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Simple Summary: Cardiac murmurs caused by aortic or mitral insufficiency in horses often prompt further diagnostics to determine if the valvular insufficiencies affect the performance, safety, and life expectancy of the horse. Ambulatory acoustic cardiography (Audicor®) provides qualitative and quantitative information on hemodynamics and cardiac mechanical function and may aid in clinical diagnosis and prognostication of heart disease. The objective of this study was to investigate the use of acoustic cardiography in horses with aortic or mitral valve insufficiency. The results do not suggest any added clinical value of using the Audicor® device to detect heart murmurs and quantify alterations in cardiac hemodynamics and mechanical function in horses with aortic and mitral insufficiency that are not experiencing heart failure. Mitral and aortic valve insufficiencies have been commonly reported in horses. The objective of this study was to establish the use of acoustic cardiography (Audicor®) in horses with aortic (AI) or mitral valve insufficiency (MI). A total of 17 healthy horses, 18 horses with AI, and 28 horses with MI were prospectively included. None of the horses was in heart failure. Echocardiography and Audicor® analyses were conducted. Electromechanical activating time (EMAT), rate-corrected EMATc, left ventricular systolic time (LVST), rate-corrected LVSTc, and intensity and persistence of the third and fourth heart sound (S3, S4) were reported by Audicor®. Graphical analysis of the three-dimensional (3D) phonocardiogram served to visually detect murmurs. Audicor® snapshot variables were compared between groups using one-way ANOVA followed by Tukey's multiple-comparisons test. The association between Audicor® snapshot variables and the corresponding echocardiographic variables was investigated by linear regression and Bland–Altman analyses. Heart murmurs were not displayed on Audicor® phonocardiograms. No significant differences were found between Audicor® variables obtained in clinically healthy horses and horses with valvular insufficiency. The Audicor® device is unable to detect heart murmurs in horses. Audicor® variables representing cardiac function are not markedly altered, and their association with corresponding echocardiographic variables is poor in horses with valvular insufficiency that are not in heart failure. [ABSTRACT FROM AUTHOR]

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

Background: Focused cardiac ultrasound examination (FoCUS) is rapidly emerging for point‐of‐care cardiac assessment using hand‐carried ultrasound (HCU) devices. A specific FoCUS protocol for horses and adequate training guidelines currently are not available. Hypothesis: To gain knowledge about the training necessary to become proficient in performing FoCUS using a HCU device. Animals: Three healthy Warmblood horses were used for practical training of veterinarians and veterinary students in equine focused cardiac ultrasound (eFoCUS). Methods: Prospective educational study. An eFoCUS protocol and 1‐day training course were developed. Pre‐ and post‐course written tests were administered to participants to evaluate proficiency in knowledge of echocardiography and echocardiographic pathology. A post‐course practical examination involved performing eFoCUS and storage of representative images. Images were evaluated using an image quality score and compared between participants with some practical experience and participants with no practical experience. Results: Participants' knowledge of echocardiography increased significantly. Recognition of echocardiographic pathology pre‐course ranged from 40% to 90% (mean score, 65.7%) and post‐course from 85% to 100% (mean score, 92%). Eighteen of 21 participants were proficient in performing eFoCUS with a median image quality score of 79% (range, 42%‐95%). Image quality did not differ between participants with some practical experience compared to participants with no experience. Conclusions and Clinical Importance: Veterinarians and veterinary students independent of previous experience can become proficient in performing eFoCUS after completion of a 1‐day training course. [ABSTRACT FROM AUTHOR]

Abstract Background This report describes the results of clinical, ultrasonographic and computed tomographic examination of a 16-year-old goat with extraskeletal osteosarcoma of the thorax. Case presentation The lead clinical signs were abnormal condition and demeanour, fever, tachycardia, tachypnoea, dyspnoea and dilated jugular veins. Ultrasonographic examination of the thorax revealed a precardial mass, measuring 16.4 by 11.4 by 14.2 cm. Computed tomographic examination showed dorsocaudal displacement of the trachea, heart and lungs to the right. A tentative diagnosis of mediastinal or pleural neoplasia was made, and the goat was euthanased and necropsied. A definitive diagnosis was based on histological examination of the mass. Conclusions To our knowledge, this case report is the first description of extraskeletal osteosarcoma of the thorax in goats and serves to broaden the diagnostic spectrum of thoracic diseases in this species. Extraskeletal osteosarcoma should be part of the differential diagnosis in goats with thoracic tumours.

