Sinus tachyarrhythmias and the specific bradycardic agents: a marriage made in heaven?

Human Sinoatrial Node Pacemaker Activity: Role of the Slow Component of the Delayed Rectifier K+ Current, IKs

The pacemaker activity of the sinoatrial node (SAN) has been studied extensively in animal species but is virtually unexplored in humans. Here we assess the role of the slowly activating component of the delayed rectifier K+ current (IKs) in human SAN pacemaker activity and its dependence on heart rate and β-adrenergic stimulation. HEK-293 cells were transiently transfected with wild-type KCNQ1 and KCNE1 cDNA, encoding the α- and β-subunits of the IKs channel, respectively. KCNQ1/KCNE1 currents were recorded both during a traditional voltage clamp and during an action potential (AP) clamp with human SAN-like APs. Forskolin (10 µmol/L) was used to increase the intracellular cAMP level, thus mimicking β-adrenergic stimulation. The experimentally observed effects were evaluated in the Fabbri-Severi computer model of an isolated human SAN cell. Transfected HEK-293 cells displayed large IKs-like outward currents in response to depolarizing voltage clamp steps. Forskolin significantly increased the current density and significantly shifted the half-maximal activation voltage towards more negative potentials. Furthermore, forskolin significantly accelerated activation without affecting the rate of deactivation. During an AP clamp, the KCNQ1/KCNE1 current was substantial during the AP phase, but relatively small during diastolic depolarization. In the presence of forskolin, the KCNQ1/KCNE1 current during both the AP phase and diastolic depolarization increased, resulting in a clearly active KCNQ1/KCNE1 current during diastolic depolarization, particularly at shorter cycle lengths. Computer simulations demonstrated that IKs reduces the intrinsic beating rate through its slowing effect on diastolic depolarization at all levels of autonomic tone and that gain-of-function mutations in KCNQ1 may exert a marked bradycardic effect during vagal tone. In conclusion, IKs is active during human SAN pacemaker activity and has a strong dependence on heart rate and cAMP level, with a prominent role at all levels of autonomic tone.

Pharmacology of Ivabradine and the Effect on Chronic Heart Failure

Chronic Heart Failure (CHF) is a complex clinical syndrome with a high incidence worldwide. Although various types of pharmacological and device therapies are available for CHF, the prognosis is not ideal, for which, the control of increased Heart Rate (HR) is critical. Recently, a bradycardic agent, ivabradine, is found to reduce HR by inhibiting the funny current (If). The underlying mechanism states that ivabradine can enter the Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels and bind to the intracellular side, subsequently inhibiting the If. This phenomenon can prolong the slow spontaneous phase in the diastolic depolarization, and thus, reduce HR. The clinical trials demonstrated the significant effects of the drug on reducing HR and improving the symptoms of CHF with fewer adverse effects. This review primarily introduces the chemical features and pharmacological characteristics of ivabradine and the mechanism of treating CHF. Also, some expected therapeutic effects on different diseases were also concluded. However, ivabradine, as a typical If channel inhibitor, necessitates additional research to verify its pharmacological functions.

Atrial Tachyarrhythmias and Atrial Flutter: the Basics of Diagnostics and Modern Opportunities of Therapy

The article is devoted to the description of all types of atrial tachyarrhythmias, including inappropriate sinus tachycardia, which, as a rule, is not paid enough attention in the domestic literature, sinoatrial node reentrant tachycardia, focal and multifocal atrial tachycardia, atrial flutter, and atrial fibrillation. The electrophysiological mechanisms of development and electrocardiographic criteria for the diagnosis of these cardiac rhythm disturbances are presented. Along with this, the article discusses the modern view of the strategy and tactics of pharmacological cardioversion and preventive therapy in patients with the main types of atrial tachyarrhythmias and atrial flutter. It is noted that the prognosis for inappropriate sinus tachycardia, as a rule, is favorable, and therefore, aim of treatment is to reduce the symptoms, and in their absence medical treatment is not necessary. Much attention is paid to drug and interventional treatment of atrial flutter. It is emphasized that catheter ablation of isthmus-dependent atrial flutter in most cases is preferred over long-term pharmacotherapy. However, in prolonged observation (more than 3 years), nearly 1/3 of patients may develop paroxysmal atrial fibrillation. At the same time, catheter ablation of atypical atrial flutter is, in most cases, substantially less effective. The indications and side effects of catheter ablation of the sinus node are also discussed. The authors provide a critical analysis of traditional approaches to the treatment of atrial tachyarrhythmias and analyze new recommendations for the management of these patients presented in Europe and the USA. Based on these recommendations, clear algorithms for the management of patients with atrial tachyarrhythmias are given. The need to prevent thromboembolic complications in some types of atrial tachyarrhythmias is emphasized.

