Lipid Lowering by Pravastatin Increases Parasympathetic Modulation of Heart Rate

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Novel strategies and underlying protective mechanisms of modulation of vagal activity in cardiovascular diseases

Cardiovascular disease remains a major cause of disability and death worldwide. Autonomic imbalance, characterized by suppressed vagal (parasympathetic) activity and increased sympathetic activity, correlates with various pathological conditions, including heart failure, arrhythmia, ischaemia/reperfusion injury and hypertension. Conventionally, pharmacological interventions, such as β-blocker treatment, have primarily targeted suppressing sympathetic over-activation, while vagal modulation has always been neglected. Emerging evidence has documented the improvement of cardiac and vascular function mediated by the vagal nerve. Many investigators have tried to explore the effective ways to enhance vagal tone and normalize the autonomic nervous system. In this review, we attempt to give an overview of these therapeutic strategies, including direct vagal activation (electrical vagal stimulation, ACh administration and ACh receptor activation), pharmacological modulation (adenosine, cholinesterase inhibitors, statins) and exercise training. This overview provides valuable information for combination therapy, contributing to establishment of a comprehensive system on vagal modulation from the aspects of clinical application and lifestyle improvement. In addition, the mechanisms contributing to the benefits of enhancing vagal tone are diverse and have not yet been fully defined. We endeavour to outline the recent findings that advance our knowledge regarding the many favourable effects exerted by vagal activation: anti-inflammatory pathways, modulation of NOS and NO signalling, regulation of redox state, improvement of mitochondrial biogenesis and function, and potential calcium regulation. This review may help to develop novel therapeutic strategies targeting enhancing vagal activity for the treatment of cardiovascular diseases.

Exploratory multivariate analysis of the effect of fatty fish consumption and medicinal use on heart rate and heart rate variability data

The overall aim of the present study was to explore the relationship between medicinal use and fatty fish consumption on heart rate variability (HRV) and heart rate (HR) in a group of forensic inpatients on a variety of medications. A total of 49 forensic inpatients, randomly assigned to a fish group (n = 27) or a control group (n = 22) were included in the present study. Before and by the end of the food intervention period HR and HRV were measured during an experimental test procedure. An additional aim of this paper is to show how multivariate data analysis can highlight differences and similarities between the groups, thus being a valuable addition to traditional statistical hypothesis testing. The results indicate that fish consumption may have a positive effect on both HR and HRV regardless of medication, but that the influence of medication is strong enough to mask the true effect of fish consumption. Without correcting for medication, the fish group and control group become indistinguishable (p = 0.0794, Cohen’s d = 0.60). The effect of medication is demonstrated by establishing a multivariate regression model that estimates HR and HRV in a recovery phase based on HR and HRV data recorded during psychological tests. The model performance is excellent for HR data, but yields poor results for HRV when employed on participants undergoing the more severe medical treatments. This indicates that the HRV behavior of this group is very different from that of the participants on no or lower level of medication. When focusing on the participants on a constant medication regime, a substantial improvement in HRV and HR for the fish group compared to the control group is indicated by a principal component analysis and t-tests (p = 0.00029, Cohen’s d = 2.72). In a group of psychiatric inpatients characterized by severe mental health problems consuming different kinds of medication, the fish diet improved HR and HRV, indices of both emotional regulation and physical health.

Attenuation of acetylcholine activated potassium current (I KACh) by simvastatin, not pravastatin in mouse atrial cardiomyocyte: possible atrial fibrillation preventing effects of statin

Statins, 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors, are associated with the prevention of atrial fibrillation (AF) by pleiotropic effects. Recent clinical trial studies have demonstrated conflicting results on anti-arrhythmia between lipophilic and hydrophilic statins. However, the underlying mechanisms responsible for anti-arrhythmogenic effects of statins are largely unexplored. In this study, we evaluated the different roles of lipophilic and hydrophilic statins (simvastatin and pravastatin, respectively) in acetylcholine (100 µM)-activated K⁺ current (I_KACh, recorded by nystatin-perforated whole cell patch clamp technique) which are important for AF initiation and maintenance in mouse atrial cardiomyocytes. Our results showed that simvastatin (1–10 µM) inhibited both peak and quasi-steady-state I_KACh in a dose-dependent manner. In contrast, pravastatin (10 µM) had no effect on I_KACh. Supplementation of substrates for the synthesis of cholesterol (mevalonate, geranylgeranyl pyrophosphate or farnesyl pyrophosphate) did not reverse the effect of simvastatin on I_KACh, suggesting a cholesterol-independent effect on I_KACh. Furthermore, supplementation of phosphatidylinositol 4,5-bisphosphate, extracellular perfusion of phospholipase C inhibitor or a protein kinase C (PKC) inhibitor had no effect on the inhibitory activity of simvastatin on I_KACh. Simvastatin also inhibits adenosine activated I_KACh, however, simvastatin does not inhibit I_KACh after activated by intracellular loading of GTP gamma S. Importantly, shortening of the action potential duration by acetylcholine was restored by simvastatin but not by pravastatin. Together, these findings demonstrate that lipophilic statins but not hydrophilic statins attenuate I_KACh in atrial cardiomyocytes via a mechanism that is independent of cholesterol synthesis or PKC pathway, but may be via the blockade of acetylcholine binding site. Our results may provide important background information for the use of statins in patients with AF.

