RECOMMENDATIONS FOR STANDARDS IN TRANSTHORACIC TWO-DIMENSIONAL ECHOCARDIOGRAPHY IN THE DOG AND CAT*

Recommendations are presented for standardized imaging planes and display conventions for two-dimensional echocardiography in the dog and cat. Three transducer locations (“windows”) provide access to consistent imaging planes: the right parasternal location, the left caudal (apical) parasternal location, and the left cranial parasternal location. Recommendations for image display orientations are very similar to those for comparable human cardiac images, with the heart base or cranial aspect of the heart displayed to the examiner's right on the video display. From the right parasternal location, standard views include a long-axis four-chamber view and a long-axis left ventricular outflow view, and short-axis views at the levels of the left ventricular apex, papillary muscles, chordae tendineae, mitral valve, aortic valve, and pulmonary arteries. From the left caudal (apical) location, standard views include long-axis two-chamber and four-chamber views. From the left cranial parasternal location, standard views include a long-axis view of the left ventricular outflow tract and ascending aorta (with variations to image the right atrium and tricuspid valve, and the pulmonary valve and pulmonary artery), and a short-axis view of the aortic root encircled by the right heart. These images are presented by means of idealized line drawings. Adoption of these standards should facilitate consistent performance, recording, teaching, and communicating results of studies obtained by two-dimensional echocardiography.     

Echocardiography of the normal bovine heart: technique and ultrasonographic appearance

Fifty-one clinically healthy cows were examined ultrasonographically from the third and fourth intercostal spaces on both sides of the thorax. A 3.0 MHz transducer was used and the heart was examined in the caudal long, caudal short and cranial long axes on the right side, and in the caudal and cranial long axes on the left side. In each position the optimal transducer orientation and the images of the structures were recorded. In the caudal long axis view of the heart on the right (transducer positioned at the fourth intercostal space), all four chambers were visible with the transducer positioned 8 to 10 cm dorsal to the level of the olecranon. The left ventricular outflow tract, consisting of the aortic valve and ascending aorta, were visible in the same position with the transducer rotated 10 to 40 degrees clockwise. In the caudal short axis view of the heart on the right, the left and right ventricles were visible in cross-section with the transducer held at right angles to the ribs in the fourth intercostal space, 3 to 6 cm dorsal to the olecranon and tipped slightly dorsally. In the cranial long axis view of the heart on the right, the right ventricular outflow tract, consisting of the pulmonary valve and pulmonary artery, was visible in the third intercostal space, 8 to 10 cm dorsal to the olecranon with the transducer angled craniodorsally and rotated 10 to 20 degrees clockwise. In the caudal long axis view of the heart on the left, the left and right ventricles and the left ventricular outflow tract were visible with the transducer placed in the fourth intercostal space. In the cranial long axis view on the left, the right ventricular outflow tract was visible.     

Comparison of the Repeatability of Echocardiographic Measurements from Different Modes and Views in Horses of Various Breeds and Sizes

The objective of this study was to compare the repeatability of echocardiographic measurements obtained from different echocardiographic modes and views in healthy adult equids of various sizes, breeds, and thorax shapes. Ten equids (body weight: 120–662 kg; age: 1–26 years) from various breeds, free of cardiac disease, were used in this study. Each animal was submitted to a standardized echocardiographic and Doppler protocol 3 times at 1 day interval. This protocol included the measurements of left and right ventricular, aortic, pulmonary, and left atrial parameters obtained from different views using the bidimensional (2D) or the motion (M) modes, and the measurement of several parameters of blood flow obtained from the pulsed wave Doppler mode. Repeatability of each measurement was estimated on the basis of the residual variance using a linear model and the coefficient of variation of repeated measurements. A two by two comparison of the repeatability of measurements performed in different views was performed using the residual variances in a variance ratio F test. Results showed that repeatability of echocardiographic or Doppler measurements in equids of various sizes, breeds, and thorax shapes are comparable to previously reported results in thoroughbred and standardbred horses. Left ventricular morphologic parameters showed a good repeatability in the classic M-mode right parasternal short axis view at the level of the chordae tendineae, but the 2D-mode right parasternal long axis four-chamber view appeared to offer an interesting alternative measurement. This latter view also allowed obtaining the most repeatable measurement of right ventricular internal diameter. The left atrial diameter was maximal and most repeatable in the 2D-mode left parasternal long axis four-chamber angled view, and the repeatability of the aortic diameter was best in the 2D-mode right parasternal long axis five-chamber view. Finally, aortic systolic time intervals were more repeatable when measured from the Doppler mode as compared with the M-mode. In conclusion, repeatability of echocardiographic measurements in horses could be optimized after the following protocol: (1) M-mode right parasternal short axis view at the level of chordae tendineae to measure left ventricular morphologic parameters, and 2D-mode right parasternal long axis four-chamber as an alternative view; (2) 2D-mode right parasternal long axis five-chambers to measure the aortic diameter; (3) 2D-mode left parasternal long axis four-chambers angled view to measure the left atrial diameter.     

