Evaluation of left ventricular function with cardiac magnetic resonance imaging and echocardiography after administration of dobutamine and esmolol in healthy beagle dogs

Unlike echocardiography, cardiac magnetic resonance imaging (cardiac MRI) results in a near-exact assessment of cardiac structures and function. However, most veterinary studies have focused on dogs with normal cardiac function. We hypothesized that there would be significant differences in cardiac measurements between cardiac MRI and echocardiography when left ventricular (LV) function was abnormal. This study was undertaken to compare measurements of LV function produced by cardiac MRI and echocardiography in dogs whose LV function was altered by pharmacological agents. This study was conducted with six healthy beagle dogs. We increased left ventricular contractility by administration of dobutamine; we decreased cardiac contractility with esmolol. Stroke volume measurements were made by using both cardiac MRI and echocardiography under seven different conditions with general anesthesia: control, three doses of esmolol (100, 200, and 500 µg/kg/min), and three doses of dobutamine (10, 20, and 50 µg/kg/min). Experiments involving each condition were conducted at least 1 week apart. When LV contractility was normal, ejection fraction (EF) and stroke volume (SV), as measured by echocardiography and cardiac MRI, were not significantly different. However, when contractility was changed by pharmacological agents, EF and SV were overestimated by echocardiography, compared to MRI. Evaluation of cardiac function in patients treated with pharmacological agents should be conducted carefully because EF and SV measured by echocardiography can be overestimated, compared with EF and SV obtained by cardiac MRI.

Use of vertebral left atrial size for staging of dogs with myxomatous valve disease

INTRODUCTION/OBJECTIVES

The American College of Veterinary Internal Medicine (ACVIM) guidelines suggest that pimobendan should be initiated in dogs which meet all criteria of stage B2 myxomatous mitral valve disease (MMVD): murmur intensity ≥ 3/6, left atrial-to-aortic ratio ≥ 1.6, normalized left ventricular internal diameter in diastole ≥ 1.7, and vertebral heart size > 10.5. Recently, a new radiographic index for left atrial enlargement, vertebral left atrial size (VLAS), was proposed. The objective of the present study was to evaluate whether VLAS is useful in staging MMVD and if it can distinguish between ACVIM stages B1 and B2.

ANIMALS

Ninety-seven client-owned dogs with MMVD were evaluated and classified as ACVIM stage B1, B2, or C-D.

MATERIALS AND METHODS

The echocardiographs and radiographs of all the dogs were retrospectively evaluated to obtain left atrial-to-aortic ratio, normalized left ventricular internal diameter in diastole, and VLAS values. The data were analyzed to assess the correlation between these measurements and VLAS, and the optimal cutoff value of VLAS was determined.

RESULTS

A VLAS cutoff value of 2.6 provided the greatest diagnostic accuracy for identification of dogs with ACVIM stage B2 MMVD (area under the curve, 0.96; sensitivity, 95%; specificity, 84%). A VLAS ≥2.5 exhibited the highest sensitivity (sensitivity, 100%; specificity, 78%), and a VLAS ≥ 3.1 exhibited the highest specificity (sensitivity, 47%; specificity, 100%).

CONCLUSIONS

VLAS is a helpful index for monitoring MMVD using radiography. A VLAS cutoff value of 2.5 could be used to identify dogs that may benefit from echocardiography to determine if they have reached ACVIM stage B2.

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.

Use of CPR in hemorrhagic shock, a dog model

INTRODUCTION

Cardiopulmonary resuscitation was designed for sudden cardiac events usually triggered by thrombotic phenomena. Despite this, it is routinely used in trauma resuscitations as per the American Heart guidelines. There is no data supporting the use of chest compressions in hemorrhagic shock. An evidence-based cardiopulmonary resuscitation (CPR) protocol has been developed for dogs. We sought to determine the effects and outcomes of chest compressions in hemorrhagic shock in a canine model.

METHODS

Eighteen dogs were randomized to three treatment groups-chest compressions only after hemorrhagic shock (CPR), CPR with fluid resuscitation after hemorrhagic shock (CPR + FLU), and fluid resuscitation alone after hemorrhagic shock (FLU). Under anesthesia, dogs were hemorrhaged until pulse was lost; they were maintained pulseless for 30 minutes and then resuscitated over 20 minutes. Vital signs and laboratory values were recorded at determined intervals. Echocardiography was performed throughout the study. Upon termination of the study, kidney, liver, heart, and brain tissue histology was evaluated for end organ damage. Statistical significance was p < 0.05 with a Bonferroni correction for multiple comparisons.

RESULTS

Blood loss and mean time to loss of pulse were similar between the groups. Dogs in the CPR group had significantly lower mean arterial pressure and higher pulse at all points compared to CPR + FLU and FLU (p < 0.05). Ejection fraction was lower in the CPR group at 5 and 10 minutes compared to the other groups (p < 0.05). Vital signs and laboratory results between CPR + FLU and FLU were equivalent. Two of six dogs in the CPR group died, while no dogs died in the CPR + FLU or FLU groups. Dogs in the CPR group were found to have more episodes of end organ damage.

