Biomedical subjects

W Anthony Lee

Publications and source records attributed to W Anthony Lee.

28 records · Page 2Linked to original sources

PubMed2002

Changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm.

OBJECTIVE: The purpose of this study was to define changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm. METHODS: A total of 154 consecutive patients who underwent endovascular repair of abdominal aortic aneurysm with the Medtronic AneuRx stent graft at Stanford University Hospital were evaluated. During a mean follow-up period of 15.8 +/- 11.3 months, serial computerized measurements of aneurysm volume and orthogonal maximal diameter were performed on helical computed tomographic scan data sets and maximal transverse diameter was measured manually from transverse computed tomographic images. Aortoiliac length (renal to hypogastric artery origin) was measured along the median luminal centerline and along the straight line. RESULTS: Aneurysm volume increased immediately after endovascular repair (from 180.2 +/- 69.9 mL to 187.9 +/- 71.6 mL; P <.001), but orthogonal and transverse diameter and aortoiliac length did not change significantly. During the follow-up period, mean volume decreased to 171.9 +/- 70.2 mL (P <.05) and straight-line and centerline aortoiliac length remained unchanged from preoperative values. Overall, volume decreased at a rate of 1.7 +/- 5.9 mL/mo (P <.001). During periods without endoleak, the rate of decrease was 3.2 +/- 5.5 mL/mo (P <.001), and during periods with endoleak, aneurysm volume increased at a rate of 2.0 +/- 5.3 mL/mo (P <.005), without a difference between types of endoleak. Predictive values for the presence of endoleak were similar for transverse and orthogonal diameter and volume. Logistic regression analysis showed volume to be most closely associated with the presence of endoleak. CONCLUSION: Aneurysm volume increases immediately after endovascular repair. After repair, aneurysm volume gradually decreases and aortoiliac length remains unchanged. Changes in volume parallel changes in maximal aneurysm diameter, and their association with the presence of an endoleak does not appear to be appreciably stronger.

Anastomosis, Surgical↗

PubMed2002

Aneurysm-related death: primary endpoint analysis for comparison of open and endovascular repair.

PURPOSE: The purpose of this study was to utilize an objective endpoint analysis of aneurysm treatment, which is based on the primary objective of aneurysm repair, and to apply it to a consecutive series of patients undergoing open and endovascular repair. METHOD: Aneurysm-related death was defined as any death that occurred within 30 days of primary aneurysm treatment (open or endovascular), within 30 days of a secondary aneurysm or graft-related treatment, or any death related to the aneurysm or graft at any time following treatment. We reviewed 417 consecutive patients undergoing elective infrarenal aortic aneurysm repair: 243 patients with open repair and 174 patients with endovascular repair. RESULTS: There was no difference between the groups (open vs endovascular) with regard to mean age +/- standard deviation (73 +/- 8 years vs 74 +/- 8 years) or aneurysm size (64 +/- 2 mm vs 58 +/- 10 mm) (P = not significant [NS]). The 30-day mortality for the primary procedure after open repair was 3.7% (9/243) and after endovascular repair was 0.6% (1/174, P <.05). The 30-day mortality for secondary procedures after open repair was 14% (6/41) compared to 0% after endovascular repair (P <.05). The aneurysm-related death rate was 4.1% (10/243) after open surgery and 0.6% (1/174) after endovascular repair (P <.05). Mean follow-up was 5 months longer following open repair (P <.05). Secondary procedures were performed in 41 patients following open surgery and 27 patients following endovascular repair (P = NS). Secondary procedures following open repair were performed for anastomotic aneurysms (n = 18), graft infection (n = 6), aortoenteric fistula (n = 5), anastomotic hemorrhage (n = 4), lower extremity amputation (n = 4), graft thrombosis (n = 3), and distal revascularization (n = 1). Secondary procedures following endovascular repair consisted of proximal extender cuffs (n = 11), distal extender cuffs (n = 11), limb thrombosis (n = 3), and surgical conversion (n = 2). The magnitude of secondary procedures following open repair was greater with longer operative time 292 +/- 89 minutes vs 129 +/- 33 minutes (P <.0001), longer length of stay 13 +/- 10 days vs 2 +/- 2 days (P <.0001) and greater blood loss 3382 +/- 4278 mL vs 851 +/- 114 mL (P <.0001). CONCLUSIONS: The aneurysm-related death rate combines early and late deaths and should be used as the primary outcome measure to objectively compare the results of open and endovascular repair in the treatment of infrarenal abdominal aortic aneurysms. In our experience, endovascular aneurysm repair reduced the overall aneurysm-related death rate when compared to open repair. Secondary procedures are required after both open and endovascular repair. However, the magnitude, morbidity, and mortality of secondary procedures are reduced significantly with endovascular repair.

