A50 MODULATION OF GOBLET CELL ACTIVITY DURING GIARDIA DUODENALIS INFECTION: A ROLE FOR PAR2

Background

Giardia duodenalis has been shown to alter the structure of the intestinal mucus layers during infection via obscure mechanisms. We hypothesize that goblet cell activity may be disrupted in part due to proteolytic activation of protease-activated receptor 2 (PAR2) by Giardia proteases, resulting in disruption of mucus production and secretion by intestinal goblet cells.

Aims

Characterize alterations in goblet cell activity during Giardia infection, focusing on the roles of Giardia protease activity and PAR2.

Methods

Chinese hamster ovary cells transfected with nano-luciferase tagged PAR2 were incubated with Giardia NF or GSM trophozoites. Cleavage within the activation domain results in release of enzymes into the supernatant. Luminescence in the supernatant was measured as an indication of PAR cleavage by Giardia.

LS174T, a human colonic mucus-producing cell line, was infected with Giardia trophozoites (isolates NF, WB, S2, and GSM). Prior to infection, trophozoites were treated with E64, a broad-spectrum cysteine protease inhibitor, and LS174T were treated with a PAR2 antagonist, a calcium chelator, or an ERK1/2 inhibitor. Quantitative PCR (qPCR) was performed for the MUC2 mucin gene.

Wild-type (WT) and PAR2 knockout (KO) mice were infected with Giardia. Colonic mucus was stained using fluorescein-coupled wheat-germ agglutinin (WGA), and qPCR was performed for Muc2 and Muc5ac.

Results

Giardia trophozoites cleaved PAR2 within the N-terminal activation domain in a cysteine protease-dependent manner. Cleavage was isolate dependent, with isolates that show higher protease activity cleaving at a higher rate.

High protease activity Giardia isolates increased MUC2 gene expression in LS714T. This increase was attenuated by inhibition of Giardia cysteine protease activity, and by antagonism of PAR2, inhibition of calcium release, or inhibition of ERK1/2 activity in LS174T cells.

Both Muc2 and Muc5ac expression were upregulated in the colons of WT mice in response to Giardia infection, while in the jejunum Muc2 expression decreased and Muc5ac expression increased. In KO, no changes in gene expression were seen in the colon in response to Giardia infection, while in the jejunum, Muc2 expression was unchanged and Muc5ac expression decreased. Both WT infected and KO noninfected mice showed thinning of the colonic mucus layer compared to WT controls. There was some recovery in thickness in KO infected mice.

Conclusions

PAR2 plays a significant role in the regulation of mucin gene expression in mice and in a human colonic cell line. Results suggest that Giardia cysteine proteases cleave and activate PAR2, leading to calcium release and activation of the MAPK pathway in goblet cells, ultimately leading to altered mucin gene expression. Findings identify a novel regulatory pathway for mucus production by intestinal goblet cells.

Funding Agencies

CAG, CCC

Radiogenomics Consortium Genome-Wide Association Study Meta-Analysis of Late Toxicity After Prostate Cancer Radiotherapy

BACKGROUND

A total of 10%-20% of patients develop long-term toxicity following radiotherapy for prostate cancer. Identification of common genetic variants associated with susceptibility to radiotoxicity might improve risk prediction and inform functional mechanistic studies.

METHODS

We conducted an individual patient data meta-analysis of six genome-wide association studies (n = 3871) in men of European ancestry who underwent radiotherapy for prostate cancer. Radiotoxicities (increased urinary frequency, decreased urinary stream, hematuria, rectal bleeding) were graded prospectively. We used grouped relative risk models to test associations with approximately 6 million genotyped or imputed variants (time to first grade 2 or higher toxicity event). Variants with two-sided Pmeta less than 5 × 10-8 were considered statistically significant. Bayesian false discovery probability provided an additional measure of confidence. Statistically significant variants were evaluated in three Japanese cohorts (n = 962). All statistical tests were two-sided.

RESULTS

Meta-analysis of the European ancestry cohorts identified three genomic signals: single nucleotide polymorphism rs17055178 with rectal bleeding (Pmeta = 6.2 × 10-10), rs10969913 with decreased urinary stream (Pmeta = 2.9 × 10-10), and rs11122573 with hematuria (Pmeta = 1.8 × 10-8). Fine-scale mapping of these three regions was used to identify another independent signal (rs147121532) associated with hematuria (Pconditional = 4.7 × 10-6). Credible causal variants at these four signals lie in gene-regulatory regions, some modulating expression of nearby genes. Previously identified variants showed consistent associations (rs17599026 with increased urinary frequency, rs7720298 with decreased urinary stream, rs1801516 with overall toxicity) in new cohorts. rs10969913 and rs17599026 had similar effects in the photon-treated Japanese cohorts.

CONCLUSIONS

This study increases the understanding of the architecture of common genetic variants affecting radiotoxicity, points to novel radio-pathogenic mechanisms, and develops risk models for testing in clinical studies. Further multinational radiogenomics studies in larger cohorts are worthwhile.

Treadmill exercise testing in an epidemiologic study of elderly subjects

We sought to characterize the physical performance of older subjects in a community-based study of aging and fitness and to establish norms of oxygen consumption during exercise in this group. A community-based census identified 3057 age-eligible individuals of whom 2092 individuals (68.4%) agreed to participate in the overall study. Of these, 1101 subjects between 55 and 94 years of age who were free of known heart disease and able to perform treadmill exercise were tested using the Cornell protocol. Of these 1101 subjects, 73.8% of women and 89.5% of men (p < .001) exceeded what was considered a minimal threshold workload [i.e., > or =2 min of exercise and a respiratory exchange ratio (RER) > or = 1.00]. Moreover, 32.9% of women and 52.7% of men achieved a RER > or = 1.10 and were considered to have achieved maximal exercise. For all subjects who exceeded the minimal exercise workload, the mean exercise duration was 10.0 +/- 4.0 min for women and 13.2 +/- 4.6 min for men. Peak VO2/kg x min(-1) decreased linearly with age for both women (y = 38.33 - 0.27 x age + 1.12 H) and men (y = 41.78 - 0.26 x age + 12.65 H - 0.15 H x age), (p < .001 for sex difference), where H is defined as presence (=1) or absence (=0) of a disease condition. However, this sex-related difference disappeared when VO2/kg x min(-1) was adjusted for lean body mass. Thus, from a community-based sample of older persons, we have provided data (by 5-year age groups) for rates of participation in treadmill exercise testing and the success rate for achieving maximal exercise. Oxygen consumption and other exercise data are presented for older, healthy subjects as well as for those with various chronic diseases associated with aging (excluding those with cardiac or cerebrovascular disease). Exercise duration, peak VO2/kg x min(-1) (normalized for total and lean body mass), and peak exercise heart rate declined with age. Most of the sex difference in peak VO2/kg x min(-1) could be explained by the greater percent of body fat in women.

Agonists of proteinase-activated receptor-2 modulate human neutrophil cytokine secretion, expression of cell adhesion molecules, and migration within 3-D collagen lattices

Proteinase-activated receptor-2 (PAR2) belongs to a novel subfamily of G-protein-coupled receptors with seven-transmembrane domains. PAR2 can be activated by serine proteases such as trypsin, mast cell tryptase, and allergic or bacterial proteases. This receptor is expressed by various cells and seems to be crucially involved during inflammation and the immune response. As previously reported, human neutrophils express functional PAR2. However, the precise physiological role of PAR2 on human neutrophils and its implication in human diseases remain unclear. We demonstrate that PAR2 agonist-stimulated human neutrophils show significantly enhanced migration in 3-D collagen lattices. PAR2 agonist stimulation also induced down-regulation of L-selectin display and up-regulation of membrane-activated complex-1 very late antigen-4 integrin expression on the neutrophil cell surface. Moreover, PAR2 stimulation results in an increased secretion of the cytokines interleukin (IL)-1beta, IL-8, and IL-6 by human neutrophils. These data indicate that PAR2 plays an important role in human neutrophil activation and may affect key neutrophil functions by regulating cell motility in the extracellular matrix, selectin shedding, and up-regulation of integrin expression and by stimulating the secretion of inflammatory mediators. Thus, PAR2 may represent a potential therapeutic target for the treatment of diseases involving activated neutrophils.

Oxygen uptake efficiency slope: an index of exercise performance and cardiopulmonary reserve requiring only submaximal exercise

OBJECTIVES

We sought to evaluate, in adults, the efficacy of the Oxygen Uptake Efficiency Slope (OUES), an index of cardiopulmonary functional reserve that can be based upon a submaximal exercise effort.

BACKGROUND

Maximal oxygen uptake (VO2,max), the most reliable measure of exercise capacity, is seldom attained in standard exercise testing. The OUES, which relates oxygen uptake to total ventilation during exercise, was proposed by Baba and coworkers (7) in a study of pediatric cardiac patients. They felt this submaximal index of cardiopulmonary reserve might be more practical than VO2max and more appropriate than the commonly used peak oxygen consumption (VO2 peak).

METHODS

Treadmill exercise tests with simultaneous respiratory gas measurement were performed in 998 older subjects free of clinically recognized cardiovascular disease and 12 male patients with congestive heart failure. During incremental exercise, oxygen uptake was plotted against the logarithm of total ventilation, and the OUES was determined.