The Relationship between Serum Lipid Fractions and Heart Rate Variability in Diabetic Patients with Statin Therapy

BACKGROUND AND AIMS

The aim of this study is to identify and highlight the relationship between serum lipid fractions and heart rate variability in diabetic patients receiving statin therapy.

PATIENTS AND METHODS

The study was performed in a group of 87 type 2 diabetic patients on statin associated therapy. All patients were on Holter ECG 24 hours monitored with three channel monitor (Labtech ECG Holter monitor), and data were analyzed on a commercially available software (Cardiospy PC SW/EV 5.02.06.02). Concentrations of biochemical parameters were determined using specific enzymatic assays on an autoanalyzer Olympus AU 680. In the studied patients, we analyzed Holter/24 hours monitoring reports with respect to heart rate variability indexes, arrhythmic events and myocardial ischemia.

RESULTS

It was noticed that the mean values of serum TG were slightly elevated, TC levels were close to the limits specified by the guidelines for diabetic patients and for patients with cardiovascular diseases, with no significant differences between males and females. After analyzing the HRV in both time and frequency domains, we found no strong correlations between any of the HRV indexes and any of the lipid fractions.

CONCLUSIONS

The results suggest that statin therapy may reduce the autonomic impairment secondary to dyslipidemia.

Statins and the autonomic nervous system

Statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) reduce plasma cholesterol and improve endothelium-dependent vasodilation, inflammation and oxidative stress. A ‘pleiotropic’ property of statins receiving less attention is their effect on the autonomic nervous system. Increased central sympathetic outflow and diminished cardiac vagal tone are disturbances characteristic of a range of cardiovascular conditions for which statins are now prescribed routinely to reduce cardiovascular events: following myocardial infarction, and in hypertension, chronic kidney disease, heart failure and diabetes. The purpose of the present review is to synthesize contemporary evidence that statins can improve autonomic circulatory regulation. In experimental preparations, high-dose lipophilic statins have been shown to reduce adrenergic outflow by attenuating oxidative stress in central brain regions involved in sympathetic and parasympathetic discharge induction and modulation. In patients with hypertension, chronic kidney disease and heart failure, lipophilic statins, such as simvastatin or atorvastatin, have been shown to reduce MNSA (muscle sympathetic nerve activity) by 12–30%. Reports concerning the effect of statin therapy on HRV (heart rate variability) are less consistent. Because of their implications for BP (blood pressure) control, insulin sensitivity, arrhythmogenesis and sudden cardiac death, these autonomic nervous system actions should be considered additional mechanisms by which statins lower cardiovascular risk.

Heart rate as a possible therapeutic guide for the prevention of cardiovascular disease

Epidemiologic evidence indicates that an elevated heart rate (HR) is an independent predictor of all-cause and cardiovascular (CV) mortality. Ivabradine, a pure HR-lowering agent, reduces CV events in patients with coronary artery disease (CAD) and chronic heart failure, and indicate that an HR greater than 70 b.p.m. is hazardous. These findings demonstrate not only that an elevated HR is an epiphenomenon of CV risk status but also that an elevated HR itself should be a therapeutic target. In addition, recent epidemiologic evidence demonstrates that the in-treatment HR or HR change predicts subsequent all-cause and CV mortality, independent of the HR-lowering strategy. Characteristics of the in-treatment HR or HR change are also important as possible therapeutic guides for risk management. However, there have been concerns regarding deleterious effects on CV event prevention owing to β-blocker-derived pharmacologic HR reduction. The potential role of HR and its modulation should be considered in future guidance documents.

