+ General Considerations

• Right atrium is a primary site for HSA and accounts for 30%-50% canine HSA
• HSA is the most common cardiac tumor in dogs and accounts for 40.4%-60.5% of cardiac tumors
• HSA has also been reported in the right ventricular free wall, interventricular septum, and main pulmonary artery
• Primary cardiac HSA has not been reported in cats, but the heart is a common site for metastatic HSA

+ CLINICAL FEATURES

• Breed predisposition: GSD, Poodle, Golden Retriever, English Setter, and Scottish Terrier
• No sex predisposition but neutered females have > 5-times risk of cardiac HSA compared to intact females
• Acute or chronic cardiac tamponade is the most common presentation due to intrapericardial hemorrhage:
• Restricted ventricular filling secondary to external cardiac compression with muffled heart sounds
• Venous congestion with abdominal effusion
• Poor cardiac output with weak peripheral pulses
• Arrhythmias
• Cardiac tumors may present for reasons other than cardiac tamponade such as CHF, arrhythmia or low cardiac output secondary to obstruction of proximal great vessels
• Thoracic radiographs: enlarged cardiac silhouette, pulmonary edema, and pleural effusion
• Echocardiography: pericardial effusion ± right atrial mass
• Pericardiocentesis is both diagnostic and therapeutic
• Cytologic analysis of pericardial fluid for the diagnosis of malignant effusions is usually unrewarding
• pH > 7.5 is consistent with neoplasia and pH < 7.5 is consistent with idiopathic pericardial effusion
• However, others show no difference in pH between idiopathic and neoplastic effusions
• Serum cardiac troponin I concentrations, which is a marker for myocardial ischemia and necrosis, are significantly higher in dogs with pericardial effusions and significantly higher in dogs with right atrial HSA compared to dogs with idiopathic pericardial effusions

+ Clinical Staging

• Metastatic rate approaches 100%
• Lungs are the most common metastatic site (64%-67%), followed by spleen (36%-60%), kidneys (55%), liver (41%-55%), brain (20%), intestines (20%), adrenal glands (20%), skeletal muscle (20%), visceral lymph nodes (15%), skin and subcutaneous tissue (15%), left ventricle (10%), and mesentery and omentum (10%)
• Metastasis to other parts of the heart (i.e., ventricles, left auricle, and pericardium) occur in 43% dogs

+ Pericardiocentesis

• Pericardiocentesis is both diagnostic and therapeutic
• Pericardiocentesis alleviates cardiac tamponade and provides immediate relief of clinical signs

+ Pericardiectomy

• Pericardiectomy is a palliative procedure
• Surgical techniques include:
• Pericardial window via thoracoscopic surgery or left 4th intercostal thoracotomy
• Subtotal pericardiectomy via left 4th intercostal thoracotomy

+ Right Atrial Appendage Resection

• Indications: HSA of right atrial appendage or atrial free wall
• Approach: median sternotomy or right 5th intercostal thoracostomy
• Atrial appendage is clamped with vascular forceps and appendage excised
• Atriotomy is closed with a continuous mattress suture pattern oversewn with a simple continuous pattern
• Complications: atrial and ventricular arrhythmia, anemia, DIC, and pneumonia

+ Right Atrial Patch Graft Reconstruction

• Pericardial patch graft can be used for reconstruction of atrial wall defects following resection of large atrial lesions to achieve tumor-free margins

+ Chemotherapy

• Doxorubicin-based protocols significantly improve MST (175 days v 42 days)

+ Prognosis

• Prognosis is better for older dogs and dogs with stage I disease
• Prognosis is poor with MST 16 days following pericardiectomy and 4 months following right atrial appendage resection
• Prognosis is significantly improved when surgery (pericardiectomy) is combined with adjunctive doxorubicin-based chemotherapy protocols, with a MST of 175 days compared to 42 days without chemotherapy