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. 2018 Aug 18;18(8):2715.
doi: 10.3390/s18082715.

A Contactless Sensor for Pacemaker Pulse Detection: Design Hints and Performance Assessment

Emilio Andreozzi  1   2 , Gaetano D Gargiulo  3 , Antonio Fratini  4 , Daniele Esposito  5 , Paolo Bifulco  6   7
Affiliations

A Contactless Sensor for Pacemaker Pulse Detection: Design Hints and Performance Assessment

Emilio Andreozzi et al. Sensors (Basel). .

Abstract

Continuous monitoring of pacemaker activity can provide valuable information to improve patients' follow-up. Concise information is stored in some types of pacemakers, whereas ECG can provide more detailed information, but requires electrodes and cannot be used for continuous monitoring. This study highlights the possibility of a continuous monitoring of pacemaker pulses by sensing magnetic field variations due to the current pulses. This can be achieved by means of a sensor coil positioned near the patient's thorax without any need for physical contact. A simplified model of coil response to pacemaker pulses is presented in this paper, along with circuits suitable for pulse detection. In vitro tests were carried out using real pacemakers immersed in saline solution; experimental data were used to assess the accuracy of the model and to evaluate the sensor performance. It was found that the coil signal amplitude decreases with increasing distance from the pacemaker lead wire. The sensor was able to easily perform pacemaker spike detection up to a distance of 12 cm from the pacemaker leads. The stimulation rate can be measured in real time with high accuracy. Since any electromagnetic pulse triggers the same coil response, EMI may corrupt sensor measurements and thus should be discriminated.

Keywords: coil sensor; pacemaker pulse; pacing monitor; personal healthcare device; pervasive patient monitoring.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure A1
Figure A1
Geometrical representation of the infinitely long current wire with a coil as seen from the top.
Figure 1
Figure 1
Schematic representation of the sensor operating principle.
Figure 2
Figure 2
Magnetic coupling of an infinitely long current wire with a coil.
Figure 3
Figure 3
(a) Waveform of the stimulation current; (b) waveform of the derivative of the stimulation current.
Figure 4
Figure 4
Electromotive force (EMF) pulse (blue line) and coil response (red line) obtained from a simulation of the equivalent RLC circuit model of the coil used for the experimental tests.
Figure 5
Figure 5
Measurement setup. (a) Top view; (b) side view.
Figure 6
Figure 6
Pick-up coil.
Figure 7
Figure 7
Amplifier circuit based on the INA217 instrumentation amplifier. The input loop is the RLC series circuit model of the coil, with a shunt capacitor to adjust the resonance frequency and a resistor to ground to bias the input of the amplifier. RG is the gain regulation resistor.
Figure 8
Figure 8
Schematic representation of the architecture proposed for the sensor.
Figure 9
Figure 9
Complete analog front-end schematic: the amplifier circuit feeds the amplified signal to the TLC3702, which compares it with the reference voltage, adjusted by the user with a potentiometer.
Figure 10
Figure 10
The assembled prototype of the sensor.
Figure 11
Figure 11
(a) Pulse waveform of St. Jude Medical™ Accent MRI pacemaker. It is possible to see a pair of negative falling edges. (b) Detail of pulse rising edge and relative coil response. (c) Detail of pulse falling edge and relative coil response. As expected, there is a pair of negative damped sine pulses corresponding to the pair of falling edges, i.e., two EMF negative pulses.
Figure 12
Figure 12
In the upper panel (blue line), the coil response acquired during the tests is shown. In the lower panel (red line), the coil response computed with the simulation is shown.
Figure 13
Figure 13
Comparison between experimental points and regression function curve.
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