Association of heart rate variability and inflammatory response in patients with cardiovascular diseases: current strengths and limitations

Many experimental and clinical studies have confirmed a continuous cross-talk between both sympathetic and parasympathetic branches of autonomic nervous system and inflammatory response, in different clinical scenarios. In cardiovascular diseases, inflammation has been proven to play a pivotal role in disease progression, pathogenesis and resolution. A few clinical studies have assessed the possible inter-relation between neuro-autonomic output, estimated with heart rate variability analysis, which is the variability of R-R in the electrocardiogram, and different inflammatory biomarkers, in patients suffering from stable or unstable coronary artery disease (CAD) and heart failure. Moreover, different indices derived from heart rate signals' processing, have been proven to correlate strongly with severity of heart disease and predict final outcome. In this review article we will summarize major findings from different investigators, evaluating neuro-immunological interactions through heart rate variability analysis, in different groups of cardiovascular patients. We suggest that markers originating from variability analysis of heart rate signals seem to be related to inflammatory biomarkers. However, a lot of open questions remain to be addressed, regarding the existence of a true association between heart rate variability and autonomic nervous system output or its adoption for risk stratification and therapeutic monitoring at the bedside. Finally, potential therapeutic implications will be discussed, leading to autonomic balance restoration in relation with inflammatory control.

The Role of Inhibitory G Proteins and Regulators of G Protein Signaling in the in vivo Control of Heart Rate and Predisposition to Cardiac Arrhythmias

Inhibitory heterotrimeric G proteins and the control of heart rate. The activation of cell signaling pathways involving inhibitory heterotrimeric G proteins acts to slow the heart rate via modulation of ion channels. A large number of Regulators of G protein signalings (RGSs) can act as GTPase accelerating proteins to inhibitory G proteins and thus it is important to understand the network of RGS\G-protein interaction. We will review our recent findings on in vivo heart rate control in mice with global genetic deletion of various inhibitory G protein alpha subunits. We will discuss potential central and peripheral contributions to the phenotype and the controversies in the literature.

Statins in non-ischaemic cardiomyopathy: an update on our current clinical and pathophysiological understanding

Statins are a cornerstone in reducing cardiovascular events. Studies show that statins are beneficial even in patients with normal or low cholesterol levels, indicating pleiotropic mechanisms of therapeutic benefit apart from their antihyperlipidemic effect. Non-randomised, observational and retrospective studies suggest that statins are associated with better outcomes in patients with heart failure (HF) of both ischaemic and non-ischaemic aetiologies. While cholesterol reduction and plaque stabilisation likely play a role in reducing cardiovascular events in ischaemic HF patients, the mechanisms underlying the benefit in non-ischaemic HF patients is less clear. This review suggests the pleiotropic effects of statin therapy can beneficially alter the pathophysiological mechanisms underlying the clinical benefit observed in non-ischaemic HF patients.

Statins and the reduction of sudden cardiac death: antiarrhythmic or anti-ischemic effect?

Sudden cardiac death is an important cause of cardiovascular mortality with the majority of cases occurring in low-risk groups. HMG-CoA reductase inhibitors (statins) have recently been shown to reduce the incidence of ventricular tachycardia (VT)/fibrillation (VF) and sudden cardiac death, and this has been attributed to their pleiotropic effects. However, it is unclear whether this occurs through an 'indirect' anti-ischemic or 'direct' antiarrhythmic effect. We systematically reviewed articles published on MEDLINE between January 1996 and December 2009 focusing on the reduction of VT/VF and sudden cardiac death by statins and the potential mechanisms. Studies reporting sudden cardiac death or VT/VF outcomes with statin use (n = 23) or the pathophysiology of sudden cardiac death reduction by statins (n = 19) were included. We found that statins have been shown to reduce VT/VF and sudden cardiac death only in subjects with underlying coronary artery disease or ischemic cardiomyopathy. No definite benefits were seen with statins in sudden cardiac death and VT/VF in patients with non-ischemic cardiomyopathy. There is insufficient evidence to point toward a benefit in populations at low risk for VT/VF. In conclusion, an anti-ischemic rather than a primary antiarrhythmic effect emerges as the likely mechanism of sudden cardiac death reduction with statins.

Absence of the inhibitory G-protein Galphai2 predisposes to ventricular cardiac arrhythmia

BACKGROUND

We explored the role that inhibitory heterotrimeric G-proteins play in ventricular arrhythmia.

