Which stress test is superior for perioperative cardiac risk stratification in patients undergoing major vascular surgery?

OBJECTIVE: to compare the additional prognostic value of Dobutamine Stress Echocardiography (DSE), Dipyridamole Stress Echocardiography (DiSE) and Perfusion Scintigraphy (DTS) on clinical risk factors in patients undergoing major vascular surgery. DESIGN: retrospective analysis. MATERIALS: 2204 consecutive patients who underwent DSE (n=1093), DiSE (n=394), or DTS (n=717) testing before major vascular surgery were studied. METHODS: primary endpoint was a composite of cardiac death and non-fatal myocardial infarction (MI). Logistic regression analysis was performed to evaluate the relation between cardiac risk factors, stress test results and the incidence of the composite endpoint. RESULTS: there were 138 patients (6.3%) with cardiac death or MI. Patients with 0, 1-2, and 3 or more risk factors experienced respectively 3.0, 5.7 and 17.4% cardiac events. We found no statistically significant difference in the predictive value of a positive test result for DiSE and DSE (Odds ratio (OR) of 37.1 [95% CI, 8.1-170.1] vs 9.6 [95% CI, 4.9-18.4]; p=0.12), whereas a positive test result for DTS had significantly lower prognostic value (OR=1.95 [95% CI, 1.2-3.2]). CONCLUSION: a result of stress echocardiography effectively stratified patients into low- and high-risk groups for cardiac complications, irrespective of clinical risk profile. In contrast, the prognostic value of DTS results was more likely to be dependent on patients' clinical risk profile.

Distribution of blood pressure and hypertension in Canada and the United States.

BACKGROUND: Two North American population based surveys, the Third National Health and Nutrition Examination Survey (NHANES III) and the Canadian Heart Health Surveys (CHHS) have similar time frames and methods that allow comparisons between these countries in terms of the distribution of systolic (SBP) and diastolic (DBP) blood pressure and the levels of hypertension awareness, treatment, and control. METHODS: Cross-sectional population surveys using similar methods conducted home interviews and clinic visits (CHHS), and medical examinations (NHANES III). The CHHS included the ten Canadian provinces (1986-1992) and NHANES III, a representative sample of the United States population (1988-1994). Blood pressure measurements were available for 23,111 Canadians (age 18-74 years), and restricted to the 15,326 US participants in the same age range (age 18-74 years) with both systolic and diastolic mean values. Standardized techniques were used for BP measurements. Mean of all available measurements was used from four measurements for the CHHS and six measurements for NHANES III. A mean SBP/DBP of 140/90 mm Hg or treated with medication defined hypertension. All measures were weighted to represent population values. RESULTS: Both surveys showed similar trends in mean BP by age, with slightly higher levels in the CHHS. Hypertension prevalence using the same definitions and the same age range (18-74 years) was NHANES III: 20.1%, CHHS: 21.1%. Although the prevalence of isolated systolic hypertension (ISH) was similar in both studies, around 8% to 9%, the CHHS had higher ISH prevalence than NHANES III in the younger age groups and lower prevalence in the older age groups. Elevated SBP dominated the prevalence figures after the 1950s in both studies. Compared to NHANES III, the CHHS showed a lower proportion (43% v 50%) of individuals with optimal BP (< 120/80 mm Hg) and a very low proportion of hypertensives under control (13% v 25%). About half of diabetic participants were hypertensive (using 140/90 mm Hg) in both countries with a very low level of control in Canada (9%) v the US (36%) for ages 18 to 74 years. CONCLUSIONS: The results of these two surveys highlight the importance of SBP, in the later decades of life, an overall low control of hypertension in both countries, and a better overall awareness, treatment, and control of hypertension in the US than in Canada for that period. Dissemination of hypertension guidelines and a more aggressive focus on SBP are urgently needed in Canada, with special attention to diabetics.

The challenge of controlling systolic blood pressure: data from the National Health and Nutrition Examination Survey (NHANES III), 1988--1994.

Clinicians tend to focus on diastolic blood pressure (DBP), rather than systolic blood pressure (SBP), to identify and treat hypertension. The authors used data from the National Health and Nutrition Examination Survey (NHANES III, 1988--1994) Mobile Examination Center to examine the distributions of SBP and DBP in treated and untreated individuals with hypertension. We identified the percentage of the hypertensive population with SBP controlled to less than 140 mm Hg and the percentage with DBP controlled to less than 90 mm Hg, stratified by treatment status, gender, race, and ethnicity. Individuals were classified as having hypertension if they had SBP of more than 140 mm Hg or DBP of more than 90 mm Hg, or if they were taking medication for hypertension. A weighted analysis was performed to project the results to the entire U.S. population from 1988--1994; these totals were further estimated for the year 2000 by extrapolation. For men, women, whites, African Americans, and Hispanics, SBP control rates were uniformly poorer than DBP control rates. The difference persisted when subgroups were categorized according to treatment status. The disparity in SBP and DBP control rates was especially great for women: only 50% of treated white women with hypertension had SBP control, but 92% had DBP control. The prevalence of isolated systolic hypertension was greater than 50% among all individuals with hypertension in the 55--60-year age group and increased with age thereafter. A greater emphasis on SBP is needed to improve population blood pressure control. (c)2001 Le Jacq Communications, Inc.

