Detection of paroxysmal atrial fibrillation preceding persistent atrial fibrillation in a horse using an implantable loop recorder with remote monitoring.

Implantable loop recorders (ILRs) are increasingly used in equine cardiology to detect arrhythmias in the context of collapse, poor performance or monitoring for recurrence of atrial fibrillation (AF). However to date, the ILR has never been reported to be used with a remote monitoring functionality in horses, therefore the arrhythmia is only discovered when a clinician interrogates the ILR using dedicated equipment, which might delay diagnosis and intervention. This case report describes the use of an ILR with remote monitoring functionality in a horse with recurrent AF. The remote monitoring consisted of a transmission device located in the stable allowing daily transmission of arrhythmia recordings and functioning messages to an online server, available for the clinician to evaluate without specialised equipment. The ILR detected an episode of paroxysmal AF approximately three months after implantation. Seven months after implantation, initiation of persistent AF was seen on an episode misclassified by the ILR as bradycardia, and the horse was retired. This report shows the feasibility and benefits of remote monitoring for ILRs in horses, but also the shortcomings of current algorithms to interpret the equine electrocardiogram.

Successful high-resolution three-dimensional electroanatomical mapping and radiofrequency catheter ablation of a posteroseptal accessory pathway in a dog using CARTO 3.

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.

Development of a three-dimensional computer model of the equine heart using a polyurethane casting technique and in vivo contrast-enhanced computed tomography.

INTRODUCTION/OBJECTIVES: Insight into the three-dimensional (3D) anatomy of the equine heart is essential in veterinary education and to develop minimally invasive intracardiac procedures. The aim was to create a 3D computer model simulating the in vivo anatomy of the adult equine heart. ANIMALS: Ten horses and five ponies. MATERIALS AND METHODS: Ten horses, euthanized for non-cardiovascular reasons, were used for in situ cardiac casting with polyurethane foam and subsequent computed tomography (CT) of the excised heart. In five anaesthetized ponies, a contrast-enhanced electrocardiogram-gated CT protocol was optimized to image the entire heart. Dedicated image processing software was used to create 3D models of all CT scans derived from both methods. Resulting models were compared regarding relative proportions, detail and ease of segmentation. RESULTS: The casting protocol produced high detail, but compliant structures such as the pulmonary trunk were disproportionally expanded by the foam. Optimization of the contrast-enhanced CT protocol, especially adding a delayed phase for visualization of the cardiac veins, resulted in sufficiently detailed CT images to create an anatomically correct 3D model of the pony heart. Rescaling was needed to obtain a horse-sized model. CONCLUSIONS: Three-dimensional computer models based on contrast-enhanced CT images appeared superior to those based on casted hearts to represent the in vivo situation and are preferred to obtain an anatomically correct heart model useful for education, client communication and research purposes. Scaling was, however, necessary to obtain an approximation of an adult horse heart as cardiac CT imaging is restricted by thoracic size.

Three-dimensional electroanatomical mapping for guidance of pulmonary vein isolation as treatment for persistent atrial fibrillation in a dog.

A two-year and four-month, male German Shepherd was referred for exercise intolerance and panting. Irregular heart auscultation (250 beats per minute (bpm)) and pulse deficits were noted on physical exam. Electrocardiogram (ECG) showed irregular, narrow-QRS tachycardia without P waves compatible with coarse atrial fibrillation (AF). A 24-h ECG showed sustained AF (mean ventricular response rate 92 bpm). Echocardiography showed no structural abnormalities. Given the young age and presence of AF-related symptoms, rhythm control was preferred. Transthoracic electrical cardioversion was successfully performed six weeks later but AF recurred within 24-h. Sotalol was started but discontinued due to poor tolerance and AF persisted. Seven months after AF diagnosis, radiofrequency catheter ablation (RFCA) aiming for pulmonary vein isolation was performed under general anaesthesia. After transseptal puncture, three-dimensional electroanatomical mapping of the left atrium was performed. Point-by-point pulmonary vein isolation was achieved by RFCA. Seventy-eight RFCA lesions were placed in the left atrium encircling the three pulmonary vein ostia followed by electrical cardioversion. No complications occurred and the dog was discharged with amiodarone. In the immediate post-operative phase, there was recurrence of persistent AF requiring electrical cardioversion. Furthermore, at one month after the ablation, the dog experienced a single and transient paroxysm of AF. Since then, stable sinus rhythm (SR) was retained on daily ECG monitoring at home and confirmed by 24-h ECG three months post-operatively. Amiodarone was stopped subsequently. At the time of writing (one year post-operative), the dog remains in SR with normal exercise tolerance.