METHODS AND RESULTS

Mice with global genetic deletion of Galpha(i2) [Galpha(i2) (-/-)] were studied and found, based on telemetry, to have a prolonged QT interval on surface ECG when awake. In vivo electrophysiology studies revealed that the Galpha(i2) (-/-) mice have a reduced ventricular effective refractory period and a predisposition to ventricular tachycardia when challenged with programmed electrical stimulation. Neither control nor combined global deletion of Galpha(i1) and Galpha(i3) mice showed these abnormalities. There was no evidence for structural heart disease at this time point in the Galpha(i2) (-/-) mice as assessed by cardiac histology and echocardiography. The absence of Galpha(i2) thus leads to a primary electrical abnormality, and we explored the basis for this finding. With patch clamping, single isolated ventricular cells showed that Galpha(i2) (-/-) mice had a prolonged ventricular action potential duration (APD) but steeper action potential shortening as the diastolic interval was reduced in restitution studies. Gene expression studies showed increased expression of L-type Ca(2+) channel subunits, and patch clamping revealed an increase in these currents in Galpha(i2) (-/-) mice. There were no changes in K(+) currents.

CONCLUSIONS

The absence of inhibitory G-protein signaling mediated through Galpha(i2) is a substrate for ventricular arrhythmias.

Differential effects of statins (pravastatin or simvastatin) on ventricular ectopic complexes: Galpha(i2), a possible molecular marker for ventricular irritability

Retrospective studies suggest that statins might exert an antiarrhythmic effect on the heart. The mechanism of this effect is unclear. Parasympathetic stimulation of the heart has been shown to protect against ventricular arrhythmias. The goal of this study was to determine the effect of statins on ventricular arrhythmias and its correlation with changes in parasympathetic responsiveness and Galpha(i2) expression. Patients were randomized to pravastatin and simvastatin in a double-blind crossover design. Ventricular arrhythmias were determined by analysis of 24-hour Holter recordings. Spectral RR interval analysis of Holter studies determined peak high-frequency power fraction, which reflects parasympathetic modulation of heart rate. Expression of Galpha(i2), a molecular component of the parasympathetic response pathway, was determined by Western blots of patients' lymphocytes. Pravastatin treatment decreased the incidence of ventricular premature complexes by 22.5 + or - 3.4% (n = 20, p <0.05), couplets, and runs of 3 to 6 beats of nonsustained ventricular tachycardia from 9.8 + or - 2.67 to 3.9 + or - 1.25 events/patient/24 hours (n = 12, p <0.05). Pravastatin increased peak high-frequency fraction by 29.8 + or - 4.3% (n = 33, p <0.001), while Galpha(i2) expression increased by 51.3 + or - 22.5% (n = 21, p <0.05). Effects of simvastatin on ventricular premature complexes and nonsustained ventricular tachycardia were not significant. Relative changes in couplets and nonsustained ventricular tachycardia in pravastatin-treated patients correlated negatively with changes in Galpha(i2) and high-frequency fraction (rho = -0.588 and rho = -0.763, respectively, n = 12, p <0.05). In conclusion, these data suggest that pravastatin might decrease cardiac irritability via an increase in parasympathetic responsiveness and that changes in Galpha(i2) expression might serve as a molecular marker for this effect, which might play a role in the molecular mechanism of the antiarrhythmic effect of statins.

Statins as anti-arrhythmics: a systematic review part II: effects on risk of ventricular arrhythmias

BACKGROUND

Recent studies have demonstrated that statins may possess anti-arrhythmic properties in addition to their lipid-lowering effects.

METHODS

Studies which reported the association of statins with the incidence of ventricular arrhythmias were identified through a systematic review of the published literature.

RESULTS

Statins have been associated with a significant reductions in ventricular arrhythmia in cardiomyopathy patients with an implantable cardioverter defibrillator, although randomized trials have not been completed.

CONCLUSIONS

Published data suggests that statins may possess anti-arrhythmic properties that reduce the propensity for ventricular arrhythmias. Most of this data is observational; more randomized, placebo-controlled trials are needed.

