Bepridil inhibits sub-acute phase of atrial electrical remodeling in canine rapid atrial stimulation model

Responsiveness to bepridil predicts atrial substrate in patients with persistent atrial fibrillation

BACKGROUND

The low voltage zone (LVZ) detected with three-dimensional electroanatomical mapping is a surrogate marker of atrial scar in patients with persistent atrial fibrillation (PeAF) and is associated with poor clinical outcomes after catheter ablation. However, fewer studies have reported the relationship between responsiveness to antiarrhythmic drugs and the LVZ.

METHODS

We retrospectively analyzed 76 patients who underwent catheter ablation for PeAF at our center. Rhythm control with bepridil was initiated before ablation in all patients, and electrical cardioversion was performed in cases of failure to restore sinus rhythm with bepridil alone. Patients with successful sinus restoration with bepridil alone (≤200 mg/d) were defined as "responders", while those who required electrical cardioversion as well were defined as "non-responders". We compared the LVZ ratio (ratio of the LVZ surface area to the left atrium surface area on three-dimensional electroanatomical mapping) and the recurrence-free rate after ablation between the two groups.

RESULTS

Of the 76 patients, 48 (63.2%) were responders to bepridil. The median LVZ ratio was significantly lower in the responder group than in the nonresponder group (7.5% vs 14.0%, P = .009). Multivariate analysis revealed that response to bepridil was an independent predictor of normal voltage (P = .02, odds ratio = 0.20, 95% confidence interval = 0.04-0.76). The recurrence-free rate at 1 year after catheter ablation was significantly higher in the responder group than in the nonresponder group (87.1% vs 62.3%, P = .03).

CONCLUSIONS

Response to bepridil is a marker of normal voltage in electroanatomical mapping and is significantly associated with better clinical outcomes after catheter ablation.

Aliskiren suppresses atrial electrical and structural remodeling in a canine model of atrial fibrillation

Aliskiren, a direct renin inhibitor is expected to achieve sufficient suppression of renin-angiotensin system. We evaluated the effect of aliskiren on the electrical and structural remodeling in a canine atrial fibrillation (AF) model. Twenty-eight dogs were divided into three groups: (1) pacing control group (n = 12), with continuous atrial rapid pacing for 3 or 6 weeks, (2) pacing + aliskiren group (n = 12), with oral aliskiren (30 mg/kg/day), and (3) sham group (n = 4), no pacing nor drug administration. Electrophysiological properties and AF inducibility were evaluated every week. After the protocol, the left atrial tissue was sampled for the further histological and mRNA analysis. The electrical remodeling, AF inducibility, the left atrial enlargement and interstitial fibrosis were observed in pacing control group and were more prominent in the 6-week protocol (vs. 3 week, p < 0.05). The mRNA expressions of matricellular proteins exhibited upregulation in 3-week pacing control, but these upregulations became insignificant in 6 weeks. In contrast, collagen type 3 exhibited significant upregulation in 6 week but not in 3-week protocol. These changes were suppressed in the pacing + aliskiren group. Aliskiren suppressed the atrial remodeling in a canine AF model. This effect was accompanied by the suppression of tissue fibrosis.

Short- and long-term inhibition of cardiac inward-rectifier potassium channel current by an antiarrhythmic drug bepridil

Bepridil is an effective antiarrhythmic drug on supraventricular and ventricular arrhythmias, and inhibitor of calmodulin. Recent investigations have been elucidating that bepridil exerts antiarrhythmic effects through its acute and chronic application for patients. The aim of this study was to identify the efficacy and the potential mechanism of bepridil on the inward-rectifier potassium channel in neonatal rat cardiomyocytes in acute- and long-term conditions. Bepridil inhibited inward-rectifier potassium current (I K1) as a short-term effect with IC50 of 17 μM. Bepridil also reduced I K1 of neonatal cardiomyocytes when applied for 24 h in the culture medium with IC50 of 2.7 μM. Both a calmodulin inhibitor (W-7) and an inhibitor of calmodulin-kinase II (KN93) reduced I K1 when applied for 24 h as a long-term effect in the same fashion, suggesting that the long-term application of bepridil inhibits I K1 more potently than that of the short-term application through the inhibition of calmodulin kinase II pathway in cardiomyocytes.

