Abstract 2396: Device-Based Heart Failure Management: Multi-Frequency Impedance Measurements to Optimize Intrathoracic Fluid Monitoring
Introduction: Recently, it was shown that continuous implant-based measurements of intrathoracic impedance (Z) as a surrogate measure of intrathoracic fluid status allows detection of cardiac decompensation in heart failure patients. However, sensitivity and specificity of current warning systems have to be optimized. In this study, a novel multi-frequency approach for measuring Z was tested and compared to standard methods regarding the evaluation of pulmonary fluid overload.
Methods: Pulmonary congestion was induced in 12 anesthetized sheep by a combination of hypervolemia and increased peripheral arterial resistance. A PiCCOplus monitor was used for continuous hemodynamic monitoring, including mean arterial blood pressure (MABP) and extravascular lung water index (EVLWI) assessed by transpulmonary thermodilution. Aditionally, left ventricular end diastolic pressure (LVEDP) was also assessed. Both a pacemaker and an external network analyzer were used to measure Z between the implanted device case and the coil of a right ventricular ICD lead in a frequency range of 200 Hz up to 1 MHz.
Results: All animals developed inclining pulmonary fluid overload leading to severe cardiac pulmonary edema. MABP increased from baseline values of 49 ± 8 to final values of 144 ± 35 mmHg, followed by a steady rise in LVEDP from 6 ± 3 to 30 ± 8 mmHg. Thermodilution confirmed an increase of EVLWI from 10 ± 1 ml/kg at baseline to 21 ± 5 ml/kg at end-stage. Reciprocals of Z showed a corresponding increase ranging from + 27% to + 40%, depending on the applied excitation frequency. By analyzing the differences of the Z reciprocals from a low and a high frequency (multi-frequency approach) better correlations (r = 0.862) were yielded, when compared to the standard mono-frequency approach (r = 0.829), due to the observed frequency dependence of impedance.
Conclusions: Our data suggest suggest that a multi-frequency approach used for continuous implant-based measurement of Z as a surrogate for intrathoracic fluid status has the potential to improve corresponding warning systems in order to detect early stages of cardiac decompensation.A combination of these device-based features with existing telemedicine concepts has a tremendous potential to improve outpatient HF management.