Coronary artery bypass in patients with severely depressed ventricular function

This study evaluates whether patients with coronary artery disease and severely depressed left ventricular ejection fraction benefit from coronary artery bypass grafting. From 1981 to 1991, 118 consecutive patients with ejection fraction less than or equal to 0.25 underwent isolated coronary artery bypass grafting at Duke University Medical Center. Operative mortality was 11%. Ventricular arrhythmia requiring treatment was the most common postoperative complication (27%), followed by low cardiac output state (22%). Median length of postoperative hospitalization was 9 days. Kaplan-Meier estimate of survival at 1 year and 5 years was 77.2% and 57.5%, and was better than estimated survival with medical therapy alone. Survivors experienced significant improvement in angina class (p < 0.0001), congestive failure class (p < 0.0001), and follow-up ejection fraction (p < 0.005). Of 22 preoperative factors evaluated by univariate survival analysis, five were associated with significantly greater mortality: other vascular disease (p < 0.005), female sex (p < 0.005), hypertension (p < 0.005), elevated left ventricular end-diastolic pressure (p < 0.05), and depressed cardiac index (p < 0.05). Considering length of hospitalization, three factors showed significant adverse effect in a multivariate Cox model: time on cardiopulmonary bypass (p < 0.005), acute presentation (p < 0.005), and female sex (p < 0.01). These data and review of the literature suggest that patients with coronary artery disease and severely depressed ejection fraction benefit from coronary artery bypass grafting, and specific preoperative factors may help determine optimal treatment.

T cell receptor V beta repertoire in HIV-infection individuals: lack of evidence for selective V beta deletion

The gradual decline of CD4+ T lymphocytes in HIV-infected individuals culminates in the lethal immunosuppression of AIDS. The mechanism of CD4+ T cell loss is currently unknown, but has recently been suggested to occur as a result of an HIV-encoded superantigen which facilitates a selective deletion of T cells expressing specific V beta genes. To verify and extend such observations, peripheral blood leucocytes (PBL) from 15 HIV+ individuals, 10 of which had very low CD4 T cell counts (< 200/mm3), were analysed for T cell receptor (TCR) V beta gene expression. In contrast to a recent study, the results presented here fail to provide evidence that selective loss of V beta-bearing T cells occurs in HIV+ individuals. Furthermore, when PBL from HIV+ individuals were stimulated with Staphylococcal enterotoxin B (SEB), T cells expressing V beta subfamilies known to engage this superantigen were expanded, indicating that such cells were not deleted and were responsive to stimulation by a bacterial superantigen. Collectively, these data suggest that CD4 loss in HIV patients does not occur in a V beta-selective, superantigen-mediated fashion.

Hemodilution induces stable changes in global cardiovascular and regional myocardial function

The cardiovascular responses associated with isovolemic hemodilution have been described. However, the stability of these responses over time remains controversial. We hypothesized that the hemodynamic responses to isovolemic hemodilution are stable over time. Nine fentanyl-midazolam-anesthetized dogs were monitored to follow global cardiovascular and regional myocardial function. Isovolemic hemodilution was performed to a moderate (hemoglobin = 7.5 g%) target hemodilutional state that was maintained for 4 h. Data were obtained at each hemodilutional state and each hour during the 4-h period of sustained moderate hemodilution. During acute hemodilution, cardiac output increased from 2.6 +/- 0.5 L/min to 3.0 +/- 0.5 L/min (P < 0.05) and mean coronary flow increased from 20.8 +/- 2.4 mL/min to 31.4 +/- 5.5 mL/min (P < 0.05). Cardiac output and mean coronary flow remained elevated during the extended hemodilutional period. In addition, norepinephrine increased from 586 +/- 152 pg/mL to 1135 +/- 247 pg/mL (P < 0.05) during acute isovolemic hemodilution and remained at this increased level during extended hemodilution. Epinephrine levels did not change with hemodilution. Compensatory mechanisms such as increases in cardiac output and mean coronary flow observed during acute hemodilution persist during extended periods of hemodilution.

