Biomedical subjects
Publications and source records attributed to M T Stewart.
Rupture due to device failure and/or endoleak is the most feared complication of endoluminal grafting for exclusion of abdominal aortic aneurysm. We present three previously unreported cases of abdominal aortic aneurysm rupture 23 months after AneuRx "repair" and describe the mechanisms of failure and discuss instructive technical aspects of their management.
Lexical activation is a core process in models of spoken word recognition. Specific words activated are candidates, with degree of activation determined by the match with sensory information. Once identified, lexical activation shifts to provide a meaningful representation, normally through activation of semantically related words. Activated words are assumed to acquire familiarity as a result of being activated, providing a basis for memories, both real and imagined. Three experiments showed a direct relationship between number of false recognitions and their presumed degree of activation. Results converge with those from spoken word recognition in implicating lexical activation during early stages of processing. For recognition memory, the message is that prerecognition lexical processing should be included in the memory equation.
Cohort theory in spoken-word recognition assumes that a cohort of word candidates consistent with incoming sensory information is activated implicitly as a spoken sound stimulus unfolds over time. Five experiments examined implications of this internal-generation-of-words mechanism. In Experiments 1 and 2, a "base" word was disqualified (the sensory information was no longer consistent with the word) either early or late in the presentation of a spoken stimulus. On a later recognition-memory test, significantly more false-positive errors occurred to base words following presentations of study items that had late, compared to early, disqualification points. Experiments 3-5 tested whether this phenomenon could be accounted for in terms of overlapping features between non-word stimuli and their base words or in terms of a post-identification processing mechanism. Experiment 3 replicated Experiments 1 and 2, and demonstrated that differences in early and late disqualification points for non-word targets, unlike word targets, were not related to false-positive recognition memory errors. The study inter-item interval in Experiment 4 was reduced to 1 s to minimize the role of post-identification processing activities, and the results for both word and non-word targets were consistent with Experiment 3. A word-association task in Experiment 5 revealed that the late non-word derivations used in this research were on the average more effective stimuli than the early non-word derivations in eliciting their base words. However, even when comparisons were restricted to item sets with early and late non-words that were equally effective in eliciting base words, false-positive recognition memory errors to target words were higher following prior presentations of their late derived non-words than following prior presentations of their early derived non-words.
In children with chronic renal failure, vascular access for hemodialysis is difficult because of the small size of the vessels and the requirement for substantial blood flow through the fistula or graft. As the child grows older, the ease of constructing a satisfactory access usually increases as the vessels increase in size. Unfortunately, this increased ease is often offset by the paucity of suitable access sites because the larger peripheral sites have already been used with only transient success. We report a child with chronic renal failure since 1 month of age with no peripheral sites available because of prior failed procedures who underwent placement of polytetrafluoroethylene limbs to the aorta and vena cava at the age of 6 years. He has continued on hemodialysis for the past 4 1/2 years with this technique of vascular access.
Orthotopic liver transplantation (OLT) has become standard therapy for patients with acute hepatic necrosis and end-stage liver disease. This study measured change in hepatic function (galactose elimination capacity [GEC]), liver blood flow (low dose galactose clearance: flow), hepatic volume (CT scan; volume) and morphology after OLT. The aim was to measure the physiologic response after OLT and compare this response with that after selective shunt (SS) and sclerotherapy (ES) to determine which patients should receive specific therapy. Between January 1987 and November 1988, 37 patients underwent OLT. Operative mortality was 18%, which was similar to that of SS in Child's C cirrhotics. GEC and volume were less in transplant patients than in cirrhotics treated with SS or ES. GEC, flow, and volume normalized after OLT; GEC was preserved after ES and SS, but volume decreased. Three preoperative patterns were observed that can aid in selection of OLT candidates. Patients with chronic cirrhosis (chronic active hepatitis; cryptogenic) need OLT when GEC is less than or equal to 225 mg/min and volume is less than or equal to 50% normal. Patients with Budd-Chiari Syndrome require OLT if cirrhosis has evolved. Patients with sclerosing cholangitis and primary biliary cirrhosis qualify for transplants when complications of the portal hypertensive syndrome develop. The studies can also direct therapy for ES failures. Selective shunt is indicated in those patients with stable disease whose GEC is greater than or equal to 300 mg/min and liver volume is greater than 75% normal; OLT is indicated for cirrhotics with GEC that is less than 225 mg/min and liver volume that is less than 50% predicted normal.
A new method of arterial grafting during orthotopic hepatic transplantations is described herein. The advantages compared with other techniques include better exposure, less extensive dissection, reduced blood loss and, with correct anatomic orientation, a reduced risk of kinking the graft in a blind tunnel.