Study of Attenuation of Hemodynamic Response to Laryngoscopy and Endotracheal Intubation using Intra-oral Ivabradine

Context

Endotracheal intubation is one of the most commonly performed procedures, where rapid and dramatic hemodynamic changes which adversely affect the patient may occur during the perioperative period. Various strategies have been applied to attenuate these responses in high-risk individuals. Ivabradine is a very unique cardiotonic drug in the medical literature which reduces the heart rate without jeopardizing hemodynamics in unhealthy, compromised patients.

Aims and Objective

The aim of this study is to evaluate the effect of oral ivabradine on the hemodynamics during laryngoscopy and endotracheal intubation in patients undergoing surgical procedure under general anesthesia and to note the side effects and complications.

Settings and Design

This was a prospective, randomized, and double-blind controlled study.

Subjects and Methods

A total of 50 American Society of Anesthesiologists physical status I patients between 20 and 50 years age comparable in demographic variables of either sex, undergoing surgery under general anesthesia were randomized into two groups, namely, Group T and Group C of 25 each. Group T (test group) received tablet ivabradine 5 mg 1 h before intubation. Group C (control group) received placebo 1 h before intubation. The pulse rate, systolic and diastolic blood pressures, and mean arterial pressure were recorded for around 10 min and surgery was not allowed to commence. These hemodynamic variables were measured preoperatively, at intubation, after 1 min, 5 min, 8 min and 10 min postintubation.

Statistical Analysis Used

The Chi-square test and ANOVA test using INDOSTAT software for hemodynamics were used in this study.

Results

There was an increase in all parameters in the control group during and postintubation and was undisturbed in the test group as compared to base line. The increase was constant up to 3 min and got settled within 5 min in the control group.

Conclusion

Ivabradine had better patient compliance in terms of blunting laryngoscopic pressor.

Effects of Ivabradine on Left Ventricular Systolic Function and Cardiac Fibrosis in Rat Myocardial Ischemia-Reperfusion Model

We evaluated the effects of Ivabradine on left ventricle (LV) ejection fraction (EF) and LV infarcted tissue in the rat myocardial ischemia-reperfusion model. Twenty rats were randomly assigned to group 1 (ischemia-reperfusion, no treatment, n=10) and group 2 (ischemia-reperfusion + Ivabradine 10 mg/kg, n=10). Ivabradine was administered for 28 days. Echocardiography was performed at 7 days and at 28 days after the induction of ischemia-reperfusion injury. Cardiac fibrosis induced by ischemia-reperfusion injury was evaluated by Masson's trichrome staining. The infarct size was quantified using the Image J program. At the 28-day follow-up, LVEF was significantly higher (36.02±6.16% vs. 45.72±2.62%, p<0.001) and fractional shortening was significantly higher (15.23±2.84% vs. 20.13±1.38%, p<0.001) in group 2 than group 1. Delta (28 day minus 7 day) EF was significantly higher in group 2 than group 1 (-4.36±3.49% vs. 4.31±5.63%, p<0.001). Also, heart rate (beats/min) was significantly lower in group 2 than group 1 (251.67±25.19 vs. 199.29±31.33, p=0.025). Group 2 had a smaller infarct size (40.70±8.94% vs. 30.19±5.89%, p<0.01) than group 1 at 28-day follow-up. Oral administration of Ivabradine could improve LV systolic function and reduce infarcted tissue area in rat myocardial ischemia-reperfusion model.