A usability evaluation of the perceived user friendliness, accessibility, and inclusiveness of a personalized digital care pathway tool.

OBJECTIVE: This study aimed to acquire insight into the perceived user friendliness, accessibility and inclusiveness of a personalized digital care pathway. MATERIALS & METHODS: Usability of the tool was tested in an experimental setting. Mixed methods data collection consisted of scenario-based eye tracking tests in a web- or mobile-based prototype of the tool, followed by a questionnaire assessing user friendliness (System Usability Scale; SUS) and a structured interview. Inclusiveness was assessed by subgroup comparisons based on language proficiency, age and education level. Via purposive sampling a heterogeneous population of users (N = 24) was recruited. Eye tracking was used to measure gaze behavior. RESULTS: Overall, participants were satisfied with the tool (scale 0-10, 7.5; SD = 1.29). User friendliness of the mobile version (68.3; SD = 21.6) was higher than the web version (50.9; SD = 17.3) measured by SUS score (0-100). With regard to accessibility, eye tracking scenarios showed that the menu bar was hard to find (17% mobile, 55% web). In all scenario's, information was found faster in the mobile version than the web version. Attention was easily drawn to images. Regarding inclusiveness of the tool, we found significantly longer completing time of the scenario tasks for low language proficiency (p-value = 0.029) and higher age subgroups (p-value = 0.049). Lower language proficiency scored a significant lower SUS score (p-value = 0.012). CONCLUSIONS: Overall, user friendliness and accessibility were positively evaluated. Assessment of inclusiveness emphasized the need for tailoring digital tools to those with low language proficiency and/or an older age. Co-creation of digital care tools with users is therefore important to match users' needs, make tools easily understandable and accessible to all users, and ultimately result in better uptake and impact.

Feasibility and safety of three-dimensional electroanatomical cardiac mapping, mapping-guided biopsy and transseptal puncture in dogs.

Three-dimensional electroanatomical mapping (3D EAM) has expanded radiofrequency catheter ablation applications in humans to almost all complex arrhythmias and has drastically reduced fluoroscopy use, yet its potential in dogs is poorly investigated. The objectives of the current study were to assess the feasibility and safety of 3D EAM of all four heart chambers, 3D EAM-guided biopsies and transseptal puncture in dogs. Eight healthy purpose-bred Beagle dogs. Electroanatomical mapping was performed under general anaesthesia during sinus rhythm using a 22-electrode mapping catheter. Left heart catheterisation was achieved by either retrograde transaortic access (n = 4) or transseptal puncture (n = 4). Successful 3D EAM of the right atrium and ventricle was achieved in all dogs at a median time of 33 (13-40) min and 17 (3-52) min, respectively. Left atrial and ventricular 3D EAM was successful in six and seven dogs, at a median time of 17 (4-27) min and 8 min (4-19 min), respectively. Complications requiring intervention occurred in one dog only and were a transient third degree atrioventricular block and pericardial effusion following transseptal puncture, which was treated by pericardiocentesis. All dogs recovered uneventfully. Fluoroscopy time was limited to a median of 7 min (0-45 min) and almost exclusively associated with transseptal puncture. Three-dimensional EAM of all cardiac chambers, including mapping-guided biopsy and transseptal puncture is feasible in small dogs. Complications are similar to those reported in human patients. This suggests a potential added value of 3D EAM to conventional electrophysiology in dogs with arrhythmias.

Relationship between atrial fibrillatory rate based on analysis of a modified base-apex surface electrocardiogram analysis and the results of transvenous electrical cardioversion in horses with spontaneous atrial fibrillation.

