The biophysics of radiofrequency catheter ablation in the heart: the importance of temperature monitoring.

Radiofrequency (RF) catheter ablation is a technique whereby high frequency alternating electrical current with frequencies of 350 kHz to 1 MHz is delivered through electrode catheters to myocardial tissue creating a thermal lesion. The mechanism by which RF current heats tissue is resistive (or ohmic) heating of a narrow rim (< 1 mm) of tissue that is in direct contact with the electrode. Deeper tissue planes are then heated by conduction from the small region of volume heating. Heat is dissipated from the region by further heat conduction into normothermic tissue, and by heat convection via the circulating blood pool and larger coronary vessels. The lesion size is proportional to the temperature at the electrode-tissue interface (which is also a function of power level if electrical factors remain constant), and to the size of the electrode. At temperatures above 100 degrees C, boiling occurs at the electrode-tissue contact point resulting in a rapid rise in electrical impedance. Therefore, a theoretical maximum lesion size exists for any given electrode geometry. Other factors that are important for RF lesion formation include electrode-tissue contact pressure and duration of RF delivery. Temperature rises monoexponentially, and duration of energy delivery should be at least 35 to 45 seconds to approach steady state.