The diagnosis of blunt cardiac injury is challenging, as patients may present with non-specific symptoms and there is no golden diagnostic test. We report the incidence of cardiac injury in patients with blunt chest injuries to be 18.32%, which is consistent with the wide range reported in the literature, ranging between 3 and 56%, depending on the diagnostic criteria [16,17,18,19,20]. Furthermore, our systematic review revealed a weighted mean mortality rate for patients presenting with BCI of around 7.6%. Mortality rates for BCI vary in the existing literature. This can be explained by different study populations and the method used to detect BCI. Patients with cardiac injuries that result in immediate death are generally not included in studies [21,22,23]. This suggests that cardiac injuries are more common than widely reported. In line with these considerations, an autopsy study examining 881 cadavers with blunt trauma found a cardiac injury rate of 32%. According to the diagnostic challenges in BCI, we identified the use of ECG in combination with cTnI as a pragmatic approach to rule out cardiac injuries. In addition, TEE with a high specificity and sensitivity may be highly accurate in identifying cardiac injuries in suspected cases.

It is worth noting that severe cardiac injuries can easily be detected, as they usually present with haemodynamic instability. However, less severe injuries can easily be masked in trauma patients, due to other severe vascular, pulmonary, or neurological injuries. The biggest challenge revolves around diagnosing trauma patients with no clinical signs of myocardial injuries, as some present with only mild symptoms, such as palpitations or precordial pain, which are often related to the associated musculoskeletal injury. For instance, we reported that 20.7%, of the patients with blunt cardiac injury presented with serious arrhythmias (AF, PVC, VT, SVT). This leaves 79.3% of patients with a cardiac injury who presented with benign, less serious, arrhythmias.

The hypothesis states that cardiac injury, in patients with blunt chest trauma, is caused by deceleration forces affecting the viscoelastic properties of the chest wall leading to either direct pressure on the myocardium or an indirect pressure through increased intrathoracic pressure leading to shearing stresses. The histological findings seen in blunt cardiac injuries are similar to those seen in myocardial infarction, and these are intramyocardial haemorrhage, oedema and necrosis of cardiac cells [24, 25]. Thus, cardiac enzymes, such as troponin and creatinine kinase MB, were the first screening tools to detect cardiac injury. We reported that the sensitivity of CPK-MB was 55.2% and the specificity 75.8%. CPK-MB tends to have higher specificity in detecting acute myocardial infarction—but not in trauma patients with associated skeletal injuries [4, 24]. Thus, creatinine kinase is useful in detecting cardiac contusion in patients with none or only minor non-cardiac injuries. However, it is also worth noting that some authors have reported reduced sensitivity and specificity in patients with mild injuries [18, 25,26,27,28].

Our study has shown that cTnT has a sensitivity and specificity of 68.4% and 85.5%, respectively. The numbers for cTnI were 64.4% and 84.1%, respectively. The increased sensitivity and specificity compared to CPK-MB can be explained by the fact that both serum cardiac troponins are regulatory contractile proteins that are only present in heart muscle cells and not in skeletal muscles. In case of heart muscle damage resulting in loss of cell membrane integrity cardiac troponins are released into the serum. That makes troponin invaluable in diagnosing heart damage. This meta-analysis has also shown that cTnT has a negative likelihood ratio of 0.217% and a positive likelihood ratio of 4.368%. The values for cTnI were 0.329% and 3.792%, respectively. This led to the conclusion that positive serum cardiac troponins are accurate in the diagnosis of cardiac contusion. Furthermore, negative serum troponin is a strong indicator of the absence of the disease. The results are consistent with previous studies [18, 20, 29, 30]. The optimal time of sampling for serum troponin after trauma has not been established. However, it is proposed that if an initial serum troponin is negative, a second measurement should be performed after 4–6 h. High troponin levels tend to persist for 4–6 days, and this can aid with the diagnosis of blunt cardiac injury in late presentations [18, 31].

This study has shown that the ECG may be normal after a blunt chest injury or may show specific or non-specific abnormalities. Non-specific changes are also seen in trauma patients, some caused by anaemia, hypoxia, electrolyte abnormality and sympathetic and parasympathetic tone. This is in accordance with many other studies [18, 32]. ECG changes tend to reflect the activity of the left ventricle, as this is larger than the right ventricle and close to the sternum. Thus, contusions affecting the left ventricle can present as significant ST-changes and serious arrhythmias on the ECG, whilst, on the other hand, right ventricle contusion can easily be missed [33]. This study showed that the ECG has a sensitivity of 55.1% and a relatively good specificity of 84.5%. For instance, ST, T, or Q wave changes were present in 45.9% of patients with blunt cardiac injury. Furthermore, 20.7% of the patients with blunt cardiac injury presented with serious arrhythmias. This might be due to electrical instability, as these patients are usually more haemodynamically compromised and this finding is often associated with sudden death [19]. If we consider patients diagnosed with a blunt cardiac injury, 24.6% presented with conduction abnormalities. According to the latest literature, a right bundle branch block resembles a severely injured right ventricle. Other types of conduction abnormalities have also been reported in patients with cardiac contusion [16, 24, 32].

In light of our results, when both the ECG AND cTnI are positive the sensitivity of the diagnosis of blunt cardiac injury decreases. When only one of the ECG OR cTnI is positive, the sensitivity of the diagnosis of cardiac injury increases and the specificity decreases. Normal ECG in combination with a normal troponin I was excellent in ruling out blunt cardiac injury (sensitivity of 87.5%). In addition, the diagnostic combination of ECG and cTnI is widely available and offers an excellent cost-effectiveness ratio.

The effects of blunt cardiac injury are not only histological and may affect the function of the heart. On a 2D echo scan, BCI can be diagnosed as the presence of localised dysfunction of the myocardial wall [16]. An echo scan can also be utilised to detect valvular abnormalities, effusions, thrombus, and dilatations. However, it can be difficult to detect myocardial oedema without abnormal motion on a 2D echo [19]. We reported moderate sensitivity (47.0%) and high specificity (91.4%) for TTE. The findings for TEE were significantly higher—at 86.7% and 72.1%, respectively. In particular, posterior cardiac structures which are close to the oesophagus can be better visualized by TEE compared to TTE. A recently published review also confirmed that TEE can be performed at the bedside in different locations and also in mechanically ventilated patients [33].

Thus TEE is a good option to confirm or exclude BCI in suspected cases. In addition, it can also be used to detect suspected lesions in the great vessels. However, both Echo examinations have their limitations: TTE cannot be used in patients with severe chest wall injuries, as it can be very painful and TEE is contraindicated in patients with diagnosed or suspected oesophageal injury and should be used carefully in cervical spine injuries. In addition, Echo is also not as widely available as ECG or cardiac biomarkers. Furthermore, TEE requires advanced skills.

Although the transoesophageal investigation has been proven to be safe in patients with blunt chest trauma, the risk of adverse events is higher than with ECG or biomarker measurements. Iatrogenic injury may occur when the endoscope is inserted into the oesophagus, and sedation with all its associated risks is also necessary [34, 35]. A study published by OH JK reported breathing problems and haemodynamic instability in patients who underwent a TEE [36].

After weighing up the various advantages and disadvantages of each diagnostic test, we propose a simple algorithm for the initial assessment of cardiac injury in blunt chest trauma (Fig. 2).

A propagated algorithm for the initial assessment of cardiac contusion

A TTE should be typically done by a cardiologist or a trained emergency physician. A TEE on the other side should be performed by a cardiologist. The exam should be interpreted by a physician trained in reading echocardiograms; ideally, that should be the cardiologist.