Beta-blocker benefit according to severity of heart failure

Dynamics of adrenergic signaling in cardiac myocytes and implications for pharmacological treatment

Dense innervation of the heart by the sympathetic nervous system (SNS) allows cardiac output to respond appropriately to the needs of the body under varying conditions, but occasionally the abrupt onset of SNS activity can trigger cardiac arrhythmias. Sympathetic activity leads to the release of norepinephrine (NE) onto cardiomyocytes, activating β₁-adrenergic receptors (β₁-ARs) and leading to the production of the second messenger cyclic AMP (cAMP). Upon sudden activation of β₁-ARs in experiments, intracellular cAMP can transiently rise to a high concentration before converging to a steady state level. Although changes to cellular cAMP concentration are important in modulating the overall cardiovascular response to sympathetic tone, the underlying mechanisms of the cAMP transients and the parameters that control their magnitude are unclear.

We reduce a detailed computational model of the β₁-adrenergic signaling cascade to a system of two differential equations by eliminating extraneous variables and applying quasi-steady state approximation. The structure of the reduced model reveals that the large cAMP transients associated with abrupt β₁-AR activation are generated by the interplay of production/degradation of cAMP and desensitization/resensitization of β₁-ARs. The reduced model is used to predict how the dynamics of intracellular cAMP depend on the concentrations of norepinephrine (NE), phosphodiesterases 3 and 4 (PDE3,4), G-protein coupled receptor kinase 2 (GRK2), and β₁-AR, in healthy conditions and a simple model of early stages of heart failure.

The key findings of the study are as follows: 1) Applying a reduced model of the dynamics of cardiac sympathetic signaling we show that the concentrations of two variables, cAMP and non-desensitized β₁-AR, capture the overall dynamics of sympathetic signaling; 2) The key factors influencing cAMP production are AC activity and PDE3,4 activity, while those that directly impact β₁-AR phosphorylation are GRK2 and PKA₁. Thus, disease states that affect sympathetic control of the heart can be thoroughly assessed by studying AC activity, PDE3,4, GRK2 and PKA activity, as these factors directly impact cAMP production/degradation and β₁-AR (de) phosphorylation and are therefore predicted to comprise the most effective pharmaceutical targets in diseases affecting cardiac β₁-adrenergic signaling.

Rationale for administering beta-blocker therapy to patients undergoing coronary artery bypass surgery: a systematic review

INTRODUCTION

Secondary preventative therapies are essential for patients undergoing coronary artery bypass graft (CABG) surgery to optimize perioperative and long-term outcomes. Beta-blockers are commonly used to treat patients with coronary artery disease and congestive heart failure (CHF), but their role for CABG patients remains unclear. The goal of this systematic review was to evaluate the rationale for administering beta-blockers to the CABG population and to assess their efficacy before and after coronary surgical revascularization.

AREAS COVERED

A systematic literature review was performed to retrieve relevant articles from the PubMed database published between 1985 and 2017.

EXPERT OPINION

Outside of the surgical field, strong evidence supports the use of beta-blockers for patients with a history of previous myocardial infarction (MI) or CHF. For the CABG population, studies have suggested that perioperative beta-blocker therapy is beneficial, with an associated reduction in mortality, particularly among those with a history of previous MI or CHF. Beta-blocker administration has also clearly been shown to lower the rate of new-onset postoperative atrial fibrillation after CABG. Among the different types of beta-blockers, perioperative carvedilol appears to be the most beneficial. In the absence of contraindications, nearly all CABG patients are candidates for perioperative beta-blocker therapy.

Effect on mode of death of heart failure treatment started with bisoprolol followed by Enalapril, compared to the opposite order: results of the randomized CIBIS III trial

BACKGROUND

Mode of death in chronic heart failure (CHF) may be of relevance to choice of therapy for this condition. Sudden death is particularly common in patients with early and/or mild/moderate CHF. β-Blockade may provide better protection against sudden death than ACE inhibition (ACEI) in this setting.

METHODS

We randomized 1010 patients with mild or moderate, stable CHF and left ventricular ejection fraction ≤35%, without ACEI, β-blocker or angiotensin-receptor-blocker therapy, to either bisoprolol (n = 505) or enalapril (n = 505) for 6 months, followed by their combination for 6-24 months. The two strategies were blindly compared regarding adjudicated mode of death, including sudden death and progressive pump failure death.

