Effect of clonidine on heart rate variability in congestive heart failure

The use of attention-deficit hyperactivity disorder medications in cardiac disease

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder with onset usually in childhood characterized by inattention, impulsivity, and hyperactivity causing a functional impairment. Untreated ADHD, or treatment delay is associated with adverse outcomes and poor quality of life. Although conservative management strategies such as behavioral and psychological interventions are important, pharmacological treatment has a strong evidence base with improved outcomes. ADHD medications are broadly divided into stimulant and non-stimulant medications. Stimulant medications are generally more effective than non-stimulants. Cardiovascular safety of ADHD medication has been a matter of debate for decades. Treatment guidelines advise the careful consideration of risks and benefits in people with cardiovascular diseases such as congenital heart disease or cardiomyopathy. Although stimulants can increase systemic blood pressure and heart rate, no significant associations were found between their use and serious cardiovascular events. Concerns regarding QT effects and attendant sudden cardiac death risks deter clinicians from initiating much-needed ADHD medications in patients with heart disease. This overly cautious approach is potentially depriving low-risk individuals from significant benefits associated with timely ADHD drug treatment. This review discusses the cardiovascular risks reportedly associated with ADHD medications, the evidence base for their safe usage in persons with established cardiovascular disease, and highlights future research directions.

Multimodal Assessment of the Pulse Rate Variability Analysis Module of a Photoplethysmography-Based Telemedicine System

Alterations of heart rate variability (HRV) are associated with various (patho)physiological conditions; therefore, HRV analysis has the potential to become a useful diagnostic module of wearable/telemedical devices to support remote cardiovascular/autonomic monitoring. Continuous pulse recordings obtained by photoplethysmography (PPG) can yield pulse rate variability (PRV) indices similar to HRV parameters; however, it is debated whether PRV/HRV parameters are interchangeable. In this study, we assessed the PRV analysis module of a digital arterial PPG-based telemedical system (SCN4ALL). We used Bland–Altman analysis to validate the SCN4ALL PRV algorithm to Kubios Premium software and to determine the agreements between PRV/HRV results calculated from 2-min long PPG and ECG captures recorded simultaneously in healthy individuals (n = 33) at rest and during the cold pressor test, and in diabetic patients (n = 12) at rest. We found an ideal agreement between SCN4ALL and Kubios outputs (bias < 2%). PRV and HRV parameters showed good agreements for interbeat intervals, SDNN, and RMSSD time-domain variables, for total spectral and low-frequency power (LF) frequency-domain variables, and for non-linear parameters in healthy subjects at rest and during cold pressor challenge. In diabetics, good agreements were observed for SDNN, LF, and SD2; and moderate agreement was observed for total power. In conclusion, the SCN4ALL PRV analysis module is a good alternative for HRV analysis for numerous conventional HRV parameters.

Intrathecal Clonidine via Lumbar Puncture Decreases Blood Pressure in Patients With Poorly Controlled Hypertension

OBJECTIVES

Oral clonidine is used to treat hypertension but often produces sedation and severe dry mouth; intrathecal clonidine is used to treat chronic pain but may produce hypotension. This clinical feasibility study was conducted to determine if intrathecal clonidine decreases blood pressure in patients with poorly controlled hypertension.

MATERIALS AND METHODS

This prospective, single-arm, open-label study was conducted in ten subjects who were taking at least three antihypertensive medications including a diuretic and had an in-office systolic blood pressure between 140 and 190 mm Hg. On the day of treatment, blood pressure was measured before and after a single lumbar intrathecal dose (150 mcg) of clonidine using an automatic oscillometric device every 10-15 min for four hours. Student's paired t-test was used for statistical comparisons.

RESULTS

Maximal reductions in systolic and diastolic blood pressures averaging 63 ± 20/29 ± 13 mm Hg were observed approximately two hours after clonidine administration. Decreases in systolic pressure were strongly correlated with baseline systolic pressure. Clonidine produced a significant decrease in heart rate of 11 ± 7 beats/min. No subject required intravenous fluids or vasopressor rescue therapy, or reported spinal headache.

