Cardiac injuries due to GSWs are uncommon but highly lethal. Early detection and triage are vital for survival. There are several scoring systems to help predict patient mortality such as Trauma Injury Severity Score (TRISS) and Thorax Trauma Severity Score (TTSS). However, there is no reliable score for predicting cardiac injury in patients with GSWs to the chest. We found that cardiac injuries can be identified through a combination of easily measurable variables in patients with GSW to the chest.
The cardiac box is an anatomical region defined as the area on the anterior thorax limited by the clavicles superiorly, midclavicular lines laterally and the line connecting midclavicular lines at the costal margin inferiorly. Degiannis et al. (10) found that mortality from injuries outside the cardiac box were higher compared to those in the box. Literature suggesting the use of cardiac box as a predictor of cardiac injury was limited by small size (11, 12). Simply relying on the anatomic borders of the cardiac box to predict cardiac injury is inadequate (13).
In 1996, Focused Assessment with Sonography in Trauma (FAST) was introduced as a diagnostic tool to detect pericardial effusions in trauma patients (14). While, FAST has high sensitivity and specificity in traumatic pericardial effusion, a negative FAST examination does not exclude penetrating cardiac injury (15). Ultrasound use is not feasible for early identification of cardiac injury during prehospital triage due to lack of availability and lack of trained staff (16). MGAP (Mechanism, GCS, Age and arterial Pressure) utilizes parameters that are simple to measure. However, the prediction for mortality is inferior to that of TRISS (17).
The trauma and injury severity score (TRISS) (18), developed by Champion et al. in 1983, has been used globally because of its high accuracy for predicting the probability of survival in trauma patients (19)(20)(21). However, TRISS has several limitations, especially for patients with GSW to the chest. Chamption et al evaluated the performance of TRISS for triage primarily on blunt injured patients (18). TRISS underestimates survival probability in patients with GSW to the chest.
Calculation of TRISS includes ISS which cannot be calculated in the prehospital setting. Pape et al developed the thoracic trauma severity score (TTSS) in 2000 (22). Similar to TRISS, Pape et al evaluated their scoring system on blunt trauma patients; however, it was designed for thoracic non cardiac trauma. TTSS is not the best model to easily and quickly detect cardiac injuries in patients with GSW to the chest.
Asensio et al (23) created a predictive model for penetrating cardiac injury outcomes using the NTDB database and included 2016 patients with penetrating cardiac injuries and 1264 patients with GSW as the mechanism of injury. The study suggested that in patients with cardiac GSW’s field CPR, the absence of spontaneous ventilation, the presence of an associated abdominal GSW, need for ED intubation and aortic cross-clamping were independent predictors of mortality. This study provides insightful information on penetrating cardiac injury; however, it’s more useful when evaluating in-hospital patients. In our study, we have evaluated a larger (47,044) but specific population (GSW patients to the chest) with 4,047 patients with cardiac injury. We primarily focused on triage and early identification of patients with cardiac injury. This model stratifies a patient’s risk of having cardiac injury due to GSW by incorporating easily measured variables including age, presence of self-inflicted injury, pulselessness, apnea, SBP and GCS. As expected, the predicted model demonstrated an excellent result with 95.6% specificity during external validation with the local database from Stroger Hospital of Cook County.
We found a close relationship between suicide intent and cardiac injury in GSW to the chest. GSWs are most commonly the result of assaults (24), however, self-inflicted injury with firearms has higher mortality rate (25). Our study shows that cardiac injury after GSW to the chest is more common in younger patients. According to Center for Disease Control (CDC), suicide by firearms was the second leading cause of death among 15 to 35 years old in 2017 (26). Prevalence of GSW in the younger age group has been studied extensively and is explained by a greater access to firearms (1, 2).
Our study shows that patients with a cardiac injury had significantly lower SBP (34.7 mmHg) compared to patients without cardiac injury (103.8 mmHg), and that most patients were found to be pulseless [59.9% (2423) vs. 12% (5166), p < 0.001]. Our results showed that one more unit of SBP (mmHg) in the ED decreased the probability of heart injury by 0.9%, and patients arriving with immeasurable pulse had a 2.2 times higher mortality rate. Despite proper triage, patients with cardiac injury require immediate resuscitation to prevent irreversible cardiac damage resulting from increased stress and anaerobic loading onto myocardial tissues and cells. Teixeira et al. found similar findings in that mortality was higher among patients with cardiac injury that presented with SBP < 90 mmHg compared to patients with SBP > 90 mmHg (85% vs 65%, p = 0.01) (27). This is consistent with other research findings, which stated that systolic BP is the best univariate predictor in pre-hospital trauma patients.
A GCS < 8 is a common finding in cardiac injury associated with increased mortality (28). As in previous studies, GCS was found to be an independent variable in our predictive model. GCS and SBP both had a 71.5% specificity and AUC of 0.768 and 0.783 respectively. Combination of variables in our suggested model including age, SBP, GCS, apnea, pulselessness and suicide intent show a specificity of 88.8% with AUC of 0.823.
The primary limitation of this study was its retrospective nature both during development and validation of the suggested model. The study is also limited by the nature of NTDB. External validation of the suggested model at a single institution might also be considered a limitation, therefore, a multi-institutional validation is required. However, our model is efficient, robust and relies on easily obtainable factors such as pulselessness and suicidal intent. We developed a model specific for patients with GSW to chest that is quick and easy to use during triage both by paramedics and ED personnel.