Differential gene expression during atrial structural remodeling in human left and right atrial appendages in atrial fibrillation

Extracellular matrix (ECM) remodeling increases the vulnerability to atrial fibrillation (AF). Some gene expressions are crucial for the metabolism of ECM. The left atrium plays an important role in maintaining AF. However, most studies investigated only the right atrial tissue. We therefore chose human tissue samples from both the left and right atrial to detect the different gene expressions during structural remodeling in AF. The atrial appendages tissue samples from 24 patients with chronic AF and 12 patients with sinus rhythm were obtained when they were undergoing mitral/aortic valve replacement operation. The mRNA levels of matrix metalloproteinases-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1), disintegrin, metalloproteases-15, and integrins β1 were determined by reverse transcription-polymerase chain reaction (RT-PCR). In AF group, the level of MMP-9 in left atrial appendage (LAA) was increased (P< 0.001), while integrin β1 level was decreased (P< 0.05) compared with those expressed in right atrial appendage (RAA) tissue. The levels of disintegrin, metalloproteinases-15, and TIMP-1 genes in the LAA and RAA had no significant differences. The results demonstrated that the gene expressions in the LAA and RAA are different during AF, which implied that the mechanism of atrial structural remodeling in AF is due to multiple sources and is complicated.

Combined effects of up- and downstream therapies on atrial fibrillation in a canine rapid stimulation model

BACKGROUND

Recent reports suggest angiotensin receptor blockers (ARBs) and some antiarrhythmic agents affect atrial remodeling in atrial fibrillation (AF). We evaluated the effect of combination therapy with olmesartan (Olm) and bepridil (Bep) in a canine model of AF.

METHODS AND RESULTS

An atrial stimulation device was implanted in 10 dogs undergoing 6-week pacing at 400 bpm. They were divided into Olm (2 mg/kg/day) (n=5) and Olm+Bep (Olm, 2 mg/kg/day; Bep, 10 mg/kg/day) groups (n=5). Atrial effective refractory period (AERP), conduction velocity (CV), and AF inducibility were evaluated weekly, and hemodynamics, atrial histology, and mRNA expression and protein expression of ion-channel and gap junction-related molecules at 6 weeks. Data were compared between groups and with non-pacing control and pacing-control groups from our previous report. The pacing-control group exhibited shortened AERP, decreased CV, increased AF inducibility and tissue fibrosis, and down-regulated L-type Ca(2+) channel (LCC), SCN5A, Kv4.3 and connexin43 (Cx43). By comparison, the Olm group exhibited suppression of the decrease in CV and of the increase in AF inducibility, but no change in AERP shortening. The Olm+Bep group exhibited suppression of AERP shortening as well as the greatest decrease in AF inducibility. Histologically, tissue fibrosis was suppressed in Olm and Olm+Bep groups. Down-regulation of Cx43 was partly suppressed in the Olm group while that of LCC, SCN5A, and Cx43 was suppressed in the Olm+Bep group.

CONCLUSION

Olm and Bep in combination suppressed AF inducibility more strongly than Olm alone, and may be more useful in the suppression of AF.

Anti-apoptotic effects of a calpain inhibitor on cardiomyocytes in a canine rapid atrial fibrillation model

PURPOSE

This study was designed to evaluate the effects of a calpain inhibitor on cardiac muscle apoptosis in rapid pacing canine atrial fibrillation (AF) models.

METHODS

Twenty one dogs were divided into three groups: a sham operation group, a control AF group and a calpain inhibitor group. Sustained AF was induced by rapid right atrium pacing at 600 beats per minute. N-Acetyl-Leu-Leu-Met (1.0 mg/kg/day) was administered in the calpain inhibitor group for three weeks. The activity of calpain I and cardiomyocyte apoptosis were measured by fluorometry and TUNEL assay, respectively. Protein expression of caspase-3 was detected by Western blot. The localizations of caspase-3, caspase-8, bcl-2 and ARC were assessed by immunohistochemistry.

