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.

Results and complications from the use of a frameless stereotactic microscopic navigator system

We present a series of 21 patients, 12 males and 9 females, aged 41-76 years, with the preoperative diagnosis of a brain tumor. Both preoperatively and postoperatively, all of our patients underwent either a brain computed tomography (CT) or magnetic resonance imaging (MRI). All the radiographic studies were taped and loaded preoperatively in the Stereotactic Microscopic Navigator (SMN) workstation (Zeiss, Germany). The mean duration of this procedure was 25 +/- 6 min. All our patients were operated on in our institute with the use of the SMN system. The specificity of tumor localization using CT scan was 2.20 +/- 0.25 mm and for the MRI scan 2.6 +/- 0.25 mm. As assessed by postoperative radiographic studies, total gross tumor resection was possible in 20 patients (95.23%). No major intraoperative or early postoperative complications were noted in our series. We believe that the SMN system is a safe, well-tolerated by the patients and simple method with extremely high accuracy and specificity.

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.

Postoperative lumbar microdiscectomy pain. Minimalization by irrigation and cooling

STUDY DESIGN

Seventy patients undergoing de novo lumbar microdiscectomy were prospectively randomized into a control group and a group in which cold intraoperative wound irrigation along with postoperative wound cooling was used. Postoperative analgesia requirements and length of hospital stay were analyzed and correlated.

OBJECTIVES

To evaluate the role of intraoperative cold irrigation and postsurgical cooling in minimizing postoperative lumbar discectomy pain.

SUMMARY OF BACKGROUND DATA

Regulated hypothermia has been used frequently in pain reduction; however, the efficacy of such a strategy in lumbar disc procedures has not been established.

METHODS

Seventy patients (43 men and 27 women), operated on the first time for lumbar disk herniation were prospectively randomized into two groups. A standard microdiscectomy was performed on all patients. In cohort A the wound site was irrigated with a cold (18 C) 5% bacitracin solution for 5 minutes. Additionally, a cooling microtemperature pump was placed on the wound site for 24 hours after surgery. The patients in the control group (cohort B) were treated in a standard fashion without additional hypothermic therapy. All patients received postoperative analgesia through a self-administered morphine pump. The amount of postoperative analgesia received was calculated in morphine equivalents per kilogram. The length of hospital stay was also noted.

RESULTS

The total amount of pain medication was significantly smaller in cohort A than in the control group (cohort B). For the statistical analysis of the results, covariate analyses for both the length of hospital stay and the morphine dose were used, demonstrating a statistically significant difference with P = 0.0001. No postoperative wound infection was noted in either group.

CONCLUSIONS

Intraoperative and postoperative wound site cooling is a safe, inexpensive, and efficient therapeutic method. It reduces the patients' postoperative pain, promotes earlier ambulation and decreases the length of hospital stay.

Velocity and wall shear stress patterns in the human right coronary artery

Blood flow dynamics in the human right coronary artery have not been adequately quantified despite the clinical significance of coronary atherosclerosis. In this study, a technique was developed to construct a rigid flow model from a cast of a human right coronary artery. A laser photochromic method was used to characterize the velocity and wall shear stress patterns. The flow conditions include steady flow at Reynolds numbers of 500 and 1000 as well as unsteady flow with Womersley parameter and peak Reynolds number of 1.82 and 750, respectively. Characterization of the three-dimensional geometry of the artery revealed that the largest spatial variation in curvature occurred within the almost branch-free proximal region, with the greatest curvature existing along the acute margin of the heart. In the proximal segment, high shear stresses were observed on the outer wall and lower, but not negative, stresses along the inner wall. Low shear stress on the inner wall may be related to the preferential localization of atherosclerosis in the proximal segment of the right coronary artery. However, it is possible that the large difference between the outer and inner wall shear stresses may also be involved.

A numerical study of blood flow patterns in anatomically realistic and simplified end-to-side anastomoses

PURPOSE

Recently, some numerical and experimental studies of blood flow in large arteries have attempted to accurately replicate in vivo arterial geometries, while others have utilized simplified models. The objective of this study was to determine how much an anatomically realistic geometry can be simplified without the loss of significant hemodynamic information.

METHOD

A human femoral-popliteal bypass graft was used to reconstruct an anatomically faithful finite element model of an end-to-side anastomosis. Nonideal geometric features of the model were removed in sequential steps to produce a series of successively simplified models. Blood flow patterns were numerically computed for each geometry, and the flow and wall shear stress fields were analyzed to determine the significance of each level of geometric simplification.

