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Biomedical subjects

W M Abbott

Publications and source records attributed to W M Abbott.

At least 37 records · Page 2Linked to original sources
PubMed1997

Prosthetic above-knee femoropopliteal bypass grafting: results of a multicenter randomized prospective trial. Above-Knee Femoropopliteal Study Group.

PURPOSE: There are excellent arguments in favor of the preferential use of prosthetic grafts above the knee for the treatment of infrainguinal occlusive disease. This approach has been popularized on the basis of the seemingly acceptable results when using polytetrafluoroethylene (PTFE). However, in many centers, knitted Dacron polyester has been used in these patients, and there are several studies that show equivalent and, in some, superior results with Dacron when compared with PTFE. The purpose of this study was to examine these results in a definitive way. METHODS: A randomized prospective trial in eight clinical academic centers in the United States and Canada was initiated in 1991. Two hundred forty-four patients eligible for such a study, by virtue of criteria extant in each institution at the time, were centrally randomized. They underwent placement of either a knitted Dacron polyester graft impregnated with collagen or a thin-wall expanded reenforced PTFE graft to the above-knee popliteal artery, usually from the common femoral artery. They were frequently observed by protocol for as long as 5 years by a physical examination noninvasive hemodynamic study, including duplex scanning in many instances. Continuing patency was noted, as were other potential adverse outcome events. The data were analyzed by the log-rank test for cumulative patency and expressed as Kaplan-Meier curves. Data were further analyzed with a Cox proportional hazards model. RESULTS: There were no differences in graft groups in demographic or comorbid factors. The procedural mortality rate was zero, and the morbidity rate was low (6.5%). The long-term patient survival rate was excellent (77% at 3 years). At the end of these years, no statistical significance in primary or secondary patency rates was observed between the two grafts (primary patency rate, 62% +/- 14.4% for Dacron; 57% +/- 15.5% for PTFE). No unexpected adverse outcomes on limb status were noted. Patency rates in both graft groups were inferior in patients who received small grafts (5 to 6 mm vs 7 to 8 mm; hazards ratio, 4.15) and younger (<65 years) smoking patients. CONCLUSIONS: The fact that these two prosthetic grafts performed in equivalent fashion in a controlled, well-conducted prospective study is not surprising in spite of the previous work that suggested differences. If the preferential use of synthetic bypass grafts above the knee is to be used, it should be restricted to older nonsmokers with favorable anatomy. In that instance, the choice of graft material will depend on handling characteristics and cost. Above-knee prostheses should be only selectively used in younger, smoking patients, and graft size should be carefully considered in patients who undergo this operation.

Arterial Occlusive Diseases↗
PubMed1997

Magnetic resonance angiography in the management of lower extremity arterial occlusive disease: a prospective study.

PURPOSE: We conducted a prospective study to clarify the clinical utility of magnetic resonance angiography (MRA) in the treatment of patients with lower extremity arterial occlusive disease. METHODS: During the interval of September 1993 through March 1995, 79 patients (43% claudicants, 57% limb-threatening ischemia) were studied with both MRA and contrast arteriography (ANGIO) and underwent intervention with either balloon angioplasty (9%), surgical inflow (28%), or outflow (63%) procedures. MRA and ANGIO were interpreted by separate blinded vascular radiologists, and arterial segments from the pelvis to the foot were graded as normal or with increasing degrees of mild (25% to 50%), moderate (51% to 75%), or severe (75% to 99%) stenosis or occlusion. Treatment plans were formulated by the attending surgeon and were based initially on hemodynamic, clinical, and MRA data and thereafter with ANGIO. Additional study surgeons formulated independent and specific treatment plans based on MRA or ANGIO alone. Indexes of agreement (beyond chance) for arterial segments depicted by MRA and ANGIO were assessed (kappa value), and treatment plans formulated were compared (chi-square). RESULTS: Precise agreement (%) and the percent of major discrepancies (segment classified as normal/mild stenosis on one study and severe stenosis/occlusion on the other) between MRA and ANGIO for respective arterial segments was as follows: common and external iliacs (n = 256) 77/3.5; superficial femoral and above-knee popliteal (n = 255) 73/6.7; below-knee popliteal (n = 131) 84/3.8; infrapopliteal runoff vessels (n = 864) 74/12.4; pedal vessels (n = 111) 69/19.8 Kappa values indicated moderate agreement (between MRA and ANGIO) beyond chance for all arterial segments. Treatment plans formulated by the attending surgeon, the MRA surgeon, and the ANGIO surgeon agreed in more than 85% of cases. Inability of MRA to assess the significance of inflow disease and inadequate detail of tibial/pedal vessels were the principal deficiencies of MRA in those cases where it was considered an inadequate examination. CONCLUSION: These findings suggest MRA and ANGIO are nearly equivalent examinations in the demonstration of infrainguinal vascular anatomy. MRA is an adequate preoperative imaging study (and may replace ANGIO), particularly in those circumstances when the risk of ANGIO is increased or when clinical and hemodynamic evaluation predict the likelihood of straightforward aortofemoral or femoral-popliteal reconstruction.

