Ibutilide

High resolution optical mapping of cardiac electrophysiology in pre-clinical models

Optical mapping of animal models is a widely used technique in pre-clinical cardiac research. It has several advantages over other methods, including higher spatial resolution, contactless recording and direct visualisation of action potentials and calcium transients. Optical mapping enables simultaneous study of action potential and calcium transient morphology, conduction dynamics, regional heterogeneity, restitution and arrhythmogenesis. In this dataset, we have optically mapped Langendorff perfused isolated whole hearts (mouse and guinea pig) and superfused isolated atria (mouse). Raw datasets (consisting of over 400 files) can be combined with open-source software for processing and analysis. We have generated a comprehensive post-processed dataset characterising the baseline cardiac electrophysiology in these widely used pre-clinical models. This dataset also provides reference information detailing the effect of heart rate, clinically used anti-arrhythmic drugs, ischaemia-reperfusion and sympathetic nervous stimulation on cardiac electrophysiology. The effects of these interventions can be studied in a global or regional manner, enabling new insights into the prevention and initiation of arrhythmia.

Influence of baseline QTc on sotalol-induced prolongation of ventricular repolarization in men and women

The extent of sotalol-induced QTc prolongation on the electrocardiogram, is variable among subjects and influenced by sex. However, the influence of baseline QTc on the extent of drug-induced QTc prolongation remains unclear. This was studied around peak plasma concentration in a large cohort of 376 healthy male and 614 healthy female subjects who received 80 mg of sotalol orally. Baseline QTc was 379±16ms in men and 393±15ms in women (p<0.0001). The change in QTc from baseline was highly variable among both sexes and was greater in women than in men (26.5±13.2 vs.13.0±10.8ms; <0.0001). The slope of the regression line between QTc on sotalol and baseline QTc did not significantly differ from unity in men and in women indicating that the extent of QTc prolongation with sotalol was not influenced by baseline QTc. Assessing QTc after administration of an I_Kr blocker may be more important than measuring a baseline QTc.

Safety and Efficacy of Ibutilide for Acute Pharmacological Cardioversion of Rheumatic Atrial Fibrillation

INTRODUCTION

Ibutilide is indicated for acute cardioversion of nonvalvular atrial fibrillation (AF). However, its efficacy and safety in the pharmacological cardioversion of rheumatic AF are unknown.

METHODS

Patients with mild-to-moderate rheumatic mitral valve (MV) disease with symptomatic, paroxysmal, or persistent AF were included in the analysis. Intravenous ibutilide was administered at doses tailored to body weight (0.5-2.0 mg) for over 10 min. The primary end point was efficacy, assessed as the rate of conversion of AF to sinus rhythm. The secondary end point was safety, including arrhythmic events and death within 24 h of drug initiation.

RESULTS

From June 2016 to October 2018, 165 patients (94 with mitral stenosis, 23 with mitral regurgitation, 11 with mixed MV disease, and 37 with MV replacement) received ibutilide (mean dose 0.90 ± 0.54 mg). Ibutilide successfully converted AF to sinus rhythm in 127/165 (76.9%) patients, with a conversion time of 7.9 ± 4.1 min. The QTc increased from 419.9 ± 15.8 to 487.5 ± 34 ms after ibutilide administration (p < 0.001). The mean change in QTc after ibutilide administration (∆QTc) was 72.01 ± 36.03. There were no deaths, but 3 patients (1.8%) developed torsades de pointes (TdP) requiring defibrillation 55 ± 37 min after infusion.

CONCLUSION

Ibutilide cardioverted 77% of rheumatic AF to sinus rhythm, indicating its potential as a clinically useful option for pharmacological cardioversion of rheumatic AF. TdP is a potentially serious adverse event that requires careful monitoring.

Artificial neural network model for predicting changes in ion channel conductance based on cardiac action potential shapes generated via simulation

Many studies have revealed changes in specific protein channels due to physiological causes such as mutation and their effects on action potential duration changes. However, no studies have been conducted to predict the type of protein channel abnormalities that occur through an action potential (AP) shape. Therefore, in this study, we aim to predict the ion channel conductance that is altered from various AP shapes using a machine learning algorithm. We perform electrophysiological simulations using a single-cell model to obtain AP shapes based on variations in the ion channel conductance. In the AP simulation, we increase and decrease the conductance of each ion channel at a constant rate, resulting in 1,980 AP shapes and one standard AP shape without any changes in the ion channel conductance. Subsequently, we calculate the AP difference shapes between them and use them as the input of the machine learning model to predict the changed ion channel conductance. In this study, we demonstrate that the changed ion channel conductance can be predicted with high prediction accuracy, as reflected by an F1 score of 0.985, using only AP shapes and simple machine learning.

Current Drug Treatment Strategies for Atrial Fibrillation and TASK-1 Inhibition as an Emerging Novel Therapy Option

Atrial fibrillation (AF) is the most common sustained arrhythmia with a prevalence of up to 4% and an upwards trend due to demographic changes. It is associated with an increase in mortality and stroke incidences. While stroke risk can be significantly reduced through anticoagulant therapy, adequate treatment of other AF related symptoms remains an unmet medical need in many cases. Two main treatment strategies are available: rate control that modulates ventricular heart rate and prevents tachymyopathy as well as rhythm control that aims to restore and sustain sinus rhythm. Rate control can be achieved through drugs or ablation of the atrioventricular node, rendering the patient pacemaker-dependent. For rhythm control electrical cardioversion and pharmacological cardioversion can be used. While electrical cardioversion requires fasting and sedation of the patient, antiarrhythmic drugs have other limitations. Most antiarrhythmic drugs carry a risk for pro-arrhythmic effects and are contraindicated in patients with structural heart diseases. Furthermore, catheter ablation of pulmonary veins can be performed with its risk of intraprocedural complications and varying success. In recent years TASK-1 has been introduced as a new target for AF therapy. Upregulation of TASK-1 in AF patients contributes to prolongation of the action potential duration. In a porcine model of AF, TASK-1 inhibition by gene therapy or pharmacological compounds induced cardioversion to sinus rhythm. The DOxapram Conversion TO Sinus rhythm (DOCTOS)-Trial will reveal whether doxapram, a potent TASK-1 inhibitor, can be used for acute cardioversion of persistent and paroxysmal AF in patients, potentially leading to a new treatment option for AF.

