Computational particle-hemodynamics analysis and geometric reconstruction after carotid endarterectomy.

Transient three-dimensional laminar incompressible dilute suspension flow in rigid in-plane carotid artery bifurcations has been solved with a user-enhanced finite-volume program. Instantaneous velocity vector and wall shear stress vector fields illustrate strong "disturbed flow" patterns. Implications of elevated surface contours of hemodynamic wall parameters, indicating such disturbed flows, and particle deposition sites are discussed and a relative comparison in terms of indicator functions between the endarterectomized carotid artery bifurcation and two design improvements is shown. Although the combined perioperative mortality and non-fatal stroke rate for carotid endarterectomy ranges only from 2% to 7%, the final geometric design recommendation presented merits consideration because it may significantly lower the chances of post-operative complications such as stroke, ischemic attack, or even death. The new carotid artery bifurcation design is based on the overall reduction of "disturbed flow" indicator functions, including the time-averaged wall shear stress angle deviation and a wall deposition parameter for critical blood particles, such as monocytes.

Hemodynamic parameters and early intimal thickening in branching blood vessels.

Intimal thickening due to atherosclerotic lesions or intimal hyperplasia in medium to large blood vessels is a major contributor to heart disease, the leading cause of death in the Western World. Balloon angioplasty with stenting, bypass surgery, and endarterectomy (with or without patch reconstruction) are some of the techniques currently applied to occluded blood vessels. On the basis of the preponderance of clinical evidence that disturbed flow patterns play a key role in the onset and progression of atherosclerosis and intimal hyperplasia, it is of interest to analyze suitable hemodynamic wall parameters that indicate susceptible sites of intimal thickening and/or favorable conditions for thrombi formation. These parameters, based on the wall shear stress, wall pressure, or particle deposition, are applied to interpret experimental/clinical observations of intimal thickening. Utilizing the parameters as "indicator" functions, internal branching blood vessel geometries are analyzed and possibly altered for different purposes: early detection of possibly highly stenosed vessel segments, prediction of future disease progression, and vessel redesign to potentially improve long-term patency rates. At the present time, the focus is on the identification of susceptible sites in branching blood vessels and their subsequent redesign, employing hemodynamic wall parameters. Specifically, the time-averaged wall shear stress (WSS), its spatial gradient (WSSG), the oscillatory shear index (OSI), and the wall shear stress angle gradient (WSSAG) are compared with experimental data for an aortoceliac junction. Then, the OSI, wall particle density (WPD), and WSSAG are segmentally averaged for different carotid artery bifurcations and compared with clinical data of intimal thickening. The third branching blood vessel under consideration is the graft-to-vein anastomosis of a vascular access graft. Suggested redesigns reduce several hemodynamic parameters (i.e., the WSSG, WSSAG, and normal pressure gradient [NPG]), thereby reducing the likelihood of restenosis, especially near the critical toe region.

Reoperations for carotid artery stenosis: role of primary and secondary reconstructions.

