Long-term results justify autogenous infrainguinal bypass grafting in patients with end-stage renal failure

INTRODUCTION

Infrainguinal bypass grafting for limb-threatening ischemia in patients with end-stage renal disease is generally thought to be associated with increased operative risk and poor long-term outcome. This retrospective study was undertaken to examine the modern-era, long-term results of infrainguinal bypass grafting in dialysis-dependent patients.

METHODS

Over the past 5 years in a single institution, 425 lower extremities (368 consecutive patients) were revascularized for the indication of limb salvage. Sixty-four patients (82 limbs) were dialysis-dependent at the time of revascularization, and this group was analyzed separately. They exhibited statistically significant higher incidences of diabetes (83% vs 56%; P <.001), hypertension (91% vs 74%; P <.001), and more distal vascular disease, which required a greater proportion of proximal anastomoses at the popliteal level (24% vs 11%; P <.01) and distal anastomoses at the infrapopliteal level (75% vs 65%; P <.05).

RESULTS

Despite the higher prevalence of comorbid conditions and distal disease in patients with renal failure, their perioperative 30-day mortality rate remained low (4.9%) and was not significantly different from that in patients with functioning kidneys (2.9%; P = not significant). After a median follow-up of 11 months (range, 0-60 months), the 3-year autogenous conduit secondary graft patency in patients with renal failure was no different than in patients with functioning kidneys (67% +/- 9% vs 64% +/- 5%; P = not significant). Nonautogenous conduits in dialysis-dependent patients exhibited a significantly poorer outcome with only 27% +/- 12% remaining secondarily patent at 2 years. As expected, both limb salvage and patient survival were significantly less in patients with renal faiture, although both exceeded 50% at 3 years (limb salvage 59% +/- 8% vs 68% +/- 5%; P <.05; patient survival 60% +/- 8% vs 86% +/- 4%; P <.001). The often-quoted phenomenon of limb loss, despite a patent bypass graft, occurred infrequently in this study (n = 3 of 82 limbs).

CONCLUSION

Infrainguinal revascularization can be performed in dialysis-dependent patients with acceptable perioperative and long-term results, especially in patients in whom adequate autologous conduit is available.

Patency and limb salvage after infrainguinal bypass with severely compromised ("blind") outflow

HYPOTHESIS

Infrainguinal graft patency and limb salvage are adversely affected by severely compromised outflow.

DESIGN

Retrospective review of all infrainguinal bypass procedures performed at a single institution during a 5-year period.

SETTING

University teaching hospital.

PATIENTS

Two hundred seventy-four patients underwent infrainguinal bypass for limb salvage (351 grafts in 307 limbs).

INTERVENTIONS

All infrainguinal bypasses originated from a femoral artery. The distal anastomosis in 279 grafts was located in an artery with at least 1 patent outflow vessel with anatomically normal end-artery runoff (Society for Vascular Surgery/International Society for Cardiovascular Surgery ad hoc committee runoff score, 1-9). The distal anastomosis of 72 grafts was located in an artery with only collateral outflow ("blind bypass"; runoff score, 10).

MAIN OUTCOME MEASURES

Perioperative morbidity and mortality, primary-assisted and secondary graft patency, limb salvage, and survival.

RESULTS

All data are presented as mean +/- SEM. Patients undergoing blind bypass were older (age, 70 +/- 2 vs. 66 +/- 1 years; P <.05) and had a higher incidence of hypertension (90% vs 70%; P <.05) and end-stage renal disease (24% vs. 13%; P <.05). Comparing patients undergoing blind bypass to bypass with at least 1 patent outflow vessel, there were no differences in the use of nonautogenous conduits (50% vs 59%; P =.21) or postoperative warfarin (30% vs 32%; P =.69), or in perioperative mortality rates (2.7% vs 3.2%; P =.79). After a median follow-up of 13 months (range, 0-60 months), 2-year secondary graft patency for the entire group was 63% +/- 4%. The secondary patency rate of blind bypass grafts was no different from that of grafts with at least 1 patent outflow vessel (67% +/- 7% vs. 64% +/- 4%; P was not significant). However, the 2-year limb salvage rate in limbs with blind outflow was significantly worse than in limbs with at least 1 patent outflow vessel (67% +/- 7% vs. 76% +/- 3%; P =.04).

CONCLUSION

Acceptable long-term patency rates can be achieved in infrainguinal bypass grafts with blind outflow, although blind outflow remains a marker for subsequent limb loss in the chronically ischemic leg.

Hypercholesterolemia superimposed by experimental hypertension induces differential distribution of collagen and elastin

We studied the mural distribution of collagen types I and III and tropoelastin in enhanced experimental atherogenesis induced in rabbits by hyperlipidemia superimposed by hypertension. Animals were fed a high-cholesterol diet for 5 weeks and also subjected to midthoracic aortic coarctation for 4 weeks. Serum cholesterol levels were increased and blood pressure was elevated proximal to the coarctation. Foam cell lesions developed in the aorta proximal to the coarctation. In situ hybridization and immunohistochemistry showed that gene expression of collagen types I and III and tropoelastin was upregulated, with a differential distribution across the arterial wall. New collagen type I was mainly distributed in the intima, the outer media, and the adventitia. New collagen type III was spread more uniformly across the wall, including the adventitia, whereas tropoelastin was mainly localized in intimal foam cell lesions. Morphometric data showed an increase in wall thickness. These results suggest that collagen types I and III play a role in remodeling of the aortic wall in response to hypertension. The remarkable involvement of the adventitia in this response indicates that the adventitia is an important component of the arterial wall. Tropoelastin is closely associated with foam cell lesion formation, suggesting a role for this component in atherogenesis as well.

Angioplasty does not affect subsequent operative renal artery revascularization

BACKGROUND

Although increased application of percutaneous renal artery angioplasty and stenting has facilitated nonoperative renal revascularization, patient outcomes after failed angioplasty are not established.

METHODS

Renal artery revascularization was performed in 31 patients (38 arteries) from 1993 to 1999. Twenty patients underwent primary surgical repair, and 11 patients underwent secondary reconstruction after angioplasty (n = 7) or angioplasty and stenting (n = 4). Before operation, all patients had severe hypertension (blood pressure 166+/-5.2/92 +/- 2.7 mm Hg) that required an average of 3.0 +/- 0.2 medications for control. In addition, 12 patients (primary 45% vs secondary 27%; P = NS) had evidence of renal insufficiency (creatinine > or =1.7 mg/dL).

