Prolongation Of Effective Refractory Period Research Articles

In vivo cardiovascular profile of ryanodine receptor 2 inhibitor M201-A: Utility as an anti-atrial fibrillatory drug for patients suffering from heart failure with preserved ejection fraction

Atrial fibrillation (AF) and heart failure with preserved ejection fraction (HFpEF) often coexist; however, clinically available anti-AF drugs can exacerbate symptoms of HFpEF. M201-A suppressed ryanodine receptor-mediated diastolic Ca2+ leakage, possibly inhibiting common pathological processes toward AF and HFpEF. To bridge the basic information to clinical practice, we assessed its cardiohemodynamic, anti-AF and ventricular proarrhythmic profile using halothane-anesthetized dogs (n = 4). M201-A hydrochloride in doses of 0.03, 0.3 and 3 mg/kg/10 min was intravenously administered, providing peak plasma concentrations of 0.09, 0.81 and 5.70 μg/mL, respectively. The high dose of M201-A showed various cardiovascular actions. Namely, M201-A increased mean blood pressure and tended to enhance isovolumetric ventricular relaxation without suppressing ventricular contraction or decreasing cardiac output. M201-A enhanced atrioventricular conduction, but hardy affected intra-atrial/ventricular conduction. Importantly, M201-A prolonged effective refractory period more potently in the atrium than in the ventricle, indicating that it may become an atrial-selective antiarrhythmic drug. Meanwhile, M201-A prolonged QT interval/QTcV, and showed reverse frequency-dependent delay of ventricular repolarization. M201-A prolonged J-Tpeakc without prolonging Tpeak-Tend or terminal repolarization period, indicating the risk of causing torsade de pointes is negligible. Thus, M201-A is expected to become a hopeful therapeutic strategy for patients having pathology of both AF and HFpEF.

Inhibition of α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptors Ameliorates Atrial Inflammation and Vulnerability to Atrial Fibrillation in Rats with Anxiety Disorders.

Previous studies have found that anxiety disorders may increase the incidence of atrial fibrillation (AF). More and more studies have shown that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are involved in the occurrence and development of cardiovascular diseases. However, the role of AMPARs in AF associated with anxiety disorder remains unclear. The aim of this study was to investigate the effect of AMPARs on AF susceptibility in rats with anxiety disorder and its possible mechanism. The anxiety disorder rat model was established by unpredictable empty bottle stimulation and was treated with AMPARs agonist and antagonist. Our results showed that AMPARs antagonist treatment significantly reduced sympathetic activity, improved heart rate variability, shortened action potential duration, prolonged effective refractory period, reduced AF induction rate, and improved cardiac electrical remodeling and the expression of inflammatory factors. In addition, inhibition of AMPARs reduced the phosphorylation of IκBα and p65. Our experimental results suggest that inhibition of AMPARs can reduce autonomic remodeling, improve atrial electrical remodeling, and suppress myocardial inflammation, which provides a potential therapeutic strategy for the treatment of AF associated with anxiety disorder.

HE EFFECT OF PROBENECID ON α-1-ADRENOCEPTOR STIMULATION INDUCED PROARRHYTHMIC CONDUCTION IN THE ATRIOVENTRICULAR NODE OF RAT HEART

Cardiac tissue contains adrenergic receptors (AR) not only of the beta type, but also of the alpha type (α-AR). Both types of ARs play signifi cant role in regulation of cardiomyocytes electrophysiology in diff erent parts of the heart, including the atrioventricular node (AVN). An augmentation of α1-AR mediated component of adrenergic signaling results in impaired conduction of excitation in the heart and onset of various rhythm disturbances including AVNassociated arrhythmias. The activation of α1-AR facilitates anionic transmembrane transport causing electrophysiological changes in myocytes. Current study is aimed to the investigation of the eff ects of anion/chloride blockade on α1-AR-mediated proarrhythmic alteration of AVN functioning. Functional characteristics of AVN including AVN conduction time, AVN refractoriness and the AVN conduction alterations were examined via recording of surface electrograms in Langendorff -perfused isolated rat heart (Wistar, 250 ± 30 g). Phenylephrine was used as α1-AR agonist. Probenecid demonstrating anion/chloride transmembrane conductance blocking activity was used to modify Phe-induced α1-AR-mediated eff ects in AVN. The activation of α1-AR by Phe results in a signifi cant increase in the duration of AV intervals (N = 10, p < 0.001) and eff ective refractory period (ERP) in the AVN (by 9.8% ± 1.2%, n = 10, p < 0.001). Also, Phe induces AV-blocks of conduction and oscillations in atrioventricular delay (N = 10) at the stimulation rates close to ERP. Probenecid signifi cantly reduces the magnitude of AVD oscillations during non-stationary conduction in the AV node. In addition, probenecid attenuates ERP prolongation caused by Phe (107 ± 4 ms, N = 6) and 114.2 ± 5.35 ms (N = 10) in presence of only Phe and Phe with probenecid, respectively, returning its values toward typical for normal conditions. In conclusion, probenecid maintains physiological mode of AVN conduction when α1-AR are stimulated. This also suggests that chloride ion channels and anion carriers may contribute to the α1-AR-mediated AVN arrhythmias.