PURPOSE: This is an analysis of the role of primary and secondary carotid artery reconstructions and systemic risk factors on the incidence and timing of reoperations and their perioperative and late outcomes. METHODS: This is a retrospective analysis of prospectively stored data. Between 1981 and 1999, 69 secondary carotid artery procedures were performed on 66 patients (3 were bilateral). Of these, 29 operations and patients came from my series of 1514 primary carotid endarterectomies (CEAs). Overall, secondary operations were performed on 37 women (1 bilateral) and 29 men (2 bilateral) with a mean age of 68 years. Indications for reoperation were transient ischemic attack in 27%, stroke in 12%, global ischemia in 9%, and asymptomatic > or = 70% recurrent stenosis in 52%. Secondary reconstruction was by saphenous vein patching in 57% (n = 39), Dacron patching in 29% (n = 20), polytetrafluoroethylene patch in 1% (n = 1), and interposition bypass graft in 13% (n = 9). The main outcome measures included restenosis, re-restenosis, and perioperative and late stroke and death. RESULTS: Reoperations were more frequent after originally primarily closed CEA (6.2%) than after patched CEA (1.6%, P =.01). Reoperations after Dacron-patched CEA occurred at a mean of 16 months compared with a mean of 84 months for vein-patched CEA (P <.001). Male sex and history of smoking have a slightly adverse but not statistically significant effect on the incidence and time of reoperation. Restenosis in the distal common carotid artery requiring reoperation had a near-linear rate of occurrence, whereas that in the internal carotid artery segment was bimodal with a higher incidence in the first 3 years and after 7 years. There were no (0%) 30-day perioperative deaths. There were two (2.9%) 30-day strokes (1 major, 1 minor). Over a mean follow-up of 50 months (range, 1-180), the Kaplan-Meier cumulative survival was 74% at 5 years and 54% at 10 years. This is significantly higher than late death after primary CEA independent of age. The cumulative freedom from stroke rate was 90% at 5 years and 86% at 10 years. After secondary procedures re-recurrent stenosis > or = 25% occurred in 25% (n = 17), > or = 50% in 13% (n = 9), and > or = 70% in 4% (n = 3). There was no statistically significant difference in stroke or re-restenosis rates between vein-patched, Dacron-patched, and bypassed reoperations, although re-recurrence tended to occur earlier after Dacron-patched than vein-patched procedures. Analysis of pooled literature data and the results of this study for stroke and re-restenosis outcomes by type secondary reconstruction (patch versus bypass graft) and by material (vein versus synthetic) give a balanced picture of near equality for each. Vein- and Dacron-patched arteries have similar outcomes, whereas polytetrafluoroethylene appears to be superior to vein and Dacron for interposition bypass graft. CONCLUSIONS: Secondary carotid artery operations are more frequent after primarily closed CEA than patched CEA. Perioperative mortality and stroke rates for reoperations are within the acceptable window of primary CEA. The incidence of late death after reoperations is higher than after primary CEA. The perioperative stroke, late stroke, and re-restenosis outcomes of vein- and Dacron-patched secondary operations are similar, as are those for patched and bypassed carotid arteries.

Restenosis after carotid endarterectomy in patients with paired vein and Dacron patch reconstruction.

This is an analysis of restenosis after bilateral carotid endarterectomy (CEA) with saphenous vein patch reconstruction on one side and Dacron patch reconstruction on the other. The possibility that differences in reconstruction geometry between vein and Dacron patched sides effected restenosis outcomes was evaluated as was the value of serial common carotid wall thickness measurements in predicting restenosis. Between 1990 and 1997, 33 bilateral CEA were performed within one year on 22 men and 11 women using a greater saphenous vein patch on one side and a knitted Dacron patch on the other. Interoperative post-CEA geometry was measured. Follow-up was by duplex scans that included wall thickness measurements in the endarterectomized common carotid bulb. Over a mean follow-up of 43 months 10 (30%) Dacron patched and one (3%) vein patched CEA developed > or = 25% restenosis (p = 0.001), seven (21%) Dacron patched and no vein patched CEA developed > or = 50% restenosis (p = 0.01) and four (12%) Dacron patched and no vein patched CEA developed > or = 70% restenosis (p = 0.11). The Kaplan-Meier cumulative > or = 25% restenosis rates for Dacron and vein patched CEA were 22% and 0% at 2 years and 41% and 5% at 5 years respectively (p = 0.002). The cumulative > or = 50% restenosis rates for Dacron and vein patched CEA were 16% and 0% at 2 years and 34% and 0% at 5 years respectively (p = 0.003). The cumulative > or = 70% restenosis rates for Dacron and vein patched CEA were 8% and 0% at 2 years and 20% and 0% at 5 years respectively (p = 0.02). For both patients with and without recurrent stenosis the mean within patient between sides differences of the diameters of the internal carotid, internal carotid bulb, common carotid bulb, and common carotid arteries and the lengths of the internal carotid and total patch segments were not significantly different and all were less than 5%. Common carotid bulb wall thickness measured at the time of identification of the nine unilateral Dacron patched CEA restenosis was 1.5 +/-0.5 mm compared to 1.4 +/-0.4 mm (m +/-1 SD) for the contralateral vein patched CEA (p = 0.45 by paired t test). Dacron patched CEA have a significantly higher incidence of mild, moderate and severe restenosis than do saphenous vein patched CEA independent of systemic risk factors. The within patient equality of Dacron and vein patched carotid reconstruction geometry in patients with unilateral restenosis indicates that patch material is the major local risk factor, not adverse hemodynamics produced by variance in geometry. Common carotid bulb wall thickness measurements after CEA are not predictors or indicators of recurrent stenosis.