RESULTS

There was no difference between primary and secondary procedures in the length of hospital stay (12+/- 1.4 vs. 12+/-3.2 days; P = NS), major morbidity (10% vs. 18%; P = NS) or perioperative mortality (overall mortality 2 of 31; primary 5% vs secondary 9%; P = NS). The majority of patients demonstrated improvement or cure of hypertension (primary 94% vs secondary 90%; P = NS) and stable or decreased creatinine (primary 74% vs secondary 82%; P = not significant). Overall survival (mean follow-up 22+/-3.5 months) was 89%+/-5.7%.

CONCLUSIONS

Although this surgical series does not address the true outcomes of renal artery angioplasty, the results suggest that renal artery angioplasty does not prejudice subsequent surgical outcomes in patients who are carefully followed after angioplasty.

Apolipoprotein (a) fragments in relation to human carotid plaque instability

PURPOSE

An elevated plasma level of lipoprotein (a) is an independent risk factor for atherothrombotic cardiovascular disease by yet undefined mechanisms. We have previously reported that matrix metalloproteinases cleave apolipoprotein (a) into 2 main fragments, F1 and F2, the latter (the C-terminal domain) exhibiting in vitro a high-affinity binding to extracellular matrix components, including fibrin(ogen). We therefore tested the hypothesis that the lipoprotein (a) matrix metalloproteinase-derived F2 is localized in potentially or morphologically unstable human carotid plaque at regions of increased matrix metalloproteinase activity.

METHODS

Carotid plaques removed after endarterectomy (n = 18) were evaluated for structural features indicative of instability (thin fibrous cap, inflammation, and proximity of the necrotic core to the lumen); each plaque was classified as unstable (n = 10) or stable (n = 8). Western blot analysis was performed to quantitate apolipoprotein (a) and its fragments F1 and F2 in plaque extracts. Immunohistochemical staining was used to localize apolipoprotein (a) and its fragments within the atherosclerotic plaque. In situ zymography was used to determine regions of gelatinase (matrix metalloproteinase 2 and matrix metalloproteinase 9) activity.

RESULTS

Western blot analyses demonstrated a 2.5-fold higher density of F2 in unstable plaques than in stable plaques (3.07 +/- 1.9 vs 1.18 +/- 0.8; P <.05). In morphologically unstable plaques, there was preferential distribution of F2 within regions of fibrous cap inflammation and/or foam cell accumulation and within abluminal necrotic cores. In morphologically stable plaques, however, localization was predominantly found in the medial smooth muscle cells. Regions of enhanced matrix metalloproteinase 2 and matrix metalloproteinase 9 activity co-localized with the transmural distribution of F2 within the plaque.

CONCLUSIONS

These findings suggest that F2 in regions of increased matrix metalloproteinase activity is a potential mechanism for superimposed thrombotic events in morphologically unstable human carotid plaques. The relationship between plasma lipoprotein (a) levels and accumulation of F2 and the potential correlation of F2 to human plaque disruption and thrombosis warrant further study.

Differential transmural distribution of gene expression for collagen types I and III proximal to aortic coarctation in the rabbit

To assess the effects on the biosynthesis of collagen types I and III associated with an acute increase in blood pressure, we established a mid-thoracic aortic coarctation in the rabbit and studied gene expression and protein accumulation of these collagen types proximal to the stenosis 1, 3 and 7 days and 2, 4 and 8 weeks after coarctation. The mRNA level of type I collagen pro-alpha2(I) was maximal at 3 days and returned to normal at 4 weeks. mRNA of pro-alpha2(I) was localized mainly in the outer media, adventitia and intima. Accumulation of type I collagen and its precursors was increased by 3 days, peaked at 4 weeks, and decreased toward normal by 8 weeks, corresponding to the distribution of pro-alpha2(I) mRNA. Gene expression for pro-alpha1(III) was similar to that of pro-alpha2(I) but was distributed throughout the media. We conclude that the mechanical stresses associated with an acutely induced alteration in pressure initiate rapid gene expression for collagen types I and III in the aortic wall. The response for collagen type I, predominantly in the outer media and adventitia, suggests that these regions play an immediate role in the resistance to excessive dilatation of the aorta. The diffuse response for collagen type III in the media suggests participation in a more extensive remodeling response associated with the reinforcement and reorganization of the musculo-elastic fascicles.

Estimating the contemporary in-hospital costs of carotid endarterectomy

Carotid endarterectomy (CEA) is the treatment of choice for symptomatic carotid stenosis and selective asymptomatic lesions. Alternative approaches have recently been championed under the guise of increased efficacy and decreased cost. The purpose of this study was to determine the results and in-hospital costs of CEA in a university hospital in the modern era. A retrospective chart review was undertaken for all patients undergoing CEA between January 1995 and December 1997. This corresponded to the implementation of a clinical path and extended efforts toward cost reduction. Patients undergoing combined CEA and cardiopulmonary bypass were excluded (n = 3). Cost was analyzed by the hospital Office of Program Planning using TSI (Transition Systems, Inc.) software. Direct costs are related to the utilization of clinical resources and are therefore manageable by clinicians (bed, room, supplies, nursing staff, OR staff, radiology, pharmacy, etc.). Total costs additionally include administration and overhead costs not directly chargeable to patient accounts. The results of this study showed that CEA can be safely performed with brief hospital stays and reasonable hospital costs. Results of alternative interventions for the treatment of carotid stenosis should be compared to these contemporary data.

Effective hemodynamic diameter: an intrinsic property of vein grafts with predictive value for patency

INTRODUCTION

Conduit size and quality are major determinants of the long-term success of infrainguinal autologous vein grafting. However, accurate measurement of the internal diameter of vein grafts is difficult given their variable wall thickness and taper. The purpose of this study was to define the "effective" internal diameter of a vein graft according to its hemodynamic properties and to determine its significance for graft patency.

METHODS

Sixty infrainguinal bypass grafts performed on 57 patients were evaluated intraoperatively. Proximal and distal graft pressure and blood flow (Q(meas)) were measured with fluid-filled catheter transduction and ultrasonic transit-time flowimetry, respectively, after unclamping. Waveforms were recorded digitally at 200 Hz under baseline conditions and after stimulation with 60 mg of papaverine. According to Fourier transformation of the measured pressure gradient (DeltaP), the Womersley solution for fluid flow in a straight rigid tube was used to calculate theoretical flow waveforms (Q(calc)) for a range of graft diameters. The theoretical waveforms were then compared with the measured flow waveforms and the best-fit diameter chosen as the "effective hemodynamic diameter" (EHD). Only grafts in which the correlation coefficient of Q(calc) versus Q(meas) was more than 0.90 were accepted (n = 47) to assure validity of the hemodynamic model. After a mean follow-up of 12.5 months (range, 0.1-43.9 months), patency was determined by the life table method. Hemodynamic and clinical variables were tabulated, and their effect on patency determined the use of univariate and multivariate Cox regression.