Abstract Background Natural heterologous valved conduits with a diameter greater than 22 mm that can be used for right ventricular outflow tract reconstruction in adults are not commercially available. The purpose of this study was to measure by ultrasonography the maximum diameter of the distended jugular veins of horses and cattle, respectively, to identify a population of animals that would be suitable for post-mortem collection of jugular veins at sizes greater than 22 mm. Methods The study population included 60 Warmblood horses, 25 Freiberger horses, 20 Brown Swiss cows, and 20 Holstein cows (including 10 Holstein and 10 Red Holstein). The maximum cross-sectional diameter of the distended jugular veins was measured at a location half-way between the mandibular angle and the thoracic inlet. The thoracic circumference (heart girth length) was used as a surrogate of body size. The jugular vein diameters of the different populations were compared by analysis of variance and the association between heart girth length and jugular vein diameter was determined in each of the four study populations by linear regression analysis. Results There was considerable individual variation of jugular vein diameters within each of the four study populations. There was no statistically significant relationship between thoracic circumference and jugular vein diameter in any of the populations. The jugular vein diameters of Brown Swiss cows were significantly larger than those of any of the other populations. Warmblood horses had significantly larger jugular vein diameters compared to Freiberger horses. Conclusion The results of this study suggest that the production of bovine or equine xenografts with diameters of greater than 22 mm would be feasible. Differences between species and breeds need to be considered. However, prediction of the jugular vein diameter based on breed and heart girth length in an individual animal is inaccurate.

Background: Echocardiographic assessment of left ventricular (LV) size and function using area‐based indices and volumetric estimates is not well established in horses. Objective: To report reference intervals and measurement variability for uni‐, 2‐, and 3‐dimensional echocardiographic indices of LV size and systolic function in Warmblood horses and to provide proof of concept for allometric scaling of variables to body weight. Unidimensional indices were to be compared to area‐based indices and LV volume estimates to establish their clinical use. Animals Thirty healthy Warmblood horses and 70 Warmblood horses with a primary diagnosis of mitral regurgitation or aortic regurgitation. Methods: Echocardiographic indices of LV size and systolic function were measured using an existing echocardiography database. Weight‐related variables were scaled to body weight (BWT). Reference intervals and measurement variability were calculated, the influence of valvular regurgitation on LV size and function was investigated and agreement between different variables for detection of reduced, normal, and increased LV size and systolic function was assessed. Results: Reference values for healthy Warmblood horses were reported. Measurement variability was sufficiently low for clinical use of all variables. Allometric scaling was effective to correct diastolic LV dimensions and cardiac output for differences in BWT. Various echocardiographic indices resulted in different conclusions regarding identification of LV enlargement and systolic dysfunction in healthy horses and horses with valvular regurgitation. Conclusions and Clinical Importance: Echocardiographic assessment of LV size and systolic function should include joint assessment of multiple uni‐ and multidimensional indices. Area‐based or volumetric indices that reflect LV long‐axis motion should be included. [ABSTRACT FROM AUTHOR]

