Cost-effectiveness of rimegepant oral lyophilisate compared to best supportive care for the acute treatment of migraine in the UK

AIMS

Migraine is the most common disabling headache disorder and is characterized by recurrent throbbing head pain and symptoms of photophobia, phonophobia, nausea, and vomiting. Rimegepant 75 mg, an oral lyophilisate calcitonin gene-related peptide antagonist, is the first treatment approved for both the acute and preventative treatment of migraine, and the first acute therapy approved in over 20-years. The objective was to assess the cost-utility of rimegepant compared with best supportive care (BSC) in the UK, for the acute treatment of migraine in the adults with inadequate symptom relief after taking at least 2 triptans, or for whom triptans are contraindicated or not tolerated.

MATERIALS AND METHODS

A de novo model was developed to estimate incremental costs and quality-adjusted life years (QALYs), structured as a decision tree followed by Markov model. Patients received rimegepant or BSC for a migraine attack and were assessed for response (pain relief at 2-h). Responders and non-responders followed different pain trajectories over 48-h cycles. Non-responders discontinued treatment while responders continued treatment for subsequent attacks, with a proportion discontinuing over time. Data sources included a post-hoc pooled analysis of the phase 3 acute rimegepant trials (NCT03235479, NCT03237845, NCT03461757), and a long-term safety study (NCT03266588). The analysis was conducted from the perspective of the UK National Health Service and Personal Social Services over a 20-year time horizon.

RESULTS

Rimegepant resulted in an incremental cost-utility ratio (ICUR) of £10,309 per QALY gained vs BSC, which is cost-effectiveness at a willingness to pay threshold of £30,000/QALY. Rimegepant generated +0.44 incremental QALYs and higher incremental lifetime costs (£4,492). Improved QALYs for rimegepant were a result of less time spent with severe and moderate headache pain.

CONCLUSION

This study highlights the economic value of rimegepant which was found to be cost-effective for the acute treatment of migraine in adults unsuitable for triptans.

Preventing coronary events by optimal control of blood pressure and lipids in patients with the metabolic syndrome

We estimated the coronary heart disease (CHD) events that are preventable by treatment of lipids and blood pressure in patients with metabolic syndrome (MetS), a contributor to coronary heart disease (CHD). Among patients aged 30 to 74 years (without diabetes or CHD) in the United States, MetS was defined by National Cholesterol Education Program criteria. CHD events over a period of 10 years were estimated by Framingham algorithms. Events that could be prevented by statistically "controlling" blood pressure, low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol to either normal or optimal levels according to national guidelines were calculated. Of 7.5 million men and 9.0 million women aged 30 to 74 years with MetS, approximately 1.5 million men and 0.45 million women, if untreated, developed CHD events in 10 years. In men and women, blood pressure control to normal levels "prevented" 28.1% and 12.5% of CHD events, respectively (p <0.01); control to optimal levels resulted in preventing 28.2% and 45.2% of events, respectively (p <0.01). Control of HDL cholesterol to normal levels resulted in preventing 25.3% of events in men and 27.3% in women; optimal control prevented 51.2% and 50.6% of events, respectively. Control of LDL cholesterol to normal levels prevented 9.3% of events in men and 9.8% of events in women; control to optimal levels prevented 46.2% and 38.1% of events (p <0.05), respectively. Control of all 3 risk factors to normal levels resulted in preventing 51.3% of events for men and 42.6% for women; control to optimal levels resulted in preventing 80.5% and 82.1% of events, respectively. Thus, many CHD events in patients with MetS may be preventable by nominal or optimal control of lipids and/or blood pressure.

Preventing heart disease by controlling hypertension: impact of hypertensive subtype, stage, age, and sex

BACKGROUND

Hypertension is related to significant morbidity and mortality rates from coronary heart disease (CHD). This report examines the relative and absolute impact on risk for CHD by controlling hypertension to high normal and optimal levels.

