Pericardial Disease in the Dog

Michael Luethy, DVM
Chicago Veterinary Emergency & Specialty Center
Chicago, IL, USA

The pericardium is composed of the tough, outer, parietal pericardium and the delicate, serous, visceral pericardium (epicardium). In a normal dog, the space between the two layers of pericardium contains 0.2 to 0.3 ml/kg body weight of fluid that is typically concentrated in the region of the heart base. The exact function of the pericardium has been debated for many decades with proposed actions including maintaining the position of the heart within the thorax, lubricating the surface of the heart to reduce friction, protection from surrounding infection and neoplasia, ventricular diastolic coupling, and restraining ventricular filling during periods of volume overload. It is interesting to note that a dog may live a normal life with the absence of the pericardium, but that diseases of the pericardium may produce myriad signs and prove rapidly life threatening.

Most pericardial diseases are acquired diseases that involve the accumulation of increased amounts of pericardial fluid within the pericardial cavity. Congenital diseases are rare with the most common abnormality being the presence of a peritoneopericardial diaphragmatic hernia (PPDH). Weimaraners are reported to be predisposed to the presence of a PPDH. These lesions may go undetected because affected individuals are asymptomatic or express only mild signs that may be ignored by the owner or confused with other disease processes. Symptoms vary depending on which abdominal organs are displaced into the pericardial sac and to what extent the blood supply of displaced organs is compromised. Symptoms commonly include diarrhea, vomiting, anorexia, and respiratory abnormalities. Surgical correction is typically recommended in young animals or in animals displaying clinical signs that can definitely be attributed to the PPDH. The surgery is a major procedure that may have post-operative complications that include reperfusion syndrome or thromboembolic disease. Because of this, surgery is typically avoided in aged asymptomatic patients or asymptomatic patients with unrelated disease processes.

Pericardial effusion secondary to a neoplastic process involving the heart or pericardial sac is the most common cause of pericardial disease in the dog and accounts for 70% to 80% of canine patients presented with clinical signs of cardiac tamponade. Cardiac tamponade is a gradual process that begins to occur as soon as increasing pericardial fluid begins to increase intrapericardial pressure. Classic right heart tamponade occurs when intrapericardial pressure exceeds right atrial pressure and signs of venous congestion with ascites and/or pleural effusion are commonly documented. Left heart tamponade occurs less frequently as intrapericardial pressure rises to the level of left atrial pressure and leads to signs of low output heart failure, and infrequently to the development of pulmonary edema. The degree of tamponade present is closely related to the rate of fluid accumulation and cannot be used as a gauge for the amount of fluid present.

Hemangiosarcoma is reported more frequently than all other tumor types combined with the Golden Retriever breed affected at higher rates than other breeds. The term heart base tumor denotes a tumor location rather than a tumor type, but it is most frequently used to denote the presence of an aortic body tumor (chemodectoma) or ectopic thyroid tumor. Aortic body tumors are reported with increased incidence in the English Bulldog, Boxer, and Boston Terrier. Aortic body tumors metastasize infrequently but may be locally invasive. Mesothelioma, lymphosarcoma, and various other tumor types are also reported to affect the pericardial sac and heart in the dog.

Idiopathic pericardial effusion is the most common non-neoplastic diagnosis for the disease and is a diagnosis of exclusion. Affected dogs are typically medium to large size (> 20 kg), and Golden Retrievers are again affected with increased frequency. Histopathology evaluation of the pericardial sac in affected individuals demonstrates consistent evidence of vasculitis and lymphangitis, but the underlying cause of the inflammation has not been determined. Bacterial and viral organisms that are known to be important causes of pericarditis in humans have not been demonstrated at significant levels in canine cases and autoimmune etiologies have not been confirmed.

Bacterial and fungal infections are infrequent causes of canine pericardial disease and are most frequently associated with migrating foreign bodies or extension of pulmonary infections.

Pericardial effusion may be present as a form of bilateral CHF in dogs with severe degenerative valve disease, but the amount of effusion is rarely clinically/hemodynamically significant.

Dogs with pericardial effusion typically present with signs that may include lethargy, respiratory abnormalities/distress, gastrointestinal signs, and abdominal distension. The signs that are present relate to the rate of fluid buildup and degree of cardiac tamponade present, as mentioned above.

