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A one-year-and-seven-month-old, 28 kg, male castrated crossbreed dog was presented for supraventricular tachycardia causing recurrent episodes of anorexia and lethargy. Sotalol (2.2 mg/kg q12 h) reduced the frequency of symptomatic episodes but did not provide full relief. Three-dimensional electroanatomical mapping was performed at the Ghent University Small Animal Teaching hospital using the CARTO 3. Right atrial activation mapping identified the earliest atrial activation right posteroseptal, near the tricuspid annulus. Fast retrograde ventriculoatrial conduction during tachycardia and extrastimulus testing confirmed the presence of a concealed right posteroseptal accessory pathway. Six radiofrequency catheter ablation applications were delivered, and tachycardia remained uninducible. The dog recovered well from the procedure. Sotalol was stopped three weeks later, and no more clinical signs were noted by the owner. Repeated 24-hour electrocardiography monitoring on day one and at one, three, and 12 months after the procedure showed no recurrence of tachycardia. [ABSTRACT FROM AUTHOR]

Summary: Background: In human medicine, local and regional arterial wall stiffness (AWS) parameters are routinely used to assess the vascular health. In horses, information regarding reproducibility of ultrasonographically derived AWS parameters is lacking. Objectives: To evaluate the inter‐day and inter‐observer and intra‐observer measurement variability of both local and regional AWS parameters in horses. Study design: Experimental study. Methods: In 10 healthy, adult Warmblood horses, B‐, M‐mode and pulsed‐wave Doppler ultrasound images were collected on two different days from aorta, cranial and caudal common carotid arteries and external iliac artery. Heart rate and noninvasive blood pressure were recorded simultaneously. From blinded data, diastolic and systolic vessel lumen areas and diameters were measured from B/M‐mode images and the velocity of the pressure wave was determined by pulsed‐wave Doppler spectra. From each horse, one examination was measured again by the same observer and by a second, independent observer. Local and regional AWS parameters were calculated and inter‐day and inter‐observer and intra‐observer measurement coefficient of variation (CV) were assessed. Results: Low CV was found for both arterial diameter and lumen area measurements. Moderate to high CV was found for local AWS parameters, while regional AWS parameters had low CV. Main limitations: The number of horses investigated was too low to obtain reference values. The inter‐operator variability was not evaluated. Conclusions: Our results show good reproducibility of aortic, carotid and external iliac artery diameter and area measurements using both B‐ and M‐mode ultrasonography. Nevertheless, the variability of the derived local AWS parameters was relatively high. Therefore, local AWS parameters might be less suitable for follow‐up studies, although they might be useful for population studies. On the other hand, regional AWS parameters showed low CV, making them valuable for both follow‐up and population studies. [ABSTRACT FROM AUTHOR]

Summary: Background: The number of atrial premature depolarisations (APDs) is a known risk factor for atrial fibrillation (AF) recurrence in humans. Objectives: To evaluate if the number of APDs over a 24‐h period 5 days post cardioversion predicts AF recurrence within 1 year in horses, taking the multifactorial nature of AF into account. Study design: Retrospective case series. Methods: Eighty horses met these inclusion criteria: first AF episode, no AF recurrence within 5 days post cardioversion, cardioversion by transvenous electrical cardioversion (TVEC), 24‐h ECG recording and echocardiographic examination 5 days post cardioversion, no antiarrhythmic treatment during the ECG recording and follow‐up of minimum 1 year. To compare the APD burden between the recurrence and non‐recurrence group a Mann–Whitney U test was used. A multivariable survival model was built to identify additional risk factors for AF recurrence. Results: The patient population mainly consisted of Warmbloods (93%). Twenty‐six horses (33%) experienced AF recurrence within 1 year. The number of APDs (median [range]) was significantly higher (P = 0.01) in the recurrence group (15 [1–152]) compared with the non‐recurrence group (7 [0–304]). In the multivariable survival model, APDs ≥25/24 h (hazard ratio [HR] 2.9, 95% confidence interval [CI] 1.2–6.8, P = 0.02), mitral regurgitation (HR 8.6, 95% CI 2.6–28.9, P<0.001), left atrial active fractional area change ≤9.6% (HR 2.6, 95% CI 1.0–6.5, P = 0.04) and lower body weight (HR 0.99, 95% CI 0.98–0.99, P = 0.001) were significantly associated with AF recurrence. Main limitations: This study did not evaluate early AF recurrence within 5 days. The results cannot necessarily be extrapolated to other treatment methods, as only horses converted by TVEC were included. Conclusions: The APD burden 5 days post cardioversion could be a useful predictive value for AF recurrence within 1 year in horses. However, other factors such as mitral regurgitation and atrial contractile function must also be taken into account. [ABSTRACT FROM AUTHOR]

