Blunt cardiac injury (BCI) encompasses a spectrum of pathologies ranging from clinically silent, transient arrhythmias to deadly cardiac wall rupture. Therefore, the real incidence of BCI is difficult to estimate and can vary widely. Of diagnosed BCIs, cardiac contusion is most common. The absence of clear diagnostic criteria and reliable diagnostic tests makes reporting difficult. Suggestive symptoms may be unrelated to BCI, while some injuries may be clinically asymptomatic. Cardiac rupture is the most devastating complication of BCI. Most patients who sustain rupture of a heart chamber do not reach the emergency department alive.

BCI occurs most often from motor vehicle collisions (MVCs). Rapid deceleration is the mechanism responsible for most BCIs. A direct blow to the precordium also accounts for a sizable number of cases [1, 2]. Any patient involved in an MVC with sudden deceleration, or who sustains significant chest trauma or severe multiple trauma is at risk.

Several forces may be involved in BCI, including compression of the heart between the spine and sternum, abrupt pressure fluctuations in the chest and abdomen, shearing from rapid deceleration, and blast injury [2]. In addition, fragments from rib fractures can directly traumatize the heart without a penetrating injury. The right heart is the most commonly injured, likely due to its position closest to the anterior chest wall. High pressure ventricular injuries appear to be as common as low pressure atrial injuries. Other pathological findings include valvular tears or rupture, septal tears and coronary artery thrombosis or laceration, however these are less common [2].

Cardiac contusions are the most common injuries to the heart resulting from blunt trauma. Mild cardiac contusions often recover without lasting consequences while severe injuries more often result in lasting consequences and mortality [3].

Histologically, it is characterized by a contused myocardium with haemorrhagic infiltrate, localised necrosis, and oedema.

Signs and symptoms of cardiac contusions include chest pain, shortness of breath, and the development of arrhythmias. Cardiac contusions are often difficult to accurately diagnose due to the lack of standardised approaches to their evaluation.

Since cardiac contusion defines a wide range of injuries, patients may have a variety of presentations. Patients presenting with cardiac contusions range from being completely asymptomatic to experiencing mild chest soreness, presenting with electrocardiographic abnormalities, contractile abnormalities, and having signs of heart failure.

Right bundle branch block (RBBB) is a common result of cardiac contusions, whilst left bundle branch block (LBBB) has rarely been reported [4]. The right ventricle is nearest to the sternum, subjecting it to the high risk of cardiac contusions [4].

As there is often variability in severity and presentation of cardiac contusions, various diagnostic modalities have been utilised to aid the evaluation and treatment process. Cardiac contusions are characterised by injury to the myocardium. Cardiac enzymes such as creatinine kinase and troponin, enzymes that are released after an injury to the heart, and have traditionally been used in evaluating patients for MI. They have also been utilised in the evaluation of cardiac trauma as both can be increased due to injury of the heart [3].

Imaging can be utilised to identify structural damage to the heart after BCI. Echocardiography provides functional and structural assessments of the heart and is important for ruling out other injuries to the heart including valvular dysfunction, septal or free wall rupture, cardiac tamponade, and muscle function. Cardiac magnetic resonance imaging (MRI) is an alternative option for the diagnosis of cardiac abnormalities with the ability to provide information regarding the extent of myocardial contusion and regional infarcts.

Nonspecific signs and concomitant injuries make the clinical diagnosis of blunt myocardial injury difficult. Signs such as hypotension associated with distended neck veins and muffled heart sounds suggest pericardial tamponade, which may occur with BCI. However, such signs may not be present; the patient with haemorrhage and hypotension may not have distended neck veins; in this case an immediate bedside ultrasound may reveal the diagnosis.

Most patients with severe BCI, such as uncontained myocardial rupture, do not reach the emergency department alive [5]. Of those who do, hypotension may reduce pressure on the injured myocardium, which in turn may then worsen as fluid resuscitation restores blood pressure and subsequent increase in myocardial pressure increases. In a minority of patients, rapid diagnosis by echocardiography or CT scan and operative intervention can be lifesaving [6].

Atrial rupture occurs far less often than ventricular rupture, likely due to the location of the atria and their compliance. Atrial injuries tend to be delayed in presentation and often present less acutely [5]. Right atrial rupture is seen in approximately 10% of wall ruptures from blunt trauma, with left atrial rupture less common [7].

Septal injury appears to be rare, and its presentation varies. Septal injury may involve insignificant tears or frank rupture, and may occur in isolation or with valvular injury [2]. Findings may include acute valvular insufficiency with widened pulse pressure and signs of acute heart failure.

Isolated valvular injury is likewise rare [8]. The aortic valve is most often injured, followed by the mitral and tricuspid valves [8]. The lesion may consist of a tear of the leaflet or a partial or full thickness tear of the papillary muscle or chordae tendineae. Presentation may vary, in part depending upon the lesion, but falls somewhere in the spectrum of acute valvular insufficiency with right-or left-sided heart failure and a new cardiac murmur.

Ismailov and colleagues noted a significant increase in tricuspid and aortic valve insufficiency, incompetence, and regurgitation among patients with a history of BCI. Milder cases may go undiagnosed initially and present late with heart failure from long-standing valvular dysfunction [9]. While less common, mitral valve insufficiency has also been reported [10].

BCI often presents with concomitant injuries. These can include injuries to the head, thorax, abdomen, and spine. In one autopsy series, sternal fractures were found in 76% of cases involving cardiac injury but only 18% of deaths without BCI [11]. Nevertheless, a sternal fracture does not necessarily imply the presence of BCI, but a high degree of suspicion for blunt cardiac injury should be considered and excluded based on the mechanism of injury.

Myocardial infarction is a rare complication of BCI reported in victims of motor vehicle collisions and minor trauma. Causes include coronary artery dissection, laceration, and thrombosis [12, 13]. The left anterior descending artery appears to be involved most often [14].