METHODS

Among all subjects with untreated or inadequately treated hypertension in the National Health and Nutrition Examination Survey (NHANES) III who were 30 to 74 years of age and without prior CHD, the 10-year risk of CHD was calculated. With the use of sampling weights, the number of CHD events by age group, hypertension subtype (isolated diastolic hypertension [IDH], systolic-diastolic hypertension [SDH], and isolated systolic hypertension [ISH]), and stage of hypertension was estimated. Risk was recalculated and the number of events reestimated, assuming a reduction in blood pressure (BP) to high normal and optimal levels. The number and proportion (population-attributable risk, or PAR%) of events that could be prevented were determined from the differences in events and risk between uncontrolled and controlled BP levels. Derived from this was the number of persons needing treatment per CHD event prevented.

RESULTS

Control of hypertension to high normal levels could prevent approximately one fifth (PAR = 19%) of CHD events in men and one third (PAR = 31%) of CHD events in women, whereas control to optimal levels may prevent 37% and 56% of CHD events, respectively (P <.01 for differences between men and women). Of CHD events that could be prevented, the greatest proportion occurred from controlling BP among older persons, men, and those with stage 1 hypertension (vs stages 2 and 3) or with ISH (vs IDH or SDH). The number of persons with hypertension needing treatment to prevent one CHD event ranged from 20.5 in men to 38.6 in women when controlled to high normal BP and 10.7 in men and 21.3 in women when controlled to optimal BP.

CONCLUSIONS

The greatest impact from control of hypertension occurs in older persons, men, and those with ISH, whereas the greatest PAR% occurred in women. Optimal control of BP could prevent more than one third of CHD events in men and more than half of events in women. Greater efforts to control hypertension in these populations may have a substantial impact in preventing CHD events.

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.

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.

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.

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.

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.

Biaxial elastic properties of rat arteries in vivo: influence of vascular wall cells on anisotropy

There is no consensus as to the degree of arterial anisotropy or to its relationship to vascular cell function. Given the relevance of the isotropic assumption in formulating elasticity models, reliable measures of biaxial displacements are needed. In this study, a video motion analyzer (VMA) was used to describe the biaxial in vivo dynamic elasticity of 22 carotid arteries and 5 abdominal aortas in 27 rats. The influence of vascular cell function was also examined by subjecting six rats to a photosensitive drug, chloroaluminum sulfonated phthalocyanine (CASPc), which is focally cytotoxic on activation by laser. Circumferential compliance (Ccirc) was greater than longitudinal compliance (Clong) for all vessels. Compliance pressure curves were nonlinear, and biaxial displacements were in phase. The circumferential elastic modulus was less than the longitudinal modulus at common stresses. CASPc + laser reduced Ccirc but not Clong, thus altering Poisson's ratio. In conclusion, rat arteries are biaxially, nonlinearly elastic and anisotropic in vivo. Vascular cells modulate Poisson's ratio by influencing Ccirc.

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.

The durability of different reconstructive techniques for atherosclerotic renal artery disease

PURPOSE

Among various surgical techniques for renal artery reconstruction (RAR), anatomic aortorenal bypass has been the preferred standard. Yet concern regarding origin of the bypass from a diseased aorta and desire to avoid a major aortic operation in these patients who are often at poor risk has led to increasing use of extraanatomic bypass grafting, particularly hepatorenal and splenorenal bypass. This study was conducted to compare the safety and long-term performance of these different techniques of renal artery reconstruction.

METHODS

We reviewed a 15-year (1976 to 1991) experience with 323 surgical RAR performed in 285 patients with atherosclerotic renovascular disease. Long-term patency and survival rates were analyzed by life-table methods. Variables potentially affecting early failure of the RAR and perioperative and late mortality rates were examined by Cox proportional hazards models.