Plasma concentration of fentanyl, with 70% nitrous oxide, to prevent movement at skin incision

BACKGROUND

The Cp50 (minimal steady state plasma concentration of an intravenous analgesic/anesthetic required to prevent a somatic response in 50% of patients following skin incision) and the Cp50-BAR (minimal plasma concentration of an analgesic/anesthetic required to prevent either a somatic, hemodynamic, or autonomic response in 50% of patients following skin incision) have been recently proposed as a measure, like minimum alveolar concentration (MAC; and MAC-BAR), to establish the relative potency of intravenous analgesics. This study was conducted to establish the Cp50 for fentanyl.

METHODS

Unpremedicated patients were administered fentanyl (in the presence of 70% N2O) via computer-assisted continuous infusion, a pharmacokinetic model-driven infusion device. After induction of anesthesia with fentanyl, the randomized target fentanyl concentration was entered into computer-assisted continuous infusion. This target fentanyl concentration was maintained until skin incision. Before induction, prior to skin incision, and immediately after skin incision, arterial blood samples were obtained for measurement of fentanyl and norepinephrine concentrations. At skin incision, patients were observed for a somatic, hemodynamic, or autonomic response. Only patients in whom the pre- and postincision fentanyl concentrations were within +/- 30% were included in the calculation of the Cp50. The Cp50 was calculated using logistic regression.

RESULTS

The Cp50 for fentanyl was 3.26 ng/ml, and the Cp50-BAR was 4.17 ng/ml.

CONCLUSIONS

Comparing these results with the previously published Cp50 of alfentanil, the potency of fentanyl relative to alfentanil is 1:58. Establishing the Cp50, once effect site equilibration has occurred, will allow pharmacodynamic comparisons between the opioids at equipotent concentrations.

Isoflurane minimum alveolar concentration reduction by fentanyl

BACKGROUND

Isoflurane is commonly combined with fentanyl during anesthesia. Because of hysteresis between plasma and effect site, bolus administration of fentanyl does not accurately describe the interaction between these drugs. The purpose of this study was to determine the MAC reduction of isoflurane by fentanyl when both drugs had reached steady biophase concentrations.

METHODS

Seventy-seven patients were randomly allocated to receive either no fentanyl or fentanyl at several predetermined plasma concentrations. Fentanyl was administered using a computer-assisted continuous infusion device. Patients were also randomly allocated to receive a predetermined steady state end-tidal concentration of isoflurane. Blood samples for fentanyl concentration were taken at 10 min after initiation of the infusion and before and immediately after skin incision. A minimum of 20 min was allowed between the start of the fentanyl infusion and skin incision. The reduction in the MAC of isoflurane by the measured fentanyl concentration was calculated using a maximum likelihood solution to a logistic regression model.

RESULTS

There was an initial steep reduction in the MAC of isoflurane by fentanyl, with 3 ng/ml resulting in a 63% MAC reduction. A ceiling effect was observed with 10 ng/ml providing only a further 19% reduction in MAC. A 50% decrease in MAC was produced by a fentanyl concentration of 1.67 ng/ml.

CONCLUSIONS

Defining the MAC reduction of isoflurane by all the opioids allows their more rational administration with inhalational anesthetics and provides a comparison of their relative anesthetic potencies.

Acute isovolemic hemodilution and blood transfusion. Effects on regional function and metabolism in myocardium with compromised coronary blood flow

The use of isovolemic hemodilution to prevent adverse side effects of homologous blood transfusions has increased. The lowest level of hemoglobin that can be tolerated without regional myocardial dysfunction, however, had not been precisely defined for left ventricular myocardium with compromised coronary blood flow. This level was determined in our study in 19 dogs with critical stenosis of the left anterior descending coronary artery during graded isovolemic hemodilution. Regional function was assessed by sonomicrometry in the territory supplied by the left anterior descending coronary artery, as well as in two noncompromised left ventricular areas; oxygen extraction and consumption in the left anterior descending coronary artery region were assessed by analysis of anterior descending coronary venous oxygen saturation. The median lowest level of hemoglobin tolerated without contractile dysfunction of the territory supplied by the left anterior descending artery was 7.5 gm/dl, with lower and upper quartiles of 6 and 9 gm/dl. In addition to a marked increase in cardiac output and transstenotic left anterior descending flow, global cardiac and regional myocardial functions were unchanged at a hemoglobin level of 7.5 gm/dl, as compared with a control level of hemoglobin of 12.0 +/- 0.4 gm/dl. At a mean level of hemoglobin of 6.0 +/- 0.4 gm/dl, marked contractile dysfunction developed in the left anterior descending region: Systolic shortening decreased from 24.2% +/- 2.1% to 17.9% +/- 1.9% (p < 0.01); postsystolic shortening increased from 4.0% +/- 3.0% to 12.2% +/- 3.8% (p < 0.01); and in the left anterior descending region, oxygen consumption decreased. The increase of arterial level of hemoglobin by only 1.9 +/- 0.2 gm/dl restored contractile function in the left anterior descending region, regional oxygen consumption, and oxygen extraction across the left anterior descending region. Moderate isovolemic hemodilution is relatively well tolerated in left ventricular myocardium with compromised coronary blood flow, and hemodilution regional contractile dysfunction induced by hemodilution is reversible by minimal blood transfusion.