Aged↗
PubMed1997

Clinical experience with epidural cooling for spinal cord protection during thoracic and thoracoabdominal aneurysm repair.

PURPOSE: This report summarizes our experience with epidural cooling (EC) to achieve regional spinal cord hypothermia and thereby decrease the risk of spinal cord ischemic injury during the course of descending thoracic aneurysm (TA) and thoracoabdominal aneurysm (TAA) repair. METHODS: During the interval July 1993 to Dec. 1995, 70 patients underwent TA (n = 9, 13%) or TAA (n = 61) (type I, 24 [34%], type II, 11 [15%], type III, 26 [37%]) repair using the EC technique. The latter was accomplished by continuous infusion of normal saline (4 degrees C) into a T11-12 epidural catheter; an intrathecal catheter was placed at the L3-4 level for monitoring of cerebrospinal fluid temperature (CSFT) and pressure (CSFP). All operations (one exception, atriofemoral bypass) were performed with the clamp-and-sew technique, and 50% of patients had preservation of intercostal vessels at proximal or distal anastomoses (30%) or by separate inclusion button (20%). Neurologic outcome was compared with a published predictive model for the incidence of neurologic deficits after TAA repair and with a matched (Type IV excluded) consecutive, control group (n = 55) who underwent TAA repair in the period 1990 to 1993 before use of EC. RESULTS: EC was successful in all patients, with a 1442 +/- 718 ml mean (range, 200 to 3500 ml) volume of infusate; CSFT was reduced to a mean of 24 degrees +/- 3 degrees C during aortic cross-clamping with maintenance of core temperature of 34 degrees +/- 0.8 +/- C. Mean CSFP increased from baseline values of 13 +/- 8 mm Hg to 31 +/- 6 mm Hg during cross-clamp. Seven patients (10%) died within 60 days of surgery, but all survived long enough for evaluation of neurologic deficits. The EC group and control group were well-matched with respect to mean age, incidence of acute presentations/aortic dissection/aneurysm rupture, TAA type distribution, and aortic cross-clamp times. Two lower extremity neurologic deficits (2.9%) were observed in the EC patients and 13 (23%) in the control group (p < 0.0001). Observed and predicted deficits in the EC patients were 2.9% and 20.0% (p = 0.001), and for the control group 23% and 17.8% (p = 0.48). In considering EC and control patients (n = 115), variables associated with postoperative neurologic deficit were prolonged (> 60 min) visceral aortic cross-clamp time (relative risk, 4.4; 95% CI, 1.2 to 16.5; p = 0.02) and lack of epidural cooling (relative risk, 9.8; 95% CI, 2 to 48; p = 0.005). CONCLUSION: EC is a safe and effective technique to increase the ischemic tolerance of the spinal cord during TA or TAA repair. When used in conjunction with a clamp-and-sew technique and a strategy of selective intercostal reanastomosis, EC has significantly reduced the incidence of neurologic deficits after TAA repair.

