Einthoven's triangle adapted for horses: Proposal for the Delta configuration.

BACKGROUND: Reliable ECGs are crucial for diagnosing arrhythmias, yet a lack of standardization impedes arrhythmia diagnosis and treatment in horses. OBJECTIVES: To objectively determine an optimal position of Einthoven's triangle for ECG recordings in horses at rest, which can form the basis for standardized ECG recording and improve diagnosis and treatment of arrhythmias. ANIMALS: The study involved 72 healthy, warmblood horses aged between 3 and 20 years. METHODS: In view of future 12-lead studies and vectorcardiography, requiring an orthogonal system, Einthoven's triangle was positioned around the heart, in the transverse plane. Therefore, 11 electrodes were placed encircling the thorax behind the olecranon, to construct triangles with a horizontal base. Electrocardiogram recordings from different triangles were analyzed. Signal processing involved filtering, R peak detection, and median complex generation. Principal component analysis (PCA) and Euclidean distance measures were employed for data analysis. RESULTS: The left mid-thoracic and ventral regions had high PCA scores, indicating high information content. Base-down triangles exhibited higher summed Euclidean distances, contributing to enhanced diagnostic capabilities. A base-down triangle, called "Delta (Δ) configuration" emerged as most informative, while meeting all criteria. CONCLUSIONS AND CLINICAL IMPORTANCE: The base-down "Delta configuration" is the optimal Einthoven's triangle adapted for horses, providing large amplitudes and potential to provide basic insights into the mechanisms and origins of cardiac arrhythmias. Because the Delta configuration is positioned in the transverse plane, it forms the ideal basis for 12-lead ECG recordings that provide vectorcardiograms in an orthogonal coordinate system. Standardizing electrode positioning could improve ECG data comparability in equine cardiology.

Intracardiac ultrasound-guided transseptal puncture in horses: Outcome, follow-up, and perioperative anticoagulant treatment.

BACKGROUND: Cardiac catheterizations in horses are mainly performed in the right heart, as access to the left heart traditionally requires an arterial approach. Transseptal puncture (TSP) has been adapted for horses but data on follow-up and closure of the iatrogenic atrial septal defect (iASD) are lacking. HYPOTHESIS/OBJECTIVES: To perform TSP and assess postoperative complications and iASD closure over a minimum of 4 weeks. ANIMALS: Eleven healthy adult horses. METHODS: Transseptal puncture was performed under general anesthesia. Serum cardiac troponin I concentrations were measured before and after puncture. Weekly, iASD closure was monitored using transthoracic and intracardiac echocardiography. Relationship between activated clotting time and anti-factor Xa activity during postoperative enoxaparin treatment was assessed in vitro and in vivo. RESULTS: Transseptal puncture was successfully achieved in all horses within a median duration of 22 (range, 10-104) minutes. Balloon dilatation of the puncture site for sheath advancement was needed in 4 horses. Atrial arrhythmias occurred in 9/11 horses, including atrial premature depolarizations (N = 1), atrial tachycardia (N = 5), and fibrillation (N = 3). Serum cardiac troponin I concentrations increased after TSP, but remained under the reference value in 10/11 horses. Median time to iASD closure was 14 (1-35) days. Activated clotting time correlated with anti-factor Xa activity in vitro but not in vivo. CONCLUSIONS AND CLINICAL IMPORTANCE: Transseptal puncture was successfully performed in all horses. The technique was safe and spontaneous iASD closure occurred in all horses. Clinical application of TSP will allow characterization and treatment of left-sided arrhythmias in horses.

Feasibility of transthoracic echocardiographic guidance for multicatheter electrophysiological mapping studies in horses.

