1 Describe the causes of blunt cardiac injury (BCI)

BCIs occur most often after motor vehicle collisions, and falls or crush injuries constitute a smaller proportion of the causes. Rapid deceleration is the mechanism of injury in these cases. Abrupt pressure fluctuations in the chest, shearing forces, and compression of the heart between the spine and sternum traumatize the heart. A rare cause of BCI occurs when a projectile strikes the chest during sports (e.g., baseball), which may cause cardiac arrest if the strike happens during a period of electrical susceptibility (commotio cordis). BCIs are commonly described in terms of anatomic injuries (e.g., valvular or septal rupture) or myocardial contusion (e.g., arrhythmia, decreased contractility).

2 What is a myocardial contusion?

The definition of myocardial contusion is established on pathologic examination as myocardial cell necrosis and interstitial hemorrhage. Histologically, contusion differs from ischemic infarction in that the transition zone is sharper and necrosis occurs in a patchy pattern. This can be established on autopsy, which means that other, less reliable, diagnostic tools are needed in the clinical setting (e.g., electrocardiography [ECG], echocardiography, laboratory markers). The incidence of BCI, including myocardial contusion, ranges from 20% to 78% of all blunt thoracic trauma, depending on the criteria and diagnostic modality used.

3 What is the pattern of injury in BCI?

The right side of the heart has the most anterior surface area and therefore is the most commonly injured chamber. Injuries may include rupture of the interventricular septum, a valve, or the ventricle (Fig. 69-1). Patients with a ruptured chamber will rarely reach the hospital alive. Less commonly, injury to coronary arteries occurs that may lead to myocardial infarction. Arrhythmias and decreased contractility may follow myocardial contusion or the previously mentioned injuries.

Figure 69-1 Blunt chest trauma injuries.

4 Are there associated chest injuries that make BCI more likely after blunt trauma?

BCI often presents with concomitant chest injuries, but it is important to note that cardiac injury may occur without apparent signs of chest trauma. Fractures of the sternum or clavicle, flail chest, and great vessel injury may suggest associated cardiac injury. Any patient with a heavy trauma burden should raise the level of suspicion for cardiac injury.

5 Describe clinical features that could suggest BCI

Few signs and symptoms are specific for BCI. Although chest pain is frequently reported by patients with suspected cardiac injury, often concurrent chest injury (e.g., musculoskeletal) of confounding nature exists. Specific signs such as cardiac arrhythmias, murmurs, or precordial thrills warrant further testing to rule out heart injury. In severe cases, patients may present with distended jugular veins and hypotension as signs of cardiogenic shock. On the other hand, myocardial contusion is commonly clinically silent, and the diagnosis may be missed unless the clinician conducts further testing.

6 What is the role of ECG in the diagnosis of myocardial contusion?

The ECG is the most frequently used screening test for patients with suspected BCI. Suggestive findings on the ECG include ventricular or atrial arrhythmias, bundle-branch block, and ST-wave abnormalities. The prevalence of abnormal ECGs in patients with myocardial contusion ranges from 40% to 83% in the literature. An abnormal ECG may also be related to noncardiac causes such as hypovolemia, electrolyte abnormalities, head injury, and illicit drug use. The ECG will not conclusively rule in or rule out BCI, but recent guidelines propose that hemodynamically stable patients with no history of cardiac disease do not need further work-up for BCI if the ECG is normal.

7 What is the role of cardiac enzyme determination in the diagnosis of myocardial contusion?

Cardiac enzymes may be measured to evaluate possible cell necrosis in myocardial contusion. Historically, creatine kinase, myocardial bound (CKMB) has been used for this purpose, but its sensitivity and specificity for myocardial contusion are poor. A meta-analysis in patients with BCI reported a positive correlation between abnormal CKMB and cardiac complications requiring treatment, but further studies have failed to corroborate these results. Currently, CKMB is not recommended as a routine screening test for BCI.

Cardiac troponins are more specific for myocardial cellular injury than CKMB but remain an inaccurate tool for diagnosing myocardial contusion. In the setting of an abnormal ECG, troponin levels are unlikely to affect clinical management, and such patients will require admission with further evaluation. However, in those patients with a nonspecific sinus tachycardia otherwise unexpected, measuring cardiac troponins in 6 hours from the time of injury can effectively rule out a significant cardiac contusion.