Pericardial Effusion in Dogs

By Malcolm Weir, DVM, MSc, MPH; Catherine Barnette, DVM

What is pericardial effusion?

Pericardial effusion refers to the abnormal accumulation of fluid within the pericardial sac.

The pericardial sac, or pericardium, is a sac that surrounds the heart. Normally, this sac contains a very small amount of clear fluid, to provide lubrication and help the heart slide within the sac. In pericardial effusion, an excessive amount of fluid accumulates within the pericardial sac, interfering with the heart’s ability to pump effectively.

Pericardial effusion is more common in certain dog breeds, including the Boston terrier, Boxer, Brachycephalic (short-nosed) breeds, English bulldog, French bulldog, German shepherd dog, Golden retriever, Great Dane, Great Pyrenees, Labrador retriever, Saint Bernard and Weimaraners. This occurs because each of these breeds are at a higher risk for conditions that lead to pericardial effusion. The condition tends to occur in middle-aged to older dogs, and occurs more often in males.

What causes pericardial effusion?

Pericardial effusion can have a number of underlying causes.

Some cases are caused by tumors. These tumors may be located within the heart or on the pericardium.

Pericardial effusion can also be caused by inflammation of the pericardium. Pericardial inflammation may be caused by infection (e.g. from a systemic infection, or from a migrating porcupine quill), or may be caused by idiopathic (undeterminable) inflammation of the pericardium.

Other causes of pericardial effusion include trauma, clotting disorders, rupture of the left atrium of the heart, and congestive heart failure. Less commonly, pericardial effusion may result from hypoalbuminemia (low blood protein levels, which can allow fluid to leak from the blood vessels) and peritoneopericardial diaphragmatic hernias (PPDH - a hereditary defect that results in chest abnormalities).

What are the effects of pericardial effusion?

As the pericardial sac fills with excessive fluid, the pressure within the pericardial sac rises. Eventually, this pressure may meet or exceed the pressure that is present within the heart. At this point, the ventricles of the heart lose their ability to fill effectively, creating a condition known as cardiac tamponade. Cardiac tamponade interferes with the heart's ability to move blood, resulting in right-sided congestive heart failure, low blood pressure, and poor circulation to the heart and other organs.

In some situations, this fluid accumulation occurs quickly. This can result in rapid development of clinical signs. In other situations, fluid accumulates slowly. This gives the body more time to adjust and compensate.

What are the signs of pericardial effusion?

Signs of pericardial effusion can vary dramatically, depending on the severity and time course of the condition.

Early signs often include abdominal fluid accumulation and the resulting visible abdominal enlargement and exercise intolerance. In some cases, fainting may be noted with physical exertion. Cough and decreased appetite may also be observed. If pericardial effusion persists at mild levels over a long period of time, affected dogs may also develop muscle wasting.

In severe cases, especially with an acute onset of disease, pericardial effusion may cause sudden collapse and death with no prior signs.

How is pericardial effusion diagnosed?

On physical exam, your veterinarian may notice a number of findings that suggest pericardial effusion. Affected dogs often have pale gums and weak pulses. Breathing may be labored, with an abnormally elevated respiratory rate. Muffled heart sounds, caused by the fluid that has accumulated around the heart, may be heard when your veterinarian listens to your cat’s heart. Other findings may include liver enlargement, abdominal fluid, distended jugular veins in the neck, and fluid accumulation under the skin; all of these findings are due to the heart’s inability to push blood normally throughout the body.

Your veterinarian may also feel abnormalities in your dog’s peripheral pulses, which can suggest pericardial effusion. If pericardial effusion occurs secondary to infection, fever may also be found on physical exam.

If your veterinarian suspects pericardial effusion, a number of tests will likely be performed. These tests may include:

  • Bloodwork (complete blood cell count and serum biochemical profile). These tests look for underlying illness and provide important information about your dog’s overall health.
  • Cardiac biomarkers. Measurement of cardiac muscle injury markers help determine the underlying cause of pericardial effusion in the dog.
  • Blood pressure measurement. Low blood pressure supports a diagnosis of pericardial effusion and cardiac tamponade.
  • Chest radiographs (X-rays). Dogs with pericardial effusion may have a characteristic appearance to the heart on radiographs, which can support the diagnosis. It is important to note, however, that a chest radiograph cannot definitively diagnose pericardial effusion and does not provide any information about how well the heart is functioning.
  • Electrocardiography (ECG). There are a number of characteristic ECG findings that can also support a diagnosis of pericardial effusion.
  • An ultrasound of the heart can provide a definitive diagnosis of pericardial effusion, while also providing information on how effectively the heart is moving blood.
  • Fluid analysis. If pericardial effusion is diagnosed, a sample taken from the fluid around the heart can be analyzed to help determine the cause of the effusion. Fluid analysis does not always provide a definitive diagnosis but can be especially helpful in diagnosing certain conditions (lymphoma and infectious pericarditis).

How is pericardial effusion treated?

When possible, pericardial effusion is treated by addressing the underlying disease. This is especially true if the effusion is associated with heart failure, left atrial rupture, clotting disorders, or hypoalbuminemia. All of these conditions can be managed medically, which typically resolves the pericardial effusion.

If your dog is critically ill due to cardiac tamponade, your veterinarian may attempt to remove the fluid surrounding the heart. This procedure is called pericardiocentesis. Pericardiocentesis may be performed with or without ultrasound guidance. It is important to understand that pericardiocentesis does not cure pericardial effusion; the underlying cause of the effusion must still be addressed because it is likely to recur. This procedure can, however, increase your dog’s chances of surviving the initial emergency period.

If pericardial effusion is associated with a tumor, treatment options vary depending upon the type of tumor that is present. Surgery may be attempted in some cases, while other patients may be treated with chemotherapy.

In some cases, pericardial effusion may be treated with a procedure called a pericardectomy. In a pericardectomy, a small opening (window) is made in the pericardium. This allows accumulating fluid to drain out of the pericardium into the surrounding tissues, alleviating pressure on the heart. In some cases, this treatment is curative; in other situations, it is attempted only for palliative care.

If pericardial effusion is associated with a peritoneopericardial diaphragmatic hernia, surgery is required to correct the hernia.

What is the prognosis for pericardial effusion?

The prognosis depends upon the underlying cause.

Cancerous causes of pericardial effusion vary in their response to treatment and rate of disease progression. The prognosis for cancer-associated pericardial effusion depends upon the specific tumor type.

Most non-cancerous causes of pericardial effusion respond well to treatment.

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