Sustained atrial tachycardia at an atrial rate of 191/min on the surface ECG was detected in a 6-year-old Warmblood mare. The vectorcardiogram obtained from a 12-lead ECG suggested a caudo-dorsal right atrial origin of the arrhythmia. Impedance-based three-dimensional electro-anatomical mapping, using the EnSite™ Precision Cardiac Mapping System revealed a clockwise macro-reentry around a line of conduction block in the caudomedial right atrium. Ten radiofrequency applications were applied to isolate the caudal vena cava myocardial sleeves at a power of 35 W and mean contact force of 14 ± 3 g until a lesion size index of 6 was reached. Sinus rhythm was restored at the first energy application. Successful isolation was confirmed by demonstrating entrance and exit block. Holter monitoring 5 days post-ablation revealed no abnormalities. To date, 9 months after treatment, no recurrence has been observed. The use of lesion size index-guided ablation and isolation of the arrhythmogenic substrate in the caudal vena cava may minimise the risk of recurrence., (© 2024 EVJ Ltd.)

Radiofrequency ablation is a promising technique for arrhythmia treatment in horses. Due to the thicker myocardial wall and higher blood flow in horses, it is unknown if conventional radiofrequency settings used in human medicine can be extrapolated to horses. The study aim is to describe the effect of ablation settings on lesion dimensions in equine myocardium. To study species dependent effects, results were compared to swine myocardium. Right ventricular and right and left atrial equine myocardium and right ventricular swine myocardium were suspended in a bath with circulating isotonic saline at 37 °C. The ablation catheter delivered radiofrequency energy at different-power-duration combinations with a contact force of 20 g. Lesion depth and width were measured and lesion volume was calculated. Higher power or longer duration of radiofrequency energy delivery increased lesion size significantly in the equine atrial myocardium and in equine and swine ventricular myocardium (P < 0.001). Mean lesion depth in equine atrial myocardium ranged from 2.9 to 5.5 mm with a diameter ranging from 6.9 to 10.1 mm. Lesion diameter was significantly larger in equine tissue compared to swine tissue (P = 0.020). Obtained data in combination with estimated wall thickness can improve lesion transmurality which might reduce arrhythmia recurrence. Optimal ablation settings may differ between species., (© 2024. The Author(s).)

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., (© 2024 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

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., (© 2024 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

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., (© 2024 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

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., (© 2023 EVJ Ltd.)

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., (© 2024 EVJ Ltd.)

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., (© 2024 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

Automated milking systems (AMSs) already incorporate a variety of milk monitoring and sensing equipment, but the sensitivity, specificity, and positive predictive value of clinical mastitis (CM) detection remain low. A typical symptom of CM is the presence of clots in the milk during fore-stripping. The objective of this study was the development and evaluation of a deep learning model with image recognition capabilities, specifically a convolutional neural network (NN), capable of detecting such clots on pictures of the milk filter socks of the milking system, after the phase in which the first streams of milk have been discarded. In total, 696 pictures were taken with clots and 586 pictures without. These were randomly divided into 60/20/20 training, validation, and testing datasets, respectively, for the training and validation of the NN. A convolutional NN with residual connections was trained, and the hyperparameters were optimized based on the validation dataset using a genetic algorithm. The integrated gradients were calculated to explain the interpretation of the NN. The accuracy of the NN on the testing dataset was 100%. The integrated gradients showed that the NN identified the clots. Further field validation through integration into AMS is necessary, but the proposed deep learning method is very promising for the inline detection of CM on AMS farms.

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., (© 2021 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)

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., (© 2022 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

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., (© 2022 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

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.

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.

