Effects of intravenous amiodarone and ibutilide on action potential duration and atrial conduction kinetics in patients with persistent atrial fibrillation

Whole-cell patch-clamp recording and parameters

The patch-clamp technique represents an electrophysiology type of method. This is one of several insightful approaches with five major configurations, namely a loose patch, cell-attached (also known as on-cell), whole-cell, inside-out, and outside-out modes. The patch-clamp method is more advanced compared to classical electrophysiology since it elucidates single-channel activation in a tiny portion of the membrane in addition to action potential (AP), junction potential (JP), endplate potential (EP), electrical coupling between two adjacent cells via Gap junction hemi-channels, excitatory/inhibitory postsynaptic potentials, and resting membrane potential (RMP). In fact, a malfunction of only one channel or even one component will alter AP amplitude or duration in vitro. If parameters are inferred appropriately and recordings are performed properly, the patch-clamp trace readouts and results are robust. The main hallmarks of currents via voltage-dependent calcium (Cav), hyperpolarization-activated cyclic nucleotide gated non-selective cation (HCN), inwardly rectifying potassium (Kir), voltage-dependent potassium (Kv), and voltage-dependent sodium (Nav) channels are similar and tractable among cells even when they are derived from evolutionary distinct organs and species. However, the size of the membrane area, where the functional subunits reside, and current magnitudes vary among cells of the same type. Therefore, dividing current magnitudes by cell capacitance- current density enables the estimate of functional and active channels relative to recorded cytoplasmic membrane area. Since the patch-clamp recordings can be performed in both current- and voltage-clamp modes, the action potential or spike durations can be adequately elucidated. Sometimes, optical methods are preferred to patch-clamp electrophysiology, but the obtained signals and traces are not robust. Finally, not only an alternans of AP durations, but also that of 'action potential shape' is observed with electrophysiology.

Effects of Antiarrhythmic Drugs on hERG Gating in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes From a Patient With Short QT Syndrome Type 1

Aims: The short QT syndrome type 1 (SQT1) is linked to hERG channel mutations (e.g., N588K). Drug effects on hERG channel gating kinetics in SQT1-cells have not been investigated. Methods: This study used hiPSC-CMs of a healthy donor and a SQT1-patient carrying the N588K mutation and patch clamp to examine the drug effects on hERG channel gating kinetics. Results: Ajmaline, amiodarone, ivabradine, flecainide, quinidine, mexiletine and ranolazine inhibited the hERG channel current (I_Kr) less strongly in hiPSC-CMs from the SQTS1-patient (SQT1-hiPSC-CMs) comparing with cells from the healthy donor (donor-hiPSC-CMs). Quinidine and mexiletine reduced, but ajmaline, amiodarone, ivabradine and ranolazine increased the time to peak of I_Kr similarly in SQT1-hiPSC-CMs and donor-hiPSC-CMs. Although regarding the shift of activation and inactivation curves, tested drugs showed differential effects in donor- and SQT1-hiPSC-CMs, quinidine, ajmaline, ivabradine and mexiletine but not amiodarone, flecainide and ranolazine reduced the window current in SQT1-hiPSC-CMs. Quinidine, ajmaline, ivabradine and mexiletine differentially changed the time constant of recovery from inactivation, but all of them increased the time constant of deactivation in SQT1-hiPSC-CMs. Conclusion: The window current-reducing and deactivation-slowing effects may be important for the antiarrhythmic effect of ajmaline, ivabradine, quinidine and mexiletine in SQT1-cells. This information may be helpful for selecting drugs for treating SQT1-patients with hERG channel mutation.

