Blunt Cardiac Injury

Blunt cardiac injury is myocardial, valvular, septal, coronary or great vessel damage from non-penetrating chest trauma. Its range is from asymptomatic myocardial contusion to cardiac rupture.

Epidemiology. It occurs in about 8 to 70% of severe blunt chest trauma depending on definition. Clinically significant injuries (arrhythmia, heart failure, structural injury) are far fewer. Cardiac rupture is usually fatal at the scene.

Mechanisms. Direct anterior impact, compression between sternum and spine, deceleration, blast and abdominal compression causing venous rise. The right ventricle is most exposed.

Pathophysiology. Contusion produces myocyte injury, haemorrhage and oedema. Complications are arrhythmia, conduction block, wall motion abnormality, pump failure, valve rupture (mitral, aortic, tricuspid), septal rupture, coronary dissection or thrombosis, pericardial effusion and free wall rupture.

Presentation is chest pain, palpitations, dyspnoea and hypotension, or no symptoms. Look for sternal fracture, chest wall bruising, new murmur, raised venous pressure and shock out of proportion to blood loss.

Red flags.

• Haemodynamic instability, new murmur or heart failure.
• Ventricular arrhythmia, high grade block or ST elevation.
• Raised troponin with abnormal ECG.

ECG on arrival in all patients with significant chest trauma. High sensitivity troponin at arrival and repeated at 6 hours. A normal ECG and normal troponin on both measurements make clinically significant injury very unlikely. Echocardiography is needed for instability, arrhythmia, new murmur, abnormal ECG or raised troponin, with transoesophageal imaging if transthoracic windows are poor. CT coronary angiography or catheter angiography for suspected coronary injury. Extended ultrasound examination for pericardial fluid.

Differential diagnosis. Acute coronary syndrome precipitating the collision, aortic injury, tension pneumothorax, cardiac tamponade and haemorrhagic shock.

Monitoring. Continuous ECG for 24 to 48 hours if the ECG is abnormal or troponin raised. Discharge if ECG and troponin are normal with no arrhythmia.

Arrhythmia.

• Treat arrhythmias on their rhythm. Amiodarone 150 mg IV over 10 minutes, then 1 mg/min for 6 hours, then 0.5 mg/min. Avoid in long QT and monitor hypotension.
• Correct potassium (4.0 to 5.0 mmol/L), magnesium (over 1.0 mmol/L), hypoxia, pain and acidosis.
• Pacing for symptomatic bradycardia or high grade block.

Heart failure and cardiogenic shock. Inotropes such as dobutamine 2.5 to 10 microgram/kg/min, and mechanical support (intra-aortic balloon pump, ECMO) in selected patients. Echo directed fluid decisions.

Surgical indications. Cardiac rupture, tamponade, acute valvular regurgitation with failure, ventricular septal defect with shock, and coronary occlusion needing repair or bypass.

Anticoagulation. Only for coronary thrombosis and with caution when other injuries bleed.

Monitoring. Serial ECG, troponin, echocardiography at 24 to 72 hours for abnormal initial studies, and outpatient review for ventricular function at 4 to 6 weeks.

Referral and escalation. Cardiology and cardiothoracic surgery for any abnormal echocardiogram, instability or structural injury.

Special groups. In older adults and heart disease, a lower threshold for admission. In anticoagulated patients, weigh bleeding.