RESULTS

The OUES, when calculated only from the first 75% of the exercise test, differed by 1.9% from the OUES calculated from 100% of exercise time in subjects with a peak respiratory exchange rate > or =1.10. On serial tests the OUES was less variable than exercise duration or VO2 peak. It correlated strongly with VO2max, with forced expiratory volume in 1 s and negatively with a history of current smoking. The OUES declined linearly with age in both women and men. A small sample of patients with congestive heart failure had OUES values much lower than those of older subjects without cardiovascular disease.

CONCLUSIONS

The OUES is an objective, reproducible measure of cardiopulmonary reserve that does not require a maximal exercise effort. It integrates cardiovascular, musculoskeletal and respiratory function into a single index that is largely influenced by pulmonary dead space ventilation and exercise-induced lactic acidosis.

Design and synthesis of thrombin receptor-derived nonpeptide mimetics utilizing a piperazine scaffold

Focal thrombus formation and vasoconstriction serve to defend vessels when vascular damage occurs, but may be detrimental when an atherosclerotic plaque is disrupted. Recently, the identification of the platelet thrombin receptor opened a new area in the development of agents that may selectively inhibit the effects of thrombin on cells, without affecting fibrin formation. In this regard, we have synthesized a number of 1,4-disubstituted piperazines which are designed to be analogues of thrombin receptor activating peptides (TRAP) and carry the pharmacophoric features of Phe and Arg residues present in the active pentapeptide SFLLR. These compounds were tested in the rat aorta relaxation assay and in platelet aggregation studies and their biological activity was consistent with a direct action on thrombin receptor. Furthermore, the structure activity relationships confirmed the importance of Phe and Arg for receptor activation and the molecular modeling revealed an intriguing relationship between their amphipathic similarity with SFLLR and their biological activity.

Association between self-reported leisure-time physical activity and measures of cardiorespiratory fitness in an elderly population

Leisure-time physical activity enhances health and functioning in older populations. However, few data are available on the correlation between self-reported leisure-time physical activity and cardiorespiratory fitness in the elderly. Treadmill exercise testing results were obtained for 1,006 members (median age 67 years) of a community-based sample. Subjects completed a standardized evaluation of medical/social history and measures of physical function. Leisure-time physical activity in the 12 months and 7 days before interview and over subjects' lifetimes was summarized as total and activity-specific METs/week and [METs * (hours/week)]. Multiple linear regression was used to investigate the cross-sectional, sex-specific associations between peak oxygen consumption (VO2) and exercise duration. After adjustment for age, body mass index, smoking history, medical morbidity, direct measures of physical functioning, forced expiratory volumes, and maximum respiratory muscle pressure, leisure-time physical activity accounted for < or = 5% of the variance of VO2 and exercise duration. Results were unchanged when analyses were restricted to subjects who achieved high levels of exercise. These data indicate that measures of aerobic capacity cannot be used to "validate" self-reported leisure-time physical activity in older subjects, and they further suggest that beneficial effects of physical activity in the elderly are the result of metabolic effects that are not reflected well by maximal aerobic capacity during exercise testing.

Prophylactic atenolol reduces postoperative myocardial ischemia. McSPI Research Group

BACKGROUND

Perioperative myocardial ischemia occurs in 20-40% of patients at risk for cardiac complications and is associated with a ninefold increase in risk for perioperative cardiac death, myocardial infarction, or unstable angina, and a twofold long-term risk. Perioperative atenolol administration reduces the risk of death for as long as 2 yr after surgery. This randomized, placebo-controlled, double-blinded trial tested the hypothesis that perioperative atenolol administration reduces the incidence and severity of perioperative myocardial ischemia, potentially explaining the observed reduction in the risk for death.

METHODS

Two-hundred patients with, or at risk for, coronary artery disease were randomized to two study groups (atenolol and placebo). Monitoring included a preoperative history and physical examination and daily assessment of any adverse events. Twelve-lead electrocardiography (ECG), three-lead Holter ECG, and creatinine phosphokinase with myocardial banding (CPK with MB) data were collected 24 h before until 7 days after surgery. Atenolol (0, 5, or 10 mg) or placebo was administered intravenously before induction of anesthesia and every 12 h after operation until the patient could take oral medications. Atenolol (0, 50, or 100 mg) was administered orally once a day as specified by blood pressure and heart rate.

RESULTS

During the postoperative period, the incidence of myocardial ischemia was significantly reduced in the atenolol group: days 0-2 (atenolol 17 of 99 patients; placebo, 34 of 101 patients; P = 0.008) and days 0-7 (atenolol, 24 of 99 patients; placebo, 39 of 101 patients; P = 0.029). Patients with episodes of myocardial ischemia were more likely to die in the next 2 yr (P = 0.025).

CONCLUSIONS

Perioperative administration of atenolol for 1 week to patients at high risk for coronary artery disease significantly reduces the incidence of postoperative myocardial ischemia. Reductions in perioperative myocardial ischemia are associated with reductions in the risk for death at 2 yr.

Electrocardiographic and hemodynamic changes and their association with myocardial infarction during coronary artery bypass surgery. A multicenter study. Multicenter Study of Perioperative Ischemia (McSPI) Research Group

BACKGROUND

Electrocardiographic (ECG) changes during coronary artery bypass graft surgery have not been described in detail in a large multicenter population. The authors describe these ECG changes and evaluate them, along with demographic and clinical characteristics and intraoperative hemodynamic alterations, as predictors of myocardial infarction (MI) as defined by two sets of criteria.

METHODS

Data from 566 patients at 20 clinical sites, collected as part of a clinical trial to evaluate the efficacy of acadesine for reducing MI, were analyzed at core laboratories. Perioperative ECG changes were identified using continuous three-lead Holter ECG. Systolic blood pressure, diastolic blood pressure, and heart rate were recorded each minute during operation. The occurrence of MI by Q wave or myocardial fraction of creatine kinase (CK-MB) or autopsy criteria, and by (Q wave and CK-MB) or autopsy criteria was determined.

RESULTS

During perioperative Holter monitoring, episodes of ST segment deviation, major cardiac conduction changes > or = 30 min, or use of ventricular pacing > or = 30 min occurred in 58% patients, primarily in the first 8 h after release of aortic occlusion. Of the 25% patients who met the Q wave or CK-MB or autopsy criteria for MI, 19% had increased CK-MB as well as ECG changes. (Q wave and CK-MB) or autopsy criteria for MI were met by 4% of patients. The CK-MB concentration generally peaked by 16 h after release of aortic occlusion. In patients with (n = 187) and without a perioperative episode of ST segment deviation, the incidence of MI was 36% and 19%, respectively (P < 0.01), by Q wave or CK-MB or autopsy criteria, and 6% and 3%, respectively (P = 0.055), by (Q wave and CK-MB) or autopsy criteria. Multiple logistic regression analysis showed that intraoperative ST segment deviation, intraventricular conduction defect, left bundle branch block, duration of hypotension (systolic blood pressure < 90 mmHg) after cardiopulmonary bypass, and duration of cardiopulmonary bypass are independent predictors of Q wave or CK-MB or autopsy MI. The independent predictors of (Q wave and CK-MB) or autopsy MI are intraoperative ST segment deviation and duration of aortic occlusion.

CONCLUSIONS

Major ECG changes occurred in 58% of patients during coronary artery bypass graft surgery, primarily within 8 h after release of aortic occlusion. Multicenter data collection revealed a substantial variation in the incidence of MI and an overall incidence of up to 25%, with most MI occurring within 16 h after release of aortic occlusion. Intraoperative monitoring of ECG and hemodynamics has incremental value for predicting MI.

Effects of perioperative dexmedetomidine infusion in patients undergoing vascular surgery. The Study of Perioperative Ischemia Research Group

BACKGROUND

Dexmedetomidine, a highly selective alpha 2-adrenergic agonist, increases perioperative hemodynamic stability in healthy patients but decreases blood pressure and heart rate. The goal of this study was to evaluate, in a preliminary manner, the hemodynamic effects of perioperatively administered dexmedetomidine in surgical patients at high risk for coronary artery disease.

METHODS

Twenty-four vascular surgery patients received a continuous infusion of placebo or one of three doses of dexmedetomidine, targeting plasma concentrations of 0.15 ng/ml (low dose), 0.30 ng/ml (medium dose), or 0.45 ng/ml (high dose) from 1 h before induction of anesthesia until 48 h postoperatively. All patients received standardized anesthesia and hemodynamic management. Blood pressure, heart rate, and Holter ECG were monitored; additional monitoring included continuous 12-lead ECG preoperatively, anesthetic concentrations and myocardial wall motion (echocardiography) intraoperatively, and cardiac enzymes postoperatively.

RESULTS

Preoperatively, there was a decrease in heart rate (low dose 11%, medium dose 5%, high dose 20%) and systolic blood pressure (low dose 3%, medium dose 12%, high dose 20%) in patients receiving dexmedetomidine. Intraoperatively, dexmedetomidine groups required more vasoactive medications to maintain hemodynamics within predetermined limits. Postoperatively, demedetomidine groups had less tachycardia (minutes/monitored hours) than the placebo group (placebo 23 min/h; low dose 9 min/h, P = 0.006; medium dose 0.5 min/h, P = 0.004; high dose 2.3 min/h, P = 0.004). Bradycardia was rare in all groups. There were no myocardial infarctions or discernible trends in the laboratory results.

CONCLUSIONS

Infusion of dexmedetomidine up to a targeted plasma concentration of 0.45 ng/ml appears to benefit perioperative hemodynamic management of surgical patients undergoing vascular surgery but required greater intraoperative pharmacologic intervention to support blood pressure and heart rate.

