The diagnosis and management of blunt cardiac injury are difficult—with no gold-standard diagnostic test, a high mortality rate, and variable presentations. Blunt cardiac injury can be a challenge to emergency physicians who must quickly and reliably determine who is at greatest risk of life-threatening injury.
More than 32,000 people die from motor vehicle crashes (MVCs) each year. (CDC. July 18, 2016; [http://bit.ly/2K6FngN].) Up to 20 percent of these patients die due to blunt cardiac injury. (Crit Care Clin 2004; 20[1]:57; [http://bit.ly/2K9f09I].) The outcome of blunt cardiac injuries can be benign (e.g., transient arrhythmias) or highly fatal (e.g., cardiac wall rupture).
Blunt cardiac injuries occur most often from MVCs, and a small number occur from falls, assaults, crush injuries, and direct projectiles in contact sports or from blast injuries (commotio cordis). The mechanism is often rapid deceleration, followed by direct blows to the precordium.
It is important to ascertain if the patient was restrained and if his airbag deployed. One retrospective review found that 20 percent of unrestrained drivers had cardiac or aortic injuries. (Trauma 1994; 37[3]:404.) Airbags have long been associated with blunt cardiac injury; rupture of the right atrium due to airbag deployment in a low-speed MVA has been reported. (N Engl J Med. 1993;328[5]:358; [http://bit.ly/2KdC87m].) Identification of pre-existing heart disease or cardiomyopathy or previous AICD or pacemaker placement may also raise suspicion.
Physical exam should focus on signs of hemodynamic instability, heart failure or shock, new cardiac murmur, or signs of significant thoracic trauma, including chest tenderness, clavicle fracture, sternal fracture, hemothorax, or pneumothorax.
An electrocardiogram must be obtained early on in all patients with any suspicion of blunt cardiac injury. Another prospective study found that 95 percent of patients with a normal admission ECG did not have a significant blunt cardiac injury. (J Trauma 2001;50[2]:237; [http://bit.ly/2K4vTCE].) Combining a normal admission serum cardiac troponin (cTnI) with a normal admission ECG, the negative predictive value for BCI increased to 100%. The powerful conclusion of this study is that patients with a normal admission ECG and cTnI can be safely discharged home. Interestingly, a 2013 retrospective study showed that a sternal fracture alone does not reliably diagnose BCI. (Emerg Med Int 2013;2013:407589; [http://bit.ly/2K5hXIp].) Similarly, CPK, CK-MB, and nuclear studies do not reliably predict blunt cardiac injury.
Classifying Injury
If the admission ECG or cTnI is abnormal, then the patient must be admitted for at least 24 hours of cardiac monitoring and serial troponin testing. If a trauma patient is diagnosed with arrhythmia, he must be medically managed according to ACLS guidelines. Hemodynamically unstable patients should also have a formal cardiac echocardiogram during their inpatient stay.
Blunt cardiac injury subtypes include cardiac, coronary artery, valvular, septal, pericardial, and myocardial contusion injuries. These subtypes coincide with those in the Cardiac Organ Injury Scaling (OIS), developed by the Association for the Surgery of Trauma (AAST), which anatomically classifies cardiac injuries on a scale of Grade I to Grade VI. (J Trauma 1994;36[3]:229.) Importantly, the OIS's anatomic descriptions correlate with those of the Abbreviated Injury Scale (AIS), which represents the threat to life posed by a single injury (with 1 being minor, 2 moderate, 3 serious, 4 severe, 5 critical, and 6 unsurvivable). (PLoS One 2015; 10[7]:e0131362; [http://bit.ly/2K6FeKe].)
The deadliest injury is cardiac rupture. More than 90 percent of these patients die prior to medical contact, and are usually diagnosed by autopsy. The right side of the heart is at higher risk of cardiac rupture due to its anterior position. Ventricular rupture occurs more often than atrial rupture. Injury of the right ventricle, right atrium, or left atrium is a Grade IV injury, blunt left ventricular perforation is a Grade V injury, and blunt avulsion of the heart is a Grade VI injury. Signs of cardiac tamponade (hypotension, distended neck veins, muffled heart sounds) or suspicion of cardiac rupture should prompt immediate bedside ultrasonography and consultation for surgical intervention.