RESULTS

Diffuse atherosclerosis characterized the patients' clinical profile. Clinically evident coronary artery disease was present in 54% of patients, and some degree of renal insufficiency was present in 60%. Ninety-five percent of patients had hypertension with poor control of hypertension seen in 50%. Aortic disease necessitated combined aortic grafting and RAR in 43% of the study group. Various techniques of RAR were used as follows: endarterectomy or patch angioplasty, 8.5%; extraanatomic bypass grafting, 37% (hepatorenal, 62; splenorenal, 52; iliorenal, 7); and aortorenal bypass grafting, 54% (native aorta, 34; combined aortic graft and RAR, 140). Early failure of the RAR occurred in 5% of cases, and the operative mortality rate for the entire cohort was 5.6%. Median follow-up duration was 9.4 years. A comparison of early and late patency for the major types of RAR revealed equivalent (p = 0.44) performance of aortorenal and extraanatomic bypass grafting. Perioperative complications occurred more frequently (p < 0.02) in patients undergoing combined operations. The cumulative 5-year survival rate for all patients was 75%.

CONCLUSIONS

Because extraanatomic bypass grafting can provide long-term results equivalent to aortorenal bypass grafting, the choice among techniques for RAR in patients with diffuse atherosclerosis should be based on both technical and operative safety considerations, rather than adherence to aortorenal bypass grafting as an inherently superior technique.

In vivo determination of human arterial compliance: preliminary investigation of a new technique

PURPOSE

To obtain more detailed information about the dynamic mechanical properties of human arteries in vivo, using a new technique based on intravascular ultrasound. (IVUS).

METHODS

Arterial compliance was measured in the common and/or external iliac arteries of 6 patients using an IVUS device, concurrently obtained intraarterial pressure measurements, and a video motion analysis system.

RESULTS

Compliance decreased with increasing vessel diameter and mean arterial pressure. Pre- and postangioplasty measurements were obtained in 2 patients but did not demonstrate a consistent change in compliance following angioplasty.

CONCLUSION

We conclude that IVUS provides an accurate means for in vivo determination of human arterial compliance, the practical value of which needs to be established.

Hemodynamics and aneurysm development in vascular allografts

PURPOSE

Mechanical and immunologic factors may play a role in the development of native arterial and biologic graft aneurysms. We developed an experimental rat aortic allograft aneurysm model in which segments of infrarenal aorta were transplanted between hypertensive and normotensive rats to study these factors in this model.

METHODS

Aortic allografts and autografts were inserted into spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. Effects of immunologic and antihypertensive therapy were evaluated. Graft diameters were followed up with magnetic resonance imaging and at harvest. Direct-pressure measurements were taken and dp/dtmax (force of ventricular contractions) was calculated before harvest.

RESULTS

Autografts remained isodiametric and maintained their histologic architecture. Aneurysmal dilation of transplanted segments occurred in SHR host allografts but not in WKY host allografts. Histologic examination of all allograft specimens noted a rejection reaction characterized by inflammatory cell infiltration and medial smooth muscle cell loss. Antigenic enhancement accelerated aneurysm development in SHR hosts but had no significant effect on WKY hosts. Rates of allograft enlargement and final allograft diameters were similar in antihypertensive treated and untreated SHR hosts. The dp/dtmax in untreated SHR hosts was greatest and differed significantly from that in the WKY rats but only marginally from that in treated SHR hosts.

CONCLUSIONS

Immunologic rejection but not abnormal hemodynamics is necessary for development of allograft aneurysm in this model.