Comparison of analytic models for estimating the effect of clinical factors on the cost of coronary artery bypass graft surgery

The cost of treating disease depends on patient characteristics, but standard tools for analyzing the clinical predictors of cost have deficiencies. To explore whether survival analysis techniques might overcome some of these deficiencies in the analysis of cost data, we compared ordinary least square (OLS) linear regression (with and without transformation of the data) and binary logistic regression with two survival models: the Cox proportional hazards model and a parametric model assuming a Weibull distribution. Each model was applied to data from 155 patients undergoing coronary artery bypass grafting. We examined the effects of age, sex, ejection fraction, unstable angina, and number of diseased vessels on univariable and multivariable predictions of costs. The significant univariable predictors of cost were consistent in all models: ejection fraction was significant in all five models, and age and number of diseased vessels were each significant in all but the OLS model, while sex and angina type were significant in none of the models. The significant multivariable predictors of cost, however, differed according to model: ejection fraction was a significant multivariable predictor of cost in all five models, age was significant in three models, and number of diseased vessels was significant in one model. All five models were also used to predict the costs for an average patient undergoing surgery. The Cox model provided the most accurate predictions of mean cost, median cost, and the proportion of patients with high cost. This study shows: (1) lower ejection fraction and older age are independent clinical predictors of increased cost of CABG, and (2) the Cox proportional hazards model shows considerable promise for the analysis of the impact of clinical factors upon cost.

Is esmolol cardioprotective? Tolerance of pacing tachycardia, acute afterloading and hemodilution in dogs with coronary stenosis

OBJECTIVES

The aim of this study was to determine whether esmolol, an ultrashort-acting beta-adrenergic antagonist, possesses cardioprotective properties unrelated to a concomitant decrease in heart rate.

BACKGROUND

Previous studies have demonstrated beneficial effects of beta-adrenergic blocking agents with unchanged heart rates.

METHODS

The effect of esmolol (100 micrograms/kg per min) on the response of global cardiovascular and regional myocardial contractile function (sonomicrometry) to pacing-induced tachycardia and acute left ventricular afterloading was assessed in dogs with a critical stenosis of the left anterior descending coronary artery (LAD). These responses were observed at the baseline hemoglobin level (12.5 +/- 0.3 g/100 ml) as well as after hemodilution-induced mild regional contractile dysfunction (7.4 +/- 0.4 g/100 ml) in the area supplied by this artery (LAD area). Data were analyzed by using a repeated measures multivariate analysis of variance with complete block design treating pacing rate and afterloading, respectively, as the repeated measure.

RESULTS

Esmolol decreased the maximal first derivative of left ventricular pressure (dP/dtmax); global cardiovascular and regional myocardial contractile function were otherwise unchanged. Esmolol did not alter the response of global cardiovascular or regional myocardial function to pacing-induced tachycardia or to acute left ventricular afterloading, both at the baseline hemoglobin level as well as during mild hemodilution-induced LAD area contractile dysfunction.

CONCLUSIONS

At an infusion rate of 100 micrograms/kg per min we were unable to demonstrate cardioprotective esmolol effects in a canine model of critical coronary stenosis with controlled heart rate and identical loading conditions.

