Atrial Fibrillation In Dogs Research Articles

Effects of SZV-2649, a new multiple ion channel inhibitor mexiletine analogue

The antiarrhythmic and cardiac electrophysiological effects of SZV-2649 that contains a 2,6-diiodophenoxy moiety but lacks the benzofuran ring system present in amiodarone, were studied in mammalian cell line, rat and dog cardiac preparations. SZV-2649 exerted antiarrhythmic effects against coronary artery occlusion/reperfusion induced ventricular arrhythmias in rats and in acetylcholine- and burst stimulation induced atrial fibrillation in dogs. SZV-2649 inhibited hERG and GIRK currents in HEK cells (IC50: 342 and 529 nM, respectively). In canine ventricular myocytes, SZV-2649 (10 µM) decreased the densities of IKr, and Ito outward and INaL and ICaL inward currents. The compound (2.5–10 µM) elicited Class IB type Vmax reducing and Class III type action potential duration prolonging effects in dog right ventricular muscle preparations. In canine atrial muscle, SZV-2629 (2.5–10 µM) moderately prolonged action potential duration and this effect was greatly augmented in preparations pretreated with 1 µM carbachol. In conclusion, SZV-2649, has antiarrhythmic effects based on its multiple ion channel blocking properties. Since its chemical structure substantially differs from that of amiodarone, it is expected that SZV-2649 would exhibit fewer adverse effects than the currently used most effective multichannel inhibitor drug amiodarone and may be a promising molecule for further development.

Evaluation of Galectin-3 in Dogs with Atrial Fibrillation.

Galectin-3 (Gal-3) is a lectin associated with fibrosis and inflammation, and increased circulating concentrations are considered a risk factor for atrial fibrillation (AF) in humans. This retrospective study aimed to evaluate the serum concentration of Gal-3 in dogs with cardiac disease, both with and without AF. Dogs with AF associated with acquired heart diseases were selected, while cardiac healthy dogs and dogs with heart diseases but without AF served as controls. We statistically compared the serum concentration of Gal-3, which was assessed using a commercial canine-specific ELISA kit, among healthy dogs and dogs with heart disease with and without AF. Additionally, associations between Gal-3 and clinical and echocardiographic variables were evaluated. A total of 73 dogs were included, of which 17/73 (23.3%) were cardiac healthy and 56/73 (76.7%) had heart disease, with 26/56 (46.4%) having AF. No significant difference in Gal-3 concentration was found between cardiac healthy dogs (3.90 ± 1.65 ng/mL) and dogs with heart disease, either with or without AF (3.37 ± 1.04 ng/mL, p = 0.436 and 4.68 ± 1.80 ng/mL, p = 0.332, respectively). Gal-3 showed a significant positive correlation with age (r = 0.47, p < 0.001) and a negative correlation with body weight (r = -0.45, p < 0.001). The results of this study suggest that Gal-3 does not have an important role in the development of AF in dogs, but it is associated with advanced age.

Risk Factors for Atrial Fibrillation in the Dog: A Systematic Review.

Different risk factors for atrial fibrillation (AF) development have been identified in numerous studies on humans, but this information is less clearly available on the dog. The aim of this systematic review is to determine the risk factors for AF in the dog. Following the PRISMA 2020 guidelines, we conducted a comprehensive search using the Web of Science and Scopus databases for articles reporting on cases of spontaneously occurring AF in dogs. The level of evidence was assessed using the Evidence Quality Grading System of the National Institute of Health. One thousand forty-three studies were initially identified, and twenty of them were included in this systematic review involving 2,359,275 dogs, of which 4807 showed spontaneously occurring AF. Genetics, for the Irish Wolfhound, increased body weight, and left atrial enlargement were the main risk factors for the development of AF in dogs with different cardiac diseases, particularly myxomatous mitral valve disease (MMVD) and dilated cardiomyopathy (DCM). However, some differences were found between these two cardiac diseases regarding additional risk factors. In particular, the presence of congestive heart failure and echocardiographic evidence of increased left atrial pressure or the presence of right atrial enlargement emerged as risk factors in dogs with MMVD or DCM, respectively. Furthermore, significant differences in risk factors were observed between dogs and humans. In particular, advanced age and male sex are not reliable indicators of an increased risk of AF in dogs.

