Observer-dependent variability of quantitative clinical endpoints: the example of canine echocardiography

The objective of this study was to determine the intra- and inter-observer variability of echocardiographic measurements in dogs. Four observers with different levels of experience in echocardiography performed 192 echocardiographic examinations of six dogs on four different days. The lowest within- and between-day coefficients of variation (CV) (%) were 13.8 and 5.2 for the right ventricle in diastole, 8.9 and 4.5 for the interventricular septal thickness in diastole (6.3 and 7.0 in systole), 7.7 and 9.4 for the left ventricular free-wall thickness in diastole (8.1 and 5.2 in systole), 3.1 and 5.0 for the left ventricular end-diastolic diameter (6.2 and 7.0 for end-systolic diameter), 10.2 and 10.8 for the left ventricular shortening fraction, and 8.2 and 9.8 for the left atrium/aorta ratio, respectively. Most of these lowest CVs were observed by the two most experienced observers. Conversely, all maximum values were obtained with the two less experienced observers. These differences in observer-dependent variability may considerably influence the minimum number of animals required to detect a treatment-associated change in echocardiographic variables.     

Influence of alterations in heart rate on echocardiographic measurements in the dog

M-mode echocardiograms were recorded from 10 conscious, clinically normal dogs at various heart rates during atrial pacing. Heart rate was recorded as cycle length (seconds), and measurements were made only during sustained 1:1 atrial-to-ventricular conduction. In all dogs studied, there was a significant (P less than 0.01) positive correlation of left ventricular internal chamber dimension in diastole and systole to cycle length. Also, there was positive correlation between these left ventricular dimensions and the square root of cycle length, which predicted a plateau in dimensional changes as cycle length increased. Echocardiographic shortening fraction and left ventricular and septal wall thickness measurements did not change consistently during pacing. We concluded that left ventricular chamber dimensions in the dog may be significantly affected by alterations in heart rate.     

Normal values of the canine M-mode echocardiogram

M-mode echocardiograms were recorded from 40 healthy dogs, awake and unsedated, in left lateral recumbent position. Fifteen echocardiographic measurements were taken and correlated with body weights using linear regression equations. The left ventricular internal dimension in systole and diastole, the left ventricular wall thickness, the aortic root dimension, and the left atrial dimension had high correlation coefficients (r2), ranging from 0.756 to 0.619. The fractional shortening of the left ventricle in systole (39% +/- 6%) and the left atrial to aortic root ratio (0.99 +/- 0.10) were not linearly related to body weights and had constant values.     

Effects of inter- and intra-observer variability on echocardiographic measurements in awake cats

The objective of this study was to determine intra- and inter-observer variability of echocardiographic measurements in awake cats. Four observers with different levels of experience in echocardiography performed 96 echocardiographic examinations in four cats on four different days over a 3-week period. The examinations were randomized and blinded. The maximum within-day and between-day CV values were 17.4 and 18.5% for inter-ventricular septal thickness in diastole, 18.7 and 22.6% for left ventricular free-wall thickness in diastole, 9.8 and 14.9% for left ventricular end-diastolic diameter, 20.8 and 15.2% for left ventricular end-systolic diameter, and 21.2 and 18.4% for left ventricular shortening fraction. The maximum within-day CV values were most often associated with the least competent observer (i.e. the graduate student) and, the minimum CV values with the most competent observer (i.e. the associate professor in cardiology). A significant interaction between cat and observer was also evidenced. Thus, the most competent observer could not be replaced by any of the other observers.     

