Heterogeneous myocardial catecholamine concentrations in patients with congestive heart failure

Heterogeneous cardiac sympathetic innervation gradients promote arrhythmogenesis in murine dilated cardiomyopathy

Ventricular arrhythmias (VAs) in heart failure are enhanced by sympathoexcitation. However, radiotracer studies of catecholamine uptake in failing human hearts demonstrate a proclivity for VAs in patients with reduced cardiac sympathetic innervation. We hypothesized that this counterintuitive finding is explained by heterogeneous loss of sympathetic nerves in the failing heart. In a murine model of dilated cardiomyopathy (DCM), delayed PET imaging of sympathetic nerve density using the catecholamine analog [11C]meta-Hydroxyephedrine demonstrated global hypoinnervation in ventricular myocardium. Although reduced, sympathetic innervation in 2 distinct DCM models invariably exhibited transmural (epicardial to endocardial) gradients, with the endocardium being devoid of sympathetic nerve fibers versus controls. Further, the severity of transmural innervation gradients was correlated with VAs. Transmural innervation gradients were also identified in human left ventricular free wall samples from DCM versus controls. We investigated mechanisms underlying this relationship by in silico studies in 1D, 2D, and 3D models of failing and normal human hearts, finding that arrhythmogenesis increased as heterogeneity in sympathetic innervation worsened. Specifically, both DCM-induced myocyte electrical remodeling and spatially inhomogeneous innervation gradients synergistically worsened arrhythmogenesis. Thus, heterogeneous innervation gradients in DCM promoted arrhythmogenesis. Restoration of homogeneous sympathetic innervation in the failing heart may reduce VAs.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

Depression in heart failure: biobehavioral mechanisms

The etiology, predictive value, and biobehavioral aspects of depression in heart failure (HF) are described in this article. Clinically elevated levels of depressive symptoms are present in approximately 1 out of 5 patients with HF. Depression is associated with poor quality of life and a greater than 2-fold risk of clinical HF progression and mortality. The biobehavioral mechanisms accounting for these adverse outcomes include biological processes (elevated neurohormones, autonomic nervous system dysregulation, and inflammation) and adverse health behaviors (physical inactivity, medication nonadherence, poor dietary control, and smoking). Depression often remains undetected because of its partial overlap with HF-related symptoms and lack of systematic screening. Behavioral and pharmacologic antidepressive interventions commonly result in statistically significant but clinically modest improvements in depression and quality of life in HF, but not consistently better clinical HF or cardiovascular disease outcomes. Documentation of the biobehavioral pathways by which depression affects HF progression will be important to identify potential targets for novel integrative behavioral and pharmacologic interventions.

Catecholamine metabolism: a contemporary view with implications for physiology and medicine

This article provides an update about catecholamine metabolism, with emphasis on correcting common misconceptions relevant to catecholamine systems in health and disease. Importantly, most metabolism of catecholamines takes place within the same cells where the amines are synthesized. This mainly occurs secondary to leakage of catecholamines from vesicular stores into the cytoplasm. These stores exist in a highly dynamic equilibrium, with passive outward leakage counterbalanced by inward active transport controlled by vesicular monoamine transporters. In catecholaminergic neurons, the presence of monoamine oxidase leads to formation of reactive catecholaldehydes. Production of these toxic aldehydes depends on the dynamics of vesicular-axoplasmic monoamine exchange and enzyme-catalyzed conversion to nontoxic acids or alcohols. In sympathetic nerves, the aldehyde produced from norepinephrine is converted to 3,4-dihydroxyphenylglycol, not 3,4-dihydroxymandelic acid. Subsequent extraneuronal O-methylation consequently leads to production of 3-methoxy-4-hydroxyphenylglycol, not vanillylmandelic acid. Vanillylmandelic acid is instead formed in the liver by oxidation of 3-methoxy-4-hydroxyphenylglycol catalyzed by alcohol and aldehyde dehydrogenases. Compared to intraneuronal deamination, extraneuronal O-methylation of norepinephrine and epinephrine to metanephrines represent minor pathways of metabolism. The single largest source of metanephrines is the adrenal medulla. Similarly, pheochromocytoma tumor cells produce large amounts of metanephrines from catecholamines leaking from stores. Thus, these metabolites are particularly useful for detecting pheochromocytomas. The large contribution of intraneuronal deamination to catecholamine turnover, and dependence of this on the vesicular-axoplasmic monoamine exchange process, helps explain how synthesis, release, metabolism, turnover, and stores of catecholamines are regulated in a coordinated fashion during stress and in disease states.

The usefulness of surface electrocardiogram as a prognostic predictor in children with idiopathic dilated cardiomyopathy

We investigated the interrelations between surface electrocardiographic changes and clinical outcomes in children with idiopathic dilated cardiomyopathy (DCMP). 33 patients (19 boys, 14 girls) were classified into two groups; group I (15) who were in poor clinical status or dead; and group II (18) who showed good clinical status. Group I had larger LV dimensions compared to group II (Gr I vs. Gr II; LVEDD, 52 +/-11 vs. 42+/-7 (mm); LVESD, 43+/-12 vs. 30+/-5 (mm); p<0.05). QRS duration was prolonged in Gr I compared to Gr II and normal (Gr I, 84+/-28; Gr II, 66+/-12; normal control, 67+/-9). The QRS duration was correlated with the dimensions of left ventricle (LV). Corrected QT and JT interval and dispersions of QT in the DCMP group showed a significant difference compared to the normal control, however there was no significant difference between Gr I and II. In conclusion, QRS duration was correlated with ventricular dimension and clinical outcome in children with idiopathic dilated cardiomyopathy. Irrespective of increased ventricular inhomogeneity, QT dispersion could not be used to predict long-term prognosis.