Predominance of isolated systolic hypertension among middle-aged and elderly US hypertensives: analysis based on National Health and Nutrition Examination Survey (NHANES) III.

The purpose of the present study was to examine patterns of systolic and diastolic hypertension by age in the nationally representative National Health and Nutrition Examination Survey (NHANES) III and to determine when treatment and control efforts should be recommended. Percentage distribution of 3 blood pressure subtypes (isolated systolic hypertension, combined systolic/diastolic hypertension, and isolated diastolic hypertension) was categorized for uncontrolled hypertension (untreated and inadequately treated) in 2 age groups (ages <50 and >/=50 years). Overall, isolated systolic hypertension was the most frequent subtype of uncontrolled hypertension (65%). Most subjects with hypertension (74%) were >/=50 years of age, and of this untreated older group, nearly all (94%) were accurately staged by systolic blood pressure alone, in contrast to subjects in the untreated younger group, who were best staged by diastolic blood pressure. Furthermore, most subjects (80%) in the older untreated and the inadequately treated groups had isolated systolic hypertension and required a greater reduction in systolic blood pressure than in the younger groups (-13.3 and -16.5 mm Hg versus -6.8 and -6.1 mm Hg, respectively; P:=0.0001) to attain a systolic blood pressure treatment goal of <140 mm Hg. Contrary to previous perceptions, isolated systolic hypertension was the majority subtype of uncontrolled hypertension in subjects of ages 50 to 59 years, comprised 87% frequency for subjects in the sixth decade of life, and required greater reduction in systolic blood pressure in these subjects to reach treatment goal compared with subjects in the younger group. Better awareness of this middle-aged and older high-risk group and more aggressive antihypertensive therapy are necessary to address this treatment gap.

The response of adult human saphenous vein endothelial cells to combined pressurized pulsatile flow and cyclic strain, in vitro.

Adult human saphenous vein endothelial cells (HVEC) were cultured in a compliant tubular device and evaluated by Northern hybridization for the effects of combined pressurized pulsatile flow and cyclic strain on the expression of mRNAs for endothelin-1 (ET-1), endothelial cell nitric oxide synthase (ecNOS), tissue plasminogen activator (tPA), and plasminogen activator inhibitor type 1 (PAI-1). The hemodynamic environment was designed to mimic shear stress conditions at the distal anastomosis of a saphenous vein graft, a common site of intimal proliferation. Steady-state mRNA levels in experimental tubes were expressed relative to that in controls. No changes were observed in ET-1 mRNA after 1 and 24 hr, but a 50% decrease in experimental cultures was observed after 48 hr in the vascular simulating device. Similar results were obtained for ecNOS mRNA, although a subgroup (4 of 11) showed a significant decrease (>50%) by 24 hr. For tPA mRNA, no change was observed after 1 hr, but a significant decrease (>60%) was measured after 24 hr and no message was detectable after 48 hr. Steady-state levels for PAI-1 mRNA remained unchanged through 48 hr of treatment. These results show that pressure, pulsatile flow, and cyclic strain, when applied in concert, differentially alter vasoactive and fibrinolytic functions in HVEC. Moreover, the dramatic decrease in steady-state levels of tPA mRNA is consistent with a shift toward an increased thrombotic state.

Long-term prognostic value of preoperative dipyridamole thallium imaging and clinical indexes in patients with diabetes mellitus undergoing peripheral vascular surgery.