Background: Arrhythmias are common in horses, but catheter-based minimally invasive electrophysiological studies and therapeutic interventions have been poorly explored in equine medicine, partly due to the lack of detailed anatomical knowledge of the equine heart., Objectives: To describe the dimensions and anatomical features of some electrophysiologically important landmarks of the right atrium in detail and assess their correlation with bodyweight and aortic diameter., Study Design: Ex vivo cadaveric study., Methods: Twenty-one hearts of Warmblood horses, subjected to euthanasia for noncardiovascular reasons, were examined post-mortem. The dimensions and anatomical features of the coronary sinus, the great cardiac vein and the oval fossa were recorded. Spearman's Rho correlation coefficients were calculated for correlations between the quantitative parameters and bodyweight and aortic diameter., Results: Median dimensions for coronary sinus, great cardiac vein and oval fossa were obtained. A Thebesian valve, partially covering the ostium of the coronary sinus, was present in 9 of the 21 hearts. A median of 6.5 (range 4-9) valves were present in the great cardiac vein. Several parameters, among which the dimensions of the oval fossa and the length of the great cardiac vein, were significantly positively correlated with bodyweight and aortic diameter., Main Limitations: Measurements do not consider the dynamic changes during the cardiac cycle as measurements were performed ex vivo. All specimens were retrieved from Warmblood horses, therefore measurements might not apply to other breeds., Conclusions: This study delivers a detailed description of important right atrial-related structures, necessary for the development of minimally invasive intracardiac procedures in horses. Adequate imaging techniques will have to be explored in order to guide these procedures., (© 2020 EVJ Ltd.)

Arterial rupture is a well-recognized cause of sudden death in horses, which mainly affects older horses. The arterial wall is known to stiffen with age, although the underlying age-related histological and biomechanical changes remain unclear. The purpose of this study was to investigate the effect of aging by histological analysis of the arterial wall and examination of the arterial wall biomechanical properties using an inflation-extension test. Entire circular samples of the proximal and distal aorta, cranial and caudal common carotid, external iliac, femoral and median artery were collected from 6 young (6 years) and 14 old horses (≥15 years). Samples of all arteries were histologically examined and intima media thickness as well as area % of elastin, smooth muscle actin and collagen type I and III were determined. Older horses had a significantly larger intima media thickness and a significantly higher area % of smooth muscle actin compared to young horses. Samples of the proximal and distal aorta, the caudal common carotid and the external iliac artery were mechanically assessed using an in-house developed inflation-extension device with ultrasound analysis. Rupture occurred in a minority of arteries (8/78) at high pressures (between 250-300 mmHg), and mostly occurred in older horses (7/8). Pressure-area, pressure-compliance and pressure-distensibility curves were constructed. A significant difference in the pressure-area curves of the distal aorta, common carotid artery and external iliac artery, the pressure-compliance curves of the proximal aorta and carotid artery and the pressure-distensibility curve of the proximal aorta was observed between young and old horses. Results demonstrate an effect of age on the histological and biomechanical properties of the arterial wall, which might explain why arterial rupture occurs more often in older horses., Competing Interests: The authors have declared that no competing interests exist.

Background: Ventricular septal defects (VSDs) are the most common congenital cardiac defect in horses., Objectives: To identify prevalence, age, breed, and sex distribution of VSD and to describe associated clinical and ultrasonographic findings., Animals: Hospital-based population of 21 136 horses presented to the equine internal medicine department., Methods: Medical records over a 12-year period were reviewed for VSD confirmed by ultrasonography. Age, breed, sex, sport discipline, murmur, clinical signs, outcome, VSD type, VSD size, shunt velocity, cardiac dimensions, concomitant cardiac anomalies, and valvular regurgitations were recorded., Results: From 1894 horses that underwent echocardiography, 54 had a VSD: 42 as an isolated lesion and 12 as part of complex congenital heart disease (CHD). Median age was 5 years (range, 0-26) and 1 year (range, 0-8), respectively. Warmbloods and males were overrepresented. In the isolated VSD group, only 15% had associated clinical signs and most horses had a perimembranous VSD (pmVSD; 36/42). Horses with a pmVSD and clinical signs showed a significantly lower maximal shunt velocity (3.77 vs 5.20 m/s; P < .001), higher VSD/Aortic root (Ao) diameter (0.52 vs 0.38; P = .05), higher left atrium/Ao diameter (1.94 vs 1.22; P < .001), and higher pulmonary artery/Ao diameter (1.15 vs 0.88; P = .005) compared to horses without clinical signs. All horses with complex CHD had clinical signs and abnormal cardiac dimensions., Conclusion and Clinical Importance: Most isolated VSD were diagnosed only at a later age and were not associated with clinical signs. Horses with complex CHD were more likely to have or develop clinical signs at younger age., (© 2021 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