BACKGROUND: Improved characterization of arrhythmias is based on minimally invasive catheterizations. However, these catheterizations have been poorly explored in horses because apart from 3-dimensional (3D) mapping systems, continuous guidance of the catheter's position with adequate detail is difficult using current imaging modalities. HYPOTHESIS: Position multiple electrophysiology catheters simultaneously at predetermined strategical positions in the heart using transthoracic echocardiographic guidance. ANIMALS: Eight adult healthy horses. METHODS: Observational study. Two electrophysiological studies were performed: 1 procedure with catheters positioned in the right heart in the standing sedated horse and 1 procedure under general anesthesia with catheters positioned in the left heart. Except for the coronary sinus catheter, each catheter positioning was simultaneously guided by right-parasternal transthoracic echocardiography and 3D electro-anatomical mapping. RESULTS: For each catheter position, a central imaging plane was taken as the starting point, after which the imaging probe was shifted, rotated, and angulated to visualize the catheter over its entire length, including its distal electrode. Catheter positionings in the right heart and left ventricle were successfully guided in the majority of the horses whereas catheter positionings in the left atrium, and especially the pulmonary veins, were challenging to guide echocardiographically. CONCLUSIONS AND CLINICAL IMPORTANCE: Ultrasound guidance of catheters to specific positions useful for electrophysiological mapping was feasible in the right heart and left ventricle but challenging for the left atrium. This approach creates a perspective for minimally invasive arrhythmia diagnosis without the need for a 3D mapping system. Left parasternal views and intracardiac echocardiography might provide better guidance for left atrial positions.

Large-scale study of blood markers in equine atypical myopathy reveals subclinical poisoning and advances in diagnostic and prognostic criteria.

Equine atypical myopathy (AM) is a severe rhabdomyolysis syndrome primarily caused by hypoglycin A (HGA) and methylenecyclopropylglycine protoxins. This study aimed to refine diagnostic and prognostic criteria for AM while exploring apparently healthy cograzers. Blood samples from 263 horses, including AM cases (n= 95), cograzers (n= 73), colic horses (n= 19), and controls (n= 76), were analyzed for HGA, its toxic metabolite, and acylcarnitines profile. Diseased horses exhibited alterations in acylcarnitines that strongly distinguished them from controls and colic horses. Regression analyses identified distinct acylcarnitines profiles among groups, with cograzers showing intermediate alterations. Age and gelding status emerged as protective factors against AM. Furthermore, serum acylcarnitines profiling was valuable in predicting AM survival, with isovaleryl-/2-methylbutyrylcarnitine (i.e., C5 acylcarnitine) showing promise as both a diagnostic and prognostic marker. Subclinical alterations in cograzers underscore a novel aspect: the presence of subclinical cases of AM.

Development of an atrial transseptal puncture procedure in horses to access the left heart: An ultrasound-guided jugular vein and transhepatic approach.

BACKGROUND: Radiofrequency ablation has been successfully applied to treat right atrial arrhythmias in horses. Ablation of left-sided arrhythmias requires a retrograde transarterial approach which is complicated. In human medicine, the left atrium is accessed through transseptal puncture (TSP) of the fossa ovalis (FO) using a caudal approach via the femoral vein. OBJECTIVES: To develop a zero fluoroscopy TSP technique for horses using a jugular vein (cranial) and transhepatic (caudal) approach. STUDY DESIGN: In vivo experimental study. METHODS: Transseptal puncture was performed in 18 horses admitted for euthanasia and donated for scientific research under general anaesthesia: using a jugular vein approach (10 horses), a transhepatic approach (2 horses) or both (6 horses). Radiofrequency energy was applied on a guidewire to perforate the FO and allow sheath advancement under intracardiac and transthoracic echocardiographic guidance. Puncture lesions were inspected post-mortem. RESULTS: Transseptal puncture was successful in 17/18 horses, of which 15/16 jugular vein approaches and 5/8 transhepatic approaches. Failure was due to technical malfunction, inability to advance the guidewire toward the heart and inability to advance the sheath through the FO. Intracardiac echocardiography was essential to safely guide the puncture process. Atrial arrhythmias caused by the TSP occurred in 13/18 horses. Puncture lesions were found in the right atrium in the FO region, and left atrium ventral to pulmonary vein ostium III. MAIN LIMITATIONS: Because in several horses two approaches were tested consecutively, it cannot be excluded that the second TSP was performed at the previous puncture site. Due to the developmental nature of the study the approaches were not randomised and did not allow comparison. CONCLUSION: Transseptal puncture is feasible in horses using ultrasound guidance and allows for electrophysiological exploration of the left heart. Further studies are needed to evaluate post-operative follow-up.

