Quantification of right ventricular volume in dogs: a comparative study between three-dimensional echocardiography and computed tomography with the reference method magnetic resonance imaging

The vertebral right heart index: A new radiographic method to assess right heart enlargement in dogs

In veterinary medicine, the radiographic assessment of right heart enlargement (RHE) is essentially subjective. The aim of this study was to evaluate the vertebral right heart index (VRHi) as a new quantitative radiographic method to detect RHE in dogs. This was a multicenter, retrospective, observational study, including dogs with RHE and control dogs. All dogs had to have a thoracic radiographic study and a complete echocardiography on the same day. Right heart enlargement was defined as the presence of right atrial enlargement, right ventricular enlargement, and/or hypertrophy based on echocardiography. For the radiographic study, all the radiographic views available for each case were considered for measurement: right lateral (RL), left lateral (LL), ventrodorsal (VD), and dorsoventral (DV). The VRHi was measured using LL, RL, VD, and DV views. A total of 204 dogs were included: 91 dogs with RHE and 113 control dogs. The VRHi (RL), the VRHi (LL), and the VRHi (VD) were significantly greater in dogs with RHE compared with controls (P < .0001). The best diagnostic accuracy was observed for VRHi (LL) (area under the curve [AUC] 0.86, P < .0001; cutoff ≥ 3.5 vertebrae, sensitivity [Se] 71%, specificity [Sp] 89%), followed by VRHi (RL) (AUC 0.85, P < .0001; cutoff ≥ 3.5 vertebrae, Se 68%, Sp 86%) and VRHi (VD) (AUC 0.80, P = .0004; cutoff ≥ 3.0 vertebrae, Se 57%, Sp 95%). In conclusion, the lateral VRHi in LL and RL and the VD VRHi could represent useful radiological tools for the detection of RHE in dogs.

Current use of real-time three-dimensional transthoracic echocardiography in animals

This review includes 36 studies of transthoracic real-time three-dimensional echocardiography (RT3DE) in animals. Most of these studies concern cardiac chamber quantification of the left atrium and left ventricle, in dogs. Comparisons of RT3DE and different two-dimensional echocardiographic (2DE) methods have been reported in dogs with myxomatous mitral valve disease (MMVD), dilated cardiomyopathy, and in healthy control dogs. Comparisons of RT3DE and standard reference methods have been reported in healthy control dogs. In dogs with MMVD, volumetric RT3DE measurements of left atrium do not appear to provide superior prognostic value compared with 2DE methods using Simpson's method of discs in dogs with MMVD. The major advantages of RT3DE compared to 2DE include improvements in visualization of the complex morphology of the mitral valve, the estimation of mitral valve regurgitation, and improved visualization of complex congenital cardiac abnormalities.

Current use of cardiac MRI in animals

Cardiovascular magnetic resonance (CMR) imaging has evolved to become an indispensable tool in human cardiology. It is a non-invasive technique that enables objective assessment of myocardial function, size, and tissue composition. Recent innovations in magnetic resonance imaging scanner technology and parallel imaging techniques have facilitated the generation of parametric mapping to explore tissue characteristics, and the emergence of strain imaging has enabled cardiologists to evaluate cardiac function beyond conventional metrics. As veterinary cardiology continues to utilize CMR beyond the reference standard, clinical application of CMR will further expand our capabilities. This article describes the current use of CMR and adoption of more recent advances such as T1/T2 mapping in veterinary cardiology.

Mechanoelectric effects in healthy cardiac function and under Left Bundle Branch Block pathology

Mechanoelectric feedback (MEF) in the heart operates through several mechanisms which serve to regulate cardiac function. Stretch activated channels (SACs) in the myocyte membrane open in response to cell lengthening, while tension generation depends on stretch, shortening velocity, and calcium concentration. How all of these mechanisms interact and their effect on cardiac output is still not fully understood. We sought to gauge the acute importance of the different MEF mechanisms on heart function. An electromechanical computer model of a dog heart was constructed, using a biventricular geometry of 500K tetrahedral elements. To describe cellular behavior, we used a detailed ionic model to which a SAC model and an active tension model, dependent on stretch and shortening velocity and with calcium sensitivity, were added. Ventricular inflow and outflow were connected to the CircAdapt model of cardiovascular circulation. Pressure-volume loops and activation times were used for model validation. Simulations showed that SACs did not affect acute mechanical response, although if their trigger level was decreased sufficiently, they could cause premature excitations. The stretch dependence of tension had a modest effect in reducing the maximum stretch, and stroke volume, while shortening velocity had a much bigger effect on both. MEF served to reduce the heterogeneity in stretch while increasing tension heterogeneity. In the context of left bundle branch block, a decreased SAC trigger level could restore cardiac output by reducing the maximal stretch when compared to cardiac resynchronization therapy. MEF is an important aspect of cardiac function and could potentially mitigate activation problems.