QT Prolongation in Cancer Patients

Background: QT prolongation and torsades de pointes pose a major concern for cardiologists and oncologists. Although cancer patients are suspected to have prolonged QT intervals, this has not been investigated in a large population. The purpose of this study was to analyze the QT interval distribution in a cancer population and compare it to a non-cancer population in the same institution. Methods: The study was a retrospective review of 82,410 ECGs performed in cancer patients (51.8% women and 48.2% men) and 775 ECGs performed in normal stem cell donors (47.9% women and 52.1% men) from January 2009 to December 2013 at the University of Texas MD Anderson Cancer Center. Pharmacy prescription data was also collected and analyzed during the same time period. Correction of the QT interval for the heart rate was performed using the Bazett and Fridericia formulas. Results: After QT correction for heart rate by the Fridericia formula (QTcF), the mean and 99% percentile QTc for cancer patients were 414 and 473 ms, respectively. These were significantly longer than the normal stem cell donors, 407 and 458 ms, p < 0.001, respectively. Among the cancer patients, the QTc was longer in the inpatient setting when compared to both outpatient and emergency center areas. The most commonly prescribed QT prolonging medications identified were ondansetron and methadone. Conclusion: Our study demonstrates significantly longer QTc intervals in cancer patients, especially in the inpatient setting. Frequently prescribed QT prolonging medications such as antiemetics and analgesics may have a causative role in QT prolongation seen in our cancer hospital.

Dual-Site Binding of Quaternary Ammonium Ions as Internal K+-Ion Channel Blockers: Nonclassical (C-H···O) H Bonding vs Dispersive (C-H···H-C) Interaction

A molecular-level study of the influence of the alkyl chain length of quaternary ammonium ions (QAs) on the blocking action and the mode of binding with the bacterial KcsA K⁺-ion channel is carried out by molecular dynamics (MD) simulations as well as quantum mechanics/molecular mechanics (QM/MM) methods. The present work unveils distinct modes of binding for different QAs, due to differences in size and hydrophobicity. The QAs bind near the channel gate as well as at the central cavity, leading to a possible dual-site blocking action. Small-sized tetraethylammonium (TEA) and tetrabutylammonium (TBA) ions enter inside the channel cavity in the open state of KcsA but bind strongly in the closed state. TEA binds to the polar hydroxyl group of threonine residues situated at the channel gate via nonclassical H-bonding interaction (C-H···O), while TBA binds to a second binding site, the central cavity, with hydrophobic benzyl and sec-butyl side chains of phenylalanine and isoleucine residues via alkyl-π and hydrophobic interactions (C-H···H-C). On the contrary, large tetrahexylammonium (THA) and tetraoctylammonium (TOA) ions bind the hydrophobic side-chain methyl and isopropyl of alanine and valine at the channel gate both in the open and closed states, thereby restricting the free movement of large QAs toward the center of the cavity. However, the binding to the hydrophobic benzyl and sec-butyl side chains of phenylalanine and isoleucine residues in the closed state is thermodynamically preferable. Also, the binding energy is found to increase with an increase in the alkyl chain length from ethyl (-16.4 kcal/mol) to octyl (-65.5 kcal/mol), due to an almost linear increase in dispersive interaction.

Comparison of the efficacy and safety of different doses of nifekalant in the instant cardioversion of persistent atrial fibrillation during radiofrequency ablation

Nifekalant has been used in the treatment of atrial arrhythmia recently. However, there is no consensus on the preferable nifekalant dose to treat atrial fibrillation (AF). The purpose of this study was to explore efficacy and safety of different doses of nifekalant in the cardioversion of persistent AF. The study was a single-centre, randomized controlled trial. All subjects received nifekalant or placebo intravenously, and the nifekalant was given at the dosage of 0.3, 0.4 or 0.5 mg/kg. Primary efficacy end-point: compared with 0.3 mg group, the rate of cardioversion to sinus rhythm from AF in 0.4 and 0.5 mg group was higher. The 0.4 and 0.5 mg/kg doses were associated with a similar magnitude of efficacy (P > .05). Secondary efficacy end-point: termination rates of AF in the group of 0.4 mg and 0.5 mg were higher than 0.3 mg. Primary safety end-point: the rate of Torsades de Pointes or ventricular fibrillation was numerically lower in the 0.4 mg group than 0.5 mg group (P = .02). Secondary safety end-point: The rates of the majority of other common drug-related adverse events in the group of 0.5 and 0.4 mg were higher than the 0.3 mg group. A 0.4 mg/kg dose of intravenous nifekalant may be recommended during the radiofrequency ablation for persistent AF considering the benefit-risk profile.

