Flecainide-induced Increase in QRS Duration and Proarrhythmia during Exercise

Orally Inhaled Flecainide for Conversion of Atrial Fibrillation to Sinus Rhythm: INSTANT Phase 2 Trial

BACKGROUND

INSTANT (INhalation of flecainide to convert recent-onset SympTomatic Atrial fibrillatioN to sinus rhyThm) was a multicenter, open-label, single-arm study of flecainide acetate oral inhalation solution (FlecIH) for acute conversion of recent-onset (≤48 hours) symptomatic atrial fibrillation (AF) to sinus rhythm.

OBJECTIVES

This study investigated the efficacy and safety in 98 patients receiving a single dose of FlecIH delivered via oral inhalation.

METHODS

Patients self-administered FlecIH over 8 minutes in a supervised medical setting using a breath-actuated nebulizer and were continuously monitored for 90 minutes using a 12-lead Holter.

RESULTS

Mean age was 60.5 years, mean body mass index was 27.0 kg/m2, and 34.7% of the patients were women. All patients had ≥1 AF-related symptoms at baseline, and 87.8% had AF symptoms for ≤24 hours. The conversion rate was 42.6% (95% CI: 33.0%-52.6%) with a median time to conversion of 14.6 minutes. The conversion rate was 46.9% (95% CI: 36.4%-57.7%) in a subpopulation that excluded predose flecainide exposure for the current AF episode. Median time to discharge among patients who converted was 2.5 hours, and only 2 patients had experienced AF recurrence by day 5. In the conversion-no group, 44 (81.5%) patients underwent electrical cardioversion by day 5. The most common adverse events were related to oral inhalation of flecainide (eg, cough, oropharyngeal irritation/pain), which were mostly of mild intensity and limited duration.

CONCLUSIONS

The risk-benefit of orally inhaled FlecIH for acute cardioversion of recent-onset AF appears favorable. FlecIH could provide a safe, effective, and convenient first-line therapeutic option. (INhalation of Flecainide to Convert Recent Onset SympTomatic Atrial Fibrillation to siNus rhyThm [INSTANT]; NCT03539302).

Cardiac sodium channel inhibition by lamotrigine: in vitro characterization and clinical implications

Lamotrigine, approved for use as an antiseizure medication as well as the treatment of bipolar disorder, inhibits sodium channels in the brain to reduce repetitive neuronal firing and pathological release of glutamate. The shared homology of sodium channels and lack of selectivity associated with channel blocking agents can cause slowing of cardiac conduction and increased proarrhythmic potential. The Vaughan‐Williams classification system differentiates sodium channel blockers using biophysical properties of binding. As such, Class Ib inhibitors, including mexiletine, do not slow cardiac conduction as measured by the electrocardiogram, at therapeutically relevant exposure. Our goal was to characterize the biophysical properties of Na_V1.5 block and to support the observed clinical safety of lamotrigine. We used HEK‐293 cells stably expressing the hNa_V1.5 channel and voltage clamp electrophysiology to quantify the potency (half‐maximal inhibitory concentration) against peak and late channel current, on‐/off‐rate binding kinetics, voltage‐dependence, and tonic block of the cardiac sodium channel by lamotrigine; and compared to clinically relevant Class Ia (quinidine), Ib (mexiletine), and Ic (flecainide) inhibitors. Lamotrigine blocked peak and late Na_V1.5 current at therapeutically relevant exposure, with rapid kinetics and biophysical properties similar to the class Ib inhibitor mexiletine. However, no clinically meaningful prolongation in QRS or PR interval was observed in healthy subjects in a new analysis of a previously reported thorough QT clinical trial (SCA104648). In conclusion, the weak Na_V1.5 block and rapid kinetics do not translate into clinically relevant conduction slowing at therapeutic exposure and support the clinical safety of lamotrigine in patients suffering from epilepsy and bipolar disorder.

