Progression of ventricular remodeling and arrhythmia in the primary hyperoxidative state of glutathione-depleted rats

BACKGROUND

Although oxidative stress is considered to promote arrhythmogenic substrates in diseased model animals, it is difficult to evaluate its primary role. In this study, we evaluated the promotion of arrhythmogenic substrates in the primary hyperoxidative state.

METHODS AND RESULTS

Sprague-Dawley rats were treated with L-buthionine-sulfoximine (BSO, 30 mmol · L(-1) · day(-1)) for 14 days. On day 7 or 14, the serum levels of derivatives of reactive oxygen metabolites (d-ROM) were measured, and immune staining of 8-hydroxy-2'-deoxyguanosine (8O HdG) was performed to assess oxidative stress. The ventricular effective refractory period (ERP), monophasic action potential duration (MAPD), and the inducibility of ventricular arrhythmia were also evaluated. BSO rats exhibited higher serum d-ROM and clearer 8OHdG staining than the controls. The inducibility of ventricular arrhythmia was higher in the BSO rats than in the controls. The ERP was shorter in the BSO rats than the control (day 14, 32 ± 1 vs. 36 ± 1 ms, P<0.05), whereas the MAPD(90) was longer in the BSO rats (day 14, 76 ± 5 vs. 55 ± 4 ms, P<0.05). The mRNA levels of Kv4.2, erg, and SERCA2a were downregulated in the BSO rats (P < 0.05), and Western blot analysis exhibited the downregulation of erg and SERCA2 expression in the BSO rats (P < 0.05).

CONCLUSIONS

Systemic oxidative stress might be one of the primary factors promoting cardiac electrophysiological remodeling and increasing the inducibility of arrhythmia independently of major organ disorders.

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.

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.

Neutral endopeptidase inhibitor suppresses the early phase of atrial electrical remodeling in a canine rapid atrial pacing model

INTRODUCTION

We examined the acute effects of neutral endopeptidase inhibitor on the hemodynamics and electrical properties of dogs subjected to rapid atrial pacing.

METHODS

Ten beagle dogs were used and divided into two groups with and without candoxatril, a neutral endopeptidase inhibitor preadministration. Before and after the 6 hours rapid atrial pacing from the right atrial appendage, the hemodynamics, atrial effective refractory period, and monophasic action potential duration of the right atrial appendage were measured and blood samples were collected. Atrial tissue was also excised after the experiment.

RESULTS

Candoxatril significantly increased plasma ANP levels (Control: 88.4 +/- 50.25 vs. Candoxatril: 197.1 +/- 32.09 pg/ml, p = 0.004) and prevented reductions in atrial effective refractory period and monophasic action potential duration. We further demonstrated that the treated animals exhibited significantly higher levels of atrial tissue cyclic GMP (Control: 28.1 +/- 1.60 fmol/mg vs. Candoxatril: 44.5 +/- 12.28 fmol/mg, p = 0.034) as well as that of plasma cyclic GMP (Control: 32 +/- 5.5 vs. Candoxatril: 42 +/- 7.1 pg/ml, p = 0.028).

CONCLUSION

Candoxatril suppressed the shortening of atrial effective refractory period and monophasic action potential duration in the rapid atrial pacing model. As plasma ANP and the atrial tissue levels of cyclic GMP were higher in the Candoxatril group than the control, this effect was considered to appear through the reduction of calcium overload caused by ANP and cyclic GMP.

Atrial natriuretic peptide (ANP) suppresses acute atrial electrical remodeling in the canine rapid atrial stimulation model

OBJECTIVES

Atrial electrical remodeling is considered to play an important role in the appearance of atrial fibrillation. The effect of atrial natriuretic peptide (ANP) on atrial electrical remodeling was evaluated in a canine atrial stimulation model.

METHODS

In 15 beagle dogs, electrodes for pacing and recording were fixed on the atrial surface. In 10/15 dogs, rapid atrial stimulation (400 bpm) was performed for 7 h at the right atrial appendage (RAA) and the remaining 5 were used as the sham without rapid pacing. In 5/10 dogs with rapid pacing, human atrial natriuretic peptide (ANP) was infused (1.0 microg/kg/min). The effective refractory period (ERP) and the monophasic action potential duration (MAP) were evaluated at 0, 3, and 7 h after rapid pacing. The expression levels of mRNAs of ion channels or transporters were evaluated from the atrial samples of sham and after a 7 hour pacing.

RESULTS

In the control group with rapid pacing (n=5), the atrial ERP and MAP duration were shortened at all atrial sites, e.g., ERP from 148+/-14 ms to 109+/-8 ms at RAA, P=0.006. In contrast in the ANP group, neither the ERP nor MAP duration showed a significant shortening and the effect of ANP on hemodynamic parameter was relatively small. Expression levels of the mRNA were not significantly different between the control and ANP groups.