Adult↗
PubMed1997

Prosthetic above-knee femoral-popliteal bypass: indications and choice of graft.

In this article, the use of prosthetic grafts for above-the-knee femoral-popliteal arterial bypass reconstruction is discussed. The issue as to whether prostheses should be used preferentially, selectively, or not at all, remains both topical and controversial in vascular surgical circles. The debate has been heightened by a recently presented, and soon to be published, randomized prospective trial comparing two different prostheses, knitted polyester and polytetrafluoroethylene. The results showed equivalent patency rates and reasonably satisfactory overall results. The general considerations (pro and con) as whether to proceed with prosthetic repair and, if so, which graft to select in such patients, is elaborated on this issue, and a recommendation appropriate to the perspective of 1997 is presented.

Anastomosis, Surgical↗
PubMed1996

Biochemical characterization and deletion analysis of recombinant human protein phosphatase 2C alpha.

The use of protein phosphatase inhibitors has been instrumental in defining the intracellular roles of protein phosphatase 1 (PP1), PP2A and PP2B. Identification of the role of PP2C in vivo has been hampered, in part, by the unavailability of specific inhibitors. In order to facilitate the identification of novel and specific inhibitors of PP2C by random screening of compounds, and to further characterize this enzyme at the molecular level by site-directed mutagenesis and X-ray crystallography, we have expressed active recombinant human PP2C alpha (rPP2C alpha) in Escherichia coli. Biochemical characterization of rPP2C alpha showed that it could hydrolyse p-nitrophenyl phosphate (pNPP) although, in contrast with native PP2C, this was not stimulated by Mg2+. As with native PP2C, okadaic acid failed to inhibit rPP2C alpha, whereas 50 mM NaF dramatically inhibited its activity. An alignment of the amino acid sequence of AMP-activated protein kinase (AMPK) with those of other serine/threonine protein kinases around the regulatory phosphorylation site (subdomains VII-VIII) revealed a high degree of conservation. Phosphopeptides derived from this region of AMPK and containing the almost invariant threonine (Thr172 in AMPK) were found to be good substrates for rPP2C alpha. We also showed that rPP2C alpha can inactivate AMPK, but only in the presence of Mg2+. To define the regions of PP2C alpha important for catalytic activity, we expressed a number of truncated proteins based on the sequence and proposed domain structure of the PP2C alpha homologue from Paramecium tetraurelia. Deletion of 75 residues (9 kDa) from the C-terminus appeared to have little effect on the catalytic activity using pNPP, phosphopeptides or AMPK as substrates. This suggests that the residues important in catalysis lie elsewhere in the protein. A further deletion of the C-terminus led to a completely inactive and very poorly soluble protein.

AMP-Activated Protein Kinases↗
PubMed1996

Laser assisted vascular welding with real time temperature control.

BACKGROUND AND OBJECTIVE: Previous studies in laser assisted vascular welding have been limited by the lack of a reliable end point for tissue fusion. As a means of improving the reproductibility of laser assisted repairs, a system incorporating real time temperature monitoring and closed loop feedback was used. STUDY DESIGN/MATERIALS AND METHODS: The system consisted of a direct view infrared thermometer for monitoring the laser heated spot, a 1.9 microns diode laser, and a microprocessor for data acquisition and feedback control of the laser power to maintain a constant tissue temperature. Rat aortas were welded under constant surface temperature conditions. RESULTS: In vivo temperature stability of +/- 2 degrees C was achieved over a temperature range of 70-90 degrees C pertinent to welding small vessels. When welds were completed using the feedback system to maintain the tissue temperature at 80 degrees C, the acute success rate was 100% and the burst pressure was 290 +/- 70 mmHg. CONCLUSION: These studies demonstrate that the use of real time monitoring and feedback control results in improved consistency for vascular tissue welding.

Anastomosis, Surgical↗
PubMed1996

Characteristics of vascular wall cells subjected to dynamic cyclic strain and fluid shear conditions in vitro.