The objective of this study is to assess the prognostic impact of preoperative dipyridamole thallium imaging and clinical variables on the long-term outcome of diabetic patients undergoing peripheral vascular surgery. Complete follow-up was obtained in 101 consecutive patients with diabetes mellitus undergoing routine dipyridamole thallium scintigraphy before vascular surgery (mean 4.2 +/- 3.2 years, range 1 month to 11 years). Low risk was defined by diabetes alone with a normal resting electrocardiogram. High risk was defined as a history of angina, myocardial infarction, congestive heart failure, or resting electrocardiogram abnormalities. There were 71 deaths in 98 patients discharged alive from the hospital (median survival 4.4 years). Age, the presence of resting electrocardiogram abnormalities, and an abnormal thallium scan were independent predictors of late death. After adjusting for age >70 years and thallium abnormalities, high-risk patients had a death rate 4.8 times (95% confidence interval 1.7 to 13.4, p <0.002) greater than low-risk patients. The presence of >2 reversible thallium defects was useful in further risk stratification of both low- and high-risk patients. Low-risk patients with >2 reversible defects had a median survival of 4.0 years compared with 9.4 years in those with < or =2 reversible defects (p <0.001). Similarly, high-risk patients with < or =2 reversible defects had an intermediate median survival rate of 4.7 years compared with 1.8 years in the group with >2 reversible defects (p <0.001). Therefore, advanced age and the presence of resting electrocardiographic or thallium abnormalities identifies a subset of diabetic patients with a poor long-term outcome after vascular surgery. Combined clinical and thallium variables may identify a population in whom intensive medical or surgical interventions may be warranted to reduce both perioperative and late cardiac events.

Neural network assessment of perioperative cardiac risk in vascular surgery patients.

Neural networks were developed to predict perioperative cardiac complications with data from 567 vascular surgery patients. Neural network scores were based on cardiac risk factors and dipyridamole thallium results. These scores were converted into likelihood ratios that predicted cardiac risk. The prognostic accuracy of the neural networks was similar to that of logistic regression models (ROC areas 76.0% vs 75.8%), but their calibration was better. Logistic regression overestimated event rates in a group of high-risk patients (predicted event rate, 64%; observed rate 30%; n=50, p<0.001). On a validation set of 514 patients, the neural networks still had ROC similar areas to those of logistic regression (68.3% vs 67.5%), but logistic regression again overestimated event rates for a group of high-risk patients. The calibration difference was reflected in the Hosmer-Lemeshow chi-square statistic (18.6 for the neural networks, 45.0 for logistic regression). The neural networks successfully estimated perioperative cardiac risk with better calibration than comparable logistic regression models.

Magnetic resonance angiography in the management of lower extremity arterial occlusive disease: a prospective study.

PURPOSE: We conducted a prospective study to clarify the clinical utility of magnetic resonance angiography (MRA) in the treatment of patients with lower extremity arterial occlusive disease. METHODS: During the interval of September 1993 through March 1995, 79 patients (43% claudicants, 57% limb-threatening ischemia) were studied with both MRA and contrast arteriography (ANGIO) and underwent intervention with either balloon angioplasty (9%), surgical inflow (28%), or outflow (63%) procedures. MRA and ANGIO were interpreted by separate blinded vascular radiologists, and arterial segments from the pelvis to the foot were graded as normal or with increasing degrees of mild (25% to 50%), moderate (51% to 75%), or severe (75% to 99%) stenosis or occlusion. Treatment plans were formulated by the attending surgeon and were based initially on hemodynamic, clinical, and MRA data and thereafter with ANGIO. Additional study surgeons formulated independent and specific treatment plans based on MRA or ANGIO alone. Indexes of agreement (beyond chance) for arterial segments depicted by MRA and ANGIO were assessed (kappa value), and treatment plans formulated were compared (chi-square). RESULTS: Precise agreement (%) and the percent of major discrepancies (segment classified as normal/mild stenosis on one study and severe stenosis/occlusion on the other) between MRA and ANGIO for respective arterial segments was as follows: common and external iliacs (n = 256) 77/3.5; superficial femoral and above-knee popliteal (n = 255) 73/6.7; below-knee popliteal (n = 131) 84/3.8; infrapopliteal runoff vessels (n = 864) 74/12.4; pedal vessels (n = 111) 69/19.8 Kappa values indicated moderate agreement (between MRA and ANGIO) beyond chance for all arterial segments. Treatment plans formulated by the attending surgeon, the MRA surgeon, and the ANGIO surgeon agreed in more than 85% of cases. Inability of MRA to assess the significance of inflow disease and inadequate detail of tibial/pedal vessels were the principal deficiencies of MRA in those cases where it was considered an inadequate examination. CONCLUSION: These findings suggest MRA and ANGIO are nearly equivalent examinations in the demonstration of infrainguinal vascular anatomy. MRA is an adequate preoperative imaging study (and may replace ANGIO), particularly in those circumstances when the risk of ANGIO is increased or when clinical and hemodynamic evaluation predict the likelihood of straightforward aortofemoral or femoral-popliteal reconstruction.

Renal failure after thoracoabdominal aortic surgery.