Background: Noninvasive blood pressures (NIBP) and pulse pressures (PP) have not been published in horses with aortic and mitral regurgitation (AR or MR). Objectives: To investigate NIBP and PP in healthy Warmblood horses and horses with AR and MR and propose PP cutoffs to identify and stage AR severity. Animals: Seventy‐three Warmblood horses (healthy, 10; AR, 31; MR, 32). Methods: Retrospective study. All horses had NIBP and an echocardiogram recorded. Cases were categorized based on severity of regurgitation. Pulse pressures were compared among healthy, MR, and AR groups and among AR severity groups. Cutoffs were determined by receiver operating characteristic curve analyses. Results: Horses with AR had higher PP than horses with MR (mean difference [95% confidence interval (CI)], +17 [9‐26] mm Hg, P < .001) and controls (+17 [5‐30] mm Hg; P =.004). Horses with severe AR had higher PP compared those with mild (+38 [20‐54] mm Hg; P < 0.001) and moderate AR (+33 [18‐47] mm Hg; P < .001). The PP cutoffs to distinguish AR from MR and controls were 38 mm Hg (sensitivity [Sn], 100%; specificity [Sp], 19%) for maximal Sn and 61 mm Hg (Sn, 43%; Sp, 100%) for maximal Sp. The PP cutoffs to distinguish severe AR from mild and moderate AR were 57 mm Hg (Sn, 100%; Sp, 70%) for maximal Sn and 77 mm Hg (Sn, 75%; Sp, 100%) for maximal Sp. Conclusions and Clinical Importance: Horses with AR have increased PP. Noninvasive PP measurements interpreted with provided cutoffs may aid clinicians in diagnosing and staging severity of AR in horses. [ABSTRACT FROM AUTHOR]

Background: Little is known about normal heart rate variability (HRV) in horses during exercise. It can be difficult to separate premature beats from normal beat‐to‐beat variation at higher heart rates. Objectives: The aim was to quantify HRV in healthy horses during a high‐speed treadmill‐standardized exercise test (HSET) and to compare with the HRV in horses observed to have arrhythmias during exercise. Animals Thirteen healthy horses (Group H), 30 horses with arrhythmias (Group A), and 11 horses with poor performance but no observed arrhythmias (Group O). Methods: Prospective, observational study. All horses performed a HSET with simultaneous electrocardiograph (ECG) recorded. The ECGs were corrected for artifacts, and arrhythmias noted. Percent instantaneous beat‐to‐beat cycle length variation (% R‐R variation) was calculated, and HRV analyses were performed on trot, canter, and recovery segments. Results: Group H showed between −4.4 and +3.8% R‐R variation during trot and between −6.1 and +5.4% R‐R variation during the canter phase of the HSET. Group A had significantly larger maximum and 1st percentile R‐R shortening and lengthening compared with Group H and Group O during the recovery phase where most arrhythmias were observed. During recovery, a cutoff of 6% maximum % R‐R shortening predicted the presence of arrhythmia with 88% sensitivity and 97% specificity and likelihood ratio of 26. Conclusions and Clinical Importance: Healthy horses have little instantaneous R‐R variation during exercise. If a cardiac cycle shortens more than 6% from the previous cycle during the recovery phase, this R‐R interval is likely to represent an arrhythmic event. [ABSTRACT FROM AUTHOR]