RESULTS

Mean EHD was 4.1 +/- 0.1 mm with a range of 2.5 to 5.7 mm. Administration of papaverine caused profound changes in DeltaP (+78% +/- 17%) and Q(meas) (+71% +/- 12%) as expected, but had no effect on EHD (+0.05% +/- 0.1%). Univariate regression identified five variables associated with decreased secondary patency (P <.10): low EHD, conduit source other than the greater saphenous vein, high baseline DeltaP(mean), female sex, and redo operation. Of these, only low EHD was significant after multivariate analysis (P =.03). Patency of small diameter grafts (EHD < 3.6 mm; n = 11) was compared with patency of larger grafts (EHD > 3.6 mm; n = 36) to test a frequently espoused clinical guideline. Grafts with an EHD less than 3.6 mm exhibited significantly lower secondary patency compared with larger grafts (P =.0001). The positive and negative predictive values for an EHD less than 3.6 mm for secondary graft failure for grafts with at least 1 year follow-up were 86% and 88%, respectively.

CONCLUSION

An EHD is a unique parameter that quantifies conduit size and has a significant impact on vein graft patency. An EHD less than 3.6 mm portends graft failure.

Gene therapy enhances the antiproliferative effect of radiation in intimal hyperplasia

BACKGROUND

Although ionizing radiation (IR) has been demonstrated to attenuate vessel wall restenosis and intimal hyperplasia (IH), dose-related mural injury and atrophy are possible deleterious side effects. We tested the hypothesis that a radiosensitizing strategy may improve IR-induced inhibition of in vivo vascular smooth muscle cells (VSMCs) without influencing apoptotic cell death.

METHODS

In 28 New Zealand White rabbits, the right common carotid artery (CCA) was injured and subjected to low-flow conditions to promote IH. The CCA was transfected with an adenoviral vector incorporating the cytosine deaminase (CD) gene (1 x 10(9) PFU/ml). 5-Fluorocytosine (5-FC), a prodrug that is converted to the radiosensitizing agent 5-fluorouracil (5-FU) by CD, was thereafter administered intravenously. The CCA was exposed to 5 Gy IR at 24 h. Intimal/medial (I/M) area and thickness ratios were determined in the harvested CCAs at 14 days. VSMC proliferative and apoptotic indices were assessed with immunohistochemistry.

RESULTS

A 50% reduction in I/M area was found in rabbits treated with IR and IR + CD/5-FC (0.19 +/- 0.03 and 0.18 +/- 0.02) when compared with untreated controls (UC) (0.37 +/- 0.06) (P = 0.005). This finding was substantiated by attenuation of I/M thickness in the IR groups [0.47 +/- 0.13 (IR), 0.41 +/- 0.11 (IR + CD/5-FC), 0.61 +/- 0.17 (UC)] (P = 0.007). The number of proliferating VSMCs was notably smaller when IR was combined with CD/5-FC (4.17 +/- 1.16 vs 2.97 +/- 1.09 log transformed cells/mm(2), P < 0.07). Apoptosis was similar in all groups.

CONCLUSIONS

Both IR alone and IR combined with a radiosensitizing agent are effective in attenuating experimental IH. However, combination therapy is synergistic and achieves greater inhibition of VSMC proliferation and may involve selective killing of radioresistant S-phase VSMCs. IR + CD/5-FC represents a novel therapeutic strategy that offers potential for long-term control of IH.

Increased flow and shear stress enhance in vivo transforming growth factor-beta1 after experimental arterial injury

We have previously demonstrated that high-flow (HF) conditions inhibit experimental intimal hyperplasia. We hypothesized that such flow conditions may alter transforming growth factor-beta1 (TGF-beta1) after mural injury. The right common carotid artery (CCA) was balloon-injured in 54 New Zealand White male rabbits. Flow was thereafter preserved (normal flow [NF]), reduced by partial outflow occlusion (low flow [LF]), or increased by ligation of the left CCA (HF). Four sham-operated animals served as uninjured controls. Mean blood flow and pressure in the right CCA were measured before and after flow modulation and before euthanasia (3, 7, and 14 days). TGF-beta1 mRNA and protein levels in the right CCA were determined by Northern and ELISA analyses at each time point. At 7 and 14 days, intimal hyperplasia was quantified, and the transmural localization of TGF-beta1 was determined by immunohistochemical analysis. Mean flow was reduced from 22+/-1 to 10+/-3 mL/min in the LF group and increased to 34+/-2 mL/min in the HF group (P<0.001). Blood pressure was not different among the flow groups for all time points. Wall shear stress was markedly decreased in the LF group to 14+/-4 dyne/cm(2) and increased in the HF group to 63+/-6 dyne/cm(2) at 7 days compared with values in uninjured controls (39+/-2 dyne/cm(2), P<0.001) and the NF group (44+/-7 dyne/cm(2), P<0.001). At 14 days, wall shear stress was similar among the flow groups. The intima-to-media ratio was 5- and 2-fold greater in the LF group than in the HF and NF groups at 14 days. mRNA levels for TGF-beta1 and its active ligand were increased in the HF group by at least 2- and 3-fold, respectively, at 3 and 7 days compared with levels in uninjured controls and the LF group (P<0.05) but were not different among the flow groups at 14 days. TGF-beta1 preferentially localized in the abluminal vascular smooth muscle cells of the HF arterial segments. Flow- and shear-mediated release of TGF-beta1 may therefore play a role in abrogating the proliferative and migratory response of vascular smooth muscle cells in the early stages after mural injury.

Biomechanical factors as regulators of biological responses to vascular grafts

Biomechanical forces have been implicated in the induction and progression of intimal hyperplastic thickening in vein, prosthetic, and endovascular bypass grafts. Graft implantation imposes significant alterations is shear and tensile forces. Such physical forces play an important role in modulating those cellular and molecular events that underlie regulation of vascular healing and adaptation. Characterization of such hemodynamic variables that induce perpetual medial vascular smooth muscle cell proliferation and migration will help in identification of those grafts at risk for occlusion and limited long-term patency and in design of therapeutic strategies that attenuate progressive intimal hyperplasia.