Intraprocedural Conversion Efficacy of Intravenous Nifekalant Administration for Persistent Atrial Fibrillation after Pulmonary Vein Isolation

The aim of this study was to prospectively assess the efficacy, safety, and predictive effect of intravenous nifekalant administration for persistent atrial fibrillation (PerAF) after pulmonary vein isolation (PVI) with second-generation cryoballoon ablation (CBA) on 1-year atrial tachyarrhythmia (ATa) -free survival by examining the pharmacological conversion rate.One hundred and two drug-refractory, consecutive PerAF patients undergoing PVI were enrolled in this prospective observational study. After PVI, nifekalant (50 mg) was given followed by 30 minutes of observation and no further intervention. PerAF was successfully converted to sinus rhythm (SR) in 60 patients (58.8%) after a median time of 7.75 (4.13-12) minutes (group N). In the remaining 42 patients (41.2%) (group C), PerAF was successfully converted to SR by external electrical cardioversion. Nonsustained ventricular tachycardia occurred in 1 patient in group N. The left atrial volume (LAV) in group C was larger than that in group N (128.2 ± 28.2 versus 111.8 ± 24.5 mL, P = 0.002). Phrenic nerve injury occurred in 4 of 102 patients (3.9%). No other complications occurred during the procedure or within the 1-year follow-up period. At the 1-year follow-up, after a 3-month blanking period (BP), ATa-free survival during 1-year follow-up in group C was significantly lower than that in group N (50.0% versus 71.7%, P = 0.026), and the overall ATa-free survival rate was 62.7%. Two patients in group C and 4 patients in group N underwent a second procedure with radiofrequency catheter ablation. Multivariate Cox regression analysis demonstrated that unsuccessful conversion to SR (P = 0.025), ATa relapse during the BP (P = 0.000), and larger LAV (P = 0.016) were independent predictors of ATa recurrence at the 1-year follow-up.In conclusion, at the 1-year follow-up, the ATa-free survival rate after PVI with CBA for PerAF patients was 62.7%, and successful conversion to SR with nifekalant could serve as a clinical predictor of reduced ATa recurrence.

Prevailing Effects of Ibutilide on Fast Delayed Rectifier K+ Channel

Effects of ibutilide, a class III antiarrhythmic drug, on delayed rectifier potassium currents (I_K) in freshly isolated guinea pig ventricular myocytes were studied. Experiments were performed using the whole-cell configuration of patch-clamp technique under blockade of L-type calcium currents (Cav1). Ibutilide at concentrations ranging between 10 nM and 100 µM inhibited I_Kr in dose-dependent manner with a half maximal effective concentration of 2.03 ± 0.74 µM (n = 5-10). The amplitude of tail currents activated by prepulse to + 20 mV was decreased from 253 ± 52 to 130 ± 25 pA (n = 8, p < 0.01) in the presence of 1 µM ibutilide. The envelope test revealed time-dependent changes in ratio of I_K-tail/ΔI_K during 0.2-2 s pulse durations in the absence of drug. With ibutilide, regardless of pulse duration, a relatively constant ratio was estimated, indicative of predominant involvement of I_Kr component. The slow I_Ks persisted to greater extent even at 100 μM ibutilide revealing a distinguishable selectivity toward the I_Kr component.

Clinical Utility of Intravenous Nifekalant Injection during Radiofrequency catheter Ablation for Persistent Atrial Fibrillation

Background

Radiofrequency catheter ablation (RFCA) for persistent atrial fibrillation (AF) is still challenging even in RFCA-era for AF. The aim of this study was to assess the clinical utility of nifekalant, a pure potassium channel blocker,during RFCA for persistent AF.

Methods and results

We retrospectively enrolled 157 consecutive persistentAF patientsundergoing first RFCA procedure withcomplex fractionated atrial electrogram (CFAE)ablation after pulmonary veins isolation and compared outcomes between patientswith (NFK group: N=79) and without (No-NFK group: N=78)additional CFAE ablation using intravenous nifekalant (0.3mg/kg). Primary endpoint was 24-month atrial arrhythmia-free survival post ablation.The prevalence of AF terminationwas significantly higher in NFK group than No-NFK group (64.6% versus 7.7%, P<0.001). Arrhythmia-free survival, however, was not significantly different between 2 groups (61.5% versus 54.1%, P=0.63).There was no significant difference between 2 groups in the prevalence of recurrent atrial tachycardia(25.0% versus 23.5%, P=0.89). Arrhythmia-free survivalin patients with AF termination during procedure was significantly higher thanthose without (73.0% versus 41.0%, P=0.002; adjusted hazard ratio 0.48, 95% confidence interval 0.17-0.84, P=0.02) amongNFK group,but not amongNo-NFK group (66.7% versus 53.2%, P=0.53).

