTN compared with patients without such history (56% versus 17%, respectively). After a mean followup period of 46 months, survival after rupture was 60% in contrast to 84% after elective repair. The majority of our patients with a history of PHTN (20 of 22) has undergone OLT, representing 0.46% of all OLT recipients (n = 4,374) during the study period. In four patients, SAA were repaired concurrently during transplantation. Of the 7 patients presented with rupture of SAA after OLT, 6 patients presented within 3 to 16 days postoperatively, with a median of 6 days and an overall mortality of 57%. CONCLUSIONS: Essential hypertension and PHTN appear to be significant risk factors for development of SAA. Rupture of SAA is associated with a significant mortality, highest among patients with PHTN. Elective repair remains a safe and effective method of treatment. The significance of SAA is recognized among patients undergoing liver transplantation. A decision should be made to screen and electively treat SAA found in liver transplant patients, especially if the aneurysm is larger than 1.5 cm. Awareness of the increased rupture risk is crucial in management during the immediate posttransplant period.

Adolescent↗
PubMed1998

Results of percutaneous coronary angioplasty in patients <40 years of age.

This study examined factors influencing the outcome of percutaneous transluminal coronary angioplasty (PTCA) in patients <40 years of age. We followed 86 patients (mean age 37 years) treated from 1982 to 1994. The primary procedural success was 90%. At follow-up of 83 patients (97%) at a mean of 48 +/- 33 months (range 5 to 147), there had been 3 late deaths. Actuarial survival at 5 and 10 years was 95% and 91%, respectively. At review only 5% of patients had class III angina and no patient had class IV angina. Repeat revascularization (PTCA alone in 21 [25%], surgery in 8 [10%], or both in 10 [12%] patients) was performed for restenosis in 29 patients (35%) and for disease progression at other sites in 10 patients (12%). On multivariate analysis, a history of diabetes mellitus (p <0.02) was the only factor associated with death or a subsequent cardiovascular event (myocardial infarction, stroke, or hospital admission with unstable angina). At follow-up, 20 patients (24%) still smoked, 64 (77%) had a total cholesterol level > or = 200 mg/dl, 20 (24%) had a body mass index > or = 30, and 15 (18%) were not taking aspirin. In conclusion, PTCA in adults <40 years of age has excellent early results with a low morbidity and mortality. The medium-term prognosis and control of symptoms was good, although by 5 years, further revascularization was required in almost half of the patients.

Adult↗
PubMed1998

Mechanical wall stress in abdominal aortic aneurysm: influence of diameter and asymmetry.

PURPOSE: Risk for rupture of an abdominal aortic aneurysm is widely believed to be related to its maximum diameter. From a biomechanical standpoint, however, risk is probably more precisely related to mechanical wall stress. Many abdominal aortic aneurysms are asymmetric (for example because of anterior bulging with posterior expansion limited by the vertebral column). The purpose of this work was to investigate the effect of maximum diameter and asymmetric bulge on wall stress. METHODS: Three-dimensional computer models of abdominal aortic aneurysms were generated. In one protocol, maximum diameter was held constant while bulge shape factor was varied. The shape factor took into account the asymmetric shape of the bulge. In a second protocol, the shape of the aneurysmal wall was held constant while maximum diameter was varied. Wall stress was computed in each instance with a commercial software package and assumption of physiologic intraluminal pressure. RESULTS: Both maximum diameter and the shape factor were found to have substantial influence on the distribution of wall stress within the aneurysm. In some instances the maximum stress occurred at the midsection, and in others it occurred elsewhere. The magnitude of peak stress acting on the aneurysm increased nonlinearly with increasing maximum diameter or increasing asymmetry. CONCLUSIONS: Our computer models showed that the stress within the wall of an abdominal aortic aneurysm and possibly the potential for rupture are as dependent on aneurysm shape as they are on maximum diameter. This information may be important in determining severity of individual abdominal aortic aneurysms and in improving understanding of the natural history of the disease.

Aorta, Abdominal↗
PubMed1998

Enhancement of tissue factor expression by vein segments exposed to coronary arterial hemodynamics.