RESULTS

During the monotherapy phase, 8 of 23 deaths in the bisoprolol-first group were sudden, compared to 16 of 32 in the enalapril-first group: hazard ratio (HR) for sudden death 0.50; 95% confidence interval (CI) 0.21-1.16; P= 0.107. At 1 year, 16 of 42 versus 29 of 60 deaths were sudden: HR 0.54; 95% CI 0.29-1.00; P= 0.049. At study end, 29 of 65 versus 34 of 73 deaths were sudden: HR 0.84; 95% CI 0.51-1.38; P= 0.487. Comparable figures for pump failure death were: monotherapy, 7 of 23 deaths versus 2 of 32: HR 3.43; 95% CI 0.71-16.53; P= 0.124, at 1 year, 13 of 42 versus 5 of 60: HR 2.57; 95% CI 0.92-7.20; P= 0.073, at study end, 17 of 65 versus 7 of 73: HR 2.39; 95% CI 0.99-5.75; P= 0.053. There were no significant between-group differences in any other fatal events.

CONCLUSION

Initiating therapy with bisoprolol compared to enalapril decreased the risk of sudden death during the first year in this mild systolic CHF cohort. This was somewhat offset by an increase in pump failure deaths in the bisoprolol-first cohort.

Selection of optimal dose of beta-blocker treatment in myocardial infarction patients based on changes in synchronization between 0.1 Hz oscillations in heart rate and peripheral microcirculation

BACKGROUND

Selection of the optimal dose of beta-blocker treatment in myocardial infarction (MI) patients is problematic because of a lack of well-established guidelines.

METHODS

We evaluated changes in synchronization between 0.1 Hz oscillations in heart rate (HR) and plethysmographic peripheral microcirculation in response to a tilt-table test and to 3-month treatment with the highest tolerated beta-blocker (metoprolol) dose in 43 patients aged between 41 and 77 years with acute MI 6 months prior to the start of the study. Before the study the patients were treated with small doses of beta-blocker. Phase differences between HR and peripheral microcirculation oscillations were used to measure the degree of synchronization (S), and relative change in S from horizontal position was used to characterize the response to vertical tilt.

RESULTS

Two groups of MI patients matched for clinical characteristics were identified on the basis of the results. The first group was composed of patients with decreased S as a response to vertical tilt at the beginning of the study. The patients with increased S during vertical tilt before treatment with the highest tolerated beta-blocker dose were attributed to the second group. The response to vertical tilt in the first group of patients was postulated to indicate the need to increase beta-blocker dose, and in turn, the response in the second group to indicate an already adequate beta-blocker dose.

CONCLUSION

Assessment of synchronization of 0.1  Hz HR and peripheral microcirculation oscillations as a response to a tilt test can possibly be used as a guideline for selecting beta-blocker dose in post-MI patients.

Systematic review of noncancer presentations with a median survival of 6 months or less

PURPOSE

We report on clinical indicators of 6-month mortality in advanced noncancer illnesses and the effect of treatment on survival.

METHODS

The MEDLINE database was searched comprehensively to find studies evaluating survival for common advanced noncancer illnesses. We retrieved and evaluated studies that reported a median survival of ≤1 year and evaluated prognostic factors or effect of treatment on survival. We extracted data on presentations with median survivals of ≤6 months for heart failure, chronic obstructive pulmonary disease, dementia, geriatric failure to thrive, cirrhosis, and end-stage renal failure. Independent risk factors for survival were combined and included if their combination was associated with a 6-month mortality of ≥50%.

RESULTS

The search identified 1000 potentially relevant studies, of which 475 were retrieved and evaluated, and 74 were included. We report the common clinical presentations that are consistently associated with a 6-month median survival. Even though advanced noncancer syndromes differ clinically, a universal set of prognostic factors signals progression to terminal disease, including poor performance status, advanced age, malnutrition, comorbid illness, organ dysfunction, and hospitalization for acute decompensation. Generally, a 6-month median survival is associated with the presence of 2-4 of these factors. With few exceptions, these terminal presentations are quite refractory to treatment.

CONCLUSION

This systematic review summarizes prognostic factors common to advanced noncancer illness. There is little evidence at present that treatment prolongs survival at these terminal stages.

