Stab and gunshot wounds frequently cause injury to the heart, with an incidence of 10% to 20% for proximity wounds. Patients with penetrating cardiac injuries generally present in one of three clinical patterns. In approximately 20% of patients, the injury will be clinically silent, at least initially, and is subsequently diagnosed at surgery or by an imaging study. Approximately 50% of patients will present with evidence of pericardial tamponade, including one or more signs in the Beck triad (hypotension, distended neck veins, and muffled heart sounds). In the remaining patients, the presentation is of hemorrhagic shock following free bleeding from an atrial or ventricular wound into one, or both, hemithoraces.

The diagnosis of penetrating injuries to the heart often requires a high index of suspicion. Location of entrance and exit wounds, trajectory path, and location of retained missiles on radiographs are helpful criteria in predicting heart injuries. Proximity wounds to the heart are defined as those which penetrate the chest wall in the area bounded superiorly by the clavicles, laterally by the midclavicular lines, and inferiorly by the costal margins. Any missile or instrument that traverses the anterior mediastinum is also considered a proximity wound. Because cardiac injuries are present in 15% to 20% of patients who present with proximity wounds, cardiac injuries must be definitively excluded.

Physical examination is often unreliable for the detection of pericardial tamponade. The presence of all three signs in the Beck triad is rarely found, and, in fact, any two of the three signs are present in only about half the number of patients with tamponade. Additionally, detecting muffled heart sounds and distended neck veins amidst the commotion in the trauma bay, and in the often agitated or intoxicated patient, can be extremely difficult. Because of this, additional diagnostic modalities must be used whenever any suspicion exists. As more surgeons are becoming familiar with the use of ultrasonography in the trauma setting, two-dimensional surface echocardiography is an accepted technique for diagnosing cardiac injuries. When performed by appropriately trained surgeons, the test detects blood within the pericardial sac with a sensitivity of 9 6% to 100% and a specificity of 100%, or essentially equivalent to pericardial window.⁵ When equipment is readily available, this noninvasive test can be performed in approximately 2 minutes. It is of vital importance that the trauma surgeon who is attending to the patient perform and interpret the examination. This allows for the quickest results, best clinical correlation, and most rapid use of the information in treatment decisions. The limitations of this test are the expense of the equipment and the specialized training required.

Although cardiac ultrasonography has many advantages, subxiphoid pericardial window remains the gold standard for exclusion of cardiac injury. In patients with equivocal ultrasonographic findings, or where ultrasound is unavailable, it should be considered in otherwise stable patients with proximity wounds and/or suggestive signs and symptoms. This procedure is usually performed in the operating room with general anesthesia, often in combination with abdominal exploration. A subxiphoid pericardial window is performed through a 10-cm vertical,
midline incision over the xiphoid, slightly favoring the epigastrium. The xiphoid is grasped with a clamp, and, after dissecting the xiphoid free from the abdominal fascia and diaphragmatic fibers, the substernal plane is accessed. While elevating the inferior portion of the sternum, the prepericardial adipose tissue is dissected to gain exposure of the acute margin of the pericardium. The pericardium can then be retracted inferiorly into the wound and incised sharply. The presence of blood or clot within the pericardial sac indicates a positive result, necessitating immediate repair of the injury. Pericardial window can also be accomplished during thoracoscopy of the left hemithorax.

The use of pericardiocentesis is advocated by some for the detection of cardiac injuries, especially where rapid access to the operating room, trauma surgeons, and anesthesiologists is not available. Problems with pericardiocentesis include the high rate of false positives, false negatives, and potential for iatrogenic cardiac injuries. Furthermore, this technique has limited use in the treatment of tamponade because, often, blood within the pericardial sac is clotted and not amenable to removal through a needle.