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.

Evaluation of the radiographic liver length/11th thoracic vertebral length ratio as a method for quantifying liver size in cats.

Abdominal radiography is a standard diagnostic test for cats with suspected liver disease, however, absolute measurements of radiographic liver size can be affected by other factors such as positioning, radiographic technique, and obesity. This prospective and retrospective, analytical, cross-sectional study evaluated the liver length/11th thoracic vertebral length (LL/T11) ratio as a method for minimizing these outside effects. In a prospectively recruited sample of 25 clinically healthy cats, measurements of radiographic LL/T11 ratio were compared with CT measurements of liver volume. Effects of radiographic technical factors (body posture, recumbency state, and beam center to LL/T11 ratio) and observer were also tested. In a retrospectively recruited sample of 324 cats with no evidence of liver disease, radiographic measurements of the LL/T11 ratio were performed using right lateral radiographs and compared among signalment groups (age, sex, body weight, and body condition score). There was a strong significant correlation between the LL/T11 ratio and CT liver volume (P < .001), and this ratio was not affected by radiographic technical factors. The reference value of the LL/T11 ratio was 4.22 ± 0.54 and the LL/T11 ratio did not differ among signalment groups. Findings supported the use of the LL/T11 ratio as a novel quantitative index of radiographic liver size in cats. Future studies in clinically affected cats are needed to further validate this method.

Computed tomographic and radiographic bronchial collapse may be a normal characteristic of forced expiration in dogs.

Tracheobronchomalacia has been diagnosed using radiography or bronchoscopy to confirm bronchial changes in luminal diameter during the respiratory cycle. However, studies in healthy humans suggest that some degree of bronchial collapse may be observed during the normal respiratory cycle. In this analytical study, the luminal diameter of the bronchus to each of the six pulmonary lobes and the mean percentage of expiratory collapse from end inspiratory, end expiratory, and two forced expiratory phases (10 and 15 ml/kg) were determined via computed tomography (CT) and radiography in 22 healthy Beagle dogs. The bronchial collapsibility was significantly greater during the forced expiration than the end expiration (P < 0.001); the same results were observed in dorsal and sagittal CT images and radiographs (P < 0.001). Median collapsibility values associated with 15 ml/kg forced expiratory collapse determined via cross-sectional CT images were measured as 16.6-45.5% and differed according to the pulmonary lobe. Median collapsibilities on radiography with 15 ml/kg forced expiration were 57.8% and 62.1% in the right cranial lobe and right caudal lobe, respectively. In conclusion, bronchial diameter may change during the respiratory cycle, and some degree of reduction in bronchial diameter may be an incidental finding in healthy dogs. More rigorous criteria are needed with regards to bronchial collapsibility during normal respiration for the diagnosis of bronchomalacia in order to avoid false-positive diagnoses.

CARDIAC MAGNETIC RESONANCE IMAGING OF PATENT DUCTUS ARTERIOSUS IN THREE DOGS.

Patent ductus arteriosus (PDA) is the most common congenital cardiovascular disorder in dogs and requires an accurate diagnosis for an appropriate treatment. Cardiac MRI (cMRI) has been reported as a method for characterization of canine thoracic vasculature. However, to the authors' knowledge, no published studies describe evaluation of canine PDA through cMRI. Three dogs were selected for this exploratory study. Electrocardiogram gating and breath-hold techniques were performed using a 3T MR scanner. Both black blood imaging and bright blood cine acquisitions were performed. Quantification of stroke volume (SV) and shunting volume were calculated using a stack of short-axis cine images. Additional 4D (three-spatial dimensions plus time)-TRAK (time-resolved MR angiography with keyhole) sequences were conducted in patient 2 to verify other vasculature abnormality. Black blood images clearly depicted the course of the ductus from the descending aorta to the pulmonary artery in all three dogs. Morphological evaluation of PDA classified patients 1 and 2 as Type 2a and patient 3 as Type 1. Patient 2 was confirmed to have a concurrent persistent left cranial vena cava. Left ventricular SV, right ventricular SV, and left-to-right SV ratio were 12.4 ml, 3.36 ml, and 3.704, respectively, in patient 1; 6.85 ml, 1.22 ml, and 5.60 in the patient 2; and 3.67 ml, 2.14 ml, and 1.702 in patient 3. Findings indicated that cMRI is a feasible method for characterizing the morphology of PDA and extracardiac vasculature anomalies in dogs.