Atrioventricular Synchrony Algorithm Modeling of a Leadless Pacemaker Family: A Virtual Patient Analysis

Figures

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  Fig. 1. Atrial Mechanical Detection Algorithm. Visual depiction of how the Micra AV device uses the accelerometer signal to detect the atrial contraction (A4) and subsequently deliver AV synchronous pacing. The A3 Threshold is set above the max A3 signal, which is the signal occurring in the A3 detection window. The A4 Threshold is set below the max A4 signal, the signal occurring in the A4 detection window, as the aim is to detect the A4 signal (atrial contraction). The A3 Window End parameter separates the A3 and A4 Thresholds. The Ventricular End (VE) marker indicates the end of the A1–A3 ventricular event signals. The Atrial Mechanical (AM) marker indicates the device detected atrial mechanical contraction or A4. The Post-ventricular atrial blanking (PVAB) period is when the A1 and A2 signals are blanked. No atrial sensing occurs during PVAB. VP ventricular pace. ©Medtronic. 2024

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  Fig. 2. 24-h recording from an AccelAV patient illustrating the A3 operation. The individual dots are the A3 amplitude measured by the device on each cardiac cycle. Periods of large A3 amplitude measurements are during high sinus rates when the A4 signal occurs in the A3 window, resulting in a large, combined A7 signal. The A3 amplitude measurements of 2.0 m/s2 and lower are during periods of lower sinus rates where the isolated A3 signal is measured. The dotted black line represents the Micra AV Auto A3 Threshold operation and during these periods of high sinus rates, the A3 Threshold adjusts too high resulting in undersensing. The red line is the Micra AV2 measurement of the A3 amplitude and is 2.1 m/s2. The Micra AV2 Auto + A3 Threshold then sets the new A3 Threshold at 3.1 m/s2 with the nominal A3 Amplitude Margin of 1.0 m/s2

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  Fig. 3. Accelerometer vector selection and A3 Thresholds are finalized in the first phase of Atrial Sensing Setup. The A3 Window End parameter is finalized in the second phase. The A4 Threshold is finalized in the third phase

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  Fig. 4. Histogram of A3 signal amplitudes used for the Micra AV2 Auto + A3 Threshold algorithm. After this histogram is collected, the 95th percentile is used to determine the daily A3 amplitude that should not be detected by the Micra AV2 device. A programmable amplitude margin can then be applied (nominal = 1.0 m/s2) to further help avoid A3 oversensing

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  Fig. 5. A 5-s strip at 10.55 h from the 24-h recording of an AccelAV patient. The accelerometer signal is plotted in red, the EGM in blue, and the ECG in green. The Micra AV Auto A3 Threshold was set to 3.2 m/s2. Two A7s (A4 occurring in the A3 window) are shown. The measured A3 amplitude of 4.5 and 5.4 m/s2 are undersensed with the Micra AV Auto A3 Threshold, but are detected with the Micra AV2 Auto + A3 Threshold

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  Fig. 6. Bench testing setup consisting of the InterSim III Interface simulator box (a), laptop with InterSim software (b), AV/AV2 hybrid adaptor box (c), and CareLink SmartSyncTM programmer (d). The InterSim interface simulator box is connected to the programmer via ECG cables

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  Fig. 7. Programmable parameters for constructing the accelerometer signal in InterSim III Interface. The Ricker waveform (Eq. 1) was used for all signals in the simulations. The amplitudes and timings of the A1, A2, A3, A4, and A7 signals can be changed using the InterSimIII software. The A2 Delay represents the time between the QRS on the ECG and the start of the A2 signal. The timing can be different following a VP (ventricular pace) or VS (ventricular sense). The default for both is 300 ms. The A3 Signal End timing can be adjusted as desired and the A3 Signal End Variation randomly varies the A3 Signal End. The random value results from a Gaussian Distribution (standard deviation is 17ms for the 50 ms option and 33 ms for the 100 ms option). The Auto-adjust A3 Signal End with Atrial Option adjusts the A3 Signal End with the Atrial Rate when rates are greater than 60 bpm. The A4 Delay represents the timing between the start of the P-wave and the start of the A4 signal. The default is 90ms. Baseline noise can be added to the signal but was not utilized in these presented simulations

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  Fig. 8. Simulated ECG, EGM, and accelerometer signals recorded simultaneously through CareLink SmartSyncTM programmer (top panel) and InterSim III software (bottom panel). The programmer’s accelerometer waveform is filtered and rectified, while the InterSim III accelerometer waveform is raw

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  Fig. 9. High-level process flow for creating virtual patients and using them to assess updated device algorithm performance

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  Fig. 10. AVS achieved during the 30-min simulation immediately following the completion of the Atrial Sensing Setup algorithm. Left: AVS with Micra AV and AV2. Gray lines indicate individual patient values. Blue line connects averages. Right: Change in AVS with Micra AV2 vs. AV. Red circles are individual patients; blue circle is the average change. Error bars are 95% confidence intervals

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  Fig. 11. Ambulatory AVS measured during simulations. Lines connect average AVS by sinus rate. Error bars represent 95% confidence intervals. Gray bars indicate the percentage of total cardiac cycles within each sinus rate category. *Upper Tracking Rate was programmed to 105 bpm for both devices; capability of delivering AV synchronous pacing beyond 105 bpm was not simulated

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  Fig. 12. Length of pre-hospital discharge device check from survey results. Results shown in percentage. Total Micra AV survey responses were 104. Total Micra AV2 survey responses were 98