Residual microvascular risk in diabetes: unmet needs and future directions

The burden of microvascular disease in patients with type 2 diabetes mellitus continues to escalate worldwide. Current standards of care reduce but do not eliminate the risk of diabetic retinopathy, nephropathy or neuropathy in these patients. Correction of atherogenic dyslipidemia, which is characterized by elevated triglyceride levels and low levels of HDL cholesterol, might provide additional benefit. Whereas promising data have been published with respect to fibrate therapy for maculopathy, fenofibrate for diabetic retinopathy, and statin or fibrate therapy for diabetic nephropathy, further studies are warranted to define optimal management strategies for reducing the residual microvascular risk. Such strategies are especially relevant in cases of diabetic peripheral neuropathy, where even optimal care fails to affect disease progression. Identification of those factors that are most relevant to residual diabetes-related microvascular risk is a priority of an ongoing multinational epidemiological study. In this Review, we highlight an urgent need to address the issue of microvascular residual risk in patients with or at risk of type 2 diabetes mellitus.

Impaired regulation of cardiac function in sepsis, SIRS, and MODS

In sepsis, systemic inflammatory response syndrome (SIRS), and multiorgan dysfunction syndrome (MODS), a severe prognostically relevant cardiac autonomic dysfunction exists, as manifested by a strong attenuation of sympathetically and vagally mediated heart rate variability (HRV). The mechanisms underlying this attenuation are not limited to the nervous system. They also include alterations of the cardiac pacemaker cells on a cellular level. As shown in human atrial cardiomyocytes, endotoxin interacts with cardiac hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels, which mediate the pacemaker current If and play an important role in transmitting sympathetic and vagal signals on heart rate and HRV. Moreover, endotoxin sensitizes cardiac HCN channels to sympathetic signals. These findings identify endotoxin as a pertinent modulator of the autonomic nervous regulation of heart function. In MODS, the vagal pathway of the autonomic nervous system is particularly compromised, leading to an attenuation of the cholinergic antiinflammatory reflex. An amelioration of the blunted vagal activity appears to be a promising novel therapeutic target to achieve a suppression of the inflammatory state and thereby an improvement of prognosis in MODS patients. Preliminary data revealed therapeutic benefits (increased survival rates and improvements of the depressed vagal activity) of the administration of statins, beta-blockers, and angiotensin-converting enzyme inhibitors in patients with MODS.

The role of inhibitory heterotrimeric G proteins in the control of in vivo heart rate dynamics

Multiple isoforms of inhibitory Galpha-subunits (Galphai1,2,3, as well as Galphao) are present within the heart, and their role in modulating pacemaker function remains unresolved. Do inhibitory Galpha-subunits selectively modulate parasympathetic heart rate responses? Published findings using a variety of experimental approaches have implicated roles for Galphai2, Galphai3, and Galphao in parasympathetic signal transduction. We have compared in vivo different groups of mice with global genetic deletion of Gialpha1/Galphai3, Galphai2, and Galphao against littermate controls using implanted ECG telemetry. Significant resting tachycardia was observed in Galphai2(-/-) and Galphao(-/-) mice compared with control and Galphai1(-/-)/Galphai3(-/-) mice (P < 0.05). Loss of diurnal heart rate variation was seen exclusively in Galphao(-/-) mice. Using heart rate variability (HRV) analysis, compared with littermate controls (4.02 ms2 +/- 1.17; n = 6, Galphai2(-/-)) mice have a selective attenuation of high-frequency (HF) power (0.73 ms2 +/- 0.31; n = 5, P < 0.05). Galphai1(-/-)/Galphai3(-/-) and Galphao(-/-) cohorts have nonsignificant changes in HF power. Galphao(-/-) mice have a different basal HRV signature. The observed HRV phenotype in Galphai2(-/-) mice was qualitatively similar to atropine (1 mg/kg)-treated controls [and mice treated with the GIRK channel blocker tertiapinQ (0.05 mg/kg)]. Maximal cardioinhibitory response to the M(2)-receptor agonist carbachol (0.5 mg/kg) compared with basal heart rate was attenuated in Galphai2(-/-) mice (0.08 +/- 0.04; n = 6) compared to control (0.27 +/- 0.04; n = 7 P < 0.05). Our data suggest a selective defect of parasympathetic heart rate modulation in mice with Galphai2 deletion. Mice with Galphao deletion also have a defect in short-term heart rate dynamics, but this is qualitatively different to the effects of atropine, tertiapinQ, and Galphai2 deletion. In contrast, Galphai1 and Galphai3 do not appear to be essential for parasympathetic responses in vivo.

