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.

The cardiovascular event reduction tool (CERT)--a simplified cardiac risk prediction model developed from the West of Scotland Coronary Prevention Study (WOSCOPS).

The clinical decision to treat hypercholesterolemia is premised on an awareness of patient risk, and cardiac risk prediction models offer a practical means of determining such risk. However, these models are based on observational cohorts where estimates of the treatment benefit are largely inferred. The West of Scotland Coronary Prevention Study (WOSCOPS) provides an opportunity to develop a risk-benefit prediction model from the actual observed primary event reduction seen in the trial. Five-year Cox model risk estimates were derived from all WOSCOPS subjects (n = 6,595 men, aged 45 to 64 years old at baseline) using factors previously shown to be predictive of definite fatal coronary heart disease or nonfatal myocardial infarction. Model risk factors included age, diastolic blood pressure, total cholesterol/ high-density lipoprotein ratio (TC/HDL), current smoking, diabetes, family history of fatal coronary heart disease, nitrate use or angina, and treatment (placebo/ 40-mg pravastatin). All risk factors were expressed as categorical variables to facilitate risk assessment. Risk estimates were incorporated into a simple, hand-held slide rule or risk tool. Risk estimates were identified for 5-year age bands (45 to 65 years), 4 categories of TC/HDL ratio (<5.5, 5.5 to <6.5, 6.5 to <7.5, > or = 7.5), 2 levels of diastolic blood pressure (<90, > or = 90 mm Hg), from 0 to 3 additional risk factors (current smoking, diabetes, family history of premature fatal coronary heart disease, nitrate use or angina), and pravastatin treatment. Five-year risk estimates ranged from 2% in very low-risk subjects to 61% in the very high-risk subjects. Risk reduction due to pravastatin treatment averaged 31%. Thus, the Cardiovascular Event Reduction Tool (CERT) is a risk prediction model derived from the WOSCOPS trial. Its use will help physicians identify patients who will benefit from cholesterol reduction.

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.

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.

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.

The effect of halothane anesthesia on platelet aggregation in vivo: decreased deposition on polytetrafluoroethylene arterial grafts in dogs.

The technique of gamma-imaging can be used to study the deposition of 111In-labeled platelets onto synthetic arterial grafts in vivo. Recent results suggested that platelet uptake on polytetrafluoroethylene (PTFE) grafts might depend on the choice of anesthetic. To evaluate the effect of anesthesia a series of experiments was performed in seven dogs wherein each animal served as its own control. The first of paired femoral or carotid PTFE grafts was inserted with the animal under pentobarbital anesthesia, and the graft was imaged for 90 minutes. A second graft was then inserted after at least 1 hour of halothane anesthesia. The mean activity ratio (describing platelet deposition) in the grafts inserted when only pentobarbital anesthesia was used was 7.04 +/- 0.55, compared to 1.20 +/- 0.07 in the grafts inserted with halothane anesthesia (P less than 0.01). Halothane anesthesia led to significantly decreased platelet uptake on canine PTFE arterial grafts. This effect was reversible, though not immediately, with no significant difference in graft activity noted by the day following surgery.

Complementary methods for evaluating carotid stenosis: a biophysical basis for ocular pulse wave delays.

Attempts to noninvasively estimate the significance of carotid arterial stenoses have resulted in a recent technological explosion. Ocular pulse wave timing [oculoplethysmography (OPG) pulse delay] has been strongly promulgated but also criticized on theoretical grounds and for lack of physiologic validation. Audiofrequency analysis of carotid bruits (carotid phonoangiography CPA) has been combined with OPG allegedly to improve accuracy. To evaluate these methods in a controlled model, we studied the effects of graded unilateral stenoses in the canine carotid artery on physiological parameters and associated OPG and CPA recordings. Arterial compliance was calculated from simultaneous diameter and pressure recordings distal to the stenosis. OPG time delay correlated directly with reductions in flow and pressure and with increasing arterial compliance (P less than 0.01). Thus, the delay is caused at least partially by a decreased pulse wave velocity, resulting from the increased compliance distal to stenoses associated with a significant pressure gradient. OPG is most discriminating for stenoses of higher grades. Because bruits arise from flow disturbances that occur even with moderate degrees of stenosis, CPA provides diagnostic information before profound flow reduction occurs. This study illustrates the value of complementary methods for analyzing complex hemodynamic phenomena and provides evidence to support use of the pulse delay concept to diagnose arterial disease.

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.

Noninvasive intraoperative assessment of arterial reconstruction. Experimental validation of the role of central and regional hemodynamics.

We developed an experimental model of graded arterial stenosis to emulate conditions that might be encountered immediately following arterial grafting. Noninvasive measurements of systolic BP and limb blood flow were recorded with a Doppler probe and segmental air plethysmography, respectively, under conditions of different cardiac output and local arterial resistance. These measurements were correlated with direct intra-arterial pressure recordings and flow measurements taken with an electromagnetic flowmeter. There was an excellent correlation between noninvasive and intra-arterial measurements of systolic pressure over a range of cardiac outputs and degree of arterial stenosis. Pulse volume recordings correlated with direct measurements of blood flow at high and baseline cardiac outputs, but the calibration of pulse volume amplitude varied between cuff applications in this canine model. Noninvasive intraoperative monitoring techniques can faithfully represent known physiologic responses to graded arterial stenoses, irrespective of a high cardiac output or peripheral vasodilation.

Anatomic localization of atherosclerotic lesions by hemodynamic tests.

