Canine Model Of Atrial Fibrillation Research Articles

Atrial cardiomyocytes from a canine model of atrial fibrillation demonstrate reduced force development and altered expression of contractile proteins.

Atrial fibrillation (AF) is the most common cardiac rhythm disturbance and associates with worse outcomes in cardiac contractile-related diseases including cardiomyopathy. As most studies surrounding AF focus on the electrophysiology of the disease, there is little known about cardiomyocyte contractile function in AF. We used atrial tissue from an established atrial tachypacing canine model of AF. Whole protein lysates were collected from the atria to conduct mass spectrometry analysis showing dysregulation of numerous molecular pathways, including contractility. Skinned atrial cardiomyocytes were isolated from the tissue for force calcium and passive tension experiments. Force calcium experiments showed a significant reduction in the maximum force of contraction of AF cardiomyocytes. To explain this, myosin heavy chain (MHC) isoform expression was evaluated because isoform switching is known to alter force of contraction. Decreased percent beta expression was found, explaining the reduction of force due to MHC alpha's capacity for reduced force of contraction. AF cardiomyocytes showed increased calcium sensitivity of force development, which may translate to prolonged contraction with slower relaxation in vivo. A significant reduction in S100A1 was seen in the AF samples via mass spectrometry, which is associated with increased calcium sensitivity. Prolonged contraction along with reduced force of each contraction could support the development of atrial clots. Atrial cardiomyocytes from the AF hearts demonstrated a significant reduction in the passive tension. Evaluation of titin isoform expression, which is known to alter passive tension, showed increased titin degradation, supporting the capacity for atrial dilation in vivo. Discerning the role of contractility in the pathology of atrial fibrillation could provide novel avenues of AF treatment, especially in instances where it is associated with contractile diseases.

Regions of Highly Recurrent Electrogram Morphology With Low Cycle Length Reflect Substrate for Atrial Fibrillation

Traditional anatomically guided ablation and attempts to perform electrogram-guided atrial fibrillation (AF) ablation (CFAE, DF, and FIRM) have not been shown to be sufficient treatment for persistent AF. Using biatrial high-density electrophysiologic mapping in a canine rapid atrial pacing model of AF, we systematically investigated the relationship of electrogram morphology recurrence (EMR) (Rec% and CLR) with established AF electrogram parameters and tissue characteristics. Rec% correlates with stability of rotational activity and with the spatial distribution of parasympathetic nerve fibers. These results have indicated that EMR may therefore be a viable therapeutic target in persistent AF.

BS-400-37 TARGETED ATRIAL EXPRESSION OF NGF SHRNA ATTENUATES NEW PARASYMPATHETIC AND SYMPATHETIC NERVE SPROUTING AND RESULTING DEVELOPMENT OF PERSISTENT ATRIAL FIBRILLATION IN A CANINE MODEL - A NOVEL GENE THERAPY APPROACH TO ATRIAL FIBRILLATION

The autonomic nervous system plays an important role in development of atrial fibrillation (AF). We previously showed marked autonomic remodeling in a canine rapid atrial pacing (RAP) model of persistent AF. Nerve growth factor (NGF), a neurotrophin essential for the growth and survival of peripheral neurons, was upregulated in fibrillating atria. However, the role of NGF in the development of autonomic remodeling in AF remains to be demonstrated. To prevent autonomic remodeling and development of persistent AF in a canine RAP model of AF. NGF shRNA was injected in the atria of 8 dogs followed by electroporation to facilitate atrial gene delivery. The animals were then subjected to RAP for up to 12 weeks. Time to AF onset was determined. At the terminal EP study, episodes of AF were recorded with high-density mapping in the posterior left atrium (PLA), left atrial free wall (LAFW) and left atrial appendage (LAA) for offline analysis of AF characteristics. Tissue of each atrial region was harvested and used for immunohistochemistry with markers for parasympathetic (acetylcholinesterase, brown) or sympathetic nerves (dopamine beta-hydroxylase, blue). After initiation of RAP, control animals developed persistent atrial fibrillation (>8 hours) after a median of 14 days. In contrast, NGF shRNA animals never developed this burden of AF over the duration of the study. Residual AF recorded at time of terminal EP study was slower (lower dominant frequency; PLA: 10.5±0.8Hz Vs 11.0±0.7Hz; LAFW: 9.7±0.8Hz Vs 10.4±0.7Hz; LAA: 8.8±0.5Hz Vs 9.9±0.5Hz; two-way ANOVA p<0.001), less fractionated (longer fractionation interval; PLA: 80.4±8.1ms Vs 68.1±5.2ms; LAFW: 79.3±9.3ms Vs 70.9±3.1ms; LAA: 87.9±7.8ms Vs 80.3±2.0ms; two-way ANOVA p<0.001) and more organized (higher organization index and lower Shannon's entropy). Tissue analysis showed that RAP induced hypertrophy of nerve bundles was significantly attenuated in dogs receiving NGF shRNA. This decrease in bundle size was accompanied by a significant decrease in parasympathetic and sympathetic fibers in the atrial myocardium. Targeted inhibition of atrial autonomic remodeling by NGF shRNA prevents development of persistent AF. Future optimization of this approach may lead to a novel, mechanism-guided therapy for AF.