COMPARABILITY OF LEFT VENTRICULAR M-MODE ECHOCARDIOGRAPHY IN DOGS PERFORMED IN LONG-AXIS AND SHORT-AXIS

The purpose of this prospective study was to determine comparability of left ventricular (LV) M-mode echocardiographic indices derived from right parasternal long-axis and short-axis imaging planes. In 104 dogs (37 healthy dogs and 67 dogs with heart disease), LV M-mode echocardiograms were recorded from both long-axis and short-axis views and interventricular septum thickness (IVS), left ventricular internal dimensions (LVD), left ventricular posterior wall thickness (LVPW), and LV shortening fraction (FS) were measured. Statistical analysis included paired t-test and graphical analysis to assess agreement between the two methods of data acquisition. Mean LVD in systole and diastole and mean IVS in systole were significantly (P<0.001) larger when measured from short-axis recordings compared to long-axis measurements. An increased magnitude of measurement resulted in increased differences between the methods for LV dimensions and fractional shortening. Differences between the two methods were small and within clinically acceptable limits in normal dogs. However, in 23 (34%) of the dogs with cardiac abnormality, one or more LV M-mode derived dimension obtained from one imaging plane did not agree sufficiently closely with the same measure from the other plane. Only for measurement of FS was there good agreement between methods in dogs with cardiac disease. Therefore, with the exception of FS, data gained from LV short-axis and long-axis M-mode recordings should not be used interchangeably in dogs with cardiac disease.     

BIPLANE TRANSESOPHAGEAL ECHOCARDIOGRAPHY IN THE DOG: TECHNIQUE, ANATOMY AND IMAGING PLANES

To determine the feasibility of transesophageal echocardiography (TEE) in dogs, biplane TEE was performed in 6 normal, anesthetized dogs, using a 10 mm × 110 cm endoscopic TEE transducer. Positioning was confirmed by fluoroscopy, and imaging planes were confirmed by necropsy examination.
A transgastric position provided only a limited view of the left ventricular apex. Three TEE positions over the base of the heart were identified. A caudal position provided excellent images in both transverse and longitudinal planes, but alignment with flow for Doppler examination was poor. A middle position provided long axis views of the left ventricular inflow region and mitral valve suitable for Doppler examination. A cranial position provided excellent views for both anatomic and Doppler examination of right and left ventricular outflow and associated great vessels.
We conclude that biplane TEE provides unique views of the heart in dogs which are complementary to, and often superior to, transthoracic views for evaluation of structures at the heart base.     

COMPARISON OF DOPPLER-DERIVED AORTIC VELOCITIES OBTAINED FROM VARIOUS TRANSDUCER SITES IN HEALTHY DOGS AND CATS

In normal dogs and dogs with subaortic stenosis, it is known that the subcostal transducer site provides higher left ventricular ejection velocities than does the left apical site. We hypothesized that aortic flow velocities could also be obtained from the right parasternal long-axis view, optimized for the placement of the Doppler cursor as parallel as possible into the aortic root. In 15 healthy dogs and 13 healthy cats, high-pulsed repetition frequency Doppler flow velocity measurements in the proximal aorta were performed using two-dimensional echocardiographic guidance. The mean [ +/- standard error of the mean (SEM)] peak aortic flow velocities in healthy dogs were as follows: subcostal site 1.46 +/- 0.05 m/s; apical site 1.12 +/- 0.06 m/s; right parasternal long-axis site 1.09 +/- 0.05 m/s. In healthy cats, the following peak aortic flow velocities were observed: apical site 0.87 +/- 0.03m/s; right parasternal long-axis site 0.87 +/- 0.03 m/s. Aortic flow velocities obtained from the subcostal site were significantly higher in healthy dogs than those obtained from the left apical and right parasternal long-axis site (P< 0.001). There was no statistical difference between the peak aortic flow velocities obtained from right parasternal long-axis and left apical transducer position in all groups. We conclude therefore that right parasternal long-axis and left apical-derived aortic flow velocities are similar and may be used interchangeably in healthy dogs and cats.     

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.     