CONCLUSIONS

Administration of ANP prevented the shortening of the ERP and MAP duration in the rapid atrial stimulation model. The effect of ANP on atrial electrical remodeling was considered to be due to its direct action on the myocardium.

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.

Beta2-Adrenergic agonists suppress rat autoimmune myocarditis: potential role of beta2-adrenergic stimulants as new therapeutic agents for myocarditis

BACKGROUND

The therapeutic potential of beta2-adrenergic receptor (AR) agonists in the treatment of autoimmune diseases has been reported. However, the role of these drugs in the myocardial structure-induced autoimmune process, which is thought to play a crucial role in the progression of myocarditis to subsequent complications, has not been elucidated.

METHODS AND RESULTS

Experimental autoimmune myocarditis (EAM) was induced in rats by immunization with cardiac myosin. On daily administration from day 0 after immunization, the beta2-selective AR agonists formoterol or salbutamol ameliorated EAM on day 21 and increased myocardial interleukin-10/interferon-gamma mRNA levels. Propranolol, a nonselective beta-AR antagonist, aggravated EAM on day 21 and decreased mRNA levels, whereas metoprolol, a beta1-selective AR antagonist, showed no effect. These results were reflected in vivo by the proliferation of cardiac myosin-primed lymph node cells from drug-treated rats. In vitro addition of beta2-selective AR agonists inhibited the activation of cardiac myosin fragment-specific myocarditogenic T lymphocytes, and this effect was reversed by ICI118,551, a beta2-selective AR antagonist. Furthermore, treatment with 2 different beta2-selective AR agonists starting on day 14 also ameliorated EAM on day 21.

CONCLUSIONS

beta2-AR stimulation suppressed the development of EAM by inhibiting cardiac myosin-specific T-lymphocyte activation in lymphoid organs and by shifting the imbalance in Th1/Th2 cytokine toward Th2 cytokine. Furthermore, it also ameliorated established myocardial inflammation. beta2-AR-stimulating agents may represent important immunomodulators of the cardiac myosin-induced autoimmune process and have potential as a new therapy for myocarditis.

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

Background The effect of bepridil, a multichannel blocker, on atrial electrical remodeling was evaluated in a canine rapid atrial stimulation model. Methods and Results In 10 beagle dogs, the right atrial appendage (RAA) was paced at 400 beats/min for 2 weeks. The atrial electrophysiological parameters, including effective refractory period (AERP), were evaluated at three atrial sites: RAA, the right atrium close to the inferior vena cava (IVC) and the left atrium (LA), during the time course of rapid pacing. Five of the dogs were given bepridil (10 mg . kg (-1) . day(-1) po). In the control group, AERP was significantly shortened at all atrial sites and the AERP shortening (DeltaAERP) was larger for the RAA and LA than at the IVC site (p<0.05). In the bepridil group, DeltaAERP was smaller than that of the controls at all atrial sites, and the AERP started to return slowly to the pre-pacing level in the second week, regardless of the continuation of rapid pacing. Conclusions In a canine rapid atrial stimulation model, bepridil suppressed AERP shortening. Bepridil might have a reverse electrical remodeling effect, at least for AERP shortening, because it showed slow recovery of AERP in the subacute phase of rapid atrial pacing. (Circ J 2006; 70: 206 - 213).

Tumor Necrosis Factor-.ALPHA. Downregulates the Voltage Gated Outward K+ Current in Cultured Neonatal Rat Cardiomyocytes A Possible Cause of Electrical Remodeling in Diseased Hearts

BACKGROUND

Inflammatory cytokines have been reported to contribute to the progression of cardiac remodeling in various heart diseases and a remarkable prolongation of the monophasic action potential duration and reductions in the expression of Kv4.2 and K+ channel-interacting protein-2 (KChIP-2) in a rat autoimmune myocarditis model have been documented. In this study, the effect of tumor necrosis factor-alpha (TNF-alpha) on cultured cardiomyocytes was evaluated, focusing on the change in the voltage-gated outward K+ current and expression of related molecules.

METHODS AND RESULTS

Cardiomyocytes isolated from 1-day-old Lewis rats were cultured for 72 h and treated with TNF-alpha (50 ng/ml) for an additional 48 h. The myocytes treated with TNF-alpha showed a 22% reduction in the peak K+ current, which consisted of a transient outward K+ current (Ito) and 1.4-fold enhancement of the cell-capacitance in comparison with the control. Among the cardiac ion channel related molecules evaluated in this study, Kv4.2 and KChIP-2 mRNA exhibited remarkable reductions (p < 0.05).

CONCLUSIONS

Treatment with TNF-alpha induced reductions in Ito as well as cellular hypertrophy in neonatal cultured myocytes, which indicates that TNF-alpha might play a role in promoting electrical remodeling of cardiomyocytes under inflammatory conditions.