OBJECTIVES: To compare the atrial fibrillatory rate (AFR) derived from a local right atrial intracardiac recording (RA-FR) and from a single-lead surface electrocardiogram (ECG) during atrial fibrillation (AF) and to evaluate the correlation with transvenous electrical cardioversion (TVEC) threshold (in Joules), number of shocks and cardioversion success rate in horses. ANIMALS: ECGs and clinical records of horses with AF treated by TVEC. Horses were included if a simultaneous recording of the right atrial intracardiac electrogram and a modified base-apex ECG were available. MATERIALS AND METHODS: Clinical records of horses with AF treated by TVEC were reviewed. Three-minute long episodes of simultaneous electrograms and surface ECG during AF were selected for analysis and compared using Bland-Altman analysis. The mean RA-FR was measured from the deflections on the intracardiac electrogram, while the AFR was extracted from the surface ECG using spatiotemporal QRS and T-wave cancellation. RESULTS: Seventy-three horses satisfied the inclusion criteria. The mean difference between RA-FR and AFR was -13 fibrillations per minute (fpm), the 95% limits of agreement were between -66 and 40 fpm, and there was a moderate (ρ = 0.65) correlation between RA-FR and AFR (p < 0.001). Neither RA-FR nor AFR appeared to influence the TVEC cardioversion threshold or the number of TVEC shocks applied. CONCLUSIONS: The AFR may allow non-invasive long-term monitoring of AF dynamics. Neither RA-FR nor AFR could be used to predict the minimal defibrillation threshold for TVEC.

Partial atrioventricular septal defect in an adult sport horse.

A partial atrioventricular septal defect, represented as a large ostium primum atrial septal defect and common (bridging) atrioventricular valve leaflets with cleft septal leaflet of the mitral valve, was diagnosed incidentally in a nine-year-old warmblood gelding used for show jumping. Initial examination findings and a three-year follow-up are documented in this report. The horse was first presented for the evaluation of chronic coughing. A left-sided, grade 4/6 holosystolic (band-shaped) murmur was identified along with a similar right-sided, grade 3/6 heart murmur. Echocardiography revealed a 6.4 cm diameter communication in the ventral atrial septum, considered an ostium primum atrial septal defect, with bidirectional shunting. A hypertrophic septomarginal trabecula, a thickened tricuspid valve, a cleft septal leaflet of the mitral valve, moderate mitral and tricuspid regurgitation likely related to leaflet prolapse, mild aortic regurgitation, and signs of moderate right ventricular volume overload were found as well. Electrocardiography showed no arrhythmias neither at rest nor during treadmill exercise. The owner continued to use the horse for show jumping. No exercise intolerance or other signs of disease were noted. Follow-up examination was performed three years after initial presentation. Contrast echocardiography confirmed the presence of right-to-left shunting through the atrial septal defect. Compared with the initial examination, the left ventricular internal diameter on M-mode echocardiography had increased. Occasional ventricular premature depolarizations were noted on the resting and exercise electrocardiogram. This is the first description of a clinically asymptomatic partial atrioventricular septal defect in an adult sport horse.

Endocardial electro-anatomic mapping in healthy horses: Normal sinus impulse propagation in the left and right atrium and the ventricles.

Understanding the depolarisation pattern of the equine heart under normal physiologic conditions, and its relationship to the surface electrocardiogram (ECG), is of uppermost importance before any further research can be done about the pathophysiology of complex arrhythmias. In the present study, a 3D electro-anatomical mapping system was used to evaluate the qualitative and quantitative depolarisation patterns and correlation to the surface ECG of both the atrial and ventricular endocardium in seven healthy horses in sinus rhythm under general anaesthesia. Bipolar activation maps of the endocardium were analysed. The first atrial activation was located at the height of the terminal crest. Only one interatrial conduction pathway was recognised. The first and second P wave deflections represent the right and left atrial depolarisation, respectively. Bundle of His electrograms could be recorded in 5/7 horses. Left ventricular activation started at the mid septum and right ventricular activation started apically from the supraventricular crest. This was followed by separate depolarisations at the height of the mid free wall. Further ventricular depolarisation occurred in an explosive pattern. Electrically active tissue could be found in all pulmonary veins. In contrast to findings of previous studies, all parts of the ventricular depolarisation contributed to the surface ECG QRS complex. This study provides a reference for the normal sinus impulse endocardial propagation pattern and for conduction velocities in equine atria and ventricles.

Assessment of left ventricular function in horses with aortic regurgitation by 2D speckle tracking.

