Linear variation analysis of intracardiac atrial impedance during internal cardioversion using rectilinear waveforms and energy step up protocol.

The major determinants of success during internal cardioversion of atrial fibrillation (AF) are voltage, duration and intracardiac impedance (ICI). However, there is a paucity of published data regarding evidence of ICI dynamics during internal cardioversion of AF using very-low-tilt rectilinear (VLTR) waveforms with stepped energy protocols. In this study, patients with persistent AF were internally cardioverted using both biphasic and monophasic very-low-tilt rectilinear (B-VLTR and M-VLTR) waveforms with a step up energy protocol (50V to 300V). The ICI of patients who had more than 4 shocks delivered were retrospectively analyzed from recorded voltage and current waveforms. A significant reduction in ICI was noticed after each of the first shocks using B-VLTR. The linear change of ICI within a shock, as characterized by its slope (Zm), increased in algebraic value and presented polarity reversal between the positive and negative phase within a B-VLTR shock, particularly after the first shock, where both B-VLTR and M-VLTR presented positive 2nd derivatives. The results obtained provide valuable evidence for understanding electrode-tissue interface factors depending on VLTR defibrillation waveform amplitude, duration and current reversal action.