PHYSICAL PRINCIPLES OF RADIOFREQUENCY CUR RENT ABLATION

Radiofrequency currents are the reference physical agent for endocavit ary ablation, especially of supraventricular tachycardias. They are de livered in a continuous mode or sinusoidal waves. Because of the high frequency between 200 and 3,000 kHz there is no stimulation of the neu romuscular cells. The mechanism of the resulting lesion is essentially related to heating of the biological surroundings of the active elect rode. The temperature increase remains localised around the active ele ctrode and its kinetics are progressive, which implies close and stabl e contact between the active electrode and the tissues. The lesional e ffect is obtained 60 to 90 degrees C in order to avoid the deleterious effects induced by temperatures of over 100 degrees C : boiling, coag ulation, vaporization and carbonization of the tissues leading to an I ncrease in impedence. The volume of lesions depends on many factors wh ich are sometimes difficult to control in vivo. It is more closely cor related to the temperature of the active electrode than to the paramet ers of delivery (power, duration...). The histological lesions corresp ond to scar tissue which respects the surrounding architecture. The ma jor technological innovations of this method have resulted in an incre ase in the volume of the lesions produced, a reduction in the frequenc y of undesirable effects such as the formation of coagulum and in an i mmediate evaluation of the anatomic lesional effect. They have consist ed in the introduction of specific electrodes and of systems of monito ring the electrical and thermal effects with the use of imaging techni ques such as endovascular and transoesophageal echocardiography and an gioscopy. New indications will require development of specific cathete r-generator equipment to create lesions of size and shape adapted to t he arrhythmogenic substrate.