Site-directed deuteration of dronedarone preserves cytochrome P4502J2 activity and mitigates its cardiac adverse effects in canine arrhythmic hearts.

Cytochrome P4502J2 (CYP2J2) metabolizes arachidonic acid (AA) to cardioprotective epoxyeicosatrienoic acids (EETs). Dronedarone, an antiarrhythmic drug prescribed for treatment of atrial fibrillation (AF) induces cardiac adverse effects (AEs) with poorly understood mechanisms. We previously demonstrated that dronedarone inactivates CYP2J2 potently and irreversibly, disrupts AA-EET pathway leading to cardiac mitochondrial toxicity rescuable via EET enrichment. In this study, we investigated if mitigation of CYP2J2 inhibition prevents dronedarone-induced cardiac AEs. We first synthesized a deuterated analogue of dronedarone (termed poyendarone) and demonstrated that it neither inactivates CYP2J2, disrupts AA-EETs metabolism nor causes cardiac mitochondrial toxicity in vitro. Our patch-clamp experiments demonstrated that pharmacoelectrophysiology of dronedarone is unaffected by deuteration. Next, we show that dronedarone treatment or CYP2J2 knockdown in spontaneously beating cardiomyocytes indicative of depleted CYP2J2 activity exacerbates beat-to-beat (BTB) variability reflective of proarrhythmic phenotype. In contrast, poyendarone treatment yields significantly lower BTB variability compared to dronedarone in cardiomyocytes indicative of preserved CYP2J2 activity. Importantly, poyendarone and dronedarone display similar antiarrhythmic properties in the canine model of persistent AF, while poyendarone substantially reduces beat-to-beat variability of repolarization duration suggestive of diminished proarrhythmic risk. Our findings prove that deuteration of dronedarone prevents CYP2J2 inactivation and mitigates dronedarone-induced cardiac AEs.

In vivo and cellular antiarrhythmic and cardiac electrophysiological effects of desethylamiodarone in dog cardiac preparations.

The aim of the present study was to study the antiarrhythmic effects and cellular mechanisms of desethylamiodarone (DEA), the main metabolite of amiodarone (AMIO), following acute and chronic 4-week oral treatments (25-50 mg·kg-1 ·day-1 ). The antiarrhythmic effects of acute iv. (10 mg·kg-1 ) and chronic oral (4 weeks, 25 mg·kg-1 ·day-1 ) administration of DEA were assessed in carbachol and tachypacing-induced dog atrial fibrillation models. Action potentials were recorded from atrial and right ventricular tissue following acute (10 μM) and chronic (p.o. 4 weeks, 50 mg·kg-1 ·day-1 ) DEA application using the conventional microelectrode technique. Ionic currents were measured by the whole cell configuration of the patch clamp technique in isolated left ventricular myocytes. Pharmacokinetic studies were performed following a single intravenous dose (25 mg·kg-1 ) of AMIO and DEA intravenously and orally. In chronic (91-day) toxicological investigations, DEA and AMIO were administered in the oral dose of 25 mg·kg-1 ·day-1 ). DEA exerted marked antiarrhythmic effects in both canine atrial fibrillation models. Both acute and chronic DEA administration prolonged action potential duration in atrial and ventricular muscle without any changes detected in Purkinje fibres. DEA decreased the amplitude of several outward potassium currents such as IKr , IKs , IK1 , Ito , and IKACh , while the ICaL and late INa inward currents were also significantly depressed. Better drug bioavailability and higher volume of distribution for DEA were observed compared to AMIO. No neutropenia and less severe pulmonary fibrosis was found following DEA compared to that of AMIO administration. Chronic DEA treatment in animal experiments has marked antiarrhythmic and electrophysiological effects with better pharmacokinetics and lower toxicity than its parent compound. These results suggest that the active metabolite, DEA, should be considered for clinical trials as a possible new, more favourable option for the treatment of cardiac arrhythmias including atrial fibrillation.