PURPOSE: Renal failure remains a common and morbid complication after complex aortic surgery. This study was performed to identify perioperative factors that contribute to postoperative renal failure. METHODS: The perioperative outcomes of 183 patients who underwent thoracoabdominal aortic surgery with supraceliac clamping were reviewed. During the interval from Jan. 1987 to Nov. 1996, thoracoabdominal aneurysm repair was performed in 154 patients (type I, 49 patients [27%]; type II, 21 patients [11.5%]; type III, 55 patients [30%]; type IV, 29 patients [16%]), suprarenal abdominal aortic aneurysm repair in 17 patients (9%), and visceral/renal revascularization procedures in 12 patients (6.5%). Intraoperative management included thoracoabdominal aortic exposure and clamp-and-sew technique with renal artery cold perfusion whenever the renal arteries were accessible (79% of cases). RESULTS: Relevant clinical features included preoperative hypertension (85%), diabetes mellitus (8%), single functioning kidney (10%), recent intravenous contrast injection (34%), renal insufficiency (creatinine level greater than 1.5 mg/dl; 24%), and emergent operation (19%). Acute renal failure, defined as both a doubling of serum creatinine level and an absolute value greater than 3.0 mg/dl, occurred in 21 patients (11.5%), of whom five required hemodialysis (2.7%). Variables associated with this complication included a preoperative creatinine level greater than 1.5 mg/dl (p = 0.004) and a total cross-clamp time greater than 100 minutes (p = 0.035). The operative mortality risk (within 30 days; 8%) was significantly increased with renal failure (odds ratio, 9.2; 95% confidence interval, 2.6 to 33; p < 0.005). CONCLUSIONS: Renal failure, although uncommon in contemporary practice, greatly increases the risk of early death after thoracoabdominal aortic surgery. The overall incidence of renal failure and dialysis requirement in the present series compare favorably with those reported using other operative techniques, specifically partial left heart bypass and distal aortic perfusion. These data suggest that patients who have preoperative renal insufficiency are prone to postoperative renal failure. Furthermore, regional hypothermic perfusion and minimal clamp times are important elements in the prevention of renal failure after thoracoabdominal aortic surgery.

Characteristics of vascular wall cells subjected to dynamic cyclic strain and fluid shear conditions in vitro.

We recently developed an in vitro silicone rubber tubular apparatus, the vascular simulating device (VSD), which simulates pressure, flow, and strain characteristics of peripheral arteries (Benbrahim et al., 1994, J. Vasc. Surg. 20, 184-194). In this report, we tested the ability of silicone rubber surfaces to support the growth and differentiation of endothelial cells (EC) and smooth muscle cells (SMC) and studied the effects of arterial levels of pressure, flow, and strain on these properties. Human umbilical and saphenous vein EC and bovine aortic EC and SMC were cultured on coated and uncoated silicone rubber in flat and tubular configurations (6 mm inner diameter) and on tissue culture plastic (TCP). Attachment, growth, and differentiation were compared on these surfaces. In addition, the effects of arterial pressure, flow, and strain conditions on adhesion and subsequent growth and differentiation were studied in the tubular configuration. Attachment and growth of vascular wall cells on fibronectin-coated silicone rubber was similar to that obtained on TCP. Application of arterial levels of pressure, flow, and strain did not alter adhesion of the cells to the tubes. Subsequent passage of these cells demonstrated that attachment, growth, and differentiation (uptake of LDL and expression of factor VIII-related antigen by EC and expression of muscle-specific actin by SMC) were similar in cells derived from experimental and control tubes which were not subjected to arterial conditions. Finally, mRNA expression of specific "housekeeping" genes was similar in cells isolated from experimental and control tubes. We conclude that the VSD supports the culture of viable and differentiated EC and SMC. These experiments demonstrate that it is possible to evaluate the effects of arterial strain and fluid shear on vascular wall cells in vitro, in a configuration similar to the blood vessel wall.

Renal artery reconstruction for the preservation of renal function.

