Case Presentation

A 35-year-old female with no past medical history is brought in by ambulance to the emergency department. She was struck by a firework (“Roman Candle”) which lodged in her mid-chest until the propellant was consumed. She transiently lost consciousness but was awake upon EMS arrival. She complains of pleuritic chest pain. Examination reveals a circular 4x4cm full-thickness burn to the mid-chest with surrounding deep and superficial partial-thickness burns. Her ECG shows normal sinus rhythm, the initial serum troponin I is 32.9 (normal <0.012). CT angiography of the thorax is obtained.

Mechanisms

Blunt cardiac injury (BCI) may be induced by multiple forces including direct thoracic trauma, crush injury of mediastinal contents between the sternum and thoracic spine, rapid deceleration causing tears at venous-atrial confluences, abrupt pressure changes from rapid compression of abdominal contents, blast injury, or laceration from bone fracture fragments¹. The most common mechanisms of injury are motor vehicle collisions (50%), auto versus pedestrian (35%), motorcycle accidents (9%) and falls from significant height (>6m)².

BCI represents a spectrum of conditions. Diagnosis is both challenging and critical as clinical manifestations can be absent or rapidly fatal.

At one end of the spectrum is myocardial contusion. The lack of a gold-standard for the diagnosis of this clinical entity has led to a preference for describing associated abnormalities if present^3,4, including cardiac dysfunction (identified on echocardiography) or the next entity along the spectrum – arrhythmia.

The most common arrhythmia identified in blunt cardiac injury is sinus tachycardia, followed by premature atrial or ventricular contractions, T-wave changes, and atrial fibrillation or flutter⁵. Commotio cordis is a unique arrhythmia induced by untimely precordial impact (often in sports) during a vulnerable phase of ventricular excitability, resulting in ventricular fibrillation².

ST-segment elevations after blunt cardiac injury should raise concern for myocardial infarction due to coronary artery dissection, laceration or thrombosis (often in already-diseased vessels) ^5,6.

The remaining disease entities are increasingly rare, require careful examination or imaging for diagnosis, and are more likely to be non-survivable. Septal injury can range from small tears to rupture. Valvular injury most commonly affects the aortic valve (followed by mitral and tricuspid valves) and involves damage to leaflets, or rupture of papillary muscles or chordae tendineae. The clinical presentation is of acute valvular insufficiency, including acute heart failure and murmur^2,7,8. A widened pulse pressure may be noted with aortic valve injury, and the manifestations of valvular injury may be delayed⁹. Finally, myocardial wall rupture is unlikely to be survivable, though patients may present with cardiac tamponade if rupture is small or contained².

Evaluation

The primary diagnostic modalities for the assessment of BCI in the emergency department include assessment for pericardial fluid during the Focused Assessment with Sonography for Trauma (FAST), electrocardiography and cardiac enzymes.

While specific for identifying patients at risk of complications of BCI, electrocardiography alone is not sufficient to exclude BCI. In one study, only 59% of patient with echocardiographic evidence of BCI (wall-motion abnormalities, other chamber abnormalities) had initially abnormal ECG’s¹⁰. In another study, 41% of patients with initially normal ECG’s developed clinically significant abnormalities¹¹. The use of specialized electrocardiography including right-sided ECG (proposed to better detect right-ventricular abnormalities which are more commonly associated with BCI) and signal-averaged ECG is not supported^11,12.

Several studies have supported the use of serum troponin for the detection of clinically significant BCI – particularly in combination with electrocardiography. A prospective study in 2001 evaluating patients with blunt thoracic trauma using ECG at admission and 8-hours, as well as troponin I at admission, 4- and 8-hours had a negative predictive value of 100% for significant BCI (arrhythmia requiring treatment, shock, or structural cardiac abnormalities) in patients with initially normal ECG and troponin¹³.

Another prospective study adding to the population evaluated by Salim et al. included 41 patients with normal ECG’s and troponin levels at admission and 8-hours who were admitted for significant mechanisms, none developed significant BCI (again described as arrhythmia requiring treatment, shock, or structural cardiac abnormalities) after 1 to 3 days of observation¹⁴. The precise timing of serum troponin analysis remains unclear.

While FAST may detect hemopericardium warranting immediate intervention, formal echocardiography is indicated for patients with unexplained hypotension (to evaluate for valvular injury or regional wall-motion abnormalities) or persistent arrhythmias (to evaluate for arrhythmogenic intramural hematomas)¹⁵. The presence of sternal fractures was previously thought to increase risk of BCI and mandate echocardiography, however this notion is no longer supported^16-18. The role of advanced imaging including helical CT (cardiac-gated), and MRI remains unclear¹⁹.

Algorithm for the Evaluation of Blunt Thoracic Trauma

Notes:
† Arrest in ED, immediate chest tube output >20ml/kg (>1.5L) or >200mL/hr for 2-4hr.

Management

Management of BCI depends on the pathologic process localized along the spectrum defined above. Persistent hypotension after appropriate evaluation for alternative etiologies may represent myocardial contusion with cardiac dysfunction and should be evaluated with echocardiography. Similarly, echocardiography and observation with continuous telemetry monitoring is indicated for any new arrhythmia or persistent and unexplained tachycardia. Patients with only elevation of the serum troponin without electrocardiographic abnormalities or obvious cardiac dysfunction should also be admitted for observation and serial cardiac enzymes. Traumatic myocardial infarction, valvular injury, or post-traumatic structural myocardial defects should be managed in consultation with cardiothoracic surgery^5,19-21.

Case Conclusion

The CT interpretation noted the soft-tissue defect identified on examination as well as associated pulmonary contusions and a non-displaced sternal fracture. The patient went to the operating room for washout and debridement. A transthoracic echocardiogram demonstrated trace mitral regurgitation and a small pericardial effusion. She remained hemodynamically stable and serial troponin measures downtrended – no dysrhythmias were noted on telemetry monitoring. She was discharged on hospital day four with a negative-pressure wound dressing.

References

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