Abnormal wall strain at distal end-to-side anastomoses

Cyclic stretch has been demonstrated to induce proliferative and secretory activities by cultured arterial endothelial and smooth muscle cells, cellular processes that contribute to the development of intimal hyperplasia. A model of an end-to-side anastomosis was developed to examine the hypothesis that regions of the artery at such anastomoses are subjected to focally increased cyclic stretch, which may stimulate the development of intimal hyperplasia. Polytetrafluoroethylene grafts were anastomosed end to side to latex rubber tubes that have elastic properties similar to those of the human femoral artery. Pulse waves with physiologic pressure, rate, and contour were applied, and systolic and diastolic diameters were measured in two planes at longitudinal intervals. Circumferential strain imposed on the latex "artery" was calculated at each interval. Strain imposed perpendicular to the suture line was also measured. Circumferential strain was consistently maximal at a distinct region of the "artery" along the proximal third of the anastomosis (6.0 +/- 1.1% vs. 3.3 +/- 0.5% at other regions of the "artery"). The maximal strain across the suture line was found at precisely the same region (3.9 +/- 0.3% vs. 2.0 +/- 0.4%). The anastomotic region of the recipient artery in a distal end-to-side anastomosis is subjected to cyclic circumferential strains two times greater than those experienced by the remainder of the artery. This corresponds to a common location of intimal hyperplasia. Such strains may be a stimulus for intimal hyperplasia.

Absorption characteristics at 1.9 microns: effect on vascular welding

A 1.9 microns laser was used to investigate the acute weld strengths for anastomoses of rat and rabbit aortas and femoral arteries. The wall thicknesses for these vessels approximately matched the optical absorption depth of 125 microns for 1.9 microns radiation in vascular tissues. A low power (150 mW) 1.9 microns laser was used. Laser power was delivered through silica fiber optics for manual control. The fiber tip was held approximately 1 mm from the target resulting in a laser spot size of 0.7 mm at the tissue. The linear delivery rate was approximately 0.3 mm/sec. Acute burst pressures of the welds showed a linear correlation with the reciprocal of the vessel radius. These results suggest that the product of the weld strength times the optical absorption depth is constant over the range of vessel sizes studied. A weld strength for a weld thickness equal to the optical absorption depth was determined to be 4 x 10(6) dynes/cm2, which is comparable to the strength of sutured anastomoses. These acute studies suggest that a laser wavelength with absorption depth in tissue matched to the vessel wall thickness should yield optimum welds. Therefore, a laser operating near 1.9 microns is suitable for small vessel welding.

Femoropopliteal reconstruction with knitted, nonvelour Dacron versus expanded polytetrafluoroethylene

No ideal prosthetic conduit exists for femoropopliteal reconstruction. Expanded polytetrafluoroethylene (PTFE) has gained much greater popularity than the less expensive Dacron, despite disappointing long-term patency for each material. Few direct comparisons of results with the two materials have been performed. The concurrent experience of a single surgeon with femoropopliteal reconstructions of PTFE (n = 85) or knitted, nonvelour Dacron (KNVD, n = 38) was reviewed. Risk factors were comparable in the two groups. Overall patency was significantly better for KNVD than for PTFE (p = 0.0096 by log rank; p = 0.039 by Cox proportional hazards; 48% vs 27% at 5 years). Since in this series the overall performance of KNVD was significantly better than PTFE, a reassessment of the prosthetic materials used in femoropopliteal reconstruction is necessary. These results justify a prospective comparison of PTFE and KNVD.

Arterial laser welding with a 1.9 micrometer Raman-shifted laser

A new 1.9 micron Raman-shifted neodymium:yttrium aluminum garnet (Nd:YAG) laser was used for small vessel welding. Bursting pressures and stresses of sutured and laser-welded arteriotomies created in the rat femoral artery and aorta were measured. Sutured arteriotomies had a significantly higher burst stress than laser-welded arteriotomies. Although there were no significant differences in burst stress at the various laser powers tested, an optimal power was identified. The laser was also used to weld transected rat aortas. The average power delivered was 200 mW for 30 seconds per anastomosis. The average time for completing an anastomosis was 6 minutes compared with 18 minutes when sutures were used. In relation to proximal aortic diameter, there was a 7.9% decrease at the anastomosis immediately (n = 4), and a 6.6% and 4.9% increase occurred at 24 hours (n = 4) and 10 weeks (n = 5), respectively. Acute anastomotic compliance, and compliance at 24 hours and 10 weeks were decreased by 47.2%, 39.5%, and 47.8%, respectively, and were similar to sutured anastomoses. Histology showed little thermal denaturation of the aorta within 0.6 mm of the anastomosis, approximately 1 mm of medial cell death, and nearly normal elastic fiber alignment. One focal false aneurysm was noted at 10 weeks. Although the sutured and laser-welded anastomoses share similar compliance changes, the laser-welded anastomoses are more isodiametric. This preliminary experience with the 1.9 micron laser shows the distinct advantages of a handheld fiber, no requirement for cooling irrigation, speed, and no difference in compliance from sutured anastomoses.

