beta-adrenergic receptor regulation and left ventricular function in idiopathic dilated cardiomyopathy

Subcellular β-Adrenergic Receptor Signaling in Cardiac Physiology and Disease

ABSTRACT

Adrenergic receptors are critical regulators of cardiac function with profound effects on cardiac output during sympathetic stimulation. Chronic stimulation of the adrenergic system of the heart under conditions of cardiac stress leads to cardiac dysfunction, hypertrophy, and ultimately failure. Emerging data have revealed that G protein-coupled receptors in intracellular compartments are functionally active and regulate distinct cellular processes from those at the cell surface. β2 adrenergic receptors internalize onto endosomes in various cell types where they have recently been shown to continue to stimulate cAMP production to selectively regulate gene expression. Other studies have identified β1 adrenergic receptors at the nuclear envelope and the Golgi apparatus. Here, we discuss data on signaling by β1 and β2 adrenergic receptors in the heart and the possible influence of their subcellular locations on their divergent physiological functions in cardiac myocytes and in cardiac pathology. Understanding the relative roles of these receptors at these locations could have a significant impact on pharmacological targeting of these receptors for the treatment of heart failure and cardiac diseases.

Different Responses of Muscle Sympathetic Nerve Activity to Dapagliflozin Between Patients With Type 2 Diabetes With and Without Heart Failure

Background Sodium-glucose cotransporter 2 inhibitors improve cardiovascular outcomes in patients with diabetes with and without heart failure (HF). However, their influence on sympathetic nerve activity (SNA) remains unclear. The purpose of this study was to evaluate the effect of sodium-glucose cotransporter 2 inhibitors on SNA and compare the responses of SNA to sodium-glucose cotransporter 2 inhibitors in patients with type 2 diabetes with and without HF. Methods and Results Eighteen patients with type 2 diabetes, 10 with HF (65.4±3.68 years) and 8 without HF (63.3±3.62 years), were included. Muscle SNA (MSNA), heart rate, and blood pressure were recorded before and 12 weeks after administration of dapagliflozin (5 mg/day). Sympathetic and cardiovagal baroreflex sensitivity were simultaneously calculated. Brain natriuretic peptide level increased significantly at baseline in patients with HF than those without HF, while MSNA, blood pressure, and hemoglobin A1c did not differ between the 2 groups. Fasting blood glucose and homeostatic model assessment of insulin resistance did not change in either group after administering dapagliflozin. MSNA decreased significantly in both groups. However, the reduction in MSNA was significantly higher in patients with HF than patients with non-HF (-20.2±3.46 versus -9.38±3.65 bursts/100 heartbeats; P=0.049), which was concordant with the decrease in brain natriuretic peptide. Conclusions Dapagliflozin significantly decreased MSNA in patients with type 2 diabetes regardless of its blood glucose-lowering effect. Moreover, the reduction in MSNA was more prominent in patients with HF than in patients with non-HF. These results indicate that the cardioprotective effects of sodium-glucose cotransporter 2 inhibitors may, in part, be attributed to improved SNA.

Caloric restriction reduces sympathetic activity similar to beta-blockers but conveys additional mitochondrio-protective effects in aged myocardium

Increased activation of sympathetic nervous system contributes to congestive heart failure (CHF) progression, and inhibition of sympathetic overactivation by beta-blockers is successful in CHF patients. Similarly, caloric restriction (CR) reduces sympathetic activity but mediates additional effects. Here, we compared the cardiac effects of CR (− 40% kcal, 3 months) with beta-blocker therapy (BB), diuretic medication (DF) or control diet in 18-months-old Wistar rats. We continuously recorded blood pressure, heart rate, body temperature and activity with telemetric devices and analysed cardiac function, activated signalling cascades and markers of apoptosis and mitochondrial biogenesis. During our study, left ventricular (LV) systolic function improved markedly (CR), mildly (BB) or even deteriorated (DF; control). Diastolic function was preserved by CR and BB but impaired by DF. CR reduced blood pressure identical to DF and BB and heart rate identical to BB. Plasma noradrenaline was decreased by CR and BB but increased by DF. Only CR reduced LV oxidative damage and apoptosis, induced AMPK and Akt phosphorylation and increased mitochondrial biogenesis. Thus, additive to the reduction of sympathetic activity, CR achieves protective effects on mitochondria and improves LV function and ROS damage in aged hearts. CR mechanisms may provide additional therapeutic targets compared to traditional CHF therapy.

The protective effect of isosteviol sodium on cardiac function and myocardial remodelling in transverse aortic constriction rat

Pathological hypertrophy contributes to heart failure and there is not quite effective treatment to invert this process. Isosteviol has been shown to protect the heart against ischaemia-reperfusion injury and isoproterenol-induced cardiac hypertrophy, but its effect on pressure overload-induced cardiac hypertrophy is still unknown. Pressure overload induced by transverse aortic constriction (TAC) causes cardiac hypertrophy in rats to mimic the pathological condition in human. This study examined the effects of isosteviol sodium (STVNa) on cardiac hypertrophy by the TAC model and cellular assays in vitro. Cardiac function test, electrocardiogram analysis and histological analysis were conducted. The effects of STVNa on calcium transient of the adult rat ventricular cells and the proliferation of neonatal rat cardiac fibroblasts were also studied in vitro. Cardiac hypertrophy was observed after 3-week TAC while the extensive cardiac dysfunction and electronic remodelling were observed after 9-week TAC. Both STVNa and sildenafil (positive drug) treatment reversed the two process, but STVNa appeared to be more superior in some aspects and did not change calcium transient considerably. STVNa also reversed TAC-induced cardiac fibrosis in vivo and TGF-β1-induced fibroblast proliferation in vitro. Moreover, STVNa, but not sildenafil, reversed impairment of the autonomic nervous system induced by 9-week TAC.

Sepsis With Preexisting Heart Failure: Management of Confounding Clinical Features

Preexisting heart failure (HF) in patients with sepsis is associated with worse clinical outcomes. Core sepsis management includes aggressive volume resuscitation followed by vasopressors (and potentially inotropes) if fluid is inadequate to restore perfusion; however, large fluid boluses and vasoactive agents are concerning amid the cardiac dysfunction of HF. This review summarizes evidence regarding the influence of HF on sepsis clinical outcomes, pathophysiologic concerns, resuscitation targets, hemodynamic interventions, and adjunct management (ie, antiarrhythmics, positive pressure ventilatory support, and renal replacement therapy) in patients with sepsis and preexisting HF. Patients with sepsis and preexisting HF receive less fluid during resuscitation; however, evidence suggests traditional fluid resuscitation targets do not increase the risk of adverse events in HF patients with sepsis and likely improve outcomes. Norepinephrine remains the most well-supported vasopressor for patients with sepsis with preexisting HF, while dopamine may induce more cardiac adverse events. Dobutamine should be used cautiously given its generally detrimental effects but may have an application when combined with norepinephrine in patients with low cardiac output. Management of chronic HF medications warrants careful consideration for continuation or discontinuation upon development of sepsis, and β-blockers may be appropriate to continue in the absence of acute hemodynamic decompensation. Optimal management of atrial fibrillation may include β-blockers after acute hemodynamic stabilization as they have also shown independent benefits in sepsis. Positive pressure ventilatory support and renal replacement must be carefully monitored for effects on cardiac function when HF is present.

Dual Behavior of Exosomes in Septic Cardiomyopathy

Sepsis is one of the main causes of ICU hospitalization worldwide, with a high mortality rate, and is associated with a large number of comorbidities. One of the main comorbidities associated with sepsis is septic cardiomyopathy. This process occurs mainly due to mechanisms of damage in the cardiovascular system that will lead to changes in cardiovascular physiology, such as decreased Ca²⁺ response, mitochondrial dysfunction and decreased β-adrenergic receptor response. Within this process the exosomes play an important role in the pathophysiology of this disease, in which the exosomal content is related to mechanisms that will trigger its development. After platelet activation through ROS exposition, exosomes containing high concentrations of NADPH are released in heart blood vessels, those exosomes will be internalized in endothelial cells leading to cell death and cardiac dysfunction. On the opposite, exosomes derived from mesenchymal stem cells contain miR-223, that have anti-inflammatory properties, are released in less quantities in septic patients causing an imbalance that leads to cardiac dysfunction.