Echocardiographic Detection of Flail Left Atrioventricular Valve Cusp From Ruptured Chordae Tendineae in 4 Dogs

Echocardiography was used to identify a flail left atrioventricular valve cusp caused by ruptured chordae tendineae in each of 4 dogs; two-dimensional echocardiography was superior to M-mode echocardiography in identifying the flail cusps. The following findings on two-dimensional imaging were characteristic: the tip of the flail cusp extended beyond the line of left atrioventricular valve cusp closure and pointed toward the left atrium in systole; the tip was thrust into the left ventricle, and then toward the left ventricular outflow tract in diastole, forming a convex surface to the cusp, which faced toward the left ventricle. The flail motion of the left atrioventricular valve cusp was best observed in the right parasternal long axis or left apical four-chamber views, in a plane parallel to the long axis of the left ventricle and left atrium. Rupture of chordae tendineae leading to flail cusp was attributed to chronic valve degeneration (endocardiosis) in all 4 dogs. Echocardiographic or clinical diagnoses were confirmed by postmortem gross and microscopic studies in all dogs.     

Congenital cardiac disease in dogs

Thoracic conformation, age, amount of body fat, and stage of respiration and cardiac contraction affect the cardiac silhouette. Deep-chested dogs have an upright, narrow cardiac silhouette about 2 1/2 intercostal spaces wide, while barrel-chested dogs have a round, wide silhouette about 3 1/2 intercostal spaces wide. On LAT films the vessels to a lung lobe should be of equal size and 0.25-1.2 times the diameter of the upper third of the 4th rib at the 4th intercostal space. On DV projections, vessels to the caudal lung lobe should be no larger than the diameter of the 9th rib. Signs of right ventricular enlargement include loss of the cranial waist, increased width of the cardiac silhouette, increased sternal contact of the heart, and an elevated cardiac apex. Signs of left ventricular enlargement include an elevated carina, loss of the caudal waist, and a more perpendicular caudal cardiac border. Signs of left atrial enlargement include separation of mainstem bronchi, compression of the bronchus to the left caudal lung lobe, and an increased distance from the carina to the dorsal border of the caudal vena cava. Enlargement of the aorta and main pulmonary artery segment on a LAT view appears as a soft tissue density obscuring the cranial waist. Pulmonary vascular fields are usually hypervascular in patent ductus arteriosus and interventricular septal defects, normal in uncomplicated aortic or pulmonic stenosis, and hypovascular in tetralogy of Fallot.     

Use of computed tomography and silicon endocasts to identify pulmonary veins with echocardiography

The pulmonary veins were identified from the silicone endocast heart models of 19 dogs. Although variation in the number of the more peripheral veins on each specimen existed, all of the casts had a consistency with regards to the most proximal coalescence of the pulmonary veins as they entered the body of the left atrium. That is, the confluence of the veins formed three ostia at the atrial entry point that consisted of 1) right cranial and right middle pulmonary lobe veins; 2) right caudal, accessory, and left caudal pulmonary lobe veins; and 3) both the left cranial and left caudal pulmonary lobe veins of the left cranial lung lobe. The location of these structures identified by the 3-dimensional endocasts were then used to assist in the identification of the pulmonary veins using computed tomography of 2 dogs. Slices were made that approximated those commonly performed during echocardiographic examination. Understanding which pulmonary veins are seen by echocardiography in the different imaging planes will permit prospective evaluations of pulmonary vein size and abnormal flow patterns.     

Partial anomalous pulmonary venous connection in a dog

A 2-year-old male intact Belgian Malinois was presented for exercise intolerance. A grade III/VI left basilar systolic murmur was detected. Echocardiography revealed moderate right atrial and ventricular dilation and increased pulmonic outflow velocity. Thoracic radiographs showed right heart enlargement and a dilated caudal vena cava. In addition, on the left lateral projection, an enlarged aberrant right cranial pulmonary lobar vein was suspected to be diverging ventrally from the course of the right cranial lobar bronchus and inserting more ventrally than normal in the region of the right atrium. A left-to-right pulmonary vascular shunt was suspected, and the patient underwent further diagnostics under general anesthesia. An agitated saline study was positive, suggestive of a concurrent right to left shunt. A right heart catheterization was performed. Angiography was inconclusive. Oximetry testing revealed an increase in oxygen saturation within the right atrium at the level of the caudal cava supportive of a left-to-right shunt in this region. Computed tomography angiography revealed a large single pulmonary vein that anomalously entered into the caudolateral aspect of the right atrium (left-to-right shunt) and was suspicious for a small arteriovenous malformation between the right caudal pulmonary artery and the right pulmonary vein returning to the left atrium (right to left shunt). The patient was diagnosed with a partial anomalous pulmonary venous connection and a possible arteriovenous malformation.     

