ISSN:
1741-0444
Keywords:
Electrogram
;
Frequency analysis
;
Nonlinear regression analysis
;
Pacemaker electrode impedance
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Abstract The signal source impedance Z of implanted pacemaker electrodes plays an important role for adequate sensing of electrogram signals and has so far been little explored. A frequency-domain method for thein vivo calculation of Z is described. Electrogram signals picked up between two electrodes were recorded unloaded, and loaded with resistors and capacitors, then amplified, and stored on magnetic tape. After time sampling and a.d. conversion, the signals were read into a digital computer as discrete time vectors with 2P samples. Each vector was subjected to a fast Fourier transform (f.f.t.), and the ratio H(jωi) between the transformed loaded and unloaded vectors was calculated. For the electrode impedance Z a linear model was chosen that consisted of the tissue and electrode resistance RT, in series with a parallel coupling between Faraday resistance RF, and Helmholtz capacitance CH. By nonlinear regression analysis the parameters (∧) in this model were estimated from the ratios H(jjωi) obtained in patients with permanent pacemaker electrodes, and in patients with temporary multicore wire electrodes after open heart surgery. As an estimate for RT was also used the voltage/current ratio R′T, 90 μs into the stimulation pulse from an external variable parameter pulse generator. The 3-component impedance model described the essential features of the electrode impedance in the frequency range up to 100 Hz. It was found that ĈH, decreased slightly with increasing frequency, and that ŘT in general was larger than R′T. A modified model with frequency dependent parameters was found to obtain a better approach to the experimental data.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02443299
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