Dietary ω-3 fatty acids reduced atrial fibrillation vulnerability via attenuating myocardial endoplasmic reticulum stress and inflammation in a canine model of atrial fibrillation

BackgroundDietary consumption of ω-3 fatty acids is correlated with a reduced incidence of cardiovascular events. Here, we investigated the effect of dietary ω-3 fatty acids on atrial fibrillation (AF) vulnerability in a canine model of AF and explored the related mechanisms. MethodsTwenty four male beagle dogs (weight, 8-10 kg) were randomly divided into four groups: (a) sham-operated group (normal chow); (b) AF+FO [AF and normal chow supplemented with fish oil (FO): 0.6 g n-3 polyunsaturated fatty acids (ω-3 PUFA) /kg/day]; (c) AF group (normal chow); (d) sham-operated FO group (chow supplemented with FO: 0.6 g ω-3 PUFA/kg/day). AF was induced by rapid atrial pacing (RAP: 400 bpm for 4 weeks). Daily oral administration of FO was initiated 1 week before surgery and continued for 4 weeks post operation. ResultsAtrial electric remodeling was significantly attenuated and AF vulnerability were significantly reduced in AF+FO group compared to AF group. Endoplasmic reticulum (ER) stress-related protein expression levels of glucose-regulated protein78, C/EBP homologous protein, cleaved-Caspase12, and phosphorylation of protein kinase R-like ER kinase as well as inflammatory cytokines interleukin-1β, interleukin-6, tumor necrosis factor-α in left atrium (LA) were significantly downregulated in AF+FO group than in AF group (all p<0.05). In addition, Masson staining revealed lower extent of LA interstitial fibrosis in AF+FO group than in AF group (p<0.01). Myocardial apoptosis was also significantly reduced in AF+FO group than in AF group (p<0.05). ConclusionsDietary ω-3 fatty acids could significantly reduce RAP-induced AF vulnerability, possibly via attenuating myocardial ER stress, inflammation, and apoptosis in this canine model of AF.

Correction to: Transcriptomic Profiling of Canine Atrial Fibrillation Models After One Week of Sustained Arrhythmia.

Correction to: Transcriptomic Profiling of Canine Atrial Fibrillation Models After One Week of Sustained Arrhythmia.

B-PO04-078 DRIVING MECHANISMS IN PERSISTENT ATRIAL FIBRILLATION DEMONSTRATE MULTI-MONTH STABILITY IN A CANINE MODEL

Previous studies suggest persistent atrial fibrillation (AF) is maintained by focused mechanisms, or drivers, outside the pulmonary veins. Single mapping sessions during AF to locate drivers for ablation have had limited success in improving over pulmonary vein isolation. Little is known about the development of drivers over time, but this development may explain current difficulties in driver-based ablation. To characterize the development of drivers in a canine model of persistent AF. We captured high-density left atrial voltage maps from a rapid-paced canine paced model of persistent AF (n=9, 1 yr. mongrel, 29±3 kg). To assess the progression of AF with time, we conducted these mapping sessions at 1, 3, and 6 months post-implant during AF using an Orion catheter and the Rhythmia mapping system (Boston Scientific). The mapping catheter was held at sites distributed in the atrium for 4 minutes each, such that the entire substrate was well covered. We examined each site for the existence of stable focal and reentrant mechanisms as guided by dominant frequency maps. For each mapping session, we measured 15.5±3.7 sites (n=357) and found an average of 1.9±0.8 drivers (n=39). ANOVA analysis showed the mean number of drivers to be stable over time (p=0.004). While duration of AF is associated with remodeling of the atrial substrate, these results support the surprising finding that the number of active drivers remains stable from the first month through at least 6 months of paced AF. This is promising for ablation as it shows a limited number of driving sites for treatment even as AF develops.

Transcriptomic Profiling of Canine Atrial Fibrillation Models After One Week of Sustained Arrhythmia.

