BACKGROUND:Twelve-lead electrocardiography (ECG) is essential in human cardiology but remains poorly investigated in equine medicine due to a lack of standardization and inconsistent findings. HYPOTHESIS/OBJECTIVES:Describe the normal vectorcardiogram (VCG) variation in horses at rest and during exercise using Delta 12-lead ECG, including repeatability and intra- and interobserver variations. ANIMALS:One hundred two healthy Warmblood horses, aged 3-20 years, were examined at rest, of which 30 also during exercise. METHODS:Prospective, observational study. Electrocardiograms were recorded using a Δ 12-lead configuration with precordial electrodes positioned at atrial and mid-ventricular levels. Data were processed with custom MATLAB scripts to generate mean ECG and VCG patterns. Repeatability and intra- and interobserver reliability were assessed using cross-correlation and circular statistics in R. RESULTS:Electrocardiographs were obtained during sinus rhythm. The Δ 12-lead configuration and derived VCG showed high repeatability, with significant intra- and interobserver reliability at rest and during exercise. The mean directions of the P wave and the QRS complex were similar during rest and exercise. The P loop and the initial QRS showed leftward and caudoventral orientation on VCG, while the remainder of the QRS loop was oriented in a dorsocranial direction and slightly to the left or right. CONCLUSIONS AND CLINICAL IMPORTANCE:The Δ 12-lead configuration and the derived VCG show consistent patterns during sinus rhythm, both at rest and during exercise. These features hold promise for improving the diagnosis of atrial and ventricular arrhythmias, particularly because the orthogonal XYZ-leads offer a format that is easier for practicing veterinarians to interpret.

In human medicine, homocysteine, a sulfur-containing amino acid, is used as a biomarker reflecting endothelial dysfunction, inflammation, thrombogenesis, oxidative stress and cardiovascular disease. An automated enzyme-cycling assay for homocysteine, established for humans, has been validated and reference ranges have been created for horses. In this study the homocysteine assay was further evaluated by assessing short-term stability (whole blood and plasma samples stored at 4 °C and room temperature for 24 h), long-term stability (two years), the effect of different anticoagulants (lithium heparin, sodium citrate, EDTA, no additives) and repeated freeze–thaw cycles (five times). Further, associations between plasma homocysteine concentrations ([HCY]p) and echocardiographic variables of left heart size, left heart function, and left-sided valve regurgitation were investigated. Homocysteine concentrations remained stable in whole blood at room temperature for at least four hours, or longer when plasma is separated and kept at 4 °C. Samples could be collected in serum blood tubes, lithium heparin (LH), or EDTA without affecting homocysteine concentrations ([HCY]). Plasma [HCY] in frozen samples increased slightly with storage time (years), though up to five freeze–thaw cycles did not affect [HCY]p. In a cohort of 169 horses with left-sided valvular regurgitation, plasma creatinine concentrations and age were positively associated with higher [HCY]p, but no association between [HCY]p and changes in cardiac size, function or severity of valvular regurgitation could be established. Homocysteine is not associated with left-sided valvular heart disease in horses and is not a useful biomarker for structural or functional cardiac changes.

IntroductionArrhythmias in non-human animals offer insights into human electrophysiology, yet physicians may be unaware of their occurrence and significance. This paper presents selected examples of arrhythmias in dogs, horses, and birds— as an invitation to human cardiologists to explore how animal models can illuminate mechanisms, genetics, and therapeutic approaches relevant to human electrophysiology.MethodsLeading veterinary cardiologists compiled overviews of common arrhythmias in dogs, cats, horses and birds. Genetic predisposition, natural history, therapeutic approaches, and epidemiology were compared across these species and humans, highlighting translational opportunities.ResultsCommon human arrhythmias including atrial fibrillation, bradycardia, ventricular tachycardia, and arrhythmogenic right ventricular cardiomyopathy occur naturally in dogs, cats, horses, and birds. Cross-species differences in disease expression provide unique insights into mechanisms of arrhythmia vulnerability and resistance. Dogs develop similar inherited arrhythmogenic diseases but with distinct phenotypes. Horses experience atrial fibrillation without thromboembolic complications, revealing potential protective pathways. They also demonstrate extreme exercise-induced arrhythmia susceptibility, isolating exercise as an arrhythmogenic trigger. Avian species exhibit remarkable adaptation to cardiac loading conditions that would be pathological in mammals. These comparative observations across species highlight novel mechanisms underlying both susceptibility and resistance to arrhythmias and conduction disorders, offering unexplored therapeutic targets for human patients.DiscussionCross-species knowledge offers direct translational value for human electrophysiology—from genetic markers in Labrador Retrievers with supraventricular tachycardia to cardiac loading paradigms in broiler chickens. Breaking down disciplinary barriers through shared research initiatives and integrated training represents an essential, underutilized strategy for advancing arrhythmia diagnosis, treatment, and prevention in human patients.