PURPOSE: We reviewed a 13-year experience with an emphasis on long-term survival and renal function response when renal artery reconstruction (RAR) was performed primarily for the preservation or restoration of renal function in patients who had atherosclerotic renovascular disease. METHODS: From January 1, 1980, to June 30, 1993, 139 patients underwent RAR for renal function salvage and were retrospectively reviewed. Inclusion criteria were either preoperative serum creatinine level > 2.0 mg/dl (67% of patients) or RAR to the entire functioning renal mass irrespective of baseline renal function. Patient survival was calculated by life-table methods. Cox regression analysis was used to determine relative risk (RR) estimates for the late outcomes of continued deterioration of renal function and late survival after RAR. A logistic regression model was used to evaluate variables associated with perioperative complications. RESULTS: Clinical characteristics of the cohort were notable for advanced cardiac (history of congestive heart failure, 27%; angina, 22%; previous myocardial infarction, 19%) and renal disease (serum creatinine level < 2.0 mg/dl, 33%; 2.0 mg/dl to 3.0 mg/dl, 40%, > 3.0 mg/dl, 27%). Cardiac disease was the principle cause of early (6 of 11 operative deaths) and late death. Operative management consisted of aortorenal bypass in 47%, extraanatomic bypass in 45%, and endarterectomy in 8%; 45% of patients required combined aortic and RAR. The operative mortality rate was 8%; significant perioperative renal dysfunction occurred in 10%. Major operative morbidity was associated with increasing azotemia (RR = 2.1; p = 0.001; 95% confidence interval [CI], 1.3 to 4.7 for each 1.0 mg/dl increase in baseline creatinine level). Of those patients who had a baseline creatinine level > or = 2.0 mg/dl, 54% had > or = 20% reduction in creatinine level after RAR. Late follow-up data were available for 87% of operative survivors at a mean duration of 4 years (range, 6 weeks to 12.6 years). Actuarial survival at 5 years was 52% +/- 5%. Continued deterioration in renal function occurred in 24% of patients who survived operation, and eventual dialysis was required in 15%. Deterioration of renal function after RAR was associated with increasing levels of preoperative creatinine (RR = 1.6; 95% CI, 1.2 to 1.8; p = 0.001 for each 1.0 mg/dl increment in baseline creatinine level), and inversely related to early postoperative improvement in creatinine level (RR = 0.41; 95% CI, 0.2 to 0.9; p = 0.04). CONCLUSIONS: Intervention before major deterioration in renal function and an aggressive posture toward the frequently associated coronary artery disease are necessary to improve long-term results when RAR is performed for renal function salvage.

Functional outcome after surgical treatment for intermittent claudication.

PURPOSE: Although patency data for lower extremity bypass grafts are readily available, few reports have focused on patients' satisfaction after surgical reconstruction for claudication. We reviewed our experience with surgical treatment for claudication, focusing on late outcome from the patients' perspective to further refine surgical decision making in patients with intermittent claudication. PATIENTS AND METHODS: From February 1987 through April 1994, 114 consecutive patients underwent surgical bypass for intermittent claudication. Nine patients were lost to follow-up, leaving the study cohort composed of 105 patients with a mean age of 63 years (range 42 to 82 years). Sixty-two percent of the procedures were inflow reconstructions, and the remainder were infrainguinal bypasses. Clinical and demographic data were gathered from record review, and late follow-up was obtained by return visit or telephone interview. Patient satisfaction and level of function were assessed by a simple five-point questionnaire administered by a research nurse. Actuarial methods were used to calculate late graft patency and survival. Cox regression analysis was used to identify clinical and anatomic factors predictive of late survival and favorable outcome. RESULTS: Cardiac risk assessment revealed that 75% of patients either had no clinical markers for cardiac disease or had been treated with previous coronary artery bypass grafting or percutaneous transluminal angioplasty; despite this 61% of patients underwent specific preoperative cardiac testing. Most (68%) inflow procedures were aortobifemoral bypass grafts, and 93% of outflow procedures were femoropopliteal bypass grafts. Two thirds of infrainguinal grafts were performed with autogenous conduits, with prosthetic femoropopliteal bypass grafts performed only to the above-knee popliteal artery. Early graft failure with successful immediate revision occurred in 5% of patients. No operative deaths or early or late amputations occurred. At a mean follow-up of 4.5 years 96% of surviving patients had a patent graft. However, primary unassisted patency at 4 years was superior for inflow (92% +/- 4%) versus outflow (81% +/- 6%) procedures (p = 0.009). Late readmission for cardiac-related events occurred in 12%, and late cardiac-related death occurred in 5%. Actuarial survival at 5 years was 80% +/- 5%, with diabetes being the only negative survival predictor (risk ratio 2.6, 95% confidence interval 1 to 7, p = 0.049); 60% of late deaths were cancer-related. Satisfactory late results were reported by 82% of patients, with age < or = 70 years (odds ratio 4.01, 95% confidence interval 1.2 to 13.7, p = 0.026) and normalization ( > or = 0.85) of ankle/brachial index (odds ratio 5.7, 95% confidence interval 1.6 to 20, p = 0.008) being powerful independent predictors of patient satisfaction. CONCLUSIONS: After considering cardiac-related short- and long-term prognosis, we conclude that lower extremity bypass grafting for intermittent claudication will produce optimal results when restricted to younger ( < 70 years) nondiabetic patients in whom near normalization of the postoperative ankle/brachial index can be anticipated.

Development and validation of a Bayesian model for perioperative cardiac risk assessment in a cohort of 1,081 vascular surgical candidates.