Careful physical examination of the patient may demonstrate muffled heart sounds, abdominal distension, distended jugular veins; tachycardia, decreased breath sounds secondary to pleural effusion, and decreased systemic blood pressure.

Classic radiographic findings include generalized cardiomegaly with a loss of cardiac angles and waists and an overall globoid appearance to the cardiac silhouette. Subjective enlargement of the caudal vena cava and the presence of pleural effusion may also be noted.

Echocardiography is the “gold standard” for demonstrating the presence of pericardial effusion and is instrumental in evaluating the heart and pericardium for the presence of mass lesions that suggest the presence of neoplasia. It is important to remember that thrombi may be present in the pericardial sac in the absence of tumors, that small tumors on the dorsal surface of the right atrium or right auricle may be missed (especially after pericardiocentesis), and that mesotheliomas due not produce defined mass lesions. The absence of gross diastolic collapse of regions of myocardium (e.g. RA free wall) does not indicate that the effusion is not having a hemodynamic effect.

Fluid analysis and cytology evaluation should be performed on pericardial effusions, but it must be remembered that hemangiosarcoma, aortic body tumors, and ectopic thyroid tumors rarely exfoliate cells; mesothelioma is frequently misdiagnosed or missed on cytological evaluation, and other tumor types are uncommon. Fluid analysis is extremely useful for diagnosing infectious pericarditis, and samples should be saved for potential bacterial culture. pH analysis of fluid samples has been reported as beneficial in differentiating between neoplastic and non-neoplastic effusions, but significant overlap occurs.

The Initial treatment of patients with pericardial effusion centers on stabilization and pericardiocentesis. It is important to remember that standard medications used in the treatment of congestive heart failure (e.g. diuretics, vasodilators) decrease venous filling pressure and increase the severity of cardiac tamponade. NO LASIX PLEASE! If the ability to perform pericardiocentesis is not immediately available, IV fluid therapy should be administered rather than standard therapy for congestive heart failure. The practitioner should also remember that in a stable patient, the presence of pericardial effusion enhances the ability to visualize intrapericardial mass lesions.

Pericardiocentesis is typically performed in the right 5th, 6th, or 7th intercostal space with the patient in left lateral recumbency. The procedure is performed from the right to avoid laceration of a coronary artery while the catheter is placed. Local anesthesia of the procedure site is performed, and an over-the–needle catheter with syringe and stopcock is steadily advanced through the skin and intercostal muscles into the pericardial sac. The catheter is advanced and the needle withdrawn when a fluid flash is obtained. Advancement of the catheter system should be stopped at any point if cardiac pulsations or ventricular arrhythmias are noted. Fluid should be removed from the sac with slow, steady suction as aggressive suction may irritate the epicardial surface and lead to ventricular arrhythmias. Pericardial effusion has a bloody appearance in almost all cases of neoplastic and non-neoplastic disease. If there is a question as to whether the catheter has entered the heart, monitor the sample for clotting and compare the PCV of the pericardial fluid to the peripheral fluid.

The long term prognosis is guarded with all forms of neoplastic disease, but patients with aortic body tumors or ectopic thyroid adenomas may do well for periods of > than 15 months with pericardiectomy as the sole treatment method. Hemangiosarcoma is typically an extremely aggressive tumor type, but our practice has achieved an anecdotal average good quality survival time of 6 months with Adriamycin as a single agent chemotherapy in patients without gross metastatic disease at the time of diagnosis. Mesothelioma and myocardial lymphoma carry a grave prognosis.

Pericardiocentesis alone has been reported to yield a clinical cure in approximately 50% of dogs with idiopathic pericardial effusion. If the effusion recurs, average time to recurrence is less than 4 weeks, although patients may have recurrent effusion as long as 9 months after the initial episode. Options for managing recurrent effusion include 1) repeat pericardiocentesis alone 2) pericardiocentesis followed by immunosuppressive therapy with corticosteroids or colchicine and non-steroidal anti-inflammatories 3) pericardiectomy.

Recurrent idiopathic effusions or other processes, such as a migrating foreign body, may lead to progressive pericardial hypertrophy and fibrosis. In these cases, the stiffened pericardial sac can lead to constrictive pericarditis with little or no fluid accumulation in the pericardial sac. Diagnosis is made by clinical presentation, echocardiographic findings, and classic venous pressure wave changes. Treatment requires aggressive pericardiectomy but is highly rewarding in many cases.

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