Cytokines and nitric oxide synthase inhibitor as mediators of adrenergic refractoriness in cardiac myocytes

Impaired heart rate regulation and depression of cardiac chronotropic and dromotropic function in polymicrobial sepsis

The scope of cardiac pathophysiology in sepsis has not been fully defined. Accordingly, we evaluated the effects of sepsis on heart rate (HR), HR variability, and conduction parameters in a murine model of sepsis. Electrocardiograms were recorded noninvasively from conscious mice before and after cecal ligation and puncture (CLP) or sham surgery. Responses of isolated atria to tyramine and isoproterenol were quantified to assess the functional state of sympathetic nerves and postjunctional sensitivity to adrenergic stimulation. Cecal ligation and puncture mice had lower HR compared with sham at 16 to 18 h postsurgery (sham, 741 ± 7 beats/min; CLP, 557 ± 31 beats/min; n = 6/group; P < 0.001), and there was significant prolongation of the PR, QRS, and QTc intervals. Slowing of HR and conduction developed within 4 to 6 h after CLP and were preceded by a decrease in HR variability. Treatment of CLP mice with isoproterenol (5 mg/kg, intraperitoneally) at 25 h after surgery failed to increase HR or decrease conduction intervals. The lack of in vivo response to isoproterenol cannot be attributed to hypothermia because robust chronotropic and inotropic responses to isoproterenol were evoked from isolated atria at 25 °C and 30 °C. These findings demonstrate that impaired regulation of HR (i.e., reduced HR variability) develops before the onset of overt cardiac rate and conduction changes in septic mice. Subsequent time-dependent decreases in HR and cardiac conduction can be attributed to hypothermia and would contribute to decreased cardiac output and organ perfusion. Because isolated atria from septic mice showed normal responsiveness to adrenergic stimulation, we conclude that impaired effectiveness of isoproterenol in vivo can be attributed to reversible effects of systemic factors on adrenergic receptors and/or postreceptor signaling.

The interface between monitoring and physiology at the bedside

Hemodynamic instability as a clinical state represents either a perfusion failure with clinical manifestations of circulatory shock or heart failure or 1 or more out-of-threshold hemodynamic monitoring values, which may not necessarily be pathologic. Different types of causes of circulatory shock require different types of treatment modalities, making these distinctions important. Diagnostic approaches or therapies based on data derived from hemodynamic monitoring assume that specific patterns of derangements reflect specific disease processes, which respond to appropriate interventions. Hemodynamic monitoring at the bedside improves patient outcomes when used to make treatment decisions at the right time for patients experiencing hemodynamic instability.

Associations of Heart Rate With Inflammatory Markers Are Modulated by Gender and Obesity in Older Adults

BACKGROUND

Faster resting heart rate (HR), which is associated with inflammation and elevated cortisol levels, is a risk factor for excess cardiovascular morbidity and mortality. Obesity is associated with increased cardiovascular morbidity and mortality, inflammation, and elevated cortisol levels. The aim of the present study was to evaluate the interaction of Body Mass Index (BMI) with inflammation and cortisol in modulating HR in older subjects.

METHODS

We analyzed data of 895 participants aged 65+ enrolled in the "InCHIANTI" study, in sinus rhythm, and not taking beta blockers or digoxin. Linear regression was performed to assess the adjusted association between HR, IL-6, and cortisol levels. The model was also analyzed stratifying for BMI tertiles. Logistic regression was adopted for evaluating the association of HR exceeding the mean value with Il-6 and serum cortisol.

RESULTS

According to multivariable linear regression, IL-6 and cortisol levels were associated with HR (B = 1.42, 95% CI = 0.43-2.42; p = .005 and B = .34, 95% CI = 0.17-.51; p < .0001, respectively). The association was significant only among women in the highest BMI tertile (B = 4.16, 95% CI = 1.40-6.91; p = .003 for IL-6 and B = .57, 95% CI = 0.14-1.01; p = .010 for cortisol). Logistic regression confirmed that IL-6 and cortisol levels were associated with HR above the mean value in the highest BMI tertile (OR = 2.13, 95% CI = 1.15-3.97; p = .009 and OR = 1.14, 95% CI = 1.03-1.25; p = .009, respectively).

CONCLUSIONS

Faster HR is associated with proinflammatory state in elderly patients; this association seems to be limited to women with higher BMI.

Clinician observation of physiological trend monitoring to identify late-onset sepsis in preterm infants

AIM

To determine whether trends in routinely collected physiological variables can be used retrospectively to classify infants according to the presence or absence of late-onset neonatal sepsis.