Relation of cardiac sympathetic innervation to proinflammatory cytokine levels in patients with heart failure secondary to idiopathic dilated cardiomyopathy

Experimental studies have shown that cytokine production by the heart may be regulated by sympathetic nervous system stimulation of cardiac beta-adrenergic receptors. Proinflammatory cytokine levels are increased in heart failure, whereas cardiac fixation of 123-I-metaiodobenzylguanidine (MIBG) has been used to study myocardial adrenergic innervation. This study was designed to assess the relation between cardiac MIBG uptake and circulating levels of proinflammatory cytokines in patients with idiopathic dilated cardiomyopathy (IDC). Forty-seven patients (12 women; mean age 56.5 +/- 9 years) with angiographically proved IDC, in New York Heart Association functional classes II to III, and who had left ventricular ejection fraction 30.6 +/- 9.5%, and 20 healthy controls were studied with planar MIBG. The early (10 minutes) and late (4 hours) heart to mediastinum uptake ratio and washout were calculated. Circulating plasma levels of interleukins (IL)-1 and IL-6, tumor necrosis factor-alpha, and solube receptors of TNF (sTNFR) I and II were measured. The patient group had significantly lower values of MIBG uptake at 10 minutes (p <0.001) and 4 hours (p <0.001) and higher washout (p <0.001) than the controls. Late MIBG uptake was significantly correlated with New York Heart Association class (r = -0.42, p = 0.02), left ventricular ejection fraction (r = 0.34, p = 0.01), left ventricular systolic wall stress (r = -0.40, p = 0.05), oxygen consumption at peak exercise (r = 0.32, p = 0.03), IL-1 (r = -0.55, p <0.001), TNF (r = -0.33, p = 0.02), and sTNFRII (r = -0.44, p = 0.001). Multivariate linear regression analysis revealed that MIBG at 4 hours was independently associated with IL-1 levels (p <0.001). Thus, reduced cardiac sympathetic innervation in heart failure is associated with elevated levels of inflammatory cytokines, suggesting that it has a potential inflammatory effect via modulation of the cardiac production of these cytokines.

Heart rate modulation by sympathetic nerves in dogs with heart failure

To clarify heart rate modulation by the sympathetic nervous system, dogs with naturally acquired and experimentally induced heart failure were examined. Heart rate and plasma catecholamine concentrations were measured in clinically healthy dogs (control dogs) and dogs with mitral regurgitation (MR) during a resting period, a standing period, a period of standing in a medical examination room (to which the dogs were unaccustomed), a running period, and a period of recovery after running. The heart rate and plasma catecholamine concentration increased in control dogs during the standing period and the medical examination room period, relative to the resting period. However, dogs with MR did not exhibit any clear increase in heart rate or catecholamine concentration under these light stress conditions. Running stress increased plasma catecholamine levels in control dogs; however, dogs with MR did not exhibit any significant changes. Thirty-two dogs with naturally acquired heart disease were classified as grades I to III on the ISACHC scale. The degree of increase in heart rate and plasma catecholamine levels in dogs with naturally acquired heart failure depended on their degree of heart failure. In conclusion, an increased heart rate and an activated sympathetic nervous system were observed, even in mild heart failure. This chronically activated sympathetic activity is expected to increase myocardial oxygen consumption, myocardial hypertrophy, and fibrosis, and to portend a poorer prognosis in heart failure.

Differential pre- and postsynaptic effects of desipramine on cardiac sympathetic nerve terminals in RHF

Right heart failure (RHF) is characterized by chamber-specific reductions of myocardial norepinephrine (NE) reuptake, beta-receptor density, and profiles of cardiac sympathetic nerve ending neurotransmitters. To study the functional linkage between NE uptake and the pre- and postsynaptic changes, we administered desipramine (225 mg/day), a NE uptake inhibitor, to dogs with RHF produced by tricuspid avulsion and progressive pulmonary constriction or sham-operated dogs for 6 wk. Animals receiving no desipramine were studied as controls. We measured myocardial NE uptake activity using [(3)H]NE, beta-receptor density by [(125)I]iodocyanopindolol, inotropic responses to dobutamine, and noradrenergic terminal neurotransmitter profiles by glyoxylic acid-induced histofluorescence for catecholamines, and immunocytochemical staining for tyrosine hydroxylase and neuropeptide Y. Desipramine decreased myocardial NE uptake activity and had no effect on the resting hemodynamics in both RHF and sham animals but decreased myocardial beta-adrenoceptor density and beta-adrenergic inotropic responses in both ventricles of the RHF animals. However, desipramine treatment prevented the reduction of sympathetic neurotransmitter profiles in the failing heart. Our results indicate that NE uptake inhibition facilitates the reduction of myocardial beta-adrenoceptor density and beta-adrenergic subsensitivity in RHF, probably by increasing interstitial NE concentrations, but protects the cardiac noradrenergic nerve endings from damage, probably via blockade of NE-derived neurotoxic metabolites into the nerve endings.