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Effect of obesity and epicardial fat/fatty infiltration on electrical and structural remodeling associated with atrial fibrillation in a novel canine model of obesity and atrial fibrillation: A comparative study.

How obesity and epicardial fat influence atrial fibrillation (AF) is unknown. To investigate the effect of obesity/epicardial fat on the AF substrate, we divided 20 beagle dogs of normal weight into four groups (n = 5 each): one of the four groups (Obese-rapid atrial pacing [RAP] group) served as a novel canine model of obesity and AF. The other three groups comprised dogs fed a standard diet without RAP (Control group), dogs fed a high-fat diet without RAP (Obese group), or dogs fed a standard diet with RAP (RAP group). All underwent electrophysiology study, and hearts were excised for histopathologic and fibrosis-related gene expression analyses. Left atrial (LA) pressure was significantly higher in the Obese group than in the Control, RAP, and Obese-RAP groups (23.4 ± 6.9 vs. 11.4 ± 2.1, 11.9 ± 6.4, and 13.5 ± 2.9 mmHg; p = .005). The effective refractory period of the inferior PV was significantly shorter in the RAP and Obese-RAP groups than in the Control group (p = .043). Short-duration AF was induced at greatest frequency in the Obese-RAP and Obese groups (p < .05). Epicardial fat/Fatty infiltration was greatest in the Obese-RAP group, and greater in the Obese and RAP groups than in the Control group. %interstitial fibrosis/fibrosis-related gene expression was significantly greater in the Obese-RAP and RAP groups (p < .05). Vulnerability to AF was associated with increased LA pressure and increased epicardial fat/fatty infiltration in our Obese group, and with increased epicardial fat/fibrofatty infiltration in the RAP and Obese-RAP groups. These may explain the role of obesity/epicardial fat in the pathogenesis of AF.

Canagliflozin Suppresses Atrial Remodeling in a Canine Atrial Fibrillation Model

BackgroundRecent clinical trials have demonstrated the possible pleiotropic effects of SGLT2 (sodium–glucose cotransporter 2) inhibitors in clinical cardiovascular diseases. Atrial electrical and structural remodeling is important as an atrial fibrillation (AF) substrate.Methods and ResultsThe present study assessed the effect of canagliflozin (CAN), an SGLT2 inhibitor, on atrial remodeling in a canine AF model. The study included 12 beagle dogs, with 10 receiving continuous rapid atrial pacing and 2 acting as the nonpacing group. The 10 dogs that received continuous rapid atrial pacing for 3 weeks were subdivided as follows: pacing control group (n=5) and pacing+CAN (3 mg/kg per day) group (n=5). The atrial effective refractory period, conduction velocity, and AF inducibility were evaluated weekly through atrial epicardial wires. After the protocol, atrial tissues were sampled for histological examination. The degree of reactive oxygen species expression was evaluated by dihydroethidium staining. The atrial effective refractory period reduction was smaller (P=0.06) and the degree of conduction velocity decrease was smaller in the pacing+CAN group compared with the pacing control group (P=0.009). The AF inducibility gradually increased in the pacing control group, but such an increase was suppressed in the pacing+CAN group (P=0.011). The pacing control group exhibited interstitial fibrosis and enhanced oxidative stress, which were suppressed in the pacing+CAN group.ConclusionsCAN and possibly other SGLT2 inhibitors might be useful for preventing AF and suppressing the promotion of atrial remodeling as an AF substrate.

Deep Learning Based Prediction of Atrial Fibrillation Disease Progression with Endocardial Electrograms in a Canine Model.

We sought to determine whether electrical patterns in endocardial wavefronts contained elements specific to atrial fibrillation (AF) disease progression. A canine paced model (n=7, female mongrel, 29±2 kg) of persistent AF was endocardially mapped with a 64-electrode basket catheter during periods of AF at 1 month, 3 month, and 6 months post-implant of stimulator. A 50-layer residual network was then trained to map half-second electrogram samples to their source timepoint. The trained network achieved final validation and testing accuracies of 51.6 and 48.5% respectively. Per class F1 scores were 24%, 59%, and 53% for 1 month, 3 month, and 6 month inputs from the testing dataset. Differentiation of AF based on its time progression was shown to be feasible with a deep learning method. This is promising for differentiating treatment based on disease progression though low accuracy with earlier timepoints may be an obstacle to identifying nascent AF.