Hypoxia Promotes Atrial Tachyarrhythmias via Opening of ATP-Sensitive Potassium Channels.

Hypoxia-ischemia predisposes to atrial arrhythmia. Atrial ATP-sensitive potassium channel (KATP) modulation during hypoxia has not been explored. We investigated the effects of hypoxia on atrial electrophysiology in mice with global deletion of KATP pore-forming subunits. Whole heart KATP RNA expression was probed. Whole-cell KATP current and action potentials were recorded in isolated wild-type (WT), Kir6.1 global knockout (6.1-gKO), and Kir6.2 global knockout murine atrial myocytes. Langendorff-perfused hearts were assessed for atrial effective refractory period (ERP), conduction velocity, wavefront path length (WFPL), and arrhymogenicity under normoxia/hypoxia using a microelectrode array and programmed electrical stimulation. Heart histology was assessed. Expression patterns were essentially identical for all KATP subunit RNA across human heart, whereas in mouse, Kir6.1 and SUR2 (sulphonylurea receptor) were higher in ventricle than atrium, and Kir6.2 and SUR1 were higher in atrium. Compared with WT, Kir6.2 global knockout atrial myocytes had reduced tolbutamide-sensitive current and action potentials were more depolarized with slower upstroke and reduced peak amplitude. Action potential duration was prolonged in 6.1-gKO atrial myocytes, absent of changes in other ion channel gene expression or atrial myocyte hypertrophy. In Langendorff-perfused hearts, baseline atrial ERP was prolonged and conduction velocity reduced in both KATP knockout mice compared with WT, without histological fibrosis. Compared with baseline, hypoxia led to conduction velocity slowing, stable ERP, and WFPL shortening in WT and 6.1-gKO hearts, whereas WFPL was stable in Kir6.2 global knockout hearts due to ERP prolongation with conduction velocity slowing. Tolbutamide reversed hypoxia-induced WFPL shortening in WT and 6.1-gKO hearts through ERP prolongation. Atrial tachyarrhythmias inducible with programmed electrical stimulation during hypoxia in WT and 6.1-gKO mice correlated with WFPL shortening. Spontaneous arrhythmia was not seen. KATP block/absence leads to cellular and tissue level atrial electrophysiological modification. Kir6.2 global knockout prevents hypoxia-induced atrial WFPL shortening and atrial arrhythmogenicity to programmed electrical stimulation. This mechanism could be explored translationally to treat ischemically driven atrial arrhythmia.

Optogenetic termination of atrial tachyarrhythmias by brief pulsed light stimulation

AimsThe most efficient way to acutely restore sinus rhythm from atrial fibrillation (AF) is electrical cardioversion, which is painful without adequate sedation. Recent studies in various experimental models have indicated that optogenetic termination of AF using light-gated ion channels may provide a myocardium-specific and potentially painless alternative future therapy. However, its underlying mechanism(s) remain(s) incompletely understood. As brief pulsed light stimulation, even without global illumination, can achieve optogenetic AF termination, besides direct conduction block also modulation of action potential (AP) properties may be involved in the termination mechanism. We studied the relationship between optogenetic AP duration (APD) and effective refractory period (ERP) prolongation by brief pulsed light stimulation and termination of atrial tachyarrhythmia (AT). Methods and resultsHearts from transgenic mice expressing the H134R variant of channelrhodopsin-2 in atrial myocytes were explanted and perfused retrogradely. AT induced by electrical stimulation was terminated by brief pulsed blue light stimulation (470 nm, 10 ms, 16 mW/mm2) with 68% efficacy. The termination rate was dependent on pulse duration and light intensity. Optogenetically imposed APD and ERP changes were systematically examined and optically monitored. Brief pulsed light stimulation (10 ms, 6 mW/mm2) consistently prolonged APD and ERP when light was applied at different phases of the cardiac action potential. Optical tracing showed light-induced APD prolongation during the termination of AT. ConclusionOur results directly demonstrate that cationic channelrhodopsin activation by brief pulsed light stimulation prolongs the atrial refractory period suggesting that this is one of the key mechanisms of optogenetic termination of AT.