Irradiation for the treatment of intimal hyperplasia

Intimal hyperplasia represents a serious complication limiting the long-term benefits of vascular interventions such as balloon angioplasty and stent placement. Although pharmacological interventions have attempted to curtail restenosis, they have not been shown to be effective to date. Radiotherapy is one alternative that has shown promise as an inhibitor of intimal hyperplasia in several animal models. Irradiation causes cell death by producing irreparable damage to DNA. This is believed to be the mechanism of inhibition of VSMC proliferation. Delivery of irradiation can be either intraluminal via an angiographically directed catheter or extraluminal using an external radiation source such as an x-ray device. Intraluminal irradiation has generally utilized either gamma or beta-emitting sources. Both have been effective in producing a dose response, although some studies advocate the use of beta-type irradiation as a safer, more efficient means of delivery. Extraluminal irradiation also has been an effective inhibitor of intimal hyperplasia. Studies suggest that this form of irradiation provides a more even-dose distribution to vessel walls than an intravascular delivery system. The use of radiotherapy has more recently been extended to clinical trials, and initial studies have shown promising results. The success of irradiation must be balanced with its potential complications including radiation-induced arteritis, coronary artery stenosis, and secondary development of malignancy. Although these have been associated with irradiation, the dose used in these cases was often considerably higher than those used in the treatment of intimal hyperplasia. Finally, with the advent of gene therapy, irradiation may provide an additional means of supplementing this new type of therapy through radiation-inducible gene therapy.

Flow regulation of 72-kD collagenase IV (MMP-2) after experimental arterial injury

BACKGROUND

MMP-2 plays a key role in basement membrane degradation and in the migration of proliferating smooth muscle cells after vascular injury. Because low flow and shear stress have been related to the localization and progression of intimal hyperplasia, we hypothesized that flow conditions modulate in vivo MMP-2 transcription and activity in a model of injury-induced intimal thickening.

METHODS AND RESULTS

The right common carotid artery (CCA) was balloon-injured in 21 New Zealand White male rabbits. Flow was thereafter preserved (normal flow, n=7), reduced by partial outflow occlusion (low flow, n=7), or increased by ligation of the left CCA (high flow, n=7). In 15 other animals (controls without injury), flow was reduced (n=5), increased (n=5), or preserved (n=5). Mean blood flow and pressure in the right CCA were measured before and after flow modulation (day 0) and before the rabbits were killed (day 7). Northern analysis, gelatin-gel zymography, and fluorometric assays were performed on day 7 to determine MMP-2 mRNA levels and activity in relation to flow and intimal thickening. Mean flow was reduced from 21+/-1 to 7+/-1 mL/min (P<0.05) by outflow occlusion and increased to 31+/-2 mL/min (P<0.05) by ligation of the contralateral CCA. Blood pressure was not different between the flow groups. Hemodynamic parameters were similar for days 0 and 7 after flow modulation. In the injured right CCA, there was a 186% increase in MMP-2 mRNA with normal flow (P<0.05), a 366% increase with low flow (P<0.005), and only a 38% increase with high flow (P>0.05) compared with the uninjured CCA with normal flow. In the uninjured CCA, MMP-2 mRNA levels were increased by only 39% and 26% in the low- and high-flow groups, respectively, compared with normal-flow controls. The zymographic signal and quantitative fluorescent activity of gelatinase were markedly increased in both injured and uninjured CCAs subjected to low flow. Intimal thickening was observed after 1 week only in CCA segments with low flow and injury.

CONCLUSIONS

Hemodynamic forces such as low flow upregulate injury-induced MMP-2 mRNA and appear to be more important in regulating MMP-2 activity than injury alone. This may facilitate migration of the smooth muscle cells and subsequent development of intimal thickening.

Assessing outcomes, costs, and benefits of emerging technology for minimally invasive saphenous vein in situ distal arterial bypasses

BACKGROUND

Instrumentation for a minimally invasive angioscopic in situ peripheral arterial bypass (MIAB) with catheter-directed side-branch occlusion has recently been approved for use. Despite the attractiveness of this approach (2 short incisions), benefits such as lower morbidity and shorter hospitalizations remain undocumented. To justify wide acceptance, minimally invasive surgical techniques must match conventional procedures in durability and cost while enhancing patient comfort. Often such comparisons are difficult during the implementation phase of a new procedure.

OBJECTIVE

To compare the outcomes of the MIAB procedures with a concurrent group of patients undergoing conventional in situ bypass procedures.

DESIGN

Retrospective review.

SETTING

University medical center.

PATIENT

The first 20 consecutive MIAB procedures in 19 patients performed between August 1, 1995, and July 31, 1997, were compared with 19 contemporaneous consecutive conventional in situ bypass procedures performed at the same institution.

MAIN OUTCOME MEASURES

Operative time, postoperative length of stay, hospital costs, complications, primary assisted and secondary patency, limb salvage, and survival.

RESULTS

The patient groups were comparable with respect to age, sex, incidence of smoking, coronary artery disease, hypertension, diabetes, renal failure, cerebrovascular disease, indication, and distal anastomosis level. The median operative time was significantly greater for the MIAB group (6.6 hours vs 5.7 hours; P=.009), and intraoperative completion arteriography more frequently showed retained arteriovenous fistulas in the MIAB group (55% vs 21%; P=.05). The median postoperative length of stay and total cost were 6.5 days and $18,000 for the MIAB group and 8 days and $27,800 for the conventional group (P > or = .05). There were no significant differences in major complications (10% in the MIAB group vs 11% in the conventional group), wound complications (10% vs 11%, respectively), primary assisted patency at 1 year (68%+/-11% vs 78%+/-10%, respectively), secondary patency at 1 year (79%+/-10% vs 88%+/-8%, respectively), limb salvage at 1 year (85%+/-10% vs 94%+/-6%, respectively), or patient survival at 1 year (89%+/-8% vs 61%+/-13%, respectively).

CONCLUSION

Patients undergoing the MIAB procedure avoided lengthy vein exposure incisions without sacrificing short-term results. There was a trend toward decreased hospital stay and cost, which may be further realized as the clinical experience broadens. Although longer follow-up and larger cohorts will always be required to define durability, immediate access to outcomes and costs on small numbers of patients facilitates the early assessment of emerging technology.