Novel role of phosphodiesterase inhibitors in the management of end-stage heart failure

In advanced heart failure (HF), chronic inotropic therapy with intravenous milrinone, a phosphodiesterase III inhibitor, is used as a bridge to advanced management that includes transplantation, ventricular assist device implantation, or palliation. This is especially true when repeated attempts to wean off inotropic support result in symptomatic hypotension, worsened symptoms, and/or progressive organ dysfunction. Unfortunately, patients in this clinical predicament are considered hemodynamically labile and may escape the benefits of guideline-directed HF therapy. In this scenario, chronic milrinone infusion may be beneficial as a bridge to introduction of evidence based HF therapy. However, this strategy is not well studied, and in general, chronic inotropic infusion is discouraged due to potential cardiotoxicity that accelerates disease progression and proarrhythmic effects that increase sudden death. Alternatively, chronic inotropic support with milrinone infusion is a unique opportunity in advanced HF. This review discusses evidence that long-term intravenous milrinone support may allow introduction of beta blocker (BB) therapy. When used together, milrinone does not attenuate the clinical benefits of BB therapy while BB mitigates cardiotoxic effects of milrinone. In addition, BB therapy decreases the risk of adverse arrhythmias associated with milrinone. We propose that advanced HF patients who are intolerant to BB therapy may benefit from a trial of intravenous milrinone as a bridge to BB initiation. The discussed clinical scenarios demonstrate that concomitant treatment with milrinone infusion and BB therapy does not adversely impact standard HF therapy and may improve left ventricular function and morbidity associated with advanced HF.

Relationship between chronotropic incompetence and β-blockers based on changes in chronotropic response during cardiopulmonary exercise testing

Background

Chronotropic incompetence (CI), an attenuated heart rate (HR) response to exercise, is common in patients with cardiovascular disease. The aim of this study was to assess changes in the chronotropic response (CR) during cardiopulmonary exercise testing (CPET) in patients undergoing cardiac rehabilitation and investigate the effects of β-blockers.

Methods

Patients undergoing cardiac rehabilitation performed CPET. Failure to achieve 80% of the age-predicted maximal HR (APMHR) defined CI. Values of the metabolic chronotropic relationship (MCR) were calculated from the ratio of the HR reserve to metabolic reserve at 4 stages, warm-up (MCR-Wu), anaerobic threshold (MCR-AT), respiratory compensation (MCR-Rc), and peak point (MCR-Pk), using the Wilkoff model. In patients who showed an increase in MCR at ≥ 3 of the 4 exercise stages, CR was considered to have improved.

Results

Patients with high BNP levels (≥ 80 pg/ml) had a lower MCR at all stages compared with those with low BNP levels (< 80 pg/ml). Of the 80 patients, 47 showed an increase in both peak VO₂ and AT, and of these 31 (66.0%) were taking β-blockers. Improvement in CR was observed in 30 of 47 patients with CI, and 70% of these were taking β-blockers. In patients not taking β-blockers, MCR-AT was lower than MCR-Rc, whereas in those taking β-blockers MCR-AT was higher than MCR-Rc.

Conclusions

An attenuated HR response may occur during the early stages of exercise. The HR response according to the presence or absence of β-blockers is clearly identifiable by comparing MCR-AT and MCR-Rc using the Wilkoff model.

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We have standardized definitions of CI objectively based on the Wilkoff model.

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An attenuated HR response may occur during the early stages of exercise.

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MCR values without β-blockers decreased from warm-up to AT and increased after AT.

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MCR values with β-blockers decreased from warm-up to Rc and increased after Rc.

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Cardiac rehabilitation increased peak VO₂ with an improvement in HR response.

Effect of β-blocker cessation on chronotropic incompetence and exercise tolerance in patients with advanced heart failure

BACKGROUND

Chronotropic incompetence is defined as the inability to reach 80% of heart rate (HR) reserve or 80% of the maximally predicted HR during exercise. The presence of chronotropic incompetence is associated with reduced peak oxygen consumption, and rate-responsive pacing therapy is under investigation to improve exercise capacity in heart failure (HF). However, uncertainty exists about whether chronotropic incompetence and reduced exercise tolerance in HF are attributable to β-blockade.

METHODS AND RESULTS

Subjects with HF and receiving long-term β-blocker therapy underwent cardiopulmonary exercise tolerance testing under 2 conditions in random sequence: (1) after a 27-hour washout period (Off-BB) and (2) 3 hours after β-blocker ingestion (On-BB). Norepinephrine levels were drawn at rest and at peak exercise. β1-response to norepinephrine was assessed using the chronotropic responsiveness index: ΔHR/Δlog norepinephrine. Nineteen patients with systolic HF (left ventricular ejection fraction, 22.8±7.7%) were enrolled. Mean age was 49.4±12.3 years. Average carvedilol equivalent dose was 29.1±17.0 mg daily. Peak HR off/on β-blockers was 62.7±18.7% and 51.4±18.2% HR reserve (P<0.01) and 79.1±11.0% and 70.3±12.3% maximally predicted HR (P<0.01). For the Off-BB and On-BB conditions, the respiratory exchange ratios were 1.05±0.06 and 1.05±0.10 (P=0.77), respectively, confirming maximal and near identical effort in both conditions. The peak oxygen consumption was 16.6±3.34 and 15.9±3.31 mL/kg/min (P=0.03), and the chronotropic responsiveness index was 19.3±7.2 and 16.2±7.1 (P=0.18).

CONCLUSIONS

Acute β-blocker cessation does not normalize the chronotropic response to exercise in patients with advanced HF and chronotropic incompetence.

Dilated cardiomyopathy with hypertension: prevalence and response to high-dose β1-adrenoceptor antagonist therapy

1. The aim of the present study was to investigate the prevalence of hypertension in patients with dilated cardiomyopathy (DCM) and to determine the tolerance and efficacy of a high dose of the β1-adrenoceptor antagonist metoprolol in the long-term treatment of DCM patients. 2. The prevalence of hypertension in DCM patients (n = 362) and age-matched controls (n = 401) was evaluated and compared. To investigate the effects of metoprolol, DCM patients were divided into hypertensive (DCM-H) or normotensive (DCM-N) subgroups. Metoprolol was administered at a starting dosage of 6.25 mg/day and increased gradually to 250 mg/day or the maximum tolerable dose. Blood pressure (BP), heart rate (HR), left ventricular (LV) end-diastolic dimension (LVEDD), left atrial end-diastolic dimension (LAEDD), LV ejection fraction (LVEF), LV posterior wall thickness (LVPWT) and ventricular septal thickness (VST) were determined at baseline and 6 and 12 months after metoprolol treatment. 3. The prevalence of hypertension was significantly higher in DCM patients than in age-matched controls (32.8 vs 20.1%, respectively; P < 0.01). Resting HR and a family history of hypertension were highest in the DCM-H group. There were no significant differences in age, gender and occupation between the DCM-H, DCM-N and age-matched control groups. 4. The tolerable dose for metoprolol was significantly higher in the DCM-H group than the DCM-N group (189.6 ± 14.8 vs 133.9 ± 12.0 mg/day, respectively; P < 0.05). Metoprolol significantly reduced BP and HR in the DCM-H group and improved LVEDD, LAEDD and LVEF in all DCM patients, with a greater effect seen in the DCM-H group. 5. In conclusion, DCM patients have a higher prevalence of hypertension than the general population. Patients in the DCM-H subgroup were characterized by a higher resting HR and a family history of hypertension and were more tolerant of and more responsive to metoprolol treatment. These data suggest that this subgroup of DCM patients could have higher sympathetic nerve activity and is suitable for treatment with a higher dose of metoprolol.

Carvedilol increases blood pressure response to phenylephrine infusion in heart failure subjects with systolic dysfunction: evidence of improved vascular alpha1-adrenoreceptor signal transduction

INTRODUCTION

Alpha(1)-adrenergic receptor (alpha(1)-AR) stimulation produces smooth muscle contraction, vasoconstriction, and myocyte hypertrophy, suggesting a potential therapeutic role for alpha(1)-AR antagonists to reduce cardiac workload and myocardial hypertrophy. Preliminary reports suggest that vascular alpha(1)-ARs are desensitized in heart failure (HF) in a manner similar to myocardial beta(1)-ARs. We examined alpha(1)-AR signal transduction by repeat phenylephrine (PE) infusions in patients with HF receiving chronic carvedilol therapy.

