CYCLIC IMPEDANCE FLUCTUATION IN RIGHT AND LEFT VENTRICLE

Purpose. Studying the relationship between cardiac activity and cyclic impedance changes in right and left ventricle (RV, LV), to search for new markers of mechanical synchronization.

Methods. The study was performed in 28 patients undergoing the implantation of a biventricular pacing system for standard indications. Screw-in RV leads were positioned in mid septum; coronary sinus leads of different types were used for transvenous LV stimulation. During the implantation procedure, impedance was sampled at 1 KHz along the cardiac cycle in bipolar configuration, keeping the atrial ring electrode as a constant reference for the RV and LV tip and ring electrodes, all tested in sequence. Thereafter, a permanent biventricular pacemaker equipped for high-resolution impedance recording (Helios 300, Medico) was implanted, connecting the impedance sensor to the LV lead.

Results. The impedance assessed by endocardial electrodes in RV (transvalvular impedance: TVI) always featured an increase in systole (71±47 and 49±27 Ohm, with RV tip and ring electrodes, respectively). In contrast, when the impedance was recorded in LV by epicardial transvenous electrodes (LVI), a marked systolic reduction was noticed (-54±29 and -36±9 Ohm, with LV tip and ring electrodes, respectively). TVI and LVI featured similar time-course, although the whole LVI waveform was delayed in the presence of LBBB or RV pacing. In case of LV stimulation, LVI started to decrease immediately after the pacing spike. 

Conclusion. TVI and LVI fluctuation is likely the expression of RV and LV contraction and relaxation. The comparative evaluation of both the waveforms could provide insight into the effects of biventricular pacing on the mechanical synchronization and be helpful in setting the stimulation timing.