What is the pericardium?

The pericardium is composed of membranes that surround the heart. We could say that, in a way, it is a bag that wraps the heart. Its main functions are to fix the correct position of the heart, to maintain the cardiac shape and to protect the heart.

It is estimated that pericardial conditions account for approximately 10-15% of cardiology consultations in dogs and cats.

The pericardium is composed of two laminae: the parietal layer and the visceral layer.

The parietal layer is the outermost layer and is composed of collagens and elastin. The visceral layer is the innermost and the one that contacts the heart. It is composed of a single layer of mesothelial cells. It covers the inner surface of the fibrous pericardium.

What is the pericardial space?

Within this space between the two layers, we find the pericardial space. This normally contains an accumulation of between 0.15-0.25 ml of fluid per kilogram of body weight. The function of this fluid is to prevent friction with the movement of the heart.  

What is a pleural effusion?

We call effusion or pericardial effusion the accumulation of fluid in the pericardial space. That is, between the two layers that make up the pericardium: the visceral layer and the parietal layer.

Within this space, we normally find an accumulation of between 0.15-0.25ml of fluid per kilogram of body weight.

What happens when more fluid accumulates than normal? Cardiac tamponade.

Larger fluid accumulations are initially tolerated by the pericardium without any problem. The problem arises when these accumulations are larger and exert pressure. This can reach the point of compressing the atrium and right ventricles, producing the phenomenon of cardiac tamponade. These cases can lead to a decrease in cardiac output (output volume), arterial hypotension and right congestive heart failure.

Causes of pericardial effusion:

Peritoneum-pericardial diaphragmatic hernias are the most common congenital cause.

Congenital causes of pericardial effusion have been reported, although acquired causes are more frequent. The main congenital cause is peritoneum-pericardial diaphragmatic hernias. These communicate the peritoneal cavity and the pericardial cavity, with extravasation of fluids into the latter. Severe gastrointestinal or respiratory symptomatology in very young animals is a typical manifestation.

Neoplasms as the most frequent acquired cause in dogs.

Neoplasms affecting both the cardiac base and the pericardium are common causes. Hemangiosarcomas, chemosarcomas or mesotheliomas are the most common tumors in dogs. However, metastases from other tumors can also occur, although less frequently. In cats, on the other hand, lymphoma is usually the most common tumor. It is followed by other cardiac-based tumors and metastases.  

Idiopathic cause is the second most common cause in dogs.

The idiopathic cause is the second most common in canines, unlike felines, where it is very rare. It has been associated in some cases with idiopathic pericarditis and hemorrhage, but without an identified immune-mediated or viral cause. It seems to be more common in middle-aged individuals and giant breeds, such as Labradors and Golden Retrievers.

Bacteria and viruses as other possible causes.

Other possible causes are infectious. In cats, feline infectious peritonitis is a common cause. Some bacterial causes have been associated with migrated foreign bodies, penetrating wounds and concurrent pulmonary infections. Similarly, it has also been associated with myxomatous mitral valve disease. Fungal infections have been reported to cause pericardial effusion.

Other less common causes.

Other causes such as rupture of the left atrium or rodenticide intoxication have been the cause of hemorrhagic pericardial effusions.

As a secondary cause and manifestation of pleural effusion, we find severe hypoproteinemia and feline hypertrophic cardiomyopathy. In the latter case, it is especially associated with hypertrophic cardiomyopathy associated with the myocardial disease.

What will be the clinical symptoms?

Clinical signs will be variable, generally depending on the volume and severity of the pericardial effusion. In milder cases, the animal may show no visible clinical signs.

In general, there will be nonspecific clinical signs such as lethargy, fatigue and weakness. If the situation persists, weight loss may occur. And these signs will progress to respiratory distress, ascites and collapse. In some cases, coughing may occur.

Given the nonspecific nature of the symptoms, it is advisable to rule out pericardial effusion in any individual with collapse, ascites or exercise intolerance.

What should we expect in the physical exam?

In pleural effusion, heart sounds are attenuated or become inaudible. Tachycardia is usually observed. In the right congestive heart failure, ascites and pleural effusion may be seen. Jugular distension and jugular venous pulse will also be seen along with a weak femoral pulse.

What will we see in the complementary tests?

In the X-ray we will observe a more spherical cardiac silhouette with the usual loss of definition. The size will depend on the severity of the effusion. Generally we will observe a distended caudal vena cava, hepatomegaly and signs of ascites. In some cases, we may suspect cardiac masses or observe neoplastic lesions in the lungs.

In the ECG we will observe low-voltage QRS. It is important to remember that this condition is normal in cats. Another common finding will be electrical alternans, especially in the most important effusions. This is explained by the movement of the heart itself within the pericardial fluid.

Echocardiography is the best method of detection.

In the ultrasound, we will observe a hypoechoic area surrounding the heart, which will be liquid. This will be more noticeable in the apex than in the area of the cardiac base. This method will allow us to estimate the amount of pleural fluid. Likewise, it will allow us to determine the presence of the aforementioned cardiac tamponade, at the same time as making a first cardiac assessment. Certain secondary pathologies, as well as the presence of certain masses, can be characterized.

Dinbeat UNO® is the best method for continuous monitoring

With the Dinbeat UNO® multiparametric harness, we can monitor these patients once they have been stabilized. By monitoring respirations per minute, heart rate and temperature we can obtain real-time data without manipulation. Not altering or stressing patients with this pathology is very important in critically ill patients.

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