Thermal injury is the principal mechanism of tissue destruction during radiofrequency catheter ablation procedures. Elevation of tissue temperature results in the denaturation of proteins, evaporation of fluids with subsequent destruction of tissue, and coagulation of tissue and blood. When the temperature at the electrode-tissue interface exceeds 100 C, tissue immediately adjacent to the electrode desiccates, and plasma proteins denature to form a coagulum. Development of a coagulum results in a rapid increase in impedance, which leads to a dramatic decrease in current density, thereby limiting further lesion growth. Catheter ablation procedures are performed in a laboratory that is also equipped to perform electrophysiological tests.
Patients receive conscious sedation before and during the procedure.
Two to five multipolar electrode catheters are inserted percutaneously under local anesthesia into a femoral, brachial, subclavian, or internal jugular vein and positioned in the heart under fluoroscopic guidance. Each electrode catheter has four or more electrodes. Typically, the most distal electrode pair is used for pacing and for the delivery of critically timed extra stimuli, and the proximal electrodes are used to record electrograms from localized regions within the heart. Because of the critical importance of temperature during these procedures, recent advances in the design of radiofrequency catheter ablation systems allow for monitoring of electrode temperature and for automatic closed-loop control of power output to achieve targeted electrode temperatures. Knowledge of the electrode temperature at a particular ablation site is useful in determining whether an unsuccessful application of radiofrequency energy resulted from inaccurate mapping or inadequate heating.