A simple, wide bandwidth, biopotential amplifier to record pacemaker pulse waveform

Abstract

Reliable detection of pacemaker pulses is getting more and more important in electrocardiography (ECG) diagnosis. Many studies recommend ECG amplifiers with higher bandwidth to prevent errors. In the past, few pilot studies showed that analysis of pacemaker pulses waveform can enhance diagnosis (eg, lead failure and fractured wire), but they were carried out with inadequate instrumentations for clinical practice. Typically, pacemaker pulses last hundreds of microseconds, edges of pulses elapse in few microseconds, and amplitude may exhibit large variations from few millivolts to volts. Pulse waveforms change often and depend on pacemaker type and programming. A simple, biopotential amplifier made of a few off-the-shelf components is proposed. The circuit fulfills specifications for biopotential amplifiers and offers a large bandwidth (~1 MHz). Therefore, it is able to accurately record time course of pacemaker pulses and allows highly accurate pulse detection and timing. Signals can be easily displayed and acquired by means of a standard, battery-powered oscilloscope. Pacemaker pulse vectorcardiography can be obtained by using two or more, wideband channels. Some exemplificative waveforms recorded during patient's periodic medical examination are reported. The proposed circuit offers simultaneous conventional ECG signal as an additional output.

Keywords: electrocardiography device; pacemaker pulse waveform; wideband biopotential amplifiers.

Figure 1

Schematic of the wideband biopotential amplifier. Abbreviations: ECG, electrocardiography; RL, right leg; R_p, protection resistors (1.1 kΩ); R_g, instrumentation amplifier gain resistor (180 kΩ); C₁ =4.7 mF, R₁ =3.3 MΩ, passive high-pass filter; C₂ =10 nF, R₂ =100 kΩ, active low-pass filter; R₃, active filter gain resistor (1 kΩ).

Figure 2

Lead I and lead II pacemaker waveform and the corresponding vectorcardiogram Notes: (A) An example of monopolar pacemaker waveforms recorded from ECG lead I (upper trace) and from ECG lead II (lower trace). (B) Frontal plane vectorcardiogram of the pacemaker pulse. Abbreviation: ECG, electrocardiography.

Figure 3

An example of a monopolar pacemaker waveform recorded from ECG lead I. Abbreviation: ECG, electrocardiography.

Figure 4

An example of a bipolar pacemaker waveform recorded from ECG lead I. Abbreviation: ECG, electrocardiography.

Figure 5

Waveform of a monopolar pacemaker with a defective output circuit. Note: The image shows the abrupt disruption of the proper exponential decay signal.