Outcome of revascularization procedures for peripheral arterial occlusive disease in Ontario between 1991 and 1998: a population-based study

PURPOSE

We describe the outcome of revascularization procedures used to treat peripheral arterial occlusive disease (PAOD), using population-based administrative data.

METHODS

A retrospective population-based cohort study utilizing administrative databases in Ontario, Canada, was conducted for fiscal years 1991 to 1998 to identify patients who underwent arterial bypass surgery and percutaneous transluminal angioplasty to treat PAOD. The Kaplan-Meier method was used to calculate cumulative survival rate and amputation-free survival rate. To analyze factors that affect these rates, multivariate analysis was performed with Cox proportional hazard models.

RESULTS

Over the study period 15,824 patients underwent bypass operations and 11,548 underwent angioplasty. For patients who underwent bypass surgery, 5-year cumulative survival rate was 61.5% and major amputation-free survival rate was 83.4%, compared with 69% and 92.2%, respectively, for patients who underwent angioplasty. Male sex, older age, diabetes, and heart disease were associated with increased risk for death after revascularization procedures. Increased risk for major amputation after revascularization procedures was associated with male sex, older age, and diabetes, whereas hypertension was linked to decreased risk.

CONCLUSION

To evaluate the long-term outcome of revascularization procedures for PAOD at the population level, survival and major amputation-free survival rates should be used, because they provide more clinically accepted estimates compared with the correlation between utilization rates for revascularization and amputation procedures, which have been used to describe outcome in previously published reports in the literature.

Use of interventional procedures for peripheral arterial occlusive disease in Ontario between 1991 and 1998: a population-based study

PURPOSE

Although peripheral arterial occlusive disease (PAOD) is a public health issue in the elderly population, limited population-based data are available on use of interventional procedures in Canada. We describe trends in use of interventional procedures to treat PAOD in Ontario over the past decade.

METHODS

A retrospective population-based cohort study was conducted for fiscal years 1991 to 1998 with Ontario administrative databases to identify all arterial bypass surgeries, angioplasty procedures, and amputations performed.

RESULTS

A total of 19,332 bypass operations, 16,334 angioplasty procedures, and 17,534 amputations were identified. Population-based rates showed that angioplasty use peaked at about 110 per 100,000 at age 65 to 74 years, arterial bypass surgery use peaked at 129 per 100,000 at age 75 to 84 years, and amputation use peaked at 138 per 100,000 at age 85 years or older. All types of interventional procedures to treat PAOD were performed more frequently in men than in women. Age-adjusted and sex-adjusted rate of arterial bypass surgery decreased significantly, from 77 to 61 per 100,000 population aged 45 years or older (P =.0002, linear regression analysis), whereas rate for PTA increased significantly, from 59 to 75 per 100,000 population aged 45 years or older (P =.0005). The overall major amputation rate declined slightly over the study period, influenced by the decreased rate in patients aged 85 years or older. The revascularization rate in patients aged 85 years or older increased (P =.055).

CONCLUSION

Reduced use of arterial bypass surgery and increased use of angioplasty procedures has occurred over the past decade and may reflect a change in the practice pattern of vascular surgeons in Ontario, who have become more conservative in treating localized disease and reserve surgical interventions for more severe forms of PAOD. The slight reduction in overall major amputation rate, driven by decreased rate in patients aged 85 years or older, may reflect a trend toward a more aggressive revascularization approach in this age group.

Guidelines for the treatment of abdominal aortic aneurysms. Report of a subcommittee of the Joint Council of the American Association for Vascular Surgery and Society for Vascular Surgery

Decision-making in regard to elective repair of abdominal aortic aneurysms (AAA) requires careful assessment of factors that influence rupture risk, operative mortality, and life expectancy. Individualized consideration of these factors in each patient is essential, and the role of patient preference is of increasing importance. It is not possible or appropriate to recommend a single threshold diameter for intervention which can be generalized to all patients. Based upon the best available current evidence, 5.5 cm is the best threshold for repair in an "average" patient. However, subsets of younger, good-risk patients or aneurysms at higher rupture risk may be identified in whom repair at smaller sizes is justified. Conversely, delay in repair until larger diameter may be best for older, higher-risk patients, especially if endovascular repair is not possible. Intervention at diameter <5.5 cm appears indicated in women with AAA. If a patient has suitable anatomy, endovascular repair may be considered, and it is most advantageous for older, higher-risk patients or patients with a hostile abdomen or other technical factors that may complicate standard open repair. With endovascular repair, perioperative morbidity and recovery time are clearly reduced; however, there is a higher reintervention rate, increased surveillance burden, and a small but ongoing risk of AAA rupture. There is no justification at present for different indications for endovascular repair, such as earlier treatment of smaller AAA. Until long-term outcome of endoluminal repair is better defined and results of randomized trials available, the choice between endovascular and open repair will continue to rely heavily on patient preference.

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.

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.

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.

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.

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.