A classification of nursing and midwifery shift systems

A classification of 122 shift systems worked by nurses and midwives in the larger general hospitals (400+ beds) in England and Wales was made. The systems were classified along two main dimensions: the degree of flexibility for shift rostering (either regular, irregular or flexible); and the speed of rotation between night and day work (either a permanent night shift or systems of fast or slow internal rotation). This resulted in nine possible categories of shift systems. The most common shift system was a flexible day shift with a permanent night shift. Other features of the systems are discussed, e.g. the start times and durations of shifts, and the relative influence of flexible rostering on these features. This classification is a prerequisite for a further research project aimed at identifying those features of shift systems which are likely to cause the least detrimental effects for the individual nurses concerned.

Observational comparison of event-free survival with medical and surgical therapy in patients with coronary artery disease. 20 years of follow-up

BACKGROUND

The purpose of this study was to describe the long-term event-free survival patterns of patients with significant coronary artery disease treated medically versus patterns of those treated surgically and to evaluate the factors associated with improved event-free survival.

METHODS AND RESULTS

We studied the results of 5,824 patients undergoing medical and surgical therapy for ischemic heart disease from 1969 to 1984, with follow-up to 1991. Events considered for this evaluation were nonfatal myocardial infarction or cardiovascular death. The Cox proportional hazards model was used to determine factors differentially affecting surgical event-free survival. The survival benefits previously reported for bypass surgery in this population were largely preserved when event-free survival was examined. The two factors associated with significant event-free survival benefits for surgically treated patients were more severe coronary artery disease and a more recent surgery data. Patients with more severe coronary obstruction had a greater relative improvement with surgery in event-free survival than did patients with less severe anatomic disease. Event-free survival with surgery progressively improved over the period of the study and, by 1984, was significantly better than medical therapy for most patient subgroups. Patients with poor prognosis because of risk factors such as older age, severe angina, or left ventricular dysfunction had a risk reduction with surgery proportional to their overall risk under medical therapy.

CONCLUSIONS

Higher-risk patients with more severe disease (due to either coronary disease or other risk factors and age) should be considered for coronary revascularization because it is in these patients that coronary artery bypass graft surgery has the greatest impact in reducing future cardiovascular events.

Effects of acute isovolemic hemodilution and anesthesia on regional function in left ventricular myocardium with compromised coronary blood flow

The effects of progressive, isovolemic hemodilution using Dextran 70 and the effect of halothane (0.7, 0.9, 1.1, and 1.3% end-tidal, administered randomly at each level of hemodilution) on global cardiovascular and regional LV contractile functions were investigated in 24 dogs with induced critical constriction of the left anterior descending coronary artery (LAD). Two additional groups of six dogs each (with and without LAD stenosis) not undergoing hemodilution served as time controls. Regional LV contractile function was assessed by sonomicrometry in the flow-compromised apical LAD territory, as well as in three non-compromised LV areas supplied by the left circumflex coronary artery. Regional myocardial function was found to be stable throughout the study period of 4-5 h in both time control groups. Mean arterial and coronary perfusion pressures as well as LV dP/dtmin decreased (P < 0.01) during hemodilution. LV dP/dtmax remained unchanged, and heart rate and LVEDP increased slightly (P < 0.05). Systolic shortening (SS) in the LAD territory was unchanged at a hematocrit (HCT) of 33.5 +/- 0.3% (mean +/- s.e. mean), and decreased marginally at an HCT of 24.2 +/- 0.1% (SS of 17.4 +/- 1.0% as compared to 20.2 +/- 1.6% at critical constriction (CC), P < 0.05). No increase in post-systolic shortening (PSS) occurred in the compromised area. Severe LAD dysfunction was observed in the LAD territory at an HCT of 14.9 +/- 0.1%, as systolic shortening decreased (11.8 +/- 1.1%, P < 0.01 vs CC) and PSS increased (31.2 +/- 3.4%, P < 0.01 vs CC). The effects of hemodilution on global cardiovascular and regional myocardial functions were unaffected by halothane.(ABSTRACT TRUNCATED AT 250 WORDS)

Performance status and outcome after coronary artery bypass grafting in persons aged 80 to 93 years

