CHAPTER 68 Cardiac Neoplasia
Tumors of the heart and pericardium are unusual in feline medicine, with an incidence of less than 0.3 per cent of the population in one report.1 Primary cardiac and pericardial tumors occur with lower frequency than metastasis to the heart and pericardium. The most commonly reported primary heart tumors in cats include lymphoma and chemodectoma, followed by myxoma, hemangiosarcoma, sarcoma, and rhabdomyosarcoma.2–7 Metastasis to the heart has been documented with lymphoma, hemangiosarcoma, pulmonary carcinoma, mammary gland carcinoma, tonsillar carcinoma, salivary gland adenocarcinoma, oral melanoma, and carcinomatosis.8–12
Primary pericardial tumors are reported rarely, having been identified at necropsy as mesothelioma and hemangiosarcoma.9,13 Metastasis to the pericardium has been demonstrated with lymphoma, bronchoalveolar carcinoma, mammary gland adenocarcinoma, pulmonary adenocarcinoma, and melanoma.8,10 Metastasis to the heart and pericardium is identified predominately at postmortem examination with the exception of lymphoma, and the most common locations for metastasis are the left ventricular free wall and interventricular septum.9
No breed, age, or gender predilections have been reported with feline cardiac neoplasms.1 In a review of the literature, the most commonly reported signalment was Domestic shorthair breed 5 years of age or older. The clinical effects of cardiac tumors are related principally to compression or obstruction of cardiac structures, infiltration of the myocardium, and fluid production. Effusions result from obstruction of venous return and pericardial pathology. Small masses may not cause clinical signs of disease and remain undetected.
Clinical signs in most feline patients with cardiac neoplasia are nonspecific and include lethargy, anorexia, and weight loss. Tachypnea and dyspnea are common complaints in the presence of pleural effusion and pulmonary edema. Other clinical signs may be unique and are related specifically to tumor location. Neoplastic cells may infiltrate the myocardium and affect the conduction system resulting in arrhythmias, conduction abnormalities, and syncope.14 Cough was reported in one cat with an aortic body tumor that had penetrated the trachea and occluded the right pulmonary bronchus completely.15
Physical examination findings may include tachypnea, dyspnea, and muffled heart and lung sounds in the presence of pleural or pericardial effusion. Auscultatory abnormalities including murmur and gallop rhythm may be detected in association with myocardial disease or anemia.10 An abnormal heart rate or rhythm often is attributed to neoplastic myocardial infiltration affecting the conduction system. Signs of right heart failure or increased right heart pressures include jugular venous distension and hepatomegaly, which occur infrequently in cats. Pale mucous membranes and decreased femoral pulse quality may occur with hemodynamic instability.
In general comprehensive laboratory evaluation including complete blood count, biochemical analysis, urinalysis, and retroviral testing (feline leukemia virus [FeLV] antigen and feline immunodeficiency virus [FIV] antibody) is recommended. Careful examination for primary tumors should focus on lymph nodes, the gastrointestinal tract, kidneys, mammary glands, and oral cavity.
Cardiac tumors typically are detected with echocardiography or discovered at necropsy evaluation. Echocardiography provides a noninvasive means of imaging the heart and surrounding structures, and is superior to conventional radiography for identifying masses, myocardial infiltrative lesions, and pericardial effusion.10 Tumors most often are located at the heart base or within the ventricular myocardium, and assessment of both the right and left imaging windows may be required for successful localization. Pericardial effusion appears as a hypoechoic space surrounding the heart and is helpful for visualizing tumors. In addition to identifying pericardial effusion, echocardiography can provide evidence of cardiac tamponade by documenting diastolic collapse of the right atrium and ventricle when intrapericardial pressures exceed right atrial or ventricular end-diastolic pressures.16
Cardiac tumors are not identified routinely with thoracic radiographs. Dorsal deviation of the trachea and visualization of a heart base mass has been reported rarely with chemodectoma and carcinomatosis.13,15,17 A globoid cardiac silhouette suggests pericardial effusion, whereas small volume pericardial effusions may go undetected. Cardiomegaly can occur with neoplastic infiltrative lesions. Pericardial calcification has been reported in a cat with pulmonary carcinoma metastasized to the pericardium.8 Radiographic evidence of pulmonary metastasis has been reported in a cat with chemodectoma.18 Thoracic radiographic findings in dyspneic patients may include pleural effusion or pulmonary edema with pulmonary venous distension.
Arrhythmias and conduction abnormalities most often are related to neoplastic myocardial infiltration. Electrocardiographic evaluation is recommended for cats with abnormally slow or rapid heart rates, irregular heart rhythm, or a history of syncope (see Chapter 42). Reported abnormalities in cats with cardiac neoplasia consist of electrical alternans, changes in the ST segment, atrial tachycardia, ventricular premature beats, atrioventricular block, bundle branch block, and sinus arrest.8,14 Although low voltage QRS complexes may be associated with pericardial effusion in cats, it is important to recognize that QRS complexes typically are small in cats, making this an insensitive indicator of effusion.
The most common causes of pericardial effusion in cats are congestive heart failure secondary to myocardial disease, neoplasia, and infectious diseases.10 Most cardiac tumors do not exfoliate well, and for this reason pericardial fluid analysis and cytological examination often are unrewarding for identifying feline cardiac tumors. Careful cytological evaluation is required so that reactive mesothelial cells are not mistaken for neoplastic cells. Lymphoma is the only tumor that may be diagnosed from pericardial fluid analysis, and lymphoblasts and atypical lymphocytes were identified in some but not all cases.19,20 Chylous effusion has been documented in a cat with chemodectoma.21
Feline cardiac tumors are located principally near important vascular structures, making definitive diagnosis challenging and obtained most often at postmortem examination. Ultrasound-guided fine-needle aspirates of heart base tumors and surgical excisional biopsy have been performed occasionally to identify chemodectoma.15,22 Multiple tumor types have been identified using immunohistochemistry including a chemodectoma positive for chromogranin A (CgA), neuron-specific enolase (NSE), and synaptophysin (SY) characteristic of neuroendocrine tumors.23 Immunopositivity for CD3 consistent with T lymphocytes has been documented in a cat with chemodectoma.17 Immunohistochemistry demonstrated positive staining for alpha-actin and desmin that aided in identifying a primary rhabdomyosarcoma.7 Diagnosis of right atrial hemangiosarcoma was confirmed with positive immunohistochemical staining for factor VIII–related antigen.5