Pericardial effusions in small animals: causes and diagnosis

Pericardial disease includes various disorders affecting the pericardium, the double-walled sac containing the heart. One of the most significant concerns is pericardial effusion, a condition that can impact both pets and veterinary professionals managing their care. This article explores pericardial effusion, including its causes, diagnosis, treatment options, and prognosis, based on the latest veterinary research. 

Functions of the pericardium 

A quick reminder - the pericardium plays several vital roles in maintaining cardiac function. It protects the heart from infection, provides a frictionless environment for heart movement during contractions, and helps maintain the heart's position within the thorax.  

What are pericardial effusions? 

Pericardial effusion occurs when excess fluid builds up in the pericardial sac, the membrane surrounding the heart. The fluid can vary in composition, ranging from clear transudate to haemorrhagic or inflammatory exudate. In severe cases, this accumulation can lead to cardiac tamponade, a life-threatening condition where the pressure from the fluid prevents the heart from filling properly, reducing cardiac output and leading to circulatory collapse. 

Causes of pericardial effusion in small animals 

Congenital pericardial disease (such as pericardial defects or even absence) is rare. Far more common are the acquired causes of pericardial effusions: 

In both cats and dogs, common causes of pericardial effusions include: 

• Idiopathic pericarditis: the cause remains unknown in many instances, leading to inflammation of the pericardium. 

• Neoplasia: tumours, particularly haemangiosarcoma, are often implicated in pericardial effusion. Cats commonly get lymphoma. 

• Congestive heart failure (CHF): left atrial rupture can lead to fluid accumulation. 

• Infectious diseases: conditions such as feline infectious peritonitis (FIP) or foreign body infections can also result in effusions. 

• Coagulopathies and uraemia: disorders affecting blood clotting or kidney function may contribute to fluid build-up. 

Pathophysiology of cardiac tamponade 

The pericardium can accommodate small amounts of fluid, but as accumulation increases, its elasticity reaches a limit, leading to cardiac tamponade. This condition causes: 

• Reduced chamber filling and cardiac output: compression of the heart chambers, particularly the right atrium and ventricle, reduces the heart’s ability to fill during diastole, therefore reducing cardiac output 

• Increased venous pressure: cardiac tamponade and impaired cardiac function can result in elevated venous pressure, leading to clinical signs such as jugular distension and ascites. 

Diagnosing canine and feline pericardial effusion 

Animals with pericardial effusions often present with vague, heart-related symptoms such as exercise intolerance, lethargy, weakness, and sometimes episodes of syncope. Where pericardial effusion is acute, they may present, acute weakness and collapse may be described. 

A good physical examination is the beginning of your investigations into potential pericardial effusion. You might record general signs of cardiac distress, such as: 

• An increased heart rate (due to reduced output) 

• Pale mucous membranes (decreased peripheral perfusion) 

• Slower Capillary Refill Time (CRT) 

• Poor pulse quality (due to lower strokes) 

Vets should also be on the lookout for the following classic clinical signs of pericardial effusion and cardiac tamponade: 

1. Muffled heart sounds observed upon auscultation due to the insulating effect of fluid. 
2. Jugular vein distension indicative of elevated venous pressure. 
3. Ascites, often secondary to right-sided heart failure. 
4. Pulsus paradoxes 

Diagnostic tests for pericardial effusion 

After the clinical exam, diagnostic tests are required. The following are most useful in diagnosing pericardial effusions in pets: 

Echocardiography 

Echocardiography remains the ‘gold standard’ diagnostic test in pericardial effusions. Early/small effusions are first seen at the posterobasal left ventricle, but often these cases aren’t scanned until the effusion is all around the heart, at which point the heart appears to be suspended in a sonolucent void. The echo-free space can be measured during diastole in order to grade the effusion as small, moderate, or large. 

Radiography 

Though less sensitive, chest X-rays can provide initial insights into heart size and shape as well as rule out other causes of coughing. Standard lateral and ventrodorsal views reveal a generally enlarged heart shape, which may be rounder than usual. 

ECG 

Electrocardiography (ECG) may reveal sinus tachycardia (and, less commonly, atrial and ventricular tachycardias), electrical alternans, and small QRS complexes. 

Treatment of pericardial effusion 

Management strategies depend on the severity of the effusion and the underlying cause, but prompt treatment is always necessary. Instead of going into detail about treating pericardial effusions here, we’ve put together a webinar by Chris Linney BVSc MSc GPCertSAP CertAVP(VC) DipECVIM-CA(Cardiology) MRCVS, European Veterinary Specialist in Small Animal Cardiology, RCVS Specialist in Veterinary Cardiology.

Conclusion 

Understanding pericardial effusions in veterinary medicine is vital to allow early diagnosis and effective treatment. We hope that in reading this article, you feel more confident diagnosing pericardial effusions in pets. Don’t forget, you can log reading this article (and watching the linked webinar) as CPD. If you need any advice about our veterinary cardiology CPD options or help reflecting on your veterinary CPD, head to our Content Hub. 

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