Effective suppression of atrial fibrillation by ivabradine: Novel target for an established drug?

Drug-induced AF: Arrhythmogenic Mechanisms and Management Strategies

AF is a prevalent condition that is associated with various modifiable and unmodifiable risk factors. Drug-induced AF, despite being commonly under-recognised, can be relatively easy to manage. Numerous cardiovascular and non-cardiovascular agents, including catecholaminergic agents, adenosine, anti-tumour agents and others, have been reported to induce AF. However, the mechanisms underlying drug-induced AF are diverse and not fully understood. The complexity of clinical scenarios and insufficient knowledge regarding drug-induced AF have rendered the management of this condition complicated, and current treatment guidelines follow those for other types of AF. Here, we present a review of the epidemiology of drug-induced AF and highlight a range of drugs that can induce or exacerbate AF, along with their molecular and electrophysiological mechanisms. Given the inadequate evidence and lack of attention, further research is crucial to underscore the clinical significance of drug-induced AF, clarify the underlying mechanisms and develop effective treatment strategies for the condition.

Ivabradine and Atrial Fibrillation: A Meta-analysis of Randomized Controlled Trials

ABSTRACT

This was a meta-analysis of randomized control trials (RCTs) to evaluate the effect of ivabradine on the risk of atrial fibrillation (AF) as well as its effect on the ventricular rate in patients with AF. The PubMed, EMBASE, Cochrane Controlled Trials Register, and other databases were searched for RCTs of ivabradine. Thirteen trials with 37,533 patients met the inclusion criteria. The incidence of AF was significantly higher in the ivabradine treatment group than in the control group (odds ratio (OR), 1.23; 95% confidence interval (CI), 1.08-1.41), although it was reduced after cardiac surgery (OR, 0.70; 95% CI, 0.23-2.12). Regarding left ventricular ejection fraction (LVEF), ivabradine increased the risk of AF in both LVEF >40% (OR, 1.42; 95% CI, 1.24 to 1.63) and LVEF ≤40% subgroups (OR, 1.16; 95% CI, 0.98-1.37). The risk of AF was increased by both small and large cumulative doses of ivabradine (small cumulative dose: OR, 3.00; 95% CI, 0.48 to 18.93; large cumulative dose: OR, 1.05; 95% CI, 0.83-1.34). Furthermore, ivabradine may reduce the ventricular rate in patients with AF. In conclusion, we found that both large and small cumulative doses of ivabradine were associated with an increased incidence of AF, and the effect was more marked in the LVEF >40% subgroup. Nevertheless, ivabradine therapy is beneficial for the prevention of post-operative AF. Furthermore, ivabradine may be effective in controlling the ventricular rate in patients with AF, although more RCTs are needed to support this conclusion.

Safe electrophysiologic profile of dexmedetomidine in different experimental arrhythmia models

Previous studies suggest an impact of dexmedetomidine on cardiac electrophysiology. However, experimental data is sparse. Therefore, purpose of this study was to investigate the influence of dexmedetomidine on different experimental models of proarrhythmia. 50 rabbit hearts were explanted and retrogradely perfused. The first group (n = 12) was treated with dexmedetomidine in ascending concentrations (3, 5 and 10 µM). Dexmedetomidine did not substantially alter action potential duration (APD) but reduced spatial dispersion of repolarization (SDR) and rendered the action potentials rectangular, resulting in no proarrhythmia. In further 12 hearts, erythromycin (300 µM) was administered to simulate long-QT-syndrome-2 (LQT2). Additional treatment with dexmedetomidine reduced SDR, thereby suppressing torsade de pointes. In the third group (n = 14), 0.5 µM veratridine was added to reduce the repolarization reserve. Further administration of dexmedetomidine did not influence APD, SDR or the occurrence of arrhythmias. In the last group (n = 12), a combination of acetylcholine (1 µM) and isoproterenol (1 µM) was used to facilitate atrial fibrillation. Additional treatment with dexmedetomidine prolonged the atrial APD but did not reduce AF episodes. In this study, dexmedetomidine did not significantly alter cardiac repolarization duration and was not proarrhythmic in different models of ventricular and atrial arrhythmias. Of note, dexmedetomidine might be antiarrhythmic in acquired LQT2 by reducing SDR.

Effect of Ivabradine on Cardiac Ventricular Arrhythmias: Friend or Foe?