PURPOSE: Although saphenous vein is the most reliable conduit for arterial interposition procedures in the coronary circulation, graft thrombosis remains a clinical problem. We hypothesized that an important factor in early graft thrombosis is sudden change in the hemodynamic environment of the vein as it is placed in the coronary circulation. METHODS: We used an ex vivo perfusion system to study freshly excised segments of human saphenous vein (HSV) and pig internal jugular vein. For coronary graft (CAVG) simulation, sections of HSV were subjected to arterial pulsatile pressure and flow and twisting and stretching to mimic deformations caused by the beating heart. Using functional and immunohistochemical assays, we investigated the effect of these conditions on expression of tissue factor (TF), an important prothrombotic surface molecule. RESULTS: In each of 11 experiments (6 human, 5 porcine), vein segments from a single donor were subjected to venous conditions (VEN), CAVG perfusion, or no perfusion. Expression of TF was measured as the amount of factor Xa generated per unit area of luminal vein surface. VEN perfusion did not cause a significant change in mean TF expression over nonperfused control values (human: 14.3 +/- 1.5 versus 11.4 +/- 2.3 U/cm2, p = 0.31; pig: 11.6 +/- 1.5 versus 12.5 +/- 1.4 U/cm2, p = 0.70). CAVG perfusion led to significant enhancement of TF expression over VEN perfusion (human: 36.8 +/- 6.2 versus 14.3 +/- 1.5 U/cm2, p < 0.05; pig: 40.0 +/- 9.9 versus 11.6 +/- 1.5 U/cm2, p < 0.05). Immunohistochemical analysis showed positive TF staining on the luminal side of a CAVG-stimulated HSV segment, but not on a VEN-stimulated segment. In four additional studies, HSV segments were subjected to arterial perfusion without twist and stretch to mimic lower extremity arterial interposition grafts. TF expression for lower extremity venous graft perfusion was significantly higher than for VEN perfusion (25.3 +/- 2.5 versus 14.3 +/- 1.5, p < 0.01) but not significantly different from CAVG perfusion. CONCLUSIONS: Our studies in a unique perfusion system suggest that exposure of vein to coronary arterial hemodynamic conditions results in elevated expression of the important prothrombotic molecule TF. This phenomenon may contribute to early graft thrombosis.

Animals↗
PubMed1998

Effect of intraluminal thrombus thickness and bulge diameter on the oxygen diffusion in abdominal aortic aneurysm.

The intraluminal thrombus (ILT) commonly found within abdominal aortic aneurysm (AAA) may serve as a barrier to oxygen diffusion from the lumen to the inner layers of the aortic wall. The purpose of this work was to address this hypothesis and to assess the effects of AAA bulge diameter (dAAA) and ILT thickness (delta) on the oxygen flow. A hypothetical, three-dimensional, axisymmetric model of AAA containing ILT was created for computational analysis. Commercial software was utilized to estimate the volume flow of O2 per cell, which resulted in zero oxygen tension at the AAA wall. Solutions were generated by holding one of the two parameters fixed while varying the other. The supply of O2 to the AAA wall increases slightly and linearly with dAAA for a fixed delta. This slight increase is due to the enlarged area through which diffusion of O2 may take place. The supply of O2 was found to decrease quickly with increasing delta for a fixed dAAA due to the increased resistance to O2 transport by the ILT layer. The presence of even a thin, 3 mm ILT layer causes a diminished O2 supply (less than 4 x 10(-10) mumol/min/cell). Normally functioning smooth muscle cells require a supply of 21 x 10(-10) mumol/min/cell. Thus, our analysis serves to support our hypothesis that the presence of ILT alters the normal pattern of O2 supply to the AAA wall. This may lead to hypoxic cell dysfunction in the AAA wall, which may further lead to wall weakening and increased potential for rupture.

Animals↗
PubMed1998

Arterial hemodynamics and wall mechanics.