Chemical cardioversion of atrial flutter and fibrillation in the pediatric population with Ibutilide

INTRODUCTION

Atrial flutter (AFL) and atrial fibrillation (AF) are common in pediatric patients with congenital heart disease and structurally normal hearts as well. Chemical cardioversion is attractive for patients with AFL/AF for a short period of time because of the ability to avoid sedation. We review a single center's experience with Ibutilide in pediatric patients in an effort to report on its safety and efficacy.

METHODS

We performed a retrospective chart review of pediatric patients (0-21 years) who underwent chemical cardioversion for AFL/AF with Ibutilide (January 2011-February 2019). Patients on another antiarrhythmic medication or attempted chemical cardioversion with another drug were excluded.

RESULTS

There were 21 patients who met inclusion criteria. Thirteen of the 21 (62%) patients were successfully cardioverted with Ibutilide (10 out of 13 had AF and four out of 13 required a second dose). There were no significant differences in baseline characteristics between those who were successfully cardioverted compared to those who were not. Administration of magnesium prior to administration did not appear to have an effect on the success rate. There was a significant increase in rate corrected QT interval (QTc) post Ibutilide administration, which returned to baseline prior to discharge. One patient had symptomatic bradycardia needing intravenous fluids and another had torsades requiring electrical cardioversion during Ibutilide administration.

CONCLUSIONS

The success rate of chemical cardioversion with Ibutilide was similar in our experience as compared to studies in the adult population and the other lone pediatric study. Although adverse events were uncommon, Ibutilide administration warrants close monitoring and fully defining its efficacy warrants further pediatric experience.

Ibutilide for the control of refractory ventricular tachycardia and ventricular fibrillation in patients with myocardial ischemia and hemodynamic instability

INTRODUCTION

Recurrent ventricular tachycardia (VT) and ventricular fibrillation (VF) in patients with myocardial ischemia requiring hemodynamic support can be refractory to available antiarrhythmic agents and even to cardioversion and defibrillation. The purpose of this study was to report the effect of intravenous ibutilide in patients with a VT and/or VF storm in the presence of incomplete revascularization requiring hemodynamic support.

METHODS AND RESULTS

Standard continuous telemetry and frequent 12-lead electrocardiograms were obtained to determine the effect of intravenous Ibutilide in these patients. We studied six consecutive patients (age 60 ± 12 years; five males) with incomplete revascularization and mechanical support (extracorporeal membrane of oxygenation = 2; left ventricular assist device = 4) with VT/VF refractory to lidocaine and amiodarone. Intravenous ibutilide was given as a last resort for management of their ventricular arrhythmias. Intravenous ibutilide (1-2 mg) allowed restoration of sinus rhythm in three patients with persistent VF that were refractory to multiple defibrillation shocks. When the 24-hour period before and after ibutilide administration was compared, this drug markedly reduced the number of required cardioversions/defibrillations in all patients from 20 ± 9 to 0.7 ± 0.8 shocks ( P = 0.036).

CONCLUSIONS

In patients with myocardial ischemia requiring hemodynamic support, intravenous Ibutilide demonstrates a potent antiarrhythmic effect and can facilitate defibrillation in patients with refractory VF.

Treatment of Acute Atrial Fibrillation: Ventricular Rate Control and Restoration of Sinus Rhythm

Atrial fibrillation (AF) is a familiar arrhythmia seen in the emergency department and the general population. In the past it was treated in the majority of cases by controlling the ventricular rate, whether the AF is acute or chronic. However, ventricular rate control alone does not address the underlying problem and the patients still remain in AF, cardiac output and symptoms have not been optimally corrected. There is definite risk of thromboembolism. Restoration of sinus rhythm is the only way of resuming the normal conduction physiology of the heart and correcting these problems This article provides a review of the two major principles of rhythm treatment of acute AF: rate control and restoration of sinus rhythm. Transthoracic electrical cardioversion is the mainstay of treatment in haemodynamically unstable AF, whereas in stable AF, there is a choice between rate control and restoration of sinus rhythm, or they can be carried out in conjunction with each other.

Ibutilide Effectiveness and Safety in the Cardioversion of Atrial Fibrillation and Flutter in the Community Emergency Department

STUDY OBJECTIVE

Little is known about the use of ibutilide for cardioversion in atrial fibrillation and flutter outside of clinical trials. We seek to describe patient characteristics, ibutilide administration patterns, cardioversion rates, and adverse outcomes in the community emergency department (ED) setting. We also evaluate potential predictors of cardioversion success.

METHODS

Using a retrospective cohort of adults who received ibutilide in 21 community EDs between January 2009 and June 2015, we gathered demographic and clinical variables from electronic health records and structured manual chart review. We calculated rates of cardioversion and frequency of ventricular tachycardia within 4 hours and estimated adjusted odds ratios (aOR) in a multivariate regression model for potential predictors of cardioversion.

RESULTS

Among 361 patients, the median age was 61 years (interquartile range 53 to 71 years) and most had recent-onset atrial fibrillation and flutter (98.1%). Five percent of the cohort had a history of heart failure. The initial QTc interval was prolonged (>480 ms) in 29.4% of patients, and 3.1% were hypokalemic (<3.5 mEq/L). The mean ibutilide dose was 1.5 mg (SD 0.5 mg) and the rate of ibutilide-related cardioversion within 4 hours was 54.8% (95% confidence interval [CI] 49.6% to 60.1%), 50.5% for atrial fibrillation and 75.0% for atrial flutter. Two patients experienced ventricular tachycardia (0.6%), both during their second ibutilide infusion. Age (in decades) (aOR 1.3; 95% CI 1.1 to 1.5), atrial flutter (versus atrial fibrillation) (aOR 2.7; 95% CI 1.4 to 5.1), and no history of atrial fibrillation and flutter (aOR 2.0; 95% CI 1.2 to 3.1) were associated with cardioversion.

