Carotid artery stenting: to be or not to be?

Carotid endarterectomy (CEA) has been the standard of care for suitable patients with symptomatic or asymptomatic high grade carotid stenosis since the landmark NASCET (North American Symptomatic Carotid Endarterectomy Trial), ECST (European Carotid Surgery Trial) and ACAS (Asymptomatic Carotid Artery Surgery) studies performed in the 1990s and more recently the ACST (Asymptomatic Carotid Surgery Trial). Carotid artery stenting (CAS) in the treatment of both symptomatic and asymptomatic patients with high grade carotid stenosis has recently been investigated as an alternative to CEA. We present a review of the most recent CAS trials and examine some of the controversies that surround them.

Intraventricular administration of rt-PA in patients with intraventricular hemorrhage.

OBJECTIVE: Intraventricular hemorrhage (IVH) represents a clinicopathologic entity with a dismal prognosis. The associated mortality rate has been reported as high as 80%; the morbidity is also quite high. The use of various fibrinolytic agents (streptokinase, urokinase, and recombinant tissue-type plasminogen activator [rt-PA]) has been reported in a small number of clinical series with a very limited number of participants, yielding significant variability regarding inclusion criteria, treatment protocol, and outcome analysis. METHODS: In our prospective study, we report our experience using rt-PA in 21 patients with IVH. Patients with IVH of aneurysmal or arteriovenous malformation origin were excluded. Intraventricular administration of rt-PA was initiated within 24 hours after the ictal event (dose, 3 mg every 24 hours) through a ventricular catheter. The patients' intracranial and cerebral perfusion pressures, cerebrospinal fluid (CSF) cell count, and head CT scans with emphasis to frontal horn dimension and inner cranium diameter at the same level ratio were collected and analyzed. RESULTS: Good outcome was observed in 47.5% of our patients, whereas 28.5% died and 24.0% survived with severe disability. The development of rt-PA-associated complications was as follows: new hemorrhage in 19%, infection in 14.3%, and CSF pleocytosis in 100% of patients. Permanent CSF shunt was required in 40%. The intermediate (3-month) follow up of our survivors showed no significant outcome changes compared with the immediate (1-month) follow up. CONCLUSIONS: Intraventricular administration of rt-PA appears to be beneficial in cases of IVH even though it is occasionally associated with serious complications. Further multi-institutional studies are required for validating this treatment modality and standardizing its parameters.

C1-C2 transarticular screw fixation for atlantoaxial instability.

OBJECTIVES: The atlantoaxial segment of the cervical spine is commonly destabilized in a variety of disorders. Transarticular screw fixation of the C1-C2 joint has been proposed as a biomechanically superior therapeutic modality. The authors present their experience with this technique. METHODS: A retrospective analysis of 23 patients treated with this technique was performed. The mean follow-up period was 39.5 +/- 0.1 months. RESULTS: Mean duration of hospitalization was 3.4 +/- 0.1 days (range, 2 to 11 days). No intraoperative or early postoperative complications were detected. Four patients (17.4%) had postoperative complications unrelated to the primary procedure. The position of the screw was judged as satisfactory in 21 patients (91.3%). Two patients (8.7%) with suboptimal positioning of the screws were neurologically intact but needed no reoperation. Solid osseous fusion was detected in 19 patients (82.6%). CONCLUSIONS: Transarticular C1-C2 screw fixation appears to be a safe and surgically reliable technique. Criteria for its application and refinements in its technical considerations continue to advance its clinically versatile therapeutic potential.

Long-term survival and temporal trends in patient and surgeon factors after elective and ruptured abdominal aortic aneurysm surgery.