Echocardiographic reference intervals for right ventricular indices, including 3-dimensional volume and 2-dimensional strain measurements in healthy dogs

BACKGROUND

There is currently a lack of reference intervals (RIs) for the novel measures like 3-dimensional (3D) echocardiography or speckle-tracking strain for assessment of right ventricular (RV) structure and function.

OBJECTIVES

To generate RIs and to determine the influence of age, heart rate, and body weight (BW) on various RV function indices using a dedicated RV software for 3D RV end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), global and free wall RV longitudinal strain (RVLS), end-diastolic area (RVEDA), end-systolic area (RVESA), fractional area change (FAC), tricuspid annular plane systolic excursion (TAPSE), and tissue Doppler imaging (TVI)-derived systolic myocardial velocity of the lateral tricuspid annulus (S').

ANIMALS

Healthy adult client-owned dogs (n = 211) of various breeds and ages.

METHODS

Prospective study. Reference intervals were estimated as statistical prediction intervals using allometric scaling for BW-dependent variables. Right-sided (upper limit) or left-sided (lower limit) 95% RIs were calculated for every variable. Inter- and intraobserver variability was determined.

RESULTS

Most variables showed clinically acceptable repeatability with coefficient of variation less than 10. Upper or respectively lower RI after allometric scaling to normalize for different BWs were: EDVn ≤ 2.5 mL/kg^0.942 , ESVn ≤ 1.2 mL/kg^0.962 , TAPSEn ≥ 4.5 mm^0.285 , RVEDAn ≤ 1.4 cm² /kg^0.665 , RVESAn ≤ 0.8 cm² /kg^0.695 , and TVI S'n ≥ 5.6 cm/s/kg^0.186 . The calculated limits for indices without allometric normalization were: EF > 42.1%, FAC > 30.0%, free wall RVLS < -20.8%, and global RVLS < -18.3%.

CONCLUSIONS

Echocardiographic RIs for RV structure and function are provided.

Echocardiographic assessment of dilated cardiomyopathy in dogs

Dilated cardiomyopathy (DCM) is a frequent cause of cardiac disability, congestive heart failure (CHF), and arrhythmic death in dogs. The etiology of DCM is usually idiopathic/genetic, but some causes of a DCM phenotype are reversible. The disease is classified into preclinical (occult) and clinical (overt) stages; the latter stems from heart failure with reduced ejection fraction. DCM is further characterized by clinical, electrocardiographic, circulating biomarker, and imaging abnormalities. The diagnosis of clinical DCM with CHF is straightforward; however, identification of the preclinical stage can be challenging. Echocardiography is central to the diagnosis of both stages and characterized by left ventricular (LV) systolic dysfunction with progressive chamber dilation and variable enlargements of the left atrium and right-sided chambers. Left ventricular dilation is defined by increased LV end-diastolic volumes, areas, and internal dimensions normalized to body size or indexed to the aorta. Systolic dysfunction is characterized by decreased LV ejection fraction, increased end-systolic volume, and reduced shortening across minor and longitudinal LV axes. Dyssynchrony can confound the interpretation of linear indices of systolic function. A comprehensive echocardiogram in DCM includes two-dimensional and M-mode studies, spectral and tissue Doppler imaging, and potentially three-dimensional echocardiography and myocardial strain imaging. Echocardiographic findings should be interpreted within the context of identifiable risks and comorbidities, physical diagnosis, complementary diagnostic testing, and limitations of current reference intervals. Ambiguous examinations should be repeated. Specific echocardiographic criteria for the diagnosis of DCM are proposed to encourage discussion and additional outcome and breed-specific echocardiographic studies of canine DCM.

Analysis of mitral valve morphology in dogs undergoing mitral valve repair with three-dimensional transesophageal echocardiography

INTRODUCTION

Information about real-time three-dimensional (3D) transesophageal echocardiography (TEE) for the evaluation of canine mitral valve morphology is lacking in veterinary medicine.

OBJECTIVES

To evaluate the feasibility of 3D TEE for the evaluation of canine mitral valves and whether there was a difference in mitral valve morphology between American College of Veterinary Internal Medicine (ACVIM) stages.