CONCLUSIONS

This is the first clinical study in subjects with hypertension that demonstrates significant and profound acute reductions in blood pressure after a single dose of intrathecal clonidine. Future placebo-controlled, dose-escalating studies are warranted to assess the long-term effects of intrathecal clonidine infusion via an implantable drug pump in patients with treatment-resistant hypertension at risk of stroke or myocardial infarction.

Muscarinic 2 receptors modulate cardiac proteasome function in a protein kinase G-dependent manner

Proteasome function insufficiency and inadequate protein quality control are strongly implicated in a large subset of cardiovascular disease and may play an important role in their pathogenesis. Protein degradation by the ubiquitin proteasome system can be physiologically regulated. Cardiac muscarinic 2 (M2) receptors were pharmacologically interrogated in intact mice and cultured neonatal rat ventricular myocytes (NRVMs). Proteasome-mediated proteolysis was measured with a surrogate misfolded protein, proteasome peptidase assay, and by characterizing key proteasome subunits. Successful M2 receptor manipulation in cardiomyocytes was determined by measuring an endogenous protein substrate, and in mice, the cardiovascular physiological response. M2 receptor stimulation was associated with increased proteasome-mediated proteolysis and enhanced peptidase activities, while M2 receptor inhibition yielded opposing results. Additionally, M2 receptor manipulation did not alter abundance of the key proteasome subunits, Rpt6 and β5, but significantly shifted their isoelectric points. Inhibition of protein kinase G abrogated the stimulatory effects on proteasome-mediated proteolysis from M2 receptor activation. We conclude that M2 receptor stimulation enhances, whereas M2 receptor inhibition reduces, proteasome-mediated proteolysis likely through posttranslational modifications. Protein kinase G appears to be the mediator of the M2 receptors actions.

Risk of serious cardiovascular problems with medications for attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a chronic neurodevelopmental disorder characterized by persistent symptoms of inattention, hyperactivity and/or impulsivity. The proportion of patients diagnosed with ADHD receiving pharmacological treatments has increased enormously in recent years. Despite the well established efficacy and the good safety and tolerability profile, there is concern about the potential for rare but serious cardiovascular adverse events, as well as sudden cardiac death, with pharmacotherapies used for treating ADHD in children, adolescents and adults. The present paper aims to comprehensively and critically review the published evidence on the controversial association between medications approved for treating patients with ADHD and the risk of serious cardiovascular problems, specifically the risk of corrected QT interval (QTc) prolongation, and the risk of sudden cardiac death. A comprehensive search of relevant databases (PubMed, EMBASE and PsychINFO) was conducted to identify studies published in peer-reviewed journals until 21 July 2012. Clinical reports, as well as retrospective or prospective population-based studies with children, adolescents or adults as participants, of pharmacotherapies for ADHD reporting cardiovascular adverse events were included. Stimulant medications for ADHD, including methylphenidate and amphetamine derivatives, are generally safe and well tolerated. Small but statistically significant increases in blood pressure (BP) and heart rate (HR) are among the adverse events of stimulant treatment in all age groups. Similarly, the non-stimulant medication atomoxetine has also been associated with increased HR and BP, although as is the case with stimulants, these are generally minor, time limited and of minor clinical significance in children, adolescents or adults. Growing evidence suggests that these medications do not cause sudden and unexpected cardiac death or serious cardiovascular problems including statistically or clinically significant increases in QTc, at therapeutic doses in ADHD patients across the lifespan. Small decreases in mean systolic BP, diastolic BP and HR have been observed in studies with guanfacine-extended release (-XR) or clonidine-XR, two α(2)-adrenergic receptor agonists, administered alone or in combination with psychostimulants to children and adolescents with ADHD. There are also no statistically or clinically significant increases in QTc associated with clonidine or guanfacine. There are no reports of torsades de pointes clearly and directly related to medications used for treating ADHD in patients of all age groups. The risk for serious cardiovascular adverse events, including statistically or clinically significant increases in QTc, and sudden cardiac death associated with stimulants, atomoxetine or α(2)-adrenergic agonists prescribed for ADHD is extremely low and the benefits of treating individual patients with ADHD, after an adequate assessment, outweigh the risks. However, great caution is advised when considering stimulant and non-stimulant medications for patients of any age with a diagnosis of ADHD and a personal or family history or other known risk factors for cardiovascular disease.

