This examination demonstrates multiple abnormalities. First, there is moderate mitral regurgitation and left atrial enlargement secondary to degenerative mitral valve disease. Secondly, there is mild to moderate pleural effusion present, an uncommon finding in small breed dogs. Given the presence of a jet of mitral regurgitation directed toward the left atrial free wall, it’s possible that the patient could have experienced a left atrial tear that has resulted in his pericardial effusion. Alternatively, his left ventricular posterior wall and papillary muscles are hyperechoic, which could potentially indicate infiltrative disease such as lymphoma as a cause of the pericardial effusion. Finally, it’s possible that the effusion could be idiopathic, though this is rare in small breed dogs.
While the absence of cardiac chamber underfilling and normal blood pressure suggest that cardiac tamponade is not present, the presence of right atrial diastolic wall collapse and clinical signs compatible with tamponade suggest that the pericardial effusion needs to be removed. There is a risk with pericardiocentesis, however, if a left atrial tear is present, as the relief of pressure on the left atrial wall that is achieved via removal of the pericardial effusion could allow for further bleeding through the tear, which could potentially be fatal. Having said that, obtaining even a small sample of the effusion for fluid analysis and cytology could potentially be very beneficial, as it may provide a more definitive cause of the effusion. Additionally, removal of the effusion may be required to relieve the clinical signs of cyanosis and collapse.