Pericardial effusion: causes and clinical outcomes in dogs (Proceedings)
Pericardial effusion is a fairly common acquired heart disease in dogs, and prevalence has been reported to be 0.43% (or 1 dog per 233 cases) of dogs presenting to a referral veterinary hospital, and accounts for approximately 7% of dogs with clinical signs of cardiac disease.1 It is a multi-etiologic disorder (including infectious, inflammatory, and neoplastic causes) with a wide spectrum of prognoses ranging from good to grave.2 Careful echocardiographic evaluation for cardiac masses is necessary, and localization of the mass to specific anatomic regions such as the heart base or right atrium is very critical to provide prognostic value.
The most common presenting complaint of dogs with pericardial effusion is collapse, weakness, syncope, or lethargy. Dogs may present with abdominal distension and ascites secondary to cardiac tamponade. Heart sounds are muffled, and lung sounds may also be muffled if there is pleural effusion. Femoral pulses are weak, and sometimes pulsus paradoxis may be palpated when the pulse is stronger during exhalation and weaker during inhalation. If there is cardiac tamponade, the animal may have signs of cardiogenic shock including pale mucous membranes, cold extremities, hypotension, tachycardia, and collapse. These cases require immediate triage for emergency diagnostics and treatment.
Initial triage of a dog with cardiovascular collapse includes a brief triage echocardiogram to assess if there is significant pericardial effusion as a cause of the collapse, as well as an abdominal scan for free abdominal fluid in cases of hemoabdomen. An intravenous catheter should be placed and shock doses of fluids given. Immediate pericardiocentesis is necessary in dogs with low output heart failure and collapse. The animal is placed in left lateral recumbency, and echocardiography is used to define the most optimal site for pericardiocentesis at the right 5-6th intercostal spaces, where there is greatest amount of pericardial fluid the furthest away from the heart and great vessels. In animals that are stable and do not have signs of cardiac tamponade, it is advisable to postpone pericardiocentesis until a detailed echocardiogram is done, as long as it is within a relatively short period of time.Echocardiography is necessary to diagnose presence and severity of pericardial effusion and a detailed echocardiogram is needed for diagnosis of cardiac masses. Masses are typically classified as right atrial (infiltrating the right atrium or auricle) or heart base (adherent to the ascending aorta), and other less common masses may be located on the pericardium or ventricles. Cardiac tamponade is diagnosed when there is diastolic collapse of the right atrium and/or right ventricle, and indicates that the pericardial effusion is hemodynamically compromising and requires timely pericardiocentesis. Very mild pericardial effusion may be seen with severe right heart disease such as dilated cardiomyopathy or severe tricuspid regurgitation, but is hemodynamically insignificant. Absence of a mass places idiopathic pericarditis, mesothelioma, or infectious causes as highest differentials.
Fluid analysis and cytology is necessary to diagnose infectious causes of pericardial effusion, but is not usually helpful to diagnose neoplastic causes or to differentiate idiopathic pericarditis from neoplastic causes. Most pericardial effusion is classified as hemorrhagic, and often there is mesothelial reactivity. Lymphoma is one neoplastic etiology that may be reliably diagnosed by fluid analysis. Over-interpretation of mesothelial hyperreactivity as mesothelioma based on fluid cytology has been common in the past.
Approximately 50% of idiopathic pericarditis cases have recurrent pericardial effusion. In cases of recurrent pericardial effusion without an identifiable mass, subtotal pericardectomy is necessary, and histopathologic evaluation of the pericardium is necessary (often with special immunohistochemical stains) for differentiation of idiopathic pericarditis from mesothelioma. Subtotal pericardectomy is curative for idiopathic pericarditis. Partial pericardectomy is indicated for dogs with heart base masses, as it relieves cardiac tamponade and is associated with a significant prolongation of survival time (median survival time of 730 days pericardectomy versus 42 days without pericardectomy).3 Pericardectomy is not recommended for dogs with hemangiosarcoma, unless it is combined with mass resection. In dogs with right auricular hemangiosarcoma, surgical resection is a feasible option, followed by chemotherapy. In a small study of 23 dogs with surgically resected right atrial or right auricular hemangiosarcoma, administration of chemotherapy increased survival time (MST with chemotherapy and surgery 175 days versus 42 days with surgery alone).4 No studies have evaluated whether chemotherapy alters survival time in dogs that do not have surgical mass resection. In the author's experience, recurrent acute hemorrhage and cardiac tamponade is common in dogs with cardiac hemangiosarcoma, and usually is lethal before the animal succumbs to metastatic disease.