Drug Use and Misuse in the Mountains: A UIAA MedCom Consensus Guide for Medical Professionals

Donegani, Enrico, Peter Paal, Thomas Küpper, Urs Hefti, Buddha Basnyat, Anna Carceller, Pierre Bouzat, Rianne van der Spek, and David Hillebrandt. Drug use and misuse in the mountains: a UIAA MedCom consensus guide for medical professionals. High Alt Med Biol. 17:157-184, 2016.-Aims: The aim of this review is to inform mountaineers about drugs commonly used in mountains. For many years, drugs have been used to enhance performance in mountaineering. It is the UIAA (International Climbing and Mountaineering Federation-Union International des Associations d'Alpinisme) Medcom's duty to protect mountaineers from possible harm caused by uninformed drug use. The UIAA Medcom assessed relevant articles in scientific literature and peer-reviewed studies, trials, observational studies, and case series to provide information for physicians on drugs commonly used in the mountain environment. Recommendations were graded according to criteria set by the American College of Chest Physicians.

RESULTS

Prophylactic, therapeutic, and recreational uses of drugs relevant to mountaineering are presented with an assessment of their risks and benefits.

CONCLUSIONS

If using drugs not regulated by the World Anti-Doping Agency (WADA), individuals have to determine their own personal standards for enjoyment, challenge, acceptable risk, and ethics. No system of drug testing could ever, or should ever, be policed for recreational climbers. Sponsored climbers or those who climb for status need to carefully consider both the medical and ethical implications if using drugs to aid performance. In some countries (e.g., Switzerland and Germany), administrative systems for mountaineering or medication control dictate a specific stance, but for most recreational mountaineers, any rules would be unenforceable and have to be a personal decision, but should take into account the current best evidence for risk, benefit, and sporting ethics.

HCN Channels Modulators: The Need for Selectivity

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, the molecular correlate of the hyperpolarization-activated current (If/Ih), are membrane proteins which play an important role in several physiological processes and various pathological conditions. In the Sino Atrial Node (SAN) HCN4 is the target of ivabradine, a bradycardic agent that is, at the moment, the only drug which specifically blocks If. Nevertheless, several other pharmacological agents have been shown to modulate HCN channels, a property that may contribute to their therapeutic activity and/or to their side effects. HCN channels are considered potential targets for developing drugs to treat several important pathologies, but a major issue in this field is the discovery of isoform-selective compounds, owing to the wide distribution of these proteins into the central and peripheral nervous systems, heart and other peripheral tissues. This survey is focused on the compounds that have been shown, or have been designed, to interact with HCN channels and on their binding sites, with the aim to summarize current knowledge and possibly to unveil useful information to design new potent and selective modulators.

Risk of emergent bradycardia associated with the use of carvedilol and metoprolol in routine clinical practice

BACKGROUND

Large randomized trials have reported mixed results regarding the risk of bradycardia between metoprolol and carvedilol. We compared the incidence of emergent bradycardia (measured by an emergency department visit or hospitalization due to bradycardia) for patients initiating metoprolol and carvedilol.

METHODS

Adult beneficiaries of Medi-Cal, the State of California Medicaid program, without a diagnosis of bradycardia who initiated metoprolol or carvedilol between May 1, 2004, and November 1, 2009, were included. Cox proportional hazard regression analysis was performed to model the time to first occurrence of emergent bradycardia after initiation of the study drugs as a dependent variable and the study drug (metoprolol vs carvedilol) as the primary predictor with adjustments for total daily metoprolol-equivalent dose, formulations, and use of nonstudy drugs as time-varying covariates, as well as demographics and comorbidities.