ECHOCARDIOGRAPHIC REFERENCE VALUES IN WHIPPETS

The aim of the study was to establish reference echocardiographic values for whippets, to compare these values with previously published reference values for the general dog population, and to determine whether there is an influence of gender and breeding lines on echocardiographic measurements. Echocardiographic parameters from 105 apparently healthy whippets without cardiac symptoms were used to establish reference values for the breed and to compare these values with two previously reported reference ranges. The coefficients of the allometric equation Y= aM(b), useful to reconstruct normal M-mode and two-dimensional average values for whippets of varying weights, were calculated, as well as the lower and upper limits of the 95% prediction interval. First, we found that whippets have a significantly larger left ventricular diameter, increased left ventricular wall, and interventricular septum thickness than expected, in diastole as well as in systole. Fractional shortening was significantly lower than the reference value. Second, comparing males and females, taking body weight differences into account, females had a significantly larger left ventricular diameter in diastole and systole. Minor differences were found between racing and show pedigree dogs. In conclusion, the results of this study confirm that breed-specific reference values are needed in echocardiography. In whippets, the values found in this study can be used as references in order to avoid overinterpretation of cardiac dilation, hypertrophy, and/or decreased contractility in these dogs.     

M-MODE ECHOCARDIOGRAPHIC PARAMETERS AND INDICES IN THE NORMAL GERMAN SHEPHERD DOG

M-mode echocardiographic measurements were made from 50 healthy German Shepherd dogs (30 males and 20 females). The dogs were awake and unsedated, in right lateral recumbent position. The following parameters were measured on the echocardiographic images: interventricular septal thickness at end-diastole (IVSd), interventricular septal thickness at end-systole (IVSs), left ventricular internal dimension at end-diastole (LVIDd), left ventricular internal dimension at end-systole (LVIDs), left ventricular posterior wall thickness at end-diastole (LVPWd), left ventricular posterior wall thickness at end-systole (LVPWs), left atrial dimension (LAD), aortic root dimension (AOD), left atrial to aortic root ratio (LAD/AOD), right ventricular internal dimension at end-diastole (RVID), amplitude of mitral valve excursion (DE amplitude), velocity of mitral valve opening (D-E slope), and velocity of mitral valve closure (E-F slope). Fractional shortening (FS) was also calculated. The effect of gender and age on each echocardiographic parameter was analyzed and the relationship between body weight (BW) and each parameter was also investigated. There was a significant relationship between gender and LVPW in systole and diastole and FS. Significant association was also found between BW and IVS, LVID, and LVPW in systole and diastole, FS, LAD, AOD, RVID, DE amplitude, and D-E slope of the mitral valve.     

Echocardiographic assessment of cardiac chamber size and functional performance in swine

Ninety nonanesthetized 7- to 16-week-old pigs were studied, using 2-dimensional echocardiography that permits orientation of a targeted M-mode beam perpendicular to structures being studied and allows serial studies of the same cardiac regions. Normative data were obtained and included body weight and measurements of left atrial diameter, mitral valve excursion, aortic root diameter, left ventricular end-diastolic and end-systolic diameters, and left ventricular fractional shortening. A positive correlation was found between body weight and measurements of left atrial diameter, mitral valve excursion, aortic root diameter, left ventricular end-diastolic and end-systolic diameters, and fractional shortening. A correlation was found between body weight and age. Best-fit analysis resulted in all measurements fitting either a first- or second-degree polynomial.     

Repeatability of the M-mode echocardiogram and the effects of acute changes in heart rate, cardiac contractility, and preload in healthy cats sedated with ketamine hydrochloride and acepromazine

In healthy cats sedated with a combination of ketamine hydrochloride and acepromazine, the reproducibility of sequential echocardiographic examinations was studied. The effects of experimental alteration in heart rate, contractility, and preload on the echocardiogram also were studied. Ten cats had M-mode echocardiograms recorded once weekly for 5 weeks. There were no statistically significant differences in echocardiographic measurements over time, although measurements of certain cardiac structures of an individual cat did vary from time to time. The cardiovascular system was altered by a constant infusion of isoproterenol, followed by a rapid intravenous infusion of isotonic fluid equal to 25% of the calculated blood volume, and then by a rapid withdrawal of blood equal to the amount of fluid previously given. Cardiac output using indocyanine green dilution curves were determined for each treatment and compared to the cardiac output calculated from the echocardiogram. The correlation coefficient was 0.90 for all treatments. During the infusion of isoproterenol a significant increase in the percent fractional shortening and left ventricular wall amplitude occurred compared to the control echocardiogram. After the rapid infusion of fluid, none of the mean echocardiographic measurements significantly changed from control values although the left ventricular chamber diameter at systole significantly increased, and the percent fractional shortening significantly decreased, when compared to values obtained during isoproterenol infusion. Significant changes recorded between echocardiographic measurements made after blood withdrawal compared to those made after fluid loading included an increase in left ventricular wall thickness at diastole, a decrease in left ventricular diameter at diastole, and a decrease in the present left ventricular wall thickening. Cats were terminated and the average of measurements made during the repeatability study of the septal and left ventricular wall thickness during systole, rather than during diastole, more closely approximated the postmortem measurements.     

