A Jack Russell Terrier was admitted with a cough. Her abdomen was visibly swollen and Emma the vet first performed an abdominal scan, where we could see ascites. She then performed a cardiac scan, and we were surprised to see a large pericardial effusion on the Sonoscape S2:
We can tell that this pericardial, because we can actually see the bright white pericardium in the image. In this instance, the effusion is global, meaning that the heart is completely surrounded by fluid.
Pericardial effusion in dogs can occur as a result of hemangiosarcoma in the right atrium or right atrial appendage which then haemorrhages into the pericardial space, tumors at the case of the heart (chemodectoma – more common in brachycephalic breeds (Jutowitz, 2008)), aortic tumors, or tumors of the pericardium itself. Pericardial effusion secondary to infection is less common.
A small pericardial effusion can be as disastrous as a large one if fluid accumulates too rapidly for the pericardial sac to be able to accommodate it. The increased pressure inside the pericardium compromises diastolic filling, and subsequently stroke volume and cardiac output. On 2D Echocardiography, the first sign of haemodynamic compromise is collapse of the right atrial wall during ventricular systole (i.e. atrial diastole, impairing filling), and then right ventricular free wall collapse during ventricular diastole, further impairing filling.
The dog’s heart rate may initially increase to compensate for the reduced cardiac output, but if pressures continue to rise within the pericardial space, left atrial and left ventricular filling will also become compromised and the patient will deteriorate very rapidly.
With further investigation on the Siui Apogee 2300, it can be seen that there is right ventricular free wall collapse in this dog:
Clearly, filling is already impaired, and the dog’s symptoms and fast heart rate further support the need for rapid intervention (pericardiocentesis).
Unlike with a pericardial effusion, in the case of accumulation of fluid in the pleural space, there is no collapse of the heart walls. In the below clip from the Sonoscape S2, you can actually see the separation of the right ventricular free wall from the pericardium in a cat.
The effusion was drained of a large quantity of lymphatic fluid (chyle).
Differentiating pericardial from pleural effusions
It is important to identify the location of the fluid in relation to the pericardium, in order to distinguish between a pericardial and pleural effusion. In some instances, both may be present, as in the example below:
Here’s another example where the pericardium can be clearly seen, separating the pericardial and pleural effusions:
Jutkowitz, L. (2008). Managing pericardial effusion in the dog (Proceedings).