Deficiency of M2 muscarinic acetylcholine receptors increases susceptibility of ventricular function to chronic adrenergic stress

Suppressed parasympathetic nervous system (PSNS) function has been found in a variety of cardiovascular diseases, such as hypertension, heart failure, and diabetes. However, whether impaired PSNS function plays a significant role in ventricular dysfunction remains to be investigated. Cardiac regulation by the PSNS is primarily mediated by the M(2) muscarinic acetylcholine receptor (M(2)-AChR). In this study, we tested the hypothesis that lack of M(2)-AChR-mediated PSNS function may adversely impact cardiac ventricular function. Using M(2)-AChR knockout (KO) and wild-type (WT) mice, we found that the basal levels of heart rate and left ventricular function were similar in M(2)-AChR KO and WT mice. A bolus injection of isoproterenol (Iso) induced a greater increase in heart rate in M(2)-AChR KO mice than in WT mice. However, the responses of change in pressure over time (dP/dt) to Iso were similar in the two groups. After chronic infusion with Iso for 1 wk, the baseline values of left ventricular function were increased to similar extents in M(2)-AChR KO and WT mice. However, the M(2)-AChR KO mice exhibited impaired ventricular function, indicated as attenuated dP/dt and increased end-diastolic pressure, during an increase in cardiac afterload induced by a bolus injection of phenylephrine. Furthermore, chronic Iso infusion significantly increased matrix metalloproteinase (MMP) activity in the heart in M(2)-AChR KO mice. In primary culture of mixed neonatal rat cardiac fibroblast and cardiomyocytes, cotreatment with muscarinic agonist bethanechol reversed phenylephrine-induced increase in MMP-9 activation. These data suggest that M(2)-AChR may mediate an inhibitory regulation on MMP function. The overall results from this study suggest that M(2)-AChR-mediated PSNS function may provide cardiac protection. Lack of this protective mechanism will increase the susceptibility of the heart to cardiac stresses.

Neostigmine and pilocarpine attenuated tumour necrosis factor α expression and cardiac hypertrophy in the heart with pressure overload

The inflammatory cytokine tumour necrosis factor alpha (TNF alpha) is known to be a major factor contributing to cardiac remodelling and dysfunction. Parasympathetic nervous system cholinergic function can inhibit TNF alpha expression during systemic infection. In the present study, we tested the effects of a cholinesterase inhibitor, neostigmine, and a muscarinic cholinergic agonist, pilocarpine, on cardiac hypertrophy and TNF alpha levels during pressure overload. Rats with transverse aortic constriction exhibited elevated TNF alpha protein levels in the heart, increased heart weight to body weight ratios (an index of cardiac hypertrophy) and decreased left ventricular diastolic function. Two weeks of infusion with neostigmine (6 microg kg(-1) day(-1)) or pilocarpine (0.3 mg kg(-1) day(-1)) significantly reduced cardiac hypertrophy, reduced TNF alpha levels and elevated interleukin-10 levels in heart tissues, and improved ventricular function in rats with transverse aortic constriction. Neither of these treatments significantly changed ventricular pressure load. Furthermore, in primary cultured neonatal cardiac cells, treatment with pilocarpine attenuated adrenergic agonist phenylephrine-induced increased TNF alpha expression and [3H]leucine (a marker of protein synthesis) incorporation in the cells. Collectively, both cholinergic agents decreased TNF alpha levels and attenuated cardiac hypertrophy. Since both agents potentially enhanced cholinergic function, the anti-inflammatory action may be involved in the cardioprotective effect of the treatments with these agents.

