Blunt Cardiac Injury (BCI) is a general term to describe all non penetrating injuries to the heart during trauma. It incorporates myocardial or cardiac contusion, structural injuries such as valvular damage, and traumatic pericardial effusion.
BCI usually results from high kinetic forces that travel through the thorax into the heart – most commonly high speed motor car accidents. Bruising is another term for contusion, and the myocardial histopathological lesions show changes that are similar to myocardial infarction, but with more sharply defined edges.
Clinical Spectrum: There is a wide clinical spectrum of disease that occurs from major thoracic trauma:
i) Rapid death at the scene (usually from free rupture of the myocardium and uncontrolled haemorrhage). Diagnosed at Autopsy.
ii) Severe hypotension/heart failure with large areas of damage to myocardium, valves or pericardium. This group will arrive to the ED HD unstable and require rapid diagnosis and treatment, often surgical.
iii) The HD stable patient with normal imaging, often with a small to moderately raised troponin. Many of these patients have few adverse outcomes, but some published series with good followup show they are at an increased risk for delayed arrhythmias and heart failure.
The Key features on Echocardiography to look for in blunt cardiac injury:
i) Pericardial effusion: usually trivial/small. Can be large causing tamponade.
ii) Regional wall motion abnormalities. Classical contusions can result in atypical non coronary RMWA. The myocardium is stunned and usually recovers over days to weeks.
iii) Acute Valvular regurgitation (particularly in an otherwise normal heart). The AV valves most commonly involved – thought be to related to a sudden increase in ventricular pressure against a closed valve.
iv) Atrial or ventricular septal defects with shunts.
Unstable vs Stable US
Unstable: As part of the initial resuscitation in the emergency department, a FAST scan is performed, usually via a subcostal approach, to look for gross cardiac structural abnormalities, or pericardial haemorrhage, that might be causing HD instability. Ultrasound can also be pivotal in allowing percutaneous drainage of a tamponade.
Stable: In the stable patient whom has suspected myocardial injury, echocardiography is a key screening tool. Although the most recent East guidelines for thoracic trauma suggest against routine TTE for suspected blunt cardiac trauma, it is important to assess the patient on a case by case basis. This is usually performed once the initial resuscitation is complete. More subtle regional wall motion abnormalities, small effusions, valvular regurgitation, or interatrial or inter ventricular shunts may all be found with echocardiography.
Transoesophageal echocardiography has advantages of having better tissue characterisation, the ability to look for thoracic dissection, and usually has higher quality images, but may be contraindicated in complex thoracic trauma, or may not be available. Transthoracic imaging has less risk to the patient, but gaining adequate windows and images can be difficult, especially in intubated patients with multiple rib fractures and pneumothoraces! The decision which one to use usually is made according to local guidelines and expertise.