METHODS

Case control study. Thirty infants born < or =32 weeks of gestation who developed late-onset sepsis were matched with 30 controls for gestational and postnatal age but remained sepsis free. For each infant, 25 clinicians inspected 48 h of routine monitoring of heart rate, respiratory rate and oxygen saturation. Clinicians were asked to determine whether the recording was obtained from an infant who did or did not develop sepsis and also indicate how confident they were in their judgement. Clinicians were stratified into three groups by professional role.

RESULTS

The median correct assignment of infant's recordings was 67% (IQR 62-72). When very confident, this improved to 82% (IQR 67-88). Overall sensitivity was 53% (IQR 43-63) and specificity 80% (IQR 67-87). Advanced neonatal nurse practitioners consistently assigned babies to the correct group more often than other professional groups.

CONCLUSION

The simple observation physiological trend graphs can classify infants according to the presence or absence of late-onset neonatal sepsis. The accuracy of this method is good to strong but varies with experience of neonatal intensive care.

Inducible nitric oxide synthase attenuates adrenergic signaling in alcohol fed rats

Chronic, excessive alcohol consumption is associated with myocardial dysfunction in humans. The molecular mechanisms and cellular signaling pathways contributing to this cardiac dysfunction remain largely unknown. This study examined the effects of chronic alcohol consumption on myocardial function and cardiac myocyte signaling pathways. Adult male rats were fed a commercially prepared diet containing either ethanol (13 g/kg/d) or isocaloric control diet for 1 month. In vivo hemodynamics were measured in awake rats after inserting a catheter tip in the left ventricle under general anesthesia. Ventricular dysfunction was evidenced in awake, alcohol-fed rats by increased left ventricular end diastolic pressure, decreased systolic developed left ventricular pressure, and decreases in both positive and negative dp/dt compared with controls. Cardiac myocytes isolated from alcohol-fed rats also demonstrated an attenuated response to the beta-adrenergic agonist, isoproterenol, compared to controls. This response was significantly reversed by the nitric oxide synthase (NOS) inhibitor, N-monomethyl-L-arginine (L-NMMA). Western analyses confirmed inducible nitric oxide synthase (iNOS) protein synthesis in cardiac myocytes isolated from alcohol fed rats. It is therefore concluded that chronic alcohol ingestion results in iNOS-mediated attenuation of adrenergic signaling and depression in both systolic and diastolic function in rats.

ROLE OF BACTERIAL ENDOTOXIN IN CHRONIC HEART FAILURE

Proinflammatory cytokines are now thought to play a key role in the pathophysiology of chronic heart failure, driving both symptomatic presentation and disease progression. We propose that this proinflammatory state, in turn, may be sustained through a chronic release of enterically derived bacterial endotoxin. Human trials have indicated that bacterial decontamination of the gut with concomitant decrease in lipopolysaccharide (LPS) has a positive outcome on heart disease patients. Antiendotoxin antibodies may thus represent therapeutic agents in this setting. Previously, antiendotoxin antibodies were targeted to the inner hydrophobic lipid A moiety of endotoxin in an attempt to neutralize its toxicity. These antibodies failed because they lacked specificity and bound to LPS weakly. In contrast, our studies on antiendotoxin antibodies have revealed that antibodies targeted to the hydrophilic oligosaccharides of the endotoxin have the potential to bind specifically with high affinity. Development of immunotherapeutics that can reduce systemic LPS or other agents, such as bactericidal/permeability-increasing protein that can neutralize LPS and limit inflammation safely, will enable the role of LPS in chronic heart failure to be elucidated and may pave the way to develop a new generation of effective therapeutic agents that may be directed to the treatment of chronic heart failure.

Heart Rate Characteristics Monitoring for Neonatal Sepsis

While heart rate variability has been measured in many clinical settings and has offered insights into how HR is controlled, rarely has it offered unique information that has led to changes in patient management. We review our experience in developing continuous HR characteristics monitoring to aid in the early diagnosis of sepsis in premature infants in the neonatal intensive care unit. A predictive algorithm, developed at one center and validated at another, has led to diagnosis and treatment of this subacute and potentially catastrophic illness prior to appearance of symptoms of severe illness.

