“Sadie”, an 11-year-old female Pit Bull, presented to the Cardiology Service at Tufts Foster Hospital for Small Animals for further evaluation and treatment of a cardiac mass and signs of persistent right-sided congestive heart failure(RCHF). Sadie had previously been treated with standard doses of furosemide and pimobendan. Previous three-view thoracic radiographs at Tufts VETS showed possible small pulmonary nodules, and an abdominal ultrasound showed large volume ascites and nodules in both the spleen and liver.
Figure 2: Right parasternal short axis echocardiographic loop showing moderate to marked mixed hypertrophy of the right ventricle with flattening of the interventricular septum and prominent RV papillary muscles.The left ventricular cavity is small and LV walls appear pseudohypertrophied due to reduced LV preload. There is no pericardial or pleural effusion.
At presentation the dog was BAR with a heart rate of 160, occasional arrhythmia, a grade V/VI systolic murmur which was heard best over the right hemithorax and jugular venous distension halfway up the neck. She had severe abdominal distension with an abdominal fluid wave and was in poor body condition with marked epaxial muscle wasting and a BCS of three. Figure 1 shows the ECG performed during the initial exam. What is your ECG diagnosis?
Figure 3: Right parasternal echocardiographic loop obtained at the level of the heart base. A large homogeneous mass can be seen attaching to the base of the aorta and pulmonary artery. A small extension of the mass is seen in the right atrium to the left of the tricuspid valve.
The ECG showed sinus rhythm with occasional atrial premature contractions. Two-dimensional echocardiography showed moderate right heart enlargement (Figure 2) and a large 7.7×4.9 cm mass at the level of the aorta and pulmonary artery (Figure 3). There was no pericardial effusion. Doppler echo showed marked tricuspid regurgitation (TR) and a severely elevated TR velocity of 5.3 m/sec. The pulmonic outflow velocity was normal at the level of the pulmonic valve, but distal flow disturbance was noted in both the right and left main pulmonary arteries beyond the pulmonary bifurcation (Figure 4).
What is your top differential diagnosis for a mass at this location and what further diagnostic and treatment options should be considered? What is the significance of the elevated TR velocity? How could the observed mass contribute to signs of RCHF in the absence of pericardial effusion?
Diagnosis and treatment:
The primary differential for a mass located at the heart base in a dog is chemodectoma (also known as aortic body tumor or paraganglionoma), a slow-growing neuroendocrine tumor that is most common in brachycephalic breeds. Other differentials include hemangiosarcoma, thyroid carcinoma, lymphoma, and other metastatic tumors. Although chemodectomas rarely metastasize, they can result in life-threatening pericardial effusion and cardiac tamponade and/or physical compression of surrounding structures. Large heart base masses can result in acquired pulmonic stenosis from compression of the pulmonary arteries. The elevated TR velocity of 5.3 m/sec seen in this dog indicates a markedly elevated pulmonary artery pressure of >112 mm Hg (normal <20-25mmHg). Combined with the flow disturbance seen on color Doppler echo, this was suggestive of severe branch pulmonic stenosis secondary to obstruction from the heart base mass causing secondary TR and RCHF.
Thoracic computed tomography (CT) and pulmonary CT angiography were performed to better define the location and extent of the mass and determine the feasibility of various treatment options (Figures 5 and 6). An ultrasound-guided fine needle aspirate of one of the splenic nodules was consistent with metastatic neuroendocrine tumor, suggestive of rare metastasis from a presumptive chemodectoma. Treatment options discussed with the owner included radiation therapy, chemotherapy, and palliative catheter-based stenting of the main pulmonary arteries to ameliorate obstruction caused by the mass. Surgical resection is rarely indicated for heart base tumors given their firm adherence to the heart and great vessels. Neither radiation therapy nor surgery were strongly considered in this case, given the extent of the tumor and diffuse metastatic disease.
Figure 8a: Right parasternal echocardiographic loop obtained at the same level as Figure 3. Nitinol stents can be seen propping open the lumens of both main pulmonary arterial branches as they traverse the region of the heart base tumor.
The owner elected for palliative pulmonary artery stenting with a plan to start subsequent chemotherapy with Palladia. Using fluoroscopic guidance, three nitinol stents were placed in the left and right pulmonary arteries through an introducer catheter in the right jugular vein (Figures 7, 8a and 8b).The stenting procedure resulted in improved pulmonary arterial flow with a 60% reduction in the obstructive gradient, and led to an immediate decrease in right heart size and improvement in congestive signs (Figure 9). Palladia, a tyrosine kinase inhibitor with broad spectrum chemotherapeutic efficacy against multiple different types of neoplasia, was started at 80 mg (2.75 mg/kg) PO every other day. Although there are no published studies on the efficacy of this drug in the treatment of neuroendocrine tumors, it has been used empirically by the Oncology Service at TCSVM and others for this purpose with possible benefit. The dog was also started on clopidogrel at 75 mg (2.6 mg/kg) once daily to prevent stent thrombosis. Pimobendan (7.5 mg [0.3 mg/kg] BID) and a lower dose once a day of furosemide (30 mg [1 mg/kg]) were continued. At the one-month recheck the dog had gained muscle mass, but lost 5 kg of fluid weight on the lower furosemide dose. She continues to do very well clinically, with no evidence of disease progression or worsening of heart failure signs, six-months following the stent procedure.
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