Modelling of myocardial temperature distribution during radio-frequency ablation

RADIO-FREQUENCY (RF) energy has been used to 6reate small and focused lesions since 1934 (BROWN and HENRY, 1934), and it has recently become the preferred type of electromagnetic energy for the percutaneous catheter ablation of some arrhythmogenic substrates (SCHLI]TER et al. 1991; JACKMAN et al., 1991; KLEIN et al., 1992). Before it became a widespread clinical tool (SCHEINMAN, 1992), RF ablation had been the subject of experimental studies using in vitro (HAINES and WATSON, 1989; HINDRICKS et aL, 1989; BLOUIN and MARCUS, 1989) and in vivo preparations (W[TTKAMPF et al., 1989; BARDY et aL, 1990; LANGBERG et al., 1990). These experiments investigated various factors that determine lesion size, such as electrode size, RF power, duration of RF exposure, peak tissue temperature (HAINES and VERROW, 1990). However, theoretical studies on the distribution of current and temperature around the tip of an RF catheter are still scarce. Haines and Watson developed an analytical model in which the RF electrode was represented by a conducting sphere at the centre of a medium with homogeneous electrical and thermal conductivities (HAINES and WATSON, 1989). More recently, Labont6 developed an inhomogeneous model and investigated the cooling effect of intracavitary blood flow, the increased efficacy of power modulation and the heat sink effect of the catheter electrode (LABONTg, 1992). The main objective of this study is to develop a realistic model of RF myocardial heating. This model will be used to determine the temperature at any point around the electrode, the sensitivity to parameters such as thermal conductivity and electrode size, the influence of the location of the passtive electrode and the interelectrode distance in bipolar catheters. Such a modelling approach can help to optimise catheter design and investigate new applications for RF catheter ablation. 2 Theoretical analysis and modelling

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