Novel preventive effect of isorhamnetin on electrical and structural remodeling in atrial fibrillation.

Isorhamnetin, a natural flavonoid, has strong antioxidant and antifibrotic effects, and a regulatory effect against Ca2+-handling. Atrial remodeling due to fibrosis and abnormal intracellular Ca2+ activities contributes to initiation and persistence of atrial fibrillation (AF). The present study investigated the effect of isorhamnetin on angiotensin II (AngII)-induced AF in mice. Wild-type male mice (C57BL/6J, 8 weeks old) were assigned to three groups: (1) control group, (2) AngII-treated group, and (3) AngII- and isorhamnetin-treated group. AngII (1000 ng/kg/min) and isorhamnetin (5 mg/kg) were administered continuously via an implantable osmotic pump for two weeks and intraperitoneally one week before initiating AngII administration, respectively. AF induction and electrophysiological studies, Ca2+ imaging with isolated atrial myocytes and HL-1 cells, and action potential duration (APD) measurements using atrial tissue and HL-1 cells were performed. AF-related molecule expression was assessed and histopathological examination was performed. Isorhamnetin decreased AF inducibility compared with the AngII group and restored AngII-induced atrial effective refractory period prolongation. Isorhamnetin eliminated abnormal diastolic intracellular Ca2+ activities induced by AngII. Isorhamnetin also abrogated AngII-induced APD prolongation and abnormal Ca2+ loading in HL-1 cells. Furthermore, isorhamnetin strongly attenuated AngII-induced left atrial enlargement and atrial fibrosis. AngII-induced elevated expression of AF-associated molecules, such as ox-CaMKII, p-RyR2, p-JNK, p-ERK, and TRPC3/6, was improved by isorhamnetin treatment. The findings of the present study suggest that isorhamnetin prevents AngII-induced AF vulnerability and arrhythmogenic atrial remodeling, highlighting its therapeutic potential as an anti-arrhythmogenic pharmaceutical or dietary supplement.

Improving effects of eplerenone on atrial remodeling induced by chronic intermittent hypoxia in rats

ObjectiveAtrial fibrillation (AF) is closely associated with the overactivation of the renin-angiotensin-aldosterone system. Large cohort studies and recent meta-analyses have shown that the utilization of mineralocorticoid receptor antagonists has positive effects on the prevention and development of AF. This study aimed to investigate the effects of eplerenone on atrial remodeling in AF model rats and elucidate its intrinsic mechanism. MethodsNinety male Sprague-Dawley rats were randomly divided into the control group, chronic intermittent hypoxia (CIH) group, and CIH-eplerenone intervention (CIH-E) group. Rats in the CIH and CIH-E groups received CIH for 6 weeks, and rats in the CIH-E group were additionally administered eplerenone gavage (10 mg/kg/d). After modeling, the baseline parameters of each group were examined. Histopathology, molecular biology, isolated electrophysiology, and patch clamp experiments were performed after sampling. ResultsCompared with the control group, rats in the CIH group showed atrial enlargement, significant aggravated fibrosis, upregulated JAK/STAT3 pathway, shortened effective refractory period (ERP), increased AF inducibility, and decreased peak current density of characteristic voltage-gated ion channels in atrial myocytes. After eplerenone intervention, rats in the CIH-E group had a smaller atrial diameter than those in the CIH group. Furthermore, downregulated JAK/STAT3 pathway, prolonged ERP, decreased AF inducibility, and increased peak current density of characteristic ion channels were also observed in the CIH-E group. ConclusionsCIH induced significant atrial remodeling in rats and eplerenone significantly ameliorated the atrial remodeling caused by CIH. This could be attributed to the downregulation of the JAK/STAT3 pathway and the increase in the characteristic ion current density of atrial myocytes.

Abstract 10814: Prolongation of the Refractory Period is a Key Mechanism of Optogenetic Termination of Atrial Fibrillation in Mouse Hearts