Potential autonomic nervous system effects of statins in heart failure

Sympathetic nervous system activation in heart failure, as indexed by elevated norepinephrine levels, higher muscle sympathetic nerve activity and reduced heart rate variability, is associated with pathologic ventricular remodeling, increased arrhythmias, sudden death, and increased mortality. Recent evidence suggests that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) therapy may provide survival benefit in heart failure of both ischemic and nonischemic etiology, and one potential mechanism of benefit of statins in heart failure is modulation of the autonomic nervous system. Animal models of heart failure demonstrate reduced sympathetic activation and improved sympathovagal balance with statin therapy. Initial human studies have reported mixed results. Ongoing translational studies and outcomes trials will help delineate the potentially beneficial effects of statins on the autonomic nervous system in heart failure.

The alteration of autonomic function in multiple organ dysfunction syndrome

Autonomic dysfunction is associated with the severity of illness and mortality in patients with multiple organ dysfunction syndrome (MODS) and may contribute significantly to the pathogenesis of this syndrome. Several treatment approaches may possibly restore autonomic function in MODS and thus cause the survival benefit.

Inflammation and ageing

An enhanced inflammatory state - i.e. "inflammatory/pathogen burden" - in the elderly on the one hand results from physiological immunosenescence and on the other hand is modified by the individual immune history: the latter is determined by sequential infectious/pathogenic events ("multiple hits"). Immunosenescence may prompt ageing of other organs. Cardiac ageing can be assessed by analysing heart rate variability. We present our hypothesis that the increasing "inflammatory/pathogen burden" of each organism during a lifetime significantly contributes to the cardiac ageing process. This hypothesis is grounded on the fact that a characteristic feature of the ageing heart - a narrowed heart rate variability - can be experimentally induced in humans by an inflammatory stimulus (endotoxin).

The altered homeostatic theory: A hypothesis proposed to be useful in understanding and preventing ischemic heart disease, hypertension, and diabetes – including reducing the risk of age and atherosclerosis

Evidence will be presented to support the usefulness of the altered homeostatic theory in understanding basic pathogenetic mechanisms of ischemic heart disease (IHD), hypertension, and diabetes, and in improving prevention of these disorders. The theory argues that: IHD, hypertension, and diabetes share the same basic pathogenesis; risk factors favor a sympathetic homeostatic shift; preventative factors favor a parasympathetic homeostatic shift; risk and preventative factors oppose each other through a dynamic risk/prevention balance; and prevention should be based on improving the risk/prevention balance. Prevention based on improving the risk/prevention balance should be more effective, as this method is regarded as reflecting more accurately basic pathogenetic mechanisms. As example, the theory argues that the risk of supposedly nonmodifiable risk factors as age and the risk of relatively nonmodifiable atherosclerosis can be reduced significantly. The possible validity of the altered homeostatic theory was tested by a study based on multiple associations. Findings support a common pathogenesis for IHD, hypertension, and diabetes based on a sympathetic homeostatic shift, and the usefulness of prevention based on improving the risk/prevention balance by using standard pharmaceutical and lifestyle preventative measures. The same set of multiple and diverse risk factors favored IHD, hypertension, and diabetes, and the same set of multiple and diverse pharmaceutical and lifestyle preventative measures prevented these disorders. Also, the same set of preventative agents generally improved cognitive function and bone density, and reduced the incidence of Alzheimer's disease, atrial fibrillation, and cancer. Unexpectedly, evidence was developed that four major attributes of sympathetic activation represent four major risk factors; attributes of sympathetic activation are a tendency toward thrombosis and vasoconstriction, lipidemia, inflammation, and hyperglycemia, and corresponding risk factors are endothelial dysfunction (which expresses thrombosis/vasoconstriction and epitomizes this tendency), dyslipidemia, inflammation, and insulin resistance. These findings, plus other information, provide evidence that dyslipidemia acts mainly as a marker of risk of IHD, rather than being the basic mechanism of this disorder. However, prevention generally is based solely on improvement of dyslipidemia; basing prevention on dyslipidemia relatively underemphasizes the importance of other significant risk factors and, by certifying its validity, discourages alternate pathogenetic approaches. Also, development of myocardial infarction is approached differently. It seems generally accepted that dyslipidemia results rather automatically in infarction through the sequence of atherosclerosis, atherosclerotic complications, and thrombosis. In contrast, distinction is made between development of atherosclerosis and acute induction of infarction--where atherosclerosis is only one of multiple risk factors.