Identification of two preclinical canine models of atrial fibrillation to facilitate drug discovery

Atrial fibrillation (AF) is the most common arrhythmia occurring in humans, and new treatment strategies are critically needed. The lack of reliable preclinical animal models of AF is a major limitation to drug development of novel antiarrhythmic compounds. The purpose of this study was to provide a comprehensive head-to-head assessment of 5 canine AF models. Five canine models were evaluated for the efficacy of AF induction and AF duration. We tested 2 acute models: short-term atrial tachypacing (AT) for 6 hours with analysis of AF at hourly increments, and carbachol injection into a cardiac fat pad followed by short-term AT. We also tested 3 chronic models: pacemaker implantation followed by either 4 weeks of AT and subsequent atrial burst pacing or intermittent long-term AT for up to 4-5 months to generate AF ≥4.5 hours, and finally ventricular tachypacing to induce heart failure followed by atrial burst pacing to induce AF. Careful evaluation showed that acute AT, AT for 4 weeks, and the heart failure model all were unsuccessful in generating reproducible AF episodes of sufficient duration to study antiarrhythmic drugs. In contrast, intermittent long-term AT generated AF lasting ≥4.5 hours in ∼30% of animals. The acute model using carbachol and short-term AT resulted in AF induction of ≥15 minutes in ≥75% of animals, thus enabling testing of antiarrhythmic drugs. Intermittent long-term AT and the combination of local carbachol injection with successive short-term AT may contribute to future drug development efforts for AF treatment.

Antiarrhythmic and cardiac electrophysiological effects of SZV-270, a novel compound with combined Class I/B and Class III effects, in rabbits and dogs.

Cardiovascular diseases are the leading causes of mortality. Sudden cardiac death is most commonly caused by ventricular fibrillation (VF). Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and a major cause of stroke and heart failure. Pharmacological management of VF and AF remains suboptimal due to limited efficacy of antiarrhythmic drugs and their ventricular proarrhythmic adverse effects. In this study, the antiarrhythmic and cardiac cellular electrophysiological effects of SZV-270, a novel compound, were investigated in rabbit and canine models. SZV-270 significantly reduced the incidence of VF in rabbits subjected to coronary artery occlusion/reperfusion and reduced the incidence of burst-induced AF in a tachypaced conscious canine model of AF. SZV-270 prolonged the frequency-corrected QT interval, lengthened action potential duration and effective refractory period in ventricular and atrial preparations, blocked I Kr in isolated cardiomyocytes (Class III effects), and reduced the maximum rate of depolarization (V max) at cycle lengths smaller than 1000ms in ventricular preparations (Class I/B effect). Importantly, SZV-270 did not provoke Torsades de Pointes arrhythmia in an anesthetized rabbit proarrhythmia model characterized by impaired repolarization reserve. In conclusion, SZV-270 with its combined Class I/B and III effects can prevent reentry arrhythmias with reduced risk of provoking drug-induced Torsades de Pointes.

Effects of subcutaneous nerve stimulation with blindly inserted electrodes on ventricular rate control in a canine model of persistent atrial fibrillation

Subcutaneous nerve stimulation (ScNS) delivered directly to large subcutaneous nerves can be either antiarrhythmic or proarrhythmic, depending on the stimulus output. The purpose of this study was to perform a prospective randomized study in a canine model of persistent AF to test the hypothesis that high-output ScNS using blindly inserted subcutaneous electrodes can reduce ventricular rate (VR) during persistent atrial fibrillation (AF) whereas low-output ScNS would have opposite effects. We prospectively randomized 16 male and 15 female dogs with sustained AF (>48 hours) induced by rapid atrial pacing into 3 groups (sham, 0.25 mA, 3.5 mA) for 4 weeks of ScNS (10 Hz, alternating 20-seconds ON and 60-seconds OFF). ScNS at 3.5 mA, but not 0.25 mA or sham, significantly reduced VR and stellate ganglion nerve activity (SGNA), leading to improvement of left ventricular ejection fraction (LVEF). No differences were found between the 0.25-mA and sham groups. Histologic studies showed a significant reduction of bilateral atrial fibrosis in the 3.5-mA group compared with sham controls. Only 3.5-mA ScNS had significant fibrosis in bilateral stellate ganglions. The growth-associated protein 43 (GAP43) staining of stellate ganglions indicated the suppression of GAP43 protein expression in the 3.5-mA group. There were no significant differences of nerve sprouting among all groups. There was no interaction between sex and ScNS effects on reduction of VR and SGNA, LVEF improvement, or results of histologic studies. We conclude that 3.5-mA ScNS with blindly inserted electrodes can improve VR control, reduce atrial fibrosis, and partially improve LVEF in a canine model of persistent AF.