CONCLUSION

The effectiveness and safety of ibutilide in this community ED setting were consistent with clinical trial results despite less stringent patient selection criteria.

Improving Atrial Fibrillation Therapy: Is There a Gene for That?

Atrial fibrillation (AF) is an all-too-common and often challenging reality of clinical care. AF leads to significant morbidity and mortality; however, currently available treatments for AF have modest efficacy and high recurrence rates. In recent years, genetic therapy approaches have been explored in preclinical models of AF, and offer potential as a treatment modality with targeted delivery, tissue specificity, and therapy tailored to address mechanisms underlying the arrhythmia. However, many challenges remain before gene therapy can advance to a clinically relevant AF treatment. In this review, we summarize the available published data on gene therapy and discuss the challenges, opportunities, and limitations of this approach.

Ibutilide treatment protects against ER stress induced apoptosis by regulating calumenin expression in tunicamycin treated cardiomyocytes

Background

Ibutilide, a class III antiarrhythmic agent has been shown to be cardioprotective in treating atrial fibrillation, promoting cardioconversion and recently this agent has been shown to protect against ER stress induced apoptosis in cardiomyocytes. In this study we begin to identify the mechanism by which ibutilide exerts its cardioprotection in tunicamycin treated cardiomyocytes. We examined ER stress markers including calumenin; a calcium binding ER chaperone protein that has recently been linked to ER stress in cardiomyocytes, in our treated cells.

Methods

To assess the effect of ibutilide we used the well characterized in vitro model of ER stress induced apoptosis in rat neonatal cardiomyocytes (RNC). RNC were treated with tunicamycin and the degree of ER stress was assessed by quantifying mRNA and protein levels of GRP78, GRP94 and calumenin, and examined the extent of apoptosis by assessing the protein levels of caspase-3/9/12, CHOP, ATF6, p-PERK, spliced XBP-1, the ratio of Bax/Bcl-2 and the percentage of deoxynucleotidyl-transferase- mediated dUTP nick end labeling (TUNEL) positive cells.

Results

We demonstrate ibutilide attenuated the up-regulation of ER stress markers GRP78 and GRP94 and rescued the decline in calumenin mRNA and protein levels in tunicamycin treated cardiomyocytes. The up-regulation of apoptotic markers caspase-3, CHOP, ATF6, p-PERK, spliced XBP-1, the ratio of Bax/Bcl-2 and the percentage of TUNEL positive cells were also attenuated after ibutilide treatment while the protein levels of Caspase-9 and Caspase-12 were unaffected.

Conclusions

This study suggests another cardioprotective effect of the antiarrhythmic agent ibutilide whereby pretreatment leads to the attenuation of ER stress induced apoptosis by regulating calumenin expression. This study provides further evidence for the role of calumenin in the cardiomyocyte ER stress response.

Antiarrhythmic Drug Therapy for Atrial Fibrillation

Atrial fibrillation (AF) is the most frequently encountered arrhythmia. Prevalence increases with advancing age and so as its associated comorbidities, like heart failure. Choice of pharmacologic therapy depends on whether the goal of treatment is maintaining sinus rhythm or tolerating AF with adequate control of ventricular rates. Antiarrhythmic therapy and conversion of AF into sinus rhythm comes with the side effect profile, and we should select best antiarrhythmic therapy, individualized to the patient. New antiarrhythmic drugs are being tested in clinical trials. Drugs that target remodeling and inflammation are being tested for their use as prevention of AF or as upstream therapy.

Antiarrhythmic and Proarrhythmic Properties of QT-Prolonging Antianginal Drugs

In recent years there has been a major reorientation of drug therapy for cardiac arrhythmias, its changing role, and above all, a radical change in the class of arrhythmia drugs because of their impact on mortality. The decline in the use of sodium-channel blockers has led to an expanding use of β-blockers and simple or complex class III agents for controlling cardiac arrhythmias. Success with these agents in the context of their side effects has spurred the development of compounds with simpler ion-channel blocking properties that have less complex adverse reactions. The resulting so-called pure class III agents, such as dofetilide or ibutilide, were found to have antifibrillatory effects in atrial fibrillation and flutter and in ventricular tachyarrhythmias. Such agents are effective and have diversity, but they have come into therapeutics with a price: the sometimes-fatal torsades de pointes. The drug amiodarone, a complex compound that was synthesized as an antianginal agent, has been an exception in this regard. Its therapeutic use is associated with a negligibly low incidence of torsades de pointes, even though the drug produces significant bradycardia and QT lengthening to 500 to 700 msec. Recent electrophysiologic studies suggest that this paradox is likely due to the differential block of ion channels in endocardium, epicardium, midmyocardial (M) cells, and Purkinje fibers in the ventricular myocardium. There is also clinical evidence suggesting that amiodarone reduces the “torsadogenic” effects of pure class III agents. Ranolazine was also synthesized for the development of antianginal properties that stem from a partial inhibition of fatty acid oxidation; it too has been found to have electrophysioloigic properties. These are somewhat similar to those of amiodarone on ion channels in endocardium, epicardium, M cells, and Purkinje fibers in the ventricular myocardium, but the drug does not prolong the QT interval to the same extent as amiodarone does. Thus, the drug produces modest increases in repolarization as judged by its effects on the action potential duration (APD) without the potential for the development of torsades de pointes. By virtue of its suppressant action on early afterdepolarizations and triggered activity in Purkinje fibers and M cells, the drug appears to have a powerful potential for reducing the torsadogenic proclivity of conventional class III antiarrhythmic compounds. The rationale for the therapeutic niche for amiodarone, and especially in the case of ranolazine, in the prevention of drug-induced torsades de pointes is discussed.