Reduction of diameter of the left ventricle of dogs by plication of the left ventricular free wall

OBJECTIVE: To determine effects of reducing the diameter of the left ventricle of dogs by plication of the left ventricular free wall. ANIMALS: 8 healthy adult mixed-breed dogs. PROCEDURE: Left lateral thoracotomy and a T-shaped pericardiotomy were performed. The free wall of the left ventricle was imbricated with 3 interrupted transfixing sutures applied in a horizontal mattress pattern, using 3-0 polypropylene suture assembled on a straight cutting needle. Surgeons were careful to avoid the coronary vessels. Echocardiography was performed 24 hours before and 48 hours after surgery. Electrocardiography was performed before and 1, 2, 7, 15, 21, 30, and 60 days after surgery. RESULTS: Echocardiographic measurements revealed that the diameter of the left ventricle was reduced by a mean of 23.5%. Electrocardiography revealed ventricular premature complexes 24 hours after surgery that regressed without treatment during the first week after surgery. CONCLUSIONS AND CLINICAL RELEVANCE: Plication of the left ventricular free wall of dogs can reduce end-diastolic and end-systolic dimensions of the left ventricle. The technique is simple and does not require cardiopulmonary bypass. According to Laplace's law, the reduction of cardiac diameter leads to reduction on free-wall tension and may improve left ventricular function in dilatated hearts. Thus, additional studies involving dogs with dilated cardiomyopathy should be conducted.     

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.     

Echocardiography in the domestic cat.

Echocardiographic examinations were performed on 25 normal healthy cats placed in left lateral recumbency. The cats were representative of serveral breeds, consisted of 12 males and 13 females, and weighed between 2 and 6.5 kg. Twelve measurements from the echocardiograms of each cat were made for the purpose of compiling a small data base (reference values). These measurements included wall thicknesses, luminal dimensions, and contractile indices. Left ventricular wall thickness averaged 0.37 +/- 0.08 cm, and the septal wall thickness averaged 0.45 +/- 0.09 cm. The average left ventricular lumen in diastole was 1.48 +/- 0.26 cm, and in systole, it was 0.88 +/- 0.24 cm, which resulted in an average shortening fraction of 41 +/- 7.3%. Velocity of circumferential shortening, an index of contractility, averaged 2.86 +/- 0.78 cm. In eight additional cats, both ventricles were catheterized for echographic chamber identification and then cineangiographic procedures. Then these cats were euthanatized, and postmortem measurements were compared with echocardiographic and cineangiographic measurements. According to the three methods of determining wall thickness, differences were less than 15%, where the range of deviations was between 0 and 0.5 mm and the average deviation was -0.01 +/- 0.26 mm.     

Echocardiographic characterisation of cardiac dilatation induced by volume overload in a canine experimental model