Aged↗

PubMed2002

Prospective validation of an algorithm to maximize native arteriovenous fistulae for chronic hemodialysis access.

OBJECTIVE: The purpose of this study was to evaluate an algorithm to maximize native arteriovenous fistulae (AVF) for hemodialysis access. METHODS: The prospective study design was set in an academic, tertiary care medical center. The study subjects were adults referred for permanent, upper extremity hemodialysis access between April 1999 and May 2001. Intervention included Doppler arterial pressures/waveforms and duplex imaging of the basilic, cephalic, and central veins. The optimal configuration for an AVF was determined (criteria: vein >3 mm, no arterial inflow stenosis, no venous outflow stenosis) on the basis of the noninvasive studies, and unilateral arteriography/venography was performed to confirm the choice. Permanent hemodialysis access was created on the basis of the imaging studies, and remedial imaging/intervention was performed if the AVF failed to mature. Outcome measures included impact of the noninvasive/invasive imaging, perioperative morbidity/mortality, incidence of successful AVF, time to cannulation, and predictors of AVF failure with multivariate analysis. RESULTS: A total of 139 new access procedures was performed in 131 patients (age, 53 +/- 16 years; male, 51%; white, 60%; diabetic, 49%; actively undergoing dialysis, 50%; prior permanent access, 26%). The noninvasive imaging showed that 83% of the patients were candidates for AVF, with a mean of 2.7 +/- 2.1 possible configurations. Invasive imaging was abnormal in 38% (forearm arterial disease > central vein stenosis > inflow stenosis) and impacted the operative plan in 19%. AVF were performed in 90% of the cases (brachiobasilic > brachiocephalic > radiocephalic > radiobasilic), with prosthetic AVF performed primarily because of inadequate veins. Among the patients who underwent AVF, the 30-day mortality rate was 1%, the complication rate was 20% (wound, 10%; hand ischemia, 8%), and 24% needed a remedial procedure. The AVF matured sufficiently for cannulation in 84% of those with sufficient follow-up and was suitable for cannulation by 3.4 +/- 1.8 months. On the basis of an intention to treat approach, an AVF sufficient for cannulation developed in 71% of the 139 cases referred for access. The multivariate analysis predicted that female gender (odds ratio, 9.7; 95% CI, 2.2 to 43.5) and the radiocephalic configuration (odds ratio, 4.6; 95% CI, 1.1 to 18.6) were both independent predictors of failure of the fistula to mature. CONCLUSION: With the aggressive algorithm, the construction of native AVF is possible in the overwhelming majority of patients presenting for new hemodialysis access.

Adult↗

PubMed2002

In vivo validation of numerical prediction of blood flow in arterial bypass grafts.

In planning operations for patients with cardiovascular disease, vascular surgeons rely on their training, past experiences with patients with similar conditions, and diagnostic imaging data. However, variability in patient anatomy and physiology makes it difficult to quantitatively predict the surgical outcome for a specific patient a priori. We have developed a simulation-based medical planning system that utilizes three-dimensional finite-element analysis methods and patient-specific anatomic and physiologic information to predict changes in blood flow resulting from surgical bypass procedures. In order to apply these computational methods, they must be validated against direct experimental measurements. In this study, we compared in vivo flow measurements obtained using magnetic resonance imaging techniques to calculated flow values predicted using our analysis methods in thoraco-thoraco aortic bypass procedures in eight pigs. Predicted average flow rates and flow rate waveforms were compared for two locations. The predicted and measured waveforms had similar shapes and amplitudes, while flow distribution predictions were within 10.6% of the experimental data. The average absolute difference in the bypass-to-inlet blood flow ratio was 5.4 +/- 2.8%. For the aorta-to-inlet blood flow ratio, the average absolute difference was 6.0 +/- 3.3%.