Backgrounds: Optogenetics is a new technique that employs light-sensitive channels and manipulates the cell membrane potential. Although painless defibrillation of reentry arrhythmias such as atrial fibrillation (AF) using optogenetics has been reported, the mechanism has not been fully elucidated because of the difficulty to evaluate the action potential (AP) modification by in/ex-vivo light illumination. Purpose: Our aim is to clarify the mechanism of optogenetic defibrillation of AF in a mouse heart by voltage-sensitive optical mapping. For this purpose, we employed a novel approach using brief light illumination combined with a systematic electrical stimulation protocol. Methods and Results: Hearts from transgenic mice expressing channelrhodopsin-2 in atrial cardiomyocytes were explanted and perfused with tyrode’s solution containing low K + concentration (2.7mM) and K ACh -channel activator carbachol (2μM). Atrial tachyarrhythmia induced by burst pacing was terminated by blue light (470nm) illumination with a pulse duration of 10 ms and a light intensity of 16 mW/mm 2 with a probability of 64.7 ± 8.1% (n=9). The termination rate depended on the pulse duration and light intensity. Then, we examined whether brief light illumination (10 ms, 6mW/mm 2 ) at different time phases from the rise of the AP (phase 0) to the repolarization (phase 4) modify AP shape and prolong the effective refractory period (ERP) using voltage-sensitive optical mapping. Brief light illumination prolonged AP duration and ERP in all time phases. The degree of ERP prolongation was dependent on the pulse duration, but not on the light intensity above 1 mW/mm 2 . Finally, we measured the attenuation of blue light intensity through the atrial tissue and observed that the intensity decreased by 38.1 ± 3.5% at 10mW/mm 2 on 3 mm 2 circular area(n=6), suggesting that high-intensity light also modulates the APs of atrial cardiomyocytes in deeper layers. Conclusion: Our results directly demonstrated that brief light illumination prolonged the atrial refractory period depending on pulse duration in a perfused heart and suggests the prolongation of the refractory period is a key mechanism of optogenetic termination of AF.

Effective termination of atrial fibrillation by SK channel inhibition is associated with a sudden organization of fibrillatory conduction.

AimsPharmacological termination of atrial fibrillation (AF) remains a challenge due to limited efficacy and potential ventricular proarrhythmic effects of antiarrhythmic drugs. SK channels are proposed as atrial-specific targets in the treatment of AF. Here, we investigated the effects of the new SK channel inhibitor AP14145.Methods and resultsEight goats were implanted with pericardial electrodes for induction of AF (30 days). In an open-chest study, the atrial conduction velocity (CV) and effective refractory period (ERP) were measured during pacing. High-density mapping of both atrial free-walls was performed during AF and conduction properties were assessed. All measurements were performed at baseline and during AP14145 infusion [10 mg/kg/h (n = 1) or 20 mg/kg/h (n = 6)]. At an infusion rate of 20 mg/kg/h, AF terminated in five of six goats. AP14145 profoundly increased ERP and reduced CV during pacing. AP14145 increased spatiotemporal instability of conduction at short pacing cycle lengths. Atrial fibrillation cycle length and pathlength (AF cycle length × CV) underwent a strong dose-dependent prolongation. Conduction velocity during AF remained unchanged and conduction patterns remained complex until the last seconds before AF termination, during which a sudden and profound organization of fibrillatory conduction occurred.ConclusionAP14145 provided a successful therapy for termination of persistent AF in goats. During AF, AP14145 caused an ERP and AF cycle length prolongation. AP14145 slowed CV during fast pacing but did not lead to a further decrease during AF. Termination of AF was preceded by an abrupt organization of AF with a decline in the number of fibrillation waves.

Absence of Rgs5 Influences the Spatial and Temporal Fluctuation of Cardiac Repolarization in Mice.

AimsThis study investigated the contribution of the regulator of G-protein signaling 5 (Rgs5) knockout to the alteration of the action potential duration (APD) restitution and repolarizing dispersion in ventricle.Methods and ResultsThe effects of Rgs5–/– were investigated by QT variance (QTv) and heart rate variability analysis of Rgs5–/– mice. Monophasic action potential analysis was investigated in isolated Rgs5–/– heart. Rgs5–/– did not promote ventricular remodeling. The 24-h QTv and QT variability index (QTVI) of the Rgs5–/– mice were higher than those of wild-type (WT) mice (P < 0.01). In WT mice, a positive correlation was found between QTv and the standard deviation of all NN intervals (r = 0.62; P < 0.01), but not in Rgs5–/– mice (R = 0.01; P > 0.05). The absence of Rgs5 resulted in a significant prolongation of effective refractory period and APD in isolated ventricle. In addition, compared with WT mice, the knockout of Rgs5 significantly deepened the slope of the APD recovery curve at all 10 sites of the heart (P < 0.01) and increased the spatial dispersions of Smax (COV-Smax) (WT: 0.28 ± 0.03, Rgs5–/–: 0.53 ± 0.08, P < 0.01). Compared with WT heart, Rgs5–/– increased the induced S1–S2 interval at all sites of heart and widened the window of vulnerability of ventricular tachyarrhythmia (P < 0.05).ConclusionOur findings indicate that Rgs5–/– is an important regulator of ventricular tachyarrhythmia in mice by prolonging ventricular repolarization and increasing spatial dispersion in ventricle.