Developing clinical skills is an essential part of veterinary education. The objective was to evaluate the clinical skills training in the veterinary curriculum at Ghent University based on a qualitative study. Semistructured interviews among 82 final-year veterinary students and 53 recent graduates were conducted by bachelor students in pedagogical sciences as part of an introductory course in pedagogical research. Veterinary students and graduates were asked to score the perceived importance of different clinical skills and comment on the reasons for higher or lower importance. They also scored their own self-efficacy in these skills and commented on what made them score high on certain skills. Finally, they were asked about the contribution of skills laboratory training, intramural clinical rotations, and extramural rotations to the development of their clinical skills. The most important skills identified by students and graduates were animal handling, clinical examination, treatments (eg, injections or bandages), and communication skills. These were seen as a basic requirement or crucial skills for the (future) job, important for use in daily clinical practice, important for clients' trust, and essential for animal and veterinarian safety. Perceived self-efficacy was high for the same skills. Although skills laboratory training was considered valuable, the main factor contributing to self-efficacy was repeated practice during intramural clinical rotations and extramural rotations along with professional experiences during the first year after graduation. Skills laboratory training can be used as a first step for teaching clinical skills, but repeated practice in a clinical setting remains crucial.

INTRODUCTION/OBJECTIVES:Mitral valve regurgitation (MR) is frequently detected in horses, but its classification and prognostication remain challenging. This study investigated whether auscultatory findings and left atrial function are associated with MR severity. ANIMALS, MATERIALS AND METHODS:Fifty controls (no/trivial MR) and 101 MR horses (58 mild, 36 moderate, seven severe) were retrospectively evaluated. All were in sinus rhythm and underwent auscultation and echocardiography. Mitral regurgitation severity was graded using a scoring system. Systolic murmur characteristics (duration, type and grade) were recorded. Left atrial function was quantified measuring left atrial fractional area change and left atrial and ventricular tissue Doppler indices. Statistics included analysis of variance, Kruskal-Wallis, chi-square, Spearman's rho and Cohen's weighted kappa tests. RESULTS:A positive association was found between MR severity and left-sided systolic murmur intensity (P < 0.001) and duration (P < 0.001), and between left-sided systolic murmur duration and largest jet duration on ultrasound (P < 0.001). Left atrial fractional area change decreased with increasing MR severity (P < 0.001). Myocardial velocity of the left atrial and ventricular free wall during atrial contraction showed non-significant differences between groups [P = 0.573 and P = 0.039 (within F-test; P ≥ 0.073 after Bonferroni correction for multiple comparisons)]. STUDY LIMITATIONS:Study limitations included the absence of a gold standard for equine MR classification and few severe MR horses. CONCLUSIONS:Although auscultation gives an indication about MR severity, echocardiography remains necessary to accurately diagnose MR and determine jet characteristics. Except for left atrial fractional area change, left atrial functional variables did not seem to be associated with MR severity in horses.

