Session P85.1

Design of Bioimpedance Monitor and Its Application to Atrioventricular Delay Optimization

V Vondra*, I Viscor, J Halamek, P Jurak

Institute of Scientific Instruments
Brno, Czech Repub.

The impedance cardiography (ICG) measures the impedance changes in the thorax to calculate the stroke volume or the cardiac output respectively as the final quantity. We concentrate on analyzing the cardiovascular system properties, and developing new noninvasive diagnostic methods. For this purpose we need a good-quality continuous signal of the stroke volume derived from ICG which can be measured together with other biological signals (ECG, breathing, blood pressure, phonocardiogram, etc.).
In the paper we introduce our conception of a bioimpedance monitor for the ICG. We describe the design of a device (ISI BM1.2)which is based on a direct digital synthesizer and a digital down converter. This solution enables us to obtain a high-quality bioimpedance signal, which can be used for computing the cardiac output beat per beat. It further enables us to analyze the impedance phase changes beat per beat. The setting of the main parameters of the measurement like the amplitude and the frequency of the measurement current depends on the user.
The testing of the functionality of our device was made in a pilot study of optimization of the atrioventricular (A-V) delay in patients with implanted pacemakers. The A-V delay is one of the important parameters of heart pacing during the cardiac resynchronization therapy. A suboptimal A-V delay setting could lead to a significant decrease of the cardiac output (CO). The second aim of this study was to test and verify the ICG based method to optimize the AVD setting for the clinical practice.
We tested a group of 26 patients with implanted pacemakers in the DDD mode. In our result we have found that proper A-V delay setting with respect to CO by ICG based method is essential in 62% of patients while the rest part is not sensitive to its setting. At the same time we proved the proper design of our bioimpedance monitor and its quality in clinical use.

(Abstract Control Number: 261)