Abstract 1865: Assessing Acute Left Ventricular Volume Changes by Intracardiac Impedance in a Heart Failure Pig Model
Introduction. It is essential to reliably assess the hemodynamic state of the circulatory system within implantable devices. There are manifold potential applications like early detection of decompensation or discrimination of arrhythmias. Furthermore, it is highly desirable to continuously monitor and optimize the success of cardiac resynchronization therapy (CRT) for heart failure (HF) patients. Automatic optimization of device parameters, especially atrioventricular (AV) and interventricular (VV) delay would significantly enhance the benefit of CRT and may reduce the number of non-responders. The objective of this animal study was to test the feasibility of measuring intracardiac impedance (Z) with an implantable device as a surrogate measure of left ventricular (LV) volumechanges.
Methods. HF was induced in 6 minipigs by high rate pacing (max. 235±12 ppm) over a echo-controlled period of 3 weeks (21±4 days). During a final open-chest examination, the hemodynamic state was altered using a graded dobutamine stress test. Stroke volume (SV) was calculated from aortic blood flow measured by an ultrasonic flow probe. End diastolic pressure (EDP) and maximum pressure slope (dP/dtmax) were calculated from LV pressure measured by use of a microtip catheter. Z was measured by an implanted pacemaker between a bipolar right ventricular lead and an epicardial bipolar LV lead. SV and EDP were correlated with stroke impedance (SZ) and end diastolic impedance (EDZ).
Results. The minipigs showed a poor LV function at HF state (mean ejection fraction was reduced by 33 %, mean EDP increased by 198 %). The acute dobutamine stress test at open-chest provoked a rise in SV by 55±16 % and in dP/dtmax by 99±82 %. EDP varied by 31±22 % during the protocol. A significant correlation between SV and SZ was found (mean r=0.88, p<0.001). Furthermore, EDP correlated inversely with EDZ (mean r=−0.82, p<0.001).
Conclusions. Changes of intracardiac impedance show a strong correlation with changes in stroke volume. This allows the application of intracardiac impedance measurement for continuously monitoring the hemodynamic state within CRT devices. Hence, intracardiac impedance might be used as a control parameter for automatic optimization of device parameters, e.g. AV and VV delay.