Morphological evidence of a potential arrhythmogenic substrate in the caudal and cranial vena cava in horses.

BACKGROUND: Three-dimensional electro-anatomical mapping, previously performed in horses with atrial arrhythmias, has demonstrated the medial region of the caudal vena cava (CaVC), 1-8 cm caudal to the fossa ovalis, as an anatomical predilection site for atrial tachycardia associated with areas of slow conduction and conduction block. Slow conduction has also been recorded in the cranial vena cava (CrVC). OBJECTIVES: To investigate the morphological characteristics of the myocardial sleeves (MS) in the CaVC and CrVC, in order to identify a potential substrate of right sided atrial arrhythmias. STUDY DESIGN: Cross sectional. METHODS: Post-mortem dissection of 37 hearts from adult warmblood horses without known cardiovascular disease. Macroscopic examination of the myocardial distribution, evaluated the MS area, length, width, and shape in the CaVC and the CrVC. At least 2 samples from each vena cava MS were histologically examined using Masson's trichrome staining. RESULTS: Myocardial sleeves into the medial CaVC and into the CrVC were observed in all horses and showed variations in distribution, shape, and size between horses. Their mean ± standard deviation length from the limbus into the CaVC reached 5.7 ± 1.0 cm (maximum 8.3 cm), and from the azygos vein into the CrVC 5.3 ± 1.6 cm (maximum 8.6 cm). Myocardium-free islands were observed in the CaVC and CrVC in 30% and 6% of horses, respectively. Histologically, MS showed a non-uniform myocardial fibre arrangement, with presence of fibroadipose tissue, features known to result in slow conduction and pro-arrhythmia. MAIN LIMITATIONS: Study only included horses without history of atrial arrhythmia. CONCLUSIONS: Myocardial sleeves are present in both CaVC and CrVC, showing anatomical variations between horses. Tissue characteristics known to favour re-entry were identified indicating that these venae cavae MS are a potential substrate for atrial tachyarrhythmias and a target for treatment by ablation.

CONTEXTE: La modélisation électro-anatomique tridimensionnelle, réalisée auparavant chez des chevaux souffrant d'arythmies atriales, a démontré que la région médiale de la veine cave caudale (CaVC), 1-8 cm caudalement à la fossae ovalis, représente un site anatomique de prédilection pour la tachycardie auriculaire associée à des zones de conduction ralentie et des blocs de conduction. Une conduction ralentie a aussi été enregistrée dans la veine cave crâniale (CrVC). OBJECTIFS: Investiguer les caractéristiques morphologiques des manchons myocardiques (Myocardial sleeve;MS) dans les CAVC et CrVC, afin d'identifier un substrat potentiel d'arythmies atriales du côté droit du cœur. TYPE D'ÉTUDE: Étude transversale. MÉTHODES: Dissection post-mortem de 37 cœurs de chevaux à sang chaud adultes sans historique de maladie cardiovasculaire. Lors de l'examen macroscopique de la distribution myocardique, la surface des MS, leur longueur, largeur et forme ont été évaluées dans les CAVC et CrVC. Les MS ont été examinées microscopiquement dans au moins 2 échantillons de chaque veine cave, en utilisant la coloration de Masson Trichrome. RÉSULTATS: Les MS à l'aspect médial de la CaVC et à l'intérieur de la CrVC ont été inspectées chez tous les chevaux et ont montré des variations de distribution, forme et grandeur entre chevaux. Leur moyenne de longueur ± déviation standard du limbe de la fossae ovalis dans la CaVC était de 5.7 ± 1.0 cm (maximum 8.3 cm) et de la veine azygos dans la CrVC, de 5.3 ± 1.6 cm (maximum 8.6 cm). Des Îlots dénudés de myocarde ont été observé dans la CaVC et CrVC dans 30% et 6% des chevaux respectivement. À l'histologie, les MS ont montré des fibres myocardiques organisées de façon non-uniforme, avec présence de tissue fibroadipeux, caractéristiques connues pour entraîner une conduction lente et favoriser l'arythmie. LIMITES PRINCIPALES: Étude incluant seulement des chevaux sans historique d'arythmie atriale. CONCLUSION: Les MS sont présentes dans les CaVC et CrVC, démontrant les variations anatomiques entre chevaux. Des caractéristiques tissulaires connues pour favoriser une conduction ralentie ont été identifiés indiquant que les MS représentent un substrat potentiel des tachyarythmies atriales et une cible pour un traitement par ablation.