Conclusions

Intravenous nifekalant injection during additional CFAE ablation did not improve sinus maintenancerate after RFCA procedure for AF, but AF termination by nifekalant injection could be a clinical predictor of better success rates after procedure.

Pretreatment with intravenous amiodarone improves the efficacy of ibutilide treatment on cardioversion rate and maintenance time of sinus rhythm in patients with persistent atrial fibrillation

The aim of the present study was to assess the efficacy and safety of the pharmacological conversion of persistent atrial fibrillation (AF) using amiodarone or/and ibutilide. Seventy-nine consecutive patients (48 males and 31 females; mean age, 64.6±11.2 years; range, 40-80 years) with non-valvular chronic AF lasting >7 days (range, 7-97 days) that were admitted to hospital for elective pharmacological cardioversion were randomly assigned to receive treatment with intravenous ibutilide (1 mg plus an additional 1 mg if required; n=39) or intravenous amiodarone (300 mg) plus intravenous ibutilide (1 mg; n=40). Success rates of cardioversion were 51.3% (20/39 patients) for ibutilide alone and 71.8% (28/39 patients) for amiodarone + ibutilide (P<0.05). A comparable increase in the QTc interval was observed in the two groups. It was observed that the co-administration of amiodarone and ibutilide was safer than ibutilide alone with regard to the risk of ventricular arrhythmia. Forty-eight patients of successful cardioversion were personally contacted for follow-up. The result indicated that the sinus rhythm maintenance time of the amiodarone + ibutilide group (4.36±2.44 months) was significantly higher than that of the ibutilide group (2.34±1.75 months; P<0.01). In conclusion, pretreatment with intravenous amiodarone + ibutilide for pharmacological cardioversion of persistent AF is considered to be more effective and safer than treatment with ibutilide alone.

An Experience of Landiolol Use for an Advanced Heart Failure Patient With Severe Hypotension

Tachyarrhythmias such as atrial fibrillation (AF) or atrial flutter (AFL) sometimes invoke life-threatening collapse of hemodynamics in patients with severe heart failure. Recently, landiolol, an ultra-short acting β1-selective antagonist, has been reported to be safe and useful for the treatment of supraventricular tachyarrhythmias with reduced left ventricular function. Here we report a case of advanced heart failure with severe hypotension who was treated successfully by landiolol for rapid AF. The patient was a 20-year old male with dilated cardiomyopathy. He presented with low output syndrome in spite of optimal medical therapy and was referred to our department to consider ventricular assist device implantation and heart transplantation. Soon after admission, he developed rapid atrial fibrillation at 180 beats per minute (bpm) followed by severe hypotension and liver enzyme elevation. Low dose landiolol at 2 μg/kg/minute was started because digoxin was not effective. After landiolol administration, his heart rate decreased to 110 bpm, and finally returned to sinus rhythm without hemodynamic deterioration. Intra-aortic balloon pumping was inserted soon after sinus recovery and he was discharged successfully with an implantable left ventricular assist device.

Early-Morning Type Ventricular Fibrillation With J Wave

A 67-year-old man who had cardiopulmonary arrest (CPA) at home was admitted to our institution. His spontaneous circulation was restored by bystander cardiopulmonary resuscitation (CPR) performed by his wife and an automated external defibrillator (AED). J waves were observed in the inferior leads of an electrocardiogram. We performed an implantable cardioverter defibrillator (ICD) implantation. After the ICD implantation, appropriate shocks due to ventricular fibrillation (VF) were observed on interrogation of the ICD at a frequency of twice a month. Most VF events occurred in the early morning between 1:00 to 6:00, and ventricular premature contractions (VPCs) were detected just before the occurrence of VF. Since the VF events always occurred in the early morning, we started long-acting disopyramide (150 mg/day, before bedtime), which has a muscarinic receptor blocking action. As a result, he has not received any appropriate ICD shocks for more than two years.