Measurement of cardiac dimensions with two-dimensional echocardiography in the living horse.

Two-dimensional echocardiography (2DE) was performed on 22 unsedated Thoroughbred and part Thoroughbred horses weighing between 411 and 650 kg to establish normal reference values for 2DE measurements. Animals stood during examinations performed with a 3.5 MHz mechanical sector transducer using various transducer positions and tomographic planes. Right ventricular diameter (RVD), ventricular septal thickness (VSTh), aortic diameter (AoD), area of the chordal lumen of the left ventricle (CTA), left ventricular diameter (LVD) and left atrial diameter (LAD) were determined at ventricular end-diastole (Ed) and/or end-systole (Es). Fractional shortening (FS) of the left ventricle and end-systolic left atrial to aortic ratio (LAD-Es:AoD-Es) also were calculated. Echocardiographic data were related to body weight by linear regression analysis. Intra-observer variability was checked in five horses by measuring each parameter during each of 10 consecutive cardiac cycles. The 2DE data were compared with M-mode values in published reports. In the 18 horses whose weight did not exceed 551 kg, repeatable recordings of good quality were obtained, and 2DE measurements could be made using intra-cardiac reference points. Increasing body weight proved to impose substantial limitations on measurements taken with the available machine and transducer. This problem might be overcome by using probes of lower frequency or equipment with higher quality image display at greater depth. The following parameters correlated significantly to body weight: VSTh-Es (r = 0.69; P less than 0.01). AoD-Es (r = 0.64; P less than 0.01) and CTA-Es (r = 0.84; P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Standardised imaging technique for guided M-mode and Doppler echocardiography in the horse.

Eighteen echocardiographic images useful for diagnostic imaging, M-mode echocardiography, and Doppler echocardiography of the equine heart were standardised by relating the position of the axial beam to various intracardiac landmarks. The transducer orientation required for each image was recorded in 14 adult horses by describing the degree of sector rotation and the orientation of the axial beam relative to the thorax. Repeatable images could be obtained within narrow limits of angulation and rotation for 14 of the 18 standardised images evaluated. Twenty-seven National Hunt horses were subsequently examined using this standardised technique. Selected cardiac dimensions were measured from two-dimensional and guided M-mode studies. Satisfactory results were achieved in 26 of the 27 horses. There was no linear correlation between any of the measured cardiac values and bodyweight. There was no significant difference between measurements taken from the left and the right hemithorax. Six horses were imaged on three consecutive days to assess the repeatability of the measurements. No significant difference was found between measurements obtained on different days. This study demonstrates a method for standardised echocardiographic evaluation of the equine heart that is repeatable, valuable for teaching techniques of equine echocardiography, applicable for diagnostic imaging and quantification of cardiac size, and useful for the evaluation of blood-flow patterns by Doppler ultrasound.     

Left ventricular volume determination in the horse by two-dimensional echocardiography: an in vitro study

This study was designed to evaluate the accuracy of two-dimensional echocardiography (2DE) in determining the left ventricular volume (LVV) of the horse in vitro. After examining the shape of the left ventricular silicon rubber casts of four equine hearts, two modified Simpson's rule methods (Model A and Model B) as combinations of conical shapes and one biplane area-length method as a single cone (Model C) were chosen for volume calculations. One long axis and three short axis planes were used for linear and area 2DE measurements, respectively. The ventricular length (L) was calculated from the chordal length (CL) by using a linear regression equation (L = 5.54 + 1.83 CL) obtained by anatomical measurement of these two parameters on 40 normal hearts. The LVV was calculated in 15 formalin-fixed hearts from 2DE measurements with the three geometric models. Left ventricular casts were then made using silicon rubber, and their volumes were determined by water displacement. The calculated volumes were plotted against cast volumes with linear regression analysis. All calculated LVVs correlated well with the cast LVVs (R = 0.921 to 0.957; P less than 0.001). The highest correlation was provided by Model A which best represented the shape of the left ventricle. This model consisted of a truncated cone bordered by the area at the level of the mitral valve and by the area at the level of the chordae tendineae, plus a cone the base of which was the area at the level of the papillary muscles. The results demonstrate the applicability of 2DE for equine LVV determinations in vitro, similar to other species.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantitative Analysis of Stress Echocardiograms in Healthy Horses with 2‐Dimensional (2D) Echocardiography,Anatomical M‐Mode,Tissue Doppler Imaging,and 2D Speckle Tracking