OBJECTIVE: Records for all patients in Ontario who underwent elective repair of abdominal aortic aneurysms (AAAs) or repair of ruptured AAAs between 1993 and 1999 were studied to determine whether the profile of surgeons or patients changed and to determine whether postoperative mortality changed over time. The secondary objective was to describe long-term survival after AAA surgery. METHODS: A population-based retrospective cohort was assembled from administrative data. Surgeon billing records were used to identify operations performed between 1993 and 1999. Chi(2) and linear regression analyses were used to determine whether variables changed over time. Kaplan-Meier survival curves were used to estimate long-term survival. RESULTS: For patients undergoing elective AAA repair, average annual surgeon volume (P <.0001) and proportion of patients operated on by vascular surgeons (P =.02) increased over the study period; similar trends were noted for patients undergoing repair of ruptured AAAs. Surgeon volume was clearly correlated with mortality after both elective AAA repair and repair of ruptured AAAs; however, the benefit of this effect was modest beyond a surgeon volume of 6 to 10 ruptured AAA repairs per year or 20 to 30 elective AAA repairs per year. No change in crude 30-day mortality (4.5% for elective AAA repair and 40.4% for repair of ruptured AAAs) was noted during the study. CONCLUSION: Despite the finding that surgery to repair ruptured AAAs and elective repair of AAAs is being increasingly performed by high-volume vascular surgeons, there was no change in early mortality between 1993 and 1999. This may have been because average surgeon volume was already relatively high at the beginning of the study period, which translated into only modest benefit to further increases in surgeon volume.

Interpretation of three-dimensional structure from two-dimensional endovascular images: implications for educators in vascular surgery.

PURPOSE: Endovascular therapy has had a major effect on vascular surgery; surgeons perform tasks in three dimensions (3D) while viewing two-dimensional (2D) displays. This fundamental change in how surgeons perform operations has educational implications related to learning curves and patient safety. We studied the effects of experience, training, and visual-spatial ability on 3D perception of 2D angiographic images of abdominal aortic aneurysms (AAA). METHODS: A novel computer-based method was developed to produce 3D depth maps based on subjects' interpretations of 2D images. Seven experts (certified vascular surgeons) and 20 novices (medical or surgical trainees) were presented with a 2D AAA angiographic image. With software specifically designed for this study, a depth map representing each subject's 3D interpretation of the 2D angiogram was produced. The novices were then randomized into a control group and a treatment group, who received a 5-minute AAA anatomy educational session. All subjects repeated the exercise on a second AAA image. Finally, all novices were given tests of visual-spatial ability, including the Surface Development Test and the Mental Rotations Test. Comparisons between experts and novices were made with depth map comparison, a subject's perception of overall object contour. RESULTS: The depth maps were significantly different (depth map comparison, P <.001) between the expert and both novice groups for the first image. After the educational intervention, the control group and the treatment group exhibited significantly different depth maps (depth map comparison, P <.001), with treatment group depth maps more similar to those of the expert group. There were no significant correlations between the visual-spatial tests and the novice depth map comparison with the expert group. CONCLUSIONS: This is the first study to examine perception of endovascular images in an educational context. Perception of overall surface contour of 3D structures from 2D angiographic images is affected by experience and training. With application of methods of vision science to an important problem in surgery, this research represents a first step in understanding the nature of visual perceptual processes involved in execution of an increasingly common clinical task. These results have implications for understanding and studying the endovascular learning curve. CLINICAL RELEVANCE: This research represents a unique collaboration in an effort to understand and solve one of the greatest problems facing surgical educators and surgeons. This research uses applied tools in vision science to understand the perceptual constraints involved in minimally invasive surgery. Specifically, we examined the mental three-dimensional maps experts use when viewing two-dimensional displays. Furthermore, we compared experts with novices in an effort to assist surgical trainees.

Vascular surgery training in general surgery residency programs: the Canadian experience.