RESULTS

The removal of small local surface features and out-of-plane curvature did not significantly change the flow and wall shear stress distributions in the end-to-side anastomosis. Local changes in arterial caliber played a more significant role, depending upon the location and extent of the change. The graft-to-host artery diameter ratio was found to be a strong determinant of wall shear stress patterns in regions that are typically associated with disease processes.

CONCLUSIONS

For the specific case of an end-to-side anastomosis, simplified models provide sufficient information for comparing hemodynamics with qualitative or averaged disease locations, provided the "primary" geometric features are well replicated. The ratio of the graft-to-host artery diameter was shown to be the most important geometric feature. "Secondary" geometric features such as local arterial caliber changes, out-of-plane curvature, and small-scale surface topology are less important determinants of the wall shear stress patterns. However, if patient-specific disease information is available for the same arterial geometry, accurate replication of both primary and secondary geometric features is likely required.

The value of late computed tomographic scanning in identification of vascular abnormalities after abdominal aortic aneurysm repair

PURPOSE

The purpose of this study was to determine the prevalence of late arterial abnormalities after aortic aneurysm repair and thus to suggest a routine for postoperative radiologic follow-up examination and to establish reference criteria for endovascular repair.

METHODS

Computed tomographic (CT) scan follow-up examination was obtained at 8 to 9 years after abdominal aortic aneurysm (AAA) repair on a cohort of patients enrolled in the Canadian Aneurysm Study. The original registry consisted of 680 patients who underwent repair of nonruptured AAA. When the request for CT scan follow-up examination was sent in 1994, 251 patients were alive and potentially available for CT scan follow-up examination and 94 patients agreed to undergo abdominal and thoracic CT scanning procedures. Each scan was interpreted independently by two vascular radiologists.

RESULTS

For analysis, the aorta was divided into five defined segments and an aneurysm was defined as a more than 50% enlargement from the expected normal value as defined in the reporting standards for aneurysms. With this strict definition, 64.9% of patients had aneurysmal dilatation and the abnormality was considered as a possible indication for surgical repair in 13.8%. Of the 39 patients who underwent initial repair with a tube graft, 12 (30.8%) were found to have an iliac aneurysm and six of these aneurysms (15.4%) were of possible surgical significance. Graft dilatation was observed from the time of operation (median graft size of 18 mm) to a median size of 22 mm as measured by means of CT scanning at follow-up examination. Fluid or thrombus was seen around the graft in 28% of the cases, and bowel was believed to be intimately associated with the graft in 7%.

CONCLUSION

Late follow-up CT scans after AAA repair often show vascular abnormalities. Most of these abnormalities are not clinically significant, but, in 13.8% of patients, the thoracic or abdominal aortic segment was aneurysmal and, in 15.4% of patients who underwent tube graft placement, one of the iliac arteries was significantly abnormal to warrant consideration for surgical repair. On the basis of these findings, a routine CT follow-up examination after 5 years is recommended. This study provides a population-based study for comparison with the results of endovascular repair.

Epidural bupivacaine-morphine analgesia versus patient-controlled analgesia following abdominal aortic surgery: analgesic, respiratory, and myocardial effects

BACKGROUND

The efficacy and effects of epidural analgesia compared with patient-controlled analgesia (PCA) have not been reported in patients undergoing major vascular surgery. We compared the effects of epidural bupivacaine-morphine with those of intravenous PCA morphine after elective infrarenal aortic surgery.

METHODS

Forty patients classified as American Society of Anesthesiologists physical status 2 or 3 received general anesthesia plus postoperative PCA using morphine sulfate (group PCA; n = 21) or general anesthesia plus perioperative epidural morphine-bupivacaine (group EPI; n = 19) during a period of 48 h. During operation, EPI patients received 0.05 mg/kg epidural morphine and 5 ml 0.25% bupivacaine followed by an infusion of 0.125% bupivacaine with 0.1% morphine (0.1 mg/ ml); group PCA received 0.1 mg/kg intravenous morphine sulfate. Continuous electrocardiographic monitoring (V4 and V5 leads) was performed from the night before surgery until 48 h afterward. Respiratory inductive plethysmographic data were recorded after tracheal extubation. Visual analog pain scores at rest and after movement were performed every 4 h after extubation.

RESULTS

Nurse-administered intravenous morphine and time to tracheal extubation were less in group EPI, as were visual analog pain scores at rest and after movement from 20 to 48 h. Complications and the duration of intensive care unit and hospital stay were comparable. There was a similar, low incidence of postoperative apneas, slow respiratory rates, desaturation, and S-T segment depression.

