Pericardial effusion is the accumulation of an abnormal amount of fluid in the pericardial sac, the thin fibrous membrane surrounding the heart. Normally, the pericardial sac contains a small amount of fluid, which provides lubrication and allows the heart to move freely. However, when fluid accumulates in excessive amounts, it puts pressure on the heart, preventing it from filling with blood normally. This condition is known as cardiac tamponade and is life-threatening because it reduces the amount of blood the heart can pump to the body, leading to decreased blood flow and oxygen deprivation in the organs.

Comparison of a normal heart and a heart with pericardial effusion

A normal heart on the left, without pericardial effusion. A schematic illustration of a large pericardial effusion (blue indicates fluid) on the right, surrounding the heart within the pericardial sac.

Causes of pericardial effusion

The causes of pericardial effusion vary significantly between dogs and cats.

The most common causes of pericardial effusion in dogs are:

Neoplasia (cancer): This is the primary cause of effusion in dogs, especially in middle-aged and older large breeds. The most common types are:

▫️Hemangiosarcoma: An aggressive tumor originating in the blood vessels, often affecting the right atrium.
▫️Hemodectoma (tumor of the cardiac base/aortic body): Usually a slow-growing tumor arising from chemoreceptors near the base of the aorta.
▫️Mesothelioma: A tumor originating from the cells of the pericardial lining, often microscopic and difficult to diagnose in the early stages.
▫️Idiopathic pericardial effusion: Cause unknown (approximately 30% of cases). This type is more common in middle-aged males of large breeds.
▫️Congestive heart failure: Although this is a rare cause of significant effusion, right-sided heart failure can lead to a small accumulation of fluid.
▫️Other causes: Less commonly, it may be caused by infections, inflammatory processes, atrial rupture, coagulopathies (blood clotting disorders), or trauma.

Pericardial effusion in cats is less common than in dogs, and the causes differ:

▫️Congestive heart failure: Most often associated with hypertrophic cardiomyopathy (HCM), which is the most common heart disease in cats.
▫️Neoplasia: Although less common than in dogs, tumors (such as lymphosarcoma) can also cause pericardial effusion in cats.
▫️Feline Infectious Peritonitis (FIP): This systemic viral disease can lead to inflammation and fluid accumulation in various body cavities, including the pericardium.
▫️Idiopathic pericardial effusion: Rare cases where the cause cannot be determined.
▫️Congenital defects: For example, peritoneo-pericardial diaphragmatic hernia (PPDH).

Diagnostic methods

The diagnosis of pericardial effusion is critically important and involves a combination of physical examination and diagnostic tests:

1 Physical examination:

▫️Dull heart sounds: The fluid acts as "sound insulation".
▫️Paradoxical pulse (Pulsus paradoxus): A significant weakening of the pulse during inhalation.
▫️Enlarged jugular veins: A sign of increased pressure in the right atrium.
▫️Pallor of the mucous membranes, weakness, lethargy, shortness of breath, distended abdomen (ascites): Symptoms associated with reduced cardiac output and right-sided heart failure.
▫️Collapse: In acute cases of tamponade.

2 Diagnostic images:

▫️Chest X-ray: May reveal an enlarged, spherical, or pear-shaped cardiac shadow. Signs of pleural effusion (fluid around the lungs) or ascites may also be visible.
▫️Echocardiography (heart ultrasound): The "gold standard" for diagnosing pericardial effusion. It allows visualization of fluid around the heart, assessment of its volume, detection of compression of the heart chambers (tamponade), and, if possible, identification of heart tumors or other structural abnormalities.
▫️Electrocardiography (ECG): May show "electrical alternans" (variable R-wave amplitude), which is characteristic but not pathognomonic for pericardial effusion. Tachycardia and signs of arrhythmia may also be observed.
▫️Pericardiocentesis: A diagnostic and therapeutic procedure involving the insertion of a needle into the pericardial sac to remove fluid. Analysis of the collected fluid (cytology, biochemistry, bacterial culture) can help determine the cause of the effusion (e.g., blood in tumors, inflammatory fluid in infections).

Echocardiography of the heart in cases of cardiac tamponade

Treatment

Treatment of pericardial effusion is primarily aimed at resolving cardiac tamponade and identifying and treating the underlying cause.

1 Emergency Care – Pericardiocentesis: This is a life-saving emergency procedure. Rapid removal of fluid from the pericardial sac using a needle and catheter allows the heart to fill normally again and restores blood flow. This procedure is often performed under ultrasound guidance.

2 Further treatment (depending on the cause):
▫️For tumors: Chemotherapy, radiation therapy, or surgical removal of the tumor (if possible) may be recommended. The prognosis depends on the type of tumor and whether it has metastasized.
▫️For idiopathic effusion: Repeated pericardiocentesis is often sufficient. In some cases, with recurrences, pericardectomy (surgical removal of part of the pericardium) may be recommended to prevent further fluid accumulation.
▫️In cases of infection/inflammation: Antibiotics or anti-inflammatory drugs are prescribed.
▫️In cases of heart failure: Treatment of the underlying heart condition with medication.

Breeds prone to pericardial effusion

Dogs: Pericardial effusion, particularly when associated with tumors, is more common in large breeds of dogs of middle and older age.

▫️Hemangiosarcoma: Golden Retrievers, German Shepherds, Boxers, Labradors.

▫️Hemodectoma (tumor of the cardiac base): Brachycephalic breeds (with short muzzles), such as Boxers, Boston Terriers, Bulldogs, and Pugs.

▫️Idiopathic effusion: German Shepherds are also prone to idiopathic pericardial effusion.

▫️Other breeds at increased risk: Afghan Hounds, Salukis, Weimaraners, Saint Bernards.

Cats: Pericardial effusion is rare in cats and is not strongly breed-specific, except in cases associated with HCM. However, breeds prone to HCM may be at increased risk:

▫️Maine Coons
▫️Ragdolls
▫️Sphynx
▫️Siamese

General conclusions

Pericardial effusion is a serious condition that requires immediate veterinary care. Although it is more common in dogs and is often associated with cancer, in cats it is usually a consequence of congestive heart failure. Early diagnosis through physical examination and echocardiography, as well as timely pericardiocentesis, are key to stabilizing the patient’s condition. The long-term prognosis depends on the underlying cause and the effectiveness of its treatment. It is important for pet owners to be alert to any signs indicating heart problems and to contact a veterinarian immediately.