The impact of selective use of dipyridamole-thallium scans and surgical factors on the current morbidity of aortic surgery

Preoperative cardiac testing in patients undergoing vascular surgery remains controversial. We have advocated selective use of dipyridamole-thallium scans based on clinical markers of coronary artery disease before aortic surgery. The present study assessed both the efficacy of this policy and the role of surgical factors in the current morbidity of aortic reconstruction. Two hundred two elective aortic reconstructions (151 abdominal aortic aneurysms, 51 aortoiliac occlusive disease) performed in the period from January 1989 to June 1990 were reviewed. Preoperative dipyridamole-thallium scanning was performed in 29% of all patients, prompting coronary angiograms in 11% and coronary artery bypass grafting/percutaneous transluminal coronary angioplasty in 9% of patients before aortic reconstruction. The overall operative mortality rate was 2%, with one cardiac-related death. Major cardiac (nonfatal myocardial infarction, unstable angina) and pulmonary complications occurred in an additional 4% and 6%, respectively, of patients. Coronary artery disease clinical markers and surgical factors were analyzed with stepwise logistic regression for the prediction of operative mortality rates and major cardiopulmonary complications. Variables retaining significance in predicting postoperative death or cardiopulmonary complications included prolonged (more than 5-hour) operative time (p less than 0.004), operation for aortoiliac occlusive disease (p less than 0.010), and a history of ventricular ectopy (p less than 0.002). Prolonged operative time (p less than 0.006) and the detection of intraoperative myocardial ischemia (p less than 0.030) were predictive of major cardiac complications after univariate analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Longterm study of a compliant biological vascular graft

Clinically implanted prostheses of biological origin have recently been shown to develop aneurysms within several years. To study this process, recently developed bovine heterografts that were implanted in canine ilio-femoral arteries for 27 to 45 months, were studied in vivo and in vitro. Seven out of seven grafts were patent with only one showing evidence of focal aneurysm. Measurements of mechanical properties, including water permeability, compliance, and burst pressure, and of heat shrink temperature and dry weight were obtained before and after a period of controlled exposure to bacterial collagenase; all data suggested that much of the original graft had been replaced with host tissue. However, enzyme susceptibility was less than that of fresh bovine arteries, indicating that at least some of the grafts' crosslinked collagen was preserved. The compliance of these explants was similar to that reported for autogenous vein. Histological examination of the graft wall revealed cellular "intimal" and adventitial zones containing host-generated collagen surrounding a central zone devoid of cellular infiltration, which appears to be unmodified graft "media" highly resistant to degradation. We conclude that, when properly processed, biological prostheses can act as a bioresorbable scaffold for the orderly replacement of structural elements during healing, promoting continued mechanical integrity of the graft. These promising results encourage the further development of prostheses of biological origin.