Beneficial effects of metoprolol on myocardial sympathetic function: Evidence from a randomized, placebo-controlled study in patients with congestive heart failure

BACKGROUND

We sought to investigate whether beta-blockers exert a presynaptic effect in the myocardium as measured by 123I-metaiodobenzylguanidine.

METHODS

The study comprised 59 patients with congestive heart failure, New York Heart Association class II or III, and left ventricular ejection fraction <35%. After an open label titration phase, patients were randomized to their maximal tolerable dose of metoprolol or placebo. Myocardial MIBG uptake was measured before the titration phase and after 6 months of treatment. Other parameters were maximal oxygen consumption, 6-minute walking test, plasma neurohormones, and echocardiographic parameters.

RESULTS

We found a 21.9% increase in mean myocardial MIBG uptake after 6 months of treatment with metoprolol. In contrast, MIBG uptake decreased by 7.8% in the placebo group (P = 0.03 compared with metoprolol). Left ventricular end-diastolic diameter decreased from 74 +/- 11 mm to 67 +/- 10 mm (P <.05, within-group comparison) and LVEF increased from 25.3% +/- 7.4% to 32.6% +/- 9.6% (P <.05, within-group comparison) in the metoprolol group. Placebo-treated patients showed no significant changes. Comparison of changes in left ventricular end-diastolic diameter and LVEF between metoprolol and placebo did not reach statistical significance (P = 0.2).

CONCLUSIONS

This randomized, placebo-controlled study demonstrates that metoprolol has a presynaptic effect as measured by myocardial MIBG scintigraphy in both ischemic and nonischemic cardiomyopathy.

Interactions between phospholamban and beta-adrenergic drive may lead to cardiomyopathy and early mortality

BACKGROUND

Relieving the inhibition of sarcoplasmic reticular function by phospholamban is a major target of beta-adrenergic stimulation. Chronic beta-adrenergic receptor activity has been suggested to be detrimental, on the basis of transgenic overexpression of the receptor or its signaling effectors. However, it is not known whether physiological levels of sympathetic tone, in the absence of preexisting heart failure, are similarly detrimental.

METHODS AND RESULTS

Transgenic mice overexpressing phospholamban at 4-fold normal levels were generated, and at 3 months, they exhibited mildly depressed ventricular contractility without heart failure. As expected, transgenic cardiomyocyte mechanics and calcium kinetics were depressed, but isoproterenol reversed the inhibitory effects of phospholamban on these parameters. In vivo cardiac function was substantially depressed by propranolol administration, suggesting enhanced sympathetic tone. Indeed, plasma norepinephrine levels and the phosphorylation status of phospholamban were elevated, reflecting increased adrenergic drive in transgenic hearts. On aging, the chronic enhancement of adrenergic tone was associated with a desensitization of adenylyl cyclase (which intensified the inhibitory effects of phospholamban), the development of overt heart failure, and a premature mortality.

CONCLUSIONS

The unique interaction between phospholamban and increased adrenergic drive, elucidated herein, provides the first evidence that compensatory increases in catecholamine stimulation can, even in the absence of preexisting heart failure, be a primary causative factor in the development of cardiomyopathy and early mortality.

Cardiac autonomic denervation in congestive heart failure: comparison of Chagas' heart disease with other dilated cardiomyopathy

Congestive heart failure (CHF) is associated with activation of the cardiac sympathetic nerves. However, impairment of the sympathetic nerve terminals in patients with CHF has been indicated by studies showing reduction of cardiac norepinephrine uptake and stores. This investigation studies the histochemical evaluation of the sympathetic nerve terminals in CHF. The cardiac parasympathetic innervation was also studied to address the question of specificity of the presumed sympathetic denervation. Nineteen patients with CHF underwent cardiac transplantation or partial ventriculectomy, which provided the heart tissue. In 11 of them, the dilated cardiomyopathy was associated with Chagas' disease. Inflammatory process and fibrosis were studied histologically. The sympathetic and parasympathetic nerve fibers were visualized through histochemical techniques for, respectively, catecholamines and acetylcholinesterase activity. By using a computer-assisted morphometric program, the inflammation, fibrosis, and parasympathetic innervation were quantified. Moderate to severe fibrosing myocarditis characterized the hearts of the chagasic patients. In cardiomyopathies not associated with Chagas' disease, the inflammation was discrete, if present, but the amount of fibrosis was similar to that found in Chagas' cardiomyopathy. Reduction of both kinds of nerve terminals occurred in the heart of all patients. The parasympathetic denervation was proven to be more severe in chagasic cardiomyopathy. Our data on the heart innervation indicate a progressive autonomic denervation in heart failure. In Chagas' heart disease, the denervation seems to be more severe or rapid, probably because of the sustained inflammatory process.

