History
A 7-year-old 26.0-kg (57.2-lb) sexually intact male American Pit Bull Terrier was referred for cardiac evaluation after being examined by the referring veterinarian because of a 24-hour history of coughing with occasional production of clear, foamy liquid. The owner reported no change in the dog's energy, appetite, or behavior and no clinically relevant prior medical history. The referring veterinarian noted an arrythmia during auscultation, but no substantial abnormalities were seen on a CBC and serum biochemical analyses, and results for an in-office testa to detect Dirofilaria immitis antigen and antibodies against Borrelia burgdorferi, Anaplasma phagocytophilum, and Ehrlichia canis were negative. The referring veterinarian performed thoracic radiography (not shown), tentatively diagnosed a cardiac-associated tumor, and referred the dog for a cardiac evaluation.
On initial examination at the Emergency Service of Angell Animal Medical Center, the dog was bright, alert, and responsive. Cardiac auscultation revealed an irregularly irregular heart rhythm, with an estimated heart rate of 140 beats/min (reference range, 80 to 120 beats/min) and occasional femoral pulse deficits. The dog's remaining vital signs were within reference limits, and other than a mildly enlarged prostate noticed on rectal examination, no other abnormalities were detected during physical examination. Thoracic radiography was performed (Figure 1)
Right lateral (A) and ventrodorsal (B) thoracic radiographic images of a 7-year-old 26.0-kg (57.2-lb) sexually intact male American Pit Bull Terrier with a 24-hour history of coughing referred for cardiac evaluation because of suspected cardiac-associated tumor.
Citation: Journal of the American Veterinary Medical Association 257, 1; 10.2460/javma.257.1.33
Formulate differential diagnoses and treatment strategies from the history, clinical findings, and Figure 1—then turn the page →
Radiographic Findings and Interpretation
Thoracic radiography revealed a well-defined, round, soft tissue opacity (approx 7 × 6 × 4 cm) cranioventral to the cardiac silhouette, the cranial margins of which were partly effaced by the abnormal soft tissue opacity (Figure 2) On the ventrodorsal radiographic image, the left side of this abnormal soft tissue opacity appeared to have a small, triangular, appendage-like projection. Mild generalized cardiomegaly, with a vertebral heart size1 of 11.3 (reference range, < 10.7), was evident and dorsally displaced the trachea. The pulmonary vasculature and pulmonary parenchyma appeared radiographically normal, and there was no evidence of pleural effusion, caudal vena caval dilation, hepatomegaly, or decreased peritoneal serosal detail, which, if present, would have suggested right-sided congestive heart failure.
Same images as in Figure 1. A soft tissue opacity (black arrows; A and B) is cranioventral to the cardiac silhouette, the cranial margins of which are partly effaced by the soft tissue opacity. The trachea (white arrow; A) is deviated dorsally, the cardiac silhouette (white arrowheads; A and B) is enlarged, and a small, triangular, appendage-like projection (asterisk; A and B) is associated with the left side of the abnormal soft tissue opacity cranioventral to the heart.
Citation: Journal of the American Veterinary Medical Association 257, 1; 10.2460/javma.257.1.33
On the basis of radiographic findings, our differential diagnoses for the soft tissue opacity cranioventral to the cardiac silhouette included cranial mediastinal or cardiac-associated tumor (eg, hemangiosarcoma or chemodectoma), lymphadenopathy, thymic branchial cyst, and focal chamber enlargement (eg, right atrial or right auricular enlargement or pericardial right atrial herniation).2–4 In addition, the radiographic appearance of a triangular appendage-like structure associated with the left side of the soft tissue opacity could have been caused by thymic remnants or right auricular enlargement.2
Echocardiography revealed marked right atrial and right auricular enlargement with right auricular spontaneous echogenic contrast, severe right ventricular (RV) dilation, and moderately decreased right ventricular wall motion (Figure 3; Supplementary Videos S1 and S2, available at: avmajournals.avma.org/doi/suppl/10.2460/javma.257.1.33). On a parasternal 4-chamber 2-D echocardiographic short-axis view, diameters of the right atrium and ventricle were 4.42 cm (reference range,5 2.13 to 3.41 cm) and 5.6 cm (reference range,5 2.69 to 5.35 cm), respectively. In addition, findings excluded tricuspid valve dysplasia, pulmonary valve stenosis, and pulmonary hypertension with cor pulmonale from pressure overload as underlying causes of cardiac enlargement affecting the right side of the heart (right-sided heart enlargement). The echocardiographic diagnosis was RV cardiomyopathy with marked or aneurysmal right auricular dilation. Results of ECG indicated atrial fibrillation, with an average ventricular response rate of 160 to 180 beats/min.