Arterial hemodynamics and wall mechanics are important considerations for the vascular clinician for a number of reasons. Hemodynamics and wall mechanics both have been shown to be affecters of disease formation. It is important for the practicing vascular surgeon to know how disease affects both blood flow and wall mechanics and to understand the consequence of hemodynamics on arterial reconstructions. In this article, we summarize the basic concepts of arterial hemodynamics and wall mechanics as they relate to the development of arterial pathology. A few practical mathematical relationships and examples are provided for both illustration and utilization. We also discuss the use of computer models for the estimation of wall stresses in individual abdominal aortic aneurysms.

Aortic Aneurysm, Abdominal↗
PubMed1998

The roles for coronary surgery and angioplasty in the management of patients with stable angina: evidence and decision making.

Evidence from the randomized studies of coronary surgery suggests that patients who benefit from surgery in terms of improved survival are those with left main stem stenosis, triple vessel coronary artery disease, impaired left ventricular function or higher angina class. Patients currently undergoing surgery are in general older, with more severe angina, more comorbidity and more extensive coronary disease as compared with the population randomized in the earlier studies. Angioplasty has been shown to improve symptoms and to reduce the need for surgery in certain patients. Recent changes in procedural techniques and adjunctive therapies have reduced the number of acute complications and the rate of restenosis. However, recent evidence suggests that some patients with mild angina (< class 2) or good exercise tolerance may not benefit as much from angioplasty as other patients with more severe angina.

Angina Pectoris↗
PubMed1997

Late regression of the dilated site after coronary angioplasty: a 5-year quantitative angiographic study.

BACKGROUND: Limited data are available on the changes that occur at the dilated site late after coronary angioplasty. The aim of this study was to evaluate with quantitative angiography the natural history of changes that occur in the dilated segment between "early" (approximately 6 months) and "late" (approximately 5 years) follow-up after angioplasty. METHODS AND RESULTS: Of 127 consecutive patients (174 lesions) with successful angioplasty, 125 underwent early angiography. Three patients subsequently died, and 24 underwent revascularization surgery or repeated angioplasty, giving a study-eligible population of 98 patients. Quantitative angiographic analysis was performed before and immediately after angioplasty and at early and late follow-up in the study population of 84 patients (115 lesions), which was 86% of study-eligible patients. Mean lesion diameter stenosis decreased from 36.3+/-14.2% at early to 29.6+/-13.5% at late follow-up (P<.0001). No lesion developed late restenosis by the 50% diameter loss criterion. Late regression was related to stenosis severity at early angiography (r=-.58, P<.001). Subgroups at early angiography of 40% to 49% stenosis and > or = 50% stenosis showed significant regression at late angiography. CONCLUSIONS: Lesion regression at the dilated site is common late after angioplasty. The more severe a stenosis is at early angiography, the more likely the chance that there will be late regression. A strategy of watchful waiting may be appropriate for patients with restenotic lesions of borderline severity.

Adult↗
PubMed1997

Cellular content and permeability of intraluminal thrombus in abdominal aortic aneurysm.

PURPOSE: A pathologic feature commonly associated with abdominal aortic aneurysms is the presence of variably sized and shaped intraluminal thrombus, which may be fundamental to the disease process. However, the precise role of the intraluminal thrombus in the formation, enlargement, and rupture of abdominal aortic aneurysms is unknown. The hypothesis tested in this study was whether there were structural features of aortic thrombi to suggest that it may be involved in the pathogenesis of abdominal aortic aneurysms. We have investigated this hypothesis using a variety of structural and biochemical techniques. METHODS: Tests performed were light, transmission, and scanning electron microscopy; fluid permeability measurements; and Western blots. RESULTS: Intraluminal thrombus found in abdominal aortic aneurysms is structurally complex and is traversed from the luminal to abluminal surface by a continuous network of interconnected canaliculi. Quantitative microscopic analysis of the thrombus shows cellular penetration for at least 1 cm from the luminal surface of the thrombus. Macro-molecular penetration may be unrestricted throughout the entire thickness of the thrombus. Fibrin deposition occurred throughout the thrombus, whereas fibrin degradation occurred principally at the abluminal surface. CONCLUSIONS: These principally structural studies support the hypothesis that the thrombus is a self-sustaining entity that may have significance in the pathophysiologic mechanism of abdominal aortic aneurysms.