Atrial fibrillation (AF) is suspected by an irregularly irregular rhythm during auscultation at rest and should be confirmed by electrocardiography. Heart rate monitoring is potentially interesting for AF detection by horse owners, based on the disproportionally high heart rate during exercise or increased heart rate variability. Echocardiography and laboratory analysis are useful to identify underlying cardiac disease. Horses with severe cardiac disease should not undergo cardioversion due to the risk of recurrence. Cardioversion is recommended especially in horses performing high intensity exercise or showing average maximal heart rates higher than 220 beats per min or abnormal ventricular complexes during exercise or stress. Pharmacological cardioversion can be performed using quinidine sulphate administered orally, with an overall mean reported success rate around 80%. Other therapeutic drugs have been described such as flecainide, amiodarone or novel atrial specific compounds. Transvenous electrical cardioversion (TVEC) is performed by delivering a shock between two cardioversion catheters positioned in the left pulmonary artery and right atrium, with a success rate of >95%. After cardioversion, most horses return to their previous level of performance. However, the recurrence rate after pharmacological or electrical cardioversion is up to 39%. Recurrence has been related to previous unsuccessful treatment attempts, valvular regurgitation and the presence of atrial premature depolarisations or low atrial contractile function after cardioversion. Large atrial size and long AF duration have also been suggested as risk factors. Different approaches for preventing recurrence have been described such as the administration of sotalol, however, large clinical studies have not been published., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Background: Echocardiographic reference intervals for Friesian horses are poorly described., Objectives: To obtain reference intervals for echocardiographic measurements in Friesians and compare these with Warmbloods., Animals: One hundred healthy adult Friesians and 100 healthy adult Warmblood horses., Methods: Cross-sectional study. Two-dimensional and M-mode echocardiographic images were obtained. Echocardiographic measurements, including size, area, and volumetric measurements of left atrium, left and right ventricle, aorta, and pulmonary artery, were performed. Measurements were compared between the 2 breeds using an independent samples t test with Bonferroni correction for multiple comparisons., Results: Reference ranges for standard echocardiographic measurements in Friesians were obtained. Several left ventricular measurements were significantly smaller in Friesians compared to Warmbloods, such as the left ventricular end-diastolic volume using the 4-chamber modified Simpsons' method (99.85% confidence interval for the difference [CI] = -245 to -63). Also the right ventricular end-diastolic and peak-systolic internal diameter were smaller in Friesians (99.85% CI = -1.33 to -0.6 and 99.85% CI = -1.54 to -0.76, respectively). Fractional shortening (99.85% CI = 0.61-6) and ejection fraction (99.85% CI = 0.21-4.6) were significantly larger. No structural effects of systemic hypertension, such as concentric hypertrophy, were detected., Conclusions and Clinical Importance: Our study provides reference intervals for echocardiographic measurements in Friesians useful in a clinical setting. In general, the left ventricular dimensions in Friesians were significantly smaller compared to Warmbloods, emphasizing the need for breed-specific reference intervals., (© 2020 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

Background: Arterial rupture mainly affects older horses. The reason why older horses are more prone to arterial rupture and which underlying vascular changes predispose older horses to aortic rupture is still unclear., Objectives: To investigate the effect of ageing on the equine arterial wall and blood pressure., Study Design: Cohort study., Methods: Non-invasive blood pressure measurement using a tail cuff and vascular ultrasound from aorta, common carotid artery and external iliac artery was performed in 50 healthy young (3-7 years) and 50 healthy old Warmblood horses (>18 years). Arterial diameters and cross-sectional areas, and arterial wall thickness were measured offline. Regional arterial wall stiffness of the aorta and common carotid artery were assessed using pulse wave velocity, while lumen area/diameter change, strain, compliance and distensibility were calculated to assess local arterial wall stiffness., Results: No difference in blood pressure was found between old and young horses. All arterial dimensions and intima-media thickness of the common carotid artery were significantly larger in old horses. A significantly higher local arterial wall stiffness was found for the aorta and the caudal common carotid artery in older horses. For the external iliac artery, no significant differences in arterial wall stiffness were found. Both aortic and carotid pulse wave velocities were higher in older horses compared with younger horses., Main Limitations: Blood pressure was measured non-invasively., Conclusions: In horses, arteries stiffen with age, in combination with luminal enlargement and arterial wall thickening. This might, at least partially, explain the increased incidence of arterial rupture in older horses., (© 2020 EVJ Ltd.)

