Propafenone: an effective agent for the management of supraventricular arrhythmias

Atrial Fibrillation Management: A Comprehensive Review with a Focus on Pharmacotherapy, Rate, and Rhythm Control Strategies

Atrial fibrillation (AF) is an increasingly common arrhythmia encountered in clinical practice that leads to a substantial increase in utilization of healthcare services and a decrease in the quality of life of patients. The prevalence of AF will continue to increase as the population ages and develops cardiac comorbidities; thus, prompt and effective treatment is important to help mitigate systemic resource utilization. Treatment of AF involves two tenets: prevention of stroke and systemic embolism and symptom control with either a rate or a rhythm control strategy. Historically, due to the safe nature of medications like beta-blockers and non-dihydropyridine calcium channel blockers, used in rate control, it has been the initial strategy used for symptom control in AF. Newer data suggest that a rhythm control strategy with antiarrhythmic medications with or without catheter ablation may lead to a reduction in major adverse cardiovascular events, particularly in patients newly diagnosed with AF. Modulation of factors that promote AF or its complications is another important aspect of the overall holistic management of AF. This review provides a comprehensive focus on the management of patients with AF and an in-depth review of pharmacotherapy of AF in the rate and rhythm control strategies.

Inherited and Acquired Rhythm Disturbances in Sick Sinus Syndrome, Brugada Syndrome, and Atrial Fibrillation: Lessons from Preclinical Modeling

Rhythm disturbances are life-threatening cardiovascular diseases, accounting for many deaths annually worldwide. Abnormal electrical activity might arise in a structurally normal heart in response to specific triggers or as a consequence of cardiac tissue alterations, in both cases with catastrophic consequences on heart global functioning. Preclinical modeling by recapitulating human pathophysiology of rhythm disturbances is fundamental to increase the comprehension of these diseases and propose effective strategies for their prevention, diagnosis, and clinical management. In silico, in vivo, and in vitro models found variable application to dissect many congenital and acquired rhythm disturbances. In the copious list of rhythm disturbances, diseases of the conduction system, as sick sinus syndrome, Brugada syndrome, and atrial fibrillation, have found extensive preclinical modeling. In addition, the electrical remodeling as a result of other cardiovascular diseases has also been investigated in models of hypertrophic cardiomyopathy, cardiac fibrosis, as well as arrhythmias induced by other non-cardiac pathologies, stress, and drug cardiotoxicity. This review aims to offer a critical overview on the effective ability of in silico bioinformatic tools, in vivo animal studies, in vitro models to provide insights on human heart rhythm pathophysiology in case of sick sinus syndrome, Brugada syndrome, and atrial fibrillation and advance their safe and successful translation into the cardiology arena.

Efficacy and economic benefits of a modified Valsalva maneuver in patients with paroxysmal supraventricular tachycardia

BACKGROUND

A modified Valsalva maneuver (VM) has been suggested to be superior to the standard VM for conversion of paroxysmal supraventricular tachycardia (PSVT).

AIM

To evaluate the efficacy and economic benefits of a modified VM in Chinese patients.

METHODS

Patients with PSVT admitted to our center between October 2017 and September 2019 were randomly assigned to the modified and standard VM groups. Conversion via VM was performed up to three times. The primary outcome of the study was the success rate of PSVT conversion to sinus rhythm. The secondary outcomes included the incidence of adverse events, economic cost during the visit, and the degree of patient acceptance of the treatment.

RESULTS

Overall, 361 patients were enrolled, with 180 allocated to the modified VM group and 181 to the standard VM group. Baseline characteristics were well matched in the groups. Overall, the modified VM group had higher success rates of PSVT conversion after single (47.78% vs 15.38%, P < 0.001) and multiple (62.22% vs 19.78%, P < 0.001) VM sessions. No significant differences in the incidences of adverse events and rates of patient acceptance were detected between the two groups (both P > 0.05). Moreover, the economic cost of the clinic visit was significantly lower for the modified VM group than for the standard VM group (P < 0.05).

CONCLUSION

The modified VM may confer both therapeutic and economic benefits as compared with the standard VM for conversion of PSVT.

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-selective sodium channel block strategy to suppress atrial fibrillation: ranolazine versus propafenone