Lipid-lowering therapy with statins, a new approach to antiarrhythmic therapy

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (statins) are the most effective and best-tolerated drugs to treat elevated levels of low-density lipoprotein cholesterol (LDL-C). In addition, they exhibit other effects unrelated to their lipid lowering effects (pleiotropic actions). In recent years, experimental and clinical evidence demonstrates that statins exert antiarrhythmic properties, reducing the recurrences of supraventricular and life-threatening ventricular arrhythmias both in patients with and without coronary artery disease (CAD). Thus, statins may constitute a novel therapeutic approach to cardiac arrhythmias. This article reviews the antiarrhythmic properties of statins as well as the possible mechanisms involved, including the lowering of LDL-C levels, the improvement of endothelial dysfunction and autonomic function, the stabilization of the atherosclerotic plaques, the antioxidant, antiinflammatory, antithrombotic and cardioprotective properties and the modulation of transmembrane ion fluxes.

Use of wavelet and fast Fourier transforms in pharmacodynamics

Progress has been made in the development and application of mechanism-based pharmacodynamic models for describing the drug-specific and physiological factors influencing the time course of responses to the diverse actions of drugs. However, the biological variability in biosignals and the complexity of pharmacological systems often complicate or preclude the direct application of traditional structural and nonstructural models. Mathematical transforms may be used to provide measures of drug effects, identify structural and temporal patterns, and visualize multidimensional data from analyses of biomedical signals and images. Fast Fourier transform (FFT) and wavelet analyses are two methodologies that have proven to be useful in this context. FFT converts a signal from the time domain to the frequency domain, whereas wavelet transforms colocalize in both domains and may be utilized effectively for nonstationary signals. Nonstationary drug effects are common but have not been well analyzed and characterized by other methods. In this review, we discuss specific applications of these transforms in pharmacodynamics and their potential role in ascertaining the dynamics of spatiotemporal properties of complex pharmacological systems.

Atorvastatin Therapy Increases Heart Rate Variability, Decreases QT Variability, and Shortens QTc Interval Duration in Patients With Advanced Chronic Heart Failure

BACKGROUND

Although statins decrease the incidence of ventricular arrhythmias in patients with atherosclerotic heart disease, their potential antiarrhythmic effects in heart failure remain undefined.

METHODS AND RESULTS

Of 80 heart failure patients enrolled, 40 were randomized to receive atorvastatin (statin group); the remaining 40 served as controls. At baseline and after 3 months, we measured heart rate variability (HRV), QT variability (QTV), and QTc interval using interactive high-resolution electrocardiogram analysis. The 2 groups did not differ in baseline HRV standard deviation of normal-to-normal intervals (SDNN) (RR): 24.6 +/- 2.8 ms in statin group versus 24.8 +/- 3.1 ms in controls, P = .72; square root of the mean of squared differences between successive intervals (rMSSD) (RR): 21.2 +/- 2.7 ms versus 21.7 +/- 2.9 ms, P = .43), QTV SDNN (QT): 6.4 +/- 1.5 ms versus 6.4+/-1.7, P = .96; rMSSD QT): 9.0 +/- 2.4 ms versus 8.7 +/- 2.9 ms, P = .65, and QTc interval 450 +/- 30 ms versus 446 +/- 27 ms, P = .59. At 3 months, the statin group displayed higher HRV SDNN RR): 27.2 +/- 4.9 ms versus 24.4 +/- 2.8 ms in controls, P = .003; rMSSD RR: 24.7 +/- 4.2 ms versus 21.3 +/- 5.6 ms, P = .004, lower QTV SDNN (QT): 5.1 +/- 1.9 ms versus 6.5 +/- 2.1, P = .004; rMSSD (QT): 6.6 +/- 2.8 ms versus 8.8 +/- 3.1 ms, P = .002, and shorter QTc interval 437 +/- 29 ms versus 450 +/- 25 ms, P = .03 than the control group.

CONCLUSIONS

Atorvastatin increases HRV, decreases QTV, and shortens QTc interval, and may thereby reduce the risk of arrhythmias in patients with advanced heart failure.

A prospective evaluation of the effect of simvastatin on heart rate variability in non-ischemic cardiomyopathy

BACKGROUND

Modulation of sympathetic tone may contribute to statin-mediated reduction in sudden cardiac death. We examined the effect of simvastatin on heart rate variability (HRV) in patients with non-ischemic dilated cardiomyopathy to evaluate for an antisympathetic effect of statins independent of anti-ischemic properties.