OBJECTIVES: Vascular surgery is traditionally considered a component of general surgery. There is growing evidence of improved patient outcome related to surgeon volume and vascular certification status. The American Board of Surgery in the United States, as well as until recently the Royal College of Physicians and Surgeons in Canada, requires that vascular surgery be considered an essential content area of general surgery training. This requirement is controversial. The purpose of this study was to describe experience and perceived competence in common vascular surgery procedures during general surgery residency training in Canada. METHODS: This web-based survey was conducted between January and June 2002. General surgery program directors (GSPDs), vascular surgeons involved in general surgery training programs (VSs), and senior general surgery residents (SRs) from the 13 English-speaking general surgery programs in Canada were surveyed. Questions were asked regarding which vascular surgery procedures are appropriate for general surgeons to perform, which procedures SRs are trained to perform, and which procedures SR intend to perform. RESULTS: The response rate was 62% for GSPDs, 57% for VSs, and 45% for SRs. Overall, 49% of SRs did not intend to perform any vascular procedures after training. GSPDs, VSs, and SRs indicated that most SRs should be and are trained to perform varicose vein surgery, leg amputation, and femoral embolectomy (P >.05). In addition, GSPDs, VSs, and SRs indicated that SRs should not be and are not trained to perform infrainguinal bypass grafting, carotid endarterectomy, or abdominal aortic aneurysm (AAA) repair (P >.05). There were significant differences with respect to ruptured AAA repair: 49% of SRs, 25% of PDs, and only 12% of VSs believe that general surgeons should be trained to perform ruptured AAA repair (P <.05). Overall, 76% of VSs believe SRs receive too little vascular training. CONCLUSION: There is similarity between GSPDs, VSs, and SRs with respect to vascular surgery training in Canadian general surgery programs. Vascular surgery training cannot be considered a component of general surgery. More rotations or fellowship training is required to become competent in management of common vascular surgery procedures. Perhaps this level of competence should not be an objective of general surgery training.

Disassociation between intracranial and systemic temperatures as an early sign of brain death.

Intracranial temperature and its normal variation, as well as its response to various pathologic conditions, has become a critical component of monitoring in neurosurgical intensive care. In a prospective clinical study of 54 neurosurgical patients, intracranial pressure, cerebral perfusion pressure, and intraventricular and systemic temperatures were monitored in a neurosurgical intensive care unit. All of our patients' intraventricular temperatures were initially higher than their systemic temperatures. In 11 patients, the intraventricular temperature became lower than the systemic temperature, in a median time of 4.43 hours (range, 4.21-5.18 hours), prior to any changes in intracranial and cerebral perfusion pressures. Reversal of the disassociation between intraventricular and systemic temperatures may be an early marker of patients with a poor prognosis.

Aortic and iliac reconstruction after kidney transplantation: experience with an algorithm for renal protection.

Advances in renal transplantation have allowed for improved survival and an increased age of recipients. This has resulted in more aortoiliac lesions requiring intervention. The optimal approach for renal protection during aortoiliac surgery remains unknown. A retrospective review of transplant patients admitted to Toronto General Hospital for aortoiliac reconstruction between 1990 and 2000 was performed. A total of 20 aortic reconstructions were carried out in 18 patients: 5 patients with ascending aortic repairs and 15 patients with aortoiliac reconstructions. Of the five ascending repairs, all had cardiopulmonary bypass and four were performed under hypothermic arrest. There was one allograft loss in the postoperative period and one mortality. Of the 15 aortoiliac reconstructions 12 had protection: 10 temporary axillofemoral artery bypasses and 2 renal cold perfusion. In the 10 patients with temporary bypass protection, there were no graft losses. There was no graft loss in the hypothermic perfusion group. Of the three patients without protection, there was one graft loss. The postoperative rise in serum creatinine was significantly higher (p <0.05) in the no-protection group than in those receiving temporary bypass protection. Our algorithm of (1). temporary axillofemoral bypass, (2). cold perfusion if temporary bypass cannot be performed, and (3). clamp and sew if the patient is too unstable allows for surgery with excellent graft survival.

Distribution of intimal and medial thickening in the human right coronary artery: a study of 17 RCAs.