Reconsidering the multiple wavelet hypothesis of atrial fibrillation

Moe and Abildskov proposed the multiple wavelet hypothesis of atrial fibrillation (AF) on the basis of observations in the canine vagal nerve stimulation (VNS) AF model. Data from mapping studies in an invitro canine AF model by Allessie etal (Allessie MA, Lammers WJEP, Bonke FIM, Hollen SJ. Experimental evaluation of Moe's multiple wavelet hypothesis of atrial fibrillation. In: Zipes DP, Jalife J, eds. Cardiac Electrophysiology and Arrhythmias. Orlando, FL: Grune & Stratton; 1985:265-275.) were used to evaluate the Moe/Abildskov hypothesis, which revealed that a critical number of wavelets sustained AF. The purpose of this study was to reassess VNS mapping data using the same methods used by Allessie to evaluate Moe's multiple wavelet hypothesis. Using the canine VNS AF model in 6 dogs, 510 unipolar atrial electrograms were recorded simultaneously from both atria. Activation sequence maps were produced from sustained AF during VNS in each dog. Per Allessie, consecutive 10 ms activation windows were analyzed over a period of 300 ms. Repetitive activation analysis was applied to Moe's canine VNS AF model. The number of wavefronts in each AF episode was 0-8 in Allessie's studies measured by sequential atrial mapping and 0-10 in our biatrial simultaneous mapping studies. In both studies, an electrically silent period was observed in each atrium and was reactivated by wavefronts emanating from focal sources. Allessie postulated that an electrically silent atrium was reactivated by a wavefront propagating from the other atrium. However, in our biatrial simultaneous mapping studies, each electrically silent atrium was reactivated by a distinct focal source. Data from both studies showed a similar number of wavefronts, similar AF activation patterns, and periods of electrical atrial silence reactivated by focal sources. Also, in our studies, independent focal sources initiated wavefronts reactivating the atria, thereby explaining the mechanism maintaining AF.

Metformin regulates adiponectin signalling in epicardial adipose tissue and reduces atrial fibrillation vulnerability

Epicardial adipose tissue (EAT) remodelling is closely related to the pathogenesis of atrial fibrillation (AF). We investigated whether metformin (MET) prevents AF‐dependent EAT remodelling and AF vulnerability in dogs. A canine AF model was developed by 6‐week rapid atrial pacing (RAP), and electrophysiological parameters were measured. Effective refractory periods (ERP) were decreased in the left and right atrial appendages as well as in the left atrium (LA) and right atrium (RA). MET attenuated the RAP‐induced increase in ERP dispersion, cumulative window of vulnerability, AF inducibility and AF duration. RAP increased reactive oxygen species (ROS) production and nuclear factor kappa‐B (NF‐κB) phosphorylation; up‐regulated interleukin‐6 (IL‐6), tumour necrosis factor‐α (TNF‐α) and transforming growth factor‐β1 (TGF‐β1) levels in LA and EAT; decreased peroxisome proliferator‐activated receptor gamma (PPARγ) and adiponectin (APN) expression in EAT and was accompanied by atrial fibrosis and adipose infiltration. MET reversed these alterations. In vitro, lipopolysaccharide (LPS) exposure increased IL‐6, TNF‐α and TGF‐β1 expression and decreased PPARγ/APN expression in 3T3‐L1 adipocytes, which were all reversed after MET administration. Indirect coculture of HL‐1 cells with LPS‐stimulated 3T3‐L1 conditioned medium (CM) significantly increased IL‐6, TNF‐α and TGF‐β1 expression and decreased SERCA2a and p‐PLN expression, while LPS + MET CM and APN treatment alleviated the inflammatory response and sarcoplasmic reticulum Ca2+ handling dysfunction. MET attenuated the RAP‐induced increase in AF vulnerability, remodelling of atria and EAT adipokines production profiles. APN may play a key role in the prevention of AF‐dependent EAT remodelling and AF vulnerability by MET.

Regions of High Dominant Frequency in Chronic Atrial Fibrillation Anchored to Areas of Atrial Fibrosis.