Ranolazine has been shown to produce atrial-selective depression of sodium channel-dependent parameters and suppress atrial fibrillation (AF) in a variety of experimental models. The present study contrasts the effects of ranolazine and those of a clinically used anti-AF class IC agent, propafenone. Electrophysiological and anti-AF effects of propafenone and ranolazine were compared at clinically relevant concentrations (i.e., 0.3-1.5 and 1-10 μM, respectively) in canine isolated coronary-perfused atrial and ventricular preparations. Transmembrane action potential and pseudo-ECG were recorded. Both ranolazine and propafenone produced atrial-selective prolongation of action potential duration. Propafenone depressed sodium channel-mediated parameters [maximum rate of rise of the action potential upstroke (V(max)), conduction time, and diastolic threshold of excitation] and induced postrepolarization refractoriness to a greater degree than ranolazine, and these effects, unlike those induced by ranolazine, were not or only mildly atrial-selective at normal rates (cycle length 500 ms). At fast pacing rates, however, the effects of propafenone on V(max) and conduction time became atrial-selective, because of the elimination of diastolic interval in atria, but not in ventricles. Propafenone (1.5 μM) and ranolazine (10.0 μM) were effective in preventing the initiation of persistent acetylcholine-mediated AF (6/7 and 9/11 atria, respectively), its termination (8/10 and 8/12 atria, respectively), and subsequent reinduction (8/8 and 7/8 atria, respectively). Thus, propafenone and ranolazine both suppress AF, but ranolazine, unlike propafenone, does it with minimal effects on ventricular myocardium, suggesting a reduced potential for promoting ventricular arrhythmias.

Review of contemporary antiarrhythmic drug therapy for maintenance of sinus rhythm in atrial fibrillation

Atrial fibrillation (AF) is the most common rhythm disturbance seen in clinical practice, and its prevalence and incidence are rising rapidly as the population ages with its attendant complications. Management of AF involves anticoagulation, and fortunately new drugs for long-term anticoagulation are now available. Maintenance of sinus rhythm, though intuitively better than rate control strategy, has not been shown to offer mortality benefit. Still, maintenance of sinus rhythm is considered an appropriate therapeutic strategy when symptoms are not adequately controlled with rate control. Though significant advances have been made in ablation techniques for AF, pharmacological therapy is still the first line of treatment for rate control and maintenance of sinus rhythm, given ease of use, noninvasive nature, and limited experience with catheter-based ablation techniques. Class IC and III agents (Vaughan Williams classification) form the backbone for pharmacological maintenance of sinus rhythm. Dronedarone, a recently approved class III agent, provides a significant advance because of its relatively safe side effect profile. Currently drugs with selective atrial channels blocking properties, like Vernakalant, are being tested in trials and may provide an opportunity to maintain sinus rhythm with limited toxicity. Large trials are also being conducted to better define the efficacy of catheter-based ablation strategy as first-line treatment. Here, we review the current status of commonly used antiarrhythmic medications for the maintenance of sinus rhythm in AF.

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.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Clinical Comparison of Ibutilide and Propafenone for Converting Atrial Flutter

OBJECTIVE

To evaluate the efficacy and safety of intravenous ibutilide and propafenone for immediate treatment of atrial flutter.

METHODS

Forty patients with atrial flutter with an arrhythmia duration of three hours to 90 days were randomized to receive up to two 10-minute infusions of ibutilide (1 and 1 mg) or propafenone (70 and 70 mg) with a 10-minute interval.

RESULTS

Ibutilide was superior to propafenone for treating atrial flutter (90% vs. 30%, p < 0.01). The median conversion time in the ibutilide group was 11 min (the 25th and 75th percentile was 10 and 45 min), and the median conversion time in the propafenone group was 35 min (range 20-55 min). In all patients, the duration of arrhythmia before treatment was a predictor of arrhythmia termination, although this was more obvious in the group that received ibutilide. Conversion of atrial flutter by ibutilide was characterized mainly by increased cycle length variability. Bradycardia (2/20) and hypotension (4/20) were more common side effects with propafenone. Of 20 patients given ibutilide, 8 (40%) who developed monomorphic ventricular extrasystoles or repetitive atrial flutter with aberrant conduction tachycardia, no one required any specific treatment except for the interruption of ibutilide infusion.

CONCLUSION

Ibutilide is highly effective for rapidly terminating atrial flutter. This new class III drug, under monitored conditions, is a potential alternative to currently available cardioversion options.

Propafenone and Its Metabolites Preferentially Inhibit IKrin Rabbit Ventricular Myocytes

Propafenone is an antiarrhythmic agent with recognized cardiac myocyte repolarizing K+ current inhibitory effects. It has two known electropharmacologically active metabolites, 5-hydroxy- and N-depropylpropafenone, whose K+ current inhibitory effects are less thoroughly elucidated than those of the parent compound. This study characterizes and directly compares the pharmacologic interaction of all three compounds with two key repolarizing K+ currents, the rapidly activating delayed rectifier IKr and the transient outward current Ito, using the whole-cell patch-clamp technique in isolated rabbit ventricular myocytes. All three agents potently inhibited IKr with IC50 values of 0.80 +/-0.14, 1.88 +/-0.21, and 5.78 +/-1.24 microM for propafenone, 5-hydroxypropafenone, and N-depropylpropafenone, respectively, based on reduction of peak tail current amplitude following repolarization from +50 mV to -30 mV. IKr inhibition was concentration- and weakly voltage-dependent, with a time course from channel activation that was well described by a single exponential model and consistent with open channel block. Propafenone and its 5-hydroxy and N-depropyl metabolites also blocked Ito with IC50 values of 7.27 +/-0.53, 40.29 +/-7.55, and 44.26 +/-5.73 microM, respectively, at +50 mV. No significant drug effects were observed with respect to Ito voltage dependence of steady-state inactivation or time course of recovery from inactivation. The preferential interaction of propafenone and its metabolites with IKr relative to Ito in ventricular myocytes sheds new light on the anti- and proarrhythmic activity of propafenone in vivo.