Background: Stress echocardiography is used to diagnose myocardial dysfunction in horses, but current methods are not well standardized. The influence of heart rate (HR) on measurements is largely unknown. Objectives: To investigate the use of 2‐dimensional echocardiography (2DE), anatomical M‐mode (AMM), tissue Doppler imaging (TDI), and 2D speckle tracking (2DST) at rest and after exercise for quantification of regional and global left‐ventricular (LV) function. Animals: Five athletic Warmblood horses; 11.6 ± 3.6 years; 529 ± 48 kg. Methods: Prospective study. Three separate echocardiographic examinations were performed before (baseline) and over 5 minutes after treadmill exercise with 2DE (1st, short‐axis view; 2nd, long‐axis view) and pulsed‐wave TDI (3rd examination). Offline analyses were performed at baseline and after exercise at HR 120, 110, 100, 90, and 80 minute^?1. Global and segmental measurements were compared by analysis of variance. Results: Quantitative analyses of stress echocardiograms were feasible in all horses. None of the AMM indices changed significantly after exercise. Stroke volume and ejection fraction by 2DE and strain by 2DST decreased, whereas strain rate by 2DST increased significantly at HR > 100 minute^?1. TDI analyses were technically difficult and provided little additional information. Conclusions and Clinical Importance: Volumetric indices by 2DE and strain and strain rate by 2DST are applicable for quantitative assessment of stress echocardiograms. In healthy horses, they are significantly altered at a HR > 100 minute^?1 and need to be evaluated in view of the instantaneous HR. Further investigations are needed to define the clinical value of stress echocardiography in horses with cardiac disease.     

Comparison of echocardiographic and autopsy measurements of cardiac dimensions in the horse

This study was initiated to determine the accuracy of M-mode echocardiography in measuring left ventricular dimensions and estimating heart weights in horses. Left ventricular free wall and interventricular septal thickness and left ventricular external and internal diameters were measured and heart weights estimated from the echocardiograms of 47 horses. Autopsy measurements of the same parameters were then recorded. Statistical comparison of the data demonstrated: (1) Systolic measurements of wall thickness more closely resembled the heart in death than the diastolic measurements; (2) good correlations existed between parameters measured echocardiographically and at autopsy, especially wall thicknesses and left ventricular external diameter (maximum r = 0.82); (3) heart weight was readily predicted from echocardiographic wall thickness regressions (maximum R-squared = 68 per cent). M-mode echocardiography demonstrated the potential for direct and accurate measurements of cardiac mass and some ventricular dimensions in the horse. The data suggested that intense rigor and exsanguination may render the autopsied heart unsatisfactory for comparative measurements when assessing techniques such as echocardiography.     

Feasibility and clinical utility of transvenous intracardiac echocardiography in conscious,sedated horses

Introduction/objectivesIntracardiac echocardiography (ICE) is a method of obtaining echocardiographic images with a steerable ultrasound catheter placed within the heart via a venous or arterial approach. The objectives of this study were to assess the feasibility of a 5–10 MHz, 8 French, 90 cm ICE catheter to evaluate cardiac structures and function in standing, sedated horses, and describe standard views in this species.AnimalsTen apparently healthy horses weighing 458.1–618.2 kg from a university teaching herd.Materials and methodsEach horse had a physical examination, transthoracic echocardiography, and ICE performed through a 10 French introducer percutaneously placed in the right jugular vein in the proximal third of the neck with continuous ECG monitoring using telemetry.ResultsThree intracardiac echocardiography positions (cranial right atrium, mid right atrium, and right ventricle) with seven views were described with the associated 2D, pulse wave Doppler, continuous wave Doppler, color Doppler, and M-mode image acquisition standardized by referencing the intracardiac positions and common landmarks. The positions were confirmed with simultaneous transthoracic echocardiography. The procedure was well tolerated with only mild, occasional ventricular, and supraventricular arrhythmias that resolved with intracardiac echocardiography catheter repositioning.ConclusionsIntracardiac echocardiography is feasible, safe, and allows for the acquisition of diagnostic images in conscious, sedated horses.     