Abnormal heart rate characteristics are associated with neonatal mortality

Estimating the risk of in-hospital mortality in the newborn intensive care unit can provide important information for health-care providers, and illness severity scores have been devised to provide mortality risk estimates. Calculation of illness severity scores is time-consuming, and the information used to predict mortality is collected only for the first 12 to 24 h of life. A noninvasive continuous measure that uses information collected throughout the hospitalization and that requires no data entry could be less costly and more informative. We have previously shown that the abnormal heart rate characteristics (HRC) of reduced variability and transient decelerations accompany neonatal illness such as late-onset sepsis. We hypothesized that more frequent and severe abnormal HRC are associated with an increased risk of death. We tested this hypothesis in two ways. Using data on infants older than 7 d of age, we first determined the association of the HRC index with death in the next week. Second, we devised a cumulative HRC score and determined its association with in-hospital death. There were 37 deaths in the 685 patients. The major findings were 1) the HRC index showed highly significant association with death in the succeeding 7 d (receiver-operating characteristic area > 0.7, p < 0.001), and 2) the cumulative HRC was highly significantly associated with neonatal in-hospital mortality (receiver-operating characteristic area > 0.80, p < 0.001). In both analyses, HRC added information to birth weight, gestational age, and postnatal age (p < 0.01). The HRC index provides independent information about the risk of neonatal death in the upcoming 7 d, and the cumulative HRC is an estimate of the risk of in-hospital neonatal mortality.

Inflammatory mediators and reversible myocardial dysfunction

A variety of seemingly unrelated clinical conditions manifest the same effects on the heart. These effects include: (1) reversible myocardial dysfunction, (2) beta-adrenergic desensitization, and (3) activation of inflammatory mediators. We provide evidence supporting a role for cytokines, mitogen activated protein kinases (MAP kinases), and nitric oxide (NO) as common mediators of reversible myocardial dysfunction and beta-adrenergic desensitization. Data from animal models and human studies support a pathogenic role for these inflammatory mediators in ischemic as well as non-ischemic myocardial dysfunction. It is suggested that compensatory cellular programs are activated to provide short-term protection from brief periods of ischemia and infection. Continuous activation of these compensatory pathways leads to cardiomyopathy and chronic (congestive) heart failure. Elucidating the signaling pathways involved has the potential to provide the opportunity to exploit the cardioprotective advantages of these agents without bearing the burden of excessive stimulation.

Sample entropy analysis of neonatal heart rate variability

Abnormal heart rate characteristics of reduced variability and transient decelerations are present early in the course of neonatal sepsis. To investigate the dynamics, we calculated sample entropy, a similar but less biased measure than the popular approximate entropy. Both calculate the probability that epochs of window length m that are similar within a tolerance r remain similar at the next point. We studied 89 consecutive admissions to a tertiary care neonatal intensive care unit, among whom there were 21 episodes of sepsis, and we performed numerical simulations. We addressed the fundamental issues of optimal selection of m and r and the impact of missing data. The major findings are that entropy falls before clinical signs of neonatal sepsis and that missing points are well tolerated. The major mechanism, surprisingly, is unrelated to the regularity of the data: entropy estimates inevitably fall in any record with spikes. We propose more informed selection of parameters and reexamination of studies where approximate entropy was interpreted solely as a regularity measure.

Interactions between cytokines and neurohormonal systems in the failing heart

The prognosis for patients with congestive heart failure (CHF) has been improved as a result of the use of angiotensin converting enzyme inhibitors and beta-adrenergic receptor blockers. The success of these therapies underscores the pathogenic role of neurohormonal activation in CHF. Clinical and experimental evidence supports a pathophysiologic role for pro-inflammatory cytokines and nitric oxide (NO) in the effects of angiotensin II and norepinephrine in CHF. Potential mechanism(s) responsible for the effects of these immunomodulators can be explained on the basis of established principles of myocardial excitation contraction coupling (E-C). A novel hypothesis is proposed that cytokines and NO-mediated alterations in E-C coupling contribute to the reversible myocardial depression and beta-adrenergic desensitization observed in a diverse group of clinical conditions that activate host inflammatory responses, including CHF. Basic studies into cytokine signaling pathways in cardiac myocytes have the potential to provide important new insights relevant to the design of new management strategies for the treatment of congestive heart failure patients.

Toward the early diagnosis of neonatal sepsis and sepsis-like illness using novel heart rate analysis

BACKGROUND AND OBJECTIVE

Abrupt clinical deterioration because of sepsis is a major cause of morbidity and mortality in neonates, and earlier diagnosis should improve therapy of this potentially catastrophic illness. In practice, clinical signs and laboratory data have not been perceived as sensitive or specific for early stages of sepsis. Because heart rate characteristics (HRC) are abnormal during fetal distress and neonatal illness, we hypothesized that abnormal HRC might precede the clinical diagnosis of neonatal sepsis, adding independent information to standard clinical parameters.