Alpha-adrenoceptor gene variants and autonomic nervous system function in a young healthy Japanese population

alpha(1A)-adrenergic receptor (alpha(1A)-AR) regulates the cardiac and peripheral vascular system through sympathetic activation, and alpha(2A)-AR and alpha(2C)-AR subtypes are essential for presynaptic feedback regulation of catecholamine release from the central and peripheral sympathetic nerve. Genetic variations in each human alpha-AR subtype gene have been identified and have been implicated in hypertension and cardiovascular disease. It is not yet clear whether these genetic variations actually have an effect on sympatho-vagal modulation. The aim of the present study was to evaluate the relation between the five representative genetic polymorphisms of alpha-AR subtypes (Arg347Cys of alpha(1A)-AR; C-1291G, Asn251Lys, and DraI RFLP of alpha(2A)-AR; and Del322-325 of alpha(2C)-AR) and autonomic nervous system (ANS) function in young and healthy Japanese males. One hundred forty-nine subjects were genotyped for each alpha-AR polymorphism, and underwent evaluation of ANS function by power spectral analysis of heart rate variability (HRV) during supine rest and in a standing position. In a supine position, the alpha(1A)-AR 347Cys allele was significantly associated with lower HRV sympathetic index (normalized low frequency power [LF(%)] and LF:HF ratio) and higher HRV parasympathetic index [HF(%)]. Meanwhile, subjects with the alpha(2C)-AR Del322-325 allele had markedly higher LF(%) and LF:HF ratio and lower HF(%) than noncarriers. Thus, the alpha(1A)-AR and alpha(2C)-AR genetic variations influence sympatho-vagal balance even in young and healthy normotensive states, which could be postulated to constitute an intermediate phenotype for future pathological episodes of various ANS dysfunction-related diseases.

Intrathecal clonidine reduces the incidence of ischemia-provoked ventricular arrhythmias in a canine postinfarction heart failure model

BACKGROUND

Intrathecal clonidine (ITC) is used clinically to manage neuropathic pain but frequently causes hypotension and bradycardia due to centrally mediated sympatholytic effects.

OBJECTIVES

The purpose of this study was to evaluate the cardiac electrophysiologic effects of thoracic ITC and its effects on ischemia-provoked ventricular arrhythmias.

METHODS

Twelve mongrel dogs with healed myocardial infarctions and heart failure were evaluated. ITC was delivered locally via catheter to the T2-T4 spinal segments and was dosed to reduce heart rate (HR) by >20% to 25%. Electrophysiologic testing was performed before and after ITC. Transient (4-minute) myocardial ischemia was induced via left circumflex coronary artery occlusion on two separate occasions to provoke ventricular arrhythmias (ventricular tachycardia [VT]/ventricular fibrillation [VF]). Ischemic episodes were separated by 1 to 2 days, and dogs were randomly assigned to receive ITC or intrathecal saline flush (control) prior to the first or the second ischemic episode.

RESULTS

ITC produced significant decrease in HR (31%) and increases in PR interval (22%), Wenckebach cycle length (122%), and atrial and ventricular effective refractory periods (19% and 9%, respectively) but had no significant effect on systemic blood pressure. The occurrence of VT/VF was reduced from 9 of 12 to 3 of 12 dogs when ITC was administered prior to transient myocardial ischemia (P = .04). ITC also blunted ischemia-induced HR increase by 74%.

CONCLUSION

ITC reduced ischemia-induced VT/VF in a canine model of healed myocardial infarction with superimposed heart failure and acute ischemia. Results from electrophysiologic testing were consistent with a clonidine-induced reduction in cardiac sympathetic activity from the spinal cord. These data suggest that ITC administration may be a novel approach to treating ventricular arrhythmias.

Cardiovascular and parasympathetic effects of dexmedetomidine in healthy subjects