Coronary artery dissection, laceration, or thrombosis rarely occurs as a result of blunt cardiac injury. The left anterior descending artery (LAD) is most commonly affected. A distal coronary arterial occlusion without heart failure is a Grade III injury, but with heart failure, it is a Grade IV injury. A proximal coronary arterial occlusion is a Grade V injury. Treatment is most likely catheterization. Bypass grafting may also be considered, however.
Septal and valvular injuries are rare, and typically present with signs of valvular insufficiency with right-sided or left-sided heart failure and a new heart murmur. The most commonly injured valve is the aortic valve, followed by the mitral and tricuspid valves. If there is septal rupture, pulmonary or tricuspid valvular incompetence, or papillary muscle dysfunction that produces cardiac failure, it is a Grade IV injury, and without heart failure, it is a Grade III injury. An aortic or mitral valve incompetence is always a Grade IV injury. The treatment is generally surgical.
Pericardial injuries occur from direct thoracic injury or indirectly from an acute increase in intra-abdominal pressure. Pericardial tears range in size, from short and insignificant to long tears that can result in cardiac herniation. A blunt pericardial wound without cardiac injury, tamponade, or herniation is a Grade I injury, while a blunt pericardial laceration resulting in cardiac herniation is a Grade III injury. CT is the diagnostic test of choice in stable patients.
Hemodynamics, ECG, and cTnI
Myocardial contusion initially presents as decreased contractility, which may manifest as arrhythmia, troponin elevation, or regional wall abnormalities on an echocardiogram. If only minor ECG abnormalities (nonspecific ST or T wave changes, unifocal PACs or PVCs, or persistent tachycardia) are present, then the myocardial contusion is a Grade I injury. If the myocardial contusion manifests as a heart block (RBBB, LBBB, LAFB, or AV block) or ischemic changes (ST depression, T wave inversion) on the ECG, it is a Grade II injury. If sustained (>6 bpm) or multifocal PVCs are present or there are ECG abnormalities as well as signs and symptoms of heart failure, then the myocardial contusion is a Grade III injury. Management includes admission for monitoring and cardiology consultation.
Myocardial contusion can lead to eventual necrosis and result in delayed cardiac rupture days after the injury, so emergency physicians should ask about any recent traumatic injury in patients with symptoms of heart failure or hemodynamic instability even if the initial blunt cardiac injury occurred days prior to ED presentation.
Patients who are determined to be at high risk from blunt cardiac injury should be stratified into stable or unstable. Signs of instability for an isolated chest trauma must raise suspicion for a severe cardiac injury, and should prompt rapid ECG and bedside ultrasonography evaluation. Ultimately, unstable patients with evidence of severe cardiac injury require emergent surgical intervention. If there is insufficient evidence of severe cardiac injury and the patient remains hemodynamically unstable, the patient should be admitted to the ICU for cardiac echocardiogram, serial troponins, antidysrhythmics, and cardiology evaluation.
If the patient is hemodynamically stable, then determine disposition based on the admission ECG and cTnI. If either the ECG or cTnI is abnormal, the patient must be admitted to the hospital for at least 24 hours of cardiac monitoring, serial troponins, and a formal echocardiogram. As noted previously, patients with a normal admission ECG and cTnI can be discharged home.
Patients with medical comorbidities and acute traumatic injury could have an acute myocardial infarction (AMI) as the underlying cause of an abnormal ECG or cTnI. Physicians must determine direct traumatic heart disease versus ischemic heart disease because catheterization and anticoagulation are indicated in AMI but contraindicated and likely harmful in blunt cardiac injury. A small case series demonstrated how cardiac multidetector CT (MDCT) and MRI can be useful in guiding the differential diagnosis and determining further medical management. (Emerg Radiol 2011;18[3]:271; [http://bit.ly/2K83zPK].)
Blunt cardiac injury is an uncommon but important diagnostic and therapeutic challenge for emergency physicians. Routine consideration of blunt cardiac injury in patients presenting with chest pain following traumatic injury, particularly in MVCs, can prevent immediate and downstream morbidity and mortality. While normal ECG and cTnI reliably exclude BCI, any abnormalities should prompt further investigation, admission, and cardiology consultation for formal echocardiogram and ongoing management.