Super-normal 201Tl retention in hibernating myocardium: an ex-vivo study using the failing human heart

OBJECTIVE

Although the relationship between delayed 201Tl distribution and blood flow in acutely ischemic and infarcted myocardium has been widely explored in the experimental setting, its behaviour in chronically hypoperfused dysfunctioning human myocardium has not yet been evaluated.

METHODS

In tissue samples of excised failing hearts taken from ischemic (IHD) patients and idiopathic dilated cardiomyopathy (IDC) controls, we evaluated the relationship between delayed 201Tl retention (4 h redistribution), blood flow (assessed by means of 99mTc-labelled human albumin microspheres injected during transplantation) and biochemically-assessed fibrosis. 201Tl activity was expressed as the percent of the activity in the region with highest flow and the least fibrosis.

RESULTS

Fibrosis and 201Tl activity were inversely related (r = -0.62, P = 0.0001). In IDC controls, low flows corresponded to uniformly preserved 201Tl retention. In IHD, 46 segments with flows < or = 0.60 ml.min-1.g-1 and 20 segments with flows > 0.60 ml.min-1.g1 showed matching delayed 201Tl retention and flow values; in the remaining 27, there was a disproportionately high tracer accumulation in comparison with flow (flow/201Tl mismatch). Despite significantly less fibrosis and lower flows, the mismatch segments showed significantly greater. 201Tl activity than the segments with concordantly high tracer retention and flow values. Conversely, at equivalent flow rates, the mismatch regions had less fibrosis than the areas with concordantly depressed 201Tl activity and perfusion.

CONCLUSIONS

This super-normal 201Tl retention in hibernating myocardium may indicate a mechanism of cell adaptation to chronic hypoperfusion.

Mechanisms of arrhythmias in heart failure

The diagnosis of heart failure infers a bad prognosis. Mortality is high and many patients die suddenly. Ventricular arrhythmias, commonly observed in patients with heart failure, are thought to underlie at least some of these sudden deaths. The mechanism of arrhythmias occurring in the setting of heart failure is still unclear. Experimental evidence points to a higher tendency for failing myocardium to develop delayed and early afterdepolarization-induced triggered activity and automaticity. Conditions favoring reentry also have been described in failing hearts. Modulating factors such as sympathetic activation, electrolyte disturbances, and chronic stretch are present in the setting of heart failure and may favor all of the mentioned mechanisms of arrhythmias. Clinical evaluation of arrhythmias in patients and animals with heart failure and the effects of pharmacologic treatment of ventricular arrhythmias in patients with depressed left ventricular function further accentuate that more than one mechanism of arrhythmia may be operating in heart failure and underscore the importance of modulating factors such as sympathetic activation and stretch.

Myocardial clearance of I-123 metaiodobenzylguanidine in dilated cardiomyopathy

We present the results of sequential imaging studies conducted in two patients with dilated cardiomyopathy whose responses to long-term beta-blocker therapy differed. We evaluated the time course of the myocardial clearance and the heart to upper mediastinal ratios of I-123 metaiodobenzylguanidine (MIBG) scintigraphy. In the first patient, the left ventricular ejection fraction as well as the clinical symptoms were improved by long-term beta-blocker therapy with a concurrent normalization of the myocardial clearance and the heart to upper mediastinal ratio of I-123 MIBG scintigraphy. The myocardial clearance and the upper mediastinal ratio of I-123 MIBG indicated no improvement in the second patient, and the left ventricular function did not change. The myocardial clearance and the heart to upper mediastinal ratio of I-123 MIBG scintigraphy were useful in evaluating the efficacy of long-term beta-blocker therapy in patients with dilated cardiomyopathy.

Differential changes in sympathetic activity in left and right ventricles in congestive heart failure after myocardial infarction

Although congestive heart failure subsequent to myocardial infarction is known to be associated with increased sympathetic activity, very little information regarding changes in the sympathetic nerves in the left and right ventricles at various stages after infarction is available. Male Sprague-Dawley rats were subjected to coronary artery ligation and studied 4 and 8 weeks later; these animals had mild and moderate stages of congestive heart failure. A sham group, without coronary ligation, was used as control. Four weeks after myocardial infarction, plasma and ventricular (left and right) epinephrine (EPI), unlike norepinephrine (NE), were markedly increased. Whereas plasma catecholamine (EPI and NE) levels were increased 8 weeks after infarction, NE concentration in the left ventricle was unchanged but EPI concentration was increased in comparison with sham control. The right ventricle showed an increased level of both NE and EPI 8 weeks after infarction. Measurement of the rate of change in the specific activity of NE (NE turnover) in the left and right ventricles 8 weeks after infarction revealed an increase in NE turnover in the left ventricle, without any changes in the right ventricle. The concentration of EPI, unlike NE, was increased in the kidney, spleen, and brain 8 weeks after coronary occlusion. These results are interpreted to mean that congestive heart failure caused by myocardial infarction is associated with differential changes in the status of sympathetic nerves in the left and right ventricles; sympathetic activity is increased only in the left ventricle, whereas the right ventricle may play an adaptive role by increasing catecholamine stores during the development of heart failure.