BACKGROUND: Aortic regurgitation (AR) may lead to left ventricular (LV) dilatation, cardiac arrhythmias and heart failure. Close follow-up of horses with AR is therefore paramount to detect onset of cardiac decompensation. The aim of this study was to examine whether two-dimensional speckle tracking (2DST) can be used to detect altered myocardial function in horses with chronic AR compared to control horses. Speckle tracking was performed on short axis and long axis images of the LV in 29 healthy Warmblood horses and 57 Warmblood horses with AR. Radial, circumferential and longitudinal strain, strain rate and displacement were measured for each segment separately and the average was calculated over all segments. Data generated from the apical segments were not included in the analysis. RESULTS: Radial (SR) and circumferential (SC) strain were significantly higher in horses with moderate AR (average SR 75.5 ± 24.3%, SC 19.3 ± 3.2%) but not in horses with severe AR (SR 65.5 ± 26.2%, SC 16.3 ± 3.5%), compared to control horses (SR 54.5 ± 18.0%, SC 16.8 ± 3.0%). Longitudinal strain did not show significant differences, but longitudinal displacement (DL) was larger in horses with moderate (average DL 29.5 ± 4.1 cm) and severe AR (DL 32.4 ± 6.1 cm) compared to control horses (DL 25.7 ± 4.0 cm), especially in the interventricular septum. Diastolic longitudinal strain rate was lower in early diastole in horses with severe AR (0.93 ± 0.18/s) compared to controls (1.13 ± 0.13/s). CONCLUSIONS: 2DST is able to detect altered myocardial motion in horses with AR, which showed significantly higher radial and circumferential strain. Further research is needed to determine whether these findings contribute to a more accurate diagnosis and prognosis in clinical cases.

Atrial premature depolarisations five days post electrical cardioversion are related to atrial fibrillation recurrence risk in horses.

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.

Aortic, common carotid and external iliac artery arterial wall stiffness parameters in horses: Inter-day and inter-observer and intra-observer measurement variability.

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.

Percutaneous transcatheter closure of an aorto-cardiac fistula in a six-year-old Warmblood mare with atrial fibrillation.

This report describes a rare case of an aorto-cardiac fistula in a six-year-old French Warmblood mare presented with atrial fibrillation, decreased performance, ventral oedema, bounding arterial pulsation and pathological jugular venous pulse. A 2.7-cm-diameter fistula connected the right aortic sinus of Valsalva to the right atrium. Atrial fibrillation was likely due to volume overload of the right heart due to left-to-right shunting. The horse was treated by percutaneous transcatheter closure of the fistula delivered under general anaesthesia using a transarterial approach. The operation was initially successful, and clinical signs of congestive heart failure improved immediately. However, the device dislodged six days after procedure, and the general condition of the horse deteriorated quickly. A second closure attempt to deliver the occluder using a transvenous approach in the standing horse failed, and the horse was eventually euthanized. Procedural aspects and several possible risk factors for device dislodgement are discussed.

Sustained atrial tachycardia in horses and treatment by transvenous electrical cardioversion.

BACKGROUND: Atrial tachycardia including focal atrial tachycardia and macroreentrant atrial tachycardia (atrial flutter), are occasionally found in horses. Diagnosis, treatment and follow-up of these arrhythmias has been inadequately described. OBJECTIVES: To describe the findings on surface electrocardiography (ECG), intra-atrial electrogram recording and tissue Doppler imaging (TDI), the response to treatment by transvenous electrical cardioversion (TVEC), and TDI follow-up, of sustained atrial tachycardia in horses. STUDY DESIGN: Case series. METHODS: Records from horses with sustained atrial tachycardia treated by biphasic TVEC at Ghent University were reviewed. Horses with atrial fibrillation were not included. RESULTS: Seven horses with sustained atrial tachycardia were treated with TVEC. In six cases an exercise ECG was available and in 4 a 12-lead ECG had been recorded. The mean bias between atrial cycle length measured from a right atrial intra-atrial electrogram and from TDI ranged between -2 and 3 ms depending on the sampled region. All seven cases converted to sinus rhythm during the first TVEC procedure. TDI showed atrial contractile function recovery similar to cases that were treated for atrial fibrillation. One case developed atrial fibrillation 1 day after TVEC treatment, another case showed recurrence 8 years post conversion. The other five cases were still in sinus rhythm at 9 months - 5 years after TVEC. MAIN LIMITATIONS: Due to the small number of patients, data on recurrence and follow-up of atrial recovery should be interpreted with caution. Since no invasive electrophysiology studies were performed, differentiation between focal atrial tachycardia and atrial flutter remains speculative. CONCLUSIONS: Treatment of focal atrial tachycardia or atrial flutter by TVEC has a very high success rate. Tissue Doppler imaging allows noninvasive measurement of atrial cycle length and suggests reduced atrial function after cardioversion. Long-term prognosis after cardioversion seemed similar compared to horses with atrial fibrillation, although early recurrence (<24 h) occurred in one horse.