Background: Heterotopic heart transplantation (HHT) in rodent animal models represents an important technique enabling studies on organ transplantation immunology and pharmaceutical development. Recent investigations used nonworking HHT designs, with the left ventricle (LV) bypassed in the anastomosis system. In spite of their principal success, the lack of orthogonal ventricular filling leads to myocardial atrophy. However, when focusing on the cellular and molecular mechanisms involved in the in vivo remodeling of the myocardium or cell-based cardiovascular implants, a nonworking model is suboptimal as it lacks the nativeanalogous hemodynamic and metabolic situation. Here we present the hemodynamic and electrical assessment of a biventricularly loaded murine HHT method without the need for a combined heart-lung transplantation approach. Methods: Heterotopic transplantations (n = 13) were performed on C57BL/6J-(H-2b) inbred mice (n = 13 donors, n = 13 recipients) by creating end-to-side anastomoses between the donors' cranial vena cava (CrVC) and the recipients' abdominal caudal vena cava (CVC), between the donors' ascending aorta and the recipients' abdominal aorta (aAo), and between the grafts' pulmonary trunk and the left atrium. After transplantation, a hemodynamic assessment using echocardiography (including 2D speckle tracking analysis) and electrocardiography was performed. Results: The loaded HHT procedure in the mice was performed with an overall success rate of 61%. In 3 of the remaining 5 cases, only atrial function was restored. The median duration of the entire surgical procedure for the recipient animal was 190 (IQR 180-250) min. The mean heart rate in the loaded HHT group was 355 ± 6 bpm in comparison to the control group with an in situ heart rate of 418 ± 61 bpm. A native-like closing and opening pattern of the aortic and mitral valves (visible on both 2D and M-mode images) was observed, confirming a native-analogous loading of the LV. Pulsed-wave Doppler provided visualization of the flow across the region of anastomoses between the pulmonary trunk and the left atrium, reaching a mean maximum velocity of 382 ± 12 mm/s. Exemplary 2D speckle tracking analysis of the LV free wall and interventricular septum revealed some differences in vector directions in one animal when compared to the orthotopic native heart, indicating an asynchronous movement of the LV. Conclusions: These results demonstrate the technical (micro)surgical feasibility of a fully loaded HHT procedure in the murine model without using a combined heart-lung transplantation approach. The acute hemodynamic performance of the HHT grafts approximated the native orthotopic situation. This model may open up new options for the investigation of cellular and molecular questions in the murine cardiovascular in vivo system in the near future. [ABSTRACT FROM AUTHOR]

Objective To assess the accuracy and reliability of a point-of-care (POC) triglyceride analyzer and to establish reference intervals for blood ([TRIG]POC/WB) and plasma triglyceride concentrations ([TRIG]POC/PL) in horses, ponies, and donkeys. Design Prospective study. Setting University teaching hospital. Animals 120 adult healthy equids (78 horses and ponies, 42 donkeys) and 79 equids suffering from hypertriglyceridemia (73 horses and ponies, 6 donkeys). Interventions None. Measurements and Main Results [TRIG]POC/WB and [TRIG]POC/PL were measured using a POC analyzer and plasma triglyceride concentrations were measured using a standard laboratory assay ([TRIG]LAB/PL). Reference intervals were determined. Test accuracy was assessed by Bland-Altman comparison of POC measurements with standard laboratory measurements and by evaluating linearity of dilutional series. Test reliability was assessed by repeated serial measurements. [TRIG]POC/WB and [TRIG]POC/PL were below the analytic range of the POC assay (<0.8 mmol/L [<70 mg/dL]) in healthy horses and ponies, whereas the reference intervals were 0.82-3.14 mmol/L (73-278 mg/dL) and 0.87-3.02 mmol/L (77-267 mg/dL), respectively, in donkeys. The POC analyzer systematically overestimated triglyceride concentrations when compared to a standard laboratory assay. The difference between [TRIG]POC/WB and [TRIG]POC/PL was small and clinically negligible. The coefficient of variation of repeated measures performed on the POC analyzer was below 10% for [TRIG]POC/WB and [TRIG]POC/PL, both in horses and donkeys and at all concentration ranges. Conclusions The POC analyzer allows accurate and reliable measurement of [TRIG]POC/WB and [TRIG]POC/PL in horses, ponies, and donkeys in clinical settings. Assay-specific reference intervals should be determined for diagnosis and clinical monitoring of hypertriglyceridemia in equids. [ABSTRACT FROM AUTHOR]

