In addition to sensing electrical activity within the heart, the electrodes are able to deliver low-level electrical current to heart muscle, much as a pacemaker does. This capability to stimulate the heart allows the specialists to reproduce the rhythm abnormality in a controlled setting of the electrophysiology laboratory. There, too, doctors can test the effects of various medications with a relative degree of safety. Typically, the electrophysiology specialists will provoke the arrhythmia and then give the patient a selected drug. Afterward, if they are unable to provoke the abnormal rhythm while the patient is medicated, the drug has a high likelihood of preventing the problem under everyday circumstances.
Electrophysiologic testing is conducted in a catheterization or electrophysiology laboratory.
The lab will be equipped with recording and stimulating devices, imaging equipment to check placement of the electrodes, and defibrillating devices in case complications arise. A cardiologist specially trained in the technique and an assistant will perform the testing, with the help of a nurse anesthetist and one or more other technicians. The procedure can take as long as two or three hours, depending on what the cardiologist finds and how many medications are tested. Less complex cases may be completed in under an hour. As with other procedures involving catheterization, the patient usually remains awake but mildly sedated during the testing.