OBJECTIVE: To quantify the distribution of intimal and medial thickening in human right coronary arteries (RCAs) obtained at autopsy. BACKGROUND: The shear and tensile stresses created by arterial bifurcation are believed to result in eccentric fibromuscular intimal thickening that leads to atherosclerosis. Vascular curvature has been cited as a cause of atherosclerosis; however, details of the location and extent of intimal and medial thickness in the largely curved human RCA are not adequately documented. METHODS: The right coronary arteries were obtained from 40 postmortem hearts and cut into 20-30 segments, each being 3-4 mm in length. Microscopic sections from the proximal, acute margin, and distal regions of the RCA were digitized around the circumference of the vessel. Seventeen arteries showed insignificant stenosis (<50%) and were selected for detailed examination. RESULTS: Seventy-one percent (12/17) of proximal sections displayed eccentric intimal thickening. Normalized ensemble averaging revealed a preferential thickening on the myocardial side of the artery. At the acute margin region where curvature is most pronounced and at the distal region, 51% (8/17) of the samples showed eccentric thickening, but the ensemble average thickening in these regions showed no preferential location. In these mildly diseased arteries, the thickened intima comprised of mainly smooth muscle cells with an extracellular matrix of collagen and some elastin. A relatively uniform medial smooth muscle layer was seen at all three locations. CONCLUSIONS: The proximal region of the RCA appears to be a site of intrinsic eccentric intimal thickening with maximum thickness on the myocardial side of the artery. Eccentric thickening does occur in the acute margin and distal regions; however, no distinct pattern or location was evident.

Sources of error in maximum velocity estimation using linear phased-array Doppler systems with steady flow.

Using linear-array Doppler ultrasound (US) transducers, the measured maximum velocity may be in error and lead to incorrect clinical diagnosis. This study investigates the existence and cause of maximum velocity estimation errors for steady flow of a blood-mimicking fluid in a tissue-mimicking phantom. A specially designed system was used that enabled fine control of flow rate, transducer positioning and transducer angle relative to the flow phantom. Doppler machine settings (transducer aperture size, focal depth, beam-steering, gain) were varied to investigate a wide range of clinical applications. To estimate the maximum velocity, a new signal-to-noise ratio (SNR) independent method was developed to calculate the maximum frequency from an ensemble averaged Doppler power spectrum. This enabled the impact of each factor on the total Doppler error to be determined. When using the new maximum frequency estimator, it was found that the effect of transducer focal depth, intratransducer, intramachine, intermachine (that was tested) and beam-steering did not significantly contribute to maximum velocity estimation errors. Instead, it was the dependence of the maximum velocity on the Doppler angle that made, by far, the greatest contribution to the estimation error. Because our maximum frequency estimator took into account the effect of intrinsic spectral broadening, the degree of overestimation error was not as great as that previously published. Thus, the effects of Doppler angle and intrinsic spectral broadening are the chief sources of Doppler US error and should be the focus of future efforts to improve the accuracy.

In vitro hemodynamic evaluation of a Simon nitinol vena cava filter: possible explanation of IVC occlusion.

PURPOSE: To evaluate the local hemodynamics in the region of the Simon nitinol filter (SNF), used to prevent pulmonary emboli by capturing clot and promoting lysis. MATERIALS AND METHODS: The hemodynamics of the Simon nitinol inferior vena cava (IVC) filter were evaluated under steady flow (Re = 600) in a 20-mm-diameter IVC model. The photochromic dye tracer technique was used to estimate the velocity and wall shear stress. These flow features were determined for the unoccluded and partially occluded (clot volume = 1,500 mm(3)) states of the SNF along its center plane. RESULTS: A region of low velocities developed around the central axis of the filter extending from the leading edge of the central strut to the filter tip. This phenomenon was created by the strong redirection of flow toward the periphery of the filter. With the presence of the clot, these effects were enhanced, causing flow separation and recirculation. In addition, the shear stress on the hip of the clot was about 30 times that of the upstream value, and turbulence developed in the near-downstream region. CONCLUSIONS: The extended region of almost-stagnant flow near the midsection of the umbrella region could lead to organization of thrombus and fibrin mesh network development. The presence of a simulated clot led to a significant increase in the size of the stagnant, thrombus-prone region as well as turbulence, which, overall, may contribute to caval occlusion.