Modulating the Infarcted Ventricle’s Refractoriness with an Epicardial Biomaterial

Patients diagnosed with heart failure with reduced ejection fraction (HFrEF) are at increased risk of monomorphic ventricular tachycardia (VT) and ventricular fibrillation. The presence of myocardial fibrosis provides both anatomical...

In vivo knockdown of SK3 channels using antisense oligonucleotides protects against atrial fibrillation in rats

IntroductionGapmeRs are oligonucleotides that bind to a specific RNA sequence and thereby affecting posttranscriptional gene regulation. They therefore hold the potential to manipulate targets where current pharmacological modulators are inefficient or exhibit adverse side effects. Here, we show that a treatment with a GapmeR, mediating knockdown of small conductance Ca2+-activated K+ channels (SK3), has an in vivo protective effect against atrial fibrillation (AF) in rats. Material and methodsA unique SK3-GapmeR design was selected after thorough in vitro evaluation. 22 rats were randomly assigned to receive either 50 mg/kg SK3-GapmeR or vehicle subcutaneously once a week for two weeks. Langendorff experiments were performed seven days after the last injection, where action potential duration (APD90), effective refractory period (ERP) and AF propensity were investigated. SK3 channel activity was evaluated using the SK channel blocker, ICA (N-(pyridin-2-yl)-4-(pyridine-2-yl)thiazol-2-amine). SK3 protein expression was assessed by Western Blot. ResultsThe designed GapmeR effectively down-regulate the SK3 protein expression in the heart (48% downregulation, p = 0.0095) and did indeed protect against AF. Duration of AF episodes elicited by burst pacing in the rats treated with SK3-GapmeR was reduced 78% compared to controls (3.7 s vs. 16.8 s, p = 0.0353). The number of spontaneous AF episodes were decreased by 68% in the SK3-GapmeR group (39 episodes versus 123 in the control group, respectively) and were also significantly shorter in duration (7.2 s versus 29.7 s in the control group, p = 0.0327). Refractoriness was not altered at sinus rhythm, but ERP prolongation following ICA application was blunted in the SK3-GapmeR group. ConclusionThe selected GapmeR silenced the cardiac SK3 channels, thereby preventing AF in rats. Thus, GapmeR technology can be applied as an experimental tool of downregulation of cardiac proteins and could potentially offer a novel modality for treatment of cardiac diseases.

Inhibition of Adenosine Pathway Alters Atrial Electrophysiology and Prevents Atrial Fibrillation.

BackgroundAdenosine leads to atrial action potential (AP) shortening through activation of adenosine 1 receptors (A1-R) and subsequent opening of G-protein-coupled inwardly rectifying K+ channels. Extracellular production of adenosine is drastically increased during stress and ischemia.ObjectiveThe aim of this study was to address whether the pharmacological blockade of endogenous production of adenosine and of its signaling prevents atrial fibrillation (AF).MethodsThe role of A1-R activation on atrial action potential duration, refractoriness, and AF vulnerability was investigated in rat isolated beating heart preparations (Langendorff) with an A1-R agonist [2-chloro-N6-cyclopentyladenosine (CCPA), 50 nM] and antagonist [1-butyl-3-(3-hydroxypropyl)-8-(3-noradamantyl)xanthine (PSB36), 40 nM]. Furthermore, to interfere with the endogenous adenosine release, the ecto-5′-nucleotidase (CD73) inhibitor was applied [5′-(α,β-methylene) diphosphate sodium salt (AMPCP), 500 μM]. Isolated trabeculae from human right atrial appendages (hRAAs) were used for comparison.ResultsAs expected, CCPA shortened AP duration at 90% of repolarization (APD90) and effective refractory period (ERP) in rat atria. PSB36 prolonged APD90 and ERP in rat atria, and CD73 inhibition with AMPCP prolonged ERP in rats, confirming that endogenously produced amount of adenosine is sufficiently high to alter atrial electrophysiology. In human atrial appendages, CCPA shortened APD90, while PSB36 prolonged it. Rat hearts treated with CCPA are prone to AF. In contrast, PSB36 and AMPCP prevented AF events and reduced AF duration (vehicle, 11.5 ± 2.6 s; CCPA, 40.6 ± 16.1 s; PSB36, 6.5 ± 3.7 s; AMPCP, 3.0 ± 1.4 s; P < 0.0001).ConclusionA1-R activation by intrinsic adenosine release alters atrial electrophysiology and promotes AF. Inhibition of adenosine pathway protects atria from arrhythmic events.