BACKGROUND:Cardiac arrhythmias are common in horses, but their clinical and prognostic relevance remains poorly defined. Despite the importance of localization for diagnosis and treatment, noninvasive methods to identify arrhythmogenic foci are limited. HYPOTHESIS/OBJECTIVES:Evaluate the ability of delta (Δ) 3- and 12-lead ECGs and 2-dimensional (2D) and 3-dimensional (3D) vectorcardiography (VCG) to identify the site of origin of focally induced atrial and ventricular premature depolarizations in horses. ANIMALS:Eight healthy horses underwent 2 electrophysiological studies, 1 standing, and 1 under general anesthesia. METHODS:Premature atrial and ventricular complexes were induced by intracardiac pacing at 29 anatomical sites. Simultaneous Δ 12-lead ECG and VCG recordings were obtained. Mean vector directions were analyzed, and classification accuracy was assessed at the chamber, regional, and site-specific levels. RESULTS:Distinct pacing sites produced reproducible and location-specific activation patterns. For differentiating left- from right-sided origins, 3D-VCG had 99% and 82% accuracies for ventricular and atrial origins, respectively. The simplified Δ-based 2D-VCG also showed strong performance on the chamber level, with accuracies of 94% and 78%, respectively. Accuracy was lower for fine-grained intra-chamber localization, especially in the atria. CONCLUSIONS AND CLINICAL IMPORTANCE:Although 3D-VCG offers superior spatial resolution, 2D-VCG provides a good balance between diagnostic accuracy and practical applicability, especially for left- vs right-sided localization. Combined Δ 12-lead ECG and VCG enables accurate, noninvasive chamber-level localization of arrhythmia origins in horses. Standardized application in larger cohorts with naturally occurring arrhythmias may support targeted ablation strategies and improve arrhythmia management and sudden cardiac death risk stratification.

BACKGROUND:Myocardial sleeves in the caudal vena cava and pulmonary veins are a potential trigger for initiation and perpetuation of atrial fibrillation (AF) in horses. OBJECTIVES:Isolation of myocardial sleeves in the caudal vena cava or pulmonary veins might reduce the risk for AF recurrence. STUDY DESIGN:Case series. METHODS:Records from seven horses with persistent, recurrent, naturally-occurring AF that were treated with three-dimensional electro-anatomical mapping and radiofrequency catheter ablation (RFCA) in order to reduce recurrence risk were reviewed. Mapping of the caudal vena cava was performed in all horses, while the pulmonary vein ostia I and IV were mapped in two horses and pulmonary vein ostia II and III in one horse. Arrhythmogenic substrate was subsequently isolated by point-by-point RFCA. RESULTS:Mapping identified arrhythmogenic substrates in the caudal vena cava (n = 6), ostium II (n = 1) and ostium IV (n = 2), which were isolated as confirmed by entrance and/or exit block. Five cases recurred (after 2 days, and 6, 11, 11 and 30 months). The horse that relapsed after 6 months underwent a second procedure to isolate ostium III, but the arrhythmia recurred 4 months later. To date, two of seven horses remain in sinus rhythm with a follow-up of 14 and 47 months. MAIN LIMITATIONS:Small number of horses and limited follow-up. CONCLUSIONS:Arrhythmogenic substrate was identified in the caudal vena cava and pulmonary veins in horses with recurrent AF. Two of seven horses remain in sinus rhythm 14-47 months after RFCA. This study does not allow to demonstrate the benefit of ablation. Catheter ablation in horses to reduce AF recurrence risk remains challenging at this point and more research is needed to identify AF triggers and improve ablation technique.

BACKGROUND:Atrial arrhythmias relevantly contribute to global morbidity and death and have been extensively studied in experimental models. However, electrophysiological disparities between animal models and humans often hinder the translation of experimental findings. This study aims to systematically characterize species-specific atrial electrophysiology to improve translation. METHODS:Atrial tissue samples were obtained from patients undergoing open heart surgery and from mice, rats, pigs, and horses, and were characterized at the cellular electrophysiological and transcriptomic level using uniform protocols. To assess the correlation of functional and transcriptomic features, action potentials were simulated from ion channel expression profiles using in silico models. RESULTS:Porcine atrial cardiomyocytes closely resembled human cells in depolarization characteristics, whereas rodents exhibited marked differences. Human atrial action potentials showed pronounced early repolarization, which was not reproduced in other species and corresponded to a greater contribution of the IKur gene group. Late repolarization, reflected by action potential duration at 90% repolarization, scaled with species and cardiomyocyte size, with humans ranging between rodents and pigs. Sex-specific differences in repolarization observed in humans were represented in pigs but not in rodents. Chamber-specific differences between left and right atrial cardiomyocytes were reflected in in silico simulations on the basis of ion channel expression. CONCLUSIONS:This study provides a reference for species-specific atrial action potential characteristics, linking functional properties to transcriptomic ion channel expression. It further demonstrates that relative changes in action potential parameters can be inferred from transcriptomic data using in silico simulations. These findings support more accurate interpretation and translation of animal experimental data to human atrial electrophysiology.