Mechanisms by which spinal cord stimulation intervenes in atrial fibrillation: The involvement of the endothelin-1 and nerve growth factor/p75NTR pathways.

Can the spinal cord stimulation (SCS) regulate the autonomic nerves through the endothelin-1 (ET-1) and nerve growth factor (NGF)/p75NTR pathways and thus inhibit the occurrence of atrial fibrillation (AF)? In our research, 16 beagles were randomly divided into a rapid atrial pacing (RAP) group (n = 8) and a RAP + SCS group (n = 8), and the effective refractory period (ERP), ERP dispersion, AF induction rate, and AF vulnerability window (WOV) at baseline, 6 h of RAP, 6 h of RAP + SCS were measured. The atrial tissue was then taken for immunohistochemical analysis to determine the localization of ET-1, NGF, p75NTR, NF-kB p65, and other genes. Our results showed that SCS attenuated the shortening of ERP in all parts caused by RAP, and after 6 h of SCS, the probability of AF in dogs was reduced compared with that in the RAP group. Moreover, the expression of ET-1, NGF, and p75NTR in the atrial tissues of dogs in the RAP + SCS group was significantly increased, but the expression of NF-kB p65 was reduced. In conclusion, SCS promotes the positive remodeling of cardiac autonomic nerves by weakening NFκB p65-dependent pathways to interfere with the ET-1 and NGF/p75NTR pathways to resist the original negative remodeling and inhibit the occurrence of AF.

Risk factors for atrial fibrillation in dogs with dilated cardiomyopathy.

Atrial fibrillation secondary to dilated cardiomyopathy (DCM) frequently affects large-breed dogs. The aim of the present study was to identify risk factors for the development of atrial fibrillation in dogs of different breeds with an echocardiographic diagnosis of DCM. In this multicenter retrospective study, we searched the electronic databases of five cardiology referral centers for dogs with an echocardiographic diagnosis of DCM. A comparison of clinical and echocardiographic variables was performed between dogs developing atrial fibrillation and those not developing atrial fibrillation and the ability to distinguish between these two groups of dogs was evaluated by receiver operating characteristic curve analysis. Univariate and multivariable logistic regression analysis estimated the odds ratio (OR) with 95% confidence interval (CI) of developing atrial fibrillation. We included 89 client-owned dogs with occult and overt echocardiographic DCM. Of these, 39 dogs (43.8%) had atrial fibrillation, 29 dogs (32.6%) maintained a sinus rhythm, and 21 dogs (23.6%) showed other cardiac arrhythmias. Left atrial diameter had high accuracy (area under the curve = 0.816, 95% CI = 0.719-0.890) to predict the development of atrial fibrillation at the cut-off of >4.66 cm. After multivariable stepwise logistic regression analysis, only increased left atrial diameter (OR = 3.58, 95% CI = 1.87-6.87; p < 0.001) and presence of right atrial enlargement (OR = 4.02, 95% CI = 1.35-11.97; p = 0.013) were significant predictors of atrial fibrillation development. Atrial fibrillation is a common complication of DCM in the dog and is significantly associated with increased absolute left atrial diameter and right atrial enlargement.

Aging-induced atrial fibrosis in If current change and its effect on atrial fibrillation in dogs.