We recently developed an in vitro silicone rubber tubular apparatus, the vascular simulating device (VSD), which simulates pressure, flow, and strain characteristics of peripheral arteries (Benbrahim et al., 1994, J. Vasc. Surg. 20, 184-194). In this report, we tested the ability of silicone rubber surfaces to support the growth and differentiation of endothelial cells (EC) and smooth muscle cells (SMC) and studied the effects of arterial levels of pressure, flow, and strain on these properties. Human umbilical and saphenous vein EC and bovine aortic EC and SMC were cultured on coated and uncoated silicone rubber in flat and tubular configurations (6 mm inner diameter) and on tissue culture plastic (TCP). Attachment, growth, and differentiation were compared on these surfaces. In addition, the effects of arterial pressure, flow, and strain conditions on adhesion and subsequent growth and differentiation were studied in the tubular configuration. Attachment and growth of vascular wall cells on fibronectin-coated silicone rubber was similar to that obtained on TCP. Application of arterial levels of pressure, flow, and strain did not alter adhesion of the cells to the tubes. Subsequent passage of these cells demonstrated that attachment, growth, and differentiation (uptake of LDL and expression of factor VIII-related antigen by EC and expression of muscle-specific actin by SMC) were similar in cells derived from experimental and control tubes which were not subjected to arterial conditions. Finally, mRNA expression of specific "housekeeping" genes was similar in cells isolated from experimental and control tubes. We conclude that the VSD supports the culture of viable and differentiated EC and SMC. These experiments demonstrate that it is possible to evaluate the effects of arterial strain and fluid shear on vascular wall cells in vitro, in a configuration similar to the blood vessel wall.

Aorta↗
PubMed1996

Continuous pulse amplitude monitoring of infrainguinal bypass grafts in the first 24 postoperative hours.

To evaluate continuous pulse amplitude monitoring (CPAM) as a method for early postoperative graft surveillance following infrainguinal bypass surgery, a prospective observational study was carried out in 34 consecutive infrainguinal bypass grafts. CPAM tracings were compared with pre- and postoperative pulse palpation, ankle/brachial index (ABI) measurements, and pulse volume recordings (PVR). The utility of each method was defined by its ability to demonstrate graft patency in the first 24 hours. Pulse palpation was considered a useful monitoring tool if a postoperative pedal pulse was found in the absence of palpable preoperative pulses. The ABI qualified in this respect if a postoperative increase of at least 0.25 could be demonstrated; for PVR tracings an increase of at least one category was required. The utility of CPAM was established by an increase of at least 5 mm compared to the preoperative values. There were no early graft failures. We were therefore unable to calculate the ability of the studies to predict graft failure. The percentages (95% confidence limits) for which pulse palpation, ABI, and PVR were found capable of demonstrating graft patency were 50% (range 34% to 66%), 53% (range 36% to 70%), and 71% (range 54% to 83%), respectively. CPAM appeared to be far superior to these three methods with a utility of 94% (range 81% to 98%; p < 0.05). Patient and operator acceptability of CPAM was high. Skin pressure problems are a potential risk if the CPAM probe is left attached to the skin for more than 24 hours. CPAM was a valuable and reliable means of monitoring infrainguinal vascular reconstructions. Apart from being inexpensive, continuous, objective, and simple, CPAM is noninvasive and painless. It is advisable to remove the probe 24 hours after surgery, when the most crucial period for graft monitoring has passed.

Adult↗
PubMed1996

Coagulation changes during thoracoabdominal aneurysm repair.