A laboratory model to quantitate the resistance of collagen vascular grafts to biodegradation

Recent reports have shown that despite extensive preclinical testing, vascular grafts of biological origin undergo severe biodegradation and aneurysm formation after two or more years of implantation in man. The purpose of this study was to develop a laboratory model to quantitate and correlate the stability of crosslinked collagen grafts in vitro and in vivo. This resistance to biodegradation was assessed by measuring changes in suture pullout force and sample weight in response to controlled digestion with bacterial collagenase, in 0.5-cm-long cylindrical graft segments (chemically processed bovine carotid artery and human umbilical cord vein) that were implanted in the rat subcutis for 2 to 12 weeks. Scar tissue was removed from the explants by brief enzymatic digestion, a process that was inhibited when graft segments had become infected. Changes in dry weight were more consistent than were changes in wet weight; drying the graft segments had no effect on their degradation in vivo or in vitro. Intact cylindrical rings suffered somewhat less damage than did opened, flattened cylinders. Graft degradation increased markedly with implantation time, and was detected after only 3 weeks. We conclude that the rat subcutis model, when combined with controlled enzymatic digestion, first to remove scar tissue and then to challenge structural integrity, provides an accelerated assay by which to predict the stability of collagen vascular grafts.

Glutaraldehyde release from vascular prostheses of biologic origin

The inhibition of growth by adult human venous endothelial cells in culture forms the basis of a sensitive assay of glutaraldehyde (GA) concentration, valid between 0 and 5 parts per million. This cytotoxicity assay was used to measure residual (unbound) GA in commercial vascular prostheses of biologic origin following manufacturer-recommended rinsing procedures, from which as much as 13.8 ppm GA per gram of tissue per 24 hours continued to be released after 1 month. A brief (1 hour) exposure of cultured endothelial cells to 2 ppm GA delayed growth, while continuous exposure to 4 ppm totally prevented growth for at least 12 days. Endothelial cells exposed to GA demonstrated a reduced efficiency of attachment to standard test surfaces, although prior GA treatment of these surfaces was not detrimental to subsequent cell attachment. GA release from vascular prostheses may contribute to their lack of endothelial cell coverage in human implants and may be indicative of collagen cross-link instability. If so, in vitro cytotoxicity may be helpful in identifying the potential for aneurysm formation in preserved biologic grafts.

Prediction of aneurysm formation in vascular grafts of biologic origin

Other than review of clinical experience, no assay exists that can reliably predict the long-term potential for aneurysm formation in an arterial prosthesis of biologic origin. Since mural degeneration probably results from proteolytic digestion, an in vitro assay was devised that used graft perfusion with 1% collagenase to induce rapid changes in mechanical properties. The effect of enzyme on graft diameter, compliance, permeability, and burst pressure was measured in ficin-digested, adipoyl chloride and glutaraldehyde-tanned bovine carotid artery and glutaraldehyde-tanned human umbilical vein. Both grafts have recently been reported to have a significant incidence of aneurysm within several years of implantation. Compliance and diameter were also measured noninvasively in patients with bovine carotid artery and human umbilical vein for more than 40 weeks after implantation. In vitro, the response to enzyme could be categorized into three groups. In group III, a diameter increase of more than 14% was associated with a significantly decreased compliance, and this paralleled the results found in aneurysmal grafts in vivo. In both grafts there was a strong correlation between postenzyme compliance change and initial compliance, loss of compliance being significantly greater in grafts with group III responses (p less than 0.01). This response may be a good predictor of a graft's overall susceptibility to aneurysmal degeneration, and initial compliance measurement may effectively identify inadequate fixation. Thus measurement of compliance may prove useful in quality control of a fixation process used in mass production. In conclusion, measurement of mechanical properties of biologic vascular grafts before and after collagenase exposure forms the basis for an effective in vitro assay of aneurysm susceptibility.