BackgroundAtrial fibrillation (AF) is a very common type of cardiac arrhythmia that threatens public health. Aging is an independent AF risk factor. However, the mechanism of age‐related AF remains unclear.MethodsA total of 36 Beagle dogs were selected and divided into three groups (12 in each group): two groups were 9‐year‐old aged dogs, and one group was 4‐year‐old adult dogs. Electrophysiological testing was employed to determine if modeling is successful. Patch‐clamp technique was employed to measure the If current. The expression of protein and mRNA related to If current were also tested. Collagen deposition was observed with the use of Masson staining.ResultsAging resulted in a higher collagen deposition percentage in the left atrium. The hyperpolarization‐activated cyclic nucleotide‐gated (HCN)2 and HCN4 expressions were increased in the atria and pulmonary veins but decreased in the sinus node of the aged group. Moreover, in the aged group, the left atrium mRNA expressions of Kcnd2 (Potassium voltage‐gated channel subfamily D member 2), Kcnh2, Kcnq1, Kcnj2, Kcnj11, and CACNA1H were significantly downregulated. The aged AF group also demonstrated sustained AF and significant changes in electrophysiological characteristics. The If current demonstrated an increased amplitude and was easier to activate in the aged AF group than in younger group. Finally, AF occurrence exacerbated aging‐induced cardiac fibrosis, thereby aggravating the above‐listed symptoms.ConclusionWith age, the increase in atrial fibrosis affected the expression of the ion channels, thereby modulating the If current. Moreover, AF also further exacerbated the degree of atrial fibrosis.

Serum digoxin concentrations in dogs with atrial fibrillation under long term digoxin treatment.

Background:Atrial fibrillation (AF) is the most common arrhythmia in dogs, most frequently diagnosed as chronic AF associated with a structural heart disease. The therapeutic strategy, in these cases, is based on the heart rate control and digoxin is one of the most used drugs.Aim:The aim of this work was to study the serum digoxin concentration changes in dogs with AF under long-term treatment with digoxin. Furthermore, the remission of clinical signs and the correlation between digoxinemia and other clinical and laboratory variables were retrospectively evaluated.Methods:The prospective study was conducted on seven large breed dogs from the time of reaching the definitive digoxin dosage. Digoxinemia was determined at month: 1, 3, 6, 9, 12, then twice a year. A post hoc statistical analysis investigated the influence of selected clinical and laboratory variables on the risk to develop spikes in digoxinemia. Clinical data, heart rate, digoxin dosage (mg/m2), and digoxinemia (ng/ml) at all available follow-ups were retrospectively evaluated from the medical records of 17 further dogs and a linear regression analysis was performed on the whole data set. The relation between the time of remission of AF clinical signs and variables was also investigated.Results:An unexpected increase in digoxin serum concentration was recorded in three dogs after one year monitoring, in absence of digoxin dosage changes. No statistical significance of all the studied variables on the risk to develop spikes of digoxinemia was registered. Two dogs, reaching digoxinemia 4.46 and 5.24 ng/ml, showed symptoms that reversed after digoxin withdrawal. From retrospective data, 88% of dogs reached complete reverse of AF clinical signs in 2.1 months from digoxin treatment starting, regardless of digoxin initial dosage, digoxinemia, and heart rate.Conclusion:Digoxin in monotherapy remain a good option to treat AF in dogs, anyway digoxin toxicity could emerge during long-term therapy, similarly to what happen in human medicine. Life-threatening spikes of digoxinemia could occur, especially after 1-year treatment with digoxin. It is very important that practitioners be aware of this possibility and encourage the owners to monitor digoxinemia during long-term treatment to avoid dangerous and toxic effects.

Pulsed Wave Doppler Echocardiographic Evaluation and Management of Atrial Fibrillation in Dogs with Dilated Cardiomyopathy

Pulsed Wave Doppler Echocardiographic Evaluation and Management of Atrial Fibrillation in Dogs with Dilated Cardiomyopathy

Prevalence and risk factors for atrial fibrillation in dogs with myxomatous mitral valve disease.