Although coronary artery bypass grafting (CABG) effectively eliminates or diminishes symptoms of myocardial ischemia, the overall performance status and functional outcome in elderly patients undergoing CABG is poorly documented. Therefore, 86 consecutive patients aged 80 to 93 years undergoing isolated CABG were reviewed. Preoperative, intraoperative, and postoperative characteristics and pre- and postoperative performance status (Karnofsky score) were examined. Forty patients (47%) were women, and most patients had highly symptomatic coronary artery disease with class III or IV angina in 94% and unstable angina in 90%. Significant co-morbid disease was present in 49% of patients, and cardiac catheterization revealed left main or 3-vessel disease in 74% of patients. The rate of significant in-hospital complications was 29%, with infection in 14%, stroke in 9%, and respiratory failure in 8% being most frequent. Median performance status (Karnofsky score) improved from 20 to 70% (p = 0.0001) with 89% of hospital survivors being discharged home. Factors associated with failure to achieve a successful functional outcome at discharge were presence of 1 or more preoperative co-morbid conditions (p = 0.048), preoperative myocardial infarction within 7 days of operation (p less than 0.01), and postoperative low cardiac output (p less than 0.01). Survival at 30 days, 6 months, and 3 years were 90, 78, and 64%, respectively. These data demonstrate that CABG can be offered to selected elderly patients with acceptable morbidity and mortality, marked improvement in performance status, and an acceptable quality of life.

Outcome of patients sustaining acute ischemic mitral regurgitation during myocardial infarction

OBJECTIVE

To describe outcomes of patients sustaining an acute myocardial infarction complicated by mitral regurgitation managed with contemporary reperfusion therapies.

DESIGN

Inception cohort case study. Long-term follow-up was obtained in 99% of all patients.

SETTING

University referral center.

PATIENTS

A series of 1,480 consecutive patients presenting between April 1986 and March 1989 who had emergency cardiac catheterization within 6 hours of infarction. Fifty patients were found to have moderately severe or severe mitral regurgitation.

OUTCOME MEASURES

Mortality; follow-up cardiac catheterization in patients with regurgitation.

RESULTS

Acute ischemic moderately severe to severe (3+ or 4+) mitral regurgitation was associated with a mortality of 24% at 30 days (95% CI, 12% to 36%), 42% at 6 months (CI, 28% to 56%), and 52% at 1 year (CI, 38% to 66%); multivariable analysis identified 3+ or 4+ mitral regurgitation as a possible independent predictor of mortality (P = 0.06). Patients with mitral regurgitation tended to be female, older, and to have cerebrovascular disease, diabetes, and preexisting symptomatic coronary artery disease. A physical examination did not identify 50% of patients with moderately severe to severe regurgitation. Acute reperfusion with thrombolysis or angioplasty did not reliably reverse valvular incompetence. In this observational study, the greatest in-hospital and 1-year mortalities were seen in patients reperfused with emergency balloon angioplasty, whereas patients managed medically or with coronary bypass surgery had lower mortalities.

CONCLUSIONS

Moderately severe to severe (3+ or 4+) mitral regurgitation complicating acute myocardial infarction portends a grave prognosis. Acute reperfusion does not reduce mortality to levels experienced by patients with lesser degrees of mitral regurgitation nor does it reliably restore valvular competence.

Renal artery stenosis: prevalence and associated risk factors in patients undergoing routine cardiac catheterization

The purposes of this study were to determine the prevalence of angiographically significant renal artery stenosis in a patient population referred for diagnostic cardiac catheterization and to develop a model that predicts the highest-risk subset of patients who have significant renal artery narrowing. A prospective validation cohort study was undertaken in a referral-based university hospital. After left ventriculography, abdominal aortography was performed to screen for the presence of renal artery disease. A convenience sample of 1,302 of 1,651 consecutive patients undergoing diagnostic cardiac catheterization were enrolled in the study. Of the 1,302 abdominal aortograms performed, 1,235 (95%) were deemed of adequate quality for the evaluation of renal artery anatomy. Renal artery disease was identified in 30% of the patients. Insignificant renal artery stenosis was found in 187 (15%) and significant (greater than or equal to 50% diameter narrowing) stenosis was found in 188 (15%). Significant unilateral disease was present in 11%, and bilateral disease was present in 4%. By univariable and multivariable logistic regression analysis, the association of both clinically and catheterization-derived variables with renal artery disease was assessed. Multivariable predictors included age, severity of coronary artery disease, congestive heart failure, female gender, and peripheral vascular disease. Hypertension was not an associated variable. These data reveal the previously undetected high prevalence of renal artery disease in patients undergoing cardiac catheterization and provide clinical and angiographic features that assist in predicting its presence.