METHODS

Twelve subjects with HF not currently receiving beta-blockers were up-titrated to maximum tolerable doses of carvedilol. Subjects underwent alpha(1)-AR stimulation testing at study baseline, 2 weeks after each dose titration, and 6 months after maintenance of maximum carvedilol dose. Phenylephrine infusions began at 0.5 microg kg(-1) min(-1), with dose titrations every 10 minutes, to a maximum of 5 microg kg(-1) min(-1). Phenylephrine dose response was evaluated by the PE rate required to elicit a 20 mm Hg increase in systolic blood pressure (BP), designated PS(20).

RESULTS

All doses of carvedilol significantly reduced preinfusion measures of heart rate, systolic BP, diastolic BP, and mean arterial pressure. However, carvedilol also produced a paradoxical trend toward PS(20) reduction (indicating increased PE response) that reached significance at the completion of carvedilol dose titration (PS(20) ratio vs baseline = 0.78; P < .001). All effects were maintained over a 6-month treatment period with no evidence of tolerance.

CONCLUSIONS

Increasing BP response to PE infusion suggests improvement in vascular alpha(1)-AR signal transduction with chronic carvedilol therapy. This effect is evident despite no detectable tolerance to preinfusion BP reductions. The varying affinities of alpha(1)-AR subtypes for carvedilol and PE may have contributed to this finding.

Ile164 variant of beta2-adrenoceptor does not influence outcome in heart failure but may interact with beta blocker treatment

BACKGROUND

The Ile164 variant of the beta2-adrenoceptor has been shown to alter cardiovascular phenotypes and adversely affect survival in heart failure patients.

AIMS

We aimed to replicate this observation by genotyping a cohort of 451 heart failure patients for the Ile164 polymorphism.

METHODS

Patient outcome was recorded over a median follow-up period of 3.09 years, and genotypes were derived by multiplex amplification refractory mutation system PCR.

RESULTS

Genotypes were obtained for 443 patients, and 3.2% of these (14 patients) were heterozygous for the Ile164 SNP. Demographic data, cardiac function and neurohormonal profiles did not differ between genotype groups. Ile164 genotype did not significantly affect survival in this cohort (Thr164 homozygotes 48.9%, Ile164 heterozygous 42.9%, p=0.66), although multivariate analysis suggested that beta-blocker treatment may negatively impact survival in the heterozygote group.

CONCLUSION

This study suggests that the Ile164 polymorphism of the beta2-adrenoceptor does not have a major impact on outcome in individuals with heart failure, although it's potential interaction with beta-blockers requires further examination.

Cardiac dysfunction and heart failure are associated with abnormalities in the subcellular distribution and amounts of oligomeric muscle LIM protein

Prolonged hemodynamic overload results in cardiac hypertrophy and failure with detrimental changes in myocardial gene expression and morphology. Cysteine-rich protein 3 or muscle LIM protein (MLP) is thought to be a mechanosensor in cardiac myocytes. Therefore, the subcellular location of MLP may have functional implications in health and disease. Our hypothesis is that MLP becomes mislocalized after prolonged overload, resulting in impaired mechanosensing in cardiac myocytes. Using the techniques of biochemical subcellular fractionation and immunocytochemistry, we found MLP exhibits oligomerization in the membrane and cytoskeleton of cultured cardiac rat neonatal myocytes. Nuclear MLP was always monomeric. MLP translocated to the nucleolus in response to 10% cyclic stretch at 1 Hz for 48 h. This was associated with a threefold increase in S6 ribosomal protein ( P < 0.01; n = 3 cultures). Adenoviral overexpression of MLP also resulted in a twofold increase in S6 protein, suggesting that MLP can activate ribosomal protein synthesis in the nucleolus. In ventricles from aortic-banded and myocardially infarcted rat hearts, nuclear MLP increased by twofold ( P < 0.01; n = 7) along with a significant decrease in the nonnuclear oligomeric fraction. The ratio of nuclear to nonnuclear MLP increased threefold in both groups ( P < 0.01; n = 7). In failing human hearts, there was almost a complete loss of oligomeric MLP. Using a flag-tagged adenoviral MLP, we demonstrate that the COOH terminus is required for oligomerization and that this is a precursor to stretch sensing and subsequent nuclear translocation. Therefore, reduced oligomeric MLP in the costamere and cytoskeleton may contribute to impaired mechanosensing in heart failure.

Comparison of Hemodynamic Changes After Acute Normovolemic Hemodilution Using Ringer’s Lactate Versus 5% Albumin in Patients on β-Blockers Undergoing Coronary Artery Bypass Surgery

OBJECTIVE

Acute normovolemic hemodilution (ANH) is used cautiously in coronary artery disease (CAD) patients because of concerns of compromised coronary blood flow. This study aimed to compare hemodynamic changes by using either Ringer's lactate or albumin for ANH in CAD patients receiving beta-blockers.

DESIGN

Prospective, randomized study.

SETTING

Postgraduate teaching hospital.

PARTICIPANTS

Thirty patients undergoing coronary artery bypass graft surgery (CABG) (hemoglobin >12 g/dL, on chronic beta-blocker therapy).

INTERVENTIONS

Monitoring, induction, and anesthesia followed a routine protocol for CABG surgery including pulmonary artery catheter placement. Patients were randomly included in group 1 (ANH by Ringer's lactate) or in group 2 (ANH by 5% albumin). A hemodynamic calculation software program was used for parameters recorded before and after ANH.

MEASUREMENTS AND MAIN RESULTS

ANH could not be completed in 5 patients (33%) in group 1 because of a fall in mean arterial pressure (MAP) of more than 25% from baseline. In both groups posthemodilution MAP, heart rate, systemic vascular resistance, and oxygen delivery index decreased, whereas stroke volume index, cardiac index, and tissue oxygen extraction increased significantly as compared to baseline values (p < 0.05). Hemodynamic parameters were better maintained during the study period in group 2 than group 1.

CONCLUSIONS

Hemodynamic stability was better maintained by 5% albumin than Ringer's lactate for ANH in chronic beta-blocked CAD patients. Despite an increase in cardiac index, systemic oxygen delivery was decreased irrespective of the hemodiluting fluid used. ANH to a hemoglobin value of 10 g/dL in chronically beta-blocked CAD patients was well tolerated.

Reverse left ventricular remodeling by intermittent dobutamine infusions and amiodarone in end-stage heart failure due to idiopathic dilated cardiomyopathy

BACKGROUND

The aim of this study was to evaluate the long-term effect of combined intermittent dobutamine infusions (IDI) and oral amiodarone on reverse left ventricular (LV) remodeling and hemodynamics of patients with idiopathic dilated cardiomyopathy (IDC) and end-stage congestive heart failure (CHF).

METHODS

This non-randomized, prospective, clinical trial included sixteen consecutive patients suffering from dyspnea for a mean of 76+/-43 months, who presented with acute cardiac decompensation and were weaned from dobutamine therapy after an initial 72-h infusion. They were then placed on a regimen of oral amiodarone, 400 mg/day and weekly IDI, 10 microg/kg/min, for 8 h. The long-term clinical outcomes and the effects of treatment on reverse LV remodeling (echocardiographic parameters) and hemodynamics were evaluated at 3, 6, and 12 months of follow up.

RESULTS

A significant degree of reverse LV remodeling, hemodynamic improvements, and survivals >1.5 years were observed in 9 of the 16 patients (56%). In addition, 5 patients (31% of entire cohort) were weaned from IDI after a mean of 61+/-41 weeks, and 4 remained clinically stable for 116+/-66 weeks thereafter. At 12 months of follow-up, LV end-diastolic and end-systolic volume indices had decreased from 231+/-91 to 206+/-80 ml/m2 (P=0.002) and from 137+/-65 to 110+/-50 ml/m2 (P=0.003), respectively, right atrial pressure from 16+/-6 to 5.6+/-4 mm Hg, (P=0.031), and pulmonary capillary wedge pressure from 29+/-4 to 16+/-5.4 mm Hg, P=0.000, while LV ejection fraction had increased from 22+/-6% to 27.3+/-8% (P=0.006).