RESULTS

In comparison to the sham operation group, the activity of calpain I was significantly increased in the control AF group (2.3 fold, p < 0.001), and decreased in the calpain inhibitor group (1.1 fold, p < 0.005). The calpain activity correlated with the apoptosis index (r = 0.9, p < 0.05). The apoptosis index was 1.0 +/- 0.2%, 11.8 +/- 6.8% and 3.5 +/- 2.1% in the sham operation group, control AF group and calpain inhibitor group, respectively. In the sham operation group, control AF group and calpain inhibitor group, the expressions of caspase-3 (13.0 +/- 1.9%, 52.8 +/- 4.3% and 33.6 +/- 3.7%), caspase-8 (40.1 +/- 5.3%, 92.6 +/- 6.5% and 55.3 +/- 5.9%), bcl-2 (65.8 +/- 6.1%, 52.0 +/- 5.7% and 69.9 +/- 5.3%) and ARC (70.2 +/- 8.6%, 68.8 +/- 7.3% and 81.5 +/- 8.8%) were calculated as immunohistochemical indexes, respectively.

CONCLUSIONS

The calpain inhibitor N-Acetyl-Leu-Leu-Met attenuated apoptosis through a complicated network of apoptosis-related proteins, which may result in improvement of structural remodeling in atrial fibrillation.

Predicting the efficacy of antiarrhythmic agents for interrupting persistent atrial fibrillation according to spectral analysis of the fibrillation waves on the surface ECG

BACKGROUND

Spectral analysis of the fibrillation waves was performed in patients with persistent atrial fibrillation (PAF) to clarify the usefulness of this method of predicting the efficacy of antiarrhythmic agents.

METHODS AND RESULTS

The 59 patients with PAF were randomly assigned to pilsicainide (150 mg/day) or bepridil (200 mg/day) therapy for 4 weeks under optimal anticoagulation therapy. When the first therapy did not interrupt PAF, the drugs were changed in a cross-over manner. The fibrillation cycle length (FCL) was calculated using spectral analysis of the fibrillation waves on the body-surface ECG every 2 weeks. Pilsicainide and bepridil were effective in 19 and 20 patients, respectively. The FCL at the basic state was longest in the pilsicainide-effective group, moderate in the bepridil-effective group and shortest in the failure group (P<0.05). The change in FCL with drug administration (DeltaFCL) was larger in the effective than in the ineffective cases (P<0.01). Successful interruption of the atrial fibrillation (AF) with pilsicainide could be expected for patients with a FCL >148 ms (sensitivity =0.917, specificity =0.612, P=0.007) and DeltaFCL >41 ms (sensitivity =0.875, specificity =0.833, P=0.001).

CONCLUSIONS

The FCL reflects the electrophysiological properties of the AF substrate and is considered useful for predicting the efficacy of antiarrhythmic agents.

Development of newer calcium channel antagonists: therapeutic potential of efonidipine in preventing electrical remodelling during atrial fibrillation

Calcium channel antagonists are most frequently prescribed for the treatment of hypertension and the majority specifically inhibit the L-type Ca2+ channel. In order to prevent reflex sympathetic over activity caused by L-type calcium channel antagonists (calcium channel blockers [CCBs]), increasing attention has focused on the blockade of the T-type Ca2+ channel. The T-type Ca2+ channel is found in the kidney and can also appear in the ventricle of the heart when in failure. Therefore, the T-type Ca2+ channel is a possible new target for the treatment of nephropathy and heart failure. In clinical trials, the efficacy and safety of T-type CCBs in hypertension and chronic renal disease have been reported. It is well known that the T-type Ca2+ channel is present in the adult atrium and plays a role in the cardiac pacemaker, but recent experimental studies suggest that this current also promotes electrical remodelling of the atrium. Using efonidipine, a dual L- and T-type CCB, it has been demonstrated that atrial electrical remodelling can be diminished in dogs. Furthermore, the T-type Ca2+ channel has recently been found in the pulmonary veins, contributing to the pulmonary vein pacemaker activity and triggered activity. A variety of drugs having T-type CCB effects have been shown to be effective in the management of atrial fibrillation, suggesting that this channel may be a novel therapeutic target.

Probucol attenuates atrial structural remodeling in prolonged pacing-induced atrial fibrillation in dogs

AIMS

Oxidative stress has recently been implicated in atrial fibrillation (AF); however, the mechanisms remain unclear. Herein, we hypothesize that probucol can attenuate atrial structure remodeling.

