SGEM#332: Think Outside the Cardiac Box

Date: May 20th, 2021 Guest Skeptic: Dr. Robert Edmonds is an emergency medicine physician in the Air Force in Dayton, Ohio, and a University of Missouri-Kansas City residency alumni from 2016. Reference: Jhunjhunwala et al. Reassessing the cardiac box: A comprehensive evaluation of the relationship between thoracic gunshot wounds and cardiac injury. Journal of Trauma and Acute Care Surgery. September 2017 DISCLAIMER: THE VIEWS AND OPINIONS OF THIS PODCAST DO NOT REPRESENT THE UNITED STATES GOVERNMENT OR THE US AIR FORCE. This SGEM episode was recored live for the Truman Medical Centers Multidisciplinary Trauma Conference. We did the session over zoom as an SGEM Journal Club. If you would like a copy of the slides from the presentation you can download them free open access at this LINK. Case: You receive a call on the Biocom for an incoming Type A trauma, three minutes out.  The patient is an adult male with a gunshot wound to the chest, and they’re combative with emergency medical services (EMS). Upon arrival in the emergency department (ED), the patient is incoherently speaking, has a pulse of 135 beats per minute, blood pressure of 85/50 mm Hg, and an obvious open wound in their left mid-axillary line at the level of the nipple. Background: Penetrating trauma is a major disease burden in the United States, and gunshot wounds cause 30,000 deaths annually [1] . As a country, penetrating trauma accounts for about 10% of all trauma cases [2] , but at some trauma centers it can reach much higher numbers. Here at the Truman Medical Center the average penetrating trauma for gunshot wounds alone represents ~19% of all traumas.  Naturally, patients with a direct cardiac injury from a gunshot wound (GSW) require prompt identification and management, so tools have sprung into existence to attempt to risk stratify patients at a higher risk of an underlying cardiac injury. One of the more common tools is the “cardiac box”. This three-dimensional area is at the highest risk of cardiac injury. The anatomical area is defined anteriorly as between the clavicle and xyphoid, and between the bilateral midclavicular lines. Per the authors, “The dogma of the cardiac box is largely based on small studies with primarily stab wounds. The underlying issue is that stab wounds are low kinetic energy and result from instruments with a fixed length. Thus, most stab wounds usually only result in a cardiac injury if the entrance is in very close proximity to the heart or there is a long weapon. Because these studies did include gunshots, the concept of the “box” was ultimately uniformly applied to all mechanisms. Injuries from high kinetic energy projectiles, however, can cause cardiac injury from entrance wounds to any area of the torso, especially the thorax.” Although it may be obvious to some that injury outside the cardiac box doesn’t rule out injury to the heart, the existence of such a tool colors our language and shifts the perceived risk in the clinician’s head.  According to a recent study in the Journal of Surgical Research [3] , 44% of all penetrating thoracic trauma patients presented to a non-trauma center (not a level 1 or level 2 ACS defined trauma center). For clinicians in these settings, use of the “cardiac box” nomenclature can have a significant impact on the perceived injuries when communicating with an on-call surgeon or when transferring the patient to another facility. If the injury is outside the cardiac box, it can be perceived as less concerning and may give the treating team a false sense of security. Clinical Question: Are the anatomic borders of the cardiac box adequate to predict cardiac injury from gunshot wounds? Reference: Jhunjhunwala et al. Reassessing the cardiac box: A comprehensive evaluation of the relationship between thoracic gunshot wounds and cardiac injury. Journal of Trauma and Acute Care Surgery. September 2017