CONCLUSIONS

In end-stage CHF due to IDC, long-term treatment with IDI and oral amiodarone caused reverse LV remodeling, and allowed permanent and successful weaning from IDI in 1/4 of patients.

Chronic heart failure, chronotropic incompetence, and the effects of beta blockade

OBJECTIVE

To establish the prevalence of chronotropic incompetence in a cohort of patients with chronic heart failure (CHF) taking modern medications for heart failure, and whether this affected exercise capacity and predicted prognosis.

METHODS

Heart rate response to exercise was examined in 237 patients with CHF in sinus rhythm, who were compared with 118 control volunteers. The percentage of maximum age predicted peak heart rate (%Max-PPHR) and percentage heart rate reserve (%HRR) were calculated, with a cut off of < 80% as the definition of chronotropic incompetence for both. Patients were followed up for an average (SD) of 2.8 (9) years. Mortality was related to peak oxygen consumption (pVo2), and the presence or absence of chronotropic incompetence.

RESULTS

%Max-PPHR < 80% identified 103 (43%) and %HRR < 80% identified 170 patients (72%) as having chronotropic incompetence. Chronotropic incompetence was more common in patients taking beta blockers than in those not taking beta blockers as assessed by both methods (80 (49%) v 23 (32%) by %Max-PPHR and 123 (75%) v 47 (64%) by %HRR, respectively). Patients with chronotropic incompetence by either method had a lower pVo2 than those without. These differences remained significant for both patients taking and not taking a beta blocker. %HRR, Max-PPHR%, and HRR were related to New York Heart Association class and correlated with pVo2. There was no difference in the slopes relating heart rate to pVo2 between patients with and those without chronotropic incompetence (6.1 (1.7) v 5.1 (1.8), p = 0.34). During an average 2.8 year follow up 40 patients (17%) died. In Cox proportional hazard models, pVo2 was the most powerful predictor of survival and neither measure of chronotropic incompetence independently predicted outcome.

CONCLUSIONS

pVo2 is a powerful marker of prognosis for patients with CHF whether they are taking beta blockers or not. A low heart rate response to exercise in patients with CHF correlates with worse exercise tolerance but is unlikely to contribute to exercise impairment.

Preserved left ventricular structure and function in mice with cardiac sympathetic hyperinnervation

Cardiac-specific overexpression of nerve growth factor (NGF), a neurotrophin, leads to sympathetic hyperinnervation of heart. As a consequence, adverse functional changes that occur after chronically enhanced sympathoadrenergic stimulation of heart might develop in this model. However, NGF also facilitates synaptic transmission and norepinephrine uptake, effects that would be expected to restrain such deleterious outcomes. To test this, we examined 5- to 6-mo-old transgenic (TG) mice that overexpress NGF in heart and their wild-type (WT) littermates using echocardiography, invasive catheterization, histology, and catecholamine assays. In TG mice, hypertrophy of the right ventricle was evident (+67%), but the left ventricle was only mildly affected (+17%). Left ventricular (LV) fractional shortening and fractional area change values as indicated by echocardiography were similar between the two groups. Catheterization experiments revealed that LV +/-dP/dt values were comparable between TG and WT mice and responded similarly upon isoproterenol stimulation, which indicates lack of beta-adrenergic receptor dysfunction. Although norepinephrine levels in TG LV tissue were approximately twofold those of WT tissue, TG plasma levels of the neuronal norepinephrine metabolite dihydroxyphenylglycol were fivefold those of WT plasma. A greater neuronal uptake activity was also observed in TG LV tissue. In conclusion, overexpression of NGF in heart leads to sympathetic hyperinnervation that is not associated with detrimental effects on LV performance and is likely due to concomitantly enhanced norepinephrine neuronal uptake.

Association between chronic heart failure and inhaled beta-2-adrenoceptor agonists

BACKGROUND

Recent reports suggest an association between beta-agonists and the risk of incident chronic heart failure (CHF). We sought to examine the association between inhaled beta-agonists and risk of incident and nonincident heart failure.

METHODS

We performed a nested case-control study within the Ambulatory Care Quality Improvement Project (ACQUIP). Case subjects were defined as having had a hospitalization with a primary discharge diagnosis of CHF. Controls were randomly selected from the ACQUIP cohort. The exposure was the number of beta-agonist canisters filled in the 90 days before an index date.

RESULTS

After adjusting for potentially confounding factors, there appeared to be no association between the use of inhaled beta-agonists and the risk of heart failure (1-2 canisters per month, OR 1.3 [95% CI 0.9, 1.8], > or =3 canisters per month, 1.1 [95% CI 0.8, 1.6]). However, among the cohort that had a history of CHF, there appeared to be a dose-response association between the number of inhaled beta-agonists and the risk of hospitalization for chronic heart failure (1-2 canisters per month, adjusted OR 1.8 [95% CI 1.1, 3.0], > or =3 canisters per month, adjusted OR 2.1 [95% CI 1.2, 3.8]).

CONCLUSION

beta-Agonists did not appear to be associated with incident heart failure but were associated with risk of CHF hospitalization among those subjects with a previous CHF diagnosis. Although a causal relationship cannot be inferred from these findings, further research is warranted to determine the safety and effectiveness of inhaled beta-agonists for patients with CHF.

Hostility is related to blunted beta-adrenergic receptor responsiveness among middle-aged women

OBJECTIVE

Based on previous findings in men, the hypothesis that hostility would be associated with blunted responsiveness of cardiovascular beta-adrenergic receptors was tested in a study sample of middle-aged women. The roles of the sympathetic nervous system and of social support in this putative relationship were also evaluated.

METHODS

Subjects were 80 healthy women (n = 23 African American; n = 57 white), aged 47 to 55 years. Hostility was assessed using the Cook-Medley Hostility Scale and social support was assessed with the Brief Social Support Questionnaire. Intravenous isoproterenol challenge was used to evaluate cardiac and vascular beta-adrenergic receptor responsiveness. Twenty-four-hour urinary catecholamine excretion was used to index sympathetic nervous system activity.

RESULTS

Hostility was related to blunted cardiac (R = 0.33, p <.01) and vascular (R = 0.23, p <.05) beta-adrenergic receptor responsiveness in simple correlation analysis and in hierarchical regression analyses controlling for race, menopausal status, weight, and resting heart rate. Low social support was also related to blunted beta-adrenergic receptor responsiveness (R = 0.3, p <.01). Twenty-four-hour norepinephrine excretion was related both to hostility (R = 0.32, p <.01) and to cardiac (R = 0.25, p <.05) and vascular (R = 0.24, p <.05) beta-adrenergic receptor responsiveness.

CONCLUSIONS

These observations replicate and extend previous findings in men by demonstrating that higher levels of hostility and low levels of social support are associated with blunted beta-adrenergic receptor responsiveness in middle-aged women. They also suggest that heightened sympathetic nervous system activity associated with hostility may contribute to beta-adrenergic receptor blunting. Because blunted beta-adrenergic receptor sensitivity is a characteristic feature of a broad range of cardiovascular diseases, these findings may reflect an early preclinical manifestation of pathophysiology accompanying hostility and low social support.

What is the role of beta-adrenergic signaling in heart failure?

This review addresses open questions about the role of beta-adrenergic receptors in cardiac function and failure. Cardiomyocytes express all three beta-adrenergic receptor subtypes-beta1, beta2, and, at least in some species, beta3. The beta1 subtype is the most prominent one and is mainly responsible for positive chronotropic and inotropic effects of catecholamines. The beta2 subtype also increases cardiac function, but its ability to activate nonclassical signaling pathways suggests a function distinct from the beta1 subtype. In heart failure, the sympathetic system is activated, cardiac beta-receptor number and function are decreased, and downstream mechanisms are altered. However, in spite of a wealth of data, we still do not know whether and to what extent these alterations are adaptive/protective or detrimental, or both. Clinically, beta-adrenergic antagonists represent the most important advance in heart failure therapy, but it is still debated whether they act by blocking or by resensitizing the beta-adrenergic receptor system. Newer experimental therapeutic strategies aim at the receptor desensitization machinery and at downstream signaling steps.

Cardiac disease in myasthenia gravis: a literature review

Patients with myasthenia gravis might develop various cardiac disorders, yet a causal relationship remains unestablished. Because causes of sudden death in this population have not been ascertained, further attention to possible cardiac disease in this population is warranted. We summarize the current literature and describe the possible etiologies and implications of cardiac disease in myasthenics.