Mycoplasma arthritidis mitogen. V beta engaged in mice, rats, and humans, and requirement of HLA-DR alpha for presentation

OBJECTIVE

Mycoplasma arthritidis mitogen (MAM) is mitogenic for mouse, rat, and human T cells, and behaves as a superantigen in mice through its capacity to bind to the alpha chain of I-E molecules and engage entire sets of T cells expressing specific V beta. Here, we have attempted to fully characterize the V beta-engaging activities of MAM in mice, and define similar activities in rats and humans.

METHODS

Multiprobe RNase-protection assays and mice transgenic for human DR alpha, DR beta, and DR alpha beta were utilized for this purpose.

RESULTS

MAM-reactive V beta in the mouse included not only the previously reported V beta 6, V beta 8.1, V beta 8.2, and V beta 8.3, but also V beta 5.1. In the rat, engagement of V beta 5.1, V beta 6, V beta 8.1, and V beta 8.2, but not V beta 8.3, was documented, whereas in humans, the engaged V beta included primarily V beta 19.1 (alternatively termed V beta 17.1) and, to a lesser extent, V beta 3.1, V beta 11.1, V beta 12.1, and V beta 13.1. In DR transgenic E alpha- E beta- mice, presentation of MAM and engagement of specific V beta was effected by DR alpha.

CONCLUSIONS

Homologous V beta are engaged by MAM in mice, rats, and humans, presumably through a binding site similar to that proposed previously for other superantigens. MAM presentation primarily via the nonpolymorphic DR alpha makes it unlikely that there is involvement of such a superantigen in the pathogenesis of autoimmune diseases known to be associated with certain DR haplotypes. The possibility cannot be excluded, however, that superantigen-activated T cells may lead to disease by cross-reactions with self-antigens presented by particular DR haplotypes.

The effect of temperature on cerebral metabolism and blood flow in adults during cardiopulmonary bypass

The effect of temperature on cerebral blood flow and metabolism was studied in 41 adult patients scheduled for operations requiring cardiopulmonary bypass. Plasma levels of midazolam and fentanyl were kept constant by a pharmacokinetic model-driven infusion system. Cerebral blood flow was measured by xenon 133 clearance (initial slope index) methods. Cerebral blood flow determinations were made at 27 degrees C (hypothermia) and 37 degrees C (normothermia) at constant cardiopulmonary bypass pump flows of 2 L/min/m2. Blood gas management was conducted to maintain arterial carbon dioxide tension (not corrected for temperature) 35 to 40 mm Hg and arterial oxygen tension of 150 to 250 mm Hg. Blood gas samples were taken from the radial artery and the jugular bulb. With decreased temperature there was a significant (p less than 0.0001) decrease in the arterial venous-oxygen content difference, suggesting brain flow in excess of metabolic need. For each patient, the cerebral metabolic rate of oxygen consumption at 37 degrees C and 27 degrees C was calculated from the two measured points at normothermia and hypothermia with the use of a linear relationship between the logarithm of cerebral metabolic rate of oxygen consumption and temperature. The temperature coefficient was then computed as the ratio of cerebral metabolic rate of oxygen consumption at 37 degrees C to that at 27 degrees C. The median temperature coefficient for man on nonpulsatile cardiopulmonary bypass is 2.8. Thus reducing the temperature from 37 degrees to 27 degrees C reduces cerebral metabolic rate of oxygen consumption by 64%.

V beta repertoire in rats and implications for endogenous superantigens

Endogenous superantigens of mice, encoded by mammary tumor virus proviral integrants, induce intrathymic deletion of entire T cell populations that express specific V beta gene products, a phenomenon proposed to be important in self-tolerance and prevention of toxic responses to exogenous microbial superantigens. Evidence for the presence of V beta selecting/deleting endogenous superantigens in other species is lacking. We report here that rats do not exhibit endogenous superantigen-induced V beta clonal deletions despite their strong response to bacterial superantigens. These findings indicate that endogenous superantigens are not obligatory in V beta repertoire shaping.

