Impedance sensor for assessing cardiac hemodynamics

A method for beat-to-beat assessment of left ventricular volume changes by means of intracardiac impedance measurement is presented. Efficient heart failure therapy requires close monitoring of the patientpsilas hemodynamic state. Implantable devices for cardiac resynchronization therapy comprise at least one lead placed in the apex of the right ventricle (RV) and a second one in a coronary vein at the left ventricle (LV). Between the RV and LV bipolar leads transfer impedance Z₂₁ is determined by injecting a sub-threshold current via the RV lead and measuring the voltage at the LV lead. Z₂₁ varies according to LV contraction during heart cycle. Thus LV volume variation can be determined without additional sensors. The potential to assess hemodynamic parameters like stroke volume with this method was demonstrated in an acute animal study. The hemodynamic performance of the heart can be detected by the impedance sensor integrated into an implantable electrotherapeutic device and used for disease monitoring and automatic optimization of therapy parameters.