OBJECTIVES: This study sought to develop and validate a Bayesian risk prediction model for vascular surgery candidates. BACKGROUND: Patients who require surgical treatment of peripheral vascular disease are at increased risk of perioperative cardiac morbidity and mortality. Existing prediction models tend to underestimate risk in vascular surgery candidates. METHODS: The cohort comprised 1,081 consecutive vascular surgery candidates at five medical centers. Of these, 567 patients from two centers ("training" set) were used to develop the model, and 514 patients from three centers were used to validate it ("validation" set). Risk scores were developed using logistic regression for clinical variables: advanced age (>70 years), angina, history of myocardial infarction, diabetes mellitus, history of congestive heart failure and prior coronary revascularization. A second model was developed from dipyridamole-thallium predictors of myocardial infarction (i.e., fixed and reversible myocardial defects and ST changes). Model performance was assessed by comparing observed event rates with risk estimates and by performing receiver-operating characteristic curve (ROC) analysis. RESULTS: The postoperative cardiac event rate was 8% for both sets. Prognostic accuracy (i.e., ROC area) was 74 +/- 3% (mean +/- SD) for the clinical and 81 +/- 3% for the clinical and dipyridamole-thallium models. Among the validation sets, areas were 74 +/- 9%, 72 +/- 7% and 76 +/- 5% for each center. Observed and estimated rates were comparable for both sets. By the clinical model, the observed rates were 3%, 8% and 18% for patients classified as low, moderate and high risk by clinical factors (p<0.0001). The addition of dipyridamole-thallium data reclassified >80% of the moderate risk patients into low (3%) and high (19%) risk categories (p<0.0001) but provided no stratification for patients classified as low or high risk according to the clinical model. CONCLUSIONS: Simple clinical markers, weighted according to prognostic impact, will reliably stratify risk in vascular surgery candidates referred for dipyridamole-thallium testing, thus obviating the need for the more expensive testing. Our prediction model retains its prognostic accuracy when applied to the validation sets and can reliably estimate risk in this group.

Laser assisted vascular welding with real time temperature control.

BACKGROUND AND OBJECTIVE: Previous studies in laser assisted vascular welding have been limited by the lack of a reliable end point for tissue fusion. As a means of improving the reproductibility of laser assisted repairs, a system incorporating real time temperature monitoring and closed loop feedback was used. STUDY DESIGN/MATERIALS AND METHODS: The system consisted of a direct view infrared thermometer for monitoring the laser heated spot, a 1.9 microns diode laser, and a microprocessor for data acquisition and feedback control of the laser power to maintain a constant tissue temperature. Rat aortas were welded under constant surface temperature conditions. RESULTS: In vivo temperature stability of +/- 2 degrees C was achieved over a temperature range of 70-90 degrees C pertinent to welding small vessels. When welds were completed using the feedback system to maintain the tissue temperature at 80 degrees C, the acute success rate was 100% and the burst pressure was 290 +/- 70 mmHg. CONCLUSION: These studies demonstrate that the use of real time monitoring and feedback control results in improved consistency for vascular tissue welding.

Magnetic resonance angiography in the preoperative evaluation of abdominal aortic aneurysms.

PURPOSE: Contrast arteriography (CA) is a useful but invasive technique for the preoperative evaluation of patients with abdominal aortic aneurysms (AAA). To evaluate the use of magnetic resonance arteriography (MRA) as a preoperative study we prospectively studied 38 patients undergoing AAA repair. METHODS: All patients underwent biplane CA and MRA with use of a gadolinium-enhanced technique. Radiographic studies were then independently evaluated by blinded radiologists for anatomic findings with CA used as the standard. Studies were then independently evaluated by blinded vascular surgeons, and a surgical plan was made. RESULTS: With CA and intraoperative findings as the standards, MRA proved highly accurate in the determination of multiple key anatomic elements. The proximal extent of aneurysmal disease was correctly predicted in 87% (33/38) patients. Significant iliofemoral occlusive disease was identified with a sensitivity of 83% (5/6). Iliac or femoral aneurysms were detected with a sensitivity of 79% (22/28) and specificity of 86% (41/48). Significant renal artery stenosis was detected with a sensitivity of 71% (12/17) and a specificity of 99% (72/73). Accessory renal arteries were correctly identified in 71% (12/17). Surgeon evaluators correctly predicted the proximal cross-clamp site in 87% (33/38) of patients with use of MRA as compared with the actual operative conduct. Proximal anastomotic sites were correctly predicted in 95% (36/38) with MRA and 97% (37/38) with CA. Renal revascularization was predicted by MRA with a sensitivity of 91% (10/11) and specificity of 100% (65/65). The use of bifurcated aortic prostheses was correctly predicted by MRA in 75% (12/16), which was similar to that predicted by CA (81%, 13/16). CONCLUSIONS: MRA can provide preoperative anatomic information that is equivalent to CA for surgical planning. Because of favorable cost and patient safety considerations MRA will assume increasing importance in the preoperative evaluation of AAA.

Comparative early and late cardiac morbidity among patients requiring different vascular surgery procedures.