BackgroundAtrial fibrillation (AF) is a common supraventricular arrhythmia more frequently observed in large breed dogs.ObjectivesEstimate the prevalence of AF in dogs with myxomatous mitral valve disease (MMVD) and identify risk factors for developing AF.AnimalsA total of 2194 client‐owned dogs with MMVD, including 1280, 588, 290, and 36 dogs in ACVIM stages B1, B2, C, and D, respectively.MethodsRetrospective, cross‐sectional study. The medical databases of 3 veterinary teaching hospitals were reviewed. Inclusion criteria were a diagnosis of MMVD after complete cardiovascular evaluation and cardiac rhythm assessment using routine 2‐minute ECG or good quality ECG tracing during echocardiographic examination.ResultsAtrial fibrillation was diagnosed in 59 dogs with a prevalence of 2.7%. Univariate analysis showed that mixed breed, male sex, advanced ACVIM stage, left atrial and ventricular enlargement, fractional shortening (FS), and presence of pulmonary hypertension were significantly associated with development of AF. According to 2 multivariable models, the left atrium (LA)‐to‐aorta ratio (odds ratio [OR] = 14.011, 7.463‐26.304), early trans‐mitral velocity (OR = 2.204, 1.192‐4.076), body weight (OR = 1.094, 1.058‐1.130), and FS (OR = 0.899, 0.865‐0.934) and LA (OR = 5.28, 3.377‐8.092), advanced ACVIM stage (OR = 4.922, 1.481‐16.353), and FS (OR = 0.919, 0.881‐0.959) were significant predictors of AF for models 1 and 2, respectively.Conclusions and Clinical ImportanceAtrial fibrillation is an uncommon complication of MMVD and is significantly associated with the more advanced stage of the disease, increased LA dimension and body weight, and decreased FS.

Diagnosis and management of canine atrial fibrillation

Atrial fibrillation (AF) is the most common non-physiological arrhythmia in dogs and humans. Its high prevalence in both species and the impact it has on survival time and quality of life of affected patients, makes it a very relevant topic for medical research. In dogs, the diagnosis of AF is usually fairly straightforward, but optimal management can be complicated. Rate control is the most commonly used strategy; rhythm control can also be considered in very specific cases. Concurrent congestive heart failure is frequently identified, which represents an extra challenge for the clinicians. This article reviews the current recommendations for the diagnosis and management considerations of AF in dogs. Future perspectives, focusing on new drugs that may prevent development of AF based on recent discoveries, will also be discussed.

Echocardiographic predictors of first onset of atrial fibrillation in dogs with myxomatous mitral valve disease.

BackgroundAtrial fibrillation (AF) occurs in dogs with myxomatous mitral valve disease (MMVD) as a consequence of left atrial (LA) dilatation, and it affects survival and quality of life.ObjectivesTo evaluate the usefulness of echocardiography in predicting the first occurrence of AF in dogs with MMVD.AnimalsForty‐four client‐owned dogs with MMVD, 22 dogs that developed AF, and 22 dogs that maintained sinus rhythm.MethodsRetrospective observational study. Medical databases were reviewed for dogs that developed AF during the year after diagnosis of MMVD (AF group). The last echocardiographic examination obtained while still in sinus rhythm was used to derive selected variables. For each dog with AF, a control dog matched for body weight, class of heart failure, and LA dimension was selected. Echocardiographic results including LA volumes and LA speckle tracking echocardiography (STE)‐derived variables were measured.ResultsAmong the tested echocardiographic variables, only LA diameter (P = .03) and left ventricular internal diameter in diastole (P = .03) differed significantly between groups, whereas body weight‐indexed variables of cardiac dimension as well as LA volumes and volume‐derived functional variables were not different. Among the STE‐derived variables, peak atrial longitudinal strain (PALS) results differed significantly between the AF group (23.8% ± 8.6%) and the control group (30.5% ± 9.6%; P = .03). A value of PALS ≤28% predicted AF occurrence with sensitivity and specificity of 0.80 and 0.65, respectively.Conclusions and Clinical ImportanceAbsolute cardiac diameters and LA STE (in particular, PALS) are useful echocardiographic predictors for the development of AF in dogs with MMVD.