Low-Intensity Ultrasound Modulation May Prevent Myocardial Infarction-induced Sympathetic Neural Activation and Ventricular Arrhythmia.

Low-intensity focused ultrasound (LIFU) has been shown to be a beneficial tool for autonomic nervous system modulation, but its effect on the left stellate ganglion (LSG) remains unknown. To seek the effect of LIFU on myocardial infarction (MI)-induced LSG activation and ventricular arrhythmias (VAs). In this study, 20 dogs were included and randomly divided into the LIFU (LIFU & MI, n = 8), Sham (sham LIFU & MI, n = 8), and Control group (sham LIFU & sham MI, n = 4). For each LIFU intervention (1.0-2.0 W, 10 minutes) of the LSG, the LSG function, ventricular effective refractory period (ERP), and temperature were tested pre-intervention and postintervention. Thereafter, MI was induced by left anterior artery ligation and VAs were recorded for 1 hour. At the end, both the LSG and the heart were extracted for biomedical and histological analysis. In the Sham group, no significant change was shown in ventricular ERP or LSG function for any intensity settings of sham LIFU intervention when compared with the group baseline. In the LIFU group, however, both 1.5 and 2.0 W LIFU modulation of LSG resulted in significant prolongation of ERP and attenuation of LSG function. Furthermore, the incidence of VAs was significantly attenuated in the LIFU group compared with the Sham group. Moreover, histological analysis showed that no damage or apoptosis was observed in LSG although a statistically significant increase was shown in temperature (maximal increase <1°C) with 1.5 and 2.0 W LIFU intervention. LIFU stimulation may be a safe and beneficial tool for LSG attenuation and VA prevention in the MI canine model.

Selective chemical ablation of transient receptor potential vanilloid 1 expressing neurons in the left stellate ganglion protects against ischemia-induced ventricular arrhythmias in dogs

ObjectivesFindings from prior investigations show that left stellate ganglion (LSG) inhibitory approaches protect the heart from ventricular arrhythmias (VAs) caused by acute myocardial infarction (AMI), which still remain many side effects. Targeted transient receptor potential vanilloid 1/tyrosine hydroxylase (TRPV-1/TH) expressing sympathetic neurons ablation is a novel neuro-ablative strategy. The aim of this investigation was to explore if targeted molecular neuro-ablative strategy by resiniferatoxin (RTX) stellate microinjection could protect against ischemia-induced VAs. MethodsTwenty-four anesthetized beagles were assigned to a control group (n = 12) and RTX group (n = 12) in a random manner. Targeted molecular neuro-ablative was produced by RTX stellate microinjection and DMSO was microinjected into LSG in the same way as control. Plasma norepinephrine (NE) level, heart rate variability (HRV), Tpeak-Tend interval (Tp-Te), LSG neural activity and function, ventricular effective refractory period (ERP), beat-to-beat variability of repolarization (BVR) and ventricular action potential duration (APD) were measured at baseline and 60 min after RTX or DMSO microinjection. AMI model was established by the ligation of left anterior descending coronary artery and 60-minute electrocardiography was continuously recorded for VAs analysis. Subsequently, HRV, Tp-Te, plasma NE level from jugular vein and coronary sinus, LSG neural activity and function, ventricular ERP, ventricular APD, BVR, action potential duration alternans (APDA) cycle length and ventricular fibrillation threshold (VFT) were evaluated after AMI. Finally, tissue collection of LSG was performed for examining the TRPV-1, nerve growth factor (NGF) protein and c-fos protein. ResultsTRPV-1 was highly expressed in the TH-expressing neurons and RTX injection significantly ablated TRPV-1/TH-positive neurons in LSG. Compared with baseline, RTX stellate microinjection significantly reduced plasma NE level, the sympathetic component of HRV, LSG neural activity and LSG function, shortened Tp-Te, prolonged ventricular ERP and APD, but there were no remarkable differences existed for control group. AMI resulted in the significant raise in plasma NE level from jugular vein and coronary sinus, the sympathetic component of HRV, LSG neural activity and LSG function, the marked prolongation in Tp-Te and BVR, the significant decrease in ERP and APD from ischemia area, and the increase in APDA cycle length in the ischemic region of the control group, which were remarkably attenuated in the RTX group. RTX pretreatment markedly rose the VFT in the RTX group. Furthermore, the AMI-triggered VAs was significantly prevented by RTX injection in the RTX group. RTX microinjection down-regulated significantly TRPV-1, NGF and c-fos expression in the LSG compared with the control group. ConclusionTargeted ablation of TRPV-1/TH positive sympathetic neurons induced by RTX stellate microinjection could suppress ischemia-induced cardiac autonomic imbalances and cardiac electrophysiology instability to protect against AMI-induced VAs.