TWO-DIMENSIONAL ECHOCARDIOGRAPHY IN THE NORMAL CAT

Two-dimensional echocardiography (2DE) and M-mode echocardiography were used to image the heart of 13 clinically healthy cats. Seven awake cats and six cats tranquilized with a combination of acetylpromazine and ketamine were studied. Six cats were studied by 2DE on 3 consecutive days to assess repeatability of the study. Long-axis and short-axis echocardiographic tomograms were obtained from the right parasternal location, and these images were used to determine internal cardiac dimensions, ventricular and septal wall thicknesses, repeatability of the study, and interobserver variability. Some but not all parameters were significantly (P < 0.05) related to body weight. Significant correlations (P <0.05) were found between measurements obtained by long-axis and by short-axis image planes. Comparison of parameters measured by 2DE and M-mode echocardiography demonstrated minimal differences between mean values. Repeatability of the 2DE study was good with 14 of 16 parameters having a mean percent error less than 10%. Interobserver variability was acceptable for some but not all parameters. The study indicates that repeatable 2DE tomograms can be obtained in the cat and that quantitation of cardiac anatomy is possible with this imaging technique.     

An investigation of the second heart sound in the normal horse

The second heart sound was evaluated in conscious, normal horses using intracardiac and external sound detection devices and echocardiography. The second heart sound (S2) in the normal horse is single or split by a narrow interval, not usually detected by external phonocardiographic evaluation. Splitting of S2 was classified as normal (aortic [A2] preceding pulmonic [P2] components) in 66.7 per cent and reversed (P2 preceding A2) in 33.3 per cent of the horses studied. Normal splitting appears to result from lower impedance of the pulmonary vasculature delaying the onset of P2. Reverse splitting appears to result from a delay in A2 resulting from prolongation of PEP and LVET. There does not appear to be variation in splitting of S2 due to respiration based on the cases in which this was measured.     

Two-dimensional echocardiographic assessment of the feline left atrium

Atrial size determined by echocardiography provides a surrogate measure of the hemodynamic burden of cardiac disease. Linear atrial dimensions often are indexed to aortic diameter. Whereas quantitative variables obtained from healthy cats, using 2-dimensional echocardiography (2DE), have been reported, indices from 2DE, have not. Using 2DE and M-mode echocardiography, we calculated indices of left atrial size and a single index of atrial function, left atrial fractional shortening, in 17 healthy cats. Specifically, left atrial dimensions from short- and long-axis 2DE planes were indexed to aortic diameter and also to end-diastolic left ventricular dimension. Additionally, left atrial circumference and area were indexed to aortic circumference and area, respectively. The same variables were obtained from 20 cats with hypertrophic cardiomyopathy (HCM), so that agreement between 2DE indices and indices from M-mode echocardiography could be evaluated over a clinically relevant range of atrial sizes. Atrial dimensions and indices of atrial size from cats with HCM exceeded those of healthy cats. Left atrial dimension from 2D short-axis images indexed to aortic diameter generally was less than the analogous index obtained from M-mode (mean bias, [95% limits of agreement] -0.13, [-0.42, 0.17]). Left atrial dimension from 2D long-axis images indexed to aortic diameter generally was greater than the index obtained from M-mode (0.15, [-0.28, 0.58]). We conclude that ratios of left atrial size and aortic diameter, from 2DE and M-mode echocardiography, are not interchangeable. Normative data that may serve as reference intervals for 2DE assessment of atrial size are presented.     

Doppler-derived velocity of blood flow across the cardiac valves in the normal dog.