Atrial Fibrillation After Cardiac Surgery: Pathophysiology and Treatment

Atrial fibrillation (AF) occurs in 25% to 60% of patients after cardiac surgery. It is most consistently associated with advanced age and valvular heart operations. Despite improving knowledge of the pathophysiology of chronic AF, postoperative AF remains an obstinate clinical problem. It is associated with an increased risk of stroke, longer hospital stay, and higher hospital expenditure. Consequently, there has been great interest in strategies to prevent and treat this arrhythmia. Treatment for postoperative AF may require immediate electrical cardioversion for hemodynamically unstable patients. Heart rate control is useful in most patients, with anticoagulation considered after 48 hours. Antiarrhythmic therapy is often effective in restoring sinus rhythm but its use needs to be balanced against the patient's risk of proarrhythmic side effects such as torsade de pointes.

Antiarrhythmic Drug Therapy for Rhythm Control in Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and affects over 33 million people worldwide. AF is associated with stroke and systemic thromboembolism, unpleasant symptoms and reduced quality of life, heart failure, and increased mortality, and treatment of AF and its complications are associated with significant cost. Antiarrhythmic drugs (AADs) can suppress AF, allowing long-term maintenance of sinus rhythm, and have the potential to relieve symptoms and reverse or prevent adverse effects associated with AF. However, large randomized controlled studies evaluating use of AADs have not demonstrated a clear benefit to maintaining sinus rhythm, and AADs often have significant limitations, including a modest rate of overall success at maintaining sinus rhythm, frequent side effects, and potentially life-threatening toxicities. Although some of the currently available AADs have been available for almost 100 years, better tolerated and more efficacious AADs have recently been developed both for long-term maintenance of sinus rhythm and for chemical cardioversion of AF to sinus rhythm. Advances in automated AF detection with cardiac implantable electronic devices have suggested that AADs might be useful for suppressing AF to allow safe discontinuation of anticoagulation in select patients who are in sinus rhythm for prolonged periods of time. AADs may also have synergistic effects with catheter ablation of AF. This review summarizes the pharmacology and clinical use of currently available AADs for treatment of AF and discusses novel AADs and future directions for rhythm control in AF.

Atrial fibrillation management: evaluating rate vs rhythm control

Atrial fibrillation (AF) is an increasing global issue leading to increased hospitalizations, adverse health related events and mortality. This review focuses on the management of atrial fibrillation, in particular in the past decade, comparing two major strategies, rate or rhythm control. We evaluate the evidence for each strategy, pharmacological options and the increasing utilization of invasive techniques, in particular catheter ablation and use of implantable cardiac pacing devices. Pharmacological comparative trials evaluating both strategies have shown rate control being non-inferior to rhythm control for clinical outcomes of mortality and other cardiovascular events (including stroke). Catheter ablation techniques, involving radiofrequency ablation and recently cryoablation, have shown promising results in particular with paroxysmal AF. However, persistent AF provides ongoing challenges and will be a particular focus of continued research.

Phase synchrony reveals organization in human atrial fibrillation

It remains unclear if human atrial fibrillation (AF) is spatially nonhierarchical or exhibits a hierarchy of organization sustained by sources. We utilize activation times obtained at discrete locations during AF to compute the phase synchrony between tissue regions, to examine underlying spatial dynamics throughout both atria. We construct a binary synchronization network and show that this network can accurately define regions of coherence in coarse-grained in silico data. Specifically, domains controlled by spiral waves exhibit regions of high phase synchrony. We then apply this analysis to clinical data from patients experiencing cardiac arrhythmias using multielectrode catheters to simultaneously record from a majority of both atria. We show that pharmaceutical intervention with ibutilide organizes activation by increasing the size of the synchronized domain in AF and quantify the increase in temporal organization when arrhythmia changes from fibrillation to tachycardia. Finally, in recordings from 24 patients in AF we show that the level of synchrony is spatially broad with some patients showing large spatially contiguous regions of synchronization, while in others synchrony is localized to small pockets. Using computer simulations, we show that this distribution is inconsistent with distributions obtained from simulations that mimic multiwavelet reentry but is consistent with mechanisms in which one or more spatially conserved spiral waves is surrounded by tissue in which activation is disorganized.

Investigation of the antifibrillatory drug interactions between Amiodarone and Ibutilide in isolated, perfused Rabbit hearts

In view of the reliability of the serial-shock method of measuring ventricular fibrillation threshold (VFT) in quantitatively assessing the antifibrillatory potency of many anti-arrhythmic drugs and the alarming reports of the proarrhythmic effects of several anti-arrhythmic agents, it was decided to use the above technique to study the possible interactions that may occur when anti-arrhythmic drugs from different classes are combined. Hearts isolated from New Zealand white rabbits of either sex weighing 1.5-2 kg were perfused by the Langendorff method with McEwen's solution. In six hearts, measurement of VFT was made in the absence of any drug throughout the experiments. Perfusion with either amiodarone or ibutilide produced significant, dose-dependent increase in VFT. In addition, there was no significant difference in the increase in VFT produced by the combined infusion of 1 μmol of amiodarone and 0.01 μmol of ibutilide and the summation of the increases produced by the separate infusion of these two concentrations. This is in contrast to a significant synergistic antifibrillatory effect of the combined use of lidocaine and propranolol that was reported previously. The lack of antifibrillatory interactions between amiodarone and Ibutilide may suggest the safety of combining the two drugs in the treatment of cardiac arrhythmias. However, further studies are required to establish this in the clinical setup.