Cardiac iodine-123 metaiodobenzylguanidine uptake in animals with diabetes mellitus and/or hypertension

The aim of the present study was to evaluate the use of the noradrenaline analogue iodine-123 metaiodobenzylguanidine ([123I]MIBG) for the assessment of cardiac sympathetic activity in the presence of diabetes mellitus and/or hypertension in animal models. One model used Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) rendered diabetic at 12 weeks of age by an intravenous injection of streptozotocin (STZ). The other model used lean and obese Zucker rats. In all groups basic haemodynamic values were established and animals received an intravenous injection of 50 microCi [123I]MIBG. Initial myocardial uptake and wash-out rates of [123I]MIBG were measured scintigraphically during 4 h. After sacrifice, plasma noradrenaline and left cardiac ventricular beta-adrenoceptor density was determined. The diabetic state, both in STZ-treated rats (direct induction) and in obese Zucker rats (genetic induction), appeared to induce a lower cardiac density of beta-adrenoceptors, indicative of increased sympathetic activity. Cardiac [123I]MIBG then showed increased wash-outs, thereby confirming enhanced noradrenergic activity. This parallism of results led to the conclusion that [123I]MIBG wash-out measurements could provide an excellent tool to assess cardiac sympathetic activity non-invasively. However, in hypertension (WKY vs SHR), both parameters failed to show parallelism: no changes in beta-adrenoceptor density were found, whereas [123I]MIBG wash-out rate was increased. Thus, either [123I]MIBG washout or beta-adrenoceptor density may not be a reliable parameter under all circumstances to detect changes in the release of noradrenaline. Changes in the initial uptake of [123I]MIBG were observed as well. This may be a good marker for the disappearance of cardiac innervation, but it seems not to be a good parameter for distinguishing between loss of sympathetic innervation and enhanced uptake of noradrenaline in pathological conditions.

Cardiac sympathetic nerve function in congestive heart failure

BACKGROUND

Increased availability of norepinephrine (NE) for activation of cardiac adrenoceptors (increased cardiac adrenergic drive) and depletion of myocardial NE stores may contribute to the pathophysiology and progression of congestive heart failure. This study used a comprehensive neurochemical approach to examine the mechanisms responsible for these abnormalities.

METHODS AND RESULTS

Subjects with and without congestive heart failure received intravenous infusions of [(3)H]NE. Cardiac spillover, reuptake, vesicular-axoplasmic exchange, and tissue stores of NE were assessed from arterial and coronary venous plasma concentrations of endogenous and [(3)H]-labeled NE and dihydroxyphenylglycol. Tyrosine hydroxylase activity was assessed from plasma dopa, and NE turnover was assessed from measurements of NE metabolites. NE release and reuptake were both increased in the failing heart; however, the efficiency of NE reuptake was reduced such that cardiac spillover of NE was increased disproportionately more than neuronal release of NE. Cardiac NE stores were 47% lower and the rate of vesicular leakage of NE was 42% lower in the failing than in the normal heart. Cardiac spillover of dopa and NE turnover were increased similarly in congestive heart failure.

CONCLUSIONS

Increased neuronal release of NE and decreased efficiency of NE reuptake both contribute to increased cardiac adrenergic drive in congestive heart failure. Decreased vesicular leakage of NE, secondary to decreased myocardial stores of NE, limits the increase in cardiac NE turnover in CHF. Decreased NE store size in the failing heart appears to result not from insufficient tyrosine hydroxylation but from chronically increased NE turnover and reduced efficiency of NE reuptake and storage.

Abnormalities of cardiac sympathetic function in pacing-induced heart failure as assessed by [123I]metaiodobenzylguanidine scintigraphy

BACKGROUND

Increased activity of the sympathetic nervous system contributes significantly to the pathophysiology of heart failure. However, cardiac efferent sympathetic function has not been well characterized in this disorder. In this study, we evaluated cardiac sympathetic innervation using [123I]metaiodobenzylguanidine (MIBG) and compared this with left ventricular (LV) tissue norepinephrine concentration and myocardial perfusion, assessed by 201Tl, in a canine model of heart failure.

METHODS AND RESULTS

Planar and tomographic cardiac imaging was performed for MIBG and 201Tl in 23 dogs: 8 normal dogs (group 1) and 15 dogs with heart failure induced by right ventricular pacing at 250 beats per minute either continuously for 3 weeks (group 2) or intermittently for 7 weeks (group 3). Plasma and LV tissue norepinephrine concentrations were also measured. Scintigraphic studies in group 2 demonstrated reduced cardiac MIBG activity at heart failure (0.17 +/- 0.04 versus 0.29 +/- 0.05 counts per megabecquerel per pixel at baseline, mean +/- SD; P = .0001), whereas thallium activity was unchanged from baseline. This reduction in cardiac MIBG activity with heart failure was associated with increased intraimage variability in the distribution of MIBG activity (21 +/- 8% versus 13 +/- 7% at baseline, mean +/- SD; P = .0001). The MIBG heart-to-lung ratio was calculated for all groups to control for the inhibitory effect that plasma norepinephrine has on the neuronal uptake of MIBG. There was a positive correlation between LV tissue norepinephrine and the MIBG heart-to-lung ratio (r = .67; P < .001; n = 22), for which the group 2 heart failure animals had the lowest values. No relation existed between plasma norepinephrine concentration and the MIBG heart-to-lung ratio. In addition, regional LV tissue norepinephrine concentration and MIBG activity were both lowest at the apex in normal (group 1) and heart failure (group 2) dogs. The MIBG heart-to-lung ratio also correlated inversely with cardiac filling pressure (r = -.59; P < .05) and heart rate (r = -.65; P < .01) and positively with cardiac output (r = .53; P < .05).