Aorta, Abdominal↗
PubMed1997

Utility of clinical pathway and prospective case management to achieve cost and hospital stay reduction for aortic aneurysm surgery at a tertiary care hospital.

PURPOSE: We reviewed our experience with a clinical pathway instituted in December 1993 for all nonurgent abdominal aortic aneurysm (AAA) surgery. METHODS: We analyzed a reference group of 49 consecutive pre-pathway AAA patients (group I) and the 44 patients enrolled in the first year of the pathway (group II). On the basis of the interim review of data collected during the first year, pathway modifications were made, and 34 patients enrolled after these modifications (group III) were also analyzed. RESULTS: Comparison of groups I and II showed that institution of the pathway resulted in a marginally significant reduction in mean charges of 14.7% (p = 0.09), and a slight fall in mean length of stay (LOS) (13.8 vs 13.1 days, NS) and mortality rate (4.1% vs 2.3%, NS). For group II, a significant correlate (p < 0.05) of increased charges was fluid overload as diagnosed by chest radiograph. This recognition led to active efforts to reduce perioperative fluid administration. Comparison of groups II and III revealed that the practice modifications led to marked reduction in the incidence of fluid overload (73% vs 24%; p < 0.01), mean charges (30.4% reduction; p < 0.05), mean LOS (13.1 vs 10.2 days; p < 0.05), and median LOS (11 vs 8 days). Multiple regression analysis of all pathway patients showed that preoperative renal insufficiency is a significant predictor of both increased LOS (p < 0.01) and charges (p < 0.01), but that age, sex, and coronary disease were not predictive. Of the postoperative parameters analyzed, important correlates of increased charges were acute renal failure (p < 0.01) and fluid overload (p < 0.01). CONCLUSIONS: Institution of a clinical pathway for AAA repair resulted in significant charge reduction and a slight reduction in stay. Practice modifications based on interim data analysis yielded further significant reductions in charges and LOS, with overall per-patient charge savings (group I vs III) of 40.6% (p < 0.05) and overall LOS reduction of 3.5 days (p < 0.05). The reduction in actual charges was seen despite an overall increase in the hospital rate structure. Comparing groups I, II, and III, we found no indication of increasing mortality rate. Ongoing analysis has identified correlates of increased charges, potentially permitting identification of high-cost subgroups and more focused cost-control efforts. Rather than restricting management, clinical pathways with periodic data analysis may improve quality of care.

Aortic Aneurysm, Abdominal↗
PubMed1997

The factor V Leiden mutation: spectrum of thrombotic events and laboratory evaluation.

PURPOSE: This study aims to describe the spectrum of clinical thrombotic events and to compare the methods of laboratory evaluation for the newly described prothrombotic factor V Leiden mutation. METHODS: Specimens from 1376 patients with thrombotic events or their relatives were tested for the factor V Leiden mutation by polymerase chain reaction plus restriction digest from Jan. 1, 1995, to Mar. 31, 1996. Activated protein C (APC) resistance test data was available for 554 of these patients. Clinical information was available for 166 patients with the mutation. RESULTS: Of 1376 patients tested for factor V Leiden mutation, 270 (19.6%) were positive, with 12 homozygotes and 258 heterozygotes. Of 554 patients for whom APC resistance data was available, 221 (39.9%) had low APC resistance ratios (< or = 2.4); of these only 97 (43.9%) were factor V Leiden-positive. Among 333 samples with normal or elevated APC resistance ratios, 19 (5.7%) were later identified with the factor V Leiden mutation, despite the normal screening test. One hundred fourteen of 166 patients (68.7%) with the mutation had at least one thrombotic event, most commonly deep venous thrombosis and pulmonary embolus. Arterial cerebrovascular thrombotic events occurred in 11 patients (10%), and myocardial infarctions in eight (7%). The mean age of all patients with arterial thrombotic events was 45.4 years. CONCLUSIONS: The factor V mutation is a common cause of venous thromboses but may also be associated with the early presentation of arterial thrombotic events. The APC resistance test is a sensitive screening assay but has limitations of its specificity in clinical practice.

Adolescent↗