[Refralon (niferidil) is a new class III antiarrhythmic agent for pharmacological cardioversion for persistent atrial fibrillation and atrial flutter]

AIM

To evaluate the efficacy and safety of refralon (niferidil), a new class III antiarrhythmic agent whose activity is related to the block of delayed rectifying potassium current and to the prolongation of atrial and ventricular action potential and refractory periods, when it is used as an agent for pharmacological cardioversion for atrial fibrillation (AF) and atrial flutter (AFL).

SUBJECTS AND METHODS

The efficacy of the drug as 3 intravenous boluses of 10 μg/kg was evaluated in 134 patients (90 men; 57.8 ± 11 years) with a mean AF duration of 3 (1.5; 6) months. Its effect was controlled by 24-hour Holter ECG monitoring. The criterion for its antiarrhythmic effect was 24-hour sinus rhythm (SR) recovery.

RESULTS

Niferidil restored SR in 47.7% of the patients with AF after administration of bolus 1, in 62% after bolus 2, and in 84.6% after bolus 3. SR was restored in all 100% patients with AFL. With the AF duration of less than 3 months, the efficacy of niferidil was 91.8%. There was nonsustained polymorphic ventricular tachycardia (VT) (torsade de pointes) in 1 (0.7%) patient and nonsustained monomorphic VT was stated in 5 (3.7%) patients. CONCLUSION> Pharmacological cardioversion with niferidil for persistent AF and VT may be regarded as a possible alternative to electrical cardioversion.

Towards a better understanding of QT interval variability

The International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) Guideline E14 recommends 'Thorough QT Study' as a standard assessment of drug-induced QT interval prolongation. At the same time, the value of drug-induced QTc prolongation as a surrogate marker for risk of life-threatening polymorphic ventricular tachycardia known as torsades des pointes remains controversial. Beat-to-beat variability of QT interval was recently proposed as an alternative metric. The following review addresses mechanisms of beat-to-beat QT variability, methods of QT interval variability measurements, and its prognostic value in clinical studies.

Efficacy of a new class III drug niferidil in cardioversion of persistent atrial fibrillation and flutter

AIMS

To study the efficacy and safety of the new class III antiarrhythmic agent niferidil for pharmacological cardioversion in patients with persistent atrial fibrillation (AF) and atrial flutter (AFl).

METHODS AND RESULTS

One hundred thirty-four adults (aged 57.8 ± 11 years, 90 males) were included with median AF duration of 3 (1.5-6) months. All patients received a total of 10-30 μg/kg, niferidil, intravenously, in 1-3 (if needed) consecutive boluses at 15-minute intervals. Holter electrocardiogram monitoring was started before infusion and was continued for 24 hours. The criterion for an antiarrhythmic effect was sinus rhythm restoration within 24 hours of the initial bolus. Niferidil converted AF to sinus rhythm in 47.7% of cases after bolus 1, in 62% of cases after bolus 2, and in 84.6% of cases bolus 3. Niferidil induced a 100% recovery rate in patients with AFl and a 91.8% recovery rate in patients with AF of duration from 8 days to 3 months. Nonsustained torsade de pointes occurred in 1 patient (0.7%), and nonsustained monomorphic ventricular tachycardia was observed in 5 patients (3.7%).

CONCLUSIONS

The new intravenous class III drug niferidil demonstrated high conversion rates of 84.6% in patients with persistent AF and 100% in patients with persistent AFl. Niferidil may be used as a possible alternative to electrical cardioversion for pharmacological cardioversion of persistent AF/AFl.

Efficacy and safety of ibutilide for chemical cardioversion of atrial fibrillation and atrial flutter in cancer patients

BACKGROUND

Atrial fibrillation and atrial flutter (AF/AFL) are the most common arrhythmias encountered in clinical practice. Rate versus rhythm control remains a difficult decision, especially in the acute setting. Ibutilide is a class III antiarrhythmic indicated for pharmacological cardioversion of recent-onset AF/AFL. At the University of Texas MD Anderson Cancer Center, restoration of sinus rhythm is desirable because many patients have contraindications to anticoagulation. In addition, most are on multiple medications that prolong the QT interval; therefore, the objective of this study was to establish the safety and efficacy of ibutilide.

METHODS

This was a retrospective chart review of 81 patients who were identified via the pharmacy database as receiving ibutilide for AF/AFL from January 2002 to May 2006. Outcomes including cardioversion rates and effects on the QT interval were recorded.

RESULTS

Ibutilide use was associated with successful cardioversion in 75% of patients. Out of 81 patients, 68 patients (84%) were on at least 1 medication that prolonged the QT interval at the time of ibutilide administration. However, no significant changes in the corrected QT interval pre and post ibutilide cardioversion were noted in any group of patients.

CONCLUSIONS

Overall, ibutilide is safe and effective in cancer patients when used for acute cardioversion of AF/AFL. Despite the use of multiple medications that can potentially prolong the QT interval, no patient experienced serious life-threatening rhythm disturbances or significant QT prolongation during ibutilide administration.