CONCLUSIONS

Heart failure is associated with severe cardiac adrenergic dysfunction manifested by reduced MIBG activity and increased heterogeneity in the LV distribution of MIBG. Furthermore, MIBG scintigraphy is a simple noninvasive method for assessing global and regional LV tissue norepinephrine levels.

Beta-blockers in heart failure: promising or proved?

Despite recent improvements in the management of congestive heart failure, the prognosis of many patients with this condition remains poor. The level of neurohormonal activation appears to be predictive of survival, and clinical studies indicate that inhibition of overactivated neurohormonal systems may be beneficial. Activation of the renin-angiotensin-aldosterone system is well documented in heart failure, and angiotensin-converting enzyme inhibition now has an established role in treatment based on evidence of hemodynamic, symptomatic and mortality benefit. Sympathetic nervous system activation also occurs as a compensatory mechanism in heart failure but with long-term deleterious effects. Increasing evidence suggests that beta-adrenergic blockade can produce hemodynamic and symptomatic improvement in heart failure of idiopathic or ischemic etiology. Trials of beta-adrenergic blocking agents in patients after myocardial infarction suggest a beneficial effect on mortality, even among those with heart failure. However, there remains uncertainty as to how generalizable are the results from the postinfarction trials, particularly in the current therapeutic environment with routine angiotensin-converting enzyme inhibitor therapy. Appropriately powered randomized, controlled trials are required to determine precisely the balance of benefit and risk resulting from long-term beta-blocker therapy in patients with heart failure of ischemic and other etiology.

Total-body and myocardial substrate oxidation in congestive heart failure

Congestive heart failure is a condition associated with increased plasma norepinephrine levels, which have been demonstrated to impair glucose handling. In the present study, 10 patients suffering from congestive heart failure and 10 healthy age- and body mass index-matched subjects were submitted to a hyperinsulinemic (insulin infusion rate, 0.5 mU/kg.min-1) glucose clamp, while simultaneous D-3H-glucose infusion and indirect calorimetry allowed for determination of glucose turnover parameters and substrate oxidation, respectively. On a separate day, basal local (myocardial) indirect calorimetry was also performed. Our data demonstrate that in congestive heart failure, fasting myocardial glucose oxidation (Gox) was inhibited with a simultaneous increase in lipid oxidation (Lox). In our patients, a significant decrease in total-body insulin-stimulated glucose metabolism (31.0 +/- 0.5 v 20.3 +/- 0.4 mumol/kg.min-1, P < .01) and nonoxidative glucose metabolism (18.9 +/- 1.1 v 11.0 +/- 0.5 mumol/kg.min-1, P < .05) was also found. Such latter changes were also associated with a simultaneous overdrive of Lox (0.4 +/- 0.2 v 1.9 +/- 0.2 mumol/kg.min-1, P < .02) that was correlated with an enhanced availability of plasma free fatty acids (FFAs).

Myocardial carnitine metabolism in congestive heart failure induced by incessant tachycardia

Persistent tachycardia induces congestive heart failure (CHF), but the mechanism(s) of progressive ventricular dysfunction is (are) unclear. This study was designed to define possible metabolic causes of myocardial dysfunction in rapid ventricular pacing induced CHF. Twelve adult mongrel dogs were paced to 250 beats/min for 19 days. Plasma carnitine, norepinephrine and renin were measured at 0, 1, 2, and 3 weeks. Myocardial high energy phosphates, carnitine, glycogen, glucose, non-collagenous protein and collagen were measured at 19 days. Cardiac output, arterial pressure and pulmonary wedge pressure, measured at baseline and with CHF, showed a decrease in cardiac output and increase in pulmonary wedge pressure. Neurohumoral activation was evident by progressively increasing plasma norepinephrine and renin activity and depletion of myocardial norepinephrine. Plasma free carnitine rose significantly from 12.6 +/- 2.0 control to 28.3 +/- 3.8 nmol/ml at 19 days (p < 0.001), whereas myocardial total carnitine was lower in paced than in control dogs (6.0 +/- 1.9 vs. 14.1 +/- 3.5 nmol/mg non-collagenous protein, p < 0.001). Myocardial ATP ATP and ADP were unchanged, while AMP decreased 22%, and creatine phosphate decreased 30% compared to control animals. Myocardial glucose was normal but glycogen was decreased 54% (p < 0.005). The low myocardial carnitine and elevated plasma carnitine in pacing induced CHF suggests altered carnitine transport or membrane integrity.