Echocardiographic identification of atrial-related structures and vessels in horses validated by computed tomography of casted hearts.

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.

Can heart rate variability parameters derived by a heart rate monitor differentiate between atrial fibrillation and sinus rhythm?

BACKGROUND: Heart rate variability (HRV) parameters, and especially RMSSD (root mean squared successive differences in RR interval), could distinguish atrial fibrillation (AF) from sinus rhythm(SR) in horses, as was demonstrated in a previous study. If heart rate monitors (HRM) automatically calculating RMSSD could also distinguish AF from SR, they would be useful for the monitoring of AF recurrence. The objective of the study was to assess whether RMSSD values obtained from a HRM can differentiate AF from SR in horses. Furthermore, the impact of artifact correction algorithms, integrated in the analyses software for HRV analyses was evaluated. Fourteen horses presented for AF treatment were simultaneously equipped with a HRM and an electrocardiogram (ECG). A two-minute recording at rest, walk and trot, before and after cardioversion, was obtained. RR intervals used were those determined automatically by the HRM and by the equine ECG analysis software, and those obtained after manual correction of QRS detection within the ECG software. RMSSD was calculated by the HRM software and by dedicated HRV software, using six different artifact filters. Statistical analysis was performed using the Wilcoxon signed-rank test and receiver operating curves. RESULTS: The HRM, which applies a low level filter, produced high area under the curve (AUC) (> 0.9) and cut off values with high sensitivity and specificity. Similar results were obtained for the ECG, when low level artifact filtering was applied. When no artifact correction was used during trotting, an important decrease in AUC (0.75) occurred. CONCLUSION: In horses treated for AF, HRMs with automatic RMSSD calculations distinguish between AF and SR. Such devices might be a useful aid to monitor for AF recurrence in horses.

Plasma homocysteine concentrations in healthy horses and horses with atrial fibrillation.

INTRODUCTION: Homocysteine (HCY) is an amino acid produced from methionine metabolism. Plasma homocysteine concentrations ([HCY]p) are elevated (>13 µmol/L) in people with atrial fibrillation (AF) and can predict the recurrence of AF after cardioversion. This study aimed to validate a commercially available human HCY assay for use in horses to develop reference intervals for [HCY]p and compare [HCY]p in healthy horses and horses with AF. ANIMALS: Healthy horses (n = 27) and horses with AF (n = 55, 34 of which were cardioverted using transvenous electrical cardioversion). MATERIALS AND METHODS: Blood samples were analysed for HCY using an automated enzyme-cycling assay (Homocysteine Cobas C, Integra, Roche) and creatinine (compensated Jaffe method). Assay linearity and precision were assessed, reference intervals calculated and [HCY]p and creatinine compared between groups. RESULTS: The assay was precise (coefficient of variation 1.6-4.3%, n = 10 repetitions) and provided linear results (r = 0.99 for spiked and natural samples) for a range of [HCY]p. The reference interval for [HCY]p was 1.5-7.8 µmol/L. The plasma concentration of homocysteine was 4.65 ± 1.5 µmol/L (mean ± standard deviation) in healthy horses and 4.65 ± 1.72 µmol/L in horses with AF (p=0.99); [HCY]p was not associated with recurrence of AF (n = 18, p=0.97). A weak, positive correlation between plasma creatinine and [HCY]p was detected (r = 0.295, p=0.008, r2 = 0.11). CONCLUSIONS: This assay allows precise measurement of [HCY]p in horses. Unlike in people, [HCY]p is not increased in horses with AF and cannot predict AF recurrence. This might be due to differences in the underlying pathological mechanisms of AF development in people and horses.

3D reconstruction of the porcine and equine pulmonary veins, supplemented with the identification of telocytes in the horse.