Effects of ibutilide on canine cardiac pacing threshold and on induction rates of atrial fibrillation

This study aims to observe the effects of ibutilide on canine cardiac pacing threshold and on induction rates of atrial fibrillation. Eighteen mongrel dogs were anesthetized and administrated with ibutilide. The pacing thresholds and induction rates of atrial fibrillation were measured with and without ibutilide (10-min infusion dose was 0.10 mg kg(-1), followed by a maintaining dose of 0.01 mg min(-1) 30 min later). This study found that ibutilide increases pacing thresholds in dogs. Moreover, there were significant differences between pacing thresholds with and without ibutilide (P < 0.05). Further, ibutilide significantly reduces the induction rates of atrial fibrillation (P < 0.05). Our findings indicate that pacing voltage changes should be closely monitored in patients taking anti-arrhythmic drugs, who are treated with cardiac stimulation or have undergone pacemaker implantation. We also found that ibutilide is an effective drug in preventing or controlling atrial fibrillation.

Novel rare variants in congenital cardiac arrhythmia genes are frequent in drug-induced torsades de pointes

Marked prolongation of the QT interval and polymorphic ventricular tachycardia following medication (drug-induced long QT syndrome, diLQTS) is a severe adverse drug reaction (ADR) that phenocopies congenital long QT syndrome (cLQTS) and is one of the leading causes for drug withdrawal and relabeling. We evaluated the frequency of rare non-synonymous variants in genes contributing to the maintenance of heart rhythm in cases of diLQTS using targeted capture coupled to next-generation sequencing. Eleven of 31 diLQTS subjects (36%) carried a novel missense mutation in genes with known congenital arrhythmia associations or with a known cLQTS mutation. In the 26 Caucasian subjects, 23% carried a highly conserved rare variant predicted to be deleterious to protein function in these genes compared with only 2-4% in public databases (P<0.003). We conclude that the rare variation in genes responsible for congenital arrhythmia syndromes is frequent in diLQTS. Our findings demonstrate that diLQTS is a pharmacogenomic syndrome predisposed by rare genetic variants.

In situ mechanical analysis of cardiomyocytes at nano scales

Nanomechanical behaviors of single living cardiomyocytes are quantitatively observed using calculated torsions and deflections of an AFM cantilever. The lateral contractions are related to the calcium intensity within rather than the vertical beating power of the cardiomyocytes. Drug-induced nanomechanical changes of cardiomyocytes were further investigated by measuring lateral contractions in real time.

Cardiac arrhythmias during pregnancy

OPINION STATEMENT

This article reviews the appropriate evaluation and management of cardiac arrhythmias in the pregnant patient. Any treatment strategy in this patient population has the inherent potential to adversely affect the health of the unborn child. As such, there is no room for empiric therapy in these patients. Adequate arrhythmia documentation is paramount, preferably by noninvasive means. The decision to treat should be based on symptom severity and the risk to both mother and fetus posed by potentially recurring arrhythmia episodes throughout the pregnancy. Minimal symptoms in the setting of a structurally normal heart call for a conservative approach. Less is better. If pharmacologic therapy is justified, drugs with historically demonstrated safety profiles in pregnancy should be tried first. The safety profiles of virtually all drugs used to treat cardiac arrhythmias during human pregnancy are based solely on an accumulation of past clinical experience. Newer antiarrhythmics therefore carry a largely unknown risk. Most inherent rhythm disorders manifest long before a woman reaches childbearing age. Women with previously diagnosed arrhythmias frequently experience a recurrence or worsening of their arrhythmia during the pregnancy. Counseling of these individuals and perhaps preemptive treatment by means such as arrhythmia ablation prior to a planned pregnancy would seem optimal.

Factors affecting the degree of QT prolongation with drug challenge in a large cohort of normal volunteers

BACKGROUND

The degree of QT prolongation by drug is highly variable and related to risk for polymorphic ventricular tachycardia due to drugs.

OBJECTIVE

The purpose of this study was to determine factors that affect the degree of QT prolongation by drugs.

METHODS

QT and QTc were measured before and after administration of the QT-prolonging drug ibutilide in 253 normal volunteers aged 18 to 40 years. Drug effect on QTc prolongation was defined as ΔQTc = QTc after drug minus QTc before drug.

RESULTS

Ibutilide prolonged QT from 396 ± 31 ms to 418 ± 39 ms (P <.001) and QTc from 406 ± 15 ms to 446 ± 33 ms (P <.001). ΔQTc did not correlate with baseline QTc (Pearson correlation 0.016, P = .8). Postdrug QTc was correlated weakly with predrug QTc (Pearson correlation 0.484, P <.001), and strongly with ΔQTc (Pearson correlation 0.882, P <.001). ΔQTc was identical for men and women (39 ± 29 ms vs 39 ± 27 ms, P = .9) but displayed significant differences among body mass index categories (P <.001). Overweight (48 ± 27 ms) and obese (61 ± 31 ms) subjects had significantly more QT prolongation by drug than normal (31 ± 25 ms) or underweight (24 ± 12 ms) subjects.

CONCLUSION

QT prolongation by ibutilide does not correlate to baseline QTc and does not differ between men and women. Overweight and obese subjects have greater drug effect on QTc than subjects with normal or low body mass index. These findings have implications for drug-induced long QT syndrome.

Pharmacologic Conversion of Atrial Fibrillation and Atrial Flutter

Atrial fibrillation and atrial flutter are common arrhythmias in everyday clinical settings. Pharmacologic cardioversion (CV) is a simple and widely used strategy for the treatment of these arrhythmias, and many drugs are currently available. The choice of drug is strongly influenced by the time elapsed from atrial fibrillation onset and by a patient's clinical subset. Electrical direct-current CV is the treatment of choice in long-lasting forms; nevertheless, some agents also show efficacy in this setting. In addition, promising results come from studies on the efficacy and safety of new antiarrhythmic drugs and from therapeutic approaches that reduce the need for hospitalization and improve quality of life.