Low flow enhances platelet activation after acute experimental arterial injury

PURPOSE

Vascular smooth muscle cell (VSMC) proliferation and migration to the subintima or intimal hyperplasia (IH) occur after arterial injury and are thought to be induced by mitogenic factors released from activated platelets. Because low flow (LF) and shear have been attributed to the localization and progression of IH, we postulated that hemodynamic factors may regulate the degree of platelet activation, as measured by plasma thromboxane B2 (TXB2) and platelet-derived growth factor-AB (PDGF-AB) release at regions of experimental arterial injury.

METHODS

The right common carotid artery (CCA) was subjected to balloon injury in 18 New Zealand White male rabbits. Flow in the injured CCA was reduced by out-flow ligation (LF group, n = 6) or increased by ligation of the left CCA (high flow [HF] group, n = 6). In six other animals, flow was preserved (normal flow [NF] group). Mean blood flow and pressure in the right CCA were measured thereafter at 10 and 30 minutes. Plasma TXB2 and PDGF-AB levels were determined with the enzyme-linked immunosorbent assay method in each animal with blood samples taken systematically before injury (baseline) and in the distal CCA at similar time points.

RESULTS

At 10 minutes, mean blood flow was reduced from 20 +/- 2 ml/min in the NF group to 7 +/- 1 ml/min in the LF group animals (p < 0.01) and increased to 32 +/- 2 ml/min in the HF group animals (p < 0.05). Mean arterial blood pressure did not differ among the groups. Hemodynamic parameters were similar at 10 and 30 minutes. TXB2 levels were more than fourfold greater in the LF group than in the HF and NF groups at both time points (p < 0.05). In addition, there was a twofold increase in plasma PDGF-AB level at 10 minutes in the LF group compared with baseline levels (p < 0.05).

CONCLUSION

Platelet activation at regions of acute vascular injury was determined to be flow dependent. Upregulated platelet activity in low flow conditions may be due to increased platelet exposure time to subendothelial collagen and is greatly attenuated if normal or increased flow is present.

Juxtalumenal location of plaque necrosis and neoformation in symptomatic carotid stenosis

PURPOSE

The structural features that underlie carotid plaque disruption and symptoms are largely unknown. We have previously shown that the chemical composition and structural complexity of critical carotid stenoses are related to plaque size regardless of symptoms. To further determine whether the spatial distribution of individual plaque components in relation to the lumen corresponds to symptomatic outcome, we evaluated 99 carotid endarterectomy plaques.

METHODS

Indications for operation were symptomatic disease in 59 instances (including hemispheric transient ischemic attack in 29, stroke in 19, and amaurosis fugax in 11) and angiographic asymptomatic stenosis > 75% in 40. Plaques removed after remote symptoms beyond 6 months were excluded. Histologic sections from the most stenotic region of the plaque were examined using computer-assisted morphometric analysis. The percent area of plaque cross-section occupied by necrotic lipid core with or without associated plaque hematoma, by calcification, as well as the distance from the lumen or fibrous cap of each of these features, were determined. The presence of foam cells, macrophages, and inflammatory cell collections within, on, or just beneath the fibrous cap was taken as an additional indication of plaque neoformation.

RESULTS

The mean percent angiographic stenosis was 82% +/- 11% and 79% +/- 13% for the asymptomatic and symptomatic groups, respectively (p > 0.05). The necrotic core was twice as close to the lumen in symptomatic plaques when compared with asymptomatic plaques (0.27 +/- 0.3 mm vs 0.5 +/- 0.5 mm; p < 0.01). The percent area of necrotic core or calcification was similar for both groups (22% vs 26% and 7% vs 6%, respectively). There was no significant relationship to symptom production of either the distance of calcification from the lumen or of the percent area occupied by the lipid necrotic core or calcification. The number of macrophages infiltrating the region of the fibrous cap was three times greater in the symptomatic plaques compared with the asymptomatic plaques (1114 +/- 1104 vs 385 +/- 622, respectively, p < 0.009). Regions of fibrous cap disruption or ulceration were more commonly observed in the symptomatic plaques than in the asymptomatic plaques (32% vs 20%). None of the demographic or clinical atherosclerosis risk factors distinguished between symptomatic and asymptomatic plaques.

CONCLUSIONS

These findings indicate that proximity of plaque necrotic core to the lumen and cellular indicators of plaque neoformation or inflammatory reaction about the fibrous cap are associated with clinical ischemic events. The morphologic complexity of carotid stenoses does not appear to determine symptomatic outcome but rather the topography of individual plaque components in relation to the fibrous cap and the lumen. Imaging techniques that precisely resolve the position of the necrotic core and evidence of inflammatory reactions within carotid plaques should help identify high-risk stenoses before disruption and symptomatic carotid disease.

Validation of a new and specific intraoperative measurement of vein graft resistance

PURPOSE

Clinical studies have revealed that the most important predictor of successful bypass grafting is the origin and quality of the bypass conduit. Attempts at intraoperative evaluation of the hemodynamic properties of the conduit, including assessment of blood flow (Q), pressure gradients (delta P), and resistance (R), have not been useful. This is because each of these parameters measures the characteristics of the graft plus the outflow bed. To date, no specific measurement of the resistive properties of the conduit only is available. The purpose of this investigation was to evaluate longitudinal impedance (ZL) as a measure of conduit-specific resistance and to evaluate its potential in predicting the outcome of infrainguinal vascular reconstructions.

METHODS

ZL was measured during surgery in 73 infrainguinal autologous vein reconstructions performed in 68 patients in two separate institutions over a 21-month period. Vein graft ultrasonic transit time Q and delta P (from proximal to distal anastomosis) were measured at baseline and after maximal peripheral vasodilatation with an intraarterial injection of papaverine 30 mg. Waveforms were recorded for 10 seconds at 200 Hz using a digital acquisition system. R was calculated as proximal mean pressure divided by mean blood flow (Q). After Fourier transformation, ZL was calculated as delta P/Q at each harmonic and total ZL (integral of ZL) was defined as the integral of moduli from 0 to 4 Hz.