The myocardial sleeve of the porcine and equine pulmonary veins were histologically investigated and reconstructed three dimensionally. Moreover, the localization of neuron cell bodies at the veno-atrial junction and alongside the myocardial sleeve was light microscopically visualized to depict the organization of nerve, myocardial and fat tissue. Finally, the presence of telocytes inside the equine pulmonary veins was demonstrated by use of transmission electron microscopy. These structures are thought to play a role in the induction of atrial fibrillation, which is frequently seen in horses, while pigs are often used as a cardiovascular model in this context. This data fills in remaining gaps in the literature concerning the histological build-up of the pulmonary veins wall in pigs and horses. In-depth knowledge on the myocardial sleeve and its surrounding cell types are important to understand the possible outcome of an ablation therapy as an atrial fibrillation treatment. In pigs and horses, the layout of the pulmonary veins wall concerning these structures is comparable to humans. However, neuron cell bodies were recovered at the veno-atrial junction in both species but not alongside the myocardial sleeve in horses.

Detection of subclinical left ventricular dysfunction by tissue Doppler imaging in horses with aortic regurgitation.

BACKGROUND: Aortic regurgitation (AR) can have an important clinical impact and in some cases leads to left ventricular (LV) failure. Tissue Doppler imaging (TDI) is an echocardiographic technique that has been used in horses to detect LV dysfunction. OBJECTIVES: To examine whether TDI detects changes in radial myocardial wall motion in horses with AR compared with control horses. STUDY DESIGN: Case-control study. METHODS: Echocardiography was performed in 30 healthy Warmblood horses and 34 Warmblood horses with AR, subdivided in groups with mild, moderate or severe AR. TDI measurements were performed on six segments of the short-axis images of the LV myocardial wall. Myocardial wall motion was evaluated by measuring velocity and deformation during isovolumetric contraction, systole, early and late diastole. Timing of different events was also measured. RESULTS: In most segments, a significantly higher systolic myocardial velocity was found in horses with AR compared with controls. Horses with AR also had higher late diastolic velocity, although the difference was not significant in all segments. TDI measurement of timing intervals demonstrated less difference between groups. MAIN LIMITATIONS: There was a significant difference in age between the control group and horses with AR, which may confound the results. The assessment of AR severity was based on subjective criteria as there is no gold standard. CONCLUSIONS: TDI showed significant differences in radial systolic and late diastolic myocardial velocity in horses with AR. This could indicate an altered LV function in these horses, but further research is needed to investigate the prognostic value of these measurements.

Pharmacokinetics and electrophysiological effects of sotalol hydrochloride in horses.

BACKGROUND: Arrhythmias in horses may require long-term anti-arrhythmic therapy. Unfortunately, oral anti-arrhythmic drugs for use in horses are currently scarce. In human patients and small animals, sotalol, a ß-blocker with class III anti-arrhythmic properties, is often used for long-term treatment. OBJECTIVES: To determine the pharmacokinetics of sotalol at multiple oral dosages in unfasted horses, as well as the effects on electro- and echocardiographic measurements, right atrial and ventricular monophasic action potential (MAP) and effective refractory period (ERP). STUDY DESIGN: Placebo controlled, double-blinded experiment. MATERIALS AND METHODS: Six healthy, unfasted Warmblood horses were given either 0, 2, 3 or 4 mg/kg bodyweight (bwt) sotalol orally (PO) twice daily (bid) for 9 days in a randomised cross-over design. Echocardiography and surface electrocardiography were performed and plasma concentrations of sotalol and right atrial and right ventricular MAPs and ERPs were determined at steady-state conditions. Statistical analysis was performed using a repeated measures univariate analysis with post hoc Bonferroni corrections. RESULTS: Calculated mean steady-state plasma concentrations determined by nonlinear mixed-effect modelling were 287 (range 234-339), 409 (359-458) and 543 (439-646) ng/mL for 2, 3 and 4 mg/kg bwt sotalol PO bid respectively. Sotalol significantly increased the QT interval and ERPs, but, despite increasing plasma concentrations, higher dosages did not result in a progressive increase in QT interval or ERPs. Echocardiographic and other electrocardiographic measurements did not change significantly. MAP durations at 90% repolarisation were not significantly different during sotalol treatment. Besides transient local sweating, no side effects were noted. MAIN LIMITATIONS: Study size and ad libitum feeding of hay. CONCLUSIONS: Sotalol at a dose of 2, 3 and 4 mg/kg bwt PO bid increases the QT interval and ERP and might be a useful drug for long-term anti-arrhythmic therapy in horses.