Usefulness of pulsed-wave tissue Doppler imaging at the mitral annulus for prediction of new-onset atrial fibrillation in dogs

IntroductionThe time from the onset of the P wave on electrocardiogram to the peak of late diastolic wave signal (PA-TDI interval) recorded by left atrial pulsed-wave tissue Doppler imaging (PW-TDI) is a surrogate of the total atrial conduction time, and it can predict the development of new-onset atrial fibrillation (AF) in people. This study investigated whether PA-TDI interval measured with PW-TDI at the level of lateral aspect of the mitral valve annulus could identify dogs which developed AF within 6 months after echocardiography. AnimalsForty-two dogs with different cardiac diseases were included; 21 dogs developed AF within 6 months after echocardiography (AF group) and 21 dogs did not (non-AF group). Each AF case was matched with a non-AF case for body weight and left atrium:aortic root ratio. MethodsThis was a retrospective study. Review of signalment, underlying disease and echocardiography data were included. PA-TDI interval was measured offline from acquired PW-TDI images. PA-TDI interval and standard echocardiographic variables were compared between groups. Receiver operator characteristic curves were used to identify the best AF predictor. Univariate and multivariate regression were used to evaluate predictors of PA-TDI interval. ResultsThe AF group had significantly greater 2D left atrial maximal diameter, left-ventricular (LV) end-diastolic volume, M-Mode LV internal diameter and LV end-systolic volume index. PA-TDI was significantly longer in the AF group, and it was superior to other echocardiographic variables in predicting AF development within 6 months (AUC = 0.896). ConclusionsPA-TDI interval measured with PW-TDI at the lateral mitral valve annulus may identify dogs at risk of developing AF.

Analysis of Haematological and Biochemical Blood Parameters After Electrical Cardioversion of Atrial Fibrillation in Dogs

IntroductionElectrical cardioversion is a therapeutic procedure used to convert various types of arrhythmias back to sinus rhythm. It is used to restore the sinus rhythm in dogs with atrial fibrillation. The effect of the electrical energy used during cardioversion on red blood cells (RBC) is not fully understood. Studies on humans reported lysis of RBC following electrical cardioversion. Similar studies have not been carried out on dogs. The aim of the study was to assess the effect of electrical cardioversion on chosen RBC parameters.Material and MethodsThe study was carried out on 14 large and giant breed dogs weighing from 30 to 84 kg with lone atrial fibrillation (lone AF). Electrical cardioversion was carried out under general anaesthesia by biphasic shock with 70–360 J of energy. Blood was collected at T0 – during atrial fibrillation, prior to cardioversion, and at T1 – 30 min after electrical cardioversion. Complete blood counts as well as total and direct bilirubin concentrations were evaluated. A maximum output of 360 J was used.ResultsIn all cases, electrical cardioversion was effective, and no significant changes in the number of RBC and RBC indices were noted. Similarly, there were no statistically significant differences in the levels of total and direct bilirubin.ConclusionElectrical cardioversion in dogs led neither to statistically nor clinically significant RBC lysis.

Dronedarone attenuates the duration of atrial fibrillation in a dog model of sustained atrial fibrillation.

Atrial fibrillation (AF) is a supraventricular arrhythmia that leads to a decrease in cardiac output and impairs cardiac function and quality of life. Dronedarone has an atrial-selective property and has been used for management of AF in humans, but limited information is available in dogs. This study was designed to evaluate efficacy of dronedarone in attenuating the duration of AF in dog model of sustained AF. Six beagle dogs were anesthetized with isoflurane and instrumented to measure atrial action potential duration (aAPD) and atrial effective refractory period (AERP). Then AF was induced by rapid right atrial pacing (20 V, 40 Hz) simultaneously with infusion of phenylephrine (2 µg/kg/min, intravenously) for 20 min. The duration of sustained AF was recorded, and the animals were allowed to recover. Dronedarone was given at a dose of 20 mg/kg, BID, orally for 7 days. On the last day, the dogs were anesthetized again to record aAPD and AERP, and AF was induced with the same procedure as described above. The results showed that after dronedarone administration the aAPD was lengthened significantly from 76.4 ± 4.2 ms to 91.2 ± 3.9 ms (P<0.05) and AERP was prolonged significantly from 97.5 ± 2.8 ms to 120 ± 4.8 ms (P<0.05). The duration of sustained AF was also significantly attenuated after receipt of dronedarone (P<0.05). It can be suggested that oral dronedarone attenuates the duration of sustained AF in a dog model of AF by extending the AERP more than the aAPD, causing post-repolarization refractoriness. Hence, dronedarone may be useful for management of AF in dogs.