Anastomosis, Surgical↗

PubMed2002

"Pseudoendoleak"--residual intrasaccular contrast after endovascular stent-graft repair.

PURPOSE: To present a unique demonstration of postoperative perigraft contrast masquerading as an endoleak following endovascular abdominal aortic aneurysm (AAA) repair. CASE REPORT: A 66-year-old man underwent endovascular stent-graft repair of a 4.6-cm infrarenal AAA. The procedure was uncomplicated, and intraoperative completion angiography demonstrated good proximal and distal fixation of the stent-graft without an endoleak. A spiral computed tomographic (CT) angiogram obtained on postoperative day 2 revealed a large amount of extrastent contrast along the posterior aspect of the aneurysm sac. This defect had the appearance of an endoleak, but it was also present on the non-contrast images. A color-flow duplex examination performed on the same day showed a widely patent stent-graft with no evidence of extrastent flow. CONCLUSIONS: Contrast trapped in the aneurysm sac during endovascular aneurysm repair may be misinterpreted as an endoleak on postprocedural CT scans. "Pseudoendoleaks" can be distinguished from true endoleaks by examination of prebolus, noncontrast CT images, as well as by duplex ultrasound scanning.

Aged↗

PubMed2002

Open versus endovascular AAA repair in patients who are morphological candidates for endovascular treatment.

PURPOSE: To compare the outcomes of open versus endovascular repair of abdominal aortic aneurysm (AAA) in a cohort of patients who fulfill morphological criteria for endovascular repair. METHODS: A retrospective review of 229 consecutive AAA patients treated over a 3-year period identified 149 patients who were candidates for endovascular repair based on preoperative computed tomography and angiography. Of the 149 patients, 79 (68 men; mean age 74 +/- 8 years) underwent endovascular repair with the AneuRx stent-graft; the remaining 70 (56 men; mean age 72 +/- 8 years) had open repair. Short-term outcome measures were 30-day mortality and procedure-related morbidity, length of stay in the intensive care unit and hospital, intraoperative blood loss, interval to oral diet, and time to ambulation. Long-term outcome measures included death and secondary procedures. RESULTS: There was no difference in the 30-day mortality between endovascular repair (2, 2.5%) and open repair (2, 2.9%), even though endovascular patients had more comorbidities (p<0.05). Overall length of stay was reduced for endovascular patients (3.9 +/- 2.4 days versus 7.7 +/- 3.1 days for surgical patients, p<0.0001). Fewer endograft patients had complications (24% versus 40% for open repair, p<0.05), and the severity of these complications was less, as evidenced by the shorter hospital stays for endovascular patients with complications compared to conventionally treated patients with complications (6.7 +/- 2.4 days versus 22.5 +/- 35.2 days, p<0.05). There were no aneurysm ruptures or late surgical conversions in either group. CONCLUSIONS: Patients with AAA who were endograft candidates but who were treated with open repair experienced more morbidity and had more complications than patients treated with stent-grafts. Despite increased comorbidities in the endograft patients, there was no increase in mortality compared to open repair. Both treatments required secondary procedures and appeared to be equally effective in preventing aneurysm rupture up to 3 years.

Aged↗

PubMed2002

The first 150 endovascular AAA repairs at a single institution: how steep is the learning curve?

PURPOSE: To determine whether increasing experience with endovascular abdominal aortic aneurysm (AAA) repair in a single institution will result in improved outcome. METHODS: A retrospective review was undertaken of 150 consecutive cases of endovascular AAA repairs performed using the AneuRx device between October 1996 and April 2000 in a university-based medical center. The population was divided into early and late groups of 75 patients each. Endpoints included technical success; complications; early (< or =30-day) morbidity, mortality and rupture; endoleak at discharge and at 1 month; early secondary intervention; proximal neck and iliac tortuosity; extender cuff placement; femoral reconstructions beyond primary repair; total fluoroscopy time; and contrast load. RESULTS: Baseline patient and aneurysm characteristics were similar between the 2 groups. Technical success was 98.7%; 2 cases were converted intraprocedurally owing to difficult iliac access (early group) and a severely angulated proximal neck (late group). There was a tendency toward more frequent use of intraoperative proximal extender cuffs in the early group (12% versus 4% in the late group, p=0.13). Femoral reconstructions were more frequent in the early group (36% versus 19%, p<0.025). While total contrast volume was similar (111 +/- 56 versus 105 +/- 45 mL, p=NS), total fluoroscopy time was significantly reduced (p<0.05) between the early and late groups. CONCLUSION: With attention to detail and careful patient selection, successful endovascular AAA repair can be achieved with very few conversions and low perioperative mortality even during the center's early experience. Evidence indicates, however, that a learning curve definitely exists, as shown by fewer access site problems, more accurate device deployments, and decreased fluoroscopy times as proficiency is attained.

