What is Cardiac Tamponade?
Cardiac tamponade is the compression of the heart through infiltration of fluid in the pericardial sac. The pericardial sac surrounds the heart and allows the heart to expand and pump with ease. When blood, pus, or fluid enters this sac, it can compress the heart and keep it from pumping as easily as it should. If the fluid collects over time, the sac can actually expand to accommodate quite a bit of fluid; however, if it happens immediately, the pericardial sac will not be able to hold much more than 100 ml of fluid.
As the fluid builds, it compresses the heart until it cannot beat. This leads to decreased cardiac output, loss of perfusion and, eventually if not treated, cardiac arrest. Unfortunately, cardiac arrest cannot be reversed unless the tamponade is relieved, and this usually doesn’t happen unless there is surgical intervention. The most common causes of tamponade are trauma and cardiac rupture. Following heart surgery, the risk of tamponade is much higher and patients should be monitored closely to ensure that the sac does not begin to fill. Progressive tamponade can progress slowly for a time, but it will eventually require treatment. Sudden tamponade is a medical emergency and must be dealt with immediately.
There are not many conditions that can cause a slow pericardial effusion. One of these is hypothyroidism, and sometimes the pericardial sac can expand to hold over a liter of fluid when the accumulation is slow. The most common reason for cardiac tamponade is penetrating trauma. This can occur to the heart itself or the vessels serving the heart. The blood floods into the sac and causes compression of the heart. Blunt trauma to the chest can also cause a cardiac tamponade, so all trauma patients presenting with trauma to the trunk should be screened for this condition.
Another possible cause is cardiac rupture. It is an uncommon cause of tamponade and can occur after an MI weakens the heart muscle. Patients on anticoagulant therapy are also at risk for tamponade due to the possibility of excess bleeding inside the pericardial sac. Pericarditis, uremia, and some forms of cancer are other infrequent causes of this condition. Those who undergo cardiac surgery should be monitored for 48 hours afterwards to ensure that the vessels do not bleed into the pericardial sac. The act of manipulating the heart during surgery can sometimes lead to bleeding that can compress the heart. Although it is usually blood that causes tamponade, pus is another possible cause of tamponade.
It is difficult to diagnose cardiac tamponade because it has so many differential diagnoses. For instance, tension pneumothorax can mimic some of the symptoms of cardiac tamponade. One way to determine that this condition is present is by looking for Beck’s triad. Hypotension is the first sign, but it is not related to hypovolemia. Jugular venous distention is often noted as the veins begin to back up. Finally, muffled heart sounds are heard when auscultating the chest. This is because the fluid present decreases the conduction of the sound of the heart beating.
Other signs may be noted, including pulsus paradoxus, which is a decrease of at least 10 mm Hg in arterial blood pressure when the patient inhales. In addition, an EKG will reveal ST wave changes and low voltage QRS complexes. Of course, signs of shock can also be present. Symptoms such as tachycardia, loss of consciousness, and difficulty breathing are quite common with this condition, although they may be misinterpreted as signs of some other condition. An echocardiogram can show the fluid around the heart and provide a more definitive diagnosis.
Treatment for cardiac tamponade may start in the pre-hospital environment. Unfortunately, paramedics cannot do very much to treat this condition in the field. Usually, treatment involves managing hypotension and shock symptoms, then transporting the patient to the hospital as quickly as possible. Some pre-hospital units are outfitted with the equipment to perform a pericardiocentesis, but this is not common. This procedure involves inserting a large needle into the pericardial sac using anatomical markers to evacuate the fluid. It is dangerous and not commonly performed, but it is sometimes the only treatment that can be performed to save the patient’s life when cardiac tamponade is acute and is threatening the patient’s life.
In the hospital, treatment is more aggressive. Pericardiocentesis is the first line of treatment; a cannula is placed to help evacuate more fluid should it continue to accumulate. Although landmarks can help in the placement of this cannula, it is far more safe and accurate when inserted under the guidance of ultrasound. If the facilities are available, a pericardial window can be surgically performed, permitting the drainage of fluid. When the cause of the tamponade is found, the window can be closed surgically. Post- open heart patients will need immediate surgery to evacuate the fluid. A decrease in chest tube secretions after these procedures can indicate that a tamponade is developing.