BIPLANE TRANSESOPHAGEAL ECHOCARDIOGRAPHY IN THE NORMAL CAT

Eight healthy, adult cats were examined with biplane transesophageal echocardiography (TEE). Cats were sedated with a combination of diazepam and propofol and were examined using a 5 mm x 80 cm pediatric biplane TEE probe. Consistent images were obtained at three imaging depths within the esophagus. The middle position porvided the best short-axis images of the left ventricle andheart base. The middle position provided the best long-axis views of the left atrium, left ventricle, and aorta satisfactory imaging of the aorta and pumonary artery and allowed Doppler examination of right ventricular and left ventricular outflow. Biplane TEE provides and additional method of imaging the feline heart which is complimentary to other imaging techniques and the images obtained were similar to those reported for dogs. Although TEE offers a slight advantage over transthoracic imaging for Doppler examination, the quality of the images of heart base structures was not as consistently superior to transthoracic images in cats as reported in dogs.     

Symptomatic partial anomalous pulmonary venous connection in a kitten

A 3-month-old intact female American Shorthair cat, with syncope and tachypnea, underwent cardiac examination which identified no heart murmur or gallop. Thoracic radiography disclosed mild generalized enlargement of the cardiac silhouette and a bronchial and interstitial pattern throughout the lungs. Echocardiography identified tubular structures near the left atrium. After agitated saline contrast imaging, persistent left cranial vena cava with unroofed coronary sinus was suspected. Computed tomography angiography showed the right cranial, right caudal and left caudal pulmonary veins draining into the coronary sinus and flowing into the right atrium. The left cranial pulmonary vein drained normally into the left atrium. Partial anomalous pulmonary venous connection (PAPVC) was diagnosed. The kitten was treated with diuretics but died of heart failure 2 months later. Permission for necropsy was not granted. This case represents symptomatic PAPVC in a kitten. Most pulmonary veins were connected abnormally with the coronary sinus. The prognosis was grave because of refractory heart failure.     

DOPPLER ECHOCARDIOGRAPHY IN THE NORMAL DOG: PART II

Doppler echocardiography was used to determine blood flow velocities in the normal canine heart. The areas examined were the mitral valve, left atrium, tricuspid valve, right atrium, aortic valve, left ventricular outflow tract, pulmonic valve and right ventricular outflow tract. This study then statistically evaluated the influence of breed, age, sex, heart rate, mass and various interactions of these factors on the cardiac flow values determined. Mass and heart rate had the most significant effect on the various determinations with decreasing mass and increasing heart rates generally resulting in increasing peak and mean velocities. The pulmonary artery was statistically judged as being the flow area most susceptible to such influences. Comparisons were made between pulsed and continuous wave Doppler for peak velocities over the four valve areas with only aortic flow, as measured from the left caudal view, showing a significant difference between the two techniques. Mitral flow as compared to tricuspid flow showed a statistically significant difference between peak late diastolic velocities only. The ratio of early mitral diastolic flow to late mitral diastolic flow was always greater than one. Pulmonary flow showed a number of statistically significant differences when compared to aortic flow.     

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.     

Surgical correction of ventricular septal defect with aortic regurgitation in a dog

An 8-month-old entire Miniature Dachshund, weighing 4.2 kg, was presented for examination following delvelopment of a cough. Ventricular septal defect had been diagnosed tentatively in its infancy on the basis of a cardiac murmur detected by auscultation and echocardiography. Echocardiography using a B mode right parasternal long-axis view showed a defect at the atrioventricular junction and a thickened cusp of the aortic valve prolapsing into the defect. Colour-flow Doppler showed shunt blood flow across the defect at the level of the atrioventricular junction, from left to right. The sinus of Valsalva was dilated, with turbulent blood flow. Aortic regurgitation was also observed. Cardiac catheterisation studies confirmed the diagnosis of a supracristal ventricular septal defect with aortic regurgitation. Despite medication with digoxin, enalapril and aminophylin, started from the first admission, left ventricular internal dimensions gradually increased, and fractional shortening of the left ventricle gradually decreased. Surgery, with the aid of extracorporeal circulation, to close the ventricular septal defect, was performed 1 year after the initial examination. The aortic valve was left untreated. Postoperatively, the systolic murmur disappeared. Shunt flow from the left to the right ventricle was no longer observed on echocardiography, however there was still a small amount of aortic regurgitation during diastole visualised with colour-flow Doppler echocardiography. The prolapse of the cusp of the aortic valve on B-mode echocardiography was no longer observed and thickening of the cusp had not progressed. Left ventricular function measurement using M mode echocardiography showed a reduced left ventricular volume overload with reduced left ventricular internal dimensions and increased fractional shortening. The cough was relieved and no follow-up medication was scheduled. Early surgical closure of the ventricular septal defect improved the patient's condition and controlled prolapse and thickening of the aortic valve.     