Atrial fibrillation (AF) is the most common clinically relevant arrhythmia in horses, with a reported prevalence up to 2.5%. The pathophysiology has mainly been investigated in experimental animal models and human medicine, with limited studies in horses. Atrial fibrillation results from the interplay between electrical triggers and a susceptible substrate. Triggers consist of atrial premature depolarizations due to altered automaticity or triggered activity, or local (micro)reentry. The arrhythmia is promoted by atrial myocardial ion channel alterations, Ca 2+ handling alterations, structural abnormalities, and autonomic nervous system imbalance. Predisposing factors include structural heart disease such as valvular regurgitation resulting in chronic atrial stretch, although many horses show so-called 'lone AF' or idiopathic AF in which no underlying cardiac abnormalities can be detected using routine diagnostic techniques. These horses may have underlying ion channel dysfunction or undiagnosed myocardial (micro)structural alterations. Atrial fibrillation itself results in electrical, contractile and structural remodelling, fostering AF maintenance. Electrical remodelling leads to shortening of the atrial effective refractory period, promoting reentry. Contractile remodelling consists of decreased myocardial contractility, while structural remodelling includes the development of interstitial fibrosis and atrial enlargement. Reverse remodelling occurs after cardioversion to sinus rhythm, but full recovery may take weeks to months depending on duration of AF. The clinical signs of AF depend on the aerobic demands during exercise, ventricular rhythm response and presence of underlying cardiac disease. In horses with so-called 'lone AF', clinical signs are usually absent at rest but during exercise poor performance, exercise-induced pulmonary hemorrhage, respiratory distress, weakness or rarely collapse may develop., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Minimally-invasive catheter-based interventional cardiology is a mainstay for the diagnosis and treatment of arrhythmias in human medicine. Very accurate imaging using fluoroscopy, CT and MRI is essential during interventional cardiology procedures. Because these imaging techniques are either not possible or provide too little anatomical detail in horses, echocardiography is currently the best technique to visualize catheters in horses. Over the past decades, catheter-based techniques have been applied to induce arrhythmias using pacing and to perform arrhythmia research using electrophysiological studies. In bradycardic animals with clinical signs, permanent pacing can be achieved by pacemaker implantation via the cephalic vein. Transvenous electrical cardioversion, based on one cardioversion catheter in the pulmonary artery and one in the right atrium, has become the treatment of choice for atrial fibrillation in horses, even for longstanding or drug-resistant atrial fibrillation. Recently, the highly advanced technique of three dimensional electroanatomical mapping has been described in horses. This technique has not only revealed essential electrophysiological data in horses, but has also facilitated the successful ablation of atrial tachycardia in horses., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Ultra-high-density cardiac mapping allows very accurate characterisation of atrial and ventricular electrophysiology and activation timing., Objective: To describe the technique and evaluate the feasibility of magnetic electro-anatomical mapping of the equine heart., Study Design: In vivo experimental method development., Methods: A mapping system using an 8.5F bidirectional deflectable catheter with a deployable mini-basket (3-22 mm) containing 64 electrodes divided over eight splines was evaluated. Based upon predefined beat acceptance criteria, the system automatically acquires endocardial electrograms and catheter location information. Electro-anatomical maps were acquired from four horses in sinus rhythm under general anaesthesia., Results: All endocardial areas within each chamber could be reached. Access to the left atrium required the use of a deflectable sheath. With the exception of the left atrial map of horse 1, all four chambers in all four horses could be mapped. Optimisation of the beat acceptance criteria led to a reduction in manual correction of the automatically accepted beats from 13.1% in the first horse to 0.4% of the beats in the last horse., Main Limitations: Only a limited number of horses were included in the study., Conclusion: Ultra-high-density 3D electro-anatomical mapping is feasible in adult horses and is a promising tool for electrophysiological research and characterisation of complex arrhythmias., (© 2020 EVJ Ltd.)

Background: Aortic rupture is more common in Friesians compared to Warmbloods, which might be related to differences in arterial wall composition and, as such, arterial wall stiffness (AWS). Currently, nothing is known about differences in AWS between these breeds., Objectives: Comparison of AWS parameters and noninvasive blood pressure between Friesians and Warmbloods., Animals: One hundred one healthy Friesians and 101 age-matched healthy Warmbloods., Methods: Two-dimensional and pulsed-wave Doppler ultrasound examination was performed of the aorta, common carotid artery, and external iliac artery to define local and regional AWS parameters. Regional aortic AWS was estimated using aortic-to-external iliac artery pulse wave velocity (PWV a-e ) and carotid-to-external iliac artery pulse wave velocity (PWV c-e ). Noninvasive blood pressure and heart rate were recorded simultaneously., Results: Systolic, diastolic, and mean arterial blood pressure and pulse pressure were significantly higher in Friesians compared to Warmbloods. No significant difference in heart rate was found. Most local AWS parameters (diameter change, compliance coefficient, distensibility coefficient) were significantly lower in Friesians compared to Warmbloods, indicating a stiffer aorta in Friesians. This difference could be confirmed by the regional stiffness parameters. A higher PWV a-e and PWV c-e was found in Friesians. For the cranial and caudal common carotid artery and external iliac artery, most local AWS parameters were not significantly different., Conclusions and Clinical Importance: Results indicate that aortic AWS differs between Friesian and Warmblood horses. Friesians seem to have a stiffer aorta, which might be related to the higher incidence of aortic rupture in Friesians., (© 2020 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)