PURPOSE: The evaluation of coronary artery disease (CAD) in patients undergoing vascular surgery can provide information with respect to perioperative and long-term risk for CAD-related events. However, the extent to which the required surgical procedure itself imparts additional risk beyond that dictated by the presence of CAD determinants remains in question. The purpose of this study was to quantify the relative contributions of specific vascular procedures and CAD markers on perioperative and long-term cardiac risk. METHODS: The study cohort comprised 547 patients undergoing vascular surgery from two medical centers who underwent clinical evaluation, dipyridamole thallium testing, and either aortic (n = 321), infrainguinal (n = 177), or carotid (n = 49) vascular surgery between 1984 and 1991. Perioperative and late cardiac risk of fatal or nonfatal myocardial infarction (MI) was compared for the three procedures before and after adjustment for the influence of comorbid factors. These adjusted estimates may be regarded as the component of risk because of type of surgery. RESULTS: Perioperative MI occurred in 6% of patients undergoing aortic and carotid artery surgery, and in 13% of patients undergoing infrainguinal procedures (p = 0.019). Significant (p < 0.05) predictors of MI were history of angina, fixed and reversible dipyridamole thallium defects, and ischemic ST depression during testing. Although patients undergoing infrainguinal procedures exhibited more than twice the risk for perioperative MI compared with patients undergoing aortic surgery (relative risk: 2.4[1.2 to 4.5, p = 0.008]), this value was reduced to insignificant levels (1.6[0.8 to 3.2, p = 0.189]) after adjustment for comorbid factors. There was little change in comparative risk between carotid artery and aortic procedures before (1.0[0.3 to 3.6, p = 0.95]) or after (0.6[0.2 to 2.3, p = 0.4]) covariate adjustment. The 4-year cumulative event-free survival rate was 90% +/- 2% for aortic, 74% +/- 5% for infrainguinal, and 78% +/- 7% for carotid artery procedures (p = 0.0001). Predictors of late MI included history of angina, congestive heart failure, diabetes, fixed dipyridamole thallium defects, and perioperative MI. Patients undergoing infrainguinal procedures exhibited a threefold greater risk for late events compared with patients undergoing aortic procedures (relative risk: 3.0[1.8 to 5.1, p = 0.005]), but this value was reduced to 1.3(0.8 to 2.3, p = 0.32) after adjustment. Long-term risk among patients undergoing carotid artery surgery was less dramatically altered by risk factor adjustment. CONCLUSION: In current practice, among patients referred for dipyridamole testing before operation, observed differences in cardiac risk of vascular surgery procedures may be primarily attributable to readily identifiable CAD risk factors rather than to the specific type of vascular surgery. Thus the cardiac and diabetic status of patients should be given careful consideration whenever possible, regardless of surgical procedure to be performed.

Sex differences in perioperative and long-term cardiac event-free survival in vascular surgery patients. An analysis of clinical and scintigraphic variables.

BACKGROUND: Little information is available regarding the occurrence of perioperative and late cardiac events in women with vascular disease. The current study was performed to examine whether sex-specific differences exist in these outcomes in a large population of vascular surgery patients and to determine the value of clinical and dipyridamole thallium variables in predicting myocardial infarction and cardiac death. METHODS AND RESULTS: Preoperative dipyridamole thallium imaging was performed in 567 vascular surgery patients, including 380 men and 187 women. The incidence of nonfatal myocardial infarction and cardiac death was noted during the perioperative period and during a follow-up period of 50 +/- 5 months. Fixed and reversible thallium perfusion abnormalities were more common in men than in women (P < .001 and P = .004, respectively). Perioperative cardiac event rates were similar in men and women, 8.4% and 7.5%, respectively (P = .07). A transient thallium defect was associated with an increased risk of cardiac events by 3.9-fold in men (CI, 1.5 to 10.2) and 5.5-fold in women (CI, 1.4 to 22). Various clinical factors also were predictive of events but demonstrated substantial sex differences. For example, dipyridamole-induced ST-segment depression was strongly associated with perioperative events in men but not in women. There were 22 nonfatal myocardial infarctions and 29 cardiac deaths in men during the follow-up period, with comparable event rates noted for women. Cardiac event-free survival rates also were similar for men and women (P = .40). Multivariate analysis demonstrated that a history of heart failure was an important prognostic variable for both sexes, as was a fixed thallium defect. Significant sex differences in the predictive value of other clinical factors for late cardiac events was apparent. CONCLUSIONS: The present study demonstrates that (1) thallium perfusion defects are more common in men; (2) transient thallium defects are associated with perioperative myocardial infarction and cardiac death in both sexes; (3) long-term survival rates after vascular surgery are similar between men and women; (4) a fixed perfusion defect is predictive of late cardiac events in women, with a trend noted in men; and (5) sex-specific differences were noted with regard to the prognostic value of various clinical risk factors. Therefore, dipyridamole thallium plays a significant role in the assessment of perioperative and long-term prognosis for both male and female vascular surgery patients. On the basis of these observations, modifications in risk stratification based on sex may be appropriate for men and women with vascular disease.

