Cardioversion is usually performed when medications have failed to restore a patient's abnormal rhythm back to a normal sinus rhythm. External cardioversion is performed by delivering high-energy shocks of 50 to 300 joules through two defibrillator pads attached to the chest, to convert an abnormal heart rhythm back to normal.
Internal cardioversion is performed by delivering a low-energy electrical shock internally to the heart through two catheters inserted in a vein in the groin or neck and an electrode pad applied to the chest. This is done in some cases when external cardioversion has failed because the electrical current cannot travel through chest muscle and skeletal structures with enough energy to reach the heart.
At UC San Diego Health System, these procedures are performed in our electrophysiology lab by a trained electrophysiologist. Both external and internal cardioversion are done after short-acting sedatives are given to help you relax and sleep during the procedure.