Carvedilol suppresses fatty acid oxidation and stimulates glycolysis in C2C12 cells

Beta adrenergic receptor blocking drugs (β-blockers) are used chronically in many cardiovascular diseases such as hypertension, ischemic heart disease, arrhythmia, and heart failure. Beneficial effects are associated with the inhibition of symphathetic nervous system hyperactivity, reduction of heart rate, and remodeling by blocking the mitogenic activity of catecholamines. A possible effect of β-blockers on substrate metabolism has also been suggested. The direct effects of β-blockers on mouse C2C12 cells were investigated in this study. C2C12 cells were grown in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum (FBS) and differentiated into myotubes in the same medium that contained 1% FBS. Palmitic acid oxidation and glycolysis were measured by using [9,10-(3)H]palmitate and [5-(3)H]glucose, respectively. The amount of (3)H(2)O was measured as an indicator of substrate usage. Carvedilol (100 µmol/L) inhibited palmitate oxidation and increased glycolysis by nearly 50%. Prazosin altered substrate metabolism in a similar fashion as carvedilol, whereas propranolol or bisoprolol were devoid of metabolic effects. When added to mimic sympathetic activation, epinephrine stimulated glycolysis but did not alter fatty acid oxidation. Based on these results, carvedilol appears to have direct effects on substrate metabolism that are related to the blockade of α1 adrenergic receptors.

Bucindolol: a pharmacogenomic perspective on its use in chronic heart failure

Bucindolol is a non-selective β-adrenergic receptor blocker with α-1 blocker properties and mild intrinsic sympatholytic activity. The Beta-Blocker Evaluation of Survival Trial (BEST), which is the largest clinical trial of bucindolol in patients with heart failure, was terminated prematurely and failed to show an overall mortality benefit. However, benefits on cardiac mortality and re-hospitalization rates were observed in the BEST trial. Bucindolol has not shown benefits in African Americans, those with significantly low ejection fraction and those in NYHA class IV heart failure. These observations could be due to the exaggerated sympatholytic response to bucindolol in these sub-groups that may be mediated by genetic polymorphisms or changes in gene regulation due to advanced heart failure. This paper provides a timely clinical update on the use of bucindolol in chronic heart failure.

Should beta-blocker therapy be reduced or withdrawn after an episode of decompensated heart failure? Results from COMET

BACKGROUND

It is unclear whether beta-blocker therapy should be reduced or withdrawn in patients who develop acute decompensated heart failure (HF). We studied the relationship between changes in beta-blocker dose and outcome in patients surviving a HF hospitalisation in COMET.

METHODS

Patients hospitalised for HF were subdivided on the basis of the beta-blocker dose administered at the visit following hospitalisation, compared to that administered before.

RESULTS

In COMET, 752/3029 patients (25%, 361 carvedilol and 391 metoprolol) had a non-fatal HF hospitalisation while on study treatment. Of these, 61 patients (8%) had beta-blocker treatment withdrawn, 162 (22%) had a dose reduction and 529 (70%) were maintained on the same dose. One-and two-year cumulative mortality rates were 28.7% and 44.6% for patients withdrawn from study medication, 37.4% and 51.4% for those with a reduced dosage (n.s.) and 19.1% and 32.5% for those maintained on the same dose (HR,1.59; 95%CI, 1.28-1.98; p<0.001, compared to the others). The result remained significant in a multivariable model: (HR, 1.30; 95%CI, 1.02-1.66; p=0.0318). No interaction with the beneficial effects of carvedilol, compared to metoprolol, on outcome was observed (p=0.8436).

CONCLUSIONS

HF hospitalisations are associated with a high subsequent mortality. The risk of death is higher in patients who discontinue beta-blocker therapy or have their dose reduced. The increase in mortality is only partially explained by the worse prognostic profile of these patients.

Sympathetic control of short-term heart rate variability and its pharmacological modulation

The static relationship between heart rate (HR) and the activity of either vagal or sympathetic nerves is roughly linear within the physiological range of HR variations. The dynamic control of HR by autonomic nerves is characterized by a fixed time delay between the onset of changes in nerve activity and the onset of changes in HR. This delay is much longer for sympathetically than for vagally mediated changes in HR. In addition, the kinetics of the HR responses shows the properties of a low-pass filter with short (vagal) and long (sympathetic) time constants. These differences might be secondary to differences in nervous conduction times, width of synaptic cleft, kinetics of receptor activation and post-receptor events. Because of the accentuated low-pass filter characteristics of the HR response to sympathetic modulation, sympathetic influences are almost restricted to the very-low-frequency component of HR variability, but the chronotropic effects of vagal stimulation usually predominate over those of sympathetic stimulation in this frequency band. Oscillations in cardiac sympathetic nerve activity are not involved in respiratory sinus arrhythmia (high-frequency component) and make a minor contribution to HR oscillations of approximately 10-s period (low-frequency component of approximately 0.1 Hz), at least in the supine position. In the latter case, HR oscillations are derived mainly from a baroreflex, vagally mediated response to blood pressure Mayer waves. Beta-blockers and centrally acting sympathoinhibitory drugs share the ability to improve the baroreflex control of HR, possibly through vagal facilitation, which might be beneficial in several cardiovascular diseases.