Factors influencing blood flow patterns in the human right coronary artery.

Evidence suggests that atherogenesis is linked to local hemodynamic factors such as wall shear stress. We investigated the velocity and wall shear stress patterns within a human right coronary artery (RCA), an important site of atherosclerotic lesion development. Emphasis was placed on evaluating the effect of flow waveform and inlet flow velocity profile on the hemodynamics in the proximal, medial, and distal arterial regions. Using the finite-element method, velocity and wall shear stress patterns in a rigid, anatomically realistic model of a human RCA were computed. Steady flow simulations (ReD=500) were performed with three different inlet velocity profiles; pulsatile flow simulations utilized two different flow waveforms (both with Womersley parameter=1.82, mean ReD=233), as well as two of the three inlet profiles. Velocity profiles showed Dean-like secondary flow features that were remarkably sensitive to the local curvature of the RCA model. Particularly noteworthy was the "rotation" of these Dean-like profiles, which produced large local variations in wall shear stress along the sidewalls of the RCA model. Changes in the inlet velocity profiles did not produce significant changes in the arterial velocity and wall shear stress patterns. Pulsatile flow simulations exhibited remarkably similar cycle-average wall shear stress distributions regardless of waveform and inlet velocity profile. The oscillatory shear index was very small and was attributed to flow reversal in the waveform, rather than separation. Cumulatively, these results illustrate that geometric effects (particularly local three-dimensional curvature) dominate RCA hemodynamics, implying that studies attempting to link hemodynamics with atherogenesis should replicate the patient-specific RCA geometry.

The influence of surgical specialty training on the outcomes of elective abdominal aortic aneurysm surgery.

OBJECTIVE: The aim of this study was to determine the independent impact of surgeon speciality training (vascular, cardiac, or general surgery) on the 30-day risk-adjusted mortality rate after elective abdominal aortic aneurysm (AAA) surgery. PATIENTS AND METHODS: All patients undergoing elective AAA surgery in Ontario between April 1, 1992, and March 31, 1996, were included. A retrospective cohort study with linked administrative databases was undertaken. RESULTS: The average 30-day mortality rate was 4.1%. Of the 5878 cases studied, 4415 (75.1%) were performed by 63 vascular surgeons, 1193 (20.3%) by 53 general surgeons, and 270 (4.6%) by 14 cardiac surgeons. After the adjustment for potential confounding factors of annual surgeon AAA volume, type of hospital, and patient age, sex, Charlson comorbidity score, and transfer status, the odds of patients dying were 62% higher when the surgery was performed by a general surgeon than when it was performed by a vascular surgeon. Cardiac surgeons' patient outcomes were similar to those of vascular surgeons. CONCLUSIONS: Patients who undergo elective AAA repair that is performed by vascular or cardiac surgeons have significantly lower mortality rates than patients who have their aneurysms repaired by general surgeons. These results provide evidence that surgical specialty training in vascular procedures leads to better patient outcomes.

Histology and morphology of 59 internal thoracic artery grafts and their distal anastomoses.

