Myocardial contusion is a nonspecific term that relates to a broad spectrum of nonpenetrating cardiac injuries. Importantly, the cardiac issues may initially be overlooked in trauma patients as the clinical focus is directed toward other, more obvious injuries. Myocardial necrosis may occur as a direct result of the blunt injury or as a result of traumatic coronary laceration, dissection, or thrombosis. The contused myocardium is pathologically similar to infarcted myocardium and may be associated with atrial or ventricular arrhythmias; conduction disturbances including bundle branch block; or abnormalities on electrocardiogram (ECG) resembling those of infarction or pericarditis. Thus, it is important to consider blunt cardiac injury as a cause of otherwise unexplained ECG changes in a trauma patient. Serum creatine kinase, myocardial band (CK-MB) isoenzyme levels are increased in ~20% of patients who experience blunt chest trauma but may be falsely elevated in the presence of massive skeletal muscle injury. Cardiac troponin levels are more specific for identifying cardiac damage; patients with normal troponin levels 4–6 h after chest trauma are very unlikely to have cardiac injury. Echocardiography is useful in detecting structural and functional sequelae of blunt cardiac injury, including regional wall motion abnormalities (most commonly involving the right ventricle, interventricular septum, or left ventricular apex), pericardial effusion, valvular dysfunction, and ventricular rupture.
Traumatic rupture of the cardiac valves or their supporting structures, most commonly of the tricuspid or mitral valve, leads to acute valvular incompetence. This complication is usually heralded by the development of a loud murmur, may be associated with rapidly progressive heart failure, and can be diagnosed by either transthoracic or transesophageal echocardiography.
The most serious consequence of nonpenetrating cardiac injury is myocardial rupture, which may result in hemopericardium and tamponade (free wall rupture) or intracardiac shunting (ventricular septal rupture). Although generally it is fatal, up to 40% of patients with cardiac rupture have been reported to survive long enough to reach a specialized trauma center. Hemopericardium also may result from traumatic rupture of a pericardial vessel or a coronary artery. Additionally, pericarditis and/or pericardial effusion may develop weeks or even months after blunt chest trauma as a manifestation of the post–cardiac injury syndrome, an inflammatory condition that resembles the postpericardiotomy syndrome (Chap. 265).
Blunt, nonpenetrating, often innocent-appearing injuries to the chest may trigger ventricular fibrillation even in the absence of structural myocardial damage. This syndrome, referred to as commotio cordis, occurs most often in adolescents during sporting events (e.g., baseball, hockey, football, and lacrosse) and is an electrical phenomenon that probably results from an impact to the chest wall overlying the heart during the susceptible phase of repolarization (just before the peak of the T wave). Survival depends on prompt defibrillation. Sudden emotional or physical trauma, even in the absence of direct cardiac trauma, may precipitate a transient catecholamine-mediated cardiomyopathy referred to as tako-tsubo syndrome or the apical ballooning syndrome (Chap. 254).
Rupture or transection of the aorta, usually just above the aortic valve or at the site of the ligamentum arteriosum, is a common consequence of nonpenetrating chest trauma and is the most common vascular deceleration injury. The clinical presentation may be similar to that of aortic dissection (Chap. 274); the arterial pressure and pulse amplitude may be increased in the upper extremities and decreased in the lower extremities, and chest x-ray may reveal mediastinal widening. Aortic rupture into the left thoracic space is almost universally fatal; however, the rupture is occasionally contained by the aortic adventitia, resulting in a false, or pseudo-, aneurysm that may be discovered months or years after the initial injury.