RESULTS

Among 38,186 subjects, 77.7% initiated metoprolol and 22.3% initiated carvedilol. The incidence of emergent bradycardia was low and comparable between the drugs (18.1 per 1000 person-years using metoprolol vs 17.7 per 100 person-years using carvedilol; unadjusted hazard ratio, 1.07; 95% confidence interval, 0.76-1.49). However, carvedilol users had substantially different population characteristics compared with metoprolol users. After adjustments for demographics, comorbidities, metoprolol-equivalent dose, formulations, and use of nonstudy drugs, initiation of metoprolol was associated with an increased risk of emergent bradycardia compared with that of carvedilol (adjusted hazard ratio, 1.64; 95% confidence interval, 1.14-2.36).

CONCLUSIONS

Initiation of metoprolol is associated with an increased risk of emergent bradycardia compared with carvedilol, although the overall incidence of emergent bradycardia is low in routine clinical practice.

Reduced heart rate and cardiac output differentially affect angiogenesis, growth, and development in early chicken embryos (Gallus domesticus)

An increase in both vascular circumferential tension and shear stress in the developing vasculature of the chicken embryo has been hypothesized to stimulate angiogenesis in the developing peripheral circulation chorioallantoic membrane (CAM). To test this hypothesis, angiogenesis in the CAM, development, and growth were measured in the early chicken embryo, following acute and chronic topical application of the purely bradycardic drug ZD7288. At hour 56, ZD7288 reduced heart rate (f(H)) by ~30% but had no significant effect on stroke volume (~0.19 ± 0.2 μL), collectively resulting in a significant fall in cardiac output (CO) from ~27 ± 3 to 18 ± 2 μL min(-1). Mean f(H) at 72 h of development was similarly significantly lowered by acute ZD7288 treatment (250 μM) to 128 ± 0.3 beats min(-1), compared with 174.5 ± 0.3 and 174.7 ± 0.8 beats min(-1) in control and Pannett-Compton (P-C) saline-treated embryos, respectively. Chronic dosing with ZD7288-and the attendant decreases in f(H) and CO-did not change eye diameter or cervical flexion (key indicators of development rate) at 120 h but significantly reduced overall growth (wet and dry body mass decreased by 20%). CAM vessel density index (reflecting angiogenesis) measured 200-400 μm from the umbilical stalk was not altered, but ZD7288 reduced vessel numbers-and therefore vessel density-by 13%-16% more distally (500-600 μm from umbilical stalk) in the CAM. In the ZD7288-treated embryos, a decrease in vessel length was found within the second branch order (~300-400 μm from the umbilical stock), while a decrease in vessel diameter was found closer to the umbilical stock, beginning in the first branch order (~200-300 μm). Paradoxically, chronic application of P-C saline also reduced peripheral CAM vessel density index at 500 and 600 μm by 13% and 7%, respectively, likely from washout of local angiogenic factors. In summary, decreased f(H) with reduced CO did not slow development rate but reduced embryonic growth rate and angiogenesis in the CAM periphery. This study demonstrates for the first time that different processes in the ontogeny of the early vertebrate embryo (i.e., hypertrophic growth vs. development) have differential sensitivities to altered convective blood flow.

HCN channels and heart rate

Hyperpolarization and Cyclic Nucleotide (HCN) -gated channels represent the molecular correlates of the "funny" pacemaker current (I(f)), a current activated by hyperpolarization and considered able to influence the sinus node function in generating cardiac impulses. HCN channels are a family of six transmembrane domain, single pore-loop, hyperpolarization activated, non-selective cation channels. This channel family comprises four members: HCN1-4, but there is a general agreement to consider HCN4 as the main isoform able to control heart rate. This review aims to summarize advanced insights into the structure, function and cellular regulation of HCN channels in order to better understand the role of such channels in regulating heart rate and heart function in normal and pathological conditions. Therefore, we evaluated the possible therapeutic application of the selective HCN channels blockers in heart rate control.

Exploring HCN channels as novel drug targets

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have a key role in the control of heart rate and neuronal excitability. Ivabradine is the first compound acting on HCN channels to be clinically approved for the treatment of angina pectoris. HCN channels may offer excellent opportunities for the development of novel anticonvulsant, anaesthetic and analgesic drugs. In support of this idea, some well-established drugs that act on the central nervous system - including lamotrigine, gabapentin and propofol - have been found to modulate HCN channel function. This Review gives an up-to-date summary of compounds acting on HCN channels, and discusses strategies to further explore the potential of these channels for therapeutic intervention.