Left (A) and right (B) parasternal 4-chamber 2-D echocardiographic images of the dog in Figures 1 and 2 showing severe enlargement of the right atrium and ventricle, which should generally be one-third to one-half the size of the left atrium and ventricle, respectively. It is apparent that the right atrium is larger than the left atrium (A and B) and that the right ventricle is larger than the left ventricle (B), indicating right-sided heart enlargement. The scale along the left angle of each echocardiographic image is in centimeters. The ECG (B) shows atrial fibrillation. LA = Left atrium. LV = Left ventricle. RA = Right atrium. RV = Right ventricle.
Citation: Journal of the American Veterinary Medical Association 257, 1; 10.2460/javma.257.1.33
Treatment and Outcome
Digoxin (0.005 mg/kg [0.002 mg/lb], PO, q 12 h) and diltiazem hydrochloride extended release (2.3 mg/kg [1.0 mg/lb], PO, q 12 h) were prescribed for rate control of atrial fibrillation, clopidogrel bisulfate (1.4 mg/kg [0.6 mg/lb], PO, q 24 h) was prescribed because of the presence of right auricular spontaneous echogenic contrast, and doxycycline (5.8 mg/kg 2.6 mg/lb], PO, q 12 h for 4 weeks) was prescribed for treatment of suspected tracheobronchitis. The dog's cough resolved, and 2 months later, treatment with pimobendan (0.29 mg/kg [0.13 mg/lb], PO, q 12 h) was initiated to aid in improvement of RV contractility. Recheck ECG and echocardiography 6 and 12 months after the initial cardiac consultation revealed persistent atrial fibrillation, adequate average ventricular response rate of 120 beats/min, improved right atrial and auricular enlargement, and resolution of right auricular spontaneous echogenic contrast.
Comments
The dog of the present report was evaluated initially because of coughing that was later determined not to have been cardiogenic in origin but attributed to suspected tracheobronchitis. However, during the dog's evaluation, concurrent right-sided heart enlargement was discovered and diagnosed as RV cardiomyopathy with aneurysmal right auricular dilation. Following cardiac consultation, it was confirmed that the marked right atrial and right auricular dilation in this dog falsely gave the radiographic impression of a possible heart-base tumor or cranial mediastinal mass.
Although, in our experience, arrhythmogenic RV cardiomyopathy (ARVC) is the most common cause for RV cardiomyopathy in dogs, the dog in the present report lacked evidence of ventricular arrhythmias, which is the typical defining characteristic of ARVC. We recognize that patients with the occult stage of ARVC may not have ventricular arrhythmias on baseline ECG and that some patients with ARVC may have echocardiographic findings of right-sided heart enlargement and an appearance of systolic dysfunction.6 However, the dog in the present report also had marked right auricular enlargement, which, when combined with the absence of ventricular arrhythmias, was atypical for ARVC; thus, we excluded ARVC as the cause of this dog's RV cardiomyopathy.
There are rare reports4,6,7 that describe findings in dogs with echocardiographic or other features of RV cardiomyopathy that do not fit with the classic features of ARVC. These lesions may resemble the rare condition of RV cardiomyopathy in humans (also called RV dysplasia), which can cause severe tachycardia or tachyarrhythmias, right-sided congestive heart failure, or sudden death.8 Lastly, findings on radiography, echocardiography, and ECG similar to those in the dog of the present report have been described4,7 in dogs with aneurysmal dilation of the right auricle that is either idiopathic or secondary to a pericardial sac defect causing herniation of cardiac structures or a right atrial diverticulum.
The tachyarrhythmia detected in the dog of the present report could have contributed to and exacerbated the marked right-sided heart enlargement, a condition known as tachycardia-induced cardiomyopathy.9 This suspicion was supported by subsequent improvement in the dog's right-sided heart enlargement 6 months following the initiation of anti-arrhythmic treatment and achievement of adequate heart rate control.
Thoracic radiography is a useful diagnostic tool to assess for changes in the shape and size of the cardiac silhouette and pulmonary vessels and the presence of pulmonary edema or other pulmonary abnormalities. However, variations exist in radiographic technique and interpretation, and findings in the dog of the present report highlighted the importance of meticulous and stepwise evaluation in diagnostic imaging. For instance, a board-certified veterinary radiologist likely would have prioritized right atrial or auricular enlargement or herniation as a primary differential diagnosis on the basis of initial radiographic findings for this dog. Beyond radiography, additional diagnostic imaging modalities (eg, echocardiography, MRI, CT, and angiography) may be useful when thoracic radiography cannot provide a definitive diagnosis; however, such modalities may not be readily available in most general small animal practice settings.
References
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