WAIKOLOA, HI. – For gunshot wounds, the current “cardiac box” was the poorest predictor of cardiac injury, results from a single-center retrospective study demonstrated.
“We determined that, from a statistical standpoint, the cardiac box should be redefined to include the area of the thorax that extends from the clavicle to xiphoid and from the anterior midline to the posterior midline of the left thorax,” Bryan C. Morse, MD, said in an interview in advance of the annual meeting of the American Association for the Surgery of Trauma. “The classic cardiac box is inadequate to discriminate whether a gunshot wound will create a cardiac injury.”
Dr. Morse of Emory University and Grady Memorial Hospital, Atlanta, and his associates recently published their experience with penetrating cardiac injuries over the past 36 years and documented an increase in the number of cardiac injuries from gunshots over the past 10 years (J. Trauma Acute Care Surg. 2016 Jul 6. doi: 10.1097/TA.0000000000001165). They also noted that several of these injuries were caused by penetrating thoracic wounds outside the cardiac box.
The cardiac box is currently defined as the area of the chest overlying the heart, bounded by the midclavicular lines (laterally) and from the clavicles to the tip of the xiphoid. “Surgical teaching dictates that penetrating injuries (i.e. stab wounds and gunshot wounds) in the box have the highest likelihood of cardiac injury and thereby mandate further evaluation,” Dr. Morse said. “These studies, however, are based on small patient sample sizes in which the majority were stab wound victims and underwent minimal statistical scrutiny.”
In what he said is the largest study of its kind, Dr. Morse and his associates conducted a retrospective review of trauma registry data from Grady’s trauma center and autopsy reports to identify patients with penetrating thoracic gunshot wounds and cardiac injury from 2011 to 2013 and to evaluate the relationship between penetrating injuries and the likelihood of a cardiac injury. Using a circumferential grid system around the thorax, the researchers employed logistic regression analysis to compare differences in rates of cardiac injury from entrance/exit wounds in the cardiac box, versus outside the box. They repeated the process to identify potential regions that yield improved predictions for cardiac injury over the current definition of the cardiac box.
Over the 3-year study period, 263 patients sustained 735 penetrating thoracic wounds, of which 80% were gunshot wounds (GSWs). Most of the patients were males (89%) with a median of two injuries each. After stab wounds were excluded, 277 GSWs to the thorax were included for study and 95 (34%) injured the heart. Of the 233 GSWs entering the cardiac box, 30% caused cardiac injury while, of the 44 GSWs outside the cardiac box, 32% penetrated the heart, suggesting that the current cardiac box is a poor predictor of cardiac injury relative to the thoracic non–cardiac box regions (OR 1.1; P = .71).
The researchers observed that the regions from the anterior to the posterior midline of the left thorax provided the highest positive predictive value, with a sensitivity of 90% and a specificity of 31%, making this region the most statistically significant discriminator of cardiac injury (OR, 4.4; P less than .01). This finding was primarily based on the fact that gunshots to the left lateral chest (an area not currently included in the box) had a high rate of cardiac injury (41%; OR, 1.4).
“The current cardiac box is unable to discriminate between gunshot wounds that will cause a cardiac injury and those that will not,” Dr. Morse said. “Any gunshot wound to the chest can cause a cardiac injury. While clinically relevant box borders would include the left chest, the bottom line for surgeons is to think outside the current cardiac box.”
The improved cardiac box that he and his associates proposed includes the area from the clavicles to the xiphoid and from the anterior to the posterior midline over the left thorax. “While this may be intuitive, it is not what we as surgeons have been teaching,” he said. “Finally, gunshots to areas such as the right posterior and posterolateral chest were associated with rates of cardiac injury greater than 30% despite their distance from the heart. This led us to conclude that a gunshot anywhere to the chest should be considered to potentially cause a cardiac injury.”
Dr. Morse acknowledged certain limitations of the study, including the fact that the study excluded graze wounds and gunshots above the clavicles and below the xiphoid. “However, a small percentage of these did cause cardiac injuries, which emphasizes the point that gunshot wounds from any entrance can cause cardiac injury.”