Reliability of the continuous ECG after cardiopulmonary bypass and CABG surgery

Because of ECG changes associated with phenomena such as myocardial stunning or reperfusion injury in patients undergoing coronary artery bypass graft (CABG) surgery, Holter recordings may not detect postoperative myocardial ischemia with the same sensitivity and accuracy achieved in patients undergoing noncardiac surgery. This study details the reasons for decreased sensitivity of Holter recordings under such circumstances and suggests guidelines for inclusion of patients undergoing CABG into future studies. Continuous ECG (Holter) recordings were obtained in 617 analyzable patients before, during, and for 24 to 48 hours after CABG surgery. Uninterpretable tracings occurred with greatest frequency in the immediate period after electrical defibrillation and decreased progressively thereafter; only 50% of recorded tracings were interpretable and the percent of interpretable recordings increased progressively for the next 9 hours and then remained constant. This study confirmed the great frequency with which ECG abnormalities occur in the early postoperative period following bypass or coronary artery revascularization; it supports the suitability of Holter monitoring in patients who undergo cardiopulmonary bypass and CABG only if rigorous criteria for ECG interpretability and patient exclusion are used. In addition, because precise data were available for analysis for two thirds of all recruited patients, these results should provide valuable guidelines for estimating the appropriate sample size in the design of future studies similar to this one.

Therapeutic approaches to postoperative ischemia. The Study of Perioperative Ischemia Research Group

Previous attempts to identify predictors of cardiac complications, an important cause of postoperative morbidity and mortality following non-cardiac surgery, have focused mainly on the patient's preoperative state. Our research group, however, has found that adverse cardiac outcome correlates most highly with the appearance of at least 1 ischemic episode determined by continuous ambulatory electrocardiographic monitoring (AEM) in the early postoperative period. Such early postoperative ischemia conferred (1) a greater than 9-fold increased risk of experiencing in-hospital cardiac death, nonfatal myocardial infarction, or postoperative unstable angina, and (2) a greater than 2-fold increased long-term (2-year) risk of cardiac death, myocardial infarction, or angina requiring coronary angioplasty or coronary artery bypass grafting (CABG). Additionally, 5 predictors of such postoperative ischemia were identified: left ventricular hypertrophy, diabetes mellitus, hypertension, definite coronary artery disease, and preoperative digoxin use. These findings suggest that patients who are at high risk for postoperative myocardial ischemia warrant more intensive postoperative monitoring. Moreover, since such ischemia is potentially reversible, the testing of strategies designed to prevent or manage postoperative ischemia appears warranted and is discussed. Our group also has established the usefulness of AEM for identifying ischemic episodes in patients undergoing CABG. However, patients who require cardiopulmonary bypass present unique problems regarding the interpretation of AEM recordings. We describe guidelines for the interpretation of AEM results obtained under these conditions and suggest criteria based on the degree of interpretability for patient inclusion in future studies.

An initial multicenter, randomized controlled trial on the safety and efficacy of acadesine in patients undergoing coronary artery bypass graft surgery. SPI Research Group

Acadesine (5-amino-4-imidazole carboxamide riboside) is a purine nucleoside analog that has been shown in animals to reduce myocardial ischemic injury by selectively increasing the availability of adenosine in ischemic tissues. Because patients undergoing coronary artery bypass graft (CABG) surgery are especially vulnerable to developing myocardial ischemia, we investigated whether perioperative use of this adenosine-regulating drug with potential anti-ischemic properties could modify the incidence and severity of perioperative myocardial ischemia. The goals of this study were to evaluate safety and the effects of acadesine on myocardial ischemia, left ventricular function, and, secondarily, on adverse clinical outcomes (myocardial infarction, heart failure, life-threatening dysrhythmias, and death) in patients undergoing CABG surgery. One hundred sixteen patients were randomized to receive one of three continuous intravenous dosing regimens (placebo [control] or one of two doses of acadesine [high- and low-dose infusion]) in double-blind fashion intraoperatively and in the early postoperative period (total infusion time was 7 h). Multidose cold crystalloid cardioplegia (each containing either acadesine or placebo) was used for myocardial protection. All were monitored for potentially drug-related adverse events and the presence of myocardial ischemia was assessed by continuous Holter electrocardiography (ECG) and transesophageal echocardiography (TEE). All patients received standardized anesthetic, surgical, and hemodynamic management during the intraoperative period. All research data (ECG, TEE, outcome data) were evaluated at the coordinating center (San Francisco) in blinded fashion to ensure that uniform data analysis criteria were employed. The administration of acadesine was safe: mild increases in plasma uric acid (a metabolite of acadesine) occurred only in patients receiving high doses (mean increase 1.6 +/- 0.2 mg/dL) and were without clinical sequelae. Before drug administration in the preoperative period (baseline), the incidence and severity of ECG ischemia did not differ among the three groups (placebo = 18%; low-dose = 14%; high-dose = 14%). During prebypass, the incidence of ECG ischemia was similar in all three groups (0%, 3%, 3%, respectively). The incidence of TEE ischemia was numerically lower in the two acadesine groups (high-dose = 6%, low-dose = 15%) than in the control group (19%), but this was not statistically significant (P = 0.22). During postbypass, the incidence of ECG ischemia was 11% in the high-dose group, 22% in the low-dose group, and 18% in the control group (P = 0.42), and TEE ischemia was similar in incidence in all groups (placebo = 29%; low dose = 27%; high-dose = 24%) (P = 0.86).(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of steal-prone anatomy on intraoperative myocardial ischemia. The SPI Research Group

OBJECTIVES

Our study objective was to determine whether the presence of steal-prone anatomy conferred an increased risk in the development of intraoperative myocardial ischemia.

BACKGROUND

Coronary artery steal of collateral blood flow has been demonstrated for many vasodilators, including isoflurane, the most commonly used inhalational anesthetic agent in the United States. It has been postulated that patients with steal-prone anatomy (total occlusion of one coronary artery that is supplied distally by collateral flow from another coronary artery with a > or = 50% stenosis) may be particularly at risk for the development of intraoperative myocardial ischemia when an anesthetic with a vasodilator property is being administered.

METHODS

We evaluated the risk of myocardial ischemia under isoflurane anesthesia (vs. a high dose narcotic technique using sufentanil) using continuous intraoperative electrocardiography and transesophageal echocardiography in patients with and without steal-prone anatomy undergoing coronary artery bypass graft surgery.

RESULTS

Sixty-two (33%) of the 186 patients had steal-prone anatomy: in 5 (8%) the collateral-supplying vessel was > or = 50% to 69% stenosed, in 24 (39%) it was > or = 70% to 89% stenosed and in 33 (53%) it was > or = 90% stenosed. The incidence of ischemia (transesophageal echocardiography or intraoperative electrocardiography, or both) was similar in patients with and without steal-prone coronary anatomy (18 [29%] of 62 patients vs. 39 [31%] of 124 patients, p = 0.87, 95% confidence interval = -0.13 to 0.17). The incidence of intraoperative ischemia was similar in patients who received isoflurane or sufentanil anesthesia (20 [32%] of 62 patients vs. 37 [30%] of 124 patients, p = 0.87). The incidence of tachycardia and hypotension was low (increases in heart rate = 9.8%, and decreases in systolic blood pressure = 10.8% of total monitoring time during the prebypass period compared with preoperative baseline values). The incidence of adverse cardiac outcome was similar in patients with and without preoperative steal-prone coronary anatomy (4 [7%] of 62 patients vs. 14 [11%] of 124 patients, p = 0.53).

CONCLUSIONS

These findings demonstrate that under strict hemodynamic control the presence of steal-prone anatomy does not confer an increased risk in the development of intraoperative myocardial ischemia.

Monitoring for myocardial ischemia during noncardiac surgery. A technology assessment of transesophageal echocardiography and 12-lead electrocardiography. The Study of Perioperative Ischemia Research Group

OBJECTIVE

Transesophageal echocardiography (TEE) and 12-lead electrocardiography (ECG) are sophisticated techniques that are increasingly being used to monitor for myocardial ischemia during noncardiac surgery. We examined whether the routine use of these techniques has incremental clinical value in identifying patients at high risk for perioperative ischemic outcomes when compared with preoperative clinical data and intraoperative monitoring using continuous two-lead bipolar ECG.

DESIGN

Cohort study.

SETTING

Veterans Affairs medical center.

PATIENTS

A total of 332 men undergoing noncardiac surgery who had or were at high risk for coronary artery disease.

INTERVENTIONS

TEE, 12-lead ECG, and two-lead ECG were performed continuously during noncardiac surgery (47% vascular, 53% nonvascular). Monitoring results were not available to anesthesiologists or surgeons, and data were blindly analyzed after surgery.

MAIN OUTCOME MEASURE

Perioperative ischemic outcomes (cardiac death, nonfatal myocardial infarction, unstable angina).

RESULTS

In a subset of 285 patients who were adequately studied by all three techniques, 111 patients (39%) were identified as having intraoperative myocardial ischemia (by one or more monitoring techniques). By univariate analysis, intraoperative ischemia was associated with all perioperative cardiac outcomes, including ischemic outcomes, congestive heart failure, and ventricular tachycardia (P less than or equal to .02 for each of the three monitoring techniques). However, when monitoring results for TEE and 12-lead ECG were added to a multivariate model that included preoperative clinical data and continuous two-lead ECG results, the incremental value of TEE was small (odds ratio, 2.6; 95% confidence interval [CI], 1.2 to 5.7; P = .02) and that of 12-lead ECG was not significant (odds ratio, 1.5; 95% CI, 0.6 to 3.8). Furthermore, when the multivariate analysis was repeated with only ischemic outcomes, neither TEE nor 12-lead ECG retained significant associations (odds ratio, 2.2; 95% CI, 0.5 to 9.4, and odds ratio, 1.1; 95% CI, 0.2 to 6.1, respectively).

