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

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

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

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

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

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

Unilateral jugular vein stenosis in five horses and experience with percutaneous transluminal angioplasty.

BACKGROUND: Venous stenosis, a possible cause of jugular dilatation and congestion, is well known in human medicine but has poorly been described in horses. OBJECTIVE: To report unilateral jugular vein stenosis as a cause of jugular vein dilatation in horses and describe treatment by percutaneous transluminal angioplasty (PTA). STUDY DESIGN: Case report. METHODS: Details of horses diagnosed with unilateral jugular stenosis were retrieved from medical records. RESULTS: Five horses were presented with a non-painful, unilateral dilatation of the jugular vein of which two horses showed headshaking during exercise. In one horse an indwelling catheter had been used and jugular dilatation developed 4 weeks later. In the other horses, no intravenous injections had been administered in the months before jugular dilatation developed. Ultrasonographic examination revealed venous stenosis in all horses approximately 5-10 cm cranial to the thoracic inlet. The internal diameter at the level of this stenosis was only 1-3.1 mm. The length of the stenosis was about 15-19 mm with a markedly thickened intima and media on ultrasonography. After enoxaparin treatment, PTA was performed in three horses. During the procedure the stenotic vein was dilated three times with progressively increasing pressures up to 12 atm. The stenotic diameter increased to a maximum of 4.9 mm with improved jugular blood flow. Aftercare included anti-inflammatory and anti-thrombotic therapy. CONCLUSION: Jugular vein stenosis occurs in horses and should be included in the differential diagnoses of unilateral jugular vein dilatation. It may present in the absence of previous intravenous treatment. PTA of the jugular vein is feasible to improve jugular blood flow.

Histological and biomechanical properties of systemic arteries in young and old Warmblood horses.

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.

Prevalence and characteristics of ventricular septal defects in a non-racehorse equine population (2008-2019).

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.

Atrial fibrillation in horses Part 2: Diagnosis, treatment and prognosis.

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.

Right atrial-related structures in horses of interest during electrophysiological studies.

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.

Reference values for 2-dimensional and M-mode echocardiography in Friesian and Warmblood horses.

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.

Catheter-based electrical interventions to study, diagnose and treat arrhythmias in horses: From refractory period to electro-anatomical mapping.

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.

Atrial fibrillation in horses part 1: Pathophysiology.

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, Ca2+ 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.

Age-related differences in blood pressure, ultrasound-derived arterial diameters and arterial wall stiffness parameters in horses.

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.

Differences in ultrasound-derived arterial wall stiffness parameters and noninvasive blood pressure between Friesian horses and Warmblood horses.

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 (PWVa-e ) and carotid-to-external iliac artery pulse wave velocity (PWVc-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 PWVa-e and PWVc-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.

Three dimensional ultra-high-density electro-anatomical cardiac mapping in horses: methodology.

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.

Correction: A 1D computer model of the arterial circulation in horses: An important resource for studying global interactions between heart and vessels under normal and pathological conditions.

[This corrects the article DOI: 10.1371/journal.pone.0221425.].

A 1D computer model of the arterial circulation in horses: An important resource for studying global interactions between heart and vessels under normal and pathological conditions.

Arterial rupture in horses has been observed during exercise, after phenylephrine administration or during parturition (uterine artery). In human pathophysiological research, the use of computer models for studying arterial hemodynamics and understanding normal and abnormal characteristics of arterial pressure and flow waveforms is very common. The objective of this research was to develop a computer model of the equine arterial circulation, in order to study local intra-arterial pressures and flow dynamics in horses. Morphologically, large differences exist between human and equine aortic arch and arterial branching patterns. Development of the present model was based on post-mortem obtained anatomical data of the arterial tree (arterial lengths, diameters and branching angles); in vivo collected ultrasonographic flow profiles from the common carotid artery, external iliac artery, median artery and aorta; and invasively collected pressure curves from carotid artery and aorta. These data were used as input for a previously validated (in humans) 1D arterial network model. Data on terminal resistance and arterial compliance parameters were tuned to equine physiology. Given the large arterial diameters, Womersley theory was used to compute friction coefficients, and the input into the arterial system was provided via a scaled time-varying elastance model of the left heart. Outcomes showed plausible predictions of pressure and flow waveforms throughout the considered arterial tree. Simulated flow waveform morphology was in line with measured flow profiles. Consideration of gravity further improved model based predicted waveforms. Derived flow waveform patterns could be explained using wave power analysis. The model offers possibilities as a research tool to predict changes in flow profiles and local pressures as a result of strenuous exercise or altered arterial wall properties related to age, breed or gender.

Electrocardiographic confirmation of a twin pregnancy in a mare at 8 months of gestation.

A 15-year-old Warmblood mare, at 8 months of gestation, was presented to the Ghent University Faculty of Veterinary Medicine for evaluation of suspected stage one labor. Transrectal ultrasonography revealed no clear signs of placentitis or stage one labor. The combined thickness of uterus and placenta was 11 mm and the cervix was closed. Twin pregnancy was suspected by transabdominal ultrasonography but could not be confirmed with certainty. An electrocardiogram (ECG) was recorded from the mare's abdominal wall to register a fetal ECG. To confirm twin pregnancy, registration of both fetal ECGs simultaneously on the same ECG trace was attempted. Twelve different electrode configurations were used. In 11 recordings, one fetal ECG was visible. Only one specific right-sided electrode configuration showed both fetal ECGs at the same time, which confirmed twin pregnancy. Although electrocardiographic diagnosis of a twin pregnancy in a mare is possible, this case highlights the need for multiple electrode configurations and the high likelihood of false negatives.