Myocardial sleeves of the caudal vena cava are the predilection site for atrial tachycardia (AT) in horses. Caudal vena cava isolation guided by the ablation index, a lesion quality marker incorporating power, duration and contact force, might improve outcome. Describe the feasibility and outcome of caudal vena cava isolation using ablation index-guided radiofrequency catheter ablation (RFCA) to treat AT in horses. Ten horses with sustained AT. Records from 10 horses with sustained AT treated by three-dimensional electro-anatomical mapping and ablation index-guided RFCA (CARTO™ 3) were reviewed. Three-dimensional electro-anatomical mapping of the right atrium identified a macro-reentry circuit in the caudomedial right atrium (n = 10). Point-by-point RFCA was performed to isolate the myocardial sleeves of the caudal vena cava in power-controlled mode with a mean of 17 ± 7 applications. The ablation index target was 400-450. A median ablation index of 436 (range, 311-763) was reached using a median maximum power of 35 (range, 24-45) W for a median duration of 20 (range, 8-45) seconds, with a median contact force of 10 (range, 3-48) g. Sinus rhythm was restored in all 10 horses. To date, 9-37 months post-ablation, none of the horses have had recurrence. Caudal vena cava isolation using ablation index-guided RFCA was feasible and effective to permanently treat sustained AT in horses. Ablation index guidance ensured efficient lesion creation, and isolation of the caudal vena cava eliminated the arrhythmogenic substrate, thereby minimizing the risk of recurrence.

Administration of N-butylscopolammonium bromide (NBB) with metamizol sodium (NBBM) causes tachycardia and hypertension, and has been associated with accentuated cardiac murmurs. To evaluate the effect of a pharmacological challenge using NBBM on valvular regurgitation and cardiac murmurs in horses with aortic (AR) and mitral valve regurgitation (MR). Twenty Warmblood horses with AR and 20 with MR. Cardiac auscultation and two-dimensional (2D), M-mode, color flow, pulsed wave Doppler flow, and tissue Doppler echocardiography were performed with simultaneous ECG recording and non-invasive blood pressure measurements during rest and pharmacological challenge using 0.2 mg/kg NBB and 25 mg/kg metamizol sodium. Cardiac dimensions and functional parameters were assessed. Regurgitant jet size was subjectively evaluated, and jet area was measured. Data at rest and during pharmacological challenge were compared using repeated measures analysis or related samples Wilcoxon signed rank test. p -values were adjusted using the Benjamini-Hochberg method. Compared with rest, pharmacological challenge resulted in decreased atrial and ventricular dimensions and increased aortic and pulmonary dimensions ( P BHa ≤ 0.02). Left ventricular end-diastolic diameter decreased in horses with AR ( P BHa < 0.02) but not in horses with MR. Pharmacological challenge resulted in increased median cardiac murmur intensity ( P BHa  = 0.03 and P BHa < 0.02) and jet area ( P BHa ≤ 0.02 and P BHa  = 0.03) in horses with AR and MR, respectively. Pharmacological challenge with NBBM affects cardiac chamber sizes, regurgitant jet, and cardiac murmur intensity in horses with AR and MR. Influences on heart rate and blood pressure should be considered during longitudinal follow-up examinations.