RESULTS

All hemodynamic variables were significantly affected by papaverine vasodilatation (delta P, 3.9 +/- 0.5 vs 6.3 +/- 0.8 mm Hg; Q, 78.2 +/- 7.0 vs 126 +/- 11 ml/min; R, 134 +/- 17 vs 72.7 +/- 6.2 x 10(3) dyne.sec.cm-5; p < 0.0001), except integral of ZL, which remained constant (31.1 +/- 2.8 vs 30.8 +/- 2.8 x 10(3) dyne.cm-5; p = NS). After follow-up of 1 week to 17 months (median, 5 months), the 1-year primary, primary-assisted, and secondary patency rates were 72% +/- 7%, 77% +/- 6%, and 81% +/- 6%, respectively. Using Cox analysis, primary patency was significantly associated with decreased integral of ZL (p = 0.0001), but not with baseline or papaverine-stimulated delta P, Q, delta P/Q, or R integral of ZL > 47 x 10(3) dyne.cm-5 predicted primary failure with 90% positive and negative predictive value.

CONCLUSIONS

Intraoperative measurement of integral of ZL in infrainguinal vein grafts is independent of outflow conditions (that is, does not change with papaverine), and hence describes the resistive properties of the conduit only. In addition, these preliminary data suggest that integral of ZL is predictive of short-term primary patency. integral of ZL is the first available hemodynamic measurement that is conduit-specific and may therefore be a better predictor of graft patency than currently available methods.

Current results of surgical therapy for chronic mesenteric ischemia

BACKGROUND

Although recognition of chronic mesenteric ischemia has increased in recent years, this disorder has continued to present diagnostic and therapeutic challenges.

OBJECTIVE

To examine the modern results of surgical revascularization for chronic mesenteric ischemia.

DESIGN

Retrospective review.

SETTING

University medical center.

PATIENTS

The management of 24 consecutive patients (mean +/- SEM age, 58 +/- 3 years; 5 men, 19 women) who were undergoing surgical treatment of chronic mesenteric ischemia between 1986 and 1996 was reviewed.

INTERVENTION

Surgical mesenteric revascularization.

MAIN OUTCOME MEASURES

Postoperative course, long-term graft patency rate, and long-term symptom-free survival rate.

RESULTS

The most frequent presenting symptoms were postprandial abdominal pain (18 patients [75%]) and weight loss (14 patients [58%]). Less specific complaints included nausea and vomiting (8 patients [33%]), diarrhea (7 patients [29%]), and constipation (4 patients [17%]). Atherosclerotic risk factors were common, including tobacco use (20 patients [83%]), coronary artery disease (10 patients [42%]), and hypertension (10 patients [42%]). The cause was identified as atherosclerosis in 21 patients, median arcuate ligament compression in 2 patients who were monozygotic twins, and Takayasu arteritis in 1 patient. Lesions were localized to all 3 major visceral vessels (celiac artery, superior mesenteric artery [SMA], and inferior mesenteric artery) in 8 patients, celiac artery and SMA in 13, SMA alone in 2, and SMA and inferior mesenteric artery in 1. Seventeen patients underwent antegrade reconstructions from the supraceliac aorta to the SMA and/or celiac artery; 7 patients underwent revascularization by use of a retrograde bypass that originated from the infrarenal aorta or a prosthetic graft. There were no perioperative deaths although 1 patient died in the hospital 6 weeks after early graft failure and sepsis (overall in-hospital mortality, 4%). Follow-up ranged from 3 months to 10 years (median, 2.4 years). The mean +/- SEM 5-year primary graft patency rate, as objectively documented by use of contrast angiography or duplex scanning in 19 of 24 patients, was 78% +/- 11%. Primary failure was documented in 3 patients (at 3 weeks, 5 months, and 7 months). Two patients required a thrombectomy; 1 of these patients subsequently died of an intestinal infarction. The mean +/- SEM 5-year survival rate by use of life-table analysis was 71% +/- 11%. No patient with a patent graft experienced a symptomatic recurrence.

CONCLUSIONS

Chronic mesenteric ischemia is usually a manifestation of advanced systemic atherosclerosis. Symptoms almost always reflect midgut ischemia in the distribution of the SMA. An antegrade bypass from the supraceliac aorta can be performed with acceptable operative morbidity and is currently the preferred reconstructive technique. Surgical revascularization affords long-term symptom-free survival in a majority of patients with chronic mesenteric ischemia.

Measurements of velocity and wall shear stress inside a PTFE vascular graft model under steady flow conditions

The flow field inside a model of a polytetrafluorethylene (PTFE) canine artery end-to-side bypass graft was studied under steady flow conditions using laser-Doppler anemometry. The anatomically realistic in vitro model was constructed to incorporate the major geometric features of the in vivo canine anastomosis geometry, most notably a larger graft than host artery diameter. The velocity measurements at Reynolds number 208, based on the host artery diameter, show the flow field to be three dimensional in nature. The wall shear stress distribution, computed from the near-wall velocity gradients, reveals a relatively low wall shear stress region on the wall opposite to the graft near the stagnation point approximately one artery diameter in axial length at the midplane. This low wall shear stress region extends to the sidewalls, suture lines, and along the PTFE graft where its axial length at the midplane is more than two artery diameters. The velocity distribution inside the graft model presented here provides a data set well suited for validation of numerical solutions on a model of this type.

Nonocclusive mesenteric ischemia

NOMI remains a challenging clinical entity that demands a heightened index of suspicion and an aggressive diagnostic and treatment strategy in order to avoid the untoward sequela of short bowel syndrome and to achieve survival. Early arteriographic diagnosis and prompt institution of vasodilator therapy have proven successful in reducing the high (70% to 90%) mortality rate observed through the 1980s to 50% to 55% during the last decade. Continued investigations into the pathophysiologic mechanisms underlying splanchnic vasospasm and intestinal IR injury will, it is hoped, add more alternate and effective therapies to the current armamentarium.

Mechanisms of neurologic deficits and mortality with carotid endarterectomy

OBJECTIVE

To evaluate the incidence and etiology of perioperative complications of carotid endarterectomy.

DESIGN

Retrospective review of carotid endarterectomies performed over 13 years. Risk factors, indications, results of electroencephalographic (EEG) monitoring, and outcomes were evaluated.

SETTING

University medical center.

PATIENTS

Three hundred sixty-seven consecutive primary carotid endarterectomies were performed on 336 patients. Indications for operation included transient ischemic attack (48.5%), asymptomatic stenosis (24%), stroke (17%), nonlateralizing ischemia (9.5%), and stroke-in-evolution (1%).

MAIN OUTCOME MEASURES

Postoperative neurologic deficits (permanent and transient) and deaths were correlated with preoperative symptoms, probable mechanism of the neurologic event, intraoperative EEG changes, and the use of intraoperative shunts.