CONCLUSIONS

Epidural morphine-bupivacaine is associated with reduced early postoperative intravenous opioid requirements, more rapid tracheal extubation, and superior analgesia after abdominal aortic surgery, with comparable respiratory effects.

A new time-domain narrowband velocity estimation technique for Doppler ultrasound flow imaging. II. Comparative performance assessment

For pt.I see ibid., vol.45, no.4, pp.939-54 (1998). The statistical performance of the new 2-D narrowband time-domain root-MUSIC blood velocity estimator described previously is evaluated using both simulated and flow phantom wideband (50% fractional bandwidth) ultrasonic data. Comparisons are made with the standard 1-D Kasai estimator and two other wideband strategies: the time domain correlator and the wideband point maximum likelihood estimator. A special case of the root-MUSIC, the "spatial" Kasai, is also considered. Simulation and flow phantom results indicate that the root-MUSIC blood velocity estimator displays a superior ability to reconstruct spatial blood velocity information under a wide range of operating conditions. The root-MUSIC mode velocity estimator can be extended to effectively remove the clutter component from the sample volume data. A bimodal velocity estimator is formed by processing the signal subspace spanned by the eigenvectors corresponding to the two largest eigenvalues of the Doppler correlation matrix. To test this scheme, in vivo common carotid flow complex Doppler data was obtained from a commercially available color flow imaging system. Velocity estimates were made using a reduced form of this data corresponding to higher frame rates. The extended root-MUSIC approach was found to produce superior results when compared to both 1- and 2-D Kasai-type estimators that used initialized clutter filters. The results obtained using simulated, flow phantom, and in vivo data suggest that increased sensitivity as well as effective clutter suppression can be achieved using the root-MUSIC technique, and this may be particularly important for wideband high frame rate imaging applications.

Recommended standards for reports dealing with lower extremity ischemia: revised version

Recommended standards for analyzing and reporting on lower extremity ischemia were first published by the Journal of Vascular Surgery in 1986 after approval by the Joint Council of The Society for Vascular Surgery and the North American Chapter of the International Society for Cardiovascular Surgery. Many of these standards have been accepted and are used in the current literature on peripheral arterial occlusive disease. With the passage of time, some oversights, aspects that require clarification, and better modifications have been recognized. This report attempts to correct these shortcomings while reinforcing those recommendations that have proven satisfactory. Explanatory comments are added to facilitate understanding and application. This version is intended to replace the original version.

Predictors of long-term patient survival after in situ vein leg bypass

PURPOSE

The objective was to determine the long-term survival rates of patients who undergo distal arterial bypass surgery and to identify the preoperative factors that are predictive of survival.

METHODS

Three hundred fifty-eight consecutive in situ distal leg bypass procedures were performed between July 1986 and December 1995. The relationship between 13 preoperative variables and late survival were determined using both univariate (Kaplan-Meier) and multivariate (Cox regression) statistical techniques.

RESULTS

The cumulative survival rates at 1, 3, 5, and 7 years were 86.6% +/- 2.0%, 63.2% +/- 3.0%, 46.9% +/- 3.4%, and 35.3% +/- 3.8%, respectively. Using Cox regression, four significant variables were found to be associated with lower late survival rates: male gender, diabetes, chronic renal insufficiency (patients with creatinine levels greater than or equal to 1.7 mg/dl or 150 SI units), and a history of cerebrovascular disease (p < 0.001 for model). When none of these four variables were present, the predicted 5-year survival rate was 71%, whereas the survival rate was reduced to 43% to 60% when one was present, 23% to 42% when two were present, 8% to 22% when three were present, and 2% when all four were present.

CONCLUSIONS

This study defines the long-term survival rates in a cohort of patients after undergoing distal bypass surgery and demonstrates that certain preoperative factors are predictive of late survival. Knowledge of these factors may be useful to assist in individual operative decisions between aggressive attempts at distal revascularization versus primary amputation.

Relation of the flow field distal to a moderate stenosis to the Doppler power

An experimental investigation was undertaken to establish how different flow regimes affect the Doppler signal. A rigid tube model consisting of a 70% asymmetric area stenosis was used with steady and pulsatile flow conditions. The characteristics of the flow field at various sites was determined using a photochromic flow visualization method. Continuous-wave Doppler measurements were made using a 41% suspension of human red blood cells (RBCs) in saline as well as a dilute suspension of 4% fixed RBCs. For steady flow, the photochromic results indicated that for Reynolds numbers (Re) of 545 and 1410, turbulence was generated and the length of the turbulent region was found to increase with increasing Re. Under pulsatile flow conditions, turbulence was triggered around peak systole and began to dissipate in late deceleration, and by the end of diastole the flow field almost relaminarized. During the turbulent phase of the flow cycle, the poststenotic flow field was seen to consist of four distinct flow regimes similar to those observed for steady flow. For higher Womersley parameters and Reynolds numbers the turbulent zone was found to be larger and to occupy a greater fraction of the flow cycle. These flow visualization results were compared with the Doppler power measurements made at the same locations and under similar flow conditions. At physiological hematocrits (41%) the onset of turbulence for both steady and pulsatile flow increased the backscattered Doppler power. The location of the peak Doppler power coincided with the region of maximum turbulence observed using the photochromic technique.