BACKGROUND:Frequent premature atrial complexes (PACs) can increase the risk of atrial fibrillation or atrial tachycardia, and pharmacological therapy can be challenging. OBJECTIVE:To report the use of three-dimensional electro-anatomical mapping of PAC originating from the right atrial free wall and treatment by radiofrequency ablation in three horses. STUDY DESIGN:Retrospective case report. CASE DESCRIPTION:Frequent premature atrial complexes (PACs) were diagnosed in three horses. Twelve-lead ECG and vectorcardiography suggested an origin in the right lateral free wall in two horses and the caudal right atrium in one horse. Three-dimensional electro-anatomical mapping (3D EAM) and radiofrequency ablation using the CARTO™ 3 system were performed. Isoprenaline or dobutamine administration allowed activating the focus of PACs during general anaesthesia. Activation mapping using Pattern Matching Filtering identified the origin of PACs at the mid portion of the right atrial free wall in all horses. In the first horse, ablation was not performed due to pacing-induced phrenic nerve stimulation at the site of earliest activation. In the second horse, PACs disappeared after the 18th energy application and were no longer inducible by dobutamine. In the last horse, ablation was not successful in eliminating PACs. MAIN LIMITATION:Small number of cases. CONCLUSION:The 3D EAM identified the focus of PACs at the right atrial free wall in three horses, revealing it as a possible arrhythmogenic area. Although still challenging, radiofrequency ablation has promise as a treatment to provide a permanent solution for frequent PACs.

BACKGROUND:Detailed characterization of arrhythmias can be performed by multiple catheter mapping; but this has not yet been explored in horses. OBJECTIVES:Perform ultrasound-guided multiple catheter mapping of the right heart during sinus rhythm and right and left atrial pacing to identify activation patterns characteristic of the origin of ectopy. Obtain His signals and effective refractory periods (ERP). ANIMALS:Eight healthy adult horses. METHODS:Experimental study. Recording catheters were placed at the terminal crest, intervenous tubercle, caudal vena cava, and coronary sinus. Right atrial pacing was performed in standing, sedated horses from each catheter and from the cranial vena cava, right atrial appendage, and right atrial free wall. Left atrial pacing was performed during general anesthesia at the four pulmonary vein ostia, left atrial appendage, and interatrial septum. Atrial activation patterns were recorded from the catheters during sinus rhythm and during pacing at the different sites. During sinus rhythm, the His bundle was recorded, and ERP at different sites was determined. RESULTS:Characteristic activation maps during sinus rhythm and pacing were identified. Late coronary sinus activation indicated ectopy originating from the right atrium or ostium III. The direction of coronary sinus electrode activation aided in differentiating left atrial ectopy locations. His signals were recorded in 5/8 horses. Atrial ERP varied between 170 and 420 ms with inter-horse and intra-horse variation. CONCLUSIONS AND CLINICAL IMPORTANCE:Performing an electrophysiological study in horses, including multiple catheter recording, was feasible. Pacing-induced ectopy resulted in characteristic activation patterns, which might aid in identifying the site of atrial ectopy.

Objective:To assess horse owners' behaviors and perceptions regarding communication about complementary and alternative veterinary medicine (CAVM) with their veterinarian. Methods:A cross-sectional online survey was combined with a qualitative study in the form of in-depth interviews with Flemish horse owners. Results:The study included 1,532 fully completed survey responses and 26 interviews. Overall, horse owners showed high trust in the veterinarian and were satisfied with veterinarian-client communication. While 61.7% of participants indicated that they had already talked about CAVM with their veterinarian, 25.1% of CAVM users had not discussed this with their veterinarian. The qualitative study revealed that nondisclosure of CAVM usage was associated with (1) horse owners' desire for autonomy and their sense of responsibility for their horse's health and (2) factors related to the owners' perceptions of veterinarians (eg, fear of negative reactions and a perceived lack of knowledge about CAVM in veterinarians). Owners wanted to be treated with respect and expected veterinarians to have a basic knowledge about CAVM and to initiate the conversation about CAVM. Conclusions:Veterinarian-client communication about CAVM is common, although disclosure does not always happen before CAVM usage due to owner-related factors and their perception of the veterinarian's reaction or response. Clinical Relevance:Nondisclosure of CAVM may pose a risk for the animal's welfare due to potential side effects, interaction with other treatments, or delayed conventional treatment. A relationship-centered approach may increase disclosure by taking into account the clients' experiences, values, concerns, and expectations.