Flecainide-Induced Left Bundle Branch Block

Flecainide is the first-line antiarrhythmic agent used in patients without structural heart disease. It is a class IC antiarrhythmic drug that inhibits inward sodium current through its dose-dependent blockade of voltage-gated calcium channels within the cardiac membrane. It has been shown to slow the conduction in the left bundle branch block. Unmonitored toxicity can cause ventricular dyssynchrony or fatal arrhythmia. We present a case in which flecainide use caused a new left bundle branch block (LBBB).

Atrial Fibrillation (AF) in Endurance Athletes: a Complicated Affair

PURPOSE OF REVIEW

A complex relationship exists between exercise and atrial fibrillation (AF). Moderate exercise reduces AF risk whereas intense strenuous exercise has been shown to increase AF burden. It remains unclear at which point exercise may become detrimental. Overall, endurance athletes remain at lower cardiovascular risk and experience fewer strokes. The questions that arise therefore are whether AF is an acceptable byproduct of strenuous exercise, whether athletes who experience AF should be told to reduce exercise volume and how should they be managed. This review aims to critically review the literature and advise on how best to manage athletes with AF.

RECENT FINDINGS

Emerging evidence suggests that female athletes may exhibit lower risk of AF, but data is limited in female endurance athletes. AF is more prevalent in endurance athletes, particularly men and those who competed at a young age. Data is lacking in females and ethnic minorities. Current evidence suggests that treatment options for AF in athletes are similar to those used in the general population; however, medical therapy may be poorly tolerated. Catheter ablation is effective and can allow return to full competition.

Initiation and outcomes with Class Ic antiarrhythmic drug therapy

BACKGROUND

Expert opinion recommends performing exercise testing with initiation of Class Ic antiarrhythmic medication.

OBJECTIVE

To evaluate the rate and reason for discontinuation of Ic agent within the first year of follow up, with particular attention to rate of proarrhythmia and the value of routine treadmill testing.

METHODS

This is a single center retrospective cohort study including consecutive patients with atrial arrhythmias who were initiated on a Class Ic agent from 2011 to 2016. Data was collated from chart review and pharmacy database.

RESULTS

The study population included 300 patients (55% male, mean age 61; mean ejection fraction, 56%) started on flecainide (n = 153; 51%) and propafenone (n = 147; 49%). Drug initiation was completed while hospitalized on telemetry and the staff electrophysiologists directed dosing. There was one proarrhythmic event during initiation (0.3%). The primary reason for not being discharged on Ic agent was due to detection of proarrhythmia (n = 15) or ischemia (n = 1) with treadmill testing (5.3%). Exercise testing was the single significant variable to affect the decision to discontinue Ic drug, p < 0.0001 (95% CI: 1.89-6.08%). During follow up, the primary reason for discontinuation of Ic agent was lack of efficacy, 32%.

CONCLUSIONS

With proper screening, initiation of Class Ic agent is associated with very low rate of proarrhythmia. Treadmill testing is of incremental value and should be completed in all patients after loading Class Ic antiarrhythmic.

Utility of Routine Exercise Testing to Detect Rate-Related QRS Widening in Patients Without Structural Heart Disease on Class Ic Antiarrhythmic Agents (Flecainide and Propafenone)

Class Ic antiarrhythmic agents are effective in the treatment of various atrial tachyarrhythmias. They are known to cause rate-related QRS widening in the presence of structural heart disease, which can lead to life-threatening arrhythmias. The role of routine exercise electrocardiography in patients without structural heart disease is unknown. All patients initiated on class Ic antiarrhythmic agents and who had exercise electrocardiography performed from June 2009 to June 2013 were included. Symptom-limited treadmill electrocardiography was performed to detect significant QRS widening at peak exercise (defined as an increase of >25% of baseline QRS). Fifty-six patients were included in the study. All patients were screened for structural heart disease before initiation of the medication. Significant QRS widening and atrial tachycardia occurred in a single patient, which terminated with cessation of exercise. This patient had a history of tachycardia-mediated cardiomyopathy with normalization of ejection fraction 3 years before being placed on flecainide. In conclusion, routine exercise testing to detect QRS widening is not warranted in patients with no structural heart disease.