The clinical usefulness of the ventrodorsal versus dorsoventral thoracic radiograph in dogs

Differences exist in the ventrodorsal (VD) and dorsoventral (DV) radiographic views of the canine thorax. One view may be preferred over another because of how it portrays different areas of interest or different disease conditions. The VD view is indicated for evaluation of the cranial and caudal mediastinum, the caudal vena cava, and the accessory lung lobe, and in cases of pleural effusion. Indications for the DV view include assessment of a consistent cardiac silhouette, evaluation of the pulmonary lobar vessels, and evaluation of the structures of the dorsal thorax, such as hilar lymph nodes, the caudal dorsal lungs, trachea, mainstem bronchi, and left atrium.     

Prognostic value of selected one-, two- and three-dimensional and Doppler echocardiographic methods to assess severity in dogs with myxomatous mitral valve disease

IntroductionAlthough challenging, predicting outcomes in dogs with myxomatous mitral valve disease (MMVD) is of importance to owners and veterinarians. Our aim was to compare the prognostic value of selected one-, two-, and three-dimensional and Doppler echocardiographic methods to predict cardiac-related and all-cause mortality in MMVD dogs. We hypothesize that three-dimensional methods would better predict prognosis than one- and two-dimensional methods.AnimalsOne-hundred thirty-eight privately-owned dogs with MMVD.Materials and methodsCox proportional Hazard analyses and Kaplan–Meier curves were used to investigate the predictive value of 14 variables; left atrial (LA) volume indexed to body weight (BW) measured by real-time three-dimensional echocardiography (RT3DE) and calculated using Simpson's modified method of discs (SMOD) and the area-length method; LA diameter in short-axis and long-axis to aortic in short-axis ratio, effective regurgitant orifice area indexed to body surface area measured in RT3DE en face view and calculated using four-chamber (4Ch) and two-chamber views alone or in combination; percentage increase in left ventricular end-diastolic and systolic internal diameters; fractional shortening; E wave velocity; regurgitant jet area/LA area.ResultsAll 14 variables were significantly predictive of cardiac-related mortality, and 11 were predictive of all-cause mortality. The prognosis was best predicted by LA volume/BW estimated by SMOD or RT3DE, consistently showing the highest predictive value in all analyses.ConclusionsLeft atrial volume calculated by SMOD showed a similar predictive value compared to RT3DE. Performing SMOD from apical 4Ch images should be considered an alternative to RT3DE for echocardiographic examinations where prognostication of disease outcome is sought.     

A clinical case of single left ventricle in a Holstein calf

A 15-day-old Holstein calf with lethargy and tachypnea presented to the Veterinary Teaching Hospital at Obihiro University of Agriculture and Veterinary Medicine for evaluation of suspected congenital heart defect. A Levine grade 6 systolic murmur was noted at right apical site auscultation and phonocardiogram also recorded systolic a murmur. Electrocardiography findings include increased R and S waves, R wave split, and negative T waves without arrhythmia. Echocardiography revealed a single ventricle with a trace of the right ventricular wall, atrioventricular valve regurgitation, and turbulent in a single ventricle. Arterial blood analysis showed a marked decrease in oxygen saturation of 78% and oxygen partial pressure of 44 mmHg. Post-mortem examination confirmed the diagnosis of a single left ventricle.     

Transducer orientation for Doppler echocardiography in dogs

The orientation of an ultrasound transducer required to provide standard echocardiographic views of the heart valves that would permit optimal alignment with blood flow for pulsed-wave Doppler studies, was investigated in 20 normal dogs. Orientation was defined by the site on the thoracic wall at which the transducer was placed and by the angulation and rotation required to produce a two-dimensional image in which the pulsed-wave Doppler beam could be aligned with flow through each of the four heart valves. Two views, each a relatively short-axis projection at the heart base, from either side of the thorax, gave alignment with the pulmonary artery. Three views gave reliable alignment with the aortic valve, from the cardiac apex on each side of the thorax and subcostally. One view was available for the mitral and tricuspid valves, from the left side of the thorax. Definition of these sites should help clinicians and technicians to develop a systematic routine for Doppler investigations in dogs and facilitate communication between investigators.