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.
Successful surgical treatment of a mycotic abdominal aortic aneurysm infected with Mycobacterium bovis is described. The infecting organism can be traced to an intraneoplastic injection of bacille Calmette-Guérin (BCG) vaccine into a cutaneous malignant melanoma nodule 14 months before aneurysm detection (17 months before operation). Treatment consisted of aneurysm excision, in situ prosthetic graft placement, and antituberculous medications. This patient represents the first reported case of BCG-induced mycotic aortic aneurysm.
The treatment of 41 patients with chronic mesenteric insufficiency is reviewed: 20 men and 21 women with a mean age of 59 years were treated and observed for an average of 42 months. Thirty-one patients had symptoms of intestinal angina whereas 10 patients underwent prophylactic revascularization during other aortic operations. All but one patient had revascularization of the superior mesenteric artery, alone or in combination with another revascularization. Various surgical techniques were used, including retrograde bypass in 24 patients, antegrade bypass in 11 patients, and endarterectomy in the remaining six patients. Seven patients had acute abdominal symptoms and required emergency operation while in the hospital awaiting elective revascularization. There were two deaths in the perioperative period (4.9%), both caused by bowel necrosis. Six patients are known to have had late revascularization failure, resulting in recurrent symptoms in three patients and two subsequent deaths. All patients who remained asymptomatic after late graft failure had undergone multiple vessel revascularization; no patient revascularized prophylactically had symptoms of intestinal angina during the follow-up period. Early mesenteric revascularization is a safe and effective method of relieving the symptoms of chronic visceral ischemia and may prevent the development of fatal bowel necrosis.
From 1980 to 1985 13 patients were identified with infected aortofemoral grafts. Potential predisposing factors identified included a history of multiple femoral arterial procedures (10 patients; 77%) as well as perioperative infections occurring at the time of a prior femoral operation (five patients; 38%). Patients presented with suppurative groin infections (11) or ruptured pseudoaneurysms (2). Two who had previously undergone bilateral amputations were managed by removal of their aortic grafts without revascularization. Eleven other patients were managed by excision of the entire prosthesis (6 aortic grafts), partial graft excision (five graft limbs) or local treatment alone (three graft limbs). Revascularization through uninfected tissue planes was performed on 14 limbs with salvage of 11 (limb salvage 79%); whereas three limbs not revascularized required major amputation (limb salvage 0%). Despite an aggressive surgical approach five patients (38%) required a major amputation and there were three deaths (23% mortality). Once the diagnosis of an infected graft is made, early graft excision and prompt revascularization are encouraged.
To our knowledge, a particularly lethal complication of carotid endarterectomy, intracerebral hemorrhage, has not been given due consideration in the literature concerning carotid surgery. In the Atlanta area, massive intracranial hemorrhage developed in ten patients following routine carotid endarterectomies performed during a recent ten-year period. All ten of the patients in this series died despite a variety of therapeutic interventions. Risk factors may include the following: extreme arterial stenosis with resultant postoperative hyperperfusion, involvement of multiple extracranial cerebral vessels, postoperative systemic hypertension, and administration of anticoagulant or antiplatelet medications. Unfortunately, identification of the subset of patients potentially at risk for this complication is difficult, and, to date, therapy has been generally ineffective.
Peripheral arterial thromboembolism and thrombosis of arterial grafts continue to threaten viability of extremities. Percutaneous intra-arterial thrombolysis (IAT) and angiodilatation have afforded limb salvage in some of these patients. Proper patient selection appears to be the hallmark of success with IAT. During a recent three-year period, we used IAT in 32 extremities in 28 patients who had acute arterial insufficiency. Before IAT, 16 extremities were painful at rest, and 16 had incapacitating claudication. The overall success rate was 38%, but some degree of thrombolysis occurred in 88%. Limb salvage was achieved in 27 of 32 extremities (84%). Only five of 17 limbs (29%) with arterial graft thrombosis required no operation or an operation of lesser magnitude than predicted before IAT. Of six extremities with native arterial embolism, four (67%) were completely cleared with IAT. Major complications occurred in eight cases (25%), with two IAT-related deaths (6%). This study suggests that IAT is best reserved for individuals with acute limb ischemia caused by arterial embolus, those whose degree of ischemia would tolerate a 24-hour trial of IAT, and those whose femoral or tibial runoff is not likely to require remedial operation.
