Cardiac tamponade

Onset may be rapid (acute) or more gradual (subacute). In phase I, the required filling pressure increases due to the high stiffness of the ventricles. This is because of the accumulation of pericardial fluid in the pericardial cavity. During phase II, the pericardial pressure exceeds the ventricular filling pressure caused by the further accumulation of pericardial fluid. This results in a decrease in cardiac input and output. A further decrease of cardiac input and output is typical in phase III of the progression of cardiac tamponade. This is caused by the equilibration of left ventricular filling and pericardial pressure, leading to “severe deterioration of end-organ perfusion.” Some of the symptoms, as a consequence, include abdominal pain due to liver engorgement. ==Causes==

Cardiac tamponade is caused by a large or uncontrolled pericardial effusion, i.e. the buildup of fluid inside the pericardium. This commonly occurs as a result of chest trauma (both blunt and penetrating), but can also be caused by myocardial infarction, myocardial rupture, cancer (most often Hodgkin lymphoma), uremia, pericarditis, or cardiac surgery, or while the person is taking anticoagulant therapy. The effusion can occur rapidly (as in the case of trauma or myocardial rupture), or over a more gradual period of time (as in cancer). The fluid involved is often blood, but pus is also found in some circumstances. After heart surgery, chest tubes are placed to drain blood. These chest tubes, however, are prone to clot formation. When a chest tube becomes occluded or clogged, the blood that should be drained can accumulate around the heart, leading to tamponade. ==Pathophysiology==

, wherein the pericardium becomes filled with blood, is one cause of cardiac tamponade. The pericardium, the double-walled sac surrounding the heart, consists of a fibrous pericardium layer on the outside and a double-layered serous pericardium on the inside. Between the two layers of the serous pericardium is the pericardial space, which is filled with lubricating serous fluid that prevents friction as the heart contracts. The outer layer of the heart is made of fibrous tissue which does not easily stretch, so once excess fluid begins to enter the pericardial space, pressure starts to increase. If fluid continues to accumulate, each successive diastolic period leads to less blood entering the ventricles. Eventually, increasing pressure on the heart forces the septum to bend in towards the left ventricle, leading to a decrease in stroke volume. The decrease in stroke volume can also ultimately lead to a decrease in cardiac output, which could be signaled by tachycardia and hypotension. == Diagnosis ==

The three classic signs, known as Beck's triad, are low blood pressure, jugular-venous distension, and muffled heart sounds. Other signs may include pulsus paradoxus (a drop of at least 10 mmHg in arterial blood pressure with inspiration), In a person with trauma presenting with pulseless electrical activity in the absence of hypovolemia and tension pneumothorax, the most likely diagnosis is cardiac tamponade. In addition to the diagnostic complications afforded by the wide-ranging differential diagnosis for chest pain, diagnosis can be additionally complicated by the fact that people will often be weak or faint at presentation. For instance, a fast rate of breathing and difficulty breathing on exertion that progresses to air hunger at rest can be a key diagnostic symptom, but it may not be possible to obtain such information from people who are unconscious or who have convulsions at presentation. ==Treatment==

Pre-hospital care Initial treatment given will usually be supportive in nature, for example administration of oxygen, and monitoring. There is little care that can be provided pre-hospital other than general treatment for shock. Some teams have performed an emergency thoracotomy to release clotting in the pericardium caused by a penetrating chest injury. Prompt diagnosis and treatment is the key to survival with tamponade. Some pre-hospital providers will have facilities to provide pericardiocentesis, which can be life-saving. If the person has already suffered a cardiac arrest, pericardiocentesis alone cannot ensure survival, and so rapid evacuation to a hospital is usually the more appropriate course of action. Hospital management Initial management in hospital is by pericardiocentesis. A left parasternal approach begins 3 to 5 cm left of the sternum to avoid the left internal mammary artery, in the 5th intercostal space. Often, a cannula is left in place during resuscitation following initial drainage so that the procedure can be performed again if the need arises. If facilities are available, an emergency pericardial window may be performed instead, during which the pericardium is cut open to allow fluid to drain. Following stabilization of the person, surgery is provided to seal the source of the bleed and mend the pericardium. Following heart surgery, the amount of chest tube drainage is monitored. If the drainage volume drops off, and the blood pressure goes down, this can suggest a tamponade due to chest tube clogging. In that case, the person is taken back to the operating room for an emergency reoperation. If aggressive treatment is offered immediately and no complications arise (shock, AMI or arrhythmia, heart failure, aneurysm, carditis, embolism, or rupture), or they are dealt with quickly and fully contained, then adequate survival is still a distinct possibility. ==Epidemiology==

The frequency of tamponade is unclear. ==References==