A pediatric case of cardiomyopathy induced by inappropriate sinus tachycardia: efficacy of ivabradine

We report the case of a 16-year-old boy with cardiomyopathy induced by inappropriate sinus tachycardia (IST). The patient was resistant to treatment with conventional rate-decreasing medications. Therapy with the selective sinus node I(f) current inhibitor ivabradine was started. After 3 months of ivabradine therapy, an improvement in ejection fraction and a successful decrease in heart rate were observed. No side effects occurred. We suggest that ivabradine, currently used to treat stable angina, could be considered as a second-line treatment in patients with symptomatic and refractory IST.

Ivabradine: recent and potential applications in clinical practice

INTRODUCTION

published data indicate that heart rate is an independent strong predictor of cardiovascular and all-cause mortality in men and women of all ages, with and without cardiovascular disease, including atherosclerosis, ventricular arrhythmias, and left ventricular dysfunction. Ivabradine is a pure heart-rate-lowering agent with well-documented antianginal and anti-ischemic properties comparable to well-established anti-anginal agents.

AREAS COVERED

this short review explores recent results with ivabradine, a new medication that lowers heart rate by selectively inhibiting the I (f) current. This review also describes future potential applications.

EXPERT OPINION

measurement of heart rate represents an important component of the assessment of patients with coronary artery disease and chronic heart failure, and should be viewed in the same light as other risk factors, because a high heart rate has direct detrimental effects not only on myocardial ischemia but also on the progression of atherosclerosis, ventricular arrhythmias and left ventricular function. Ivabradine has anti-ischemic and antianginal efficacy equivalent to that of β-blockers and calcium channel antagonists in the treatment of chronic stable angina pectoris. Recently ivabradine has been shown to improve cardiac outcomes in stable coronary artery disease and left ventricular systolic dysfunction in patients who have heart rates of ≥ 70 bpm and in patients with stable angina.

Ivabradine: beyond heart rate control

Chronic stable angina pectoris (CSAP) usually occurs in patients with coronary artery disease (CAD) that affects one or more large epicardial arteries. It results when myocardial perfusion is insufficient to meet cardiac metabolic demand. Elevated heart rate (HR) is an important factor in the development of myocardial ischemia and angina pectoris. The pharmacologic agents most commonly administered in the treatment of CSAP are beta-blockers and calcium channel blockers (CCBs). However, the use of beta-blockers is limited by poor compliance related to contraindications and comorbidities, especially in elderly patients. Ivabradine is a new selective HR-lowering agent that selectively inhibits the pacemaker current I (f) in the sinus atrial node. In several randomized controlled trials, ivabradine 5-10 mg twice daily has demonstrated equivalent anti-ischemic and anti-anginal activity to beta-blockers and CCBs, with a good safety and tolerability profile. Although ivabradine has been shown not to improve cardiac outcomes in patients with stable CAD and left ventricular systolic dysfunction, it may be used to reduce the incidence of CAD outcomes in a subgroup of patients with HR > or =70 bpm. The aim of this short review is to summarize the use of ivabradine in the treatment of CSAP, and its potential utility in atherosclerosis, primitive and dilatative cardiomyopathy, and arrhythmias, such as postural tachycardia syndrome and inappropriate sinus tachycardia, where exclusive lowering of elevated HR may prove beneficial.