Delayed diagnosis of diltiazem overdose in a patient presenting with thrombosis of femoral artery

Previous cases of diltiazem overdose described patients who presented with hypotension, heart block, bradycardia, or ultimately death. This report concerns an elderly patient presenting to the emergency room with hypotension, an ischemic leg and confusion. He underwent an emergency thrombectomy of the femoral artery. He had severe lactic acidosis, persistent hypotension requiring prolonged inotropic support and difficulty being weaned from the ventilator after the operation. Subsequent investigations confirmed that he attempted suicide by taking an unknown quantity of diltiazem. Because diltiazem has been increasingly prescribed to treat various cardiovascular disorders, overdose may become a more common problem. A high index of suspicion is required to ensure prompt diagnosis and appropriate treatment when patients taking this medication present with sudden circulatory collapse. A guide to the management of diltiazem overdose is provided.

Defining the limitations of measurements from Doppler spectral recordings

PURPOSE

The purpose of this study was to determine whether Doppler measurements of peak velocity and four other quantitative measures of spectral shape are affected significantly by the site of the Doppler recording in relation to the location of the maximum stenosis.

METHOD

Continuous-wave and pulsed Doppler recordings were made distal to a 70% (area reduction or 45% diameter reduction) asymmetric stenosis in an in vitro flow model under steady and pulsatile flow conditions. Recordings were taken at six different locations proximal and distal to the stenosis. A photochromic dye technique was used to visualize the actual flow field in the model.

RESULTS

Distal to the stenosis, the flow visualization results demonstrated a strong radial and axial variation of the velocity field and thus explained why the Doppler measurements of peak frequency and spectral broadening were strongly dependent on the recording site. The peak frequency was maximum within the throat of the stenosis and returned to the prestenotic value five tube diameters distal to the stenosis. Other measurements of spectral broadening and spectral shape varied greatly depending on the location of the recording site in the poststenotic region. Higher order spectral moments such as the coefficient of kurtosis were found to exhibit large temporal variability, which makes them inappropriate as diagnostic indicators.

CONCLUSIONS

Because of the complex nature of the poststenotic flow field, these results clearly demonstrate that no single Doppler measurement can accurately quantify the severity of a stenosis. Of the Doppler measurements only peak velocity is related to the severity of stenosis. Reproducible peak velocity measurements are obtained only if the Doppler sample volume is positioned at or very near the throat of the stenosis and at an appropriate radial site that may not necessarily be at the center of the vessel.

Indications and results of balloon angioplasty for arterial occlusive lesions

This paper describes the current techniques for percutaneous transluminal angioplasty (PTA) of peripheral arteries, summarizes the long-term results of the procedure, and identifies the variables that are predictive of long-term success of PTA performed in the iliac and femoropopliteal segments.

Sociologic factors are major determinants of prolonged hospital stay after abdominal aneurysm repair

BACKGROUND

With increasing pressure to optimize the utilization of hospital resources, it is important to identify patients who may have prolonged hospital length of stay (LOS). The purpose of this report was to identify the preoperative variables that are predictive of prolonged postoperative hospital LOS for patients undergoing elective infrarenal abdominal aneurysm repair and to discuss strategies that might assist in minimizing LOS for these patients.

METHODS

Three hundred sixty-five consecutive patients underwent elective infrarenal abdominal aneurysm repair between 1989 and 1994. The relationship between 13 preoperative variables and LOS was analyzed by using both univariate (Kaplan-Meier) and multivariate (Cox regression) statistical techniques.

RESULTS

By using Cox regression a model was developed to estimate LOS (p < 0.001 for model). The independent predictors for prolonged LOS were (1) age older than 70 years and (2) absence of a spouse.

CONCLUSIONS

Knowledge of the predictive factors that are associated with prolonged LOS should identify those patients who may require prompt and efficient discharge planning, early consultation with a home care nurse, or transfer to a convalescent facility. This approach may significantly improve the utilization of hospital resources.