We evaluated the cardiovascular effects of intravenously (i.v.) and buccally administered dexmedetomidine, a selective α2-adrenoceptor agonist. Six healthy male subjects were studied unmedicated and after 2 µg/kg i.v. or buccal doses of dexmedetomidine, using repeated recordings of ECG and blood pressure. Cardiac parasympathetic activity was estimated by measurements of high-frequency (HF) heart rate variability. Intravenous, but not buccal, dexmedetomidine raised systolic blood pressure by 11 ± 5 mmHg (mean ± SEM) and diastolic by 16 ± 3 mmHg (maxima at 10 min). Later on, both i.v., and buccal dexmedetomidine produced a very similar hypotensive effect: on average, [Formula: see text]10 mmHg reductions in systolic and diastolic pressure at 3 h. Intravenous dosing was followed by a decline in heart rate (–11 ± 2 beats/min) accompanied by a trend toward enhanced HF variability (maximal effect at 10 min), which probably reflected baroreflex-mediated parasympathetic efferent neuronal activation. Buccal dexmedetomidine increased significantly the HF variability (maximum at 45 min) without influencing heart rate. We conclude that dexmedetomidine, when administered by a method that avoids concentration peaks, e.g., buccal dosing, can be used to produce a prolonged augmentation of cardiac parasympathetic efferent neuronal activity.Key words: dexmedetomidine, parasympathetic nervous system, heart rate, blood pressure.

Heart rate and QT interval variability: abnormal alpha-2 adrenergic function in patients with panic disorder

Anxiety disorders are associated with an increase in cardiovascular mortality. Studies using heart rate (HR) and QT interval variability measures suggest a decreased cardiac vagal function and a relatively increased sympathetic function in anxiety. This is important, as increased sympathovagal balance is associated with life-threatening arrhythmias. Several studies have shown that panic disorder is associated with an increased sensitivity to yohimbine and a blunted growth hormone response to clonidine, which are alpha-2 adrenoceptor antagonist and agonist, respectively. This study investigated the changes in QTvi (QT variance corrected for mean QT interval squared/HR variance corrected for mean HR squared) during placebo, oral clonidine (150 mg) and oral yohimbine (20 mg) in a double-blind design in 12 normal controls and 19 patients with panic disorder. HR and QT variability measures, especially QTvi, were obtained before and after the administration of these drugs to patients in supine and standing postures. As expected, patients with panic disorder became more anxious after yohimbine. In addition, the patients had a significant increase in QTvi after yohimbine and a significant decrease in QTvi after clonidine, which was not seen in the control group. The decreased anxiety after placebo was associated with decreased QTvi in patients. This study supports the previous reports of an abnormal sensitivity of alpha-2 adrenergic receptors in patients with panic disorder compared to controls and partly explains the association of increased cardiovascular mortality with conditions of anxiety. QTvi, a non-invasive indicator of cardiac repolarization lability, appears to be a useful tool to study cardiac sympathetic function.

Neurohormonal abnormalities in heart failure: impact of exercise training

Endurance exercise training appears to beneficially alter the clinical course of chronic heart failure. The specific mechanisms responsible for exercise-induced benefits, however, are not completely understood. This review examines the impact of endurance exercise training on neurohormonal mechanisms, which play a central role in the progression of chronic heart failure. Few studies, however, have been specifically designed to elucidate exercise-induced mechanisms responsible for the suppression of neurohormonal activation in patients with chronic heart failure and the literature on this topic is derived from a limited number of small, single-center studies. The available data suggests that endurance exercise training programs of moderate duration (approximately 16 weeks) are efficacious in suppressing circulating levels of catecholamines, angiotensin II, arginine vasopressin, and aldosterone. Additionally, endurance exercise training improves baroreceptor sensitivity and heart rate variability, suggesting that exercise ameliorates the autonomic derangement in chronic heart failure by increasing the parasympathetically mediated component of heart rate variability. Pharmacologic suppression of sympathetic activity has proved, by and large, to be successful at reducing mortality in patients with chronic heart failure. Exercise-induced modulation of sympathetic activity may also be instrumental at reducing morbidity and mortality but this has not been carefully investigated and is a fertile area for further research.

Oral clonidine premedication preserves heart rate variability for patients undergoing larparoscopic cholecystectomy

BACKGROUND

Clonidine has been shown to reduce perioperative circulatory instability. This postoperative analgesic effect of clonidine was also known in previous studies. The aim of the study was to investigate the clinical efficiency of oral clonidine premedication in anesthesia and analgesia in patients undergoing laparoscopic cholecystectomy.