Pharmacotherapy changes following pacemaker implantation in patients with bradycardia-tachycardia syndrome

The management of bradycardia-tachycardia syndrome (BTS) includes bradycardia and tachyarrhythmia therapy. At present, the treatment for symptomatic bradycardia in BTS patients is permanent cardiac pacing. The pharmacological treatment of atrial tachyarrhythmias comprises of rhythm and rate control, and prevention of thromboembolism. Patients with BTS often require both pacemaker and drug therapy. This article reviews the interactions of pacing and drug therapies in BTS. Drugs that alter cardiac electrophysiological properties may influence pacemaker indications, pacing mode selection, efficacy of pacing algorithms and pacing performance. Pacing by preventing drug-induced bradycardia increases the safety of pharmacotherapy and, thus, allows the intensification of those treatments. Pacing therapy and antiarrhythmic drugs used together as a hybrid therapy have a synergistic effect in the prevention of atrial tachyarrhythmias. Atrial-based pacing may reduce atrial tachyarrhythmia burden, allowing reduction of rhythm and rate control. Contemporary pacemakers' memory functions may help guide rhythm and rate control, as well as anticoagulation pharmacotherapy.

Deciphering the sinus tachycardias

Sinus tachycardia is the most common rhythm disturbance encountered in clinical practice. Primary sinus tachycardia without an underlying secondary cause, despite often being associated with troublesome symptoms, is often neglected leading to multiple consultations and frustration on part of both the practitioner and the patient. The fact that primary sinus tachycardias are a heterogeneous group of disorders is seldom appreciated; hence, a firm diagnosis is rarely reached and management is haphazard. Furthermore, there may be prognostic implications for prolonged or recurrent sinus tachycardia, making it imperative that this group of arrhythmias receive adequate and appropriate attention. Normal sinus tachycardia (i.e., secondary), inappropriate sinus tachycardia, postural orthostatic tachycardia syndrome (POTS) and sinus node reentry tachycardia make up this group of arrhythmias. Their definitions, clinical features, diagnostic criteria, pathophysiologic mechanisms, and optimum management are discussed in this review.

Physiology and pharmacology of the cardiac pacemaker (“funny”) current

First described over a quarter of a century ago, the cardiac pacemaker "funny" (I(f)) current has been extensively characterized since, and its role in cardiac pacemaking has been thoroughly demonstrated. A similar current, termed I(h), was later described in different types of neurons, where it has a variety of functions and contributes to the control of cell excitability and plasticity. I(f) is an inward current activated by both voltage hyperpolarization and intracellular cAMP. In the heart, as well as generating spontaneous activity, f-channels mediate autonomic-dependent modulation of heart rate: beta-adrenergic stimulation accelerates, and vagal stimulation slows, cardiac rate by increasing and decreasing, respectively, the intracellular cAMP concentration and, consequently, the f-channel degree of activation. Four isoforms of hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels have been cloned more recently and shown to be the molecular correlates of native f-channels in the heart and h-channels in the brain. Individual HCN isoforms have kinetic and modulatory properties which differ quantitatively. A comparison of their biophysical properties with those of native pacemaker channels provides insight into the molecular basis of the pacemaker current properties and, together with immunolabelling and other detection techniques, gives information on the pattern of HCN isoform distribution in different tissues. Because of their relevance to cardiac pacemaker activity, f-channels are a natural target of drugs aimed at the pharmacological control of heart rate. Several agents developed for their ability to selectively reduce heart rate act by a specific inhibition of f-channel function; these substances have a potential for the treatment of diseases such as angina and heart failure. In the near future, devices based on the delivery of f-channels in situ, or of a cellular source of f-channels (biological pacemakers), will likely be developed for use in therapies for diseases of heart rhythm with the aim of replacing electronic pacemakers.

The sinus tachycardias

Sinus tachycardia, in the forms of four distinct rhythm disturbances, is frequently encountered in clinical practice but is often overlooked. The most common rhythm, normal sinus tachycardia, whether physiologic, pathologic or iatrogenic, is predominantly catecholamine driven, is virtually asymptomatic and is managed by identifying and treating the underlying cause. The other so-called primary sinus tachycardias, which include inappropriate sinus tachycardia, postural orthostatic tachycardia syndrome and sinus node re-entry tachycardia, have fundamentally different clinical features, basic underlying etiologic mechanisms and treatment strategies. Differentiation of these types from normal sinus tachycardia and from other atrial arrhythmias is crucial for successful management. Accurate diagnosis and appropriate therapy of the sinus tachycardias not only prevents multiple consultations but might also have important long-term prognostic implications.