Effect of physiological and pharmacological stress on heart rate, blood pressure, and echocardiographic measurements in healthy Warmblood horses.

BACKGROUND: Echocardiographic measurements are important prognostic indicators but might be influenced by heart rate and blood pressure. This is particularly important when comparing repeated examinations. HYPOTHESIS: To determine the effect of physiological stress at mildly increased heart rates and pharmacological challenge using IV administration of N-butylscopolammonium bromide and metamizol sodium on heart rate, blood pressure, and echocardiographic measurements. ANIMALS: Twenty healthy Warmblood horses. METHODS: Randomized crossover study. Horses were examined echocardiographically by 2-dimensional, M-mode, pulsed wave (PW) Doppler, and PW tissue Doppler imaging with simultaneous ECG recording and noninvasive blood pressure measurements during rest, physiological stress, and pharmacological challenge. Cardiac dimensions and functions were measured by a blinded observer. Data were analyzed using repeated-measures analysis of variance. RESULTS: Mean heart rate and arterial blood pressure were significantly higher during physiological stress (46 ± 2 bpm, 93 ± 16 mm Hg) and pharmacological challenge (62 ± 13 bpm, 107 ± 17 mm Hg) compared with rest (34 ± 3 bpm, 86 ± 12 mm Hg; P < .05). Compared with rest, physiological stress resulted in increased left atrial fractional area change (34.3 ± 7.5 vs 27.3 ± 5.1%; P = .01) and left ventricular late diastolic radial wall motion velocity (13 ± 3 vs 10 ± 2 cm/s; P = .01) but had no significant effect on most other echocardiographic variables. Compared with rest, pharmacological challenge led to significantly decreased left atrial and diastolic ventricular dimensions (left ventricular internal diameter: 10.3 ± 0.9 vs 10.7 ± 0.8 cm; P = .01), increased aortic and pulmonary diameters, and ventricular wall thickness. CONCLUSIONS AND CLINICAL IMPORTANCE: Physiological stress at mildly increased heart rates significantly enhanced atrial pump function. Larger heart rate and blood pressure increases during pharmacological challenge resulted in altered cardiac dimensions. This should be taken into account when evaluating echocardiographic measurements at increased heart rates.

Successful caudal vena cava and pulmonary vein isolation in healthy horses using 3D electro-anatomical mapping and a contact force-guided ablation system.

BACKGROUND: Recently, treatment of equine atrial tachycardia by three-dimensional electro-anatomical mapping (3D EAM) and radiofrequency catheter ablation (RFCA) has been described. Myocardial sleeves in the caudal vena cava and pulmonary veins are a potential trigger for initiation and perpetuation of atrial tachycardia and atrial fibrillation in the horse. Isolation of these myocardial sleeves by RFCA may be an effective treatment for these arrhythmias. OBJECTIVES: To describe the feasibility of 3D EAM and RFCA to isolate caudal vena cava and pulmonary veins in adult horses using 3D mapping and a contact force (CF)-guided ablation system. STUDY DESIGN: In vivo experiments. METHODS: 3D EAM and RFCA was performed in five horses without cardiovascular disease under general anaesthesia, using the CF-guided system CARTO®3. Point-by-point RFCA aimed for isolation of caudal vena cava and pulmonary veins. Radiofrequency energy was delivered in power-controlled mode with a target power of 45 W, CF between 10 and 15 g and 30 mL/min irrigation rate, until an ablation-index of 450-500 was reached. RESULTS: In the right atrium, myocardial sleeves of the caudal vena cava were isolated (n = 5). In the left atrium, isolation of ostium II (n = 3), ostium III (n = 1) and ostium I, II and III en bloc (n = 1) was performed. Successful isolation was confirmed by entrance and exit block. MAIN LIMITATIONS: Horses were euthanised at the end of the procedure, so long term effects such as potential reconnection of isolated veins could not be studied. CONCLUSIONS: This is the first description of 3D EAM and RFCA with CARTO®3 in horses, thereby showing the technical feasibility and successful caudal vena cava and pulmonary vein isolation. CF measurement allowed monitoring of catheter-tissue contact, resulting in efficient acute lesion creation as confirmed by entrance and exit block. This is a promising treatment for cardiac arrhythmias in horses.