Automatic or semi-automatic analysis of the equine electrocardiogram (eECG) is currently not possible because human or small animal ECG analysis software is unreliable due to a different ECG morphology in horses resulting from a different cardiac innervation. Both filtering, beat detection to classification for eECGs are currently poorly or not described in the literature. There are also no public databases available for eECGs as is the case for human ECGs. In this paper we propose the use of wavelet transforms for both filtering and QRS detection in eECGs. In addition, we propose a novel robust deep neural network using a parallel convolutional neural network architecture for ECG beat classification. The network was trained and tested using both the MIT-BIH arrhythmia and an own made eECG dataset with 26.440 beats on 4 classes: normal, premature ventricular contraction, premature atrial contraction and noise. The network was optimized using a genetic algorithm and an accuracy of 97.7% and 92.6% was achieved for the MIT-BIH and eECG database respectively. Afterwards, transfer learning from the MIT-BIH dataset to the eECG database was applied after which the average accuracy, recall, positive predictive value and F1 score of the network increased with an accuracy of 97.1%.

Background: Echocardiography is the imaging technique of choice for the equine heart. Nevertheless, knowledge about ultrasonographic identification of dorsally located structures and vessels, related to the atria, in horses is scarce., Objectives: To describe the echocardiographic approach and the identification of structures and vessels in relation to the atria in healthy horses., Methods: CT images from two equine hearts, casted with self-expanding foam, were segmented and used to identify atrial-related structures and vessels. These images were compared with standard and nonstandard ultrasound images from ten healthy horses obtained from a left and right parasternal view optimised to visualise the dorsal cardiac area., Results: On new standard ultrasound views, specific atrial anatomical landmarks such as vena cava, pulmonary arteries, intervenous tubercle and oval fossa were identified in all horses. In addition, ultrasound views were defined to visualise the brachiocephalic trunk, pulmonary veins and their ostia. The 3D segmented CT images from casted hearts were used to reconstruct slices that corresponded with the echocardiographic images and allowed correct identification of specific structures., Main Limitations: Ultrasound examinations and casts were from different animals. A small number of casts and horses were used; therefore, anatomical variation or individual differences in identifying structures on ultrasound could not be assessed., Conclusions: Important cardiac structures and vessels, even the different pulmonary veins, could be identified on standard and nonstandard ultrasound images in adult horses. This knowledge is important to guide and develop interventional cardiology and might be useful for diagnostic and therapeutic purposes., (© 2018 EVJ Ltd.)

Substantial knowledge of auditory processing within mammalian nervous systems emerged from neurophysiological studies of the mustached bat (Pteronotus parnellii). This highly social and vocal species retrieves precise information about the velocity and range of its targets through echolocation. Such high acoustic processing demands were likely the evolutionary pressures driving the over-development at peripheral (cochlea), metencephalic (cochlear nucleus), mesencephalic (inferior colliculus), diencephalic (medial geniculate body of the thalamus), and telencephalic (auditory cortex) auditory processing levels in this species. Auditory researchers stand to benefit from a three dimensional brain atlas of this species, due to its considerable contribution to auditory neuroscience. Our MRI-based atlas was generated from 2 sets of image data of an ex-vivo male mustached bat's brain: a detailed 3D-T2-weighted-RARE scan [(59 × 63 x 85) μm 3 ] and track density images based on super resolution diffusion tensor images [(78) μm 3 ] reconstructed from a set of low resolution diffusion weighted images using Super-Resolution-Reconstruction (SRR). By surface-rendering these delineations and extrapolating from cortical landmarks and data from previous studies, we generated overlays that estimate the locations of classic functional subregions within mustached bat auditory cortex. This atlas is freely available from our website and can simplify future electrophysiological, microinjection, and neuroimaging studies in this and related species., (Copyright © 2018 Elsevier Inc. All rights reserved.)