Cardiac Trauma

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.

8 How is echocardiography used in the diagnosis of BCI?

Transthoracic echocardiography (TTE) provides rapid visualization of the heart and is a useful diagnostic tool for BCI. It can be used to identify anatomic abnormalities (e.g., valvular injury, pericardial effusion), ventricular dyskinesia, shunting of blood, and intracardiac thrombi. It provides necessary information in patients who manifest hemodynamic instability or abnormal screening tests (ECG, cardiac enzymes) but has lower sensitivity in the patient whose condition is stable.

Transesophageal echocardiography (TEE) provides better visualization of wall motion abnormalities and valvular injuries than TTE, albeit in a more invasive fashion. It has superior sensitivity to TTE for injuries that require therapeutic intervention and can be performed with relative ease in the bedside or concurrent with other surgical procedures.

Either form of echocardiography is indicated only if the patient is hemodynamically unstable.

9 What is the optimal approach to the diagnosis of myocardial contusion?

Patients should initially be evaluated according to the principles of advanced trauma life support. On arrival, a clinician should identify any life-threatening conditions of BCI through physical examination, ECG, and bedside ultrasound (i.e., focused abdominal sonography for trauma [FAST]). An ECG is routinely performed in trauma patients with complaints of chest pain, history of heart disease, or other symptoms and signs suggestive of active cardiac pathologic condition. If the FAST is negative or equivocal for hemopericardium in patients with significant arrhythmias or unexplained hemodynamic instability, a formal TTE should be performed. In cases of continued diagnostic uncertainty, patients may undergo TEE. Routine examination of cardiac biomarkers (troponin, CKMB) is not recommended because of their poor sensitivity and specificity for BCI and myocardial contusion. However, serial laboratory examinations are warranted in cases of symptoms or ECG signs of cardiac ischemia.

10 Describe the standard management of BCI

The management of patients with no symptoms and with minimal or no associated injuries is debated, but discharge from the hospital after a short observation period (6 to 8 hours) with negative or minimal ECG findings and negative troponin levels at 6 hours is supported. Patients who are elderly, have a history of cardiac disease, or are hemodynamically unstable require close continuous cardiac monitoring. The use of antiarrhythmic agents in patients with myocardial contusion is controversial and should occur in close concert with cardiologists. Also, consultation of cardiothoracic surgeons should occur in suspected cases of surgically amenable injuries.

11 Is follow-up needed in patients with BCI?

Long-term prognosis of patients with myocardial contusion is good, and functional recovery of the heart should be expected. As such, follow-up is not routinely required in patients with an uneventful cardiac course in the hospital. For those patients with a complicated course, a follow-up echocardiography is warranted to exclude formation of an aneurysm, cardiac thrombus, or valve anomaly.

12 When should penetrating cardiac injury (PCI) be suspected?

The presentation of PCI is variable and depends on the location of the wound and cardiorespiratory compensation. Any gunshot wound or stab wound to the cardiac box, defined as the region medial to the midclavicular lines, inferior to the clavicles, and superior to the costal margin, is highly concerning for cardiac injury (Fig. 69-2). Of note, an injury outside of the box does not exclude PCI; mortality has been reported as higher for cardiac injuries through wounds outside of the box, possibly because of delayed diagnosis.

Figure 69-2 Penetrating trauma thoracic box.

13 Describe the clinical presentation of patients with PCI

Clinical presentation varies widely from hemodynamic stability to cardiac arrest. PCI can cause exsanguinating hemorrhage or cardiac tamponade. The classical findings of cardiac tamponade are described as Beck triad (distended neck veins, hypotension, and muffled heart sounds) but are present only infrequently and should not create a false sense of security if absent. Other signs of shock, such as tachycardia, hypotension, and agitation, are more useful indicators of severity and should be assessed. Less commonly, patients may present with myocardial infarction after coronary artery transection due to PCI.

14 What is the optimal method of diagnosis of PCI?

An initial focused physical examination along with a rapid FAST examination of the pericardium offers the optimal method of preoperative diagnosis of PCI. FAST has an excellent sensitivity (90%-100%), specificity (96%-97%), and accuracy (96%-100%) in prospective studies with trained operators. A pericardial window was previously considered the gold standard for diagnosing hemopericardium but has been largely replaced with echocardiography today. Pericardiocentesis has low specificity and sensitivity as well as a limited therapeutic role, and, in light of better alternatives, it is generally not recommended in trauma.

15 How should PCI be treated?

It has classically been mentioned for PCIs that “perhaps in no other injury is rapid transport of such paramount importance” as traditional means of resuscitation provide limited improvement in pathophysiology. Expeditious surgical repair is necessary, and access to the heart can be gained through a median sternotomy (preferred approach) or an anterolateral thoracotomy. Digital control of cardiac wounds is an effective method to control bleeding ahead of definitive repair. If possible, intubation should occur after the patient is prepared and draped in the operating room because of potential cardiovascular collapse after anesthetic induction. In cases of cardiac collapse before arrival in the operating room, an emergency department thoracotomy can be performed; its benefit is highest in patients with previously witnessed signs of life.

16 Describe factors associated with survival in PCI

Mortality remains high, 41% to 84%, and, despite many surgical advances, survival has not improved significantly over several decades. This could possibly be due to an increasing proportion of gunshot wounds and faster prehospital transport of patients in extremis who previously would have been declared dead in the field. Predictors of survival include initial hemodynamic stability, stab wounds, and cardiac tamponade. Gunshot wounds often cause devastating cardiac injury and have a reported mortality of 77% to 86%. Unlike wounds causing exsanguinating hemorrhage, injuries associated with cardiac tamponade may have a protective effect by limiting bleeding, which can prolong survival until therapeutic intervention.