Defining Hemodynamic Significance of Renal Artery Stenosis: Insights From a Porcine Model of Graded Renal Artery Stenosis.

RATIONALE AND OBJECTIVES: To investigate the renal pressure-flow relationship and its relation to renin release, because the renal perfusion pressure below which renal flow starts to decline and renin secretion is upregulated is unclear. MATERIALS AND METHODS: A porcine model of graded unilateral renal artery stenosis was created. The severity of the stenosis was expressed as the ratio between distal renal pressure (Pd) and aortic pressure (Pa). Pd and renal flow velocity were continuously measured using a combined pressure-flow wire (Combowire®). Hemodynamic measurements and blood sampling for renin, angiotensin and aldosterone were performed in baseline conditions and during progressive balloon inflation in the renal artery leading to Pd decrease per 5% increment. Resistive index (RI) was computed as (1 - (End Diastolic V/Peak Systolic V))*100. RESULTS: For a 5% decrease in renal perfusion pressure (95% of aortic pressure or 5% decrease compared to Pa), peak systolic velocity started to decrease. A significant decrease in average peak flow velocity was observed when distal renal perfusion pressure decreased by 25% and was associated with activation of ipsilateral renin secretion. The RI decreased already for minimal changes in Pd/Pa ratio. CONCLUSION: In an animal model of unilateral graded renal artery stenosis, a 25% decrease in perfusion pressure results in a significant decrease in distal renal flow, causing upregulation of renin secretion.

Three-dimensional electro-anatomical mapping and radiofrequency ablation as a novel treatment for atrioventricular accessory pathway in a horse: A case report.

We describe the diagnosis and treatment of an atrioventricular accessory pathway (AP) in a horse using 3-dimensional electro-anatomical mapping (3D EAM) and radiofrequency catheter ablation (RFCA). During routine evaluation of the horse, intermittent ventricular pre-excitation was identified on the ECG, characterized by a short PQ interval and abnormal QRS morphology. A right cranial location of the AP was suspected from the 12-lead ECG and vectorcardiography. After precise localization of the AP using 3D EAM, ablation was performed and AP conduction was eliminated. Immediately after recovery from anesthesia an occasional pre-excited complex still was observed, but a 24-hour ECG and an ECG during exercise 1 and 6 weeks after the procedure showed complete disappearance of pre-excitation. This case shows the feasibility of 3D EAM and RFCA to identify and treat an AP in horses.

Echocardiographic Features of the Ductus Arteriosus and the Foramen Ovale in a Hospital-Based Population of Neonatal Foals.

The ductus arteriosus (DA) and foramen ovale (FO), including the septum primum (SP) and septum secundum (SS), are important structures in fetal circulation and are unexplored in neonatal equids. The objective of this study is to describe echocardiographic characteristics in a hospital-based population of neonatal foals. On days 2, 5 and 10 after parturition, cardiac ultrasound was performed, and clinical data were collected in healthy and diseased Warmblood foals. Fifty healthy (n = 15) and diseased (n = 35) Warmblood foals were examined. A left-sided and right-sided holosystolic murmur was audible in 98% (n = 42) and 51% (n = 22), respectively, on day 2; in 81% (n = 25) and 19% (n = 6) on day 5; and in 44% (n = 4) and 11% (n = 1) on day 10. The median grade of the systolic murmurs was higher when the DA was open. Flow through the DA could be visualized with color flow and continuous wave (CW) Doppler from the left parasternal long-axis view of the pulmonary artery in 40/43 foals on day 2, 9/31 foals on day 5 and 2/9 foals on day 10. The DA diameter was 2 ± 1 mm on day 2, 2 ± 1 mm on day 5 and 1 mm on day 10. The thickness of both septa of the FO was similar. The SP fluttered into the left atrium at all ages, but the maximal distance between the SP and SS decreased over time. In conclusion, cardiac murmurs, a patent DA and fluttering FO are frequent findings in neonatal foals. While these findings are probably physiological, the clinical importance needs to be further elucidated.