Life-threatening ventricular arrhythmias, such as ventricular tachycardia and ventricular fibrillation remain an ongoing clinical problem and their prevention and treatment require optimization. Conventional antiarrhythmic drugs are associated with significant proarrhythmic effects that often outweigh their benefits. Another option, the implantable cardioverter defibrillator, though clearly the primary therapy for patients at high risk of ventricular arrhythmias, is costly, invasive, and requires regular monitoring. Thus there is a clear need for new antiarrhythmic treatment strategies. Ivabradine, a heartrate-reducing agent, an inhibitor of HCN channels, may be one of such options. In this review we discuss emerging data from experimental studies that indicate new mechanism of action of this drug and further areas of investigation and potential use of ivabradine as an antiarrhythmic agent. However, clinical evidence is limited, and the jury is still out on effects of ivabradine on cardiac ventricular arrhythmias in the clinical setting.

Effect of ivabradine on cardiac arrhythmias: Antiarrhythmic or proarrhythmic?

Cardiac arrhythmias are a major source of mortality and morbidity. Unfortunately, their treatment remains suboptimal. Major classes of antiarrhythmic drugs pose a significant risk of proarrhythmia, and their side effects often outweigh their benefits. Therefore, implantable devices remain the only truly effective antiarrhythmic therapy, and new strategies of antiarrhythmic treatment are required. Ivabradine is a selective heart rate-reducing agent, an inhibitor of hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, currently approved for treatment of coronary artery disease and chronic heart failure. In this review, we focus on the clinical and basic science evidence for the antiarrhythmic and proarrhythmic effects of ivabradine. We attempt to dissect the mechanisms behind the effects of ivabradine and indicate the focus of future studies.

Acute electrophysiologic effects of the polyphenols resveratrol and piceatannol in rabbit atria

The natural polyphenol resveratrol and its analogue piceatannol have various beneficial effects including antiarrhythmic properties. The aim of the present study was to examine potential electrophysiologic effects in an experimental whole-heart model of atrial fibrillation (AF). Simultaneous infusion of resveratrol (50 μmol/L) or piceatannol (10 μmol/L) in rabbit hearts resulted in an increase in atrial refractory period. Both agents induced a significant slowing of atrial conduction and of intrinsic heart rate. In both groups, a trend toward a reduction in AF and a regularization of AF was observed.

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.

Hypertension and Atrial Fibrillation: Doubts and Certainties From Basic and Clinical Studies

Hypertension and atrial fibrillation (AF) are 2 important public health priorities. Their prevalence is increasing worldwide, and the 2 conditions often coexist in the same patient. Hypertension and AF are strikingly related to an excess risk of cardiovascular disease and death. Hypertension ultimately increases the risk of AF, and because of its high prevalence in the population, it accounts for more cases of AF than other risk factors. Among patients with established AF, hypertension is present in about 60% to 80% of individuals. Despite the well-known association between hypertension and AF, several pathogenetic mechanisms underlying the higher risk of AF in hypertensive patients are still incompletely known. From an epidemiological standpoint, it is unclear whether the increasing risk of AF with blood pressure (BP) is linear or threshold. It is uncertain whether an intensive control of BP or the use of specific antihypertensive drugs, such as those inhibiting the renin-angiotensin-aldosterone system, reduces the risk of subsequent AF in hypertensive patients in sinus rhythm. Finally, in spite of the observational evidence suggesting a progressive relation between BP levels and the risk of thromboembolism and bleeding in patients with hypertension and AF, the extent to which BP should be lowered in these patients, including those who undergo catheter ablation, remains uncertain. This article summarizes the main basic mechanisms through which hypertension is believed to promote AF. It also explores epidemiological data supporting an evolutionary pathway from hypertension to AF, including the emerging evidence favoring an intensive BP control or the use of drugs, which inhibit the renin-angiotensin-aldosterone system to reduce the risk of AF. Finally, it examines the impact of non-vitamin K antagonist oral anticoagulants compared with warfarin in relation to hypertension.

Ivabradine Aggravates the Proarrhythmic Risk in Experimental Models of Long QT Syndrome