The aim of this study was to characterise the development of cardiac dilatation induced by chronic volume overload in 12 dogs. Bilateral arteriovenous fistulas were created between the common femoral arteries and the femoral veins, and the animals were serially studied with transthoracic echocardiography for a period of 12 weeks after the operation. Compared to the measurements obtained before the operation (week 0), the data obtained at the end of the experimental period showed significantly increased left ventricular volume measured by 2D-echocardiography (from 25.1 cm3 to 43.8 cm3, p < 0.0001 in diastole and from 8.6 cm3 to 16.8 cm3, p < 0.001 in systole), and left ventricular diameter measured by M-mode echocardiography (from 26.2 mm to 32.6 mm, p < 0.0001 in diastole and from 17.1 mm to 20.6 mm, p < 0.001 in systole). The size of the left atrium also increased in transversal (from 29.2 mm to 33.6 mm, p < 0.01) but not in longitudinal diameter. In spite of a significant cardiac chamber dilatation over the 12-week period, left ventricular systolic functional variables (fractional shortening, FS % and ejection fraction, EF %), and also the left ventricular systolic and diastolic free wall thickness remained unchanged. In this study we demonstrated that chronic progressive volume overload resulted in gradual dilatation of the canine heart, and that the pathological process can be monitored successfully by serial echocardiography. We found that left atrial dilatation occurred without the development of mitral regurgitation and/or detectable left ventricular dysfunction.     

Echocardiographic characteristics of chickens with ascites syndrome

1. B- and M-mode echocardiography was used to compare cardiac function in broilers with spontaneous ascites syndrome with that of normal chickens. 2. Thirty ascitic chickens and 15 normal chickens aged three, 4, 5, and 6 weeks from the same flock (180 birds in total) were examined. They were restrained gently in a natural standing position, and echocardiographs were obtained from a 7.0-MHz linear transducer placed on the left pectoral apterium. Indices of cardiac structure and functioning were calculated from the echocardiographs, and some were normalised to body weight. Heart rate was also measured. 3. All cardiac structural indices in both ascitic and normal chickens increased with age. Compared with normal chickens, right ventricular diameter at the end of systole in ascitic chickens was greater at 4, 5 and 6 weeks of age. Ventricular septal thickness at the end of both systole and diastole was greater in ascitic chickens at 5 and 6 weeks. Left ventricular free wall thickness at the end of diastole was less in ascitic chickens at 3 weeks. However, all the structural indices decreased with age after normalisation with body weight. 4. The heart rate of ascitic chickens was lower at 4, 5 and 6 weeks. Normalised left ventricular fractional shortening was lower in ascitic chickens at 4, 5 and 6 weeks, as was normalised right ventricular fractional shortening. Incrassation of the ventricular septum (Delta T), which changed little in normal chickens, was less at 4, 5 and 6 weeks in ascitic chickens. Left ventricular fractional shortening, right ventricular fractional shortening and Delta T were all negatively correlated with ascites heart index at all ages. 5. Taken together the results suggest heart failure of both ventricle, but that right ventricular dysfunction is more extensive than left ventricular dysfunction. We suggest that secondary pulmonary hypertension would result in these ascitic chickens due to volume overload.     

Reference Values and Repeatability of B-Mode and M-Mode Echocardiographic Parameters in Healthy Donkey (Equus asinus)—The Guide to Assess Healthy Heart

Donkey (Equus asinus), the cheapest form of agricultural power in Egypt, is used principally as draught or pack animals and may also be ridden, or used for threshing, raising water, milling, and other work. The aim of the present study was to provide B-mode and M-mode echocardiographic reference ranges from a sample of population of donkeys (E. asinus) based on the probability theory and statistics. In the present study, B-mode and 2-dimensional guided M-mode echocardiography were performed on 44 clinically healthy donkeys (E. asinus) (22 males and 22 females), without any neither clinical nor echocardiographic evidence of cardiovascular diseases, aged 2–25 year old, and weighed 150–350 kg. The echocardiographic dimensions, including interventricular septum thickness at end diastole, interventricular septum thickness at end systole, left ventricular internal diameter at end diastole, left ventricular internal diameter at end systole, left ventricular posterior wall thickness at end diastole, and left ventricular posterior wall thickness at end systole were assessed. The cardiac function indices, including end diastolic volume, end systolic volume, stroke volume, ejection fraction, and fractional shortening were also measured. B-mode and guided M-mode echocardiographic examination of healthy donkeys revealed that both the interventricular septum thickness and the left ventricular posterior free wall were greater during systole than diastole. However, the left ventricular dimension during diastole was greater than systole. Furthermore, the recorded data of cardiac function indices, including end diastolic volume, end systolic volume, stroke volume, ejection fraction, and fractional shortening using B-mode echocardiography were closer to those recorded by guided M-mode echocardiography. To our knowledge, this is the first Egyptian study to report the echocardiographic reference ranges of donkeys (E. asinus) based on the probability theory and statistics, the coefficient of variation. The results of the present study can be used as standard and reference values for further echocardiographic studies in donkeys and represent a step in the identification, interpretation, and evaluation of cardiovascular disorders in such animals.     