Regions within the atria with sustained rapid reentrant or focal activity have been defined as a mechanism of persistent atrial fibrillation (AF). However, the mechanism behind the anchoring of these sites and their stability over time is unknown. We tested the hypothesis that fibrosis anchors sites of high frequency activation during AF and that these sites can be non-invasively determined using cardiac T1 Mapping with MRI. A canine rapid atrial paced model of persistent AF was used (n=12, including 6 controls) for the study. Whole heart T1 Mapping was performed prior to an electrical mapping study. Spatial maps of high dominant frequency (DF) probability were constructed to determine stability of the highest DF sites. These sites were then correlated with fibrotic regions determined by T1 Mapping. The chronic AF animals had at least one site of stable, high DF for at least 22.5 (75%) of 30 minutes of AF. Regions of stable high DF bordered regions of fibrosis as determined by T1 Mapping MRI 82% of the time (p<0.05). Heterogeneous atrial remodeling, specifically fibrosis, arising from chronic AF may provide a substrate that anchors sites of high DF. Cardiac T1 Mapping with MRI may determine such sites non-invasively.

Changes in atrial electrophysiological and structural substrate and their relationship to histology in a long-term chronic canine atrial fibrillation model.

Atrial fibrillation (AF) is related to numerous electrophysiological changes; however, the extent of structural and electrophysiological remodeling with long-term AF is not well characterized. Dogs (n=6) were implanted with a neurostimulator in the right atrium (AF group). No implantation was done in the Control group (n=3). Electroanatomical mapping was done prior to and following more than 6 months of AF. Magnetic resonance imaging was also done to assess structural remodeling. Animals were euthanized and tissue samples were acquired for histological analysis. A significant increase was seen in the left atrial (LA) volume among all AF animals (22.25 ± 12.60 cm3 vs 34.00 ± 12.23 cm3 , P=.01). Also, mean bipolar amplitude in the LA significantly decreased from 5.96 ± 2.17mV at baseline to 3.23 ± 1.51mV (P<.01) after chronic AF. Those significant changes occurred in each anterior, lateral, posterior, septal, and roof regions as well. Additionally, the dominant frequency (DF) in the LA increased from 7.02 ± 0.37Hz to 10.12 ± 0.28Hz at chronic AF (P<.01). Moreover, the percentage of fibrosis in chronic AF animals was significantly larger than that of control animals in each location (P<.01). Canine chronic AF is accompanied by a significant decrease in intracardiac bipolar amplitudes. These decreased electrogram amplitude values are still higher than traditional cut-off values used for diseased myocardial tissue. Despite these "normal" bipolar amplitudes, there is a significant increase in DF and tissue fibrosis.

Metformin regulates lipid metabolism in a canine model of atrial fibrillation through AMPK/PPAR-\u03b1/VLCAD pathway

BackgroundAtrial lipid metabolic remodeling is critical for the process of atrial fibrillation (AF). Abnormal Fatty acid (FA) metabolism in cardiomyocytes is involved in the pathogenesis of AF. MET (Metformin), an AMPK (AMP-activated protein kinase) activator, has been found to be associated with a decreased risk of AF in patients with type 2 diabetes. However, the specific mechanism remains unknown.MethodsFifteen mongrel dogs were divided into three groups: SR, ARP (pacing with 800 beats/min for 6 h), ARP plus MET (treated with MET (100 mg/kg/day) for two weeks before pacing). We assessed metabolic factors, speed limiting enzymes circulating biochemical metabolites (substrates and products), atrial electrophysiology and accumulation of lipid droplets.ResultsThe expression of AMPK increased in the ARP group and significantly increased in the MET+ARP group comparing to the SR group. In the ARP group, the expressions of PPARα、PGC-1α and VLCAD were down-regulated, while the concentration of free fatty acid and triglyceride and the lipid deposition in LAA (left atrial appendage) increased. Moreover, AERP and AERPd have also been found abnormally in this process. Pretreatment with MET before receiving ARP reversed the alterations aforementioned.ConclusionsThe FA metabolism in LAA is altered in the ARP group, mainly characterized by the abnormal expression of the rate-limiting enzyme. Metformin reduces lipid accumulation and promotes β-oxidation of FA in AF models partially through AMPK/PPAR-α/VLCAD pathway. Our study indicates that MET may inhibit the FA lipid metabolic remodeling in AF.