ABSTRACT
Mapping the myocardial electric field during a defibrillation pulse requires the recording of potential differences between electrodes. The field is then calculated from these quantities and the corresponding calibration matrix. One straightforward calibration technique involves alignment of a known electric field along each of the orthogonal axes of an electrode array and recording the resulting potential differences. However, no results have been reported to support the efficacy of this technique. This study performs a detailed error analysis including a one-to-one comparison to a precision calibration technique, and quantitatively establishes the efficacy of the orthogonal field technique.
Subject(s)
Electromagnetic Fields , Electrophysiologic Techniques, Cardiac/standards , Heart/physiopathology , Calibration/standards , Electric Conductivity/therapeutic use , Electric Countershock/methods , Electric Countershock/standards , Electrodes , Electrophysiologic Techniques, Cardiac/methods , Humans , Reference Values , Research DesignABSTRACT
The design of a calibrated resistive-network current divider for precision current delivery during transthoracic defibrillation shocks is presented together with test results. The current divider presents a constant 50-ohm load to the defibrillator and thus maintains a constant pulse shape. Current is selected before the shock by setting three rheostats using a computer-generated calibration table. Following each shock, the data acquisition and display software updates the calibration table based on the measured value of transthoracic resistance. Over a range of 15-27 A, the root-mean-square (rms) error for delivered versus selected current was 0.48% for a 45-ohm resistive load, and 0.71% for a 100-ohm load. These test results were confirmed by animal experiments. Over 3 dogs, the rms error was 0.49% from 15-27 A and not greater than 1.5% over the entire 8-44 A range.
Subject(s)
Defibrillators , Electronics, Medical , Energy Transfer , Calibration , Electric Impedance , Equipment Design , Equipment Failure Analysis , Humans , Thorax/physiopathologyABSTRACT
In an earlier study, the authors presented a calibration technique for a triaxial bipolar electrode array (EA) that used 72 data points collected during a global sweep of the electric field vector relative to the EA axes. Although necessary for the initial characterization of the EAs, this data requirement has to be significantly reduced for the technique to become a practical tool. Therefore, in the present study, an analysis is performed to determine the relation between the number of data points used in the calibration and the mean root-mean-square error. The analysis shows that 18 data points can produce results nearly identical to those obtained with the 72-point calibration, thus reducing the required amount of data fourfold.