METHODS

Twenty dogs were randomly divided into sham-operated, control, and probucol-treated groups. We identified apoptosis and histopathological changes in the atria. Oxidative stress was measured by lipid peroxidation and echocardiographic examinations were performed.

RESULTS

Atrial apoptosis indexes were dramatically decreased in the probucol-treated group compared to the control group. Relative to the control group, the percentage of myolysis was dramatically decreased in the probucol-treated group (p < 0.01). There was less lipid peroxidation in the probucol-treated group than the control group. Atrial function was dramatically elevated in the probucol-treated group.

CONCLUSIONS

The results of this study indicate that the antioxidant probucol suppresses atrial structural remodeling and may act as a new therapy for AF.

Inhomogenic effect of bepridil on atrial electrical remodeling in a canine rapid atrial stimulation model

BACKGROUND

The antiarrhythmic or reverse remodeling effects of bepridil, a multi-ion channel blocker, have been recently reported, but inhomogeneity of the electrical remodeling and effects of bepridil have been observed in previous reports. In this study, the effect of long-term administration of bepridil on atrial electrical remodeling was evaluated in a comparison of the right and left atrium (RA and LA) in a canine rapid atrial stimulation model.

METHODS AND RESULTS

In 10 beagle dogs, rapid atrial pacing (400 beats/min) was delivered for 6 weeks and the atrial effective refractory period (AERP), conduction velocity (CV) and inducibility of atrial fibrillation (AF) were evaluated every week. In 5 of the pacing dogs, bepridil (10 mg . kg(-1) . day(-1)) was administered orally, starting 2 weeks after the initiation of the rapid pacing. At the end of the protocol, the hemodynamic parameters and extent of tissue fibrosis were evaluated and the mRNA of SCN5A, Kv4.3, the L-type Ca2+ channel (LCC) and connexin (Cx) 40, 43, and 45 in both atria were examined by quantitative real-time reverse transcriptase-polymerase chain reaction. In the pacing control group, AERP shortening, decreased CV, increased AF inducibility and downregulation of the expression of SCN5A and LCC were observed. In the bepridil group, the AERP exhibited a relatively quick recovery after bepridil was started in the first week and continued to recover gradually until the end of the protocol, but that recovery was smaller in the LA than in the RA. The CV was not affected by bepridil administration. AF inducibility was well suppressed in the RA in the bepridil group, but the induction of short-duration AF could not be suppressed in the LA. The mRNA downregulation of the LCC and SCN5A was negated by bepridil administration in the RA; but not in the LA; however, the data showed similar tendencies. There were no significant differences in the hemodynamic parameters or tissue fibrosis and the mRNA expression of Kv4.3, Cx40, 43, and 45 between the pacing control and bepridil groups.

CONCLUSION

Bepridil exhibited an anti-electrical remodeling effect in this study as previously reported, but the effect was inhomogeneous between the RA and LA, with the LA appearing to be more resistant to the effect of bepridil.

Bepridil Reverses Atrial Electrical Remodeling and L-Type Calcium Channel Downregulation in a Canine Model of Persistent Atrial Tachycardia

INTRODUCTION

This study tested whether bepridil, a multichannel blocker, would reverse electrical remodeling induced by persistent atrial tachycardia.

METHODS AND RESULTS

Fourteen dogs were subjected to rapid atrial pacing at 400 bpm for 6 weeks after atrioventricular block was created to control the ventricular rate. During the study period, seven dogs were given placebo for 6 weeks (Control group), and seven were given placebo for 3 weeks, followed by 3 weeks of bepridil (10 mg/kg/day, Bepridil group). The atrial effective refractory period (ERP) and the inducibility and duration of atrial fibrillation (AF) were determined on a weekly basis. After 6 weeks, expression of L-type calcium channel alpha1C messenger ribonucleic acid (mRNA) was quantified by real-time reverse transcription-polymerase chain reaction. In the Control group, ERP was shortened and the inducibility and duration of AF increased through the 6-week period. In the Bepridil group, the same changes occurred during the first 3 weeks, but were gradually reversed with bepridil. After 6 weeks, ERP was longer, AF inducibility was lower, and AF duration was shorter in Bepridil group than in the Control group. Expression of alpha1C mRNA was decreased by 64% in the Control group (P < 0.05 vs sham), but in the Bepridil group, it was not different compared with the sham dogs. As a whole group of dogs, ERP was positively correlated with alpha1C mRNA expression.