Sympathetic dysfunction in heart failure

CHF is a common, complex and life-threatening clinical syndrome. It is widely accepted that enhanced peripheral vascular tone plays a major role in the pathophysiology of CHF. Increased activity of the sympathetic nervous system is one of the most important factors responsible for the increased afterload in CHF. This increase in sympathetic activity occurs early in the course of development of CHF. Efferent sympathetic activity is distributed in a non-uniform way in CHF, with significant increases to the heart and kidney but normal activity to some other organs such as the lung. Increased renal sympathetic activity contributes significantly to altered neural haemodynamics, sodium and water retention, and modulation of the actions of other vasoactive hormones. The regional alteration in sympathetic activity may be largely responsible for the changes in resting regional blood flow to different organs in CHF and the maldistribution of blood flow that occurs during the stress of exercise. Disordered function of cardiovascular reflexes is observed in CHF and may contribute to disordered sympathetic function. In CHF there are significant interactions between the sympathetic nervous system and other humoral systems such as the renin-angiotensin system, AVP, ANP, endothelin and renal DA. The various drugs used in the treatment of CHF have different effects on sympathetic activity: digitalis and ACE inhibitors tend to suppress activity while diuretics may have the opposite effect. Following cardiac transplantation, there is a prompt return of sympathetic function towards normal, although the heart may remain significantly denervated for a long time, with gradual reinnervation. Cyclosporin therapy tends to increase sympathetic activity and this may contribute to post-transplant hypertension.

Beta-adrenergic neuroeffector abnormalities in the failing human heart are produced by local rather than systemic mechanisms

In order to investigate the general cause of beta-adrenergic receptor neuroeffector abnormalities in the failing human heart, we measured ventricular myocardial adrenergic receptors, adrenergic neurotransmitters, and beta-adrenergic receptor-effector responses in nonfailing and failing hearts taken from nonfailing organ donors, subjects with endstage biventricular failure due to idiopathic dilated cardiomyopathy (IDC), and subjects with primary pulmonary hypertension (PPH) who exhibited isolated right ventricular failure. Relative to nonfailing PPH left ventricles, failing PPH right ventricles exhibited (a) markedly decreased beta 1-adrenergic receptor density, (b) marked depletion of tissue norepinephrine and neuropeptide Y, (c) decreased adenylate cyclase stimulation in response to the beta agonists isoproterenol and zinterol, and (d) decreased adenylate cyclase stimulation in response to Gpp(NH)p and forskolin. These abnormalities were directionally similar to, but generally more pronounced than, corresponding findings in failing IDC right ventricles, whereas values for these parameters in nonfailing left ventricles of PPH subjects were similar to values in the nonfailing left ventricles of organ donors. Additionally, relative to paired nonfailing PPH left ventricles and nonfailing right ventricles from organ donors, failing right ventricles from PPH subjects exhibited decreased adenylate cyclase stimulation by MnCl2. These data indicate that: (a) Adrenergic neuroeffector abnormalities present in the failing human heart are due to local mechanisms; systemic processes do not produce beta-adrenergic neuroeffector abnormalities. (b) Pressure-overloaded failing right ventricles of PPH subjects exhibit decreased activity of the catalytic subunit of adenylate cyclase, an abnormality not previously described in the failing human heart.

Metabolic and cardiovascular benefits deriving from beta-adrenergic blockade in chronic congestive heart failure

Ten patients with congestive heart failure were given metoprolol (50 mg/day) or placebo during a double-blind, crossover, randomized study. After a run-in period of 4 weeks, metoprolol and placebo were administered over a period of 3 months, which was separated by a washout period of 4 weeks. At the end of the run-in, metoprolol, and placebo periods, all patients underwent metabolic (oral glucose tolerance and hyperinsulinemic glucose clamp tests) and noninvasive cardiologic (New York Heart Association classification, bimodal echocardiographic left ventricular end-diastolic determination, maximal oxygen consumption, left ventricular radionuclide ejection fraction) tests. Our results show that beta-adrenergic blockade significantly enhances insulin-mediated suppression of hepatic glucose output (p less than 0.005) and increase in glucose uptake (p less than 0.01) with a concurrent improvement in New York Heart Association functional class (p less than 0.05) and the multistage exercise treadmill test score (p less than 0.05). After administration of metoprolol all changes in glucose turnover parameters were found to correlate with the decrease in basal plasma free fatty acid levels. In conclusion, our findings confirm the beneficial cardiologic effects of beta-adrenergic blockade in congestive heart failure and demonstrate that metoprolol is also useful for reversing the metabolic damage caused by exaggerated plasma norepinephrine levels.

Myocardial catecholamine and neuropeptide Y depletion in failing ventricles of patients with idiopathic dilated cardiomyopathy. Correlation with beta-adrenergic receptor downregulation

BACKGROUND

Myocardial adrenergic neurotransmitters and beta-adrenergic receptor levels were measured in left and right ventricular myocardial specimens obtained from 30 patients with biventricular failure resulting from idiopathic dilated cardiomyopathy.

METHODS AND RESULTS

Nonfailing myocardium obtained from 12 organ donors provided control data. Norepinephrine, dopamine, and neuropeptide Y concentrations were significantly decreased in failing compared with nonfailing control hearts. The mean ratio of dopamine to norepinephrine and of dopamine to neuropeptide Y in failing hearts was also significantly decreased compared with nonfailing control hearts. Compared with nonfailing control hearts, Bmax and beta 1-receptor density were significantly decreased in failing hearts and there were weak but significantly positive correlations of Bmax and beta 1-adrenergic receptors with norepinephrine, dopamine, and neuropeptide Y.