Doppler echocardiography is a relatively new procedure used to assess certain cardiovascular disorders in the dog. The objectives of this study were to determine the range of values for the maximal peak velocity of blood flow across each of the four cardiac valves in a sample population of normal adult dogs, using duplex continuous wave Doppler echocardiography, and to determine the optimal tomographic planes to use for an adequate continuous wave Doppler evaluation of the canine heart. Twenty normal dogs were examined to obtain values for peak transvalvular velocity for each of the four cardiac valves. The mean values +/- 1 SD, in cm/s were: 98.1 +/- 9.4 for the pulmonary valve imaged from the left side of the chest, 95.5 +/- 10.3 for the pulmonary valve imaged from the right side of the chest (n = 19), 118.1 +/- 10.8 for the aortic valve, 86.2 +/- 9.5 for the mitral valve and 68.9 +/- 8.4 for the tricuspid valve. Regurgitation was detected across the pulmonic valve in 14 of the 20 dogs, and across the tricuspid valve in ten dogs. The analysis of the tomographic images confirmed that for a complete assessment of a given intracardiac valve, the valve must be examined from all possible directions to obtain maximum values for peak velocity.     

Quantitative M-mode and two-dimensional echocardiography in calves

A standardised echocardiographic protocol was applied to 18 healthy calves for the estimation of 51 anatomical and functional cardiac variables. These variables were measured in a long axis and a short axis view of the heart, and both two-dimensional and cursor-directed time-motion (M-) modes were used. The repeatability of each of the measurements was estimated by comparing values obtained twice within 24 hours, and most of the 51 variables showed a high degree of repeatability. Statistical analysis revealed a close correlation between cardiac measurements taken post mortem and by in vivo echocardiography, and between the echocardiographic values obtained in different scanning planes of the heart or ultrasonic modes, indicating that quantitative echocardiography is a reliable technique in calves.     

TWO-DIMENSIONAL, REAL-TIME ECHOCARDIOGRAPHY IN THE DOG Technique and Anatomic Validation

Two-dimensional, real-time echocardiography (2DE), studied extensively in humans, has only recently been utilized in veterinary medicine. To develop standardized transducer locations and examination technique and to validate cardiac anatomy as imaged from these locations, 2DE was performed in 12 normal, anesthetized dogs. Anatomic structures were identified by shape, position and motion, selective microbubble-laden saline injections, and percutaneous pin insertion followed by necropsy dissection. Consistent echotomographic images were obtained from right intercostal and left intercostal transducer locations. From the right, long-axis and short-axis views of the heart were obtained. From the left, several long-axis views were possible. One or more views of all four cardiac chambers, atrioventricular and semilunar valves, and the proximal portions of the great vessels were obtained by systematic examination from both sides of the thorax. It was concluded that complete anatomic evaluation of the canine heart by 2DE was possible using a standardized, systematic examination technique.     

Systematic exploration of the equine tarsus by ultrasonography

The authors propose a standard protocol of ultrasonographic exploration of the tarsal region in transversal and longitudinal planes, with the aim to spread with an accurate location of the anatomical structures. For this study, 10 adult horses of different races and ages (ranged 5-10 years) were used, with the characteristic of not having suffered any kind of tarsic pathology. The equipment was a real time ultrasound machine with a 7.5 mHz lineal transducer. Some different anatomical structures in this region of the hind-limb such as the tendons, ligaments, muscles and articular components were identified and labelled as regards their echoic characteristics.     