Pharmacokinetics/Pharmacodynamics of Antiarrhythmic Drugs

This article describes the pharmacology of antiarrhythmic medications. Although these medications are broadly considered in terms of their blockade of either sodium or potassium channels, they act by a variety of pharmacodynamic mechanisms. Elimination may be via hepatic metabolism or renal mechanisms, or a combination. In particular, interactions between antiarrhythmic medications and other drugs that interfere with hepatic metabolism by P450 enzymes is a source for toxicity.

Ibutilide-induced changes in the temporal lability of ventricular repolarization in patients with and without structural heart disease

INTRODUCTION

Ibutilide has been shown to prolong repolarization times and increase the risk of ventricular tachyarrhythmias particularly in patients with structural heart disease. The mechanisms underlying its proarrhythmic effects remain incompletely understood. We sought to define the effects of ibutilide on the temporal lability of ventricular repolarization in patients with and without structural heart disease.

METHODS

Twenty-four patients referred for electrophysiology study underwent monophasic action potential (MAP) recordings in the right ventricle during sinus rhythm and random interval right atrial pacing (RIAP). Ibutilide was subsequently administered and the recordings repeated both in sinus rhythm and with RIAP. Digitized recordings were analyzed offline for calculation of the QT variability index (QTVI) based on surface ECG, and the MAP duration variability index (MAPDVI) based on the intracardiac MAP signal.

RESULTS

Of 24 patients enrolled, analyses were performed in 21 patients (mean age 59 +/- 15 years, 38% women). In three patients, the data were not analyzed due to frequent premature ventricular complexes. Ibutilide resulted in significant changes in heart rate (mean difference: -7.4 +/- 0.91 bpm, P < 0.0001) and the surface QT interval (mean difference: 59.6 +/- 12.2 ms, P = 0.0001) during sinus rhythm. After ibutilide, QTVI remained unchanged from baseline during sinus rhythm but was significantly different in the setting of RIAP (mean difference: 0.345 +/- 0.098, P = 0.0022). With subgroup analyses, these differences remained significant regardless of the presence or absence of heart disease.

CONCLUSION

Ibutilide results in overall prolongation of ventricular repolarization and reductions in baseline sinus rates. Ibutilide increases temporal lability of repolarization only with enriched fluctuations in heart rate.

Acute management of atrial fibrillation and atrial flutter in the critical care unit: should it be ibutilide?

BACKGROUND

Ibutilide is currently indicated for the rapid conversion of atrial fibrillation (Afb) or atrial flutter (Afl) of recent onset but limited to patients who are hemodynamically stable and without symptomatic cardiovascular conditions.

HYPOTHESIS

The study was undertaken to assess the efficacy and safety of ibutilide in patients with Afb or Afl associated with acute cardiovascular-medical disorders and in patients receiving prior selective antiarrhythmic drug therapy.

METHODS

The study included 34 patients, mean age 75 +/- 16.3 years, with Afb (n = 25) or Afl (n = 9) having a variety of disorders, for example, congestive heart failure, unstable angina, borderline hypotension, respiratory failure, and chronic renal failure. Prior antiarrhythmic drugs consisted of propafenone (n = 5) or amiodarone (n = 3). Eligibility for cardioversion was established with appropriate anticoagulation or transesophageal echocardiography findings. Ibutilide was given as up to two 10 min infusions of 1 mg separated by 10 min.

RESULTS

The overall conversion rate after ibutilide was 79.4% (27/34 patients): 80% for Afb and 78% for Afl. More than 90% converted within 1 h of treatment. A high conversion rate of 92% resulted in those with an arrhythmia duration of < or = 1 week. All eight patients with prior antiarrhythmic therapy converted to sinus rhythm. The average baseline QTc interval for all patients increased 17.1% (397 +/- 63.3 to 465 +/- 60.2 ms) at 30 min. For eight patients (including four who received prior antiarrhythmic drugs), QTc interval prolongation > or = 500 ms was associated with nearly half the entire incidence of arrhythmic events. Proarrhythmia, the exclusive adverse effect, consisted of ventricular extrasystoles (n = 10) and nonsustained monomorphic ventricular tachycardia (VT) (n = 2) managed with intravenous MgSO4, and sustained polymorphic VT (n = 1) requiring electrical cardioversion.

CONCLUSION

Ibutilide is an effective and well tolerated drug for the rapid termination of Afb or Afl of recent onset associated with symptomatic and/or hemodynamically unstable disorders, and it is most efficacious (> or = 90%) when the atrial arrhythmia is < or = 1 week in duration. Proarrhythmic events are readily manageable in a monitored unit with access to appropriate treatment.

Ibutilide therapy for atrial fibrillation: 5-year experience in a community hospital

Many institutions restrict the use of ibutilide because of the potential risk of polymorphic ventricular tachycardia (PMVT). Over a 5-year period from June 2000 to May 2005, 238 patients, 151 men and 87 women, with a mean age of 67.1 years (range, 22-94 years), received intravenous ibutilide at our institution. Ibutilide was administered by nurses or physicians in 4 clinical settings: emergency department (n = 80), intensive care unit (n = 11), patient room on telemetry (n = 107), and in the cardiac catheterization/electrophysiology laboratory (n = 40). Conversion to sinus rhythm occurred in 59% of patients outside the catheterization/electrophysiology laboratory. The incidence of PMVT was 1.7%. Three patients had brief nonsustained PMVT and 1 patient had a sustained PMVT. There was no difference in outcome whether a physician was present at the time of ibutilide administration. Our data suggest that ibutilide is a safe and efficacious drug when ordered by experienced physicians in properly selected patients in a variety of monitored settings.