ANIMALS

Thirty-one dogs were evaluated, including nine dogs classified as ACVIM stage B2, 15 as stage C, and seven as stage D.

MATERIALS AND METHODS

Three-dimensional TEE was performed after anesthetic induction for mitral valve surgery, and the 3D geometry of the mitral valve apparatus was measured.

RESULTS

The intraclass correlation coefficient was good in both inter- and intraobserver analyses of the 3D measurements of mitral valve annulus geometry and excellent in both inter- and intraobserver analyses in the 3D measurements of mitral valve annular and leaflet sizes. Annulus height to commissural width ratio of stage D dogs showed significantly lower values than B2 dogs (B2: 14.2% [9.1-20.5%]; C: 10.6% [6.5-24.1%]; D: 9.5% [4.7-13.8%]). The aortic-mitral angle of stages C and D were significantly flatter than stage B2 (B2: 122.32 ± 9.39; C: 133.66 ± 8.43; D: 140.70 ± 10.70).

CONCLUSIONS

Real-time 3D echocardiography using TEE is a feasible method to evaluate the morphology of the mitral valve in dogs. The saddle shape of the mitral annulus and aortic-mitral angle were flatter in stage D. Further studies are required to understand the pathology of mitral valve disease in dogs.

Selected advanced imaging techniques were unable to quantify in vivo parasitic burden in heartworm-infested dogs

This prospective exploratory study aimed to determine whether certain noninvasive advanced imaging techniques could estimate parasitic burden in heartworm-infested dogs; a noninvasive method is needed for ethical considerations and permitting longitudinal drug studies. Three cardiac-gated and respiratory-gated 3T MRI techniques and CT pulmonary angiography (CTPA) were performed in three healthy beagles to optimize imaging techniques. Once the imaging techniques were established, a pilot study was performed to determine which one of the MRI techniques would be used in an observer comparison study. Ultimately, spoiled gradient recalled (SPGR)-cine-MRI and CTPA were performed in four and five heartworm-infested dogs, respectively. Heartworms were detected in the pulmonary arteries in all dogs during SPGR-cine-MRI and in no dog during CTPA. However, counting the number of worms was unsuccessful. In conclusion, CTPA and SPGR-cine-MRI were unable to replace necropsy for quantifying parasitic burden in heartworm-infested dogs.

Utility of tricuspid annular plane systolic excursion normalized by right ventricular size indices in dogs with postcapillary pulmonary hypertension

Background

Tricuspid annular plane systolic excursion (TAPSE) is a common right ventricular (RV) function indicator. However, TAPSE was not decreased in dogs with myxomatous mitral valve disease (MMVD) and postcapillary pulmonary hypertension (PH) because of its load, angle, and body weight dependency, and TAPSE was considered a preload‐dependent index.

Objectives

To evaluate the utility of TAPSE normalized by RV size in dogs with postcapillary PH.

Animals

Twenty healthy dogs and 71 MMVD dogs with or without PH.

Methods

In this prospective observational study, end‐diastolic RV internal dimension (RVIDd), end‐diastolic and end‐systolic RV area, and end‐diastolic RV wall thickness were measured as RV size indices. The TAPSE was measured using B‐mode and M‐mode methods. Normalized TAPSE was calculated by dividing TAPSE by each RV size index. The RV strain was obtained as the detailed RV function using 2‐dimensional speckle tracking echocardiography. All indices were compared among the PH severity groups and in the presence of right‐sided congestive heart failure (R‐CHF).

Results

Although nonnormalized TAPSE was higher with PH severity progression, each normalized TAPSE showed a significant decrease in the severe PH group (P < .05). The TAPSE_B‐mode/RVIDd ratio had high area under the curve to predict R‐CHF and had moderate correlation with RV strain (P < .05). The TAPSE_B‐mode/RVIDd and left atrial‐to‐aortic diameter ratios were independent predictors for R‐CHF.

Conclusions and Clinical Importance

Normalized TAPSE could reflect RV systolic dysfunction in dogs with severe PH, which could not be detected by nonnormalized TAPSE. The TAPSE_B‐mode/RVIDd ratio might predict R‐CHF with high sensitivity and reproducibility.