PURPOSE: The cause of coagulopathic hemorrhage during thoracoabdominal aneurysm (TAA) repair has not been well defined in human studies. We investigated changes in the coagulation system associated with supraceliac versus infrarenal cross-clamping to address this critical issue. METHODS: Blood levels of fibrinogen, the prothrombin fragment F1.2, D-dimer, and factors II, V, VII, VIII, IX, X, XI, and XII were analyzed in 19 patients with TAAs and four patients with abdominal aortic aneurysms (AAAs) at: (A) induction; (B) 30 minutes into supraceliac (TAA) or infrarenal (AAA) clamping; (C) 30 minutes after release of supraceliac or infrarenal clamps; and (D) immediately after surgery. Preoperative and intraoperative variables, including but not limited to aneurysm type, pathologic findings, comorbid conditions, clamp times, volume and timing of blood products, and clinical outcome, were prospectively recorded. Significance was determined by analysis of variance, Student's t test, and univariate linear regression. RESULTS: Levels of fibrinogen and factors II, V, VIII, VIII, IX, X, XI, and XII decreased (p < 0.05) at time B versus time A and returned to near baseline by time D. D-dimer and F1.2 increased starting at time B and reached significance (p < 0.05) by time D. Data points were compared for the TAA and AAA groups. Although AAA groups demonstrated a trend to factor activity reduction and increased fibrinolysis, the effect was much less pronounced than in TAA and did not approach significance. No correlation of coagulation change with clamping time was present; however, visceral clamping times were all less than 65 minutes (mean, 44 minutes). Blood and factor replacement was initiated after time B. Univariate regression analysis of factor level versus total blood replacement demonstrated a significant (p < 0.04) correlation between the reduction in the levels of factors II, V, VII, VIII, X, and XII, and the increase in the level of D-dimer at time B and subsequent total blood replacement. CONCLUSIONS: Thoracoabdominal aneurysm repair is associated with a reduction in clotting factor activity and an increase in fibrinolytic function, which occurs after placement of the supraceliac clamp. Explanations include visceral ischemia or a greater and longer ischemic tissue burden as the likely cause of coagulation alterations. Total blood replacement during TAA procedures was correlated to the degree of factor reduction and fibrinolysis at the time of visceral cross-clamping. An aggressive approach to early blood component replacement and to coagulation monitoring could lessen blood loss during TAA repair and avoid potentially disastrous bleeding complications.

Aortic Aneurysm, Abdominal↗
PubMed1996

Renal artery reconstruction for the preservation of renal function.

PURPOSE: We reviewed a 13-year experience with an emphasis on long-term survival and renal function response when renal artery reconstruction (RAR) was performed primarily for the preservation or restoration of renal function in patients who had atherosclerotic renovascular disease. METHODS: From January 1, 1980, to June 30, 1993, 139 patients underwent RAR for renal function salvage and were retrospectively reviewed. Inclusion criteria were either preoperative serum creatinine level > 2.0 mg/dl (67% of patients) or RAR to the entire functioning renal mass irrespective of baseline renal function. Patient survival was calculated by life-table methods. Cox regression analysis was used to determine relative risk (RR) estimates for the late outcomes of continued deterioration of renal function and late survival after RAR. A logistic regression model was used to evaluate variables associated with perioperative complications. RESULTS: Clinical characteristics of the cohort were notable for advanced cardiac (history of congestive heart failure, 27%; angina, 22%; previous myocardial infarction, 19%) and renal disease (serum creatinine level < 2.0 mg/dl, 33%; 2.0 mg/dl to 3.0 mg/dl, 40%, > 3.0 mg/dl, 27%). Cardiac disease was the principle cause of early (6 of 11 operative deaths) and late death. Operative management consisted of aortorenal bypass in 47%, extraanatomic bypass in 45%, and endarterectomy in 8%; 45% of patients required combined aortic and RAR. The operative mortality rate was 8%; significant perioperative renal dysfunction occurred in 10%. Major operative morbidity was associated with increasing azotemia (RR = 2.1; p = 0.001; 95% confidence interval [CI], 1.3 to 4.7 for each 1.0 mg/dl increase in baseline creatinine level). Of those patients who had a baseline creatinine level > or = 2.0 mg/dl, 54% had > or = 20% reduction in creatinine level after RAR. Late follow-up data were available for 87% of operative survivors at a mean duration of 4 years (range, 6 weeks to 12.6 years). Actuarial survival at 5 years was 52% +/- 5%. Continued deterioration in renal function occurred in 24% of patients who survived operation, and eventual dialysis was required in 15%. Deterioration of renal function after RAR was associated with increasing levels of preoperative creatinine (RR = 1.6; 95% CI, 1.2 to 1.8; p = 0.001 for each 1.0 mg/dl increment in baseline creatinine level), and inversely related to early postoperative improvement in creatinine level (RR = 0.41; 95% CI, 0.2 to 0.9; p = 0.04). CONCLUSIONS: Intervention before major deterioration in renal function and an aggressive posture toward the frequently associated coronary artery disease are necessary to improve long-term results when RAR is performed for renal function salvage.

