Kellie A. Coyle

Optimal graft diameter: Effect of wall shear stress on vascular healing ☆ ☆☆ ★

Arterial walls tend to adapt to maintain a specific wall shear stress. The formation of neointimal hyperplasia and endothelial cell healing of polytetrafluoroethylene grafts may also be governed by wall shear stress, which suggests that an optimal graft diameter may exist. To test this, 40 polytetrafluoroethylene grafts with internal diameters of 3, 6, and 8 mm were inserted end to end in the femoral and carotid arteries of 10 mongrel dogs. Total flow and diameter were measured, and grafts were stained with Evans blue dye, fixed by pressure perfusion, and analyzed by computer for anastomotic neointimal thickening, graft pseudointimal thickening, and degree of endothelial coverage. Mean calculated shear stress was 41 dyne/cm2 for the 3 mm grafts, 7 dyne/cm2 for the 6 mm grafts, and 3 dyne/cm2 for the 8 mm grafts. Fifteen weeks later the patency rate was 0 of 10 for the 3 mm grafts, 16 of 20 for the 6 mm grafts, and 7 of 10 for the 8 mm grafts. The mean graft shear stress was calculated to be 10 dyne/cm2 for the 6 mm grafts and 4 dyne/cm2 for the 8 mm grafts. Pseudointima lining the graft was composed of disorganized protein and cell remnants. The rough surface contained no overlying endothelium. Anastomotic neointima contained a layer of well-organized smooth muscle cells covered by a single layer of polygonal-shaped endothelial cells. A transition zone of thrombus, which is sandwiched by a wedge of smooth muscle cells near the graft surface and covered by endothelial cells, is described. Mean thickness of pseudointima of the patent 8 mm grafts was 150 microns thicker than that of the 6 mm grafts. Anastomotic neointimal thickness was 110 microns thicker in the 8 mm grafts compared with the 6 mm grafts. Among the 6 mm grafts, the carotid grafts had an average initial shear stress of 10 dyne/cm2, whereas the femoral grafts averaged a lower 5 dyne/cm2 and yielded pseudointima and neointima that were 40 microns thicker. The percent graft surface area covered with neointima did not differ among the grafts of differing diameter either proximally or distally. Lower shear stresses produced greater amounts of pseudointimal thickening within polytetrafluoroethylene grafts and neointimal thickening at their anastomoses. Conversely, the high shear stress from small-diameter grafts was associated with poor graft patency. These results suggest that an optimal graft diameter may help to prevent neointimal hyperplasia and graft thrombosis.

Morbidity and Mortality Associated With Carotid Endarterectomy: Effect of Adjunctive Coronary Revascularization

The occurrence of significant carotid disease in patients requiring coronary revascularization results in the dilemma of whether simultaneous or staged operations should be performed. To determine appropriate therapy we reviewed this experience at Emory University Hospital. During a 10-year period from 1983 to 1992, 110 patients underwent carotid endarterectomy during the same hospitalization or simultaneously with coronary artery bypass; 907 patients underwent carotid endarterectomy alone during the same period. The combined 30-day postoperative stroke and death rate was 18.2% for the 110 patients undergoing concomitant procedures. When comparing morbidity and mortality rates for those having simultaneous carotid endarterectomy and coronary artery bypass with those having delayed coronary artery bypass, the latter group was found to have a 6.6% combined risk of postoperative stroke or death within 30 days, whereas those undergoing simultaneous procedures had a 26.2% rate. In the control group of 907 patients undergoing carotid endarterectomy alone during the same period, the combined 30-day mortality and stroke morbidity rate was 2.1%. Although the patient population undergoing simultaneous carotid and coronary revascularization may have more severe disease, we believe that combining the procedures during the same operative setting results in an increased perioperative stroke and death rate. Consequently only extremely high-risk patients are selected for simultaneous procedures; otherwise our experience suggests that delaying coronary artery bypass by several days will reduce overall postoperative mortality and stroke morbidity.

Ischemic nephropathy and concomitant aortic disease: a ten-year experience.