CONCLUSION

Bepridil reverses the electrophysiological consequences of atrial remodeling to some extent and L-type calcium channel downregulation in a canine model of atrial tachycardia.

Pharmacological Cardioversion of Long-Lasting Atrial Fibrillation

Pharmacological therapy for atrial fibrillation (AF) is difficult because AF induces atrial remodeling. Randomized prospective studies using amiodarone could not show the superiority of rhythm control strategy to rate control strategy for treatment of AF. Bepridil is a multichannel blocker like amiodarone and expected to be effective for termination of AF without exacerbation of extracardiac adverse effects. Efficacy and safety of bepridil in pharmacological cardioversion of long-lasting AF (≥3 months) was assessed. To avoid the risk of excessive QT prolongation, bepridil dosage was limited to ≤200 mg/day and aprindine (class Ib) was added if necessary. Bepridil alone or in combination with aprindine restored sinus rhythm in 69% of patients. No adverse effects necessitating drug termination occurred. The average time to conversion after starting bepridil was 30 days and cardioversion was associated with significant increase in fibrillation cycle length. After cardioversion, atrial contraction recovered faster within 1 week and sinus rhythm was maintained better than conventional electrical cardioversion. The history of drug-resistant AF did not affect efficacy of bepridil. These observations suggest that pharmacological cardioversion of long-lasting AF could become a new therapeutic option. Although the precise mechanism of cardioversion by bepridil is not clear, reversal of the remodeled atria may play an important role.

Efficacy and Safety of the Additional Bepridil Treatment in Patients With Atrial Fibrillation Refractory to Class I Antiarrhythmic Drugs

BACKGROUND

Bepridil has multiple ion-channel blocking effects and is expected to be useful for managing atrial fibrillation (AF). The purpose of this study was to clarify the efficacy and safety of additional treatment with bepridil in patients with AF who had been treated with class I antiarrhythmic drugs (AADs).

METHODS AND RESULTS

Bepridil (50-200 mg/day) was given to 76 patients with either paroxysmal (n=49) or persistent AF (n=27). All patients had been treated with class I AADs (1.9+/-0.9 drugs/patient) that failed to control the AF. With the addition of bepridil, the frequency of symptomatic AF episodes decreased to less than 10% in 38 (78%) patients with paroxysmal AF, and sinus rhythm was restored within 3 months and maintained during the follow-up in 20 (74%) patients with persistent AF. Efficacy was usually obtained with a small to moderate dose (50-150 mg/day) of bepridil. During a mean follow-up period of 27+/-22 months, no potential complications occurred in any of the patients.

CONCLUSIONS

The addition of bepridil to class I AADs is effective and safe for AF, but careful observation using periodic ECG recordings is essential for avoiding torsades de pointes caused by QT prolongation.

Arrhythmogenic Difference Between the Left and Right Atria During Rapid Atrial Activation in a Canine Model of Atrial Fibrillation

BACKGROUND

Continuous rapid atrial stimulation causes atrial remodeling, but little is known about the difference in the arrhythmogenicity of the left (LA) and right atria (RA).

METHODS AND RESULTS

In 14 beagle dogs, continuous rapid pacing (400 beats/min) was delivered from the right (n=7) or left (n=7) atrial appendage (RAA or LAA) for 2 weeks. The atrial effective refractory period (ERP), ERP dispersion, and inducibility of atrial fibrillation (AF) were evaluated along the time course from 4 atrial sites: (1) RAA, (2) area close to the inferior vena cava (IVC), (3) Bachmann's bundle (BB) and (4) LA. The ERP exhibited progressive shortening at all sites, but the degree of shortening differed among them. In the RA stimulation group, ERP shortening was more prominent in the RAA and LA than in the IVC or BB. In contrast, in the LA stimulation group, ERP shortening was more prominent in the LA than in the other sites. As a result, ERP dispersion was larger in the LA stimulation group than in the RA stimulation group and the AF inducibility was higher in the LA stimulation group than in the RA stimulation group, especially at the LA site (p<0.05).

CONCLUSION

LAA stimulation was more arrhythmogenic than RAA stimulation in this model. This result may partly explain the importance of premature contractions occurring from the pulmonary veins in clinical cases of AF.