Trauma, including to the heart and great vessels, can be divided in to blunt and penetrating trauma. Myocardial contusion is a common diagnosis in patients with a history of blunt chest trauma. Trauma to the major great blood vessel; aortic injury either aortic transection or acute rupture, is one of the leading causes of posttraumatic death with the majority of the patients dying before presenting to the hospital.
Blunt Cardiac Trauma
Nonpenetrating or blunt cardiac trauma has replaced the term cardiac contusion and describes injury ranging from minor bruises of the myocardium to cardiac rupture. It can be caused by direct energy transfer to the heart or compression of the heart between the sternum and vertebral column at the time of the accident. Blunt cardiac trauma includes injuries sustained during external cardiac massage as a part of cardiopulmonary resuscitation, such as cardiac contusion and cardiac rupture. Blunt cardiac injury usually results from high-speed motor vehicle accidents, in which the chest wall strikes against the steering wheel. Other causes, such as falls from heights, crushing injuries, blast injuries, and direct blows are less common.
Clinical picture blunt cardiac trauma: Most patients with myocardial contusion have external signs of thoracic trauma (e.g., contusion, abrasions, sternum fractures, visible flail segments), absence of visible thoracic lesions decreases the suspicion but does not exclude cardiac injury. Other associated injuries may include pulmonary contusion, pneumothorax, hemothorax, external fracture, and great vessel injury. Patients are at increased risk for dysrhythmia, such as heart block and ventricular fibrillation. Elective surgery should be postponed until all signs of heart injury resolve.
Penetrating Cardiac Trauma
Penetrating trauma is the most common cause of significant cardiac injury seen in hospital settings, with the predominant injury being from guns and knives. Victims of gunshot wounds usually have more severe physiologic impairment than those with stab wounds. Gunshot wounds cause larger defects in the myocardium and pericardium, through-and-through wounds, and a larger number of injuries in other vital organs leading to hemorrhage and exsanguination. Cardiac tamponade and exsanguination (the removal of blood from the body) are immediately life-threatening complications of penetrating cardiac trauma. Prompt recognition and treatment is required to avoid poor outcomes. Occasionally, penetrating cardiac trauma can occur from a blunt injury. If sufficient blunt force to the thorax results in fracture of the rib or sternum, the sharp bone fragments can be displaced into the heart with a resultant penetrating wound. Mortality from penetrating heart trauma is high.
Cardiac tamponade results when sufficient pressure is exerted on the heart by blood, fluid, or air accumulated in the pericardial sac that interferes with its diastolic filling and systolic output. As pericardial fluid accumulates, a decrease in ventricular filling occurs, leading to a decrease in stroke volume. As little as 60-100 mL of blood in the pericardial sac can produce the clinical picture of tamponade. The clinical manifestations of acute cardiac tamponade may vary with the rate and volume of accumulation of blood in the pericardial sac. Massive and rapid accumulation of blood within the pericardium usually results in severe tamponade, cardiac arrest, and sudden death. Patients with less rapid and massive accumulation of blood may be restless, complaining of air hunger, or they may be in shock. The skin may be cold and moist, and the lips may be mildly cyanotic. The visible superficial neck veins are distended and may have paradoxical filling during inspiration
Pericardiocentesis is performed by directing a 16-gauge over-the-needle catheter (at least 15 cm long) from the xiphochondral junction toward the tip of the left scapula at a 45° angle. Pericardiocentesis provides temporary relief. Definitive treatment of pericardial tamponade requires thoracotomy.
The classic findings of pericardial tamponade-tachycardia, hypotension, distant heart sounds, distended neck veins, pulsus paradoxus (a condition in which there is a sharp fall in blood pressure and pulse when the patient breathes in), or pulsus alternans (a pulse with a beat which is alternately weak and strong)-are difficult to appreciate or may be absent in a hypovolemic trauma patient.
Evacuation of the pericardial blood by pericardiocentesis (Figure 5.9) or surgery should be performed as soon as possible. Electrocardiographic changes during pericardiocentesis indicate over advancement of the needle into the myocardium.