RESULTS

Four new permanent neurologic deficits (1.1%) and one transient postoperative deficit were noted. Of the five deficits, three were related to undiagnosed intraoperative cerebral ischemia and two were related to perioperative emboli. Three perioperative deaths (0.8%) occurred: two of myocardial infarction and one of an intracerebral hemorrhage from a ruptured arteriovenous malformation. Intraoperative EEG tracings for the most recent consecutive 175 procedures were analyzed. Shunts were used in 45 patients (26%), 38 of whom demonstrated significant EEG changes with carotid clamping.

CONCLUSIONS

Carotid endarterectomy can be performed with a low risk of stroke (1.1%) and death (0.8%). Stroke was due to cerebral ischemia or embolization. With meticulous surgical technique, death is due to myocardial ischemia and not neurologic events.

Noninvasive evaluation of the lower extremity arterial tree and graft surveillance

The application of duplex ultrasonography in the evaluation of lower extremity arterial occlusive disease and in graft surveillance has enhanced significantly the vascular surgeon's diagnostic armamentarium. With continued refinements in gray scale image resolution, color flow, and spectral analysis, color duplex ultrasonography eventually will replace angiographic evaluation in carefully selected patients as the primary pre-interventional testing modality.

Pathobiology of plaque modeling and complication

The artery wall adapts to changes in wall tension and wall shear stress by means of enlargement and changes in both thickness and composition. The intima may participate in these changes, and these compensatory adaptive-reactive modifications continue in the presence of atherogenesis. Further understanding of the interaction of the evolving plaque with the artery wall and the associated effects of the physical forces associated with the circulation should provide new insights into the nature of plaque instability and into the outcome of direct interventions.

Hemodynamic stress and experimental aortoiliac atherosclerosis

PURPOSE

Human aortic atherosclerosis is predominantly localized to the infrarenal aorta where flow is bidirectional and wall shear stress oscillates. Similar flow patterns have been related to carotid atherosclerosis. The thoracic aorta is usually spared, where flow and shear stress are unidirectional. We hypothesized that because heart rate and systemic blood pressure modulate flow velocity and shear stress oscillation, both these hemodynamic forces may enhance aortoiliac atherogenesis.

METHODS

Eighteen male cynomolgus monkeys were fed an atherogenic diet for 6 months (mean serum cholesterol = 535 +/- 35 mg/dl). Heart rate was determined with 24-hour electrocardiographic telemetry at monthly intervals and blood pressure was measured by direct arterial cannulation. The product of mean heart rate and mean blood pressure was used to define hemodynamic stress for each animal. Atherosclerotic lesion formation at three standard thoracic aortic sites was quantitatively compared with lesion formation at five standard infrarenal aortoiliac locations with computer-assisted morphometry.

RESULTS

There was significantly more plaque in the aortoiliac segment than in the thoracic aorta (12.4% +/- 9.0% vs. 6.4% +/- 4.5% area stenosis, p = 0.02). No correlation was found between the degree of serum lipid elevations and lesion formation in either aortic location. Mean heart rate was 113 +/- 18 beats/min (87 to 163 beats/min) and mean blood pressure was 85 +/- 19 mm/Hg (62 to 130 mm Hg). Heart rate and blood pressure alone were not significantly related to lesion formation. A significant correlation was, however, found between hemodynamic stress and maximum lesion thickness (r = 0.47, p < 0.05) in the aortoiliac region but not in the thoracic aorta (r = 0.19, p > 0.10).

CONCLUSIONS

This study demonstrates that heart rate and blood pressure exert a mutually potentiating effect on aortoiliac atherosclerosis but not on thoracic aortic atherosclerosis. Regional differences in aortic atherosclerosis may therefore be attributable to the interaction between these hemodynamic forces and the local flow patterns specific to each aortic location. Additional investigation of these hemodynamic factors in relation to human aortic atherosclerosis is warranted.

Anastomotic intimal hyperplasia: mechanical injury or flow induced

All anastomotic intimal thickening may not be the same, and the underlying mechanism(s) regulating the different types may vary. We investigated the localization of experimental anastomotic intimal thickening in relation to known biomechanical and hemodynamic factors. Bilateral iliofemoral saphenous vein and polytetrafluoroethylene grafts were implanted in 13 mongrel dogs. The distal end-to-side anastomotic geometry was standardized, and the flow parameters were measured. After 8 weeks, seven of 10 animals (group I) with patent grafts were killed and the anastomoses fixed by perfusion. Histologic sections from each anastomosis were studied with light microscopy, and regions of intimal thickening were identified and quantitated with use of oculomicrometry. To characterize the anastomotic flow patterns, transparent silicone models were constructed from castings of the distal anastomosis of three animals (group II), and flow was visualized with use of helium-neon laser-illuminated particles under conditions simulating the in vivo pulsatile flow parameters. Histologic sections revealed two separate and distinct regions of anastomotic intimal thickening. The first, suture line intimal thickening, was greater in polytetrafluoroethylene anastomoses (0.35 +/- 0.23 microns) than in vein anastomoses (0.15 +/- 0.03 microns, p less than 0.05). The second distinct type of intimal thickening developed on the arterial floor and was the same in polytetrafluoroethylene (0.11 +/- 0.11 microns) and vein anastomoses (0.12 +/- 0.03 microns). Model flow visualization studies revealed a flow stagnation point along the arterial floor resulting in a region of low and oscillating shear where the second type of intimal thickening developed. High shear and short particle residence time were observed along the hood of the graft, an area devoid of intimal thickening.(ABSTRACT TRUNCATED AT 250 WORDS)

Cryopreserved saphenous vein allogenic homografts: an alternative conduit in lower extremity arterial reconstruction in infected fields

Autologous saphenous veins are considered the best arterial substitute for lower extremity revascularization in infected fields. The search continues for a vascular conduit in instances when an autologous biologic grafting is not feasible. Herein we report our experience with eight patients in whom cryopreserved saphenous vein allogenic homografts were used in 10 lower extremity arterial reconstructions for limb salvage with coexisting infection. Six patients with eight prosthetic grafts including four femoropopliteal, two femorotibial, a femorofemoral, and a femoroperoneal graft required complete or partial graft excision as a result of overt infection. The two remaining patients included one with an infected femoral pseudoaneurysm and another with extensive chemical burns. All cryopreserved saphenous vein allogenic homografts were of identical match to the ABO/Rh blood groupings of the recipient patients. No immunosuppressive drugs were administered after operation. Mean follow-up was 9.5 months (range, 6.0 to 14.0 months). One patient died 5 weeks after operation with a patent graft. Two grafts occluded during follow-up; in one graft, patency was restored with thrombectomy alone. The remaining seven arterial reconstructions continue to be patent with no evidence of aneurysmal dilation with complete eradication of the primary infection. These preliminary findings suggest that cryopreserved saphenous vein allogenic homografts can serve as interim conduits for lower extremity arterial reconstruction to preserve limb viability when autogenous conduits are unsatisfactory or unavailable. Further definitive reconstruction may thereafter be necessary once sepsis is eradicated and sufficient wound healing is achieved.