Transient outward current inhibition by propafenone and 5-hydroxypropafenone in cultured neonatal rat ventricular myocytes

The antiarrhythmic agent propafenone and its primary electropharmacologically active metabolite, 5-hydroxypropafenone, are known inhibitors of cardiac myocyte repolarizing currents. We recently documented potent propafenone inhibition of the transient outward potassium current (Ito) in human atrial myocytes from patients in the newborn and infant age range. In the current study we characterized ventricular Ito inhibition by propafenone and 5-hydroxypropafenone in neonatal myocytes enzymatically isolated from 2-day-old Sprague-Dawley rat pups. Using the whole-cell patch-clamp technique in ventricular myocytes kept in primary culture for 1-4 days, we observed comparably potent Ito inhibition by both agents, yielding 50% maximal inhibitory concentration (IC50) values of 2.1 +/- 0.5 and 1.5 +/- 0.2 microM for propafenone and 5-hydroxypropafenone, respectively. Ito blockade by both of these agents was time, concentration, and voltage dependent, but use independent. There was no drug effect on steady-state voltage dependence of Ito inactivation, or on the time course of Ito recovery from inactivation. These findings are consistent with an open channel-blocking mechanism as suggested by other models. We conclude that both propafenone and 5-hydroxypropafenone are potent Ito inhibitors in neonatal rat ventricular myocytes, with potencies exceeding those demonstrated for propafenone in adult rat ventricular myocytes or in human atrial myocytes from patients of all ages.

Electropharmacologic effects of class I and class III antiarrhythmia drugs on typical atrial flutter: insights into the mechanism of termination

BACKGROUND

Acute effects of class I and class III antiarrhythmia drugs on the reentrant circuit of typical atrial flutter are not fully studied. Furthermore, the critical electrophysiologic determinants of flutter termination by antiarrhythmia drugs are not clear.

METHODS AND RESULTS

The study population consisted of 36 patients (mean age, 53+/-17 years) with clinically documented typical atrial flutter. A 20-pole "halo" catheter was positioned around the tricuspid annulus. Incremental pacing was performed to measure the conduction velocity along the isthmus and lateral wall, and extrastimulation was performed to evaluate atrial refractory period in the baseline state and after intravenous infusion of ibutilide, propafenone, and amiodarone. Efficacy of these drugs in conversion of typical atrial flutter and patterns of termination were also determined. Ibutilide significantly increased the atrial refractory period and decreased conduction velocity in the isthmus at short pacing cycle length. It terminated atrial flutter in 8 (67%) of 12 patients after prolongation of flutter cycle length due to increase (86+/-19%) of conduction time in the isthmus. Propafenone predominantly decreased conduction velocity with use dependency and significantly increased atrial refractory period, but it only converted atrial flutter in 4 (33%) of 12 patients. Amiodarone had fewer effects on atrial refractory period and conduction velocity than did ibutilide and propafenone, and it terminated atrial flutter in only 4 (33%) of 12 patients. Termination of typical atrial flutter was due to failure of wave front propagation through the isthmus, which occurred with cycle length oscillation, abruptly without variability of cycle length, or after premature activation of the reentrant circuit.

CONCLUSIONS

Ibutilide, with a unique increase in atrial refractoriness, was more effective in conversion of atrial flutter than were propafenone and amiodarone.

Mechanisms of action of antiarrhythmic drugs: from ion channel blockage to arrhythmia termination

Over the past decade, the strategies for arrhythmia management have been in transition. Physical methods to treat arrhythmias, such as ICDs and RF ablation, have undergone considerable refinement and wider application. Ischemic heart disease and congestive heart failure have been identified as clinical situations in which antiarrhythmic drugs have a significant proarrhythmic potential. However, drugs retain an important role in arrhythmia management. Strategies to mitigate the structural and functional changes that occur in hypertrophy, ischemia, and infarction have not been thoroughly explored. Membrane ion channels and receptors are the targets for the action of currently available drugs. The cloning and sequencing of these ion channels and receptors should improve the efficacy and specificity of drug design. Cardiac Na+, Ca2+, K+, and nonspecific cation channels have a clearly defined role in the generation of the normal action potential. Their specific roles in the various clinical arrhythmias is less certain. There are sufficient data to associate specific ionic channels with normal and abnormal automaticity and with reentry occurring in specific regions of the heart. A rational choice of antiarrthymic drugs can be made when an arrhythmogenic mechanism and the putative underlying membrane currents can be identified based on the clinical characteristics of the arrhythmia. For a majority of clinical arrhythmias, this ideal has not been achieved. When a particular drug is used to treat an arrhythmia, the full complement of its actions will depend on which multiple ion channels or receptors are blocked and the kinetics of drug interaction with these sites.