Objectives To assess the measurement reliability of rotational thromboelastometry (ROTEM) measurements in horses, establish reference intervals for healthy horses, and evaluate the relationship between ROTEM variables, hematologic variables, and standard coagulation tests. Design Prospective observational study. Setting University teaching hospital. Animals Fifty healthy and 10 diseased adult horses. Interventions None. Measurements and Main Results Blood was sampled from 10 healthy and 10 diseased horses and samples were repeatedly analyzed to evaluate measurement reliability of various ROTEM variables. Four different ROTEM assays (ie, EXTEM, INTEM, FIBTEM, and APTEM) were run simultaneously under standardized conditions. The device-related, operator-related, and day-to-day variability for the majority of ROTEM variables was very low to low, as indicated by a coefficient of variation (CV) of < 15%. Most of test-retest variability of ROTEM variables appeared to be device-related. Blood samples from 50 clinically healthy horses were used to establish reference intervals for ROTEM variables. Multiple stepwise regression analyses identified associations of different ROTEM variables with hematocrit, total protein concentration, fibrinogen concentration, platelet count, prothrombin time, activated partial thromboplastin time, and thrombin time. Conclusions ROTEM is a feasible method to evaluate coagulation in horses. Its measurement reliability is acceptable, but device-related measurement variability has to be considered. Reference intervals are presented, but the influence of hematocrit, platelet count, and fibrinogen concentration may need to be taken into account when interpreting individual test results. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Veterinary Journal / Revue Vétérinaire Canadienne is the property of Canadian Veterinary Medical Association and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Assessment of left ventricular (LV) systolic function can be achieved by conventional echocardiographic methods, but quantification of contractility, regional myocardial function, and ventricular synchrony is challenging. The goal of this study was to investigate the applicability of two-dimensional speckle tracking (2DST) to characterize segmental and global wall motion for assessment of LV function and LV synchrony in healthy goats. We aimed to describe the techniques, report normal values of a variety of 2DST indices, and determine the influence of general anesthesia. Methods: Prospective study on 22 healthy female Saanen goats (3.7 ± 1.1 y, 60.2 ± 10.5 kg [mean ± SD]). All goats underwent two transthoracic echocardiographic examinations, the first standing and unsedated and the second 7.4 ± 3.5 days later during isoflurane anesthesia and positioned in sternal recumbency. Data analyses were performed offline, blinded, and in random order. Left ventricular longitudinal, radial and circumferential strain and strain rate as well as longitudinal and radial displacement were measured using 2DST methods. Summary statistics were generated and differences of 2DST variables between myocardial segments and treatments (i.e., awake vs. anesthetized) were assessed statistically (alpha level=0.05). Results: Echocardiographic analyses by 2DST were feasible in all goats and at both time points. Longitudinal systolic strain, strain rate and displacement followed a gradient from apex to base. Absolute systolic strain was generally lower and strain rate was higher in awake goats compared to anesthetized goats. Circumferential and radial indices did not consistently follow a segmental pattern. Generally, peak strain occurred later in anesthetized goats compared to awake goats. General anesthesia did not significantly influence LV synchrony. Conclusions: 2SDT is a valid method for non-invasive characterization of LV wall motion in awake and anesthetized goats. The results of this study add to the understanding of LV mechanical function, aid in the diagnosis of global and segmental LV systolic dysfunction, and will be useful for future cardiovascular studies in this species. However, effects of anesthesia and species-specific characteristics should be considered when goats are used as animal models for human disease. [ABSTRACT FROM AUTHOR]

