Cardiac Tamponade

Definition: Accumulation of fluid in the pericarial space leading to restriction of the heart's pumping action and reduced cardiac output which may lead to hypoperfusion and failure of other organs.

Different to cardiac effusion which is an umbrella term for a fluid collection in the pericardial space with or without haemodynamic compromise. 

Pathophysiology

A cardiac tamponade is caused by an increase in the pressure in the pericardial sac. The pericardial sac usually has a level of compliance (stretch) and therefore an increase in fluids in this space initially has little effect on the pressure. It is only when the sac has reached the limit of it's stretch that the pressure increases. The compliance of the pericardial sac can also be increased in a chronic effusion and as much of 2000mls of fluid can be present before it causes a tamponade. Compliance can also be reduced by some disease states. 

Early phase: Right heart pressures are lower and are therefore first to be exceeded by the pressure in the pericardial sac. This leads to low R ventricular filling and output, and increased central venous pressure. 

Late phase: As the Left side of the heart becomes more compromised there is a rapid reduction in cardiac output. The body compensates by increasing heart rate and retaining more water, obstructive shock occurs. There is reduced coronary flow in tamponade but as the work of the heart decreases this is initially not ischaemic - however in later stages ischaemia may occur. 

Presentation: 

• Maybe insidious or readily apparent
• Obstructive shock - tachycardia, tachypnoea, hypotension
• Beck's triad : hypotension, raised JVP, muffled heart sounds (uncommon + more seen in acute causes)
• Pulsus paradoxus: large (more than 10mmHg is highly sensitive, but not diagnostic) drop in mean arterial pressure during spontaneous inspiration due to increase in flow in R heart causing bulging of the interventricular septum  leading to reduced volume in the L heart combined with increased vasodialation in inspiration leading to pooling of blood and hence reduced preload in L heart. Radial pulse may be absent during inspiration whilst heart sounds are heard on auscultation. 
• History may help differentiate

Causes: 

• Bleeding due to cardiac surgery (up to 2 weeks)
• Trauma - penetrating more than blunt
• Aortic dissection - if retrograde
• Infective -TB, Viral, HIV
• Massive pleural effusion
• Malignancy - lung cancer, pericardial mesothelioma, secondary to treatment such as radiotherapy. 
• Pericarditis- caused by;collagen vascular disease, systemic lupus erythematous, rheumatoid arthritis, myxoedema or uremia. 
• Iatrogenic

*red= acute/immediate blue=chronic

Differential Diagnoses: 

• Cardiogenic shock- massive MI
• Constrictive pericarditis - echocardiography
• Massive pulmonary embolism
• Tension pneumothorax
• tension pneumopericardium (rare)

Investigations: 

• Bloods: Creatinine Kinase, FBC (infection), Renal function (uraemia), Antinuclear antibodies, ESR, Rheumatoid factor. 
• HIV/TB testing
• Chest xray: normal (esp. acutely) or enlarged globular cardiac silhouette. 
• ECG: smaller QRS, electrical alterans, tachycardia, possible atrial ectopics. non-specific and does not diffrentiate from pericaridal effusion. 

• Echocardiography- Swinging heart, R ventricular/atrial and left atrial collapse, pseudohypertrophy of L ventricle, vena cava dialation, fluctuation of flow with inspiration and expiration

Management

• Depends on haemodynamic stability
• Airway, Breathing, Circulation
• Monitor and treat in ITU
• Oxygen + dont intubate/mechanically ventilate if possible, if ventilated minimise positive end expiratory pressure. 
• Raise legs to improve venous return
• Invasive haemodynamic monitoring (central venous line/arterial line)
• Fluid challenge
• Inotropes/vasopressors
• Pericardiocentesis or surgical drainage
• Treat underlying cause

Prognosis: Medical emergency, fatal if untreated, prognosis depends on quick diagnosis and treatment and underlying cause. 

http://totw.anaesthesiologists.org/2013/03/18/1804/

http://www.patient.co.uk/doctor/Cardiac-Tamponade.htm

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