Isolation of pulmonary veins using a thermoreactive implantable device with external energy transfer: Evaluation in a porcine model.

BACKGROUND: Pulmonary vein isolation (PVI) is a well-established method for the treatment of symptomatic paroxysmal atrial fibrillation, but is only partly successful with a high rate of electrical reconnection. We introduce a novel technique in which PVI is accomplished by noninvasive heating of a dedicated thermoresponse implant inserted into the pulmonary veins (PV), demonstrated in a porcine model. METHODS: A self-expanding nitinol-based implant was positioned in the common inferior PV of 11 pigs, using a fluoroscopy-guided transatrial appendage approach. Ablation was performed through contactless energy transfer from a primary extracorporal coil to a secondary heat ring (HR) embedded in the proximal part of the implant. Electrophysiological conduction was assessed prior to and postablation, and at 3 months. Histological samples were obtained acutely (n  =  4) and after 3 months (n  =  7). RESULTS: In total, 13 PV implants were successfully positioned in the inferior PVs of 11 animals. Ablation was performed without injury of adjacent structures. PVI and bidirectional block was electrophysiologically confirmed in all cases immediately at the time of implantation and 3 months later in seven chronic animals in whom testing was repeated. Marked evidence of ablation around the proximal HR was evident at 3 months postprocedure, with scar tissue formation and only mild neointimal proliferation. CONCLUSIONS: Successful PVI can be obtained by external electromagnetic heat transfer to a novel pulmonary vein implant.

Measurement variability of right atrial and ventricular monophasic action potential and refractory period measurements in the standing non-sedated horse.

BACKGROUND: In human and veterinary medicine, monophasic action potential (MAP) analysis and determination of local refractory periods by contact electrode technique gives valuable information about local cardiac electrophysiological properties. It is used to investigate dysrhythmias and the impact of drugs on the myocardium. Precise measurement of total MAP duration is difficult, therefore the MAP duration is usually determined at a repolarization level of 90% (APD90). Until now, no studies are published about the feasibility of this technique in the standing non-sedated horse. In 6 healthy Warmblood horses, on two different days, an 8F quadripolar contact catheter was passed through a jugular introducer sheath and placed under ultrasound guidance at the level of the intervenous tubercle or right atrial free wall (RA), and in the right ventricular apex (RV) to record the MAP. The MAP amplitude and APD90 were measured at a resting sinus rhythm (heart rate of 30-42 bpm) and at pacing cycle lengths (PCL) of 1000 and 600 ms. The effective refractory period (ERP) was determined at PCL of 1000 and 600 ms. RESULTS: The overall mean (±SD) APD90 (rest), APD90 (1000) and APD90 (600) were 263 ± 39 ms, 262 ± 41 ms, 236 ± 47 ms for the RA and 467 ± 23 ms, 412 ± 38 ms, 322 ± 29 ms for the RV. The mean ERP1000 and ERP600 were 273 ± 24 ms and 256 ± 22 ms for the RA and 386 ± 40 ms and 293 ± 30 ms for the RV. The measurement variability for the amplitude, APD90 and ERP measurements in the RA ranged between 36 and 44, 9-22 and 7-8%, respectively. The measurement variability for the amplitude, APD90 and ERP measurements in the RV ranged between 49 and 66, 6-7 and 10-12%, respectively. CONCLUSIONS: RA and RV MAP duration and ERP can be obtained by a contact electrode in standing non-sedated horses. The measurement variability varies with catheter location.

Effect of sotalol on heart rate, QT interval, and atrial fibrillation cycle length in horses with atrial fibrillation.

BACKGROUND: Based on its pharmacokinetic profile and electrophysiological effects in healthy horses, sotalol potentially could be used as a long-term PO antiarrhythmic drug in horses. OBJECTIVES: To evaluate the effect of sotalol on heart rate (HR), QT interval, atrial fibrillatory rate, and success of cardioversion in horses with naturally occurring chronic atrial fibrillation (AF). ANIMALS: Twenty-eight horses referred for transvenous electrical cardioversion of AF were treated with 2 mg/kg sotalol PO q12h for 3 days before cardioversion, and 13 horses underwent the same protocol without sotalol administration. METHODS: Retrospective study. Before and after sotalol or no treatment, the HR was measured at rest and during an exercise test. The QT interval and atrial fibrillation cycle length (AFCL) were measured at rest using tissue Doppler velocity imaging. RESULTS: In the control group, no significant differences were found between the 2 examinations. In the sotalol group, the HR at rest and during exercise was significantly lower after sotalol treatment, whereas the QT interval and AFCL measured by tissue Doppler increased significantly. Cardioversion to sinus rhythm was achieved in 25/28 horses in the sotalol group and all horses in the control group, but the median number of shocks and energy at cardioversion were significantly lower in the sotalol group. CONCLUSIONS AND CLINICAL IMPORTANCE: In horses with AF, sotalol administration results in class III antiarrhythmic effects and ß-blocking activity, with moderate HR reduction during exercise.