CONCLUSION

When compared with preoperative clinical data and intraoperative monitoring using two-lead ECG, routine monitoring for myocardial ischemia with TEE or 12-lead ECG during noncardiac surgery has little incremental clinical value in identifying patients at high risk for perioperative ischemic outcomes.

Long-term cardiac prognosis following noncardiac surgery. The Study of Perioperative Ischemia Research Group

OBJECTIVE

To determine the long-term (2-year) cardiac prognosis of high-risk patients undergoing noncardiac surgery and to determine the predictors of long-term adverse cardiac outcome.

DESIGN

Prospective cohort study. Historical, clinical, and laboratory data were collected during the in-hospital period, and at 6 months, 1 year, and 2 years following surgery. Data were analyzed using proportional hazards models.

SETTING

University-affiliated Veterans Affairs medical center.

POPULATION

A consecutive sample of 444 patients with or at high risk for coronary artery disease who had undergone elective noncardiac surgery and were discharged from the hospital in stable condition.

MAIN OUTCOME MEASURES

Cardiac death, myocardial infarction, unstable angina, progressive angina requiring coronary artery bypass graft surgery or coronary angioplasty, and new unstable angina requiring hospitalization.

RESULTS

Forty-seven patients (11%) had major cardiovascular complications during a 728-day (median) follow-up period: 24 had cardiac death; 11, nonfatal myocardial infarction; six, progressive angina requiring coronary artery bypass graft surgery or coronary angioplasty; and six, new unstable angina requiring hospitalization. Thirty percent of outcomes occurred within 6 months of surgery and 64% within 1 year. Five independent predictors of long-term outcome were identified. Three predictors reflected the preexisting chronic disease state: (1) the presence of known vascular disease (hazard ratio, 6.1; 95% confidence interval [CI], 2.5 to 15.0; P less than .0001); (2) a history of congestive heart failure (hazard ratio, 5.0; 95% CI, 2.0 to 12.0; P less than .0005); and (3) known coronary artery disease (hazard ratio, 3.7; 95% CI, 1.7 to 8.0; P less than .0007). Two predictors reflected acute postoperative ischemic events: (1) myocardial infarction/unstable angina (hazard ratio, 20; 95% CI, 7.5 to 53.0; P less than .0001) and (2) myocardial ischemia (hazard ratio, 2.2; 95% CI, 1.1 to 4.3; P less than .03). Patients surviving a postoperative in-hospital myocardial infarction had a 28-fold increase in the rate of subsequent cardiac complications within 6 months following surgery, a 15-fold increase within 1 year, and a 14-fold increase within 2 years (95% CI, 5.8 to 32; P less than .00001). Seventy percent of all long-term adverse outcomes were preceded by in-hospital postoperative ischemia that occurred at least 30 days (median, 282 days) before the long-term event. The development of congestive heart failure or ventricular tachycardia (without ischemia) during hospitalization was not associated with adverse long-term outcome.

CONCLUSIONS

The incidence of long-term adverse cardiac outcomes following noncardiac surgery is substantial. At increased risk are patients with chronic cardiovascular disease; at highest risk are patients with acute perioperative ischemic events. We conclude that survivors of in-hospital perioperative ischemic events, specifically myocardial infarction, unstable angina, and postoperative ischemia, warrant more aggressive long-term follow-up and treatment than is currently practiced.

Predictors of postoperative myocardial ischemia in patients undergoing noncardiac surgery. The Study of Perioperative Ischemia Research Group

OBJECTIVE

To identify predictors of postoperative myocardial ischemia in patients scheduled to undergo major noncardiac surgery.

DESIGN

Historical, clinical, laboratory, and physiological data were obtained prospectively before and during surgery to identify potential univariate predictors of postoperative myocardial ischemia, which then were entered into multivariate logistic models. Continuous two-lead electrocardiograms before, during, and after surgery were used to identify episodes of myocardial ischemia.

SETTING

Department of Veterans Affairs tertiary care hospital.

PATIENTS

A consecutive sample of 474 men at high risk for or with coronary artery disease who were scheduled to undergo major noncardiac surgery (95% compliance rate).

MAIN OUTCOME MEASURE

Significant variables identified by multivariate logistic models that are associated with postoperative myocardial ischemia.

RESULTS

Five major preoperative predictors of postoperative myocardial ischemia were identified: (1) left ventricular hypertrophy by electrocardiogram; (2) history of hypertension; (3) diabetes mellitus; (4) definite coronary artery disease; and (5) use of digoxin. The risk of postoperative myocardial ischemia increased progressively with the number of predictors present: in 22% of patients with no predictors, in 31% with one predictor, in 46% with two predictors, in 70% with three predictors, and in 77% with four predictors.

CONCLUSION

Patients subgroups who are at high risk for developing postoperative myocardial ischemia and who might benefit the most from intensive Holter monitoring in the postoperative period now can be identified preoperatively.

Postoperative myocardial ischemia. Therapeutic trials using intensive analgesia following surgery. The Study of Perioperative Ischemia (SPI) Research Group

Recent data suggest that postbypass and postoperative myocardial ischemia are related to adverse cardiac outcome following myocardial revascularization. Therapeutic trials to suppress postoperative ischemia are warranted. Because anesthetics can suppress a variety of physiologic responses to stress as well as myocardial ischemia intraoperatively, we examined whether use of intensive analgesia in the stressful postoperative period could decrease postoperative ischemia. In 106 patients undergoing elective myocardial revascularization, we standardized the anesthetic prior to bypass (sufentanil 5-10 micrograms/kg [induction] and 4.2-6.0 micrograms.kg-1.h-1 [infusion] supplemented with up to 0.5 mg/kg of diazepam). During bypass, patients were randomly assigned to receive either morphine sulfate (group M, n = 54, up to 2 mg/kg) or sufentanil (group S, n = 52, 1 microgram/kg and 1 microgram.kg-1.h-1). In the intensive care unit (ICU), group M received low-dose analgesia (morphine sulfate 1-10 mg intravenously every 30 min, average dose = 2.2 +/- 2.1 mg/h), while group S continued to receive intensive analgesia (infusion of sufentanil at 1 microgram.kg-1.h-1). Both groups received supplemental midazolam in the ICU (group M = 1.1 +/- 1.1 mg/h; group S = 0.6 +/- 0.6 mg/h; P = 0.01). All analgesic and sedative-hypnotic medications were discontinued at 18 hours following myocardial revascularization. Using continuous two-channel electrocardiographic (ECG) monitoring (CC5 and CM5), we documented and characterized ECG changes consistent with ischemia during the preoperative, intraoperative (pre- and postbypass), and postoperative (on- and off-treatment) periods. The total ECG monitoring time was 8,486 h, averaging 81 h per patient. During the prebypass (anesthetic control) period, groups M and S had a similar incidence, but group S episodes were more severe: maximum ST-segment change (median), S versus M: -1.8 mm versus -1.4 mm (P = 0.04). During the postbypass period, both groups had a similar incidence of ischemia, but episodes in group S were less severe: maximum ST-segment change, S versus M: -1.8 mm versus -2.7 mm (P = 0.0005). During the ICU-on-therapy period, the incidence of ischemic episodes was less in group S patients, and the severity was less: area-under-the-ST-time curve, S versus M: -21 mm.min versus -161 mm.min (P = 0.05). After discontinuation of the drug regimen in the ICU, the incidence and severity of ischemic episodes was similar. The incidence of hypotension, hypertension, and tachycardia was similar in both groups in both the intraoperative and ICU periods.(ABSTRACT TRUNCATED AT 400 WORDS)

Dipyridamole thallium-201 scintigraphy as a preoperative screening test. A reexamination of its predictive potential. Study of Perioperative Ischemia Research Group

BACKGROUND

We examined the value of dipyridamole thallium-201 (201Tl) scintigraphy as a preoperative screening test for perioperative myocardial ischemia and infarction.

METHODS AND RESULTS

We prospectively studied 60 patients undergoing elective vascular surgery. We performed 201Tl scintigraphy preoperatively and blinded all treating physicians to the results. Historical, clinical, laboratory, and physiological data were gathered throughout hospitalization. Myocardial ischemia was assessed during the intraoperative period using continuous 12-lead electrocardiography (ECG) and transesophageal echocardiography (TEE) and during the postoperative period using continuous two-lead ambulatory ECG. Adverse cardiac outcomes (cardiac death, myocardial infarction, unstable angina, severe ischemia, or congestive heart failure) were assessed daily throughout hospitalization. Twenty-two patients (37%) had defects that improved or reversed on delayed scintigrams (redistribution defects), 18 (30%) had persistent defects, and 20 (33%) had no defects on 201Tl scintigraphy. There was no association between redistribution defects and adverse cardiac outcomes: 54% (seven of 13) of adverse outcomes occurred in patients without redistribution defects, and the risk of an adverse outcome was not significantly increased in patients with redistribution defects (relative risk 1.5, 95% confidence interval 0.6-3.9, p = 0.43). Consistent with these findings, there was also no association between redistribution defects and perioperative ischemia: 54% (19 of all 35) of perioperative ECG and TEE ischemic episodes and 58% (14 of 24) of severe ischemic episodes occurred in patients without redistribution defects. The sensitivity of 201Tl scintigraphy for perioperative ischemia and adverse outcomes ranged from 40% to 54%, specificity from 65% to 71%, positive predictive value from 27% to 47% and negative predictive value from 61% to 82%.