Risk of mortality and heart failure exacerbations associated with inhaled beta-adrenoceptor agonists among patients with known left ventricular systolic dysfunction

OBJECTIVES

Recent studies suggest that myocardial beta(2)-adrenoceptors may be important in chronic heart failure. We sought to determine if use of selective beta(2)-agonists was associated with hospitalization for heart failure and all-cause mortality.

METHODS

We studied a cohort of patients with left ventricular systolic dysfunction (LVSD). The outcome was the first hospitalization with a primary diagnosis of chronic heart failure or death from any cause. The exposure was the average number of beta-agonist canisters filled per month in the 90 days prior to and 15 days after enrollment.

RESULTS

Among 1,529 subjects, the relative risk (RR) of chronic heart failure hospital admission associated with inhaled beta-agonists followed a dose-response relationship: RR for one canister per month, 1.4 (95% confidence interval [CI], 0.9 to 2.0), RR for two canisters per month, 1.7 (95% CI, 1.2 to 2.5), and RR for three canisters per month, 2.1 (95% CI, 1.4 to 3.1). The RR of death demonstrated a similar finding: RR for one canister per month, 0.9 (95% CI, 0.5 to 1.5), RR for two canisters per month, 1.3 (95% CI, 0.9 to 2.1), and RR for three canisters per month, 2.0 (95% CI, 1.3 to 3.1). Adjusting for potential confounding factors did not affect the estimates.

CONCLUSION

Among subjects with LVSD, inhaled beta-agonists were associated with an increased risk of heart failure hospitalization, and all-cause mortality. Clinicians should carefully consider the etiology of dyspnea when prescribing beta-agonists to patients with LVSD.

Use of beta-blockers in congestive heart failure

While beta-adrenergic blockers have been used for decades in a variety of cardiovascular illnesses, they have traditionally been avoided in chronic heart failure. In spite of significant advances in management, mortality in patients suffering from heart failure remains unacceptably high and new therapies are urgently needed. Recently, several large clinical trials have shown a significant reduction in both morbidity and mortality in heart failure patients when beta-blockers are added to standard therapy. While further investigation is warranted in certain subgroups, the use of beta-adrenergic blockers in New York Heart Association (NYHA) class II to IV heart failure should now be considered routine. The purpose of this article is to outline and review the five major clinical trials of beta-blocker therapy in chronic heart failure; the US Carvedilol heart failure Program (USCP), the Cardiac Insufficiency Bisoprolol Study II (CIBIS-II), the Metoprolol CR/XL Randomized Intervention Trial in chronic Heart Failure (MERIT-HF), the Beta-blocker Evaluation of Survival Trial (BEST) and the Carvedilol Prospective Randomized Cumulative Survival trial (COPERNICUS), and to aid the reader in the selection of appropriate candidates for beta-blocker therapy.

The importance of beta-adrenergic receptors in immune regulation: a link between neuroendocrine and immune system

Our knowledge of autoimmunity and autoimmune diseases has been advanced in the past decades. Receptors present on the immune cells may potentially regulate the immune system, among them, beta-adrenergic receptors are of special interest. As neurotransmitter receptors which are also present on lymphocytes, beta-adrenergic receptors play an important role as the linkage of two important systems, neuroendocrine and immune systems. Here I summarize several lines of evidence of the importance of the beta-adrenergic receptors in immune regulation.

Beta-blocking in heart failure patients. Balancing the evidence

Evidence for the effectiveness of beta-blockers in the management of patients with heart failure is now compelling with a database of over 13000 patients enrolled in randomised prospective placebo-controlled clinical trials. However this therapy remains vastly underused in clinical practice. The different points challenging the widespread use beta blockade agents in the routine treatment in heart failure are presented and discussed. After a review of the potential mechanism hypothesised behind the benefits of beta-blockers in heart failure, the controversial effects on the haemodynamics, exercise tolerance, hospitalisation and mortality are underlined.

Beta-blocker therapy in heart failure

beta-blocker therapy in heart failure offers the possibility of arresting or reversing the progressive deterioration in this clinical syndrome. While the mechanism is unclear, improvement in cardiac function has been apparent in virtually every study. Clinical results have shown less consistent improvement. Decrease in hospitalization has been noted, but large-scale clinical trials are underway to assess the effect of beta-blockers on mortality.

Successful weaning from milrinone of a patient with severe congestive heart failure using carvedilol

Congestive heart failure is a major and growing health care concern worldwide, and mortality in patients with severe heart failure is high. Few options are available to patients with New York Heart Association class IV heart failure refractory to oral medical therapy. Over the last 15-20 years milrinone, a phosphodiesterase-III inhibitor, has been used occasionally to treat patients with acute heart failure and as a bridge to heart transplantation and, more recently, has been used intermittently or continuously on an outpatient basis. We report a patient with severe, chronic congestive heart failure, whom we treated successfully with continuous milrinone infusions as an outpatient. We were able to wean him of the milrinone after successful up-titration of carvedilol. Nine months after discontinuation of milrinone the patient remains stable in New York Heart Association class I on high dose carvedilol. Research is required to validate the possibility that patients with severe heart failure may be successfully weaned from milrinone using carvedilol and achieve significant improvement of their functional status and quality of life. This may prove to be an effective strategy for the treatment of selected patients with severe, chronic congestive heart failure. (c)2001 by CHF, Inc.

Acute changes of myocardial creatine kinase gene expression under beta-adrenergic stimulation

Creatine kinase (CK) plays a crucial role in myocardial energy metabolism. Alterations in CK gene expression are found in hypertrophied and failing heart, but the mechanisms behind these changes are unclear. This study tests the hypothesis that increased adrenergic stimulation, which is observed in heart failure, induces changes of myocardial CK-activity, -isoenzyme distribution and -gene expression that are characteristic of the failing and hypertrophied heart. Isolated rat hearts were perfused (constant pressure of 80 mmHg) with red cell suspensions. Following a 20-min warm-up period, perfusion for 3 h with 10(-8) M (iso 3 h) or without (control 3 h) isoproterenol was started or experiments were immediately terminated (control 0 h). Left ventricular tissue was analyzed for total CK-activity, CK-isoenzyme distribution and, by use of quantitative RT-PCR, for B-CK, M-CK, mito-CK and GAPDH- (as internal standard) mRNA. After beta-adrenergic stimulation (iso 3 h) but not after control perfusion (control 3 h) a roughly threefold increase in B-CK mRNA levels and a decrease in M-CK mRNA levels by 18% was found. There were no significant differences among the three groups in total CK-activity and in distribution of CK-MM, CK-BB, CK-MB and mito-CK. Thus, beta-adrenergic stimulation induces a switch in CK gene expression from M-CK to B-CK, which is characteristic for the hypertrophied and failing heart. This may be interpreted as an adaptive mechanism making energy transduction via CK more efficient at times of increased metabolic demand.

Modification of beta-adrenoceptor signal transduction pathway by genetic manipulation and heart failure

The beta-adrenoceptor (beta-AR) mediated signal transduction pathway in cardiomyocytes is known to involve beta1- and beta2-ARs, stimulatory (Gs) and inhibitory (Gi) guanine nucleotide binding proteins, adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA). The activation of beta1- and beta2-ARs has been shown to increase heart function by increasing Ca2+ -movements across the sarcolemmal membrane and sarcoplasmic reticulum through the stimulation of Gs-proteins, activation of AC and PKA enzymes and phosphorylation of the target sites. The activation of PKA has also been reported to increase phosphorylation of some myofibrillar proteins (for promoting cardiac relaxation) and nuclear proteins (for cardiac hypertrophy). The activation of beta2-AR has also been shown to affect Gi-proteins, stimulate mitogen activated protein kinase and increase protein synthesis by enhancing gene expression. Beta1- and beta2-ARs as well as AC are considered to be regulated by PKA- and protein kinase C (PKC)-mediated phosphorylations directly; both PKA and PKC also regulate beta-AR indirectly through the involvement of beta-AR kinase (betaARK), beta-arrestins and Gbeta gamma-protein subunits. Genetic manipulation of different components and regulators of beta-AR signal transduction pathway by employing transgenic and knockout mouse models has provided insight into their functional and regulatory characteristics in cardiomyocytes. The genetic studies have also helped in understanding the pathophysiological role of PARK in heart dysfunction and therapeutic role of betaARK inhibitors in the treatment of heart failure. Varying degrees of defects in the beta-AR signal transduction system have been identified in different types of heart failure to explain the attenuated response of the failing heart to sympathetic stimulation or catecholamine infusion. A decrease in beta1-AR density, an increase in the level of G1-proteins and overexpression of betaARK are usually associated with heart failure; however, these attenuations have been shown to be dependent upon the type and stage of heart failure as well as region of the heart. Both local and circulating renin-angiotensin systems, sympathetic nervous system and endothelial cell function appears to regulate the status of beta-AR signal transduction pathway in the failing heart. Thus different components and regulators of the beta-AR signal transduction pathway appears to represent important targets for the development of therapeutic interventions for the treatment of heart failure.