P1905Propofol suppresses atrial fibrillation in an experimental whole-heart model

Abstract Background Many clinical studies suggest an impact of propofol on the occurrence of atrial arrhythmias. Purpose Since experimental data is sparse, purpose of this study was to investigate the influence of propofol on atrial electrophysiology and the vulnerability to atrial fibrillation in a sensitive whole-heart model of atrial fibrillation. Methods 11 hearts of New Zealand white rabbits were isolated and Langendorff-perfused. Two catheters were placed on both atria to record atrial monophasic action potentials. Hearts were stimulated at three different cycle lengths (350ms, 250ms, 150ms), thereby obtaining cycle-length dependent atrial action potential durations (aAPD90) and effective refractory periods (aERP). Atrial post-repolarization (aPRR) refractoriness was defined as the difference between aERP and aAPD90. To increase the occurrence of atrial fibrillation, hearts were perfused with a combination of acetylcholine (ACh, 1μM) and isoproterenol (Iso, 1μM) after obtaining baseline data. Vulnerability to atrial fibrillation was tested by a standardized protocol consisting of several trains of burst pacing. Results Acetylcholine/isoproterenol infusion reduced aAPD90 (−3ms), aERP (−16ms) and aPRR (−14ms). Additional treatment with propofol prolonged aAPD90 (+5ms), aERP (+24ms) and aPRR (+20ms). Under baseline conditions, 13 episodes of atrial fibrillation lasting longer than 1s occurred. Additional treatment with acetylcholine/isoproterenol provoked more episodes of atrial fibrillation (33 episodes, p&lt;0.05). Infusion of propofol on top of acetylcholine/isoproterenol significantly suppressed atrial fibrillation (2 episodes, p&lt;0.05). Conclusion In this study, propofol prolonged aAPD90 and significantly reduced the occurrence of atrial fibrillation. Prolongation of effective refractory periods and especially of post-repolarization refractoriness protects the atrial myocardium against premature excitation and thereby prevents arrhythmias.

Gastroesophageal reflux disease and atrial fibrillation: Insight from autonomic cardiogastric neural interaction.

The relationship between gastroesophageal reflux disease (GERD) and atrial fibrillation (AF) has been previously reported. However, the detailed mechanism remains unknown. In this study, we investigated the effects of acid reflux on the intrinsic cardiac autonomic nervous system, atrial/ventricular electrophysiology, and AF inducibility. Eighteen rabbits were randomized into three groups: acid reflux (group 1, n = 6), control (group 2, n = 6), and acid reflux with periesophageal vagal blockade (group 3, n = 6). Atrial and ventricular effective refractory periods (ERPs) and AF inducibility were checked at baseline and then hourly until 5 hours after the experiment. Three hours after the experiment, atrial ERP prolongation was noted in groups 2 and 3 (P < .05), whereas shortening of the atrial ERPs was observed in group 1, compared with the baseline. However, no changes were observed in ventricular ERPs in the three groups. The AF inducibility was higher in group 1 than in groups 2 and 3. Pathological examination showed clear esophageal mucosal breaks in groups 1 and 3. In this study, we found that the antimuscarinic blockade prevents GERD induced changes to atrial electrophysiology and susceptibility to AF-making it highly likely that autonomic activity is important in mediating this effect.

Dose-Dependent Effects of Ranolazine on Reentrant Ventricular Arrhythmias Induced After Subacute Myocardial Infarction in Rabbits.

Ranolazine has been found to prevent ventricular arrhythmias (VAs) during acute myocardial infarction (AMI). This study aimed to investigate its efficacy on VAs induced several days post-MI. For this purpose, 13 anesthetized rabbits underwent coronary artery ligation. Ten of these animals that survived AMI were reanesthetized 3 to 7 days later for electrophysiologic testing. An endocardial monophasic action potential combination catheter was placed in the right ventricle for simultaneous pacing and recording. Monophasic action potential duration, ventricular effective refractory period (VERP), and VAs induced by programmed stimulation were assessed. Measurements were performed during control pacing, and following an intravenous infusion of either a low-dose ranolazine (2.4 mg/kg, R1) or a higher dose ranolazine (4.8 mg/kg cumulative dose, R2). During control stimulation, 2 animals developed primary ventricular fibrillation (VF), 6 sustained ventricular tachycardia (sVT), and 2 nonsustained VT (nsVT). R1 did not prevent the appearance of VAs in any of the experiments; in contrast, it aggravated nsVT into sVT and complicated sVT termination in 2 of 6 animals. Sustained ventricular tachycardia cycle length and VERP were only slightly decreased after R1 (112 ± 5 vs 110 ± 6 ms and 101 ± 11 vs 98 ± 10 ms, respectively). R2 suppressed inducibility of control nsVT, VF, and sVT in 2 animals. In 4 animals with still inducible sVT, R2 significantly prolonged VT cycle length by 150 ± 23 ms (P < .01), and VERP by 120 ± 7 ms (P < .001) versus control. In conclusion, R2 exerted antiarrhythmic efficacy against subacute-MI VAs, whereas R1 rather aggravated than prevented these arrhythmias. Ventricular effective refractory period prolongation could partially explain the antiarrhythmic action of R2 in this rabbit model.