Detection of the origin of atrial tachycardia by 3D electro-anatomical mapping and treatment by radiofrequency catheter ablation in horses.

BACKGROUND: Atrial tachycardia (AT) can be treated by medical or electrical cardioversion but the recurrence rate is high. Three-dimensional electro-anatomical mapping, recently described in horses, might be used to map AT to identify a focal source or reentry mechanism and to guide treatment by radiofrequency ablation. OBJECTIVES: To describe the feasibility of 3D electro-anatomical mapping and radiofrequency catheter ablation to characterize and treat sustained AT in horses. ANIMALS: Nine horses with sustained AT. METHODS: Records from horses with sustained AT referred for radiofrequency ablation at Ghent University were reviewed. RESULTS: The AT was drug resistant in 4 out of 9 horses. In 8 out of 9 horses, AT originated from a localized macro-reentrant circuit (n = 5) or a focal source (n = 3) located at the transition between the right atrium and the caudal vena cava. In these 8 horses, local radiofrequency catheter ablation resulted in the termination of AT. At follow-up, 6 out of 8 horses remained free of recurrence. CONCLUSIONS AND CLINICAL IMPORTANCE: Differentiation between focal and macro-reentrant AT in horses is possible using 3D electro-anatomical mapping. In this study, the source of right atrial AT in horses was safely treated by radiofrequency catheter ablation.

Three-dimensional and catheter-based intracardiac echocardiographic characterization of the interatrial septum in 2 horses with suspicion of a patent foramen ovale.

This case report describes the 2-dimensional transthoracic (2D-TTE), 3-dimensional transthoracic (3D-TTE) and intracardiac echocardiographic (ICE) characterization of the fossa ovalis region in 2 horses. The first case was presented for poor performance and showed an anechoic zone in the interatrial septum on 2D-TTE. Based on 3D-TTE a deepened fossa ovalis could be identified and using ICE the presence of an interatrial shunt could be excluded. The second case was referred for a cardiac murmur and the presence of turbulent flow in and around the interatrial septum on 2D-TTE color flow Doppler. The complementary use of 2D-TTE, 3D-TTE, and ICE allowed detailed characterization of a patent foramen ovale, with evidence of a left-to-right shunt in a dorsocranial to ventrocaudal direction with limited hemodynamic implications. These 2 cases underline the feasibility of 3D-TTE and ICE in horses and especially show the added value of ICE in a clinical setting.

An Exploratory Study on Vectorcardiographic Identification of the Site of Origin of Focally Induced Premature Depolarizations in Horses, Part I: The Atria.

In human cardiology, the anatomical origin of atrial premature depolarizations (APDs) is derived from P wave characteristics on a 12-lead electrocardiogram (ECG) and from vectorcardiography (VCG). The objective of this study is to differentiate between anatomical locations of APDs and to differentiate APDs from sinus rhythm (SR) based upon VCG characteristics in seven horses without cardiovascular disease. A 12-lead ECG was recorded under general anaesthesia while endomyocardial atrial pacing was performed (800−1000 ms cycle length) at the left atrial free wall and septum, right atrial free wall, intervenous tubercle, as well as at the junction with the cranial and caudal vena cava. Catheter positioning was guided by 3D electro-anatomical mapping and transthoracic ultrasound. The VCG was calculated from the 12-lead ECG using custom-made algorithms and was used to determine the mean electrical axis of the first and second half of the P wave. An ANOVA for spherical data was used to test if the maximal directions between each paced location and the maximal directions between every paced location and SR were significantly (p < 0.05) different. Atrial pacing data were not available from the LA septum in three horses, the intervenous tubercle in two horses, and from the LA free wall in one horse. The directions of the maximal electrical axes showed significant differences between all paced locations and between the paced locations and SR. The current results suggest that VCG is useful for identifying the anatomical origin of an atrial ectopy.