PURPOSE The durability of renal preservation after surgical intervention has not been well defined, particularly in patients with associated aortic disease. A review of all patients at the Emory University Hospital with renal insufficiency (creatinine level > or = 1.8) and concomitant atherosclerotic aortic and renovascular disease was undertaken. METHODS Fifty patients underwent both renal revascularization (71 kidneys) and the repair of aneurysmal or symptomatic aortic occlusive disease between 1982 and 1992. Hypertension was present in 96% of patients and diabetes was present in 10%. The preoperative estimated glomerular filtration rate (EGFR) was 25.18 +/- 8.29 ml/min (creatinine level 3.1 +/- 1.5 mg/dl). Operative management included bilateral renal artery repair (n = 21), unilateral repair alone (n = 17), and unilateral repair with contralateral nephrectomy (n = 12). The relative percent change in the postoperative EGFR (> or = 7 days after operation) increased by at least 20% in 42% of the patients, had decreased by 20% or more in only 4%, and was otherwise categorized as unchanged in the remaining 54% of the study group. RESULTS The 30-day operative mortality rate was 2.0% (1 of 50). Forty-five of the surviving 49 patients (91.8%) were available for follow-up (median 49 months). During this period nine patients (18.4%) eventually required dialysis, four within 6 months of operation, and 19 patients died. Neither subgroup experienced a retrieval of renal function after operation. Five-year survival rate was 61%, and a trend was noted between the risk of death and the relative change in EGFR after operation (p = 0.13). The likelihood of eventually requiring long-term dialysis was highest among those patients with low preoperative functional renal reserve as measured by preoperative creatinine level of 3 mg/dl or greater (p < 0.0001), or preoperative EGFR less than 20 ml/min (p = 0.0001). Blood pressure was cured or improved in 50% at late follow-up. CONCLUSIONS Early improvement of renal function may be observed in nearly one half of patients subjected to combined aortic and renal revascularization. Nonetheless, renal preservation may not be sustainable in patients with compromised preoperative function. Intervention before marked functional decline remains the best option for minimizing the risk of eventual dialysis.

Carotid endarterectomy in the octogenarian

During a 10-year period from January 1983 to December 1992, 79 carotid endarterectomies were performed in patients aged 80 years or older. This represented 7.4% of the total patient population undergoing carotid endarterectomy at Emory University Hospital. The indications for surgery in this elderly population were transient ischemic attacks in 24 (30.3%), cerebrovascular accident in 12 (15.2%), amaurosis fugax in seven (8.9%), vascular tinnitus in one (1.3%), and asymptomatic stenosis in 35 (44.3%). The average degree of ipsilateral stenosis was 76.8%. Concomitant risk factors included coronary artery disease in 43%, systemic arterial hypertension in 51.9%, diabetes mellitus in 10.1%, and significant smoking history in 53.2%. Seventy-six percent of the procedures were performed under local anesthesia, and in all but two intraluminal shunts were used. Combined 30-day mortality and postoperative stroke morbidity in this population was 1.3% (one patient). Long-term follow-up ranging from 1 to 10 years (average 35 months) revealed no ipsilateral strokes. This experience suggests that carotid endarterectomy can be performed in an elderly population with morbidity and mortality rates similar to those in a younger cohort.

Carotid Endarterectomy in Patients with Contralateral Carotid Occlusion: Review of a 10-Year Experience

A total of 116 carotid endarterectomies were performed in patients with a totally occluded opposite internal carotid artery over a 10-year period from 1983 until 1992. The average age of patients was 66.4 years; 75% were men and 25% were women. The average degree of stenosis on the operated side was 76.7%. Twenty-one patients (18.1%) had had a documented previous stroke referrable to the side of the occlusion; 22 had a neurologic deficit attributable to the occluded vessel at the time of preoperative evaluation. Indications for surgery included transient ischemic attacks in 35 (30.2%), ipsilateral stroke in 10 (8.6%), amaurosis fugax in 11 (9.5%), and high-grade asymptomatic stenosis in 60 (51.7%). Forty-eight percent of the procedures were performed using local anesthesia, with intraluminal shunts inserted in all except one patient. The combined 30-day mortality and stroke morbidity in this population was 4.3%, which is comparable with a combined stroke and death rate of 4.0% among 956 patients without contralateral carotid occlusion undergoing endarterectomy during this period. This experience suggests that endarterectomy can be performed safely in the patient with internal carotid occlusion and is an important mechanism for the prevention of stroke.

Treatment of recurrent cerebrovascular disease. Review of a 10-year experience.

