Cardioversion

In order for the heart to work effectively, it needs to pump in a controlled and regular rhythm, with coordination between the atria and ventricles. If these cease to work in unison, then the result in the worst case scenario may be death, depending on the type of arrhythmia. Cardioversion is the procedure used to convert an abnormal heart rhythm or arrhythmia to a normal or sinus heart rhythm. There are two types of cardio-version: The first uses pharmacologic agents and the second uses direct current. Depending on the type of arrhythmia, the stable patient will usually be offered a pharmacologic agent prior to being offered electrical cardioversion. There are many antiarrhythmic pharmacologic agents that work by various mechanisms to try to modify the heart rhythm and return it to sinus. However, the term cardioversion usually refers to electrical cardioversion. This can be an emergency procedure on an unconscious patient in ventricular fibrillation (VF) or ventricular tachycardia (VT); this is called defibrillation. It can also be an elective procedure, referred to as direct current cardioversion, for a patient failing to respond to antiarrhythmic pharmacologic interventions or with a case of recent onset that may respond to a direct electrical shock.

The patient will be brought in as an elective day case and will be made nil by mouth. The patient will be put under general anesthesia and will be anesthetized for the whole duration. Two electrical pads are placed on the front of the chest under the right clavicle and on the back of the patient on the left side, or a wire can be passed into the heart and the heart is directly shocked.

The patient is under electrocardiogram (ECG) monitoring throughout and the pads are directly connected to a machine that delivers a certain amount of shock at the correct time according to the ECG. The electrical shock has to be delivered on the R-wave of the ECG; failure to do this may induce a ventricular arrhythmia that can be fatal. The energy level applied varies; 100 joules is used for atrial fibrillation and 200 joules for VF/VT.

Once the patient is ready to be shocked, the machine synchronizes and prepares to deliver the shock. The shock only lasts a few milliseconds. The heart momentarily stops and the hope is that it will be reset in normal sinus rhythm. Another shock can be given at a higher energy value if the heart is unresponsive. [Page 351]Following the shock, the patient will need to have ECG monitoring in recovery.

As with all procedures, there are some risks, the main one being dislodging emboli, which may travel in the arterial system to the brain and lead to a stroke. Therefore, only new onset arrhythmic patients are offered cardioversion. The patient will usually be followed up to ensure that there are no adverse complications and to make certain that they do not become arrhythmic once again, which is also a known risk.