METHODS

In the neonatal intensive care unit at the University of Virginia, we prospectively studied infants admitted from August 1995 to April 1999 who were at risk for developing sepsis. Infants in the sepsis (culture-positive) and sepsis-like illness (culture-negative) groups had an abrupt clinical deterioration that raised clinical suspicion of infection and prompted physicians to obtain blood cultures and start antibiotic therapy. Infants without sepsis raised no clinical suspicion of illness and had no cultures obtained. We measured novel characteristics-moments and percentiles-of normalized heart rate (HR) time series for 5 days before and 3 days after sepsis, sepsis-like illness, or a random time in controls. We also calculated the Score for Neonatal Acute Physiology (SNAP) and the Neonatal Therapeutic Intervention Scoring System (NTISS) as clinical scores of the severity of illness.

RESULTS

There were 46 episodes of culture-positive sepsis in 40 patients and 27 episodes of culture-negative sepsis-like illness in 23 patients. We analyzed 29 control periods in 26 patients. Infants with sepsis and sepsis-like illness had lower birth weights and gestational ages and higher SNAP and NTISS scores than did infants without sepsis. The most important new finding was that the infants in the sepsis and sepsis-like illness groups had increasingly abnormal HRC for up to 24 hours preceding their abrupt clinical deterioration. The abnormal HRC were reduced baseline variability and short-lived decelerations in HR. These abnormalities led to significant changes in HRC measures, for example, the third moment (skewness:.59 +/-.10 for sepsis and.51 +/-. 12 for sepsis-like illness, compared with -.10 +/-.13 for control over the 6 hours before abrupt deterioration). Culture-positive and culture-negative patients had similar HRC and clinical scores, including a significant rise in SNAP in the 24 hours before the event. Multivariable logistic regression analysis showed that HRC and clinical scores independently added information in distinguishing infants with sepsis and sepsis-like illness from control patients in the 24 hours before abrupt deterioration.

CONCLUSIONS

Newborn infants who had abrupt clinical deterioration as a result of sepsis and sepsis-like illness had abnormal HRC and SNAP that worsened over 24 hours before the clinical suspicion of sepsis. A strategy for monitoring these parameters in infants at risk for sepsis and sepsis-like illness might lead to earlier diagnosis and more effective therapy.heart rate variability, neonatal sepsis, Score for Neonatal Acute Physiology, Neonatal Therapeutic Intervention Scoring System, newborn.

Acute effect of tumor necrosis factor-alpha is minimal on mechanics but significant on energetics in blood-perfused canine left ventricles

OBJECTIVES

We hypothesized that tumor necrosis factor-alpha (TNF-alpha) acutely alters left ventricular mechanoenergetics in blood-perfused hearts. To test this hypothesis, we examined the relation between left ventricular mechanics and energetics, both before and after infusion of TNF-alpha.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory.

SUBJECTS

Nine isolated, blood-perfused canine hearts.

INTERVENTIONS

Recombinant human TNF-alpha (90 microg/min) was infused into the coronary circulation of the isolated hearts for 20 mins.

MEASUREMENTS AND MAIN RESULTS

In the isolated, cross-circulated, blood-perfused canine left ventricles, left ventricular contractility was assessed through measurement of end-systolic elastance (Ees). Energetics were examined in terms of the end-systolic pressure-volume area-myocardial oxygen consumption (MVo2) relation. TNF-alpha concentration in coronary venous blood was >1000 ng/mL throughout the experiments. Nevertheless, infusion of TNF-alpha barely affected contractility acutely, i.e., there was a minimal decrease during the infusion (8.1+/-2.8% at 10 mins, p < .01) and a minimal increase after the infusion (11.2+/-2.5% at 10 mins, p< .01). Neither did the TNF-alpha infusion affect the slope of the end-systolic pressure-volume area-MVo2 relation. This finding indicated that the chemomechanical conversion efficiency remained unchanged. However, TNF-alpha infusion significantly increased the oxygen cost of contractility by 40% (1.25+/-0.13 vs. 1.75+/-0.24 mL oxygen.mL/mm Hg/beat, p< .05), indicating that MVo2 for the excitation-contraction coupling increased.

CONCLUSIONS

TNF-alpha minimally alters left ventricular mechanics, but significantly changes energetics. The latter effect may result from changes in intracellular calcium handling.