ULTRASONOGRAPHIC ANATOMY OF THE TEMPOROMANDIBULAR JOINT IN HEALTHY PURE-BRED SPANISH HORSES

The objective was to describe the normal ultrasonographic appearance of the soft tissue and bony structures of the temporomandibular joint in Pure-Bred Spanish horses using frozen and plastinated sections performed as anatomical references. The temporomandibular joint of five healthy Pure-Bred Spanish horses and the head specimens from 12 Pure-Bred Spanish cadavers that were subjected to euthanasia for reasons other than temporomandibular joint problems were studied sonographically and anatomically. An 11 MHz linear-array transducer was used to obtain longitudinal ultrasonographic images of the temporomandibular joint from rostral, lateral, and caudal approaches. For anatomic study, a gross dissection was performed on six temporomandibular joints. The other six head specimens were first frozen at -30 degrees C for 48h and then, at -70 degrees C for a week. Three millimeter thick anatomic sections were collected in the same plane as the sonographic planes. These sections were plastinated, photographed, and compared with the corresponding ultrasonographic images. The articular surfaces, the articular cartilage, the disc, the intra-articular fat tissue, the joint capsule, and other structures were clearly visualized sonographically. Structures identified on the ultrasonographic images were in accordance with those identified on the corresponding anatomic sections. We confirmed the appearance of structures of the equine temporomandibular joint that have been described previously but we also identified the caudal fibrous expansion of the disc, the caudal compartment of the dorsal synovial pouch, and the lateral ligament. Our results define a reference that will aid in sonographic evaluation of the equine temporomandibular joint region.     

Anatomical and functional communications between the synovial sacs of the equine stifle joint

The anatomical and functional communications of the synovial sacs of the equine stifle joint were evaluated in 50 stifle joints of 25 horses. Femoropatellar joint (FPJ) sacs were injected with 50 ml of gelatin-based dye and horses were then walked for 50 m. Horses were subsequently killed, the stifle joints dissected and the location of the dye recorded. Twenty-three horses (46 joints) had clinically normal stifle joints and in this group, anatomical communications of the stifle joints were bilaterally symmetrical in each horse. In 15 of these 23 horses (65 per cent), direct anatomical communication between the FPJ sac and the medial sac of the femorotibial joint (FTJ) was demonstrated. The FPJ sac communicated with both the medial and lateral sacs of the FTJ in four of these 23 horses (17.5 per cent). There were no anatomical communications between the FPJ sac and either sac of the FTJ in the remaining four horses (17.5 per cent). Functional communication, which was established by finding dye in the FTJ sacs were anatomical communication with the FPJ sac existed, was demonstrated in 14 of 19 horses (74 per cent). Two horses were affected with degenerative joint disease of one stifle joint. In both of these joints the FPJ sac communicated with both the medial and lateral FTJ sacs. This distribution was different from that of the contralateral joint. When performing intra-articular anaesthesia of equine stifle joints, each synovial sac needs to be injected separately to ensure that anaesthesia of the appropriate synovial sac is obtained.     

QUANTITATIVE CROSS-SECTIONAL ECHOCARDIOGRAPHY IN THE NORMAL DOG

Two-dimensional echocardiography was performed on 18 unanesthetized, normal dogs (4.5 to 30 kg). Measurements of wall thickness, intracavitary dimensions, and cross-sectional area of the left atrium, left ventricle, and aorta were made. Satisfactory data were obtained from 17 dogs, and were used to determine normal values. Normal data were tested for significant correlation to body weight (kg) by linear regression. Repeatability was studied in six dogs examined, on three separate occasions, during a 5-day period. Differences between values obtained on different days were evaluated by analysis of variance.
Satisfactory qualitative echocardiograms were repeatedly obtained by using consistent sites of transducer placement and by identifying internal cardiac structures. These tomographic planes were highly reproducible, with only ventricular length, and some views of the ventricular septum, showing statistically significant (P < 0.05) differences. Almost all linear and area measurements were significantly correlated to body size, while most indices of left ventricular function were independent of body weight. Dimensions obtained from the left and right parasternal position were nearly identical. Cross-sectional echocardiography allows repeatable assessment of cardiac anatomy, and it should prove useful for identification and quantitation of heart disease in the dog.     