Cardiac Sympathetic Afferent Denervation Protects Against Ventricular Arrhythmias by Modulating Cardiac Sympathetic Nerve Activity During Acute Myocardial Infarction.

BackgroundAugmented cardiac sympathetic afferent reflex (CSAR) plays a role in enhanced sympathetic activity. Given that a strategy for abolishing augmented CSAR-induced sympathetic activation may be beneficial for protecting against ventricular arrhythmias (VAs) triggered by acute myocardial infarction (AMI), we investigated whether cardiac sympathetic afferent denervation (CSAD) could protect against VAs by modulating cardiac sympathetic nerve activity in an AMI dog model.Material/MethodsTwenty-two anesthetized dogs were assigned to the CSAD group (n=9) and the sham group (n=13) randomly. CSAD was produced by epicardial application of resiniferatoxin. Heart rate variability (HRV), ventricular action potential duration (APD), APD dispersion, beat-to-beat variability of repolarization (BVR), effective refractory period (ERP) of ventricles, ERP dispersion, plasma norepinephrine (NE) concentration, and left stellate ganglion (LSG) neural activity were determined at baseline and after CSAD. We designed an AMI model by occluding the left anterior coronary artery, and performed analysis of VAs for 60 minutes using electrocardiography. Then, levels of c-fos and nerve growth factor (NGF) were determined.ResultsRelative to baseline values, CSAD prolonged ERP and APD of ventricles, increased HRV, decreased APD dispersion, BVR, ERP dispersion and serum NE concentration, and attenuated LSG activity in the CSAD group. AMI triggered a remarkable increase in LSG activity and function but decreased the HRV of the sham group animals relative to the CSAD group. Moreover, the CSAD group had higher levels of VAs relative to the sham group. This was accompanied by a corresponding decrease in proteins quantities of NGF and c-fos in the CSAD group in the LSG after AMI compared to the sham group.ConclusionsCSAD can suppress LSG neural activity, hence enhance the electrophysiological stability and protect the heart from AMI-triggered VAs.

Identification of Verapamil Binding Sites Within Human Kv1.5 Channel Using Mutagenesis and Docking Simulation.

The phenylalkylamine class of L-type Ca2+ channel antagonist verapamil prolongs the effective refractory period (ERP) of human atrium, which appears to contribute to the efficacy of verapamil in preventing reentrant-based atrial arrhythmias including atrial fibrillation. This study was designed to investigate the molecular and electrophysiological mechanism underlying the action of verapamil on human Kv1.5 (hKv1.5) channel that determines action potential duration and ERP in human atrium. Site-directed mutagenesis created 10 single-point mutations within pore region of hKv1.5 channel. Wholecell patch-clamp method investigated the effect of verapamil on wild-type and mutant hKv1.5 channels heterologously expressed in Chinese hamster ovary cells. Docking simulation was conducted using open-state homology model of hKv1.5 channel pore. Verapamil preferentially blocked hKv1.5 channel in its open state with IC50 of 2.4±0.6 μM (n = 6). The blocking effect of verapamil was significantly attenuated in T479A, T480A, I502A, V505A, I508A, L510A, V512A and V516A mutants, compared with wild-type hKv1.5 channel. Computer docking simulation predicted that verapamil is positioned within central cavity of channel pore and has contact with Thr479, Thr480, Val505, Ile508, Ala509, Val512, Pro513 and Val516. Verapamil acts as an open-channel blocker of hKv1.5 channel, presumably due to direct binding to specific amino acids within pore region of hKv1.5 channel, such as Thr479, Thr480, Val505, Ile508, Val512 and Val516. This blocking effect of verapamil on hKv1.5 channel appears to contribute at least partly to prolongation of atrial ERP and resultant antiarrhythmic action on atrial fibrillation in humans.