Cardiovascular protection using beta-blockers: a critical review of the evidence

For more than 3 decades, beta-blockers have been widely used in the treatment of hypertension and are still recommended as first-line agents by national and international guidelines. Recent meta-analyses indicate that, in patients with uncomplicated hypertension, compared with other antihypertensive agents, first-line therapy with beta-blockers was associated with an increased risk of stroke, especially in the elderly cohort with no benefit for the end points of all-cause mortality, cardiovascular morbidity, and mortality. In this review, we critically analyze the evidence supporting the use of beta-blockers in patients with hypertension and evaluate evidence for its role in other indications. The review of the currently available literature shows that in patients with uncomplicated hypertension, there is a paucity of data or absence of evidence to support use of beta-blockers as monotherapy or as first-line agents. Given the increased risk of stroke, their "pseudo-antihypertensive" efficacy (failure to lower central aortic pressure), lack of effect on regression of target end organ effects like left ventricular hypertrophy and endothelial dysfunction, and numerous adverse effects, the risk benefit ratio for beta-blockers is not acceptable for this indication. However, beta-blockers remain very efficacious agents for the treatment of heart failure, certain types of arrhythmia, hypertropic obstructive cardiomyopathy, and in patients with prior myocardial infarction.

Treatment of heart failure in Dutch general practice

Background

To study the relation between the prescription rates of selected cardiovascular drugs (ACE-inhibitors and Angiotensin receptor blockers, beta-blockers, diuretics, and combinations), sociodemographic factors (age, gender and socioeconomic class) and concomitant diseases (hypertension, coronary heart disease, cerebrovascular accident, heart valve disease, atrial fibrillation, diabetes mellitus and asthma/COPD) among patients with heart failure cared for in general practice.

Methods

Data from the second Dutch National Survey in General Practice, conducted mainly in 2001. In this study the data of 96 practices with a registered patient population of 374.000 were used.

Data included diagnosis made during one year by general practitioners, derived from the electronic medical records, prescriptions for medication and sociodemographic characteristics collected via a postal questionnary (response 76%)

Results

A diagnosis of HF was found with 2771 patients (7.1 in 1000). Their mean age was 77.7 years, 68% was 75 years or older, 55% of the patients were women. Overall prescription rates for RAAS-I, beta-blockers and diuretics were 50%, 32%, 86%, respectively, whereas a combination of these three drugs was prescribed in 18%. Variations in prescription rates were mainly related to age and concomitant diseases.

Conclusion

Prescription is not influenced by gender, to a small degree influenced by socioeconomic status and to a large degree by age and concomitant diseases.

Programme to improve the use of beta-blockers for heart failure in the elderly and in those with severe symptoms: results of the BRING-UP 2 Study

BACKGROUND

Beta-blockers are underused in HF patients, thus strategies to implement their use are needed.

OBJECTIVES

To improve beta-blocker use in elderly and/or patients with severe heart failure (HF) and to evaluate safety and outcome.

METHODS

Patients with symptomatic HF and age>/=70 years or left ventricular EF<25% and symptoms at rest were enrolled, including those already on beta-blocker treatment. Patients who were not receiving a beta-blocker were considered for carvedilol treatment. All patients were followed up for 1-year.

RESULTS

Of the 1518 elderly patients, 505 were already on beta-blockers, and carvedilol was newly prescribed in 419 patients. At 1-year, patients treated with carvedilol had a lower incidence of death [10.8% vs. 18.0% in already treated (adjusted RR 0.68; 95%CI 0.49-0.96) and 11.2% in newly treated patients (adjusted RR 0.68; 95%CI 0.48-0.97)]. Of the 709 patients with severe HF, 38.4% were already on beta-blockers, and carvedilol was newly prescribed in 189 patients. Patients not treated with carvedilol showed the worst clinical outcome. Total rate of discontinuation (including adverse reaction and non-compliance) was 14% and 9%, respectively, in elderly and severe patients.

CONCLUSIONS

In a real world setting, beta-blocker treatment was not associated with an increased risk of adverse events in elderly and severe HF patients.