Cardiac Tamponade

Cardiac tamponade is a great imitator and may fool the physician since it is sometimes difficult to diagnose. Classic findings are distended neck veins, hypertension, plethora from impeded venous return and obvious distress. Tamponade usually results from penetrating injuries although blunt injury may also result in tamponade. A constellation of signs includes plethora, venous pressure elevation, hypotension, tachycardia, muffled heart tones and pulsus paradoxicus. Pulsus paradoxicus is defined as a decrease in the systolic blood pressure by at least 10 mm on inspiration. This is usually not clinically identifiable in the emergency room because of loud emergency room noise, but should be kept in the back of one's mind when evaluating such a patient. The physiologic basis for this phenomenon is that with inspiration, there is increased venous drainage to the right side of the heart which shifts the interventricular septum towards the left side. This results in decreased volume of the left ventricle and decreased cardiac output. Normally, the heart is able to distend within the pericardium, but in the tamponade situation, the heart is compressed from the outside and therefore respiration may effect the blood pressure. This, of course, is true only for those breathing spontaneously, as mechanical ventilation is p ositive pressure breathing, rather than the normal negative pressure of spontaneous ventilation.

The diagnosis of cardiac tamponade can be very allusive, as patients who initially present with shock may have had massive blood loss, and despite the fact that they also have tamponade, they may not have distended neck veins because of the volume loss. Conversely, cardiac tamponade may be overdiagnosed such as in a young trauma patient who has massive volume resuscitation resulting in massive over distention of his neck veins. In addition, tension pneumothorax may mimic cardiac tamponade. This is particularly true on the left side where a massive pneumothorax may distort the mediastinum such that there is diminished venous drainage into the heart, thus mimicking the physiologic consequences of cardiac tamponade.

The management of cardiac tamponade is taught by many to include pericardiocentesis. However, it must be emphasized that pericardiocentesis is, at best, a dangerous procedure which may or may not have any benefit toward relieving a tamponade. If tamponade is present in the pericardium, this may have been converted to a blood clot such that it cannot be drawn through the pericardiocentesis needle. Additionally, if there is no tamponade present and the needle is passed into the pericardium and into the heart, one may get a rush of blood back and think that this is decompression of a tamponade when, in fact, it is actually ventricular blood. There is an additional risk of laceration of the coronary arteries. We feel that pericardiocentesis should rarely, if ever, be done in the trauma situation. For suspected cardiac tamponade with hemodynamic compromise, the patient should undergo either a subxiphoid window (if necessary in the emergency room but preferably in the operating room), or if the patient has fully decompensated, then a left anterolateral thoracotomy should be done with decompression of the tamponade.

The most important aspect of managing a cardiac tamponade is to volume load the patient, and to increase the preload of the heart so as to offset the increased pressure on the outside of the heart. This cannot be overemphasized. Volume must be given to buy enough time to bring the patient to the operating room so that definitive management can be done.

The initial chest x-ray after blunt or penetrating cardiac injury with tamponade may be completely normal and not reveal an enlarged cardiac silhouette (Figs. 19.2 and 19.3). It is frequently assumed by many physicians that injury of the heart from blunt or penetrating trauma with cardiac tamponade will result in dilation of the cardiac shadow. This is completely false since the pericardium is nondistensible and this, in fact, is part of the physiology of cardiac tamponade. In a distressed trauma patient with distended neck veins, tamponade should be suspected despite a completely normal cardiac shadow.

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