Radiofrequency multielectrode catheter ablation in the atrium

We developed a temperature-controlled radiofrequency (RF) system which can ablate by delivering energy to up to six 12.5 mm long coil electrodes simul taneously. Temperature feedback was obtained from temperature sensors place d at each end of coil electrodes, in diametrically opposite positions. The coil electrodes were connected in parallel, via a set of electronic switche s, to a 150 W 500 kHz temperature-controlled RF generator. Temperatures mea sured at all user-selected coil electrodes were processed by a microcontrol ler which sent the maximum value to the temperature input of the generator. The generator adjusted the delivered power to regulate the temperature at its input within a 5 degrees C interval about a user-defined set point. The microcontroller also activated the corresponding electronic switches so th at temperatures at all selected electrodes were controlled within a 5 degre es C interval with respect to each other. Physical aspects of tissue heatin g were first analysed using finite element models and current density measu rements. Results from these analyses also constituted design input. The per formance of this system was studied in vitro and in vivo. In vitro, at set temperatures of 70 degrees C, 85% of the lesions were cont iguous. All lesions created at set temperatures of 80 and 90 degrees C were contiguous. The lesion length increased almost linearly with the number of electrodes. Power requirements to reach a set temperature were larger as m ore electrodes were driven by the generator. The system impedance decreased as more electrodes were connected in the ablation circuit and reached a lo w of 45.5 Omega with five coil electrodes in the circuit. In vivo, right atrial lesions were created in eight mongrel canines. The po wer needed to reach 70 degrees C set temperature varied between 15 and 114 W. The system impedance was 105 +/- 16 Omega, with one coil electrode in th e circuit, and dropped to 75 +/- 12 Omega when two coil electrodes were sim ultaneously powered. The length and the width of the lesion set varied betw een 17.6 +/- 6.1 and 59.2 +/- 11.7 mm and 5.9 +/- 0.7 and 7.1 +/- 1.2 mm re spectively. No sudden impedance rises occurred and 75% of the lesions were contiguous. From the set of contiguous lesions, 90% were potentially therap eutic as they were transmural and extended over the entire target region. T he average total procedure and fluoroscopy times were 83.4 and 5.9 min resp ectively. We concluded that the system can safely perform long and contiguo us lesions in canine right atria.