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Detecting, identifying cardiac-pacing artifacts

11 Jul 2013  | John Kruse, Catherine Redmond

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The pace-detection algorithm runs three instances of a digital algorithm on three of four possible leads (I, II, III, or aVF). It runs on the high-frequency ECG data, in parallel with the internal decimation and filtering, and returns a flag that indicates pacing was detected on one or more of the leads, providing the measured height and width of the detected signal. For users who wish to run their own digital pace algorithm, the ADAS1000 supplies a high-speed pace interface that provides the ECG data at a 128kHz data rate; the filtered and decimated ECG data remains unchanged on the standard interface.

A minute-ventilation filter is built into the ADAS1000 algorithm. MV pulses, which are conducted from the ring of a bipolar lead to the housing of the pacemaker, detect respiration rates to control the pacing rate. They're always less than 100µsec wide, varying from about 15 to 100µsec.

The simultaneous three-vector pacing-artifact system can detect pacing artifacts in noisy environments. Each of the three instances of the pace algorithm can be programmed to detect pace signals on different leads (I, II, III, or aVF). Programmable threshold levels tailor the algorithm to detect the range of pulse widths and heights presented, with internal digital filters designed to reject heartbeat, noise, and MV pulses. When a pace has been validated in an individual instance of the pace signal, the device outputs a flag so that the user can mark or identify the pace signal in the ECG capture strip.

The choice of sample rate for the pacing-artifact algorithm is significant because it cannot be exactly the same frequency as those used for the H-field telemetry carrier by the three pacing-systems companies (Boston Scientific, Medtronic, and St Jude). All three vendors use different frequencies, and each has many different telemetry systems. Analog Devices believes that the ADAS1000's sampling frequency does not line up with that of any of the major telemetry systems.


References
1. National Academy of Engineering, "What is a pacemaker?" 2012.

2. Fruitsmaak, Steven, "St Jude medical pacemaker with ruler," image, 2007, Wikipedia, The Free Encyclopaedia.


About the authors
John Kruse is a field applications engineer for Analog Devices in Minneapolis. He joined ADI in 2005 and specialises in medical applications. He has authored many articles and patents; several of the patents cover pacing-artifact acquisition. Kruse graduated with a bachelor of science degree in electronics engineering from the University of Minnesota in 1980. In 1997, he received a master of science degree in electronics engineering from the University of St Thomas (St Paul, MN), where he currently is an adjunct professor.

Catherine Redmond is an applications engineer at Analog Devices in Limerick, Ireland. Since joining ADI in 2005, she has gained industrial-market expertise by supporting precision DACs as applied in automatic test equipment. Redmond currently focuses on precision ADC products. She graduated from Cork Institute of Technology in Ireland with a bachelor's degree in electronics engineering.


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