Use of noninvasive tests to assess the severity of lower-extremity occlusive lesions is generally accepted. To evaluate the effectiveness of noninvasive vascular-laboratory tests in locating atherosclerotic lesions, the results of hemodynamic studies in 100 patients were reviewed by both skilled observers and a vascular computer, and compared with angiograms. The results of the comparison suggest a remarkable sensitivity of the vascular-laboratory tests in locating significant arterial obstructions, and underscore that the great predictive value of a negative results gives the physician reliable information on the patency of a given arterial segment. Computer interpretation proved less accurate than that of the vascular-laboratory personnel.

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.

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.

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.

Metabolic profile and cardiovascular risk factors among Latin American HIV-infected patients receiving HAART.

OBJECTIVE: Determine the prevalence of metabolic abnormalities (MA) and estimate the 10-year risk for cardiovascular disease (CVD) among Latin American HIV-infected patients receiving highly active anti-retroviral therapy (HAART). METHODS: A cohort study to evaluate MA and treatment practices to reduce CVD has been conducted in seven Latin American countries. Adult HIV-infected patients with at least one month of HAART were enrolled. Baseline data are presented in this analysis. RESULTS: A total of 4,010 patients were enrolled. Mean age (SD) was 41.9 (10) years; median duration of HAART was 35 (IQR: 10-51) months, 44% received protease inhibitors. The prevalence of dyslipidemia and metabolic syndrome was 80.2% and 20.2%, respectively. The overall 10-year risk of CVD, as measured by the Framingham risk score (FRF), was 10.4 (24.7). Longer exposure to HAART was documented in patients with dyslipidemia, metabolic syndrome and type 2 diabetes mellitus. The FRF score increased with duration of HAART. Male patients had more dyslipidemia, high blood pressure, smoking habit and higher 10-year CVD than females. CONCLUSIONS: Traditional risk factors for CVD are prevalent in this setting leading to intermediate 10-year risk of CVD. Modification of these risk factors through education and intervention programs are needed to reduce CVD.

Determinants of discontinuation of initial highly active antiretroviral therapy regimens in a US HIV-infected patient cohort.

OBJECTIVES: Optimization of initial highly active antiretroviral therapy (HAART) for complete viral suppression and better tolerability is paramount for the prognosis of HIV-infected patients. Observational studies provide a better means than clinical trials of studying the determinants of discontinuation in actual practice. METHODS: A longitudinal cohort of US HIV-positive patients who initiated HAART for the first time from 1996 to 2003 were included in the analysis. Stratified Cox proportional hazards models, considering time-updated viral load and CD4 count data, were developed for analyzing time to first discontinuation. RESULTS: A total of 3414 antiretroviral-naive HAART patients were identified. In a median follow-up period of 211 days (mean 324 days), 628 patients (18.4%) reportedly discontinued the HAART regimen because of drug toxicity, 456 (13.4%) because of non-compliance, and 257 (7.5%) because of treatment failure. In addition to the recorded reasons for discontinuation, black ethnicity [relative risk (RR) 1.28, 95% confidence interval (CI) 1.13-1.45], current smoking (RR 1.33, CI 1.18-1.50), high pill burden (RR 1.44, CI 1.22-1.70), and recent viral control (RR 0.63, CI 0.56-0.70) were all predictive of discontinuation. Only high pill burden (>15 pills/day), which is considered to be a surrogate for treatment regimen complexity, and the most recent poor viral control (HIV RNA) were found to be consistently associated with a higher likelihood of discontinuation. CONCLUSIONS: Risk factors other than physician- or patient-reported reasons play a role in discontinuation of initial HAART regimens. Identification of these risk factors and simplification of treatment regimens in those at high risk for discontinuation appear to be necessary in order to maximize the effectiveness of HAART regimens.

Protease inhibitor exposure and increased risk of cardiovascular disease in HIV-infected patients.

OBJECTIVES: To study the relationship between exposure to protease inhibitor (PI) therapy and increased risk of cardiovascular events in HIV-infected patients. METHODS: We estimated the risk of cardiovascular disease (CVD) events with PI exposure in a cohort of HIV-infected patients using a time-dependent Cox proportional hazards model adjusting for the major CVD risk factors. Only the first CVD event for each subject was counted. RESULTS: Of a total of 7542 patients, 77% were exposed to PIs. CVD event rates were 9.8/1000 and 6.5/1000 person-years of follow-up (PYFU) in the PI-exposed and nonexposed groups, respectively (P=0.0008). PI exposure >/=60 days was associated with an increased risk of CVD event [adjusted hazards ratio (HR(adj)) 1.71; 95% confidence interval (CI) 1.08-2.74; P=0.03]. Results from a subgroup of patients aged between 35 and 65 years were similar (HR(adj) 1.90; 95% CI 1.13-3.20; P=0.02). Other significant risk factors included smoking status, age, hypertension, diabetes mellitus and pre-existing CVD. CONCLUSIONS: Patients exposed to PI therapy had an increased risk of CVD events. Clinicians should evaluate the risk of CVD when making treatment decisions for HIV-infected patients.

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.

Effect of compliance mismatch on vascular graft patency.

The hypothesis that a mismatch in compliance between a vascular graft and its host artery is detrimental to graft patency was tested by implanting paired arterial autografts, prepared with differential glutaraldehyde fixation of carotid arteries in the femoral arteries of dogs. These grafts differed only in circumferential compliance: they were 100% (compliant) vs. 40% (stiff) as compliant as the host artery. Their flow surfaces were equivalent, as determined by physicochemical measurements and scanning electron microscopy; both lacked viable cells, as determined by in vitro cell culture. In 14 dogs, eight stiff and two compliant grafts became occluded within 3 months, the latter doing so within 24 hours after their contralateral counterparts. Cumulative patencies were 85% and 37% for compliant and stiff grafts, respectively (p less than 0.05) and 100% and 43%, excluding the two dogs with bilateral graft failures (p less than 0.01). We conclude that even with near optimal flow surfaces, compliance mismatch is deleterious to graft patency.

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.