Use of echocardiography in the diagnosis of dilated cardiomyopathy in Irish wolfhounds.

The purpose of this study was to compare the echocardiographic features of Irish wolfhounds with clinically inapparent dilated cardiomyopathy (DCM) (n = 33) to dogs with advanced DCM (n = 33) and to normal dogs (n = 262). Significant differences were detected between the three groups. In dogs with DCM, the most sensitive diagnostic measurements were: end-systolic volume index (ESVI), E-point to septal separation (EPSS), fractional shortening (FS), and left ventricular internal dimensions (LVIDd and LVIDs). Left atrial diameter was increased markedly in dogs with DCM and 83.3% of affected Irish wolfhounds had concurrent atrial fibrillation. Compared with early DCM, in advanced DCM there was a significant increase in end-diastolic right ventricular diameter, often combined with extensive pleural effusion, the leading sign of congestive heart failure in Irish wolfhounds.     

Effects of respiratory cycle on pulmonary venous flow and cardiac cycle on pulmonary venous diameter of dogs: a transesophageal echocardiography study

We investigated 12 anesthetized normal dogs using transesophageal echocardiography to understand the effects of respiration on the pulmonary venous flow. Additionally, we observed whether the diameter of the pulmonary vein changes with the heart beat. The pulsed Doppler wave form of pulmonary venous flow predominantly demonstrated two backward flows, with one peak occurring during ventricular systole and another during ventricular diastole. Sometimes a small forward flow occurred during left atrial contraction. In comparison with expiration, the peak velocity and velocity-time integral of the flow wave under inspiration occurred during both systole and diastole were significantly smaller. The diameter of the pulmonary vein decreased during left atrial contraction and increased during left ventricular systole and diastole.     

Transthoracic echocardiography in Estrela Mountain dogs: reference values for the breed

Of 100 Estrela Mountain dogs, 74 were examined to obtain echocardiographic reference values for the breed. The influence of bodyweight, age and sex on different echocardiographic parameters was studied using either analysis of variance or regression analysis. Statistically significant differences were found between sex and heart rate as well as interventricular septal thickness at end-systole and left ventricular internal dimension at end-diastole. A statistically significant linear correlation was also found between several parameters and (1) age (mean arterial pressure, left ventricular internal dimension at end-systole, fractional shortening, circularity index in systole, aortic valve velocity time integral, pulmonic valve velocity time integral and mitral valve E wave peak velocity), (2) weight (left ventricular posterior wall thickness at end-diastole and end-systole, end-diastolic volume index, left atrium diameter, aortic valve peak velocity and mitral valve E wave deceleration time), (3) sex and age (left ventricle end-diastolic volume), and (4) sex and weight (aortic root diameter and pulmonic valve peak velocity). Reference values for the breed are presented, as well as dispersion graphics for selected parameters, based on a regression equation.     