True aneurysmal disease in the hand and upper extremity

Ten patients with true aneurysmal disease of the hand and forearm vessels were treated at our institution between 1981 and 1990. Pseudoaneurysms resulting from penetrating trauma or mycotic aneurysms were specifically excluded. Eight patients were male, two were female; mean patient age was 38 years (range 26 to 72 years). A history of repetitive occupational or recreational trauma was elicited in five patients. All patients presented with painful masses or neurologic symptoms due to nerve compression. Ischemic changes were evident in five patients due to thrombosis or distal embolization. Arteriography and transcutaneous Doppler ultrasound aided in documentation of flow characteristics and planning for operative intervention. Three patients underwent excision and ligation once collateral flow was demonstrated to be adequate and reconstruction was not felt to be feasible. Seven patients underwent resection with vein graft reconstruction. Immediate postoperative and interval patency rates were 100%. No digital amputations were required even in those patients presenting with severe distal ischemia.

Penile duplex sonography in the diagnosis of venogenic impotence

This study tested the hypothesis that measurements of cavernous arterial diastolic velocity and resistance index could provide a quantitative but noninvasive measure of penile corporal venous leakage. Seventy-four men were studied with duplex ultrasonography after intracavernosal injection of 60 mg of papaverine. Fourteen men had normal erection and served as controls. Sixty men had a 1-year history of transient fading or incomplete erections. In all subjects the peak systolic velocity and end-diastolic velocity were measured, and the resistance index was calculated (peak systolic velocity--end-diastolic velocity/peak systolic velocity). Men with normal erections had peak systolic velocities greater than 35 cm/sec and end-diastolic velocities less than 4.5 cm/sec (group 1). Patients with incomplete erections (group II) could be classified into three subgroups. Twenty-three patients with end-diastolic velocities greater than 4.5 cm/sec and normal peak systolic velocities greater than 35 cm/sec were suspected to have corporal venous leakage (group A). Eighteen patients had normal end-diastolic velocities less than 4.5 cm/sec. Twelve of this group had peak systolic velocities less than 35 cm/sec, and six had peak systolic velocities ranging from 37 to 44 cm/sec. These patients were suspected of having arterial insufficiency (group B). Fifteen patients with end-diastolic velocities greater than 4.5 cm and peak systolic velocities less than 35 cm were suspected of having both venous leakage and arterial insufficiency (group C). Twenty-one patients with abnormal diastolic flow underwent infusion pharmacocavernosometry to determine the saline maintenance infusion rate necessary to maintain an intracavernosal pressure of 90 to 100 mm Hg or a full erectile response.(ABSTRACT TRUNCATED AT 250 WORDS)

Current results of elective aortic reconstruction for aneurysmal and occlusive disease

Decisions to resect small aortic aneurysms or employ non-operative treatment for aorto-iliac occlusive disease must depend on current rather than historical surgical results. To assess current morbidity and mortality, we reviewed 200 consecutive aortic resections in two groups of patients treated from 1981 to 1989: those undergoing elective aortofemoral bypass for occlusive disease (AFB, no. 100) or resection of infrarenal abdominal aortic aneurysms (AAA, no. 100). Indications for AFB included claudication (54%), rest pain (32%), and gangrene (13%). AAA size ranged from 3 to 14 cm (mean 6.5 +/- 2.4 cm); 45% presented with abdominal or back pain. Patients undergoing AFB were younger (AFB 61.5 +/- 10 years vs AAA 68.7 +/- 8.9 years) with a higher incidence of some atherosclerotic risk factors, diabetes mellitus 30% vs 10%, tobacco use 77% vs 49%, hyperlipidemia 21% vs 7%; p less than 0.001). Coronary artery disease (CAD) was more prevalent in AAA patients (49% vs 34%; p less than 0.001). Postoperative mortality was not different in occlusive or aneurysmal disease (3% AFB vs 2% AAA), nor was the occurrence of serious complications such as myocardial infarction (2% vs 1%) or pulmonary embolism (2% vs 3%). Improvements in patient selection, perioperative care and surgical technique have lowered the mortality of elective aortic surgery. Given the current standard of care, an aggressive approach to AAA even in high risk patients is appropriate. The low morbidity of AFB for occlusive disease mandates a critical appraisal of less effective nonoperative therapies.

Critical carotid stenoses: morphologic and chemical similarity between symptomatic and asymptomatic plaques

To identify microanatomic and chemical features that may mark the transition from asymptomatic to symptomatic atherosclerotic carotid lesions, we evaluated 62 carotid artery bifurcation plaques including 45 high-grade stenoses removed at endarterectomy and 17 nonstenotic plaques recovered at autopsy. Morphologic features were evaluated on multiple-interval histologic sections and were graded for the presence of hemorrhage, ulceration, thrombosis, lumen surface irregularity, and calcification. Plaque hemorrhage, recent and remote, was found in most of the specimens, and did not discriminate between symptomatic and asymptomatic stenotic plaques. High-grade carotid stenotic plaques were associated with a significantly higher incidence of ulceration (53%), thrombosis (49%), and lumen irregularity (78%) when compared to nonstenotic asymptomatic plaques (6%, 0%, and 17%, respectively; p less than 0.01). Although these features were more prominent in lesions that produced symptoms, they were present in 80% of the stenotic bifurcations, and did not distinguish between symptomatic and asymptomatic endarterectomy plaques. No significant differences were found between symptomatic and asymptomatic high-grade lesions with respect to collagen, DNA, total cholesterol, fibrinogen, lipase, elastase, or collagenase content. We conclude that intraplaque hemorrhage is commonly seen in carotid plaques even without severe stenosis, and it does not appear to be a dominant determinant of symptoms. Ulceration and surface thrombi that may lead to cerebral embolization are prominent features in markedly stenotic plaques even when symptoms are absent. The disruptive processes that underlie plaque instability appear to be closely associated with plaque size and stenosis rather than plaque composition.