Recommendations for standardized plane definition in canine cardiac MRI

With the growing interest in cardiac magnetic resonance imaging (cMRI), veterinary radiologists will increasingly be asked to use this modality to answer complex cardiological questions. Plane alignment is crucial for reproducible assessment of the heart. Anesthesia time is a limiting factor in cMRI. Aims of this prospective experimental study were to introduce a flow chart for standardized cMRI-examination in dogs, to test it for reproducibility using a cardiac CT simulation and to estimate time requirements needed to complete the examination accurately. Six operators (3 radiologists, 1 cardiologist, 1 imaging-resident, 1 technician) simulated a cMRI examination on CT-scans of 6 healthy Beagle dogs twice within two to four weeks. Assessment included qualitative and quantitative scoring of plane quality and time requirements. The quality of planes was high for the left and moderate for the right side of the heart. The intraclass correlation coefficient (ICC) of linear measurements of structures on the left was good to excellent (ICC-range: 0.789-0.948) but dropped to moderate to poor levels for the right side (ICC-range: 0.429-0.738). The median time required to complete a full examination was 30 (range: 13-103) min in the first and 24 (range: 15-62) min in the second evaluation. It differed significantly between operators and was consistently shorter for the left than for the right side. In conclusion, a new standardized scheme for cMRI can be quickly adopted by radiologists with some expertise in cross sectional imaging. Qualitative and quantitative results were highly reproducible for the left but less for the right side.

Comparison of left and right atrial volumes determined by two- and three-dimensional echocardiography with those determined by multidetector computed tomography for healthy dogs

OBJECTIVE

To compare left atrial volume (LAV) and right atrial volume (RAV) determined by 2-D and 3-D echocardiographic methods with the LAV and RAV determined by ECG-gated multidetector CT (MDCT) for healthy dogs.

ANIMALS

11 healthy purpose-bred young adult hound-type dogs.

PROCEDURES

Each dog was anesthetized and underwent MDCT and a complete echocardiographic examination. Modality-specific software was used to measure the respective atrial volumes at ventricular end systole, and LAV and RAV measurements were subsequently indexed to body weight and compared among imaging modalities.

RESULTS

The LAV determined by echocardiographic methods did not differ significantly from the LAV determined by MDCT. However, the RAV determined by 3-D echocardiography and 2-D echocardiography via the left apical and left cranial windows differed significantly from the RAV determined by MDCT. Bland-Altman analyses indicated that the indexed LAV and RAV determined by echocardiographic methods were systematically underestimated, compared with MDCT measurements, but the bias was much smaller for LAV than for RAV.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that, for dogs, echocardiography might be an acceptable alternative to MDCT for measurement of LAV but not for measurement of RAV. However, the study population was small and homogenous in terms of breed, age, and weight. These findings need to be validated in a larger, more varied population of dogs with and without cardiac disease.

ACVIM consensus statement guidelines for the diagnosis, classification, treatment, and monitoring of pulmonary hypertension in dogs

Pulmonary hypertension (PH), defined by increased pressure within the pulmonary vasculature, is a hemodynamic and pathophysiologic state present in a wide variety of cardiovascular, respiratory, and systemic diseases. The purpose of this consensus statement is to provide a multidisciplinary approach to guidelines for the diagnosis, classification, treatment, and monitoring of PH in dogs. Comprehensive evaluation including consideration of signalment, clinical signs, echocardiographic parameters, and results of other diagnostic tests supports the diagnosis of PH and allows identification of associated underlying conditions. Dogs with PH can be classified into the following 6 groups: group 1, pulmonary arterial hypertension; group 2, left heart disease; group 3, respiratory disease/hypoxia; group 4, pulmonary emboli/pulmonary thrombi/pulmonary thromboemboli; group 5, parasitic disease (Dirofilaria and Angiostrongylus); and group 6, disorders that are multifactorial or with unclear mechanisms. The approach to treatment of PH focuses on strategies to decrease the risk of progression, complications, or both, recommendations to target underlying diseases or factors contributing to PH, and PH‐specific treatments. Dogs with PH should be monitored for improvement, static condition, or progression, and any identified underlying disorder should be addressed and monitored simultaneously.

Assessing Right Ventricular Function in the Perioperative Setting, Part II: What About Catheters?

An-depth assessment of right ventricular function is important in a many perioperative settings. After exploring 2-dimensional echo-based evaluation, other proposed monitoring modalities are discussed. Pressure-based methods of right ventricular appraisal is discussed. Flow-based assessment is reviewed. An overview of the state of current right ventricular 3-dimensional echocardiography and its potential to construct clinical pressure-volume loops in conjunction with pressure measurements is provided. An overview of right ventricular assessment modalities that do not rely on 2-dimensional echocardiography is discussed. Tailored selection of monitoring modalities can be of great benefit for the perioperative physician. Integrating modalities offers optimal estimations of right ventricular function.