OBJECTIVE The authors determined whether carotid endarterectomy in patients with recurrent cerebrovascular disease poses a greater perioperative risk than for those individuals undergoing first-time carotid endarterectomy. SUMMARY BACKGROUND DATA A percentage of patients undergoing carotid endarterectomy for atherosclerosis experience recurrent cerebrovascular disease. Reoperation may be difficult because of postoperative scarring of the soft tissues of the neck and the carotid artery itself. Such patients were believed to be at greater risk for perioperative morbidity than those undergoing first-time carotid endarterectomy. METHODS To address this concern, the authors retrospectively reviewed their experience with 69 patients who underwent repeat carotid endarterectomies over a recent 10-year period of time. This subgroup represented 6.4% of 1072 total carotid endarterectomies performed during the same time period. The average extent of stenosis on the operated side was 81% and the time elapsed after previous endarterectomy averaged 83 months. Twelve patients (17.4%) had contralateral internal carotid occlusion, and 30 patients (43.5%) had undergone previous endarterectomies on the contralateral side. RESULTS Complications within 30 days of operation included two deaths (2.9%) and one stroke (1.4%), for a combined stroke and death rate of 4.3%. Six patients developed cervical hematomas requiring drainage; one of these had rupture of a saphenous vein patch. No patient had a significant cranial nerve injury in the reoperative group, whereas 2.0% of patients undergoing first-time carotid endarterectomy had cranial nerve injuries. Overall, these results compared favorably with a combined stroke and death rate of 4.0% among 1003 patients who underwent first-time carotid endarterectomy during the same period. CONCLUSIONS This review suggests that repeat carotid endarterectomy can be performed safely in individuals with severe recurrent carotid stenosis, with morbidity and mortality rates similar to those for patients undergoing first-time carotid endarterectomies. For this population, reoperative carotid endarterectomy represents a safe and important mechanism for the prevention of stroke.

Carotid artery shortening: A safe adjunct to carotid endarterectomy

PURPOSE Kinks and coils of the extracranial carotid artery system have been described in conjunction with atherosclerotic disease of the internal carotid artery. The purpose of this study was to determine whether adding a carotid artery shortening procedure to carotid endarterectomy affected perioperative mortality and stroke-morbidity rates or late restenosis. METHODS A retrospective chart review of all patients who concurrently underwent carotid endarterectomy and ipsilateral carotid artery shortening between 1983 and 1992 was performed. Long-term follow-up was obtained by contacting the primary physician or patient, and carotid artery duplex scans were obtained. RESULTS One hundred seven patients were found to have undergone concurrent carotid endarterectomy and carotid artery shortening. The age range was 47 to 89 years, with 53 female and 54 male patients. Indications for surgery in this group were transient ischemic attacks in 28%, stroke in 18%, amaurosis fugax in 7%, and high-grade asymptomatic stenosis in 47%. Shortening procedures were performed by use of a variety of techniques at the completion of endarterectomy. The combined 30-day mortality and stroke morbidity rate was 2.7%, with two postoperative deaths and one stroke. In this same period, a total of 1072 carotid endarterectomies were performed, and the combined 30-day mortality and stroke morbidity rate was 4.0%. During late follow-up there were no ipsilateral strokes, recurrent symptoms, or significant restenoses. CONCLUSIONS This experience suggests that the addition of a shortening procedure to carotid endarterectomy can be performed without increased morbidity and mortality rates and, when deemed appropriate, is a procedure with which the vascular surgeon should be familiar.

Reduced Blood Flow Accelerates Intimal Hyperplasia in Endarterectomized Canine Arteries

The purpose of this study was to evaluate a technique that accelerates intimal hyperplasia by reduction of blood flow. Bilateral endarterectomies were performed in both femoral and carotid arteries in six dogs. One week later, all animals underwent banding of an artery distal to the injured region to reduce the blood flow by 50%. The contralateral injured arteries served as controls. At 11 weeks, the specimens were harvested and analyzed. Five of 12 (42%) of the flow-restricted arteries and nine of 12 (75%) of the non-flow-restricted arteries were patent at 11 weeks (P<0.05). Marked stenotic intimal hyperplastic lesions developed in the flow-restricted arteries (69% stenosis) as compared with the non-flow-restricted arteries (37% stenosis). Mean(s.d.) intimal thickness, intimal areas, and intimal/medial area ratio were 0.52(0.19) mm, 3.17(1.11) mm2, and 1.12(0.33)%, respectively, in the flow-restricted arteries. Their counterparts in the non-flow-restricted arteries were 0.21(0.09) mm, 1.70(1.09) mm2, and 0.58(0.14)%, respectively (P<0.05). Extracellular matrix comprised 48% of total intimal volumes in the flow-restricted arteries. Cell proliferation and occluded arteries were also characterized. These data demonstrate that reduction of blood flow significantly accelerated intimal hyperplasia and occlusion rates in endarterectomized arteries. Advanced intimal hyperplastic lesions (>50% stenosis) possess a high extracellular matrix content. This new animal model is a reliable generator of advanced stenotic lesions in a relatively short time period and can be used to study biologic mechanisms of stenosis and evaluate therapeutic interventions.