Cardiac Tamponade

Introduction

Cardiac tamponade is compression of the heart. It develops when the intrapericardial pressure increases due to unchecked fluid accumulation within the pericardial sac. As the pericardium is fibrous and inelastic this fluid creates a compression on the heart. Intrapericardial compression leads to diastolic collapse of the right atrium and sometimes the right ventricle, decreased ventricular filling and a resultant decrease in cardiac output. This will lead to arterial hypotension.
Compensatorty mechanisms are activated by the failing heart and include the sympathetic nervous system and the renin-angiotensin-aldosterone system.

Causes of cardiac tamponade include all pericardial diseases such as traumatic reticulitis- pericarditis in cattle, fibrinous pericarditis in pigs in 'Glassers disease' and hydropericardium due to congestive heart failure or mulberry heart disease in pigs. Sudden causes of cardiac tamponade and death occur in haemopericardium due to rupture of the intrapericardial section of the aorta. This occurs in horses spontaneously or in pigs due to copper deficiency.

Clinical Signs

Clinical Signs are predominantly those of right sided heart failure as the right chambers have thinner walls and so are more greatly affected by the raised intrapericardial pressure.

Signs will also include ascites, hepatomegaly, splenomegaly, hepato-jugular reflux and venous distension due to raised central venous pressure etc. In severe circumstances sudden death may occur without previous clinical signs.

Diagnosis

On auscultation, heart sounds are muffled or seem distant and a sinus tachycardia may be present. Arterial pulses will be weak and there may be presence of pulsus paradoxus, which is an exaggerated decline in arterial pulse pressure during inspiration, typical of a pericardial effusion.

Ultrasonography of the heart will reveal fluid in the pericardial sac and compression of the cardiac chambers.

Post mortem examination in cases of sudden death due to cardiac tamponade will reveal blood in the pericardial sac.

Treatment and Control

Treatment is to reduce compression immediately by pericardial drainage.

References

Andrews, A.H, Blowey, R.W, Boyd, H and Eddy, R.G. (2004) Bovine Medicine (Second edition), Blackwell Publishing.
Cowart, R.P. and Casteel, S.W. (2001) An Outline of Swine diseases: a handbook, Wiley-Blackwell.
Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition), W.B. Saunders Company.
Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition), Mosby Elsevier.

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