Assessing acute ventricular volume changes by intracardiac impedance in a chronic heart failure animal model.

Background: Implantable device diagnostics may play an essential role in simplifying the care of heart failure patients by providing fundamental insights into their complex clinical patterns. Early recognition of heart failure progression by a continuous hemodynamic monitoring would allow for timely therapeutic interventions to prevent decompensation and hospitalization. In this study, the feasibility of assessing ventricular volume changes by implant-based measurements of intracardiac impedance was tested in a heart failure animal model.

Methods: Heart failure was induced in five minipigs by high-rate pacing over 3 weeks. During a final open-chest examination a graded dobutamine stress test was performed. Stroke volume (SV) was measured by an ultrasonic flow probe at the ascending aorta. End diastolic pressure (EDP) and maximum pressure slope (dP/dtmax) were calculated from a left ventricular microtip catheter signal. Impedance was measured by an implanted pacemaker between biventricular leads. Stroke impedance (SZ) was calculated as the difference between end-systolic and end-diastolic impedance (EDZ).

Results: Administration of dobutamine led to an increase in SV (55+/-16%), dP/dtmax (107+/-89%), and SZ (56+/-30%). EDP changed by 37+/-21% whereas EDZ changed by 7.4+/-4%. Significant correlations were found between SZ and SV (r=0.88), and between EDZ and EDP (r=-0.82).

Conclusion: The strong correlation with SV allows the application of intracardiac impedance measurements for an implant-based continuous monitoring of cardiac function. Impedance may also be used for hemodynamic optimization of cardiac resynchronization therapy.