BACKGROUND: The left internal thoracic artery (LITA) is accepted as a superior graft for the left coronary system because of its better long-term patency rate than saphenous grafts. The postsurgical histomorphometric changes at the distal anastomosis of LITA grafts are not well documented. METHODS: The cellular changes within the intima of 59 LITA grafts were analyzed by light microscopy. RESULTS: Grafts implanted 1 week or less (n = 34) showed no postsurgical tissue proliferation. Of the 7 grafts implanted 1 to 8 weeks, only the suture sites exhibited intimal thickening (6 of 7 grafts, 0.08 +/- 0.07 mm). The remaining grafts (n = 18), aged 2 months to 10 years, showed significant intimal thickening at the suture sites (0.39 +/- 0.17 mm) and on the hood (0.29 +/- 0.25 mm), with variable thickening on the floor (10 of 18 left anterior descending coronary arteries, 0.11 +/- 0.12 mm). The graft body showed insignificant intimal changes (10 of 18, 0.03 +/- 0.04 mm), with mild focal atherosclerotic lesions in 2 of 18 late LITA grafts. CONCLUSIONS: Left internal thoracic artery grafts develop fibromuscular intimal hyperplasia primarily around the anastomosis. The response on the hood appears to be a hemodynamic response, secondary to that of the suture sites.

Anaphylaxis after thrombin injection of a femoral pseudoaneurysm: recommendations for prevention.

After the injection treatment of a femoral pseudoaneurysm, an anaphylactic reaction occurred in a patient undergoing hemodialysis who previously had repeated exposure to thrombin. Before injecting bovine thrombin in patients with a history of prior exposure, we recommend that they undergo skin prick testing to detect possible allergy.

An in vitro comparison of the hemodynamics of two inferior vena cava filters.

PURPOSE: The effectiveness of an inferior vena cava (IVC) filter in preventing pulmonary embolism while preserving caval flow is significantly affected by its hemodynamic characteristics. Flow fields surrounding two types of IVC filters were compared to assess how the design of a filter may influence performance. METHODS: The 12F Titanium Greenfield and VenaTech LGM inferior vena cava filters were studied in vitro with a noninvasive flow visualization technique, the photochromic flow visualization and measurement technique. Axial velocity profiles and wall shear stress distributions were measured. These results were compared with analytical data corresponding to the flow field in the absence of a filter to determine the relative extent of the flow disturbances. RESULTS: The reductions in near-wall axial velocity and wall shear stress caused by the VenaTech filter were more extensive and severe than those caused by the Greenfield filter. These changes were the consequence of differences in the geometry and dimensions of the struts of the two filters. The measurements showed the flow fields to be laminar, with no evidence of turbulence in both cases. CONCLUSION: Two factors that have been linked to thrombogenesis, near-wall velocity and wall-shear stress, were significantly affected by the larger frontal profile area of the VenaTech filter. Although a larger area may increase clot-trapping efficiency, as shown by previous studies, the reduced near-wall velocities and wall shear stresses may increase the potential for thrombogenesis and, thus, caval occlusion. In contrast to other in vitro flow visualization studies, no turbulence was observed with either filter.

In vivo proton magnetic resonance spectroscopy of brain tumors.

The ability of magnetic resonance spectroscopy (MRS) to differentiate neoplastic brain cells and their metabolic and structural characteristics is evaluated. We examined 120 patients with brain tumors using a 1.5-tesla MRI unit and MRS. The peak areas of N-acetyl-aspartate (NAA), phosphocreatine-creatine (Pcr-Cr), choline-containing compounds (Cho), lactate, lipids, myoinositol, amino acids and the ratios of NAA/Pcr-Cr, NAA/Cho and Cho/Pcr-Cr were calculated by a standard integral algorithm. In normal brain tissue, the following metabolites were identified: NAA at 2.0 ppm, Pcr-Cr at 3.0 ppm and Cho at 3.2 ppm. The different concentrations of the metabolites examined and their role in the biochemical profile of different types of tumors are discussed. The confidence interval of the MRS versus pathology was between 0.9 and 0.954, while it was between 0.52 and 0.631 for MRI versus pathology. The Cho/Pcr-Cr ratio is a very important malignancy marker for histologic tumor grading of astrocytomas. The greater this ratio, the higher the grade of the astrocytoma. NAA/Pcr-Cr together with Cho/Pcr-Cr help specify the presence or absence of a neoplasm. Proton MRS is a useful and promising diagnostic modality not only in diagnosing but also in grading solid brain tumors.