Lack of evidence of areas of slow conduction early after radiofrequency current application at porcine atrial myocardium.

Electrophysiological sequelae after creation of atrial myocardial lesions by radiofrequency current (RFC) application have not been studied in vitro. During general anesthesia, a steerable 6 French electrode catheter, equipped with a thermistor at the 4-mm tip electrode, was positioned at the lateral atrial aspect of the tricuspid valve annulus in 5 piglets (German Landrace, mean body weight 12.5 kg). Temperature-guided (75 degrees C) RFC (500 kHz) was delivered over 30 seconds. Forty-eight hours later, the hearts were removed and placed in ice-cold Turner's solution. The right atria were dissected, and the RFC lesions with surrounding tissue were cut out and transferred to an organ bath according to Steiert. Preparations were superfused with Turner's solution at 37 degrees C. Pacing of the viable tissue at the border of the preparations was accomplished at a cycle length of 500 ms. Whole atrial preparations were impaled (76 to 150 impalements per specimen) with KCl capillary microelectrodes containing 3 MKCl. In the surrounding viable tissue of the five preparations, mean maximum diastolic transmembrane potential ranged from -61.3 to -63.7 mV, mean action potential duration at 90% repolarization ranged from 135.2 to 156.1 ms, and mean maximum upstroke velocity of phase 0 of the action potential was between 104.7 and 112.9 V/sec. Statistical analysis revealed no significant differences among all 3 variables. No intracellular action potential was recorded from the surface of all 5 lesions. The surrounding tissue was sharply demarcated, with unaltered transmembrane action potential characteristics in the vicinity of the lesions. Areas of slow conduction were not observed. Lack of evidence of areas of slow conduction after RFC application to the atrial myocardium may imply that this technique is safe regarding occurrence of atrial tachyarrhythmias.