Veterinary Echocardiography Newsletter 1: Effusions

Regardless of your level of experience with ultrasound, ruling out pleural and pericardial effusions is essential.

For those who are new to imaging around the heart with ultrasound, differentiating a pericardial from a pleural effusion can be tricky, particularly when the pleural effusion is circumferential around the heart. In the following article, we present two cases, concluding with a third case in which both types of effusion can be seen simultaneously.

Screening for effusions can be performed with 2D echocardiography only, and advanced haemodynamic compromise can also be seen on 2D imaging alone. Pulsed Wave Doppler and Tissue Doppler Imaging can be used in more equivocal cases, but is not covered in this article due to the unavailability of TDI on many ultrasound systems. If you have TDI and you’d like to learn more about how you can use it, just ask.



In this cat below, it is difficult at first glance to be able to state whether this effusion is pleural or pericardial.

Pleural effusion on ultrasound












In the moving clip, however, you can actually see the separation of the right ventricular free wall from the pericardium in a cat. There is some fluid in the pericardium, but this is normal – and only seen during systole. This confirms that the large amount of fluid seen on the scan is extracardiac. In addition, a pericardial effusion of this size would frequently cause some compression of the heart, particularly the lower pressure right sided chambers, which are not seen to collapse in this scan.


Feline effusion case:



Pleural Effusion Diagram














Pleural Effusion















The effusion was drained of a large quantity of lymphatic fluid (chyle).

Pleural effusion








Pericardial effusion

Compare this now to the following case in a small dog. This patient was admitted with a cough. Her abdomen was visibly swollen and ascites was seen on abdominal ultrasound.

Canine effusion case:

We can tell that this effusion is 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.



Canine pericardial effusion













The pericardium has a fibrous outer layer, which is what makes it so echogenic on ultrasound. You can see how thick it is from the below photograph taken during a pericardiectomy. A full pericardiectomy or creation of a pericardial window can be performed where there are chronic idiopathic pericardial effusions, or as a therapy for chronic pericarditis.













A pericardial effusion in a dog can be idiopathic, or can occur as a result of hemangiosarcoma in the right atrium or right atrial appendage which then haemorrhages into the pericardial space. It can also be caused by tumors at the base 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 a higher end cardiac system – the Siui Apogee 2300 – notice the unusual way the heart is moving, which becomes even more obvious when scanned in the long axis view. By rotating the probe 90 degrees, it is easy to see the reason for the way the heart is rocking, as well as an explanation for the animal’s fast heart rate, coughing and breathlessness: the right ventricular free wall is collapsing under the pressure of the fluid around the heart. A further increase in pressure would result in diastolic free wall collapse, complete inability to fill, and cardiac tamponade.



This case highlights the importance of obtaining more than one view. While a pericardial effusion could be confirmed from the initial screen performed on a Sonoscape system, a more thorough investigation from different views was able to investigate the haemodynamic effects and the most appropriate course for treatment. In this instance, pericardiocentesis was performed immediately and the dog made a full recovery, with no recurrence of the effusion on follow-up one week later.


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:

Pericardial and pleural effusions in the same patient:


Pericardial and Pleural Effusion














Here’s another example where the pericardium can be clearly seen, separating the pericardial and pleural effusions:



Taking the time to correctly diagnose an effusion is important, because the urgency, prognosis and treatment are clearly very different. Most small animal practices are used to encountering pleural effusions, and it can be easy to jump to this conclusion when large effusions are seen. Careful identification of the pericardium and the behaviour of the lower pressure right atrium and right ventricle will elucidate the problem.




Ultrasound machine featured: Siui Apogee 2300 with cardiac package.

Jutkowitz, L. (2008). Managing pericardial effusion in the dog (Proceedings).