Changes

===Introduction===

===Introduction===

The pericardium is a sac that surrounds the heart and serves to protect the heart as well as maintain its position and shape. The pericardium is comprised of an outer fibrous layer and an inner serous layer. The fibrous outer layer is composed of collagen and elastin. The serous layer is composed of a single layer of mesothelial cells. The serous pericardium lines the inside of the fibrous layer, where it is known as the parietal layer, and also overlies the heart, where it is referred to as the visceral layer of the serous pericardium. The pericardial cavity is the space between the visceral and parietal layers, which usually contains a very small amount of fluid.  

The pericardium is a sac that surrounds the heart and serves to protect the heart, as well as maintain its position and shape. The pericardium is comprised of an outer fibrous layer and an inner serous layer. The fibrous outer layer is composed of collagen and elastin. The serous layer is composed of a single layer of mesothelial cells. The serous pericardium lines the inside of the fibrous layer, where it is known as the parietal layer, and also overlies the heart, where it is referred to as the visceral layer of the serous pericardium. The pericardial cavity is the space between the visceral and parietal layers, which usually contains a very small amount of fluid.  

Pericardial effusion is a pathological accumulation of fluid within the pericardial sac. The rate of this fluid accumulation within the pericardium determines the haemodynamic effects, and therefore clinical signs. A slow accumulation is initially well-tolerated, but can eventually lead to increased pressure causing compression of the right atrium and right ventricle (cardiac '''''tamponade'''''). Rapid fluid accumulation results in acute tamponade.  

Pericardial effusion is a pathological accumulation of fluid within the pericardial sac. The rate of this fluid accumulation within the pericardium determines the haemodynamic effects, and therefore clinical signs. A slow accumulation is initially well-tolerated, but can eventually lead to increased pressure causing compression of the right atrium and right ventricle (cardiac '''''tamponade'''''). Rapid fluid accumulation results in acute tamponade.  

* Right-sided congestive heart failure: jugular venous distension, jugular pulses, ascites, pleural effusion

* Right-sided congestive heart failure: jugular venous distension, jugular pulses, ascites, pleural effusion

* Weak pulses due to poor cardiac output

* Weak pulses due to poor cardiac output

* '''Pulsus paradoxicus''' (pulse quality varies excessively with respiration)

* '''Pulsus paradoxicus''' (pulse quality varies excessively with respiration). During inspiration, the normal negative thoracic pressure is transmitted to the pericardium and right atrium. This results in better right atrial and right ventricular filling during inspiration and shifts the interventricular septum toward the left ventricle. However, because the degree of cardiac distension is limited by the pericardial effusion, left ventricular filling is decreased with a resultant reduction in stroke volume during the next cardiac cycle. Therefore, the pulse is weak during inspiration and strong during expiration.

* Sinus tachycardia, compensatory mechanism for reduced cardiac output in order to maintain systemic blood pressure

* Sinus tachycardia, compensatory mechanism for reduced cardiac output in order to maintain systemic blood pressure

==== Laboratory Tests====

==== Laboratory Tests====

Haematology:

''Haematology'':

* Increased numbers of circulating nucleated erythrocytes or large numbers of acanthocytes are indicative of Haemangiosarcoma (cardiac, splenic)

* Increased numbers of circulating nucleated erythrocytes or large numbers of acanthocytes are indicative of Haemangiosarcoma (cardiac, splenic)

* Anaemia and thrombocytopaenia are more common in dogs with pericardial effusion due to Haemangiosarcoma

* Anaemia and thrombocytopaenia are more common in dogs with pericardial effusion due to Haemangiosarcoma

Biochemistry:  

''Biochemistry'':  

* Mild increase in liver enzymes, due to hepatic congestion

* Mild increase in liver enzymes, due to hepatic congestion

* Mild hypoproteinaemia, presumed secondary to right-sided congestive heart failure

* Mild hypoproteinaemia, presumed secondary to right-sided congestive heart failure

* Pre-renal azotemia, due to poor cardiac output

* Pre-renal azotemia, due to poor cardiac output

Cardiac biomarkers:  

''Cardiac biomarkers'':  

* Cardiac troponin I may be increased in dogs with pericardial disease and can be higher in dogs with Haemangiosarcoma than those with idiopathic haemorrhagic pericardial effusion.

* Cardiac troponin I may be increased in dogs with pericardial disease and can be higher in dogs with Haemangiosarcoma than those with idiopathic haemorrhagic pericardial effusion.

====Pericardial Fluid Analysis====

====Pericardial Fluid Analysis====

Fluid should always be sent for further analysis, including total and differential cell counts, packed cell volume, specific gravity, cytology, bacterial culture and sensitivity. Pericardial effusions can be classified as haemorrhagic, transudate, modified transudate and exudate and the classification informs the likely underlying cause. Differentiating reactive mesothelial cells from neoplastic mesothelial cells can be incredibly difficult, sometimes a diagnosis can only be made following histopathological and immunohistochemical examination of the excised pericardium.  

Fluid should always be sent for further analysis, including total and differential cell counts, packed cell volume, specific gravity, cytology, bacterial culture and sensitivity. Pericardial effusions can be classified as haemorrhagic, transudate, modified transudate and exudate and the classification informs the likely underlying cause. Differentiating reactive mesothelial cells from neoplastic mesothelial cells can be incredibly difficult, sometimes a diagnosis can only be made following histopathological and immunohistochemical examination of the excised pericardium.  

Differentials are as follows:  

Differentials are as follows:  

* Haemorrhagic: idiopathic, neoplastic (Haemangiosarcoma, heart base tumour, lymphoma, mesothelioma), trauma, coagulopathy, ruptured left atrium

* ''Haemorrhagic'': idiopathic, neoplastic (Haemangiosarcoma, heart base tumour, lymphoma, mesothelioma), trauma, coagulopathy, ruptured left atrium

* Transudate: hypoproteinaemia

* ''Transudate'': hypoproteinaemia

* Modified transudate: right-sided congestive heart failure, neoplasia

* ''Modified transudate'': right-sided congestive heart failure, neoplasia

* Exudate: feline infectious peritonitis (FIP), infection (bacterial, fungal), foreign body

* ''Exudate'': feline infectious peritonitis (FIP), infection (bacterial, fungal), foreign body

===Treatment===

===Treatment===

====Surgery====

====Surgery====

The most common surgical treatment is '''pericardectomy'''. This can be approached from an intercostal thoracotomy or midline sternotomy, or can be done with thoracoscopy. Although total pericardiectomy is possible, usually subtotal pericardiectomy is performed.

The most common surgical treatment is '''pericardiectomy'''. This can be approached from an intercostal thoracotomy or midline sternotomy, or can be done with thoracoscopy. Although total pericardiectomy is possible, usually subtotal pericardiectomy is performed.

===Prognosis===

===Prognosis===

===References===

===References===