The methods used in management of 102 femoral anastomotic aneurysms (FAAs) were analyzed, and a case control study was performed in an effort to define potential etiologic factors. Most FAAs resulted from host vessel degeneration, although broken sutures, infection, and prosthetic graft dilatation contributed in some cases. Patients forming FAAs after aortofemoral bypass more often were hypertensive, had progression of distal disease, and showed diffuse atherosclerosis when compared with control patients. The use of braided synthetic sutures, woven Dacron grafts, and concomitant femoral endarterectomy correlated with FAA development, whereas diabetes mellitus, multiple femoral operations, local wound-healing problems, and occlusion of the superficial femoral artery did not correlate with the formation of FAAs. Ninety FAAs (88%) were treated surgically with an operative mortality rate of 3%. The most common surgical technique was aneurysmectomy with interposition prosthetic graft replacement. Durability of the repair was better if a simultaneous outflow procedure was performed and if the reconstruction was done before complications developed. Complicated FAAs are still responsible for significant morbidity and loss of life despite aggressive surgical management. Elective FAA repair is the preferred method of treatment.
Although graduated internal dilatation has proved to be an effective, safe, and durable operation for the treatment of symptomatic patients with fibromuscular dysplasia of the extracranial internal carotid artery, the role of surgical treatment in this entity remains unclear because the natural history is not well defined. Forty-nine patients, aged 29 to 82 years (mean, 58.5 years), with angiographically proven fibromuscular dysplasia of 88 internal carotid arteries have been evaluated since 1969. Twenty patients showed symptoms of focal cerebral or retinal ischemia, 10 patients had nonlateralizing neurologic symptoms, three patients sustained intracerebral hemorrhage, five patients complained of nonischemic symptoms, and 11 patients were asymptomatic. The three patients with intracranial hemorrhage and one person who suffered a massive stroke after angiography died within weeks of admission; no surgical therapy was performed. Initial management of the other patients included four internal carotid endarterectomies in four patients for associated atherosclerosis, one with simultaneous graduated internal dilatation; seven graduated internal dilatations in five patients; and one extracranial-to-intracranial bypass in a patient with occlusion occurring after graduated internal dilatation. Seventy-three nondilated arteries in 42 patients have been followed for up to 16 years (mean, 6.8 years). During this time only three patients have undergone surgical therapy; one carotid endarterectomy was done for an asymptomatic atherosclerotic lesion and two graduated internal dilatations in patients with nonfocal ischemia. Through follow-up of all 49 patients, none has had a new neurologic deficit. Fourteen patients who initially presented with focal ischemia were not treated surgically and all but one are now asymptomatic.(ABSTRACT TRUNCATED AT 250 WORDS)
The treatment of 77 patients with wounds of the inferior vena cava admitted to Grady Hospital, Atlanta, Georgia, from January 1972 through December 1983, was reviewed. All injuries were identified by laporotomy and/or thoracotomy. Trauma resulted from gunshot wounds in 79 per cent of patients, stab wounds in 18 per cent, and blunt trauma in 3 per cent, with an overall mortality of 30 per cent. The chief determinates of survival were preoperative hypotension, location of the injury and the presence of other major vascular injuries. Of the 49 patients admitted in shock, 22 (45%) died, all of complications related to organ ischemia. Only one patient not hypotensive on admission succumbed. Of the 29 patients with at least one additional injury to a major vascular structure, 45 per cent died. The mortality of infrarenal and suprarenal injuries was relatively low (22% and 33% respectively), compared with retrohepatic and supradiaphragmatic injuries, both of which were fatal in 67 per cent of the cases. Despite advances in the care of the trauma patient, significant improvement in survival has not occurred, and the patient mortality has remained at 30 per cent.
Sixty-three patients who underwent renal revascularization at the time of aortic surgery were retrospectively reviewed. These patients had significant renal artery stenosis in addition to either severe aortoiliac occlusive disease or aortic aneurysmal disease. Fifty-eight patients were hypertensive, whereas five patients were normotensive and these renal lesions were treated prophylactically. The operative mortality rate was 3%. Despite lack of selectivity in these patients with diffuse atherosclerosis, 60% (35 of 58) of the patients with hypertension could be classified as either "cured" or "improved." Patients with bilateral renal artery involvement and moderate azotemia were noted to improve with respect to renal function postoperatively. No patient has required chronic dialysis at a mean follow-up period of 22.6 months. Simultaneous aortic and renal artery surgery may be performed with low morbidity and mortality rates and produce a gratifying improvement in hypertension. Renal functional improvement and perhaps preservation of renal mass may be anticipated in selected patients.
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An approach to the repair of injuries of the bifurcation of the inferior vena cava and aorta is presented. This method involves division of the right common iliac artery with mobilization of the aorta for exposure of wounds to the confluence of the common iliac arteries as well as of the posterior wall of the distal aorta. Wide exposure of this area allows for more rapid control of bleeding vessels in addition to more precise vascular repair.