Assessment of left atrial volume in dogs: comparisons of two-dimensional and real-time three-dimensional echocardiography with ECG-gated multidetector computed tomography angiography

INTRODUCTION

We hypothesized that real-time three-dimensional echocardiography (RT-3DE) was superior to two-dimensional echocardiography for the estimation of left atrial volume (LAV), using electrocardiographic (ECG)-gated multidetector computed tomography angiography (MDCTA) as a volumetric gold standard. The aim was to compare maximum LAV (LAV_max) and minimum LAV (LAV_min) measured by biplane area-length method (ALM), biplane method of disk (MOD) and RT-3DE with 64-slice ECG-gated MDCTA in dogs ANIMALS: The study included twenty dogs, anaesthetized for various diagnostic purposes and without evidence of cardiovascular disease.

METHODS

Left atrial volume was estimated by ALM, MOD and RT-3DE following ECG-gated MDCTA. The results were compared with LAV from MDCTA and correlations were performed. The limits of agreement (LoA) between methods were evaluated using Bland-Altman analysis and intraclass correlations. Coefficients of variation were calculated.

RESULTS

Area-length method (r = 0.79 and 0.72), MOD (r = 0.81 and 0.70) and RT-3DE (r = 0.94 and 0.82) correlated with MDCTA for LAV_max and LAV_min, respectively (all p < 0.05). Biases for LAV_max (-0.96 mL, 95% LoA: -5.6 to 3.7) and LAV_min (-0.67 mL, 95% LoA: -5.4 - 4.1) were minimal with RT-3DE, reflecting a slight underestimation. Conversely, MOD (LAV_maxbias = 3.19 mL, 95% LoA: -5.7 - 12.1; LAV_minbias = 1.96 mL, 95% LoA: -4.6 - 8.5) and ALM (LAV_maxbias = 4.05, 95% LoA: -5.7 - 13.8; LAV_minbias = 2.80 mL, 95% LoA: -3.9 - 9.5) suggested LAV overestimation. Intraobserver and interobserver variability were adequate.

CONCLUSIONS

Real-time three-dimensional echocardiography is a non-invasive, accurate and feasible method with superior accuracy to two-dimensional methods.

Anatomical assessment of intrathoracic cardiovascular structures using fast spin-echo double inversion recovery and steady-state free precession magnetic resonance imaging in a normal cat

In human medicine, non-contrast cardiac magnetic resonance imaging (CMRI) is routinely used to assess the cardiovascular system. In this study, using non-contrast CMRI, we provide a thorough description of the normal appearance of the intrathoracic cardiovascular structures in one healthy cat using a magnet operating at a field of 1.5-Tesla. The CMRI protocol was based on the use of fast spin-echo double inversion recovery and steady-state free precession pulse sequences in oblique short-axis, vertical long-axis, and horizontal long-axis imaging planes. After imaging the feline heart, four cadaver cats injected with latex substance into their arterial and venous systems were sectioned to facilitate interpretation of the intrathoracic cardiovascular structures to the corresponding CMRI. The fast spin-echo double inversion recovery images showed the best evaluation of gross intrathoracic anatomy, giving excellent contrast of the myocardium and vessels walls as they appeared with intermediate signal intensity compared to the lumen that appeared with low signal intensity. By contrast, steady-state free precession images showed details of the heart cavities and vascular lumen due to the high signal intensity of fast-flowing blood. The results of this study provide some anatomic detail for the heart and associated vessels as seen by non-contrast CMRI in the domestic cat.

Quantitative assessment of two- and three-dimensional transthoracic and two-dimensional transesophageal echocardiography, computed tomography, and magnetic resonance imaging in normal canine hearts

INTRODUCTION

The objective of the study was to evaluate the accuracy of two- and three-dimensional (2D, 3D) transthoracic echocardiography (TTE), 2D transesophageal echocardiography, and computed tomography angiography (CTA) compared with cardiac magnetic resonance imaging (CMR) in normal dogs and to assess repeatability of 2D and 3D TTE for the assessment of left ventricular (LV) and left atrial (LA) dimensions.

ANIMALS

The study was performed on six healthy dogs.

MATERIALS AND METHODS

Transthoracic echocardiography, transesophageal echocardiography, CTA, and CMR were performed on each dog. Right ventricular (RV) and LV volumes (in systole and diastole), ejection fraction (EF), and LA and right atrial (RA) volumes were assessed. Repeatability and intrarater and interrater measurements of variability were quantified by average coefficient of variation (CV) for 2D and 3D TTE.