Aged↗

PubMed2002

Eligibility rates of ruptured and symptomatic AAA for endovascular repair.

PURPOSE: To determine the anatomical eligibility rate for endovascular repair of ruptured and symptomatic abdominal aortic aneurysms (AAA) using commercially available endografts. METHODS: In a retrospective review, 28 preoperative computed tomographic (CT) scans were examined from among 83 patients who underwent surgical repair of a ruptured or acutely symptomatic AAA at a university-based tertiary care center during the past 10 years. The proximal aortic neck, aneurysm, and iliac dimensions were compared to corresponding measurements from 100 preoperative CT scans from patients who underwent elective repair of asymptomatic AAA. Based on expanded selection criteria for the 2 FDA-approved endografts (AneuRx and Ancure), eligibility rates for endovascular repair were compared between patients with ruptured/symptomatic and asymptomatic AAAs. RESULTS: The proximal neck of the ruptured/symptomatic AAAs was on the average 2 mm larger in diameter (25 +/- 4 versus 23 +/- 3 mm, p=0.04) and 7 mm shorter (16 +/- 10 versus 23 +/- 14, p=0.017) than asymptomatic AAAs. The maximum AAA diameter was significantly larger in the ruptured/symptomatic group (64 +/- 16 mm) than in the asymptomatic group (58 +/- 11 mm, p=0.033). Of the 28 ruptured/symptomatic AAAs assessed morphologically, 13 (46%) were anatomically eligible for endovascular repair compared to 74 of the 100 asymptomatic AAAs (p=0.006). The main cause for exclusion was an unfavorable proximal neck, which was present in 15 (54%) of the 28 ruptured/symptomatic AAAs and in 24 (24%) of the 100 asymptomatic AAAs (p=0.003). CONCLUSIONS: A significantly smaller proportion of patients presenting with ruptured/symptomatic AAA are anatomically eligible for endovascular AAA repair compared to patients with asymptomatic AAA due to unfavorable proximal neck anatomy.

Adult↗

PubMedDate not supplied

Endovascular treatment of popliteal artery aneurysms.

Popliteal artery aneurysms are relatively uncommon but potentially limb-threatening lesions that can thrombose or cause distal embolization. Identification of these aneurysms, especially in patients with abdominal aortic aneurysms, is imperative, and prophylactic treatment with either surgical exclusion and bypass or endoluminal stent grafting is critical to prevent these poor outcomes. Endovascular approaches currently using the Viabahn stent graft offer several advantages, including a minimally invasive approach, fewer perioperative complications, and a faster recovery. This must be balanced with a potentially higher failure rate or requirement for reintervention, although contemporary series report comparable short-term outcomes. We present our approach to the evaluation and diagnosis of popliteal aneurysms, the technical aspects of endovascular popliteal aneurysm repair, and a representative case study.

Aged↗

PubMedDate not supplied

Management of aortic aneurysms and dissections with the Zenith TX2 stent graft.

Endovascular repair of thoracic aortic aneurysms offers a less invasive alternative to conventional surgery, similar to its counterpart in the abdominal aorta. Although its long-term durability and outcome remain relatively unknown, published midterm results from clinical trials suggest comparable rates of aneurysm-related mortality and significant reductions in early morbidity compared with open repair. The Zenith TX2 stent graft (Cook Endovascular, Bloomington, IN) is an investigational endovascular device that is designed to treat aneurysms and other degenerative pathologies of the thoracic aorta. At the time of this writing, it is nearing completion of its pivotal trial. Clinical experience with this device is limited to countries outside the United States and to sites participating in the clinical trials. The purpose of this article is to provide a description of the Zenith TX2 device and its application in the repair of thoracic aortic aneurysms and dissections.

Aortic Dissection↗