Definitions

Cardiac tamponade

Cardiac tamponade

Cardiac tamponade, also known as pericardial tamponade, is an emergency condition in which fluid accumulates in the pericardium (the sac in which the heart is enclosed). If the fluid significantly elevates the pressure on the heart it will prevent the heart's ventricles from filling properly. This in turn leads to a low stroke volume. The end result is ineffective pumping of blood, shock, and often death.

Causes

Cardiac tamponade occurs when the pericardial space fills up with fluid faster than the pericardial sac can stretch. If the amount of fluid increases slowly (such as in hypothyroidism) the pericardial sac can expand to contain a liter or more of fluid prior to tamponade occurring. If the fluid occurs rapidly (as may occur after trauma or myocardial rupture) as little as 100 ml can cause tamponade.

Causes of increased pericardial effusion include hypothyroidism, physical trauma (either penetrating trauma involving the pericardium or blunt chest trauma), pericarditis (inflammation of the pericardium), iatrogenic trauma (during an invasive procedure), and myocardial rupture.

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 rupture, cancer, uraemia, pericarditis, or cardiac surgery, and rarely occurs during aortic dissection, or whilst the patient 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.

Myocardial rupture is a somewhat uncommon cause of pericardial tamponade. It typically happens in the subacute setting after a myocardial infarction (heart attack), in which the infarcted muscle of the heart thins out and tears. Myocardial rupture is more likely to happen in elderly individuals without any previous cardiac history who suffer from their first heart attack and are not revascularized either with thrombolytic therapy or with percutaneous coronary intervention or with coronary artery bypass graft surgery.

Pathophysiology

The outer pericardium is made of fibrous tissue which does not easily stretch, and so once fluid begins to enter the pericardial space, pressure starts to increase.

If fluid continues to accumulate, then with each successive diastolic period, less and less blood enters the ventricles, as the increasing pressure presses on the heart and forces the septum to bend into the left ventricle, leading to decreased stroke volume. This causes obstructive shock to develop, and if left untreated then cardiac arrest may occur (in which case the presenting rhythm is likely to be pulseless electrical activity)

Diagnosis

Initial diagnosis can be challenging, as there are a number of differential diagnoses, including tension pneumothorax, and acute heart failure. In a trauma patient presenting with PEA in the absence of hypovolemia and tension pneumothorax, the most likely diagnosis is cardiac tamponade..

Classical cardiac tamponade presents three signs, known as Beck's triad. Hypotension occurs because of decreased stroke volume, jugular-venous distension due to impaired venous return to the heart, and muffled heart sounds due to fluid inside the pericardium.

Other signs of tamponade include pulsus paradoxus (a drop of at least 10mmHg in arterial blood pressure on inspiration), and ST segment changes on the electrocardiogram, which may also show low voltage QRS complexes (Longmore et al 2004), as well as general signs & symptoms of shock (such as tachycardia, breathlessness and decreasing level of consciousness).

Tamponade can often be diagnosed radiographically, if time allows. Echocardiography often demonstrates an enlarged pericardium or collapsed ventricles, and a chest x-ray of a large cardiac tamponade will show a large, globular heart (Longmore et al 2004)

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.

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 patient 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. This involves the insertion of a needle through the skin and into the pericardium, and aspirating fluid. 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 patient, surgery is provided to seal the source of the bleed and mend the pericardium.

See also

References

External links

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