METHODS

The study was a prospective, open-label, self-controlled trial. Frequency domain analysis of HRV was assessed in 25 patients with non-ischemic dilated cardiomyopathy at baseline and after a 6-week course of simvastatin. The primary end point was the change in 5-minute sitting total spectral power (TSP) as a composite measurement of autonomic nervous system modulation. Secondary end points included the change in respiratory frequency area (RFa) with deep breathing (parasympathetic stress) and in low-frequency area (LFa) with Valsalva (sympathetic stress).

RESULTS

Simvastatin had no effect on 5-minute sitting TSP (baseline 1932 +/- 1165 vs posttreatment 2570 +/- 1877 square milliseconds, P = .770), RFa with deep breathing (baseline 19 +/- 7 vs posttreatment 14 +/- 4 [beat/min]2, P = .31), or LFa with Valsalva (baseline 26 +/- 6 vs posttreatment 32 +/- 8 [beat/min]2, P = .342). Bivariate analysis demonstrated no correlation between low-density lipoprotein (LDL) change and change in TSP or RFa, but did demonstrate an inverse relationship between change in LDL and change in LFa with Valsalva stress (r = -0.45 and P = .041).

CONCLUSION

Although simvastatin did not change baseline HRV, a modest relationship exists between the extent of LDL reduction and sympathetic responsiveness to stress.

Glutathione-S-transferase M1, obesity, statins, and autonomic effects of particles: gene-by-drug-by-environment interaction

RATIONALE

Air pollution by particulate matter (PM) has been associated with cardiovascular deaths, although the mechanism of action is unclear. One proposed pathway is through disturbances of the autonomic control of the heart.

OBJECTIVES

We tested the hypothesis that such disturbances are mediated by PM increasing oxidative stress by examining the association between PM and the high-frequency (HF) component of heart rate variability as modified by the presence or absence of the allele for glutathione-S-transferase M1 (GSTM1) and the use of statins, obesity, high neutrophil counts, higher blood pressure, and older age.

METHODS

We examined the association between particles less than 2.5 microM in aerodiameter (PM2.5) and HF in 497 participants in the Normative Aging Study, using linear regression controlling for covariates.

MAIN RESULTS

A 10-microg/m3 increase in PM2.5 during the 48 h before HF measurement was associated with a 34% decrease in HF, 95% confidence interval (-9%, -52%), in subjects without the allele, but had no effect in subjects with GSTM1 present. Among GSTM1-null subjects, the use of statins eliminated the effect of PM2.5. Obesity and high neutrophil counts also worsened the PM effects with or without GSTM1.

CONCLUSION

The effects of PM2.5 on HF appear to be mediated by reactive oxygen species. This may be a key pathway for the adverse effects of combustion particles.

Association of triglyceride-to-HDL cholesterol ratio with heart rate recovery

OBJECTIVE

Insulin resistance is associated with autonomic dysfunction. An attenuated decrease in heart rate after exercise (or heart rate recovery [HRR]) predicts all-cause mortality and is believed to reflect decreased parasympathetic activity. Utilizing triglyceride/HDL cholesterol concentration as a marker of insulin resistance, we sought to assess the association between insulin resistance and HRR.

RESEARCH DESIGN AND METHODS

Our study population included 4,963 healthy adults who participated in the Lipid Research Clinics Prevalence Study and underwent exercise testing. HRR was considered abnormal if it did not drop > or = 42 bpm 2 min after completion of exercise. Fasting blood specimens were drawn.

RESULTS

Individuals in the highest quartile of triglyceride/HDL cholesterol had a significantly higher prevalence of abnormal HRR (40 vs. 30%, multivariable-adjusted prevalence ratio 1.18, 95% CI 1.01-1.39; P = 0.04). As a continuous variable, an increase in 1 SD of triglyceride-to-HDL cholesterol ratio was associated with a greater likelihood of an abnormal HRR, even after adjusting for >20 covariates (adjusted OR 1.16, 95% CI 1.07-1.25; P < 0.001). During 12 years of follow-up, there were 284 deaths. In age- and sex-adjusted analysis, participants with an abnormal HRR and high triglyceride-to-HDL cholesterol ratio had significantly higher mortality than those with a normal HRR and high triglyceride-to-HDL cholesterol ratio (hazard ratio = 1.49, 95% CI 1.08-2.04; P = 0.015).

CONCLUSIONS

HRR is associated with triglyceride-to-HDL cholesterol ratio and identifies patients with insulin resistance who are at increased risk of death.