Adult↗
PubMed1996

Avoiding infrainguinal bypass wound complications in patients with chronic renal insufficiency: the role of the anatomic plane.

OBJECTIVE: To study the factors leading to wound problems in patients with chronic renal insufficiency (CRI) with emphasis on subcutaneous vs. deep placement of grafts. METHODS: The outcomes of patients undergoing an infrainguinal bypass with preoperative CRI (serum creatinine > or = 2.0 mg/dl) were reviewed. Surgical site infection (SSI) was classified as superficial or deep according to the Centres for Disease Control standards. RESULTS: Forty-two patients underwent a total of 47 infrainguinal bypasses for ischaemic rest pain or tissue loss. The graft location was partially or predominantly subcutaneous in 21 limbs (Group I) and 26 grafts were positioned in the anatomic or subfascial planes (Group II). In Group I, seven early (< 30 days postoperative), one intermediate (4-6 weeks postoperative), and one late (> 6 weeks postoperative) SSI's were found (9/21, 43%). In three of these patients the graft was exposed and two required removal. In contrast, only two early and one intermediate SSI's (3/26, 12%) were noted in Group II (p = 0.02). A logistic regression analysis, with twelve possible covariables wound healing, confirmed the subcutaneous location to be the only controllable factor significantly predicting SSI (relative risk = 11.6, p = 0.01). CONCLUSIONS: The infrainguinal bypass in patients with CRI is associated with a high incidence of wound complications. In our retrospective series, the presence of a vascular conduit in the subcutaneous plane was connected with a higher rate of SSI. Despite the growing trend toward the use of the in situ bypass, CRI may represent a circumstance where deeply placed grafts should be used preferentially.

Adult↗
PubMed1996

Carotid Doppler ultrasound criteria for internal carotid artery stenosis based on residual lumen diameter calculated from en bloc carotid endarterectomy specimens.

BACKGROUND AND PURPOSE: Carotid duplex ultrasound is widely used to screen patients for carotid endarterectomy and if combined with MR angiography and transcranial Doppler may be an alternative to conventional angiography in the preoperative assessment. We have examined the correlation between Doppler velocities and the residual lumen diameters of internal carotid arteries from surgical pathological specimens to establish Doppler criteria for residual lumen diameter independent of percent stenosis. METHODS: Ninety-one patients who underwent 99 carotid endarterectomies for internal carotid artery stenosis within 6 months of their carotid duplex ultrasound evaluation were studied. The endarterectomy specimens were removed en bloc, and the minimal residual lumen diameter was calculated by computer analysis. The sensitivity and specificity of the Doppler criteria for determining high-grade stenosis were calculated and receiver-operator curves generated. RESULTS: Peak systolic velocity (PSV), end-diastolic velocity (EDV),and carotid index (peak internal carotid artery velocity/ common carotid artery velocity) correlated with the residual lumen diameter. PSV > 440 cm/s, EDV > 155 cm/s, or carotid index > 10 indicated a residual lumen diameter of < or = 1.5 mm (specificity of 100% and sensitivity of 58%, 63%, and 30%, respectively). When these criteria were combined, the sensitivity increased to 72%. A PSV > 200 cm/s combined with either an EDV > 140 cm/s or a carotid index > 4.5 has a sensitivity of 96% and a specificity of 61%. CONCLUSIONS: Doppler criteria can be both specific and sensitive for detecting a significant stenosis, defined as a < or = 1.5 mm residual lumen diameter. By adjustment of the velocity criteria, it can be 100% specific or a highly sensitive test (96%).

Blood Flow Velocity↗