Evaluation of in‐hospital electrocardiography versus 24‐hour Holter for rate control in dogs with atrial fibrillation

To determine if the in-clinic ECG-derived heart rate could predict the at-home Holter-derived 24-hour average heart rate (Holter24h ), and whether it is useful to identify slow versus fast atrial fibrillation in dogs. 82 pairs of 1-minute ECGs and 24-hour Holter recordings were acquired in 34 dogs with atrial fibrillation. The initial 24-hour Holter was used to test if the ECG heart rate can identify dogs with "slow" versus "fast" atrial fibrillation based on a Holter24h threshold value of 140 bpm. ECG heart rate overestimated Holter24h by 26 bpm (95% CI: 3 bpm, 48 bpm; P < 0 · 015) with a 95% limit of agreement of -21 to 83 bpm. The in-clinic ECG-derived heart rate Ä155 bpm had a sensitivity of 73% and a specificity of 100% for identifying a Holter24h HR Ä140 bpm; an in-clinic ECG-derived HR <160 bpm had a sensitivity and specificity of 91% each. In-clinic ECG assessment of heart rate in dogs with atrial fibrillation does not reliably predict the heart rate in their home environment. However, an in-clinic heart rate greater than 155 bpm is useful in identifying "fast" atrial fibrillation, allowing clinicians to stratify which case may benefit from antiarrhythmic therapy.

ASSA13-03-6 Effects of Renal Sympathetic Denervation on the Development of Atrial Fibrillation Substrates in Dogs with Pacing-Induced Heart Failure

<h3>Objective</h3> We examined the role of renal denervation on the inducibility of AF in dogs with pacing-induced HF. <h3>Background</h3> Atrial fibrillation (AF) and heart failure (HF) are common interrelated conditions that are associated with renin-angiotensin-aldosterone system activity. <h3>Methods and Results</h3> Nineteen dogs were randomised into sham-operated (7 dogs), HF (6 dogs) and HF+renal artery ablation (RAA, 6 dogs) groups. Sham-operated dogs were implanted with transvenous cardiac pacemakers without pacing. Dogs in the HF group were implanted with pacemakers and underwent right ventricular pacing for 3 weeks at 240 bpm to induce HF. The dogs in the HF+RAA group received double renal artery ablation. The dogs recovered for 8 weeks and underwent the same HF-inducing procedure. Compared to the baseline, the atrial dimensions increased and the right atrial ERP (131 ± 14 ms to 112 ± 12 ms, p = 0.02) decreased significantly after 3 weeks in the HF dogs but not the HF+RAA dogs. A greater number of AFs were induced in the HF dogs than the HF+RAA dogs (2.2 ± 0.6 vs. 0.3 ± 0.3, p = 0.03). The atrium from HF hearts revealed a large amount of fibrosis, whereas control and HF+RAA dogs showed minimal fibrous tissue. The levels of BNP, Ang II, TNF-α and expression of TGF-β and Cx43 in atrial tissue were increased in the HF dogs compared to the sham-operated and HF+RAA dogs. <h3>Conclusion</h3> RAA suppressed the atrial substrate remodelling and the AF vulnerability that was induced by long-term rapid ventricular pacing.

