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Bryan Morse Urges Redefinition of the Cardiac Box

October 2016

At the 75th Annual Meeting of the American Association for the Surgery of Trauma and Clinical Congress of Acute Care Surgery, Emory trauma and surgical critical care surgeon Bryan Morse, MD, presented a study that described the current boundaries of the "cardiac box"—the area of the chest overlying the heart, bounded by the midclavicular lines (laterally) and from the clavicles to the tip of the xiphoid—as a deficient predictor of cardiac injury from gunshot wounds.

"Surgical teaching dictates that penetrating injuries in the box have the highest likelihood of cardiac injury and thereby mandate further evaluation," Morse says. "These studies, however, are based on small patient sample sizes in which the majority were stab wound victims and underwent minimal statistical scrutiny."

This study was preceded by Morse and his associates' evaluation of 36 years of penetrating cardiac injuries data at Grady Memorial Hospital, which was recently published in the October 2016 edition of the Journal of Trauma and Acute Care Surgery. Using records obtained from the Trauma Registry of the American College of Surgeons and the Emory Department of Surgery database, the study found that cardiac injuries from gunshots increased between 2000 and 2010, and noted that several of these injuries were caused by penetrating thoracic wounds outside the cardiac box. Morse decided that the continued utility of the cardiac box required further investigation.

For the study, Morse and his team conducted a retrospective review of trauma registry data from Grady's trauma center and autopsy reports from 2011-2013 to identify patients with penetrating thoracic gunshot wounds and cardiac injury, 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 could yield improved predictions for cardiac injury over the current definition of the cardiac box.

Over the three-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. Thirty percent of the 233 GSWs entering the cardiac box caused cardiac injury, while 32% of the 44 GSWs outside the cardiac box penetrated the heart, suggesting that the current cardiac box is a poor forecaster of cardiac injury relative to the thoracic non-cardiac box regions.

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. 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 at 41%.

"The current cardiac box is unable to discriminate between gunshot wounds that will cause a cardiac injury and those that will not," 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 Morse 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 says. "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."

Morse acknowledged certain limitations of the study, including the fact that it 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."

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