CONCLUSIONS

These results differ from those of previous studies and suggest that the routine use of 201Tl scintigraphy for preoperative screening of patients undergoing vascular surgery may not be warranted.

Isoflurane anesthesia and myocardial ischemia: comparative risk versus sufentanil anesthesia in patients undergoing coronary artery bypass graft surgery. The SPI (Study of Perioperative Ischemia) Research Group

Whether isoflurane has the potential to produce coronary artery steal and associated myocardial ischemia is still controversial. Previous studies addressing this issue in humans did not purposefully control hemodynamics or use continuous measures of myocardial ischemia. The authors used transesophageal echocardiography (TEE) and continuous Holter electrocardiography (ECG) to study the relative risk of myocardial ischemia during isoflurane or sufentanil anesthesia under strict control of hemodynamics in 186 high-risk patients undergoing elective coronary artery bypass graft (CABG) surgery. Overall, hemodynamics were well controlled (increased heart rate = 9.8%; increased systolic blood pressure = 7.1%; decreased systolic blood pressure = 10.8% of total prebypass time compared with preoperative baseline values), with no difference between the two anesthetics. In the 162 patients with interpretable TEE recordings, moderate to severe TEE ischemic episodes (grade change greater than or equal to 2) developed in 33 (21%) during the prebypass period, with no difference between isoflurane (12 of 56 = 21%) and sufentanil (21 of 106 = 20%) (P = 0.97). The duration and severity of TEE episodes were not significantly different between the two groups. No correlation was observed between TEE ischemic episodes and isoflurane concentrations (range 0.47-1.75%). In the 181 patients with interpretable ECG recordings, ECG evidence of ischemia developed in 34 (19%) during the prebypass period, with no difference between isoflurane (12 of 59 = 20%) and sufentanil (22 of 122 = 18%) (P = 0.87). The duration and severity of electrocardiographic ischemic episodes were also similar in patients receiving either isoflurane or sufentanil. Four of the 62 patients (6%) who received isoflurane had an adverse cardiac outcome versus 15 of 124 patients (12%) who received sufentanil (P = 0.34). The authors' findings demonstrate that, when hemodynamics are controlled, the incidence of myocardial ischemia (TEE or ECG) during isoflurane and sufentanil anesthesia is similar.

Physiological assessment of sensitivity of noninvasive testing for coronary artery disease

The sensitivity of three noninvasive tests for coronary artery disease was assessed by means of quantitative indexes of disease severity in three different groups of patients. The overall population consisted of 110 subjects with limited coronary artery disease and no myocardial infarction. Planar dipyridamole-201Tl scintigraphy was evaluated in 31 patients, computer-assisted exercise treadmill in 28, and high-dose dipyridamole echocardiography testing in 51. Sensitivity was assessed by rigorous gold standards to define disease severity, such as measurement of minimum cross-sectional area and percent area of stenosis, by quantitative computerized coronary angiography (Brown/Dodge method). On the basis of the results of previous studies, the presence of physiologically significant coronary artery disease was indicated by a stenotic minimum cross-sectional area (MCSA) of less than 2.0 mm2 or a greater than 75% area of stenosis. With MCSA as the gold standard, dipyridamole-201Tl scintigraphy, computerized exercise treadmill, and dipyridamole echocardiography testing showed sensitivities of 52%, 54%, and 61%, respectively, in the three different patient cohorts enrolled. With percent area of stenosis as the gold standard, the sensitivity figures obtained for dipyridamole-201Tl, computerized exercise treadmill, and dipyridamole echocardiography testing were 64%, 54%, and 69%, respectively. For each of the three tests, sensitivity increased with increasing lesion severity. Sensitivity was also better in patients with left anterior descending coronary (LAD) disease when compared with patients with left circumflex or right coronary artery disease. Results of these studies, which were obtained with more strict patient selection criteria and by more rigorous gold standards than previous studies, demonstrate that in patients with limited coronary artery disease none of the tests evaluated is definitely superior in sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of the beta-adrenergic-response in cultured rat heart cells. II. Mammary-derived growth inhibitor (MDGI) blocks induction of beta-adrenergic supersensitivity. Dissociation from lipid-binding activity of MDGI

'Mammary-derived growth inhibitor (MDGI)' is a 14.5 kDa polypeptide with growth-inhibitory activity for various mammary epithelial cells in vitro which is highly homologous to cardiac fatty acid-binding protein (H-FABP). Here we describe a new biological activity of MDGI: Inhibition of L(+)-lactate-, arachidonic acid- and 15-S-hydroxyeicosatetraenoic acid-induced supersensitivity of neonatal rat heart cells for beta-adrenergic stimulation, concerning particularly a small population of beta 2-receptors. Synthetic peptides corresponding to the MDGI-sequence, residue 121-131 mimic the effect of MDGI. Measurements of lipid-binding to MDGI and synthetic peptides excluded the binding of arachidonic acid, 15-S-hydroxyeicosatetraenoic acid or beta-adrenergic agonists to MDGI or the peptides as the mechanism for this effect. Also, no direct interference of MDGI and the synthetic peptides with the binding of the beta-adrenergic agent CGP 12177 to its receptor on A431 cells could be detected. We suggest that MDGI and the peptides act by interference with the function of the beta 2-adrenergic receptor and that this mechanism might also be relevant for the growth-inhibitory activity of MDGI. Furthermore, the data point to a possible function of H-FABP for the modulation of beta-adrenergic sensitivity of cardiac myocytes.

Perioperative myocardial ischemia in patients undergoing noncardiac surgery--I: Incidence and severity during the 4 day perioperative period. The Study of Perioperative Ischemia (SPI) Research Group

To determine the incidence and characteristics of perioperative myocardial ischemia, the electrocardiographic (ECG) changes consistent with ischemia during the 4 day perioperative period were documented and characterized in 100 patients with or at risk for coronary artery disease undergoing noncardiac surgery. Using continuous two channel ECG monitoring (leads CC5 and CM5), the frequency and severity of ECG ischemic episodes defined by ST segment depression greater than or equal to 1 mm or elevation greater than or equal to 2 mm during the preoperative (up to 2 days), intraoperative and early postoperative (first 2 days) periods were compared. Preoperatively, 28 patients (28%) exhibited 105 episodes of ischemia; intraoperatively, 27 patients exhibited 39 episodes and postoperatively, 42 patients exhibited 187 episodes. There was no difference between the pre- and intraoperative episode characteristics. However, postoperative ischemic episodes were the most severe. The mean ST change was 1.5, 2 and 2.6 mm for pre-, intra- and postoperative episodes, respectively (p less than 0.0001 postoperative versus pre- or intraoperative); duration of ischemic episodes was 69, 45 and 207 min, respectively (p less than 0.005 postoperative versus preoperative, p less than 0.001 versus intraoperative) and area under the ST curve was 88, 74 and 383 mm.min (p less than 0.009 postoperative versus preoperative, p less than 0.005 versus intraoperative). Ninety-four percent of all postoperative ischemic episodes were silent; 80% of all episodes occurred without acute change (+/- 20% of control) in heart rate and 77% of intraoperative episodes occurred without acute change in blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of perioperative myocardial ischemia with cardiac morbidity and mortality in men undergoing noncardiac surgery. The Study of Perioperative Ischemia Research Group

BACKGROUND

Adverse cardiac events are a major cause of morbidity and mortality after noncardiac surgery. It is necessary to determine the predictors of these outcomes in order to focus efforts on prevention and treatment. Patients undergoing noncardiac surgery sometimes have postoperative cardiac events. It would be helpful to know which patients are at highest risk.

METHODS

We prospectively studied 474 men with coronary artery disease (243) or at high risk for it (231) who were undergoing elective noncardiac surgery. We gathered historical, clinical, laboratory, and physiologic data during hospitalization and for 6 to 24 months after surgery. Myocardial ischemia was assessed by continuous electrocardiographic monitoring, beginning two days before surgery and continuing for two days after.

RESULTS

Eighty-three patients (18 percent) had postoperative cardiac events in the hospital that were classified as ischemic events (cardiac death, myocardial infarction, or unstable angina) (15 patients), congestive heart failure (30), or ventricular tachycardia (38). Postoperative myocardial ischemia occurred in 41 percent of the monitored patients and was associated with a 2.8-fold increase in the odds of all adverse cardiac outcomes (95 percent confidence interval, 1.6 to 4.9; P less than 0.0002) and a 9.2-fold increase in the odds of an ischemic event (95 percent confidence interval, 2.0 to 42.0; P less than 0.004). Multivariate analysis showed no other clinical, historical, or perioperative variable to be independently associated with ischemic events, including cardiac-risk index, a history of previous myocardial infarction or congestive heart failure, or the occurrence of ischemia before or during surgery.

CONCLUSIONS

In high-risk patients undergoing noncardiac surgery, early postoperative myocardial ischemia is an important correlate of adverse cardiac outcomes.