CONCLUSION

There was no benefit to chest compressions in the hypovolemic animals. Chest compressions in addition to fluid did not reverse signs of shock better than fluid alone. Further research is needed to define if there is a role of CPR in the trauma patient with hemorrhagic shock.

QUANTITATIVE PLANAR AND VOLUMETRIC CARDIAC MEASUREMENTS USING 64 MDCT AND 3T MRI VS. STANDARD 2D AND M-MODE ECHOCARDIOGRAPHY: DOES ANESTHETIC PROTOCOL MATTER?

Cross-sectional imaging of the heart utilizing computed tomography and magnetic resonance imaging (MRI) has been shown to be superior for the evaluation of cardiac morphology and systolic function in humans compared to echocardiography. The purpose of this prospective study was to test the effects of two different anesthetic protocols on cardiac measurements in 10 healthy beagle dogs using 64-multidetector row computed tomographic angiography (64-MDCTA), 3T magnetic resonance (MRI) and standard awake echocardiography. Both anesthetic protocols used propofol for induction and isoflourane for anesthetic maintenance. In addition, protocol A used midazolam/fentanyl and protocol B used dexmedetomedine as premedication and constant rate infusion during the procedure. Significant elevations in systolic and mean blood pressure were present when using protocol B. There was overall good agreement between the variables of cardiac size and systolic function generated from the MDCTA and MRI exams and no significant difference was found when comparing the variables acquired using either anesthetic protocol within each modality. Systolic function variables generated using 64-MDCTA and 3T MRI were only able to predict the left ventricular end diastolic volume as measured during awake echocardiogram when using protocol B and 64-MDCTA. For all other systolic function variables, prediction of awake echocardiographic results was not possible (P = 1). Planar variables acquired using MDCTA or MRI did not allow prediction of the corresponding measurements generated using echocardiography in the awake patients (P = 1). Future studies are needed to validate this approach in a more varied population and clinically affected dogs.

Quantification of left ventricular volumes and function in anesthetized beagles using real-time three-dimensional echocardiography: 4D-TomTec™ analysis versus 4D-AutLVQ™ analysis in comparison with cardiac magnetic resonance imaging

Backround

Real-time three-dimensional echocardiography (RT3DE) enables accurate volume determination of the left ventricle (LV), since measurements in foreshortened depicted views are avertable. Different analyzing programs are available for this RT3DE. The commonly used semi-automatic software 4D-AutLVQ™ showed underestimation of LV volumes in comparison with CMRI in healthy anesthetized dogs (Am J Vet Res 74(9):1223–1230, 2013). TomTec 4D LV-Function™ is an offline analysis program for morphological and functional analyses of the left ventricle by using manual measurement optimization, showing excellent agreement with CMRI in human medicine (Echocardiography 27(10):1263–1273, 2010; Eur J Echocardiogr 11(4):359–368, 2010; Echocardiography 24(9):967–974, 2007). The aim of the present study was to compare these different RT3DE analyzing software programs to test the possibility of one performing better than the other by assessing accuracy and reproducibility in comparison with the reference method cardiac magnetic resonance imaging (CMRI) by determining the left ventricular end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and ejection fraction (EF).

RT3DE and CMRI were performed during anesthesia in 10 healthy beagles. The analyzing programs 4D-AutLVQ™ (based on semi-automated border detection) and TomTec 4D LV-Function™ (primary manual tracking with semi-automated border detection) were used for RT3DE volume analysis of the left ventricle. Left ventricular EDV, ESV, SV and EF were measured and compared to those measured by the reference method CMRI. Repeated measurements were performed to determine inter- and intra-observer variability.

Results

Both, 4D-AutLVQ™ and 4D-TomTec™ showed small but significant underestimation for EDV and ESV with quite good correlation (r = 0.34–0.69) in comparison with CMRI, without significant difference between each of them. Ejection fraction (EF) measured by 4D-TomTec™ showed no significant differences compared to CMRI (p = 0.12), while 4D-AutLVQ™ significantly underestimated LV-EF (p = 0.03). Analyzing time was shorter using 4D-AutLVQ™ compared to 4D-TomTec™. The inter-observer variability was higher using 4D-TomTec™ than with 4D-AutLVQ™, whereas both methods present excellent intra-observer variability.

Conclusion

4D-TomTec™ and 4D-AutLVQ™ are feasible RT3DE analyzing programs, allowing accurate volume quantification of the left ventricle, albeit with significant underestimation of ventricular volumes in comparison with the gold standard CMRI. 4D-AutLVQ™ is performed faster with less inter-observer variability than 4D-TomTec™. Therefore, 4D-AutLVQ™ is the more practicable measurement method when comparing the different analyzing programs.