An Exploratory Study on Vectorcardiographic Identification of the Site of Origin of Focally Induced Premature Depolarizations in Horses, Part II: The Ventricles.

In human cardiology, the anatomical origin of ventricular premature depolarizations (VPDs) is determined by the characteristics of a 12-lead electrocardiogram (ECG). Former studies in horses had contradictory results regarding the diagnostic value of the 12-lead ECG and vectorcardiography (VCG), which results were attributed to the different cardiac conduction system in this species. The objective of this study was to determine if the anatomical origin of pacing-induced VPDs could be differentiated in horses based upon VCG characteristics. A 12-lead ECG was recorded in seven horses under general anesthesia while right and left ventricular endomyocardial pacing was performed (800−1000 ms cycle length) at the apex, mid and high septum and mid and high free wall, and at the right ventricular outflow tract. Catheter positioning was guided by 3D electro-anatomical mapping and echocardiography. A median complex, obtained from four consecutive complexes, was calculated for each pacing location and sinus rhythm. The VCG was calculated from the 12-lead ECG-derived median complexes using custom-made algorithms and was used to determine the initial and maximum electrical axes of the QRS complex. An ANOVA for spherical data was used to test if VCGs between each paced location and between pacing and sinus rhythm were significantly (p < 0.05) different. The model included the radius, azimuth and elevation of each electrical axis. Pacing induced significantly different initial and maximum electrical axes between different locations and between pacing and sinus rhythm. The current results suggest that VCG is a useful technique to identify the anatomical origin of ventricular ectopy in horses.

Transvenous electrical cardioversion of atrial fibrillation in horses: Horse and procedural factors correlated with success and recurrence.

BACKGROUND: Transvenous electrical cardioversion (TVEC) is 1 of the main treatment options for atrial fibrillation (AF) in horses. Large-scale studies on factors affecting success and prognosis have primarily been performed in Standardbred populations. HYPOTHESIS/OBJECTIVES: To determine factors affecting cardioversion success, cardioversion difficulty and recurrence in a predominant Warmblood study sample. ANIMALS: TVEC records of 199 horses. METHODS: Retrospective study of TVEC procedures of horses admitted for AF without severe echocardiographic abnormalities. Horse and procedural factors for success and cumulative amount of energy (≤ 600 J vs > 600 J) were determined using multivariable logistic regression. A survival analysis was performed to determine risk factors for recurrence. RESULTS: Two hundred and thirty-one TVEC procedures were included, with a 94.4% success rate and 31.9% recurrence rate (51/160). Mitral regurgitation (OR 0.151, 95% CI 0.032-0.715, P = .02) and AF cycle length (OR 1.05, 95% CI 1.01-1.09, P = .02) were independent determinants for success. Catheter type (OR 0.154, 95% CI 0.074-0.322, P < .001), previous AF episode (OR 3.10, 95% CI 1.20-8.01, P = .02), tricuspid regurgitation (OR 2.54, 95% CI 1.25-5.13, P = .01), and body weight (OR 1.009, 95% CI 1.003-1.015, P = .004) were significantly correlated with cumulative amount of energy delivered. Significant risk factors for recurrence after a first AF episode were sex (stallion; HR 3.05, 95% CI 1.34-6.95, P = .008), mitral regurgitation (HR 1.91, 95% CI 1.08-3.38, P = .03), and AF duration (HR 1.001, 95% CI 1.0001-1.0026, P = .04). CONCLUSIONS AND CLINICAL IMPORTANCE: Both horse and procedural factors should be considered when assessing treatment options and prognosis in horses with AF.

Treatment of atrial fibrillation with doxapram: TASK-1 potassium channel inhibition as a novel pharmacological strategy.