Low dose carvedilol inhibits progression of heart failure in rats with dilated cardiomyopathy

The cardioprotective properties of carvedilol (a vasodilating beta-adrenoceptor blocking agent) were studied in a rat model of dilated cardiomyopathy induced by autoimmune myocarditis. Twenty-eight days after immunization, surviving Lewis rats (32/43=74%) were divided into three groups to be given 2 mg kg(-1) day(-1) (Group-C2, n=10) or 20 mg kg(-1) day(-1) (Group-C20, n=10) of carvedilol, or vehicle (0.5% methylcellulose, Group-V, n=12). After oral administration for 2 months, body weight, heart weight (HW), heart rate (HR), rat alpha-atrial natriuretic peptide (r-ANP) in blood, central venous pressure (CVP), mean blood pressure (mean BP), peak left ventricular pressure (LVP), left ventricular end-diastolic pressure (LVEDP), +/-dP dt(-1) and area of myocardial fibrosis were measured. Values were compared with those for normal Lewis rats (Group-N, n=10). Two out of 12 (17%) rats in Group-V died from day 28 to day 42 after immunization. No rat died in Groups-C2, -C20 and -N. Although the CVP, mean BP, LVP and +/-dP dt(-1) did not differ among the three groups, the HW, HR and r-ANP in Group-C2 (1.14+/-0.03, 339+/-16 and 135+/-31) and Group-C20 (1.23+/-0.04, 305+/-8 and 156+/-24) were significantly lower than those in Group-V (1.36+/-0.04 g, 389+/-9 beats min(-1) and 375+/-31 pg ml(-1), respectively). The LVEDP in Group-C2 was significantly lower than that in Group-V (7.4+/-1.4 and 12.2+/-1.2 mmHg, respectively, P<0. 05). The area of myocardial fibrosis in Group-C2 was smaller than that in Group-V (12+/-1 and 31+/-2%, P<0.01). These results indicate that a low dose of carvedilol has beneficial effects on dilated cardiomyopathy.

Effect of carvedilol in comparison with metoprolol on myocardial collagen postinfarction

OBJECTIVES

We sought to compare the effects of two different beta-blockers, carvedilol and metoprolol, to an angiotensin-converting enzyme (ACE) inhibitor (captopril) on myocardial collagen deposition during healing and ventricular remodeling after myocardial infarction (MI).

BACKGROUND

Beta-adrenergic blockade has been shown to be beneficial post-MI and in chronic heart failure. Carvedilol is a new-generation vasodilating beta-blocker with additional alpha1-adrenoceptor antagonism and an antiproliferative action, but it is not known if it is more beneficial than standard selective beta-blockers.

METHODS

Using a rat model of MI, induced by left coronary ligation, we studied the effects of 11 weeks of therapy with oral carvedilol, metoprolol or captopril on hemodynamics, tissue weights, collagen volume fraction and hydroxyproline content.

RESULTS

Both beta-blockers caused similar decreases in heart rate and LVEDP compared with untreated post-MI rats. At equivalent beta-adrenoceptor blocking doses, however, carvedilol, but not metoprolol, attenuated the increase in collagen content in noninfarcted regions and prevented the increase in right ventricular weight/body weight (all p < 0.05), and its effect was similar to captopril. Metoprolol treatment tended to increase right ventricular weight and heart weight (p < 0.05). There were no differences in infarct size between the groups.

CONCLUSIONS

Long-term treatment with both beta-blockers, as well as an ACE inhibitor, benefited the healing process in rats post-MI. At equivalent myocardial beta-adrenoceptor blocking doses, however, carvedilol significantly reduced myocardial collagen in the noninfarcted myocardium and cardiac hypertrophy in the right ventricle, whereas metoprolol had no effect on myocardial collagen deposition.

Different intrinsic activities of bucindolol, carvedilol and metoprolol in human failing myocardium

1. Clinical studies have shown different effects of beta-blockers on the beta-adrenergic system, tolerability and outcome in patients with heart failure. 2. The study examines beta-adrenoceptor-G-protein coupling and intrinsic activity of bucindolol, carvedilol and metoprolol in human ventricular myocardium. 3. Radioligand binding studies ([(125)I]-Iodocyanopindolol) were performed in membrane preparations of human failing and nonfailing myocardium. Functional experiments were carried out in isolated muscle preparations of human left ventricular myocardium from failing hearts. 4. Bucindolol and carvedilol bound non-selectively to beta(1)- and beta(2)-adrenoceptors and exerted guanine nucleotide modulatable binding. Metoprolol was 35-fold beta(1)-selective and lacked guanine nucleotide modulatable binding. 5. All beta-blockers antagonized isoprenaline-induced enhancement of contractility. 6. In preparations in which the coupling of the stimulatory G-protein to adenylate cyclase was facilitated by forskolin, bucindolol increased force of contraction in three and decreased it in five experiments. Carvedilol increased force in one and decreased it in six experiments. Metoprolol decreased force in all experiments by 89. 4+/-2.2% (P<0.01 metoprolol vs carvedilol and bucindolol). The negative inotropic effect of metoprolol was antagonized by bucindolol. 7. It is concluded that differences in intrinsic activity can be detected in human myocardium and have an impact on cardiac contractility. In human ventricular myocardium, bucindolol displays substantially higher intrinsic activity than metoprolol and carvedilol. Bucindolol can behave as partial agonist or partial inverse agonist depending on the examined tissue. 8. Differences in intrinsic activity may contribute to differences in beta-adrenoceptor regulation and possibly to differences in tolerability and outcomes of patients with heart failure.

Usefulness of beta blocker therapy in patients with Takayasu arteritis and moderate or severe aortic regurgitation

The objective of the present study was to evaluate the benefit of beta-blocker therapy for patients with Takayasu arteritis complicated by moderate or severe aortic regurgitation. Clinical and echocardiographic evaluation was performed in 20 Japanese women in a follow-up period of 7.0 +/- 2.0 years. The patients were divided into 2 groups: Group A (n=10) patients who did not receive beta-blockers, and Group B (n=10) patients treated with long-term (5.1 +/- 1.6 years) therapeutic doses of beta-blockers. Left ventricular wall thickness increased significantly in all Takayasu patients who did not receive beta-blockers. Consequently, a remarkable increment in left ventricular mass took place (232 +/- 59 to 361 +/- 79 g; p < 0.005). In the same group, progressive worsening of the symptoms, with no reduction in the percent fractional shortening, was observed in 2 patients, while reduction of this last index was present in 1 asymptomatic patient. On the other hand, among the patients who were treated with beta-blockers, left ventricular mass still increased in 6 cases, while it clearly decreased in the other 4 cases (290 +/- 171 to 284 +/- 61 g; NS). The increment in wall thickness or left ventricular mass observed among patients with beta-blocker therapy was clearly less than the one registered among those who had not received beta-blockers. Furthermore, no worsening of the symptoms and/or left ventricular performance was observed during the follow-up period for patients receiving beta-blockers. We conclude that beta-blocker therapy can slow and even reverse the progression of left ventricular hypertrophy in patients with Takayasu arteritis complicated by moderate or severe aortic regurgitation. The mechanism still needs to be elucidated. We believe an effective reduction in the excessive afterload imposed on the left ventricle to be most likely responsible, but cardiac beta-receptor up-regulation might also be involved. Deterioration of the clinical status and/or impairment of left ventricular function were not associated with beta-blocker therapy in our patients. Therefore, these agents can be used safely alone or in addition to standard anti-hypertensive therapy when attempting to reduce excessive afterload, in spite of the presence of severe aortic regurgitation.

