LACK OF EVIDENCE OF AREAS OF SLOW CONDUCTION EARLY AFTER RADIOFREQUENCY CURRENT APPLICATION AT PORCINE ATRIAL MYOCARDIUM

Electrophysiological sequelae after creation of atrial myocardial lesi ons by radiofrequency current (RFC) application have not been studied in vitro. During general anesthesia, a steerable 6 French electrode ca theter, equipped with or thermistor at the 4-mm tip electrode, was pos itioned at the lateral atrial aspect of the tricuspid valve annulus in 5 piglets (German Landrace, mean body weight 22.5 kg). Temperature-gu ided (75 degrees C) RFC (500 kHz) was delivered over 30 seconds. Forty -eight hours later, the hearts were removed and placed in ice-cold Tur ner's solution. The right atria were dissected, and the RFC lesions wi th surrounding tissue were cut out and transferred to an organ bath ac cording to Steiert. Preparations were superfused with Turner's solutio n at 37 degrees C. Pacing of the viable tissue at the border of the pr eparations was accomplished at a cycle length of 500 ms. Whole atrial preparations were impaled (76 to 150 impalements per specimen) with KC I capillary microelectrodes containing 3 MKCl. In the surrounding viab le tissue of the five preparations, mean maximum diastolic transmembra ne potential ranged from -61.3 to -63.7 mV, mean action potential dura tion at 90% repolarization ranged from 135.2 to 156.1 ms, and mean max imum upstroke velocity of phase 0 of the action potential was between 104.7 and 112.9 V/sec. Statistical analysis revealed no significant di fferences among all 3 variables. No intracellular action potential was recorded from the surface of all 5 lesions. The surrounding tissue wa s sharply demarcated, with unaltered transmembrane action potential ch aracteristics 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 techniqu e is safe regarding occurrence of atrial tachyarrhythmias.