TRANSVALVULAR IMPEDANCE RECORDING IN THE ASSESMENT OF VENTRICULAR MECHANICS IN CARDIAC RESYNCHRONIZATION THERAPY

Aim of the study:
Electric impedance fluctuation during the cardiac cycle is modulated by structural and volumetric modifications occurring at every beat and can be detected by standard pacing electrodes.Evaluating the impedance signals derived in two particular configurations: the Trans-Valvular Impedance (TVI, measured with endocardial electrodes positioned in right atrium and ventricle) and the Left-Ventricular Impedance (LVI, measured between the electrodes in right atrium and one trans-venous electrode on the left ventricle).
Methods:
TVI and LVI were derived by an external recorder on implantation and then by the implanted pacemakers in the follow-up (Sophòs 155 and Helios 300, Medico, Italy). Standard screw-in leads were used for endocardial placement in righ heart; different types of unipolar or bipolar leads were applied for trans-venous LV stimulation.
Results:
On implantation, a physiological TVI waveform (increasing throughout the QT period and decreasing during passive an active filling) was recorded in 25 out of 27 cases, respectively, with apical and septal position. The two patients who did not show a normal TVI waveform featured the lowest EF in the group. Ventricular stimulation affected the TVI signal, inducing amplitude reduction and extra-peaks. Such alterations were more frequently observed with apical than septal pacing (38% vs 17% of the cases). The LVI waveform was characterized by a marked decrease in systole (-4824 Ohm in 10 cases), with time-course similar to TVI in presence of good interventricular synchronization and delayed in case of LBBB or RV pacing.  The individual waveform shape was stable during 12 M follow-up.

Conclusions:
TVI and LVI are expression of RV and LV mechanical activity and could be in the future applied together with other parameters to optimise both  LV lead position and pacemaker timing in CRT.