Computer simulation and geometric design of endarterectomized carotid artery bifurcations.

The main goal of this computational study is to establish surgical guidelines for optimal geometries of carotid endarterectomy reconstructions that may measurably reduce postoperative complications, that is, thrombosis, stroke, and/or restenosis. The underlying hypotheses are that nonuniform hemodynamics, or "disturbed flows," are linked to arterial diseases and consequently that minimization of "disturbed flow" indicators leads to geometric bifurcation designs that lower postoperative complication rates. Considering transient 3-D laminar blood flow in partially occluded, in-plane, rigid-wall carotid artery bifurcations, the results presented include time-averaged indicators of "disturbed flow", such as the wall shear stress, spatial wall shear stress gradient, and wall shear stress angle deviation. In addition, trajectories and deposition patterns of critical blood particles (i.e., monocytes) are shown and evaluated. Within given physiological constraints, the vessel geometry was then changed in order to reduce the magnitudes of key indicators associated with thrombosis (i.e., blood clot formation) or restenosis (e.g., renewed atherosclerosis and/or hyperplasia). The quantitative results and knowledge base generated will be crucial for future clinical trials.

Hemodynamics analyses of arterial expansions with implications to thrombosis and restenosis.

It is assumed that critical hemodynamic factors play an important role in the onset, localization and degree of post-operative complications, for example, thrombosis and restenosis. Of special interest are sudden expansion flows, which may occur in straight artery segments such as the common carotid after endarterectomy or end-to-end anastomoses. Sudden expansion geometries are possible origins of early post-operative emboli and significant myointimal hyperplasia resulting in early or late complications. Transient laminar axisymmetric and fully three-dimensional blood flows were simulated employing a validated finite volume code in conjunction with a Runge-Kutta particle tracking technique. Disturbed flow indicators, which may predict the onset of thrombosis and/or restenosis, were identified and employed to evaluate 90 degrees -step and smooth expansion geometries. Smooth expansion geometries have weaker disturbed flow features than step expansion geometries. Specifically, the regions near the expansion wall and the reattachment point are susceptible to both atherosclerotic lesion and thrombi formations as indicated by non-uniform hemodynamic indicators such as near-zero wall shear stress and elevated wall shear stress gradients as well as blood particle accumulation and deposition. A new parameter, the wall shear stress angle deviation (WSSAD) has been introduced, which indicates areas of abnormal endothelial cell morphology and particle wall deposition. In turn, regions of low wall shear stress and high wall shear stress gradients are recognized as susceptible sites for arterial diseases. Thus, it is interesting to note that high WSSAD surface areas cover low wall shear stress, high wall shear stress gradient locations as well as high wall particle deposition.A gradual change in step expansion geometry provides better results in terms of WSSAD values and hence potentially reducing atherosclerosis as well as thrombi formation.

A fifteen-year experience with carotid endarterectomy after a formal operative protocol requiring highly frequent patch angioplasty.