Validation of 133Xe clearance as a cerebral blood flow measurement technique during cardiopulmonary bypass

133Xe clearance to measure cerebral blood flow (CBF) was examined in 10 dogs during cardiopulmonary bypass. As a reference method, a continuous Kety-Schmidt technique (CBFKS) with 133Xe as indicator was used. Extracranial tissue was removed to directly place the 133Xe detectors on the skull, and the head was covered with a 3 mm lead shield to minimize contamination of the 133Xe clearance curve with extracranial radiation. 133Xe detectors for the Kety-Schmidt technique were embedded in a shielded brass block to minimize interference with radiation from the animal's body. 133Xe clearance data were analyzed using stochastic (CBF10, CBF15, and CBFINF) and initial slope methods (CBFIS), and the results were compared with CBFKS using linear regression. CBF15 and CBFINF yielded similar CBF values as CBFKS (CBFKS = 0.97.CBF15-2.08, r = 0.92, p less than 0.01; CBFKS = 1.13.CBFINF-1.21, r = 0.92, p less than 0.01). CBF10 slightly overestimated CBFKS but still showed a close correlation to CBFKS (CBFKS = 0.89.CBF10-2.58, r = 0.92, p less than 0.01) and CBFIS considerably overestimated CBFKS (CBFKS = 0.60.CBFIS-1.27, r = 0.87, p less than 0.01). With extracranial contamination of the 133Xe clearance curve minimized, all 133Xe clearance techniques used to measure CBF were consistently related to CBFKS in a constant, significant manner. 133Xe clearance therefore is a valid method to assess CBF during cardiopulmonary bypass.

Influence of anesthesia on the threshold of pacing-induced ischemia

Increased myocardial oxygen demand, induced by increased heart rate, may cause myocardial ischemia in the presence of significant coronary artery disease. Alterations in anesthetic depth or technique might put at risk or protect myocardium with compromised blood flow. In 20 dogs with critical left anterior descending coronary artery (LAD) stenosis, atrial pacing rates from 100 to 160 beats/min were achieved, with end-tidal halothane 0.7% (LowH) and 1.1% (HighH), end-tidal isoflurane 1.1% (LowI) and 1.5% (HighI), as well as with continuous fentanyl plus midazolam (FM) infusion anesthesia. Despite significantly different mean arterial and coronary perfusion pressures, rate-pressure product, and left ventricular dP/dtmax, the pacing rate at which systolic shortening decreased below the lower limit of the physiologic response, indicating regional dysfunction, was the same in all investigated anesthesia conditions (LowH: 127 +/- 4 beats/min; HighH: 128 +/- 5 beats/min; LowI: 125 +/- 4 beats/min; HighI: 122 +/- 5 beats/min; FM: 124 +/- 4 beats/min [mean +/- SEM], P greater than 0.05). None of the investigated anesthesia conditions either increased ischemia tolerance or showed a detrimental effect on myocardium with compromised coronary blood flow.

Determinants of early versus late cardiac death in patients undergoing coronary artery bypass graft surgery

Most analyses of risk factors affecting survival after coronary artery bypass graft surgery have not differentiated among factors that influence early and late survival. For this reason, a multiphase model was applied to survival data from 2,967 patients undergoing a first coronary artery bypass graft at the Duke University Medical Center between 1969 and 1984. There were 709 deaths during follow-up to 19.6 years. The data were analyzed using a multivariable survival model that separates the underlying hazard function into as much as three different phases, each incorporating separate risk factors. Two distinct phases were detected. One phase dominated early survival (0-1 year), and the second phase dominated late survival (greater than 1 year). Surgery performed earlier in our experience was associated with elevated risk of dying in both phases but with different magnitudes, whereas lower ejection fraction, greater extent of coronary disease, older age, conduction abnormality, and history of hypertension were associated with elevated risk of dying similarly in both phases (p less than 0.05). Severity of angina symptoms and lower weight were associated with an elevated risk of dying only in the early phase (p less than 0.05; because few of the patients were obese, estimates of the relative risk of morbid obesity could not be estimated), whereas vascular disease, diabetes, and extent of myocardial damage were associated with an elevated risk of dying only in the late phase (p less than 0.05). These data illustrate both the differential influence of risk factors over time and the importance of multiphase models.