Copyright of Veterinary Dermatology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Laterality defects are rare in cattle and usually manifest as asplenia or polysplenia syndrome. These syndromes may be associated with situs ambiguus, which is a dislocation of some but not all internal organs. The objective of this report was to describe the clinical and post-mortem findings including the macroscopic and microscopic anatomy of selected organs in a cow with polysplenia and situs ambiguus. Case presentation: A 3.5-year-old Brown Swiss cow was referred to the Department of Farm Animals, Vetsuisse Faculty, University of Zurich, because of poor appetite and recurrent indigestion. A diagnosis of situs ambiguus was based on the results of physical examination, ultrasonography, exploratory laparotomy and post-mortem examination. The latter revealed that the rumen was on the right side and lacked compartmentalisation. There were two spleens, one on the left (26.5 x 12.0 cm) and one on the right (20.5 x 5.5 cm), and the omasum was located craniolateral to the ruminoreticulum on the left. The abomasum was located on the right, although it had initially been displaced to the left. The three-lobed liver occupied the left and central cranioventral aspect of the abdominal cavity (cavum abdominis). Only the right and left hepatic veins (vena hepatica dextra and sinistra) drained into the thoracic segment of the caudal vena cava (vena cava caudalis), and histological changes in the liver were indicative of impaired haemodynamics. The mesojejunum was not fused with the mesentery of the spiral loop (ansa spiralis) of the ascending colon (colon ascendens). The latter was folded and the transverse colon (colon transversum) ran caudal to the cranial mesenteric artery (arteria mesenteria cranialis). Fibrotic constrictions were seen in the lumen of the caecum and proximal loop (ansa proximalis) of the ascending colon. Both kidneys were positioned retroperitoneally in a lumbar position. The lumbar segment of the caudal vena cava did not descend to the liver and instead drained into the right azygous vein (vena azygos dextra). Conclusions: Recurrent digestive problems and poor production in this patient may have been caused by a lack of rumen compartmentalisation, abnormal abomasal motility, constrictions in the large intestine (intestinum crassum) and fibrosis of the liver. The abomasum had abnormal motility most likely because it was anchored inadequately and only at its cranial aspect to the liver by the lesser omentum (omentum minus) and to the dorsal abdominal wall and rumen by a short greater omentum (omentum majus). [ABSTRACT FROM AUTHOR]

A 6-year-old thoroughbred gelding was presented with a history of blepharospasm and opacity in the OS of 1 weeks’ duration. Ophthalmic examination findings were consistent with acute uveitis in the OS, and traditional treatment was initiated with systemic antibiotics and anti-inflammatory drugs, topical mydriatics, and corticosteroids. During the total treatment period of 4 weeks response to treatment was weak and the horse developed further problems such as cellulitis of the right hind limb with fever and eventually weight loss and dependent edema. Blood work was indicative of liver disease. Abdominal sonography revealed severe splenomegaly and slight hepatomegaly, and a liver biopsy confirmed malignant T-cell lymphoma. The horse was euthanized due to deteriorating general condition and subsequently underwent postmortem examination. Necropsy and histologic examination revealed a multicentric lymphoma with involvement of spleen, mesenteric lymph nodes, and OU. The findings in this case demonstrate that the differential diagnosis of intraocular and systemic lymphoma should be considered in any horse presenting with anterior uveitis, especially when uveitis is unresponsive to treatment and when additional systemic signs of illness such as lethargy, fever, weight loss, or dependent edema arise. Cytological examination of aqueous humor may provide a rapid diagnosis of intraocular lymphoma in eyes with clinical uveitis. [ABSTRACT FROM AUTHOR]

Objective--To assess the feasibility, describe the techniques, and determine the reliability of transthoracic echocardiography for characterization of left atrial (LA) size and LA mechanical function in horses. Animals--6 healthy adult horses. Procedures--Repeated echocardiographic examinations were performed independently by 2 observers in standing, unsedated horses by use of 2-dimensional echocardiography, pulsed-wave flow Doppler, and tissue Doppler imaging (TDI) techniques. Test reliability was determined by estimating measurement variability, within-day interobserver variability, and between-day inter- and intraobserver variability of all echocardiographic variables. Variability was expressed as the coefficient of variation (CV) and the absolute value below which the difference between 2 measurements will lie with 95% probability. Results--Most echocardiographic variables of LA size had low overall variability (CV, < 15%). Among the 2-dimensional indices of LA mechanical function, area-based and volume-based ejection phase indices had moderate between-day variability (CV usually < 25%). Transmitral Doppler flow indices were characterized by low to high between-day variability (CV, 6% to 35%). The TDI wall motion velocities had high between-day variability (CV, > 25%), whereas most TDI-derived time intervals had low variability (CV, < 15%). Conclusions and Clinical Relevance--LA size and mechanical function can be reliably assessed in standing, unsedated horses by use of 2-dimensional echocardiography, transmitral blood flow velocity profiles, and analyses of LA wall motion by use of TD1. These results may provide useful recommendations for echocardiographic assessment of LA size and function in horses. [ABSTRACT FROM AUTHOR]