Ivabradine has recently been demonstrated to have antiarrhythmic properties in atrial fibrillation. The aim of the present study was to assess the electrophysiologic profile of ivabradine in an experimental whole-heart model of long-QT-syndrome. In 12 isolated rabbit hearts long-QT-2-syndrome (LQT2) was simulated by infusion of D,L-sotalol (100 µM). 12 rabbit hearts were treated with veratridine (0.5 µM) to mimic long-QT-3-syndrome (LQT3). Sotalol induced a significant prolongation of QT-interval (+ 40 ms, p < 0.01) and action potential duration (APD, + 20 ms, p < 0.01). Similar results were obtained in veratridine-treated hearts (QT-interval: +52 ms, p < 0.01; APD: + 41 ms, p < 0.01). Of note, both sotalol (+ 26 ms, p < 0.01) and veratridine (+ 42 ms, p < 0.01) significantly increased spatial dispersion of repolarisation. Additional infusion of ivabradine (5 µM) did not change these parameters in sotalol-pretreated hearts but resulted in a further significant increase of QT-interval (+ 26 ms, p < 0.05) and APD (+ 49 ms, p < 0.05) in veratridine-treated hearts. Lowering of potassium concentration in bradycardic AV-blocked hearts resulted in the occurrence of early afterdepolarizations (EAD) or polymorphic ventricular tachycardias (VT) resembling torsade de pointes in 6 of 12 sotalol-treated hearts (56 episodes) and 6 of 12 veratridine-treated hearts (73 episodes). Additional infusion of ivabradine increased occurrence of polymorphic VT. Ivabradine treatment resulted in occurrence of EAD and polymorphic VT in 9 of 12 sotalol-treated hearts (212 episodes), and 8 of 12 veratridine-treated hearts (155 episodes). Treatment with ivabradine in experimental models of LQT2 and LQT3 increases proarrhythmia. A distinct interaction with potassium currents most likely represents a major underlying mechanism. These results imply that ivabradine should be employed with caution in the presence of QT-prolongation.

Atrial Fibrillation in Patients with Heart Failure: Current State and Future Directions

Heart failure affects nearly 26 million people worldwide. Patients with heart failure are frequently affected with atrial fibrillation, and the interrelation between these pathologies is complex. Atrial fibrillation shares the same risk factors as heart failure. Moreover, it is associated with a higher-risk baseline clinical status and higher mortality rates in patients with heart failure. The mechanisms by which atrial fibrillation occurs in a failing heart are incompletely understood, but animal studies suggest they differ from those that occur in a healthy heart. Data suggest that heart failure-induced atrial fibrosis and atrial ionic remodeling are the underlying abnormalities that facilitate atrial fibrillation. Therapeutic considerations for atrial fibrillation in patients with heart failure include risk factor modification and guideline-directed medical therapy, anticoagulation, rate control, and rhythm control. As recommended for atrial fibrillation in the non-failing heart, anticoagulation in patients with heart failure should be guided by a careful estimation of the risk of embolic events versus the risk of hemorrhagic episodes. The decision whether to target a rate-control or rhythm-control strategy is an evolving aspect of management. Currently, both approaches are good medical practice, but recent data suggest that rhythm control, particularly when achieved through catheter ablation, is associated with improved outcomes. A promising field of research is the application of neurohormonal modulation to prevent the creation of the "structural substrate" for atrial fibrillation in the failing heart.

Ivabradine Reduces Digitalis-induced Ventricular Arrhythmias

The I_(f) channel inhibitor ivabradine is recommended for treatment of heart failure but also affects potassium currents and thereby prolongs ventricular repolarization. The aim of this study was to examine the electrophysiological effects of ivabradine on digitalis-induced ventricular arrhythmias. Thirteen rabbit hearts were isolated and Langendorff-perfused. After obtaining baseline data, the digitalis glycoside ouabain was infused (0.2 μM). Monophasic action potentials and ECG showed a significant abbreviation of QT interval (-34 ms, p < 0.05) and action potential duration (APD₉₀ ; -27 ms, p < 0.05). The shortening of ventricular repolarization was accompanied by a reduction in effective refractory period (ERP; -27 ms, p < 0.05). Thereafter, hearts were additionally treated with ivabradine (5 μM). Of note, this did not exert significant effects on QT interval (-4 ms, p = ns) or APD₉₀ (-15 ms, p = ns) but resulted in an increase in ERP (+17 ms, p < 0.05). This led to a significant increase in post-repolarization refractoriness (PRR, +32 ms, p < 0.01) as compared with sole ouabain treatment. Under baseline conditions, ventricular fibrillation (VF) was inducible by a standardized pacing protocol including programmed stimulation and burst stimulation in four of 13 hearts (31%; 15 episodes). After application of 0.2 μM ouabain, eight of 13 hearts were inducible (62%, 49 episodes). Additional infusion of 5 μM ivabradine led to a significant suppression of VF. Only four episodes could be induced in two of 13 hearts (15%). In this study, ivabradine reduced digitalis-induced ventricular arrhythmias. Ivabradine did not affect ventricular repolarization in the presence of digitalis treatment but demonstrated potent anti-arrhythmic properties based on an increase in both ERP and PRR. The study further characterizes the beneficial electrophysiological profile of ivabradine.