CONCLUSIONS

Norepinephrine and its cotransmitter neuropeptide Y are depleted in failing human ventricular myocardium. Decreased norepinephrine stores correlate weakly with beta 1-adrenergic receptor downregulation consistent with the hypothesis that norepinephrine depletion occurs in response to increased adrenergic drive. Decreased dopamine relative to norepinephrine implies that an abnormality of dopamine conversion to norepinephrine is not present in failing human heart.

Comparison of the haemodynamic effects of dopexamine and dobutamine in patients with severe congestive heart failure

Dopexamine hydrochloride is a novel compound with properties of DA1-dopaminergic and beta 2-adrenergic receptor agonism and neuronal noradrenaline uptake inhibition. It has been shown to produce beneficial renal and haemodynamic effects in patients with severe heart failure. We compared the haemodynamic effects of dopexamine (0.5 to 6 micrograms/kg/min) with those of dobutamine (5 to 25 micrograms/kg/min) in 9 patients with severe congestive heart failure. The two drugs were similar in their effects at peak infusion rates: heart rate increased (dopexamine 87 +/- 17 to 100 +/- 14; dobutamine 91 +/- 18 to 103 +/- 17 min-1), cardiac index increased (dopexamine 1.7 +/- 0.5 to 2.8 +/- 1.1; dobutamine 1.8 +/- 0.5 to 3.0 +/- 1.1 l.min-1.m-2) and systemic vascular resistance decreased (dopexamine 1553 +/- 221 to 1117 +/- 432; dobutamine 1721 +/- 347 to 1280 +/- 433 dyne.s.cm-5). Neither drug affected pulmonary artery wedge pressure (dopexamine 24 +/- 6 to 22 +/- 6; dobutamine 25 +/- 9 to 24 +/- 10 mm Hg). Dopexamine had significantly lower peak effects on left ventricular stroke work index (dopexamine 20 +/- 9, dobutamine 27 +/- 15 g.m.m-2, P less than 0.05) and cardiac power output (dopexamine 0.71 +/- 0.36, dobutamine 0.93 +/- 0.46 W, P less than 0.05). These haemodynamic effects, due largely to vasodilatation but with some contributory positive inotropy, indicate that dopexamine will be useful in the acute treatment of congestive heart failure.

Usefulness of dopexamine hydrochloride versus dobutamine in chronic congestive heart failure and effects on hemodynamics and urine output

The hemodynamic effects of dopexamine hydrochloride and dobutamine were compared during dose-response infusions of dopexamine (1.0 to 4.0 micrograms/kg/min) and dobutamine (2.5 to 10.0 micrograms/kg/min) and during 48-hr infusions at doses producing initial matched increases in cardiac output. Thirty-three patients with severe, stable, chronic congestive heart failure (CHF) (New York Heart Association class III to IV) participated. Both drugs produced an increase in cardiac index, brought about by increased stroke volume index and heart rate, and systemic vasodilatation. The relative contribution of these mechanisms differed, dopexamine proving the more potent vasodilator. The effects of dopexamine were maintained without variation during the 48-hr infusion, apart from a reduction in the increase in heart rate. The effects of dobutamine, while remaining above control at most time-points during the 48-hr infusion, attenuated toward control values. Dopexamine also appeared to promote increased urine output and creatinine clearance during the 48-hr infusion. Both drugs were well tolerated. Dopexamine elicited larger peak hemodynamic effects at dosages that had equivalent effects on cardiac output, and favorable renal responses, and demonstrated no long-term attenuation of effect.

Current therapeutic principles in the acute management of severe congestive heart failure

The phrase "heart failure" encompasses many clinical entities. The therapeutic principles determining the treatment of these entities vary according to the etiology of congestive heart failure (CHF), the existing hemodynamics, and the mode of action of different drugs. In acute CHF due to myocardial ischemia, intracellular acidosis and the accumulation of phosphate may be the initial underlying causes of contractile failure while, minutes later, lack of high-energy compounds may be an important contributory factor. The cause of contractile failure in chronic syndromes is less well understood. There is evidence for the desensitization of beta receptors on the cell surface but the precise location of the defect is unclear. The receptors may be down-regulated but, in addition, abnormalities have been reported in several other parts of the contractile pathway including the contractile proteins and the sarcoplasmic reticulum. Deficiency of cyclic adenosine monophosphate has also been suggested as a mechanism of contractile failure. In both acute and chronic CHF, there is a redistribution of blood flow to the body organs. Of particular significance is the reduction of blood flow to the kidneys, and a reversal of this defect is one of the major therapeutic objectives. Positive inotropic drugs, vasodilators and drugs altering relaxation of the heart, have been evaluated in the treatment of CHF. Pure inotropic drugs can cause tachycardia, ischemia and "metabolic exhaustion" of the myocardium. The most advantageous profile for an "inotropic" drug in many patients with CHF would be a drug combining systemic vasodilatation, renal vasodilatation, increased relaxation of the myocardium only a mild positive inotropic effect and no chronotropic effect.