The "natural history" of segmental wall motion abnormalities in patients undergoing noncardiac surgery. S.P.I. Research Group

Intraoperative segmental wall motion abnormalities (SWMA) detected by transesophageal echocardiography (TEE) are sensitive, but not always specific, markers of myocardial ischemia. To determine their incidence, characteristics, and relation to postoperative cardiac morbidity, we continuously recorded the left ventricular short-axis view and 12-lead ECG in 156 high-risk patients undergoing non-cardiac surgery. Monitoring was clinically blinded. Wall motion was scored at predefined clinical, hemodynamic, and ECG events and at periodic intervals (26 +/- 11 samples per patient). We detected 44 episodes of new or worsened SWMA in 32 patients (20%). The severity of most episodes was limited to severe hypokinesis (24/44, 55%) followed by akinesis (16/44, 36%) and dyskinesis (4/44, 9%). The remaining 124 patients had normal wall motion or only mild hypokinesis (56/156, 36%) or chronic SWMA (68/156, 44%). The incidence of new SWMA did not differ for patients with known coronary artery disease (CAD) and those with cardiac risk factors only (22% vs. 19%, P = not significant), although CAD patients had a significantly greater incidence of chronic SWMA (62% vs. 41%, P = 0.02). The incidence of new or worsened SWMA was significantly greater during aortic vascular surgery (38% vs. 17%, P = 0.05). Approximately 40% of all new TEE changes occurred in the absence of either an apparent clinical event or a significant change in systolic blood pressure or heart rate. Ten patients had new or worsened SWMA persisting until the end of surgery, 8 with new akinesis, only 1 developing myocardial infarction. The distribution of new or worsened SWMA and significant intraoperative ST-T changes (n = 19) in this cohort was discordant: temporal overlap between modalities was present in only 5 patients. Major cardiac complications occurred in 5 patients (3.2%), all of whom underwent peripheral vascularization. All patients with cardiac complications and new or worsened SWMA also had intraoperative or early postoperative ST-T changes. We conclude that: 1) continuous TEE recording with offline analysis in this high-risk group of patients revealed a relatively low incidence of new or worsened SWMA (20%), most episodes of which were characterized by severe hypokinesis (55%); 2) episodes were more common in patients undergoing aortic vascular surgery; 3) approximately 40% of episodes were unaccompanied by clinical events or significant hemodynamic changes; 4) episodes were poorly correlated with postoperative cardiac complications; and 5) the discordant relation between TEE and ECG changes observed here necessitates careful monitoring of the ECG when TEE is used clinically.

Prognostic importance of postbypass regional wall-motion abnormalities in patients undergoing coronary artery bypass graft surgery. SPI Research Group

Regional wall motion abnormalities (RWMA) detected by intraoperative transesophageal echocardiography (TEE) are thought to be sensitive markers of myocardial ischemia. To assess the prognostic significance of RWMA as compared with other less costly technologies such as electrocardiography (ECG) and hemodynamic measurements [blood pressure (BP) and pulmonary artery (PA) pressure], 50 patients were prospectively studied who were undergoing elective coronary artery bypass graft (CABG) surgery using continuous TEE, ECG (Holter), and hemodynamic measurements during the prebypass, postbypass, and early postoperative intensive care unit (ICU) periods (first 4 h). Echocardiographic and ECG evidence of ischemia was characterized during each of these three periods and related to adverse clinical outcomes (postoperative myocardial infarction, ventricular failure, and cardiac death). Clinicians were blinded to the TEE and ECG information. The prevalence of myocardial ischemia during the perioperative periods was as follows: prebypass, 20% (TEE) versus 7% (ECG); postbypass, 36% (TEE) versus 25% (ECG); ICU 25% (TEE) versus 16% (ECG). Neither prebypass TEE ischemia nor ECG ischemia occurring in any of the three periods predicted adverse outcome. In contrast, postbypass TEE ischemia was predictive of outcome: six of 18 patients with postbypass TEE ischemia had adverse outcomes versus 0 of 32 without TEE ischemia (P = 0.001). Seventy-three percent of the echocardiographic ischemic episodes occurred without acute change (+/- 20% of control) in heart rate, BP, or PA pressure. The authors conclude that: 1) prebypass myocardial ischemia was relatively uncommon, 2) the incidence of ECG and TEE ischemia was highest in the postbypass period, and 3) postbypass RWMA were related to adverse clinical outcome.

Usefulness of thallium-201 scintigraphy in predicting the development of angina pectoris in hypertensive patients with left ventricular hypertrophy

Hypertension and left ventricular (LV) hypertrophy are independent risk factors for the development of coronary artery disease. To determine whether patients at higher risk for coronary artery disease can be identified, 40 asymptomatic hypertensive men with LV hypertrophy were prospectively studied using exercise thallium-201 scintigraphy and exercise radionuclide angiography. Endpoints indicative of coronary artery disease were defined as the subsequent development of typical angina pectoris, which occurred in 8 patients during a median follow-up of 38 months, or myocardial infarction, which did not occur. The exercise electrocardiogram was interpreted by standard ST-segment criteria and by a computerized treadmill exercise score. Abnormal ST-segment responses were present in 16 of the 40 hypertensives (40%), whereas the treadmill score was positive in 8 of those same 40 patients (20%). Scintigraphic perfusion defects assessed both visually and semiquantitatively were observed in 8 of 40 (20%) patients. An abnormal ejection fraction response to exercise was present in 40% (16 of 40) of patients, and 3 of 40 (7.5%) developed new wall motion abnormalities during exercise. Six of 8 patients with either perfusion defects or abnormal treadmill score developed typical angina during follow-up. All 5 patients with concordant positive exercise scintigrams and treadmill score developed chest pain during follow-up and had coronary artery disease confirmed by coronary angiography. However, only 7 of 16 (44%) patients with positive ST changes or abnormal ejection fraction responses during exercise developed chest pain during follow-up. In contrast, of 32 patients with negative scintigrams only 2 developed atypical chest pain syndromes, and significant coronary artery disease was excluded by angiography in 1 patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial ischemia in patients awaiting coronary artery bypass grafting

The results of ambulatory ECG monitoring are described in a group of patients that have not previously been characterized. Fifty men who were initially seen for elective CABG surgery underwent 48 hours of continuous ambulatory ECG monitoring. ST segment deviation from baseline, trended every 15 seconds, was quantified for duration, maximum ST segment change, area under the ST segment-time curve (AUC), and average ST segment change for the episode (AUC/duration). Ischemic episodes, 87% of which were silent, occurred in 42% of the patients. Symptomatic episodes had greater maximum ST segment change than silent episodes (-2.4 vs -1.9 mm; p less than 0.05) but were shorter in duration (11 vs 18 minutes; p less than 0.05). Episodes that were unrelated to heart rate, that is, episodes with less than 20% increase in heart rate over the baseline rate at the onset of ischemia, made up 75% of all ischemic events and occurred in 90% of patients (19 of 21). Heart rate-related and unrelated ischemic episodes did not differ in duration, maximum ST segment change, AUC, or average ST segment change. It was concluded that: (1) as with patients with unstable angina, patients with severe coronary artery disease continue to have frequent episodes of silent myocardial ischemia despite intensive medical therapy; (2) painful episodes have greater maximum ST segment change but are shorter than silent ones; (3) most ischemic episodes (75%) occur without an initial increase in heart rate; and (4) heart rate-related and unrelated episodes are quantitatively similar.

Intraoperative myocardial ischemia: localization by continuous 12-lead electrocardiography

Based primarily on results obtained during exercise treadmill testing, electrocardiographic (ECG) leads II and V5 are the suggested optimal leads for detecting intraoperative myocardial ischemia. However, these recommendations have not been validated in this setting using all 12 ECG leads. Accordingly, the authors studied 105 patients with known or suspected coronary artery disease (CAD) undergoing noncardiac surgery with general anesthesia by continuously recording the 12-lead ECG intraoperatively in all patients. The average duration of monitoring was 8.2 +/- 2.7 h (mean +/- SD). Ischemic episodes (i.e., greater than or equal to 1-mm horizontal or downsloping ST depression, greater than or equal to 1.5-mm slowly upsloping ST depression or greater than or equal to 1.5-mm ST elevation in a non-Q wave lead) occurred in 25 patients (24%). Out of 51 ischemic episodes, 45 involved ST depression alone, and the remaining six involved both ST depression and elevation. ST segment changes occurred in a single lead only in 14 episodes, while multiple leads were involved in 37 episodes. Lead sensitivity was estimated assuming that all ST segment changes were true positive responses. Sensitivity using a single lead was greatest in V5 (75%) and V4 (61%), and intermediate in II, V3, and V6 (33%, 24%, and 37%, respectively). The remaining seven leads demonstrated very low sensitivity (2-14%) or exhibited no ischemic changes (I and a VL). Combining leads V4 and V5 increased sensitivity to 90%, while the standard clinical combination, II and V5, was only 80% sensitive. Sensitivity increased to 96% by combining II, V4, and V5. The further addition of V2 and V3 (five leads) increased sensitivity to 100%. This study confirms previous recommendations for the routine use of a V5 lead (either uni- or bipolar) in all patients at risk for ischemia. V4 is more sensitive than lead II, and should be considered as a second choice. However, lead II, superior for detection of atrial dysrhythmias, is more easily obtained with conventional monitors. The use of all three would appear to be the optimal arrangement for most clinical needs, and is recommended if the clinician has the capability.

