Transvalvular impedance (TVI) recording under electrical and pharmocological cardiac stimulation.

The cardiac electric impedance was recorded between right atrium and ventricle, throughout the cardiac cycle, by means of a tripolar single pass lead for VDD pacing. The transvalvular impedance signal (TVI) is a sharp periodic wave, with high signal-to-noise ratio, that is detected exclusively in the presence of cardiac mechanical activity. The minimum TVI value is attained during the atrial systole, the maximum at the end of ventricular systole. Different parameters of TVI waveform are affected by changes in the inotropic state, and could therefore be proposed as potential signals for new rate responsive algorithms based on the correlation between inotropic and chronotropic regulation. The signal might be used, moreover, for pacing and sensing validation in autoregulating pacemakers and for fibrillation recognition in ICDs.