Clinical Pharmacology of Carvedilol

BACKGROUND: There is now a wealth of data supporting the use of beta-blockers in heart failure and the additional pharmacological properties of carvedilol are thought to play an important role in the therapeutic efficacy of carvedilol in this disease. METHODS AND RESULTS: Carvedilol is licensed for the treatment of essential hypertension, chronic stable angina, and mild to moderate chronic heart failure. This article provides an up-to-date review of the clinical pharmacology of carvedilol, with particular emphasis on its clinical effects in heart failure. CONCLUSION: Carvedilol is a multiple-action neurohormonal antagonist that offers nonselective beta-blockade, alpha-1 blockade, antioxidant, anti-ischemic mortality, and anti-proliferative properties. In addition to reductions in hospitalization and mortality rates, benefits of carvedilol in heart failure include dramatic improvements in left ventricular function and other parameters of cardiac remodeling.

Agonist-like beta-adrenoceptor antibodies in heart failure

Anti-beta1-adrenoceptor antibodies may play a harmful role, and the elimination of these antibodies could have beneficial effects for some patients with dilated cardiomyopathy. In vitro experiments showed that the antibody was able to influence the function of cultured cardiomyocytes. In these experiments, the antibody prevented the down-regulation of the beta-adrenoceptor-mediated chronotropic response. This lack of desensitization, which resulted in permanent stimulation, could also influence the Ca2+ homeostasis of cardiomyocytes. However, in longer-term (72 hours)-treated cells, the antibodies were able to decrease subtype-specific expression of the beta1 adrenoceptor. In animal experiments, it was shown that long-term immunization with a peptide corresponding to the second extracellular loop of the beta1 adrenoceptor induced a failing heart similar to that in dilated cardiomyopathy. In humans, we observed a remarkable correlation between disappearance of the antibodies and improvement of heart function. Furthermore, in anti-beta1-adrenoceptor-positive patients with dilated cardiomyopathy treated with the immunoadsorption technique, removal of the antibodies also led to improvement of cardiac function and quality of life. This finding indicates that autoimmune processes may be involved in some patients with dilated cardiomyopathy.

Potential risk of beta-blockade withdrawal in congestive heart failure due to abrupt autonomic changes

Beta-Blockers reduce mortality in patients with congestive heart failure and a proposed mechanism has been changes of autonomic tone. Heart rate variability is a non-invasive tool to estimate cardiac autonomic tone. The aim was to study changes of heart rate variability in patients with congestive heart failure on placebo, on the beta1-selective antagonist metoprolol or 24 h after metoprolol withdrawal. Forty-five patients with congestive heart failure were studied with Holter recordings. Heart rate variability measurements were performed before, after 6-12 months of treatment with 150 mg metoprolol/placebo, or 24 h after discontinued metoprolol. After treatment, patients on beta-blockade had a significantly longer mean RR interval and changes of heart rate variability, suggesting elevated vagal tone. Patients monitored in the rebound phase of beta-blocker withdrawal had a significant vagal reduction to the level of the placebo group. There was also a nonsignificant trend towards increased sympathetic tone (LF/HF over 24 h), compared with the beta-blockade group. Heart rate variability indicates an elevated vagal tone during treatment with metoprolol but beta-blockade withdrawal shifts the autonomic balance towards lower vagal and higher sympathetic tone within 24 h. These results could imply a potential risk when abruptly discontinuing beta-blockade medication in these patients.

Antibodies against beta1 and beta2 adrenergic receptors in myasthenia gravis

Patients with myasthenia gravis have antibodies and T cells that react with the beta1- and beta2-adrenergic receptors. These receptors, as well as other auto-antigens, are present on cardiomyocytes, skeletal muscle cells and lymphocytes and are of importance for the regulation of the functions of these organs. Antibodies against the beta1-adrenergic receptor have been implicated in dilated cardiomyopathies. Myasthenia gravis (MG) patients have been suggested to have a higher than normal prevalence of heart disease. We have analysed the isotypes, subclasses, and binding sites of the beta-adrenergic receptors antibodies in both MG patients and healthy individuals and the correlation between beta-adrenergic receptors antibodies and heart disease in MG patients. The patients have IgG antibodies that react with both beta1- and beta2-adrenergic receptors. The subclasses were predominantly IgG2 and IgG4. By using synthesised overlapping peptides representing the immunodominant regions on the receptors, it was shown that the antibodies bound to partially overlapping sites on both beta1- and beta2-adrenergic receptors, but not to peptides from the acetylcholine receptor. beta-adrenergic receptor antibodies were found in 34/125 MG patients. Seven out of these 34 patients had symptomatic heart disease, all seven were over 70 years of age and had arteriosclerotic heart disease. There was no difference in the prevalence of clinical heart disease in patients with and without beta-adrenergic receptor antibodies. However, patients with heart disease had significantly higher levels of antibodies than healthy individuals and other patients. Antibodies against beta-adrenergic receptors in patients with myasthenia gravis binds to both beta1- and beta2-adrenergic receptors and might be implicated in the few patients with myasthenia gravis who have heart disease.

The Ile164 beta2-adrenergic receptor polymorphism adversely affects the outcome of congestive heart failure

The beta2-adrenergic receptor (beta2AR), an important modulator of cardiac inotropy and chronotropy, has significant genetic heterogeneity in the population. Because dysfunctional betaARs play a role in the pathogenesis of the failing ventricle, we tested the hypothesis that beta2AR polymorphisms alter the outcome of congestive heart failure. 259 patients with NYHA functional class II-IV heart failure due to ischemic or dilated cardiomyopathy were genotyped and prospectively followed, with the endpoint defined as death or cardiac transplantation. The allele frequencies between this group and those of 212 healthy controls also were compared and did not differ between the groups. However, those with the Ile164 polymorphism displayed a striking difference in survival with a relative risk of death or cardiac transplant of 4.81 (P < 0.001) compared with those with the wild-type Thr at this position. Age, race, gender, functional class, etiology, ejection fraction, and medication use did not differ between these individuals and those with the wild-type beta2AR, and thus the beta2AR genotype at position 164 was the only clear distinguishing feature between the two groups. The 1-yr survival for Ile164 patients was 42% compared with 76% for patients harboring wild-type beta2AR. In contrast, polymorphisms at amino acid positions 16 (Arg or Gly) or 27 (Gln or Glu), which also alter receptor phenotype, did not appear to have an influence on the course of heart failure. Taken together with cell-based and transgenic mouse results, this study establishes a paradigm whereby genetic variants of key signaling elements can have pathophysiologic consequences within the context of a disease. Furthermore, patients with the Ile164 polymorphism and heart failure may be candidates for earlier aggressive intervention or cardiac transplantation.

Cardiac sympathetic innervation in patients with idiopathic right ventricular outflow tract tachycardia

OBJECTIVES

This study investigated the neuronal reuptake of norepinephrine (uptake-1) and the beta-adrenoceptor density in patients with idiopathic right ventricular outflow tract tachycardia (RVO-VT).

BACKGROUND

Clinical findings, such as the inducibility of ventricular tachycardia by stress or catecholamine infusion, and the therapeutic efficacy of antiarrhythmic drugs with antiadrenergic properties suggest abnormalities of cardiac sympathetic innervation in patients with idiopathic RVO-VT.

METHODS

Eight patients with idiopathic RVO-VT and a total of 29 age-matched control subjects were investigated by positron emission tomography using [11C]hydroxyephedrine (HED) (volume of distribution of [11C]HED) to assess presynaptic norepinephrine reuptake; [11C]CGP 12177 (maximal binding capacity of [11C]CGP 12177) to measure postsynaptic beta-adrenoceptor density; and oxygen-15-labeled water for quantification of myocardial blood flow (MBF).

RESULTS

Both myocardial catecholamine reuptake and beta-adrenoceptor density were significantly reduced in patients with idiopathic RVO-VT. The volume of distribution of [11C]HED in patients with RVO-VT was (mean +/- SD) 41.0 +/- 13.5 versus 71.0 +/- 18.8 ml/g in control subjects (p < 0.002). The maximal binding capacity of the beta-adrenoceptor antagonist [11C] CGP 12177 was 6.8 +/- 1.2 pmol/g in patients with RVO-VT versus 10.2 +/- 2.9 pmol/g in control subjects (p < 0.004). There were no significant differences in MBF at rest (0.98 +/- 0.14 vs. 0.97 +/- 0.24 ml/min per g, p = NS) between patients with RVO-VT and control subjects.