AIMS: TASK-1 (K2P3.1) two-pore-domain potassium channels are atrial-specific and significantly up-regulated in atrial fibrillation (AF) patients, contributing to AF-related electrical remodelling. Inhibition of TASK-1 in cardiomyocytes of AF patients was shown to counteract AF-related action potential duration shortening. Doxapram was identified as a potent inhibitor of the TASK-1 channel. In this study, we investigated the antiarrhythmic efficacy of doxapram in a porcine model of AF. METHODS AND RESULTS: Doxapram successfully cardioverted pigs with artificially induced episodes of AF. We established a porcine model of persistent AF in domestic pigs via intermittent atrial burst stimulation using implanted pacemakers. All pigs underwent catheter-based electrophysiological investigations prior to and after 14 days of doxapram treatment. Pigs in the treatment group received intravenous administration of doxapram once per day. In doxapram-treated AF pigs, the AF burden was significantly reduced. After 14 days of treatment with doxapram, TASK-1 currents were still similar to values of sinus rhythm animals. Doxapram significantly suppressed AF episodes and normalized cellular electrophysiology by inhibition of the TASK-1 channel. Patch-clamp experiments on human atrial cardiomyocytes, isolated from patients with and without AF could reproduce the TASK-1 inhibitory effect of doxapram. CONCLUSION: Repurposing doxapram might yield a promising new antiarrhythmic drug to treat AF in patients.

Atrial fibrillatory rate as predictor of recurrence of atrial fibrillation in horses treated medically or with electrical cardioversion.

BACKGROUND: The recurrence rate of atrial fibrillation (AF) in horses after cardioversion to sinus rhythm (SR) is relatively high. Atrial fibrillatory rate (AFR) derived from surface ECG is considered a biomarker for electrical remodelling and could potentially be used for the prediction of successful AF cardioversion and AF recurrence. OBJECTIVES: Evaluate if AFR was associated with successful treatment and could predict AF recurrence in horses. STUDY DESIGN: Retrospective multicentre study. METHODS: Electrocardiograms (ECG) from horses with persistent AF admitted for cardioversion with either medical treatment (quinidine) or transvenous electrical cardioversion (TVEC) were included. Bipolar surface ECG recordings were analysed by spatiotemporal cancellation of QRST complexes and calculation of AFR from the remaining atrial signal. Kaplan-Meier survival curve and Cox regression analyses were performed to assess the relationship between AFR and the risk of AF recurrence. RESULTS: Of the 195 horses included, 74 received quinidine treatment and 121 were treated with TVEC. Ten horses did not cardiovert to SR after quinidine treatment and AFR was higher in these, compared with the horses that successfully cardioverted to SR (median [interquartile range]), (383 [367-422] vs 351 [332-389] fibrillations per minute (fpm), P < .01). Within the first 180 days following AF cardioversion, 12% of the quinidine and 34% of TVEC horses had AF recurrence. For the horses successfully cardioverted with TVEC, AFR above 380 fpm was significantly associated with AF recurrence (hazard ratio = 2.4, 95% confidence interval 1.2-4.8, P = .01). MAIN LIMITATIONS: The treatment groups were different and not randomly allocated, therefore the two treatments cannot be compared. Medical records and the follow-up strategy varied between the centres. CONCLUSIONS: High AFR is associated with failure of quinidine cardioversion and AF recurrence after successful TVEC. As a noninvasive marker that can be retrieved from surface ECG, AFR can be clinically useful in predicting the probability of responding to quinidine treatment as well as maintaining SR after electrical cardioversion.

Successful application of closed loop stimulation pacemakers with remote monitoring in 3 miniature donkeys with syncope.

Rate-adaptive single chamber pacemakers with accelerometer, closed loop stimulation (CLS), and remote monitoring functionality (Eluna 8 SR-T, Biotronik, SE & Co, Germany) were implanted in 3 miniature donkeys with third-degree atrioventricular block and syncope. After recovery, different pacemaker programming modes were tested at rest, during stress without physical exercise and during physical exercise. Pacing rates were compared to actual atrial rates and showed that CLS functionality allowed physiological heart rate adaptation. A transmitter installed in the stable provided wireless connection of the pacemaker to the internet. Home monitoring was activated which performed daily wireless transmission of pacemaker functional measurements to an online server allowing diagnosis of pathological arrhythmias and pacemaker malfunction from a distance. Closed loop stimulation and remote monitoring functionality resulted in nearly physiological rate adaptation and allowed remote "from-the-stable" patient follow-up.