METHODS

Thirty-two patients scheduled for elective laparoscopic cholecystectomy were recruited for a prospective, randomized, double-blinded comparative study. They were allotted randomly to two groups: placebo or clonidine. Patients in the placebo group (n = 16) were premedicated with oral antacid (alugel hydroxide 300 mg), while those in the clonidine group (n = 16) were premedicated with oral clonidine 150 micro g before anesthesia. Analysis of heart rate variability was used to quantify the control of heart rate at baseline, and during the pneumoperitoneum and recovery periods. Time of the first request for postoperative analgesic and cumulative analgesic requirements in 24 h were recorded. Data are expressed as mean +/- SD.

RESULTS

Heart rate variability was reduced in the pneumoperitoneum and postoperative period in the placebo group. Clonidine resulted in a greater perioperative (pneumoperitoneum period) power at all frequency ranges compared with placebo (671.5 +/- 470.5 vs. 55.1 +/- 51.6 ms2/Hz for total power variability, 170.1 +/- 94.4 vs. 16.9 +/- 21.1 ms2/Hz for low-frequency variability and 206.1 +/- 95.7 vs. 16.4 +/- 15.1 ms2/Hz for high-frequency variability, P < 0.05). The postoperative analgesic requirement was less (2.3 +/- 0.8 vs. 3.2 +/- 1.2 dose, P < 0.05) in comparison with the placebo group.

CONCLUSION

Clonidine preserves heart rate control in pneumoperitoneum and recovery periods. Oral clonidine premedication also reduces the requirement for postoperative analgesia.

The alpha2 -adrenergic receptors in hypertension and heart failure: experimental and clinical studies

This is a brief overview of experimental and clinical studies exploring the hemodynamic functions of the alpha2A and alpha2B adrenergic receptor (AR) subtypes in animals submitted to genetic manipulations or gene treatment, as well as the clinical effects of central sympathetic suppression with the alpha2-AR agonist clonidine in patients with ischemic heart disease and/or heart failure. The animal experiments have led us to conclude that the sympathetic outflow is regulated by activation of the presynaptic alpha2A-AR subtype, which is the predominant alpha2-AR subtype in the central nervous system and exerts a sympathoinhibitory (hypotensive) action; on the contrary, activation of the central alpha2B-AR elicits a sympathoexcitatory response (such as seen in salt-induced hypertension, which requires functionally intact alpha2B-AR). Since there are no selective pharmacologic agents yet capable of discriminating among alpha2-AR subtypes, clinical studies utilize clonidine, the central sympathetic suppressant effect of which has been used for 35 years to treat hypertension. In small clinical trials, clonidine was used successfully for treatment of acute or chronic heart failure, acute myocardial infarct or hypertensive cardiomyopathy with subclinical diastolic dysfunction. We speculate that future development of agents capable of selectively activating the alpha2A-AR or blocking the alpha2B-AR may further improve our capability to treat hypertension, ischemic heart disease and heart failure.

Selegiline improves cardiac sympathetic terminal function and beta-adrenergic responsiveness in heart failure

Selegiline is a centrally acting sympatholytic agent with neuroprotective properties. It also has been shown to promote sympathetic reinnervation after sympathectomy. These actions of selegiline may be beneficial in heart failure that is characterized by increased sympathetic nervous activity and functional sympathetic denervation. Twenty-seven rabbits with rapid cardiac pacing (360 beats/min, 8 wk) and twenty-three rabbits without pacing were randomly assigned to receive selegiline (1 mg/day, 8 wk) or placebo. Rapid pacing increased plasma norepinephrine (NE) and decreased left ventricular fractional shortening, baroreflex sensitivity, cardiac sympathetic nerve terminal profiles, cardiac NE uptake activity, and myocardial beta-adrenoceptor density. Selegiline administration to animals with rapid ventricular pacing attenuated the increase in plasma NE and decreases in fractional shortening, baroreflex sensitivity, sympathetic nerve profiles, NE uptake activity and beta-adrenoceptor density. Thus selegiline appears to exert a sympatholytic and cardiac neuroprotective effect in pacing-induced cardiomyopathy. The effects are potentially beneficial because selegiline not only improves cardiac function but also increases baroreflex sensitivity in heart failure.