BACKGROUND:Accessory pathways (APs) are muscular bundles directly connecting the atria and ventricles, bypassing the atrioventricular (AV) node-His-Purkinje system. Anterograde conduction along the AP results in ventricular preexcitation. A retrograde conducting AP allows ventriculo-atrial (VA) conduction, creating a reentry circuit that mediates orthodromic atrioventricular reentry tachycardia (OAVRT). This condition is well described in humans and small animals, but has not been reported previously in horses. OBJECTIVES:Describe clinical and electrocardiographic findings of horses with retrograde AP conduction and reporte mapping and radiofrequency ablation results in one horse. ANIMALS:Six horses with retrograde AP conduction. METHODS:Records from six horses with retrograde AP conduction were reviewed. RESULTS:Resting ECGs showed P' waves in the ST segment with fixed coupling intervals to the preceding QRS complexes. In five of six horses, P' waves were conducted back to the ventricles along the AV node, resulting in OAVRT. All horses had episodes where P' waves were blocked at the AV node, which resulted in orthodromic atrioventricular reentry bradycardia (OAVRB). In one horse, the AP conducted bidirectionally resulting in ventricular preexcitation. An electrophysiological study in one horse identified a left-atrial AP insertion by the shortest VA interval. Radiofrequency ablation using an impedance-based mapping system could not eliminate the AP. CONCLUSIONS:Retrograde conducting APs in horses caused OAVRT and OAVRB. APs in horses behaved differently compared to those in humans and dogs. Further research is necessary to elucidate AP behavior, evaluate risk and effect on performance, and assess treatment by ablation.

INTRODUCTION:Ultrasonographic guidance of catheter-based interventions in horses is based primarily on transthoracic echocardiography (TTE). Intracardiac echocardiography (ICE) has the potential to provide detailed imaging of specific cardiac regions. Insight and training in echocardiographic guidance can be acquired using an echocardiography simulator. HYPOTHESIS/OBJECTIVES:Use an echocardiography simulator for horses to determine specific ICE views for catheter-based interventions and validate these in live horses. ANIMALS:Six adult healthy experimental horses. METHODS:Observational study. An echocardiographic phantom based on a three-dimensional computer model of the equine heart was used. This phantom was positioned in a water tank, allowing simultaneous TTE and ICE catheter introduction. Novel ICE images from within the thoracic inlet and right atrium were determined on the ultrasound simulator, with TTE as back-up modality to determine ICE catheter position in the simulator if necessary. Images were validated in six horses, with adaptations to catheter manipulations where needed. RESULTS:Novel ICE images developed on the ultrasound simulator could be replicated in live horses, with no changes in catheter manipulations. These views allowed visualization of the tributaries of the cranial vena cava, both atria, pulmonary veins, aorta, and pulmonary artery. CONCLUSIONS AND CLINICAL IMPORTANCE:The ultrasound simulator was useful in developing additional ICE images in order to understand echocardiographic anatomy. This simulator creates possibilities for ICE diagnosis of specific cardiac conditions and further development of ICE-guided catheter-based interventions in horses. The ultrasound simulator can be helpful for providing echocardiographic training and reduction of experimental animal use.

BACKGROUND:Administration of N-butylscopolammonium bromide (NBB) with metamizol sodium (NBBM) causes tachycardia and hypertension, and has been associated with accentuated cardiac murmurs. OBJECTIVES:To evaluate the effect of a pharmacological challenge using NBBM on valvular regurgitation and cardiac murmurs in horses with aortic (AR) and mitral valve regurgitation (MR). ANIMALS:Twenty Warmblood horses with AR and 20 with MR. METHODS:Cardiac auscultation and two-dimensional (2D), M-mode, color flow, pulsed wave Doppler flow, and tissue Doppler echocardiography were performed with simultaneous ECG recording and non-invasive blood pressure measurements during rest and pharmacological challenge using 0.2 mg/kg NBB and 25 mg/kg metamizol sodium. Cardiac dimensions and functional parameters were assessed. Regurgitant jet size was subjectively evaluated, and jet area was measured. Data at rest and during pharmacological challenge were compared using repeated measures analysis or related samples Wilcoxon signed rank test. p-values were adjusted using the Benjamini-Hochberg method. RESULTS:Compared with rest, pharmacological challenge resulted in decreased atrial and ventricular dimensions and increased aortic and pulmonary dimensions (PBHa ≤ 0.02). Left ventricular end-diastolic diameter decreased in horses with AR (PBHa < 0.02) but not in horses with MR. Pharmacological challenge resulted in increased median cardiac murmur intensity (PBHa = 0.03 and PBHa < 0.02) and jet area (PBHa ≤ 0.02 and PBHa = 0.03) in horses with AR and MR, respectively. CONCLUSIONS AND CLINICAL IMPORTANCE:Pharmacological challenge with NBBM affects cardiac chamber sizes, regurgitant jet, and cardiac murmur intensity in horses with AR and MR. Influences on heart rate and blood pressure should be considered during longitudinal follow-up examinations.