RESULTS

No clinically relevant differences in LV volume were detected between CMR and all modalities. Importantly, 3D TTE had the lowest CV (6.45%), correlated with (r_s = 0.62, p = 0.01), and had the highest overlap in distribution with CMR (OVL >80%). Left ventricular EF and LA size via CTA compared best with CMR and RV and RA volumes were best estimated by 3D TTE. Assessment of LV and LA volumes via 3D TTE had moderate repeatability (15-21%) compared with LV M-mode measurements and 2D LA-to-aortic ratio (<10%), respectively. For LV size, interrater CV for 3D TTE (19.4%) was lower than 2D TTE (23.1%).

CONCLUSIONS

Measurements of LV, RV, and RA volumes via 3D TTE and LA volume and LV EF assessed by CTA compared best with CMR. Three-dimensional echocardiography had lower interrater and intrarater CV compared with 2D TTE.

Electrocardiography-gated cardiac CT angiography can differentiate brachycephalic dogs with and without pulmonary valve stenosis and findings differ from transthoracic echocardiography

Pulmonary valve stenosis (PS) is one of the most commonly diagnosed congenital heart defects in dogs. Currently, transthoracic echocardiography (TTE) is the standard modality used to evaluate PS. Image acquisition by TTE can be challenging in some brachycephalic breeds of dogs. The use of echocardiographic-gated CT angiography (ECG-gated CTA) in veterinary medicine is limited. This retrospective method comparison study investigated right and left ventricular outflow diameters by sedated ECG-gated CTA and unsedated TTE in 14 brachycephalic dogs with PS and 12 brachycephalic dogs without PS. Measurements of ventricular outflow structures were made in early systole and end diastole for both modalities and then compared for significance between systolic and diastolic phases, as well as between the two modalities. Ratios of the pulmonary trunk diameter to the aorta at different locations (aortic valve, aortic annulus, and ascending aorta) and in different planes (transverse, sagittal) were compared between dogs with PS and without PS, as well as within dogs, by both TTE and ECG-gated CTA. Transthoracic echocardiography and ECG-gated CTA both detected significantly greater pulmonary trunk to aorta ratios in dogs with PS at all aortic locations (P < 0.05). Pulmonary valve to aortic valve ratios were significantly smaller in dogs with PS (P < 0.05). Pulmonary trunk to aorta and pulmonary valve to aorta ratios were achieved with good anatomic detail using ECG-gated CTA. Ratios of the pulmonary trunk and pulmonary valve relative to the aorta may be useful to evaluate for PS using a modality that is underutilized for cardiac assessment.

Quantification of right ventricular volume measured by use of real-time three-dimensional echocardiography and electrocardiography-gated 64-slice multidetector computed tomography in healthy dogs

OBJECTIVE To evaluate accuracy of quantification of right ventricle volume (RVV) by use of 3-D echocardiography (3DE) and ECG-gated multidetector CT (MDCT). ANIMALS 6 healthy hound-cross dogs. PROCEDURES ECG-gated MDCT and complete 3DE examinations were performed on each dog. Right ventricular end-diastolic volumes (EDVs), end-systolic volumes (ESVs), stroke volume (SV), and ejection fraction (EF) were measured for 3DE and MDCT data sets by use of software specific for RVV quantification. Correlation and level of agreement between methods were determined. Intraobserver and interobserver variability were assessed for 3DE. RESULTS No significant differences were detected between SV and EF obtained with MDCT and 3DE. Significant differences were detected between right ventricular EDV and ESV obtained with MDCT and 3DE. No significant difference in heart rate was detected between methods. The correlation between MDCT and 3DE was very good (r = 0.87) for EDV and ESV, moderate (r = 0.60) for EF, and poor (r = 0.31) for SV. Bland-Altman analysis revealed a systematic underestimation of RVV derived by use of 3DE, compared with the RVV derived by use of MDCT (mean bias, 15 and 10.3 mL for EDV and ESV, respectively). Intraobserver (EDV, 12%; ESV, 18%) and interobserver (EDV, 14%; ESV, 11%) variability were acceptable for 3DE. CONCLUSIONS AND CLINICAL RELEVANCE There was substantial variance for RVV measured by use of 3DE in healthy dogs and a significant underestimation of volumes, compared with results for MDCT, despite the fact there were no significant differences in SV and EF.