Influence of diabetes and mammary artery grafting on survival after coronary bypass

The effect of diabetes on survival after coronary bypass surgery is uncertain. Also, although the overall clinical benefits of internal mammary artery (IMA) grafting are well established, the survival benefit attributable to IMA grafting in diabetics is not well characterized. To determine the influence of diabetes and IMA grafting on survival after bypass surgery in the current surgical era, characteristics related to subsequent outcome were analyzed in 5,654 consecutive patients undergoing surgery in the decade of the 1980s. The 1,132 diabetic patients (20%) had more extensive coronary disease, had more left ventricular dysfunction, were older, were more frequently female, received a greater number of grafts (mean, 3.5 versus 3.1), and received more IMA grafts (67% versus 58%) than the 4,522 nondiabetic patients (all p less than 0.001). Overall 5-year survival probability was 0.91 in nondiabetic and 0.80 in diabetic patients (p less than 0.0001). Nondiabetic survival exceeded diabetic survival even in high-risk subgroups such as ejection fraction less than or equal to 0.40 (0.80 versus 0.66, p less than 0.02), age greater than or equal to 65 years (0.85 versus 0.73, p less than 0.0003), and, urgent surgery (0.89 versus 0.76, p less than 0.0001). By multivariate analysis, impairment of left ventricular function, advanced age, failure to use an IMA graft, diabetes, female sex, urgent surgery, number of diseased vessels, and mitral insufficiency were incremental risk factors for cardiac mortality (all p less than 0.006). Failure to use an IMA graft and diabetes were equally strong predictors of outcome. Use of an IMA graft conveyed an independent survival benefit to both nondiabetic (p less than 0.0001) and diabetic (p less than 0.02) patients. The magnitude of the survival benefit attributable to IMA grafting in the two groups did not differ (p = 0.4). Diabetes is an important risk factor for late cardiac mortality after bypass surgery and should be included in analyses of the efficacy of therapies for coronary artery disease. IMA grafting conveys a similar benefit to diabetic and nondiabetic patients but does not negate the adverse effect of diabetes on survival.

Effects of cardiopulmonary bypass and cardioplegia on regional and global cardiac actions of halothane in dogs

Cardiopulmonary bypass (CPB) with aortic cross-clamping represents a controlled period of global cardiac ischemia. We hypothesized that CPB (asanguineous prime), with aortic cross-clamping and repeated cardioplegia, alters myocardial function, which would be manifested as an exaggerated myocardial depression caused by halothane after CPB. In nine dogs anesthetized with fentanyl and midazolam, halothane dose-response curves (0.0%-2.0%) were compared before and after CPB. A reduced mean arterial blood pressure (46.4 +/- 3.7 vs 85.8 +/- 5.9 mm Hg), associated with a marked hemodilution (hematocrit, 19% +/- 1% vs 41% +/- 2%), was observed after CPB. Cardiac output and systolic shortening were not significantly different after versus before CPB during fentanyl-midazolam anesthesia. Normalized to fentanyl-midazolam hemodynamics, halothane dose-response curves before and after CPB were identical for all variables except cardiac output, where halothane caused a slight but statistically significantly more pronounced decrease after CPB compared with before CPB. The effect of halothane on left ventricular function, therefore, is relatively unaffected by CPB with cardioplegia.

Comparison of bicycle and treadmill radionuclide angiocardiography

The purpose of this study was to test motion-correction algorithms for initial-transit radionuclide angiocardiograms acquired at rest and during bicycle and treadmill exercise. Treadmill data was spatially reoriented by computer software designed to eliminate motion of a 125I point source simultaneously recorded at a lower energy window. A second algorithm based on left ventricular centroid counts further corrected for motion on all studies. Exercise left ventricular ejection fraction was higher on the treadmill (0.68 +/- 0.07) compared to the bicycle (0.64 +/- 0.08) (p less than 0.0001, r = 0.88). Treadmill exercise also resulted in larger end-diastolic volumes (180 +/- 30 versus 157 +/- 36, p less than 0.0001), stroke volumes (124 +/- 28 versus 101 +/- 29, p less than 0.0001) and cardiac outputs (19.9 +/- 4.6 versus 15.9 +/- 5.0, p less than 0.0001). Similar variances for these hemodynamic measurements suggest that the mean differences observed were physiologic and that error from body motion was effectively corrected by this approach. We conclude that the measurement of left ventricular function during treadmill exercise, when combined with these techniques for correcting motion, is a reasonable alternative to conventional bicycle exercise.