PURPOSE: The early and late outcomes of carotid endarterectomy (CEA) following a rigid protocol of patch angioplasty or occasionally interposition bypass grafting, when the arteriotomy required to obtain a complete internal carotid end point extended distal to the bulb segment, and primary closure, when it was limited to the bulb, were studied. METHODS: From November 1983 to August 1998, 1360 consecutive primary CEAs were performed on 1133 patients (621 men, 512 women), with a mean age of 67 years. Of these patients, 3.8% (51) had primary closure, 66.4% (903) had greater saphenous vein patch angioplasty, 28.4% (386) had synthetic (359 Dacron, 27 polytetrafluoroethylene) patch angioplasty, and 1.4% (20) had vein interposition bypass grafting procedures. Indications were transient ischemic attack in 34.7% of patients (472), stroke in 16.6% of patients (226), nonlateralizing symptoms in 10.9% of patients (148), and asymptomatic stenosis 70% or greater in 37.8% of patients (514). The mean follow-up period was 4.6 years. RESULTS: The 30-day mortality rate was 1.0% (13 patients; 11 cardiac-related deaths, 2 strokes). The 30-day stroke rate was 1.3% (18 patients; 13 ipsilateral strokes, 5 major, 8 minor). The combined 30-day stroke and death rate was 2.1%. Four of the strokes (1 death) were caused by the hyperperfusion syndrome. The 30-day ipsilateral major stroke or mortality rate was 1.2% (16 patients). The 30-day rate of ipsilateral major stroke or death from stroke was 0.4% (5 patients). There were two synthetic and one vein patch internal carotid occlusions in 30 days. Synthetic-patched CEAs were predicted by means of Cox proportional hazards analysis to have higher risk ratios than saphenous vein-patched CEAs for early and late stroke (1. 3; 95% CI, 1.7 to 1.0; P =.04), for 50% or greater restenosis (2.4; 95% CI, 3.4 to 1.6; P <.001), and for 70% or greater restenosis (2. 5; 95% CI, 3.6 to 1.7; P <.001). The cumulative mortality rate (Kaplan-Meier) was 13% at 5 years and 31% at 10 years. The cumulative stroke rate was 7% at 5 years and 14% at 10 years. The 50% or greater restenosis rate was higher in women than in men at 5 years (9% versus 5%; P =.02, Wilcoxon), but tended to equalize later. The 50% or greater restenosis rate was higher in synthetic-patched CEAs than in saphenous vein-patched CEAs (12% versus 1% at 1 year; 17% versus 3% at 4 years; and 24% versus 10% at 8 years; P <.001 by means of log-rank and Wilcoxon). Restenosis after 5 years was more frequently located in the distal common carotid artery (13 of 20 cases). Late reoperations were more frequent and occurred earlier in synthetic-patched CEAs (eight cases at a mean of 1.6 years) than vein-patched CEAs (14 cases at a mean of 6.9 years; P =.01). No strokes and one restenosis of 50% or greater occurred in the 51 primarily closed CEAs. CONCLUSION: Patch angioplasty reconstruction of CEAs with arteriotomies that extend distal to the carotid bulb gives excellent early and long-term outcomes. Saphenous vein-patched CEAs are superior to synthetic patched CEAs for stroke and restenosis prevention. Primary closure is safe and durable when complete end points and arteriotomies are within the carotid bulb.

Axillary-to-carotid artery bypass grafting for symptomatic severe common carotid artery occlusive disease.

PURPOSE: Revascularization of the internal or external carotid arteries is occasionally indicated for symptomatic atherosclerotic common carotid artery occlusion or long-segment high-grade stenosis beginning at its origin. I report the outcome of axillary artery-based bypass grafts to the distal common, internal, or external carotid arteries. METHODS: Between 1981 and 1997, 29 axillary-to-carotid bypass grafting procedures were performed on 28 patients, 15 men and 13 women, with a mean age of 68 years. Indications were transient ischemia in nine patients, amaurosis fugax in four patients, completed stroke in six patients, and nonlateralizing global ischemia in nine patients. Twenty-three common carotid arteries were totally occluded, and six had long-segment stenosis of 90% or greater beginning at the origin. Saphenous vein grafts were used in 25 procedures, and synthetic grafts were used in four. Grafts were placed to 13 internal, eight distal common, and eight external carotid arteries. RESULTS: There were no perioperative deaths; one stroke occurred (3.4%). No lymphatic or peripheral nerve complications occurred. In a 1- to 11-year follow-up period (mean, 4.5 years), there were no graft occlusions, one restenosis of 50% or greater, and two restenoses of 70% or greater. The 1-year stenosis-free rate for 50% or greater stenosis was 93%, and the 5- and 10-year rates were 87%. No late ipsilateral strokes occurred. The 5- and 10-year survival rates were 64% and 28%, respectively. Coronary artery disease was the major cause of late mortality. CONCLUSION: Axillary-to-carotid bypass grafting for severe symptomatic common carotid occlusive disease is safe, well tolerated, durable, and effective in stroke prevention. There is a high late mortality rate because of coronary artery disease in patients with severe proximal common carotid occlusive disease.