Use of Procainamide for Conversion of Acute Onset AF Following Pericardiocentesis in a Dog

A 9 yr old spayed female golden retriever was evaluated for anorexia and suspected gastric dilatation. Subsequent evaluation the following day determined the dog to have pericardial effusion. Muffled heart sounds and jugular pulses were noted on physical exam, and the dog was diagnosed with pleural and pericardial effusion. A sinus rhythm with a rate of 142 beats/min was documented on a surface electrocardiogram (EKG). Following pericardiocentesis, the heart rate increased to 260 beats/min, the rhythm became irregular, and the systemic blood pressure decreased. Atrial fibrillation (AF) was confirmed by EKG. Procainamide was administered IV over 15 min, resulting in successful conversion of AF to sinus rhythm and clinical improvement. Procainamide is one of several antiarrhythmic medications that are used for the conversion of acute AF in humans; however, its utility and efficacy in dogs in the setting of AF has not previously been reported. This case highlights a unique complication of performing a pericardiocentesis that requires immediate treatment and describes a potential treatment option for the conversion of acute AF in dogs.

Thrombotic complications associated with atrial fibrillation in three dogs

Atrial fibrillation (AF) is the most common chronic pathologic arrhythmia in dogs, and whereas thromboembolism is a common complication of AF in humans, this complication has not been previously reported in dogs. This report describes thrombotic complications associated with AF in three dogs. A spherical left atrial mass consistent with a thrombus was identified in two dogs during echocardiographic examination. A third dog experienced arterial thromboembolism confirmed with ultrasound and postmortem examination. These cases provide a unique antemortem description of intra-atrial thrombus formation and cardioembolic disease associated with AF in dogs, and raise awareness of the importance of thorough echocardiographic evaluation of the atria for thrombus prior to pharmacologic cardioversion or direct current cardioversion.

Atrioventricular node functional remodeling induced by atrial fibrillation

The atrioventricular node (AVN) plays a vital role in determining the ventricular rate during atrial fibrillation (AF). AF results in profound electrophysiological and structural remodeling in the atria as well as the sinus node. However, it is unknown whether AVN undergoes remodeling during AF. To determine whether AVN undergoes functional remodeling during AF. AVN conduction properties were studied in vitro in 9 rabbits with AF and 10 normal controls. A previously validated index of AVN dual-pathway electrophysiology, His-electrogram alternans, was used to monitor fast-pathway or slow-pathway (SP) AVN conduction in these experiments. AVN conduction properties were further studied in vivo in 7 dogs with chronic AF and 8 controls. Compared with the control rabbits, the rabbits with AF had a longer AVN conduction time (83 ± 16 ms vs 68 ± 7 ms; P <.01), longer AVN effective refractory period (141 ± 27 ms vs 100 ± 9 ms; P <.01), an earlier transition from fast-pathway to SP conduction (at a longer prematurity, 249 ± 60 ms vs 171 ± 24 ms; P <.01), and a slower ventricular rate during simulated AF (RR interval 249 ± 42 ms vs 202 ± 12 ms; P <.01). Notably, a larger proportion of conducted beats utilized the SP in AF preparations (92% ± 12% vs 63% ± 32%; P <.05). Long-term AF in dogs resulted in a longer atrioventricular conduction time and AVN effective refractory period and a slower ventricular rate during AF compared with the controls. Pronounced AVN functional electrophysiological remodeling occurs after long-term AF, which could lead to a spontaneous slowing of the ventricular rate. Furthermore, the SP dominance during AF underscores the effectiveness of its modification by ablation for ventricular rate control during AF.

P-Wave Dispersion in Prediction of Maintenance of Sinus Rhythm After an Electrical Cardioversion of Atrial Fibrillation in Dogs

Abstract The aim of this study was to demonstrate the diagnostic accuracy of P-wave dispersion in predicting recurrence of atrial fibrillation in dogs with sinus rhythm restoration after external cardioversion. The study was performed on 15 dogs, which underwent electrical external cardioversion after atrial fibrillation. Nine-lead surface electrocardiogram of each dog was recorded 1 min after the cardioversion process to measure the P-wave duration. Dogs with recurrent atrial fibrillation had significantly higher P-wave dispersion compared to dogs that had a sinus rhythm lasting more than 3 months (9.26 ±2.01 ms vs 20.9 ±2.18 ms, P=0.001). This study suggests that P-wave dispersion analysis in dogs after a successful external electrical cardioversion has diagnostic accuracy to predict the recurrence of atrial fibrillation.