Determination of heart dimensions in cattle via 2-D-mode echocardiography

The goal of this study was to determine via echocardiography the size of the left and right cardiac ventricles and the width of the interventricular septum and the left free ventricular wall in 51 healthy cows. The heart regions were examined in standing cows using a 3.0 Mhz sector transducer in 2-D-Mode. The dimensions of the heart were measured in the caudal long and short axes on the right side and in the caudal and cranial long axes on the left. The diameter of the ventricles was determined in a plane immediately beneath the mitral or tricuspid valves and that of the aorta and pulmonary artery in a plane immediately above the aortic and pulmonary valves, respectively. At the end of the study, all of the cows were slaughtered, the hearts were removed and the same parameters were determined using a tape measure. Results of in vivo and in vitro measurements were compared. In the right caudal long axis, the diameters of the left ventricle during both diastole (x +/- s = 7.0 +/- 0.73 cm) and systole (4.5 +/- 0.69 cm) were larger than those of the right ventricle during diastole (4.1 +/- 1.02 cm) and systole (3.6 +/- 0.98 cm). The diameter of the ventricles during diastole was larger than that during systole. Analogous results were obtained in both other axes. The diameter of the right ventricle during systole was larger when measured in the right caudal long axis (3.6 +/- 0.98 cm) than in the right caudal short axis (3.2 +/- 1.15 cm). This was also true for measurements obtained during diastole. The interventricular septum and the left ventricular wall were thicker during systole than during diastole. The diameter of the pulmonary artery was larger during diastole (5.6 +/- 0.82 cm) than systole (5.2 +/- 0.84 cm). The diameter of the aorta was smaller than that of the pulmonary artery and did not change significantly during diastole (4.9 +/- 0.92 cm) and systole (4.8 +/- 0.80 cm). The diameters of both ventricles measured at post mortem were smaller than those measured in vivo during diastole and larger than those measured during systole. There were no significant differences between the measurements performed twice, three days apart, in 11 of the cows.     

Effect of amlodipine on echocardiographic variables in cats with systemic hypertension

Left ventricular hypertrophy signals a poor prognosis in hypertensive humans. Cardiac disease is common in cats with systemic hypertension. The aims of this study were to characterize the echocardiographic findings of cats with systemic hypertension and to determine if reducing the degree of hypertension is associated with resolution of cardiac hypertrophy. Echocardiographic examinations were performed on 19 cats with naturally occurring systemic hypertension. Fourteen of these cats were subsequently studied after a minimum of 3 months of treatment with the antihypertensive agent amlodipine. Hypertensive cats had a significantly thicker interventricular septum in both systole and diastole, thicker left ventricular free wall in both systole and diastole, and larger left atrium compared to the published normal values and 74% (14/19) of the cats met criteria for left ventricular hypertrophy (diastolic septal or free-wall thickness > 0.60 cm). Systolic blood pressure was lower after treatment (217 +/- 25 mm Hg, range: 180-275 mm Hg; and 142 +/- 27 mm Hg, range: 90-200 mm Hg). No difference was found in any of the echocardiographic measurements between the untreated and treated cats, although more cats had ventricular hypertrophy before treatment (11/14) than after initiating amlodipine (6/14; P = .006). Ventricular hypertrophy is common in hypertensive cats and may resolve after the initiation of amlodipine.     

Correlation of cardiac enlargement as assessed by vertebral heart size and echocardiographic and electrocardiographic findings in dogs with evolving cardiomegaly due to rapid ventricular pacing

Vertebral heart size (VHS) has been proposed as a method for quantifying cardiomegaly in dogs. This study was designed to determine how well echocardiographic and electrocardiographic findings correlated with VHS. Dogs were rapid-paced into varying degrees of cardiomegaly and were monitored by thoracic radiography, echocardiography, and electrocardiography during development of cardiomegaly. Echocardiographic and electrocardiographic parameters were compared with VHS. VHS increased with increased duration or rate of pacing or both, and left atrium-to-aorta ratio, left ventricular end-diastolic diameter, left ventricular end-systolic diameter, P wave duration, and QRS duration correlated significantly with VHS. VHS (a score obtained from routine thoracic radiographs) seems to correlate well with both echocardiographic and electrocardiographic parameters. When 9 veterinarians, experienced in interpretation of cardiac silhouettes on radiographs, measured VHS from 1 normal dog and 1 dog with severe cardiomegaly, coefficients of variation (ratio of standard deviation to the mean) for their measurements were 2.7% and 2.8%, respectively. Thus, VHS could be established with great uniformity by experienced interpreters.