Perioperative myocardial ischemia: importance of the preoperative ischemic pattern

Previous studies investigating the incidence of myocardial ischemia in patients undergoing coronary-artery bypass grafting (CABG) surgery have not considered the potential significance of the preoperative ischemic pattern in the development of intra- and postoperative myocardial ischemia and infarction. Accordingly, the authors compared the frequency and severity of pre-, intra-, and postoperative ischemic episodes (ST-segment depression greater than or equal to 0.1 mV or elevation greater than or equal to 0.2 mV) in 50 men with severe coronary artery disease scheduled for elective CABG. All subjects were monitored by continuous electrocardiography (ECG) (Holter monitor) for 2 preoperative days, intraoperatively, and 2 postoperative days (total monitoring time = 4,363 h). Routine anti-anginal medications were continued until the morning of surgery, and the anesthetic management of the patient was not controlled. During the preoperative period, 42% of the patients had ECG ischemic episodes, 87% of which were clinically silent. Only 18% developed intraoperative ischemia. Postoperatively, the incidence increased to 40%. The number of ischemic episodes/hour (epis/h) of monitoring among the three monitoring periods was similar (0.09 +/- 0.12 epis/h preoperatively, 0.11 +/- 0.20 epis/h intraoperatively, and 0.05 +/- 0.08 epis/h postoperatively; P = NS). The median duration of ischemic episodes was similar pre- and intraoperatively (16 vs. 18.5 min, P = NS), but greater postoperatively (41 min, P less than 0.05). Seventy-six per cent of the perioperative ECG ischemia occurred without acute change (+/- 20% of control) in blood pressure or heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic hypertension, left ventricular hypertrophy and coronary artery disease

The potential mechanisms for the development of myocardial ischemia in hypertensive left ventricular (LV) hypertrophy involve changes in the coronary circulation characterized by a reduction of coronary vascular reserve and an acceleration of the atherosclerotic process. This combination of factors is probably reflected in the epidemiologic findings of increased coronary morbidity and mortality in hypertension, particularly when it is associated with LV hypertrophy. The failure of several antihypertensive trials to reduce coronary morbidity and mortality emphasizes the importance of early detection of significant coronary artery disease (CAD) among hypertensive patients with LV hypertrophy. A strategy to detect asymptomatic CAD based on combined probability of 2 noninvasive tests is discussed. Results obtained in hypertensive LV hypertrophy showed a 20% to 30% incidence of abnormal exercise test results, and these positive findings were predictive for the development of typical angina during a 3-year follow-up. Based on these results and reported data, it is extrapolated that patients with silent ischemia may contribute up to 40% of the coronary mortality observed in previous antihypertensive trials. These findings suggest the need for an early detection and separate follow-up of these patients with silent CAD, to better assess the influence of antihypertensive treatment on coronary morbidity and mortality.

Effect of epidermal growth factor on growth and postnatal development of the rabbit liver

The effect of epidermal growth factor (EGF) on the postnatal development of the liver was examined. New Zealand White rabbits received 40 micrograms.kg-1.day-1 EGF from days 3 to 17 of age either intraperitoneally or orogastrically, whereas controls received saline. At days 18-20, animals underwent cannulation of the common duct using halothane anesthetic. Biliary output was measured directly for three 1-h periods: under basal conditions and in response to intravenous infusion of exogenous glycodeoxycholic acid at 0.75 and 1.5 mumol.min-1.kg-1, respectively. The bile salt pool size was measured by isotope dilution. Final mean body weight of intraperitoneal and orogastric groups did not differ from controls. Liver we weight, DNA, and protein content were significantly increased in intraperitoneally treated animals without morphological or biochemical evidence of fat deposition. Both intraperitoneal and orogastric EGF significantly increased bile salt secretion in the basal period and as a response to exogenous bile acid infusion. Bile flow was significantly increased in response to 1.5 mumol.min-1.kg-1 infusion of glycodeoxycholic acid. The bile salt pool was increased by both intraperitoneal and orogastric EGF. Administration of EGF resulted in a precocious development of glucokinase (EC 2.7.1.2) activity in the liver. EGF had no effect on serum cortisol, corticosterone, triiodothyronine, thyroxine, or free thyroxine levels. These findings suggest that in the neonatal period EGF can promote hepatic growth and maturation.

Effect of epidermal growth factor on ontogeny of the gastrointestinal tract

The effect of epidermal growth factor (EGF) on the ontogeny of the gastrointestinal tract was examined in New Zealand White rabbits. EGF, 40 micrograms X kg-1 X day-1, was administered to suckling animals from 3-18 days of age either intraperitoneally or orogastrically. Controls received saline. Animals were killed at 17-18 days of age. Body weight and wet weight of stomach, pancreas, and 10-cm segments of proximal, mid, and distal small intestine were measured. The total pancreas was homogenized for determination of protein, DNA, and amylase, and the intestinal mucosa was scraped, weighed, and homogenized for estimation of protein, DNA, sucrase, and lactase. While body weights were similar wet weight of stomach and pancreas were increased by intraperitoneal and orogastric EGF. Small intestinal wet weights were increased in all segments by intraperitoneal but not orogastric EGF, and both routes significantly increased mucosal DNA in the distal segment. EGF administered orogastrically induced precocious maturation of intestinal brush-border disaccharidase activities but had no effect on pancreatic amylase, whereas EGF administered intraperitoneally induced precocious maturation of pancreatic amylase but had no effect on brush-border disaccharidase activities. These findings suggest that both systemic and oral EGF play a role in regulating growth and postnatal maturation of the gastrointestinal tract.

Comparison of a quantitative treadmill exercise score with standard electrocardiographic criteria in screening asymptomatic young men for coronary artery disease

A computer-derived treadmill exercise score that quantifies the electrocardiographic response to exercise has been reported to have a high sensitivity (87 per cent) and specificity (92 per cent) in patients with a high prevalence of coronary artery disease. To test its accuracy in young, asymptomatic men with a low prevalence of coronary artery disease, we evaluated the responses of 377 military officers (mean age, 36.6 years) by two independent methods. According to standard electrocardiographic criteria, 45 of the subjects (12 per cent) had positive tests, whereas the treadmill exercise score indicated that only 3 (less than 1 per cent) had positive tests. Since two of these three had left ventricular hypertrophy and met only the criteria for the latter without associated coronary artery disease, the treadmill exercise score predicted that only 1 of 377 subjects would have clinically important coronary artery disease. Coronary arteriography, performed in 10 persons with the most positive scores on standard treadmill tests and the highest scores for risk factors, showed that nine subjects did not have coronary artery disease and that one had single-vessel disease (the same subject who the treadmill score predicted would have mild disease). The treadmill exercise score appears to improve the diagnostic specificity of exercise electrocardiography and may be more useful than values on standard stress tests in screening asymptomatic populations for coronary artery disease.

Influence of R-wave amplitude on exercise-induced ST depression: need for a "gain factor" correction when interpreting stress electrocardiograms

Does 2 mm of ST depression induced by exercise have the same clinical significance in a patient with a 30-mm R wave as a patient with a 10-mm R wave in the same monitored lead? To answer this question the exercise responses of 85 patients were compared by 2 quantitative methods of assessing myocardial ischemia. A computer-derived treadmill exercise score, based largely on the characteristics of exercise-induced ST-segment depression, was compared with a thallium exercise score. Both scores correlated well over a wide range of values (r = 0.71, p less than 0.001). Then, the treadmill exercise score was corrected (by adjusting the magnitude of the ST depression to a standardized R-wave amplitude of 12 mm in V5 and 8 mm in aVF) to determine if this would improve its correlation with the thallium exercise score. The patients were separated into 2 groups by R-wave amplitude: 53 had an RV5 of 9 to 17 mm and 32 had an RV5 less than 9 or greater than 17 mm. Correction of the treadmill exercise score for R-wave amplitude did not change the slope and intercepts of the regression line for patients with an RV5 amplitude of 9 to 17 mm, but did for those with an RV5 amplitude less than 9 or greater than 17 mm. In this latter group, R-wave correction changed the regression line from one that differed significantly from that of patients with less extreme RV5 voltage to one that was indistinguishable from it. Correction of the treadmill exercise score also increased the correlation coefficient from 0.54 to 0.68 in this group.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical studies with transdermal nitroglycerin

The short- and long-term effects of various Nitro-Dur formulations on performance and hemodynamics were studied in 15 men with stable angina pectoris who also had a positive treadmill exercise test. A treadmill exercise score (TES) was used that quantified the "ischemic" ST segment response to exercise. The score incorporated information that reflected the rapidity of evolution of ST segment depression during exercise and the time required for it to resolve after cessation of exercise. In early tests (n = 10) Nitro-Dur improved both the TES (by 31%: p less than 0.0001) and the time required for 1 mm ST segment depression (by 33%: p less than 0.0001). At all dosage levels, Nitro-Dur also decreased resting systolic blood pressure and increased resting heart rate. No dose-response patterns emerged. Changes in TES and time to ST segment depression were greater with sublingual nitroglycerin than they were with Nitro-Dur. In tests conducted after prolonged dosage (n = 5), the effects of Nitro-Dur on blood pressure and heart rate became attenuated at weeks 2 and 4, although cardiac responsiveness was preserved, as reflected in the increased time required before the occurrence of 1 mm ST segment depression. The latter effect was also observed with sublingual nitroglycerin. The clinical relevance of these data to the design of individual patient therapy is discussed.