OBJECTIVES:This study aimed to compare two-dimensional, M-mode, color, pulsed-wave Doppler (PWD) and continuous-wave Doppler (CWD) echocardiography, and PWD ultrasonography of the caudal common carotid artery (CCA) in horses with aortic regurgitation (AR). ANIMALS:Warmblood horses without (n = 20) and with mild, moderate, and severe AR (n = 60) were included in the study. MATERIALS AND METHODS:A retrospective descriptive study focused on cardiac dimensions, aortic and CCA Doppler flow. Non-invasive blood pressure and presence of ventricular arrhythmia were recorded. Groups were compared using analysis of variance, chi-square, Spearman's rho, and Kruskal-Wallis tests. RESULTS:Maximal aortic antegrade flow velocity was higher in horses with moderate and severe AR than in normal horses and higher in those with severe AR than in those with mild AR (P<0.001). Mean (standard deviation) antegrade CCA flow velocities were 0.9 m/s (0.3 m/s) in normal horses and 1.0 m/s (0.2 m/s), 1.2 m/s (0.3 m/s), and 1.5 m/s (0.4 m/s) in horses with mild, moderate, and severe AR, respectively. Retrograde mid-to-end diastolic PWD ultrasonography of the common carotid artery (PWD-CCA) flow occurred in horses with moderate (6/20) and severe (13/20) AR. The presence of pathologic retrograde PWD-CCA flow was associated with presence of increased left ventricular dimensions and pulse pressures >60 mmHg. The CWD regurgitant jet pressure half-time failed to differentiate between AR severity grades. STUDY LIMITATIONS:The limitations of this study included retrospective design with missing values, AR classification system not validated by longitudinal follow-up, and CCA retrograde velocities <10 cm/s not measured. CONCLUSIONS:Pulsed-wave Doppler ultrasonography of the common carotid artery identifies moderate and severe AR in horses with hemodynamic overload. Presence of retrograde PWD-CCA flow was associated with moderate and severe AR and with left ventricular dilation. Quantification of CWD pressure half-time appeared unreliable for AR severity assessment.

Abstract Background Myocardial sleeves of the caudal vena cava are the predilection site for atrial tachycardia (AT) in horses. Caudal vena cava isolation guided by the ablation index, a lesion quality marker incorporating power, duration and contact force, might improve outcome. Objectives Describe the feasibility and outcome of caudal vena cava isolation using ablation index‐guided radiofrequency catheter ablation (RFCA) to treat AT in horses. Animals Ten horses with sustained AT. Methods Records from 10 horses with sustained AT treated by three‐dimensional electro‐anatomical mapping and ablation index‐guided RFCA (CARTO™ 3) were reviewed. Results Three‐dimensional electro‐anatomical mapping of the right atrium identified a macro‐reentry circuit in the caudomedial right atrium (n = 10). Point‐by‐point RFCA was performed to isolate the myocardial sleeves of the caudal vena cava in power‐controlled mode with a mean of 17 ± 7 applications. The ablation index target was 400‐450. A median ablation index of 436 (range, 311‐763) was reached using a median maximum power of 35 (range, 24‐45) W for a median duration of 20 (range, 8‐45) seconds, with a median contact force of 10 (range, 3‐48) g. Sinus rhythm was restored in all 10 horses. To date, 9‐37 months post‐ablation, none of the horses have had recurrence. Conclusions and Clinical Importance Caudal vena cava isolation using ablation index‐guided RFCA was feasible and effective to permanently treat sustained AT in horses. Ablation index guidance ensured efficient lesion creation, and isolation of the caudal vena cava eliminated the arrhythmogenic substrate, thereby minimizing the risk of recurrence.