Compliance changes in glutaraldehyde-treated arteries

Glutaraldehyde tanning of carotid arteries was used to develop a model for studying the effects of compliance on arterial graft performance, independent of other graft parameters. Canine carotid segments were filled with dilute phosphate-buffered glutaraldehyde (0-0.5%, pH 7.4), maintained at physiological pressure, and then immersed in either saline or 10.0% glutaraldehyde for up to 1 hr. After rinsing with saline, compliance was measured in vitro. All vessels which were immersed in 10% glutaraldehyde exhibited a significant reduction in compliance compared to native artery control [C = 11.8 +/- 1.3 (mean +/- SEM), % radial change/mm Hg X 10(-2), measured at 100 mm Hg], but maximum stiffness (C = 1.1 +/- 0.3) required that the lumen be specifically exposed to at least 0.025% glutaraldehyde in addition to simple immersion of the vessel segment in 10% fixative. Exposing the artery to 0.5% glutaraldehyde internally, without immersion of the entire structure, caused a decrease in compliance similar to that obtained after immersion in 10% glutaraldehyde, with only saline present in the lumen. Matched pairs of stiff and compliant grafts were generated by exposing the lumen to 0.025% glutaraldehyde and immersing the vessels in 10% fixative or saline, respectively. Light and scanning electron microscopy, internal reflection spectroscopy, and measurements of critical surface tension revealed nearly identical wall morphology and lumenal surface chemistry for these matched pairs. Differential tanning of the internal and external surfaces of carotid arteries thus provides a good model of arterial prostheses, wherein a substantial compliance mismatch can be studied without the complicating influences of varying diameter or differing flow surface properties.

Noninvasive measurements of nonlinear arterial elasticity

To describe fully the compliance characteristics of an artery with nonlinear elastic properties, measurements must be obtained over a wide range of pressures. Furthermore, repeated measurements, as required in temporal studies of arterial implants, require that the measuring technique be noninvasive. The application of a pulsed ultrasound echo-tracking device is described, which fulfills both criteria. Nonlinear compliance-pressure (CP) curves were obtained from the femoral arteries of dogs, with the use of halothane anesthesia to vary systemic pressure, and were used to compare the gross elastic properties of different vessels. Studies using controlled hemorrhage or the vasoactive drugs, nitroprusside and levarterenol (norepinephrine), were used to verify that the CP curves obtained during halothane anesthesia did not reflect varying degrees of smooth muscle activation. However, surgical exposure did temporarily reduce arterial compliance at pressures between 60 and 140 mmHg. The effect of vasoactive intervention and of postsurgical changes in arterial or graft compliance can thus be quantitated by use of CP curves or by comparing incremental elastic moduli, which can also be estimated from the noninvasively derived measurements.

Matched elastic properties and successful arterial grafting

Clinical results from medium- and small-caliber arterial bypass grafts are unsatisfactory. Since elastic properties of grafts tested experimentally have been correlated with patency results, the compliance of the human femoral artery was compared with grafts currently in use: human saphenous vein (HSV), knitted Dacron (DAC), glutaraldehyde-treated umbilical cord vein (DBM), bovine heterograft, and expanded polytetrafluoroethylene (PTFE). This was correlated with clinical patency data for the different conduits in the femoropopliteal position. Increased patency correlated with a decreasing disparity between host artery and graft compliance. After two years, patency rates of the more compliant materials (HSV, DBM) exceeded 80%, while less than 45% of the incompliant grafts (DAC, PTFE) remained patent. Thus, clinical performance with synthetic grafts might be improved by use of prostheses in which the viscoelastic characteristics match those of arteries more closely.

Dynamic compliance of arterial grafts

A cantilever transducer has been developed which allows measurements of diastolic diameter and diameter change in response to pulse pressure in dissected blood vessels during sterile procedures. Preliminary results indicate that it will detect subtle changes in wall elastic properties of arterial grafts at subtle changes in wall elastic properties of arterial grafts at and following implantation, which changes may influence graft function. Compliance, the percentage change in volume per unit pressure, was greater in normal canine femoral artery than in autogenous vein grafts (AVG). Two new graft materials were tested. Mesh-covered modified human umbilical cord vein (DBM) was similar in compliance to AVG but more compliant than double-velour Dacron. Diastolic diameter changes were also recorded. After 2 wk, all three graft materials had increased in diameter: AVG by 8%, DBM by 6%, and Dacron by 5%. After 3 mo, AVG diameter increased by 24%.