CONCLUSIONS

The findings of the present study suggest that myocardial beta-adrenoceptor downregulation in patients with RVO-VT occurs subsequently to increased local synaptic catecholamine levels caused by impaired catecholamine reuptake.

Innovations in the pharmacologic management of heart failure

Improved understanding of the pathophysiologic course of heart failure has led to many advances in pharmacologic therapy. Angiotensin-converting enzyme inhibitors represent the first effort at targeting neurohormonal activation in chronic heart failure. More recently, beta-adrenergic receptor antagonists have been shown effective in blocking chronic sympathetic nervous system activation. The roles of digoxin and the newer, vasoselective calcium channel blockers in heart failure have been better defined. Other agents targeting the neurohormonal system are under investigation. These include angiotensin-receptor antagonists, aldosterone inhibitors, and endothelin antagonists. Experience with phosphodiesterase inhibitors and adrenergic agents has confirmed the importance of neurohormonal activation in progression of heart failure. Despite angiotensin-converting enzyme inhibitor, diuretic, and digoxin therapy, mortality in heart failure remains high. Careful manipulation of the neurohormonal response to heart failure holds promise for altering the course of the disease.

[Regulation of myocardium beta-adrenoceptors pathway in ventricular remodeling of heart failure patients]

To study the role of myocardium beta-adrenoceptors pathway in ventricular remodeling of heart failure patients. beta-adrenegic receptor density (Bmax) and the content of cAMP were measured in the papillae of left ventricle and blood lymphocyte of 20 patients suffered from heart failure (CHF) (NYHZ classification II to III) Bmax were investigated using 3H-dihydroalpheolol as ligand. cAMP were assessed by competitive immunoassay. Left ventricle mass index (LVMI) were measured using echocardiogram. The results showed that the Bmax and cAMP in failing myocardium significantly negatively correlated with LVMI (r = -0.77, P < 0.01 and r = -0.46 P < 0.05 respectively); the Bmax of myocardium and blood lymphocyte in CHF patients with NYHA III (63 +/- 12 fmol/mgpro and 514 +/- 115 fmol/10(7) cell) significantly lowered than that of NYHA II patients (94 +/- 20 fmol/mgpro and 702 +/- 138 fmol/10(7) cell); and the Bmax of myocardium and blood lymphocyte in patients with abnormal LVMI (62 +/- 12 fmol/mgpro and 516 +/- 122 fmol/10(7) cell) decreased more significantly than that with normal LVMI patients; even in nromal LVMI patients (92 +/- 21 fmol/mgpro and 682 +/- 146 fmol/10(7) cell), the Bmax of blood lymphocyte was already decreased (P < 0.01), when comparing with controls. The intralymphocyte cAMP content sygnificantly decreased than that of controls (P < 0.05). These results indicated that Bmax could reflect the severity of ventricle remodeling and the impairment of myocardium. The regulation of myocardium intracellular messenger transduction was earlier than the pathologic structural change of LV remodeling.

Efficacy of beta blockers in idiopathic dilated cardiomyopathy and ischemic cardiomyopathy

Despite the well-documented benefits of beta blockade in a variety of cardiovascular conditions, the value of beta blockade in congestive heart failure (CHF) is still in question. The concept of neurohormonal blockade in heart failure has, however, brought beta blockade into focus. There is experimental evidence for the value of blocking sympathetic activation in CHF, and increased sympathetic activation may be an etiologic factor for development of CHF. Clinical studies have shown that long-term beta blockade improves both systolic and diastolic function. The effects on exercise tolerance and quality of life seem to differ between beta1-selective and nonselective beta blockers in favor of the beta1-selective blockers. To date, results of all trials reveal a consistent pattern of decreased cardiovascular morbidity. In one trial of metoprolol, fewer heart transplantations were required; such a reduction may have a great impact on healthcare costs associated with heart failure. Improved long-term survival found by one study must be confirmed in additional trials: 3 such survival trials (with metoprolol, bisoprolol, and bucindolol) are now in progress.

Improvement of postreceptor events by metoprolol treatment in patients with chronic heart failure

OBJECTIVES

This study tested the hypothesis that metoprolol restores the reduction of the inotropic effect of the cyclic adenosine monophosphate (cAMP)-phosphodiesterase inhibitor milrinone, which is cAMP dependent but beta-adrenoceptor independent.

BACKGROUND

Treatment with beta-adrenergic blocking agents has been shown to lessen symptoms and improve submaximal exercise performance and left ventricular ejection fraction in patients with heart failure. Restoration of the number of down-regulated beta-adrenoceptors has been suggested to be one mechanism of beta-blocker effectiveness. However, the reversal of postreceptor events, namely, an increase in inhibitory G-protein alpha-subunit concentrations, could also play a role.

METHODS

Fifteen patients with heart failure due to dilated cardiomyopathy (left ventricular ejection fraction 24.6 +/- 1.5% [mean +/- SD], New York Heart Association functional class II or III) were treated with metoprolol (maximal dose 50 mg three times daily) for 6 months. Before and after metoprolol treatment, inotropic responses to milrinone (5 to 10 micrograms/kg body weight per min) were measured echocardiographically. For comparison, responses to milrinone were determined under control conditions and after accelerated application of 150 mg of metoprolol to inactivate beta-adrenoceptors in subjects with normal left ventricular function.

RESULTS

In subjects with normal left ventricular function, treatment with metoprolol did not alter the increase in fractional shortening or pressure/dimension ratio of circumferential fiber shortening after application of milrinone. In patients with heart failure, treatment with metoprolol significantly increased left ventricular ejection fraction, fractional shortening and submaximal exercise tolerance and reduced heart rate, plasma norepinephrine concentrations and functional class. After metoprolol treatment, milrinone increased fractional shortening but had no effect before beta-blocker treatment.

CONCLUSIONS

Milrinone increases inotropic performance independently of beta-adrenoceptors in vivo. Metoprolol treatment restores the blunted inotropic response to milrinone in patients with heart failure, indicating that postreceptor events (e.g., increase in inhibitory G-protein) are favorably influenced. This mechanism could contribute to the beneficial effects observed in the study patients and represents an important mechanism of how beta-blocker treatment influences the performance of the failing heart.

Effects of acidosis or alkalosis on the actions of nifedipine on excitation-contraction coupling in the rat tail artery

1. The clinical success of calcium channel blockers in the management of organ ischaemia is less than theoretically anticipated. Blood gas/pH changes are associated with organ ischaemia; therefore, we studied the possibility that pH changes could alter the pharmacological effects of the calcium channel blocker nifedipine on rat tail artery contracted by either noradrenaline (NA) or potassium. 2. Segments (2-2.5 cm) of the proximal third of the male Sprague-Dawley rat tail ventral artery were initially bathed and perfused with a physiological salt solution (PSS; pH 7.48) for 25-30 min, after which time bathing/perfusion was continued with a nominally calcium-free PSS made acidotic (pH 7.20), alkalotic (pH 7.67) or unaltered (control). After equilibration, the perfusion pressure (PP) responses to increasing concentrations of calcium in the presence of NA (3.0 mumol/L) or potassium (100 mmol/L) with nifedipine or its vehicle were recorded. 3. The calcium sensitivity of potassium- or NA-stimulated rat tail arteries was reduced during acidosis, as was the maximum PP in potassium- but not NA-stimulated tissues. Alkalosis reduced the calcium sensitivity in potassium- but not NA-stimulated contraction and had no effect on maximum PP. 4. The inhibitory effect of nifedipine (0.6 mumol/L) on contraction was enhanced during acidosis in either NA- or potassium-stimulated arteries and also during alkalosis in NA-treated arteries, although it had little effect during normal conditions. 5. The results indicate that changes in pH alter the vascular contractility profile in a manner dependent on the excitation-contraction coupling mode. The calcium antagonistic effect of nifedipine is pH dependent and it is suggested that pH changes associated with ischaemic conditions may alter the therapeutic profile of nifedipine.