Detection and quantification of previous myocardial infarction by exercise-redistribution tomographic thallium-201 scintigraphy

Although myocardial perfusion scintigraphy at rest accurately diagnoses myocardial infarction (MI), the prevalence and size of previous MI is overestimated by exercise-redistribution thallium-201 studies. A new, quantitative approach to the analysis of tomographic thallium-201 scintigrams was developed in order to determine whether the presence and extent of MI could be determined. Sixty patients undergoing cardiac catheterization for chest pain syndromes, including 28 with previous MI, were studied by exercise and 3-hour delayed thallium-201 scintigraphy, with use of the 7-pinhole tomographic technique. Circumferential profiles of the postexercise and 3-hour radiotracer distribution were generated from apical, midventricular and basal left ventricular slices. The 3-hour profile fell below normal limits in 24 of 28 patients (86%) with remote MI, but was also abnormal in 9 of 22 patients (41%) with coronary disease but no MI. All missed MIs were either inferior or subendocardial and were associated with normal ejection fractions. To distinguish between MI and slowly resolving ischemic defects, a quantitative approach was used. MI area was calculated as the area in which the 3-hour profile fell below the 3-hour normal limits, and a redistribution area in the MI zone was determined as the area between the postexercise and 3-hour profiles in the region where the 3-hour profile was abnormal. The MI area was 1,000 +/- 980 units in patients with MI, vs 79 +/- 120 units in patients without MI (p less than 0.001), whereas the redistribution area was higher in patients without MI (1,240 +/- 810 vs 430 +/- 400 units, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of seven-pinhole tomographic thallium-201 scintigrams: improved sensitivity and estimation of the extent of coronary involvement by evaluation of radiotracer uptake and clearance

Recent studies have shown that the sensitivity of conventional thallium-201 scintigraphy can be increased by the quantitative assessment of myocardial radiotracer clearance rates in conjunction with the evaluation of radionuclide uptake. In this study, a similar analysis of tomographic scintigrams was performed to determine the feasibility and value of this approach, particularly in estimating the extent of disease and detecting three vessel coronary involvement. Seventy patients undergoing cardiac catheterization for chest pain were studied by exercise and 3 hour delayed thallium-201 scintigrams using the seven-pinhole tomographic technique. Each study was evaluated by visual inspection of the tomographic sections and quantitative analysis. The latter approach consisted of comparing circumferential profiles of the initial post-exercise radionuclide uptake and the 3 hour clearance rates generated from each of three left ventricular slices with similar profiles representing the lower 95% confidence limits derived from 15 middle-aged volunteers. An abnormality was considered present when a patient's profile fell below these limits for a 30 degrees arc, and was ascribed to disease in a particular artery when it involved that vessel's usual distribution. Among the 61 patients without apparent primary myocardial or valvular disease, the diagnostic sensitivity of thallium scintigraphy was increased from 86% (43 of 50) to 96% (48 of 50) without a change in specificity (both 9 of 11 or 82%). More importantly, the quantitative approach permitted detection of 85% (107 of 126) of significantly obstructed coronary vessels compared with 47% (59 of 126) by visual analysis (p less than 0.001), again without sacrificing specificity (85 versus 87%).(ABSTRACT TRUNCATED AT 250 WORDS)

Improved efficacy of high-dose versus medium- and low-dose diltiazem therapy for chronic stable angina pectoris

The efficacy of therapy with diltiazem, 360 mg/day, was studied in 11 men with chronic, stable angina pectoris. An initial dose-titration schedule in which diltiazem was increased weekly from placebo to 120, 240 and 360 mg/day (Period I) was followed by a randomized, double-blind, 1-month crossover trial of placebo vs diltiazem at 360 mg/day (Period II). A computer-assisted treadmill exercise test was performed at the end of each dose and each 2-week crossover period. Diltiazem at 360 mg/day, compared with placebo (Period II), significantly improved exercise performance. Exercise duration to onset of chest pain increased 40% from 5.3 +/- 2.1 to 7.4 +/- 2.7 minutes (p less than 0.01). Time to reach 1 mm of ST-segment depression increased 33%, from 5.1 +/- 2.0 to 6.8 +/- 1.8 minutes (p less than 0.01). Total exercise duration increased 16%, from 7.5 +/- 2.0 to 8.7 +/- 2.0 minutes (p less than 0.005). A computer-derived quantitative treadmill exercise score improved 27%, from -13.1 +/- 9.4 to -9.5 +/- 7.6 units (p less than 0.005), and the ST-segment depression at peak exercise improved from -1.9 +/- 1.1 to -1.6 +/- 1.2 mm (p less than 0.05). Progressive improvement in these variables was seen during the single-blind dose-titration period between 120 and 240 mg/day and between 240 and 360 mg/day (Period I). Baseline heart rate (HR) and diastolic blood pressure (BP) in the supine and upright position were significantly lower with diltiazem than with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer-derived treadmill exercise score quantifies the degree of revascularization and improved exercise performance after coronary artery bypass surgery

A computer-derived treadmill exercise score (TES) that quantifies the severity of the ischemic ST response to exercise was used to detect noninvasively graft occlusion or the progression of new lesions after coronary artery bypass surgery. Three months after surgery TES completely normalized in 68% of patients and improved by more than 70% in another 18% of patients, thus reflecting excellent improvement in exercise-induced ischemia in 87% of patients. Surgical results correlated well with completeness of revascularization as shown by repeat coronary angiography. When TES, done serially up to 4 years after surgery, remained unchanged, grafts were patent and no new critical lesions had occurred. Deterioration in TES always predicted either late graft occlusion or appearance of new, high-grade lesions in the native vessels. Thus TES provides a new, accurate method that quantifies the ischemic response to exercise and detects graft occlusion or new obstructive lesions in the native coronary arteries.

Comparison of myocardial thallium-201 clearance after maximal and submaximal exercise: implications for diagnosis of coronary disease: concise communication

Recently the quantitation of regional thallium-201 clearance has been shown to increase the sensitivity of the scintigraphic detection of coronary disease. Although TI-201 clearance rates might be expected to vary with the degree of exercise, this relationship has not been explored. We therefore evaluated the rate of decrease in myocardial TI-201 activity following maximal and submaximal stress in seven normal subjects and 21 patients with chest pain, using the seven-pinhole tomographic reconstruction technique. In normals, the mean TI-201 clearance rate declined from 41% +/- 7 over a 3-hr period with maximal exercise to 25% +/- 5 after 3 hr at a submaximal level (p less than 0.001). Similar differences in clearance rates were found in the normally perfused regions of the left ventricle in patients with chest pain, depending on whether or not a maximal end point (defined as either the appearance of ischemia or reaching 85% of age-predicted heart rate) was achieved. In five patients who did not reach these end points, 3-hr clearance rates in uninvolved regions averaged 25% +/- 2, in contrast to a mean of 38% +/- 5 for such regions in 15 patients who exercised to ischemia or an adequate heart rate. These findings indicate that clearance criteria derived from normals can be applied to patients who are stressed maximally, even if the duration of exercise is limited, but that caution must be used in interpreting clearance rates in those who do not exercise to an accepted end point.

Oxygen enhances fusion of cultured chick embryo myoblasts

Fusion of mononucleate myoblasts to form multinucleated myotubes increases when skeletal muscle cells are grown in progressively higher oxygen concentrations (5%, 20%, and 40% oxygen). At four days of growth fusion of myoblasts (as expressed by the percent of all muscle nuclei that are located in myotubes) is 57 +/- 2% in 5% oxygen, 68 +/- 1% in 20% oxygen, and 78 +/- 2% in 40% oxygen (P less than 0.001). However, at a concentration of 40%, oxygen depresses the rate of cell division and thereby affects the number of myoblasts available for fusion. Thus, oxygen concentration significantly modifies growth of skeletal muscle in vitro. Its net effect on myotube formation results from the interaction of its separate effects to enhance cell fusion and to depress cell proliferation.

Poly(adenosine dephosphate ribose) metabolism and regulation of myocardial cell growth by oxygen

Control of the rate of cardiac cell division by oxygen occurs most probably by altering the redox state of a control substance, e.g. NAD(+)right harpoon over left harpoonNADH. NAD(+) (and not NADH) forms poly(ADP-ribose), an inhibitor of DNA synthesis, in a reaction catalysed by poly(ADP-ribose) polymerase. Lower partial pressure of oxygen, which increases the rate of division, would shift NAD(+)-->NADH, decrease poly(ADP-ribose) synthesis, and increase DNA synthesis. Chick-embryo heart cells grown in culture in 20% O(2) (in which they divide more slowly than in 5% O(2)) did exhibit greater poly(ADP-ribose) polymerase activity (+83%, P<0.001) than when grown in 5% O(2). Reaction product was identified as poly(ADP-ribose) by its insensitivity to deoxyribonuclease, ribonuclease, NAD glycohydrolase, Pronase, trypsin and micrococcal nuclease, and by its complete digestion with snake-venom phosphodiesterase to phosphoribosyl-AMP and AMP. Isolation of these digestion products by Dowex 1 (formate form) column chromatography and paper chromatography allowed calculation of average poly(ADP-ribose) chain length, which was 15-26% greater in 20% than in 5% O(2). Thus in 20% O(2) the increase in poly(ADP-ribose) formation results from chain elongation. Formation of new chains also occurs, probably to an even greater degree than chain elongation. Additionally, poly(ADP-ribose) polymerase has very different K(m) and V(max.) values and pH optima in 20% and 5% O(2). These data suggest that poly(ADP-ribose) metabolism participates in the regulation of heart-cell division by O(2), probably by several different mechanisms.