Arterial geometric abnormalities produce two-dimensional compliance disturbances.

PURPOSE: This study describes the two-dimensional compliance changes that develop in low-grade hemodynamically insignificant stenoses. METHODS: Twenty-four male Sprague-Dawley rats were used in the study. In 14 rats, balloon injury and endothelial denudation of the common carotid artery was followed by the application of a ligature, which produced a 20% narrowing of the outer diameter; five other rats were similarly injured without creating a stenosis, and five were stenosed without injury. The latter two groups served as control. Two-dimensional measures of arterial wall motions were obtained 30 minutes and 3 days after surgery by use of a video motion analyzer. Subsequently, circumferential (Cc) and longitudinal (Cl) compliance values were calculated and analyzed. RESULTS: At 30 minutes, in the injured stenosed arteries, overall Cc was significantly greater than in the nonstenosed injured arteries at all measured points along the artery. Both stenosed injured and stenosed noninjured arteries also displayed increased Cc both proximal and distal to the stenoses compared with Cc values furthest from the stenosis. Cl values in the stenosed arteries, both injured and noninjured, became negative across the stenosis. All two-dimensional compliance changes occurred within the area of arterial narrowing and gradually resolved approaching the nonstenotic region of the artery. At systole, in the adjacent to the stenosis arterial segments, circumferential distension was accompanied by simultaneous longitudinal compression. Three days after surgery, although Cc increased proximal and distal to the stenosis and Cl decreased in the areas adjacent to the stenoses, no statistically significant difference was found. CONCLUSIONS: Low-grade stenosis results in a longitudinal compression accompanied by a relatively increased circumferential distension of arterial segments adjacent to the stenotic region. This pattern is not initiated or influenced by the presence or absence of endothelial cells.

Device for the application of a dynamic biaxially uniform and isotropic strain to a flexible cell culture membrane.

A large number of studies have demonstrated that mechanical perturbation modulates cellular metabolism; however, the systematic characterization of the molecular and cellular transduction mechanisms underlying mechanically induced metabolic modulation has been impeded, in part, by the limitations of the mechanical device. The objective of this investigation was to develop an in vitro experimental system that would provide independent control of the spatial and temporal biaxial strain distribution imposed on a flexible transparent tissue culture membrane that permits attachment, proliferation, and maintenance of the phenotypic expression of cultured embryonic osteoblasts. Such a device would permit a systematic investigation of the cellular response to specific, independently controlled parameters of mechanical deformation. Using a prototype device designed to impose a dynamic sinusoidal spatially isotropic biaxial strain profile, we confirmed experimentally that the strain was biaxially uniform and isotropic (radial = circumferential strain over the entire culture membrane) to within 14% (SD/mean) for the range of the peak strains tested (2.3-9.4%). Additionally, the uniformity was maintained at 1 Hz for at least 5 days of continuous operation. This experimental verification of the theoretically predicted isotropic strain profile suggests that the design principle is sound. Embryonic osteoblasts cultured on the flexible substrate proliferated and exhibited a temporal pattern of phenotypic expression (extracellular matrix accumulation and mineralization) comparable with that observed on polystyrene of tissue culture grade.

A compliant tubular device to study the influences of wall strain and fluid shear stress on cells of the vascular wall.

PURPOSE: Cellular constituents of the blood vessel wall are continuously subjected, in vivo, to both mechanical and hemodynamic forces, which elicit structural and biologic responses. We have developed a compliant tubular system, the vascular simulating device (VSD), that reproduces these forces, while supporting the attachment and the experimental manipulation of endothelial and smooth muscle cells. METHODS: The VSD consists of a compliant silicone rubber tube coupled to a pump system, which permits the simultaneous application of known levels of pressure and flow, to vascular wall cells cultured on the inner surface of the tube. Seeded cells can be monitored visually under phase contrast or fluorescent optics, as well as harvested and analyzed for biologic responses. RESULTS: The elastic modulus and compliance of the silicone rubber tube are similar to those of canine and human arteries. Endothelial and smooth muscle cells cultured on the lumenal surface of the tubes remain attached and viable after subjecting them to physiologic pulsatile flow and cyclic strain. CONCLUSION: The VSD makes it possible to approximate, in vitro, those forces encountered by vascular wall cells, in vivo and therefore may make it possible to determine whether specific combinations of mechanical and hemodynamic forces are causally associated with specific vascular diseases.