Evaluation of two applanation tonometers in horses

Comparisons were made of measurements obtained in horses, using 2 applanation tonometers in vivo and in vitro. In vitro comparisons indicated that although neither instrument accurately recorded intraocular pressure (IOP), compared with manometric measurements, results of both instruments indicated linear digression from manometric IOP values that could readily be corrected, thereby accurately estimating IOP in horses. For tonometer 1 (MacKay-Marg), calculated actual IOP = 1.48 - 0.9 mm of Hg; and for tonometer 2 (Tono-Pen), calculated actual IOP = 1.38 + 2.3 mm of Hg. The coefficients of determination (r2) values were markedly high (0.99 for both equations). In vivo comparisons in clinically normal horses did not reveal significant differences in measured IOP between the 2 instruments, and IOP was not altered from baseline after auriculopalpebral nerve block. Mean (+/- SD) IOP in clinically normal horses was 23.5 +/- 6.10 mm of Hg and 23.3 +/- 6.89 mm of Hg, for tonometers 1 and 2, respectively.     

Echocardiographic evidence of left atrial mechanical dysfunction after conversion of atrial fibrillation to sinus rhythm in 5 horses

BACKGROUND: Atrial contractile dysfunction occurs in some species after conversion of atrial fibrillation (AF) to normal sinus rhythm (NSR) but has not been reported in horses with naturally occurring AF. HYPOTHESIS: Transthoracic echocardiography allows detection of left atrial (LA) mechanical dysfunction in horses after conversion of AF to NSR. ANIMALS: Five Standardbreds with AF and 6 healthy Standardbreds of similar age, weight, and athletic condition were included in this study. METHODS: Four horses were treated pharmacologically (quinidine), and 1 horse was treated by means of transvenous electrical cardioversion. Echocardiographic examinations were performed in normal horses (once) and in AF horses (24 hours and 72 hours after conversion to NSR) by means of 2-dimensional echocardiography (2DE), transmitral flow Doppler, and tissue Doppler imaging (TDI) techniques. Echocardiographic indices of LA mechanical function were compared between normal horses and AF horses. RESULTS: Two-dimensional echocardiography and TDI indices of LA mechanical function revealed significant decreases in LA contractile function and LA reservoir function 24 hours after cardioversion. This decrease was no longer statistically significant 72 hours after cardioversion, but changes in echocardiographic variables between 24 and 72 hours varied among horses. CONCLUSIONS AND CLINICAL IMPORTANCE: LA contractile dysfunction can be evaluated in horses by use of 2DE, transmitral Doppler flow velocity profiles, and analyses of LA wall motion by TDI. The results of this study are consistent with AF-induced atrial remodeling, although residual treatment effects or influence of underlying primary myopathy cannot be excluded.     

Computed tomographic study of the effect of a tongue-tie on hyoid apparatus position and nasopharyngeal dimensions in anesthetized horses.

OBJECTIVE: To determine the effect of manual tongue protrusion on the dimensions of the hyoid apparatus, nasopharynx, and oropharynx in anesthetized horses. tongue protrusion on the dimensions of the hyoid. ANIMALS: 5 adult horses. PROCEDURE: Horses were anesthetized and positioned in sternal recumbency for 2 sequential computed tomographic (CT) scans. Images were acquired with the tongue in a natural position inside the mouth. Then, the tongue was pulled rostrally and secured, and a second CT scan was performed. Dorsoventral length of the hyoid apparatus and angles of the basisphenoid, basihyoid, and ceratohyoid were measured on 3-dimensional reconstructed CT images. Cross-sectional diameters and areas of the nasopharynx and oropharynx were determined on reformatted images in the transverse and longitudinal planes, using osseous landmarks for consistency. Results were tested between the 2 groups to determine significant differences. RESULTS: We were unable to detect a significant difference between any of the lengths or angles of the hyoid apparatus measured with or without rostral protrusion of the tongue. Similarly, nasopharyngeal and oropharyngeal diameters and cross-sectional areas were not significantly different with or without rostral protrusion of the tongue. CONCLUSIONS AND CLINICAL RELEVANCE: Tying the tongue rostrally out of a horse's mouth did not influence the position of the hyoid apparatus or dimensions of the nasopharynx or oropharynx in anesthetized horses. Currently, no data suggest that application of a tongue-tie is effective for maintaining stability and patency of the nasopharyngeal or orolaryngeal airways in horses during races.