Late Fractionated Potentials and Continuous Electrical Activity Caused by Electrode Motion

Late fractionated potentials, recorded during cardiac mapping to find the source of a ventricular arrhythmia, have been ascribed particular localizing value. Re-entry is assumed when these highly amplified and filtered recordings span diastole during tachycardia. The purpose of this study was to see if such potentials can occur artifactually. A saline soaked 7 X 2 X 3 cm sponge was sewn to the epicardium of the right ventricle in five non-infarcted, open-chest dogs. Two bipolar button electrodes, one with 1 mm and one with 1 cm interelectrode spacing, were attached to the outer surface of the sponge and a bipolar wire hook electrode was placed just under the outer surface of the sponge. Thus all three electrodes were 3 cm from the nearest myocardium yet still subjected to cardiac motion. The electrodes were recorded at gains of 4,000-40,000 and filtered to pass 50-300 hertz. One to three rapid deflections were recorded during the QRS from all electrodes. In seven of the the 15 electrode recordings, two or three additional deflections, 1100-200 microV in amplitude, occurred after the QRS. These late potentials were fractionated and recurred reproducibly from cycle to cycle. In two cases, these late fractionated potentials could be made to span diastole by rapid pacing to simulate tachycardia. Clamping the sponge to sliminate motion between the sponge and electrode caused this late activity to disappear. Thus, in highly amplified and filtered recordings, electrode motion can cause artifacts resembling late fractionated potentials and continuous electrode activity.