Novel method of atrial mechanical sensing for leadless atrioventricular synchronous pacing

Figures

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  Figure 1. A: Unusual atrial mechanical sensing within the A3 window after implantation of a leadless pacemaker in this case. The figure shows a surface electrocardiogram (leads II and III) and a mechanical sensing signal of the atria after the implantation. Interestingly, no VE marker was observed, although atrial mechanical sensing and synchronous pacing were performed in the first beat, suggesting sensing of the atrial signal in the A3 window. All the subsequent beats showed VE markers, indicating that atrial signals were normally sensed in A4 windows. B: A manual atrial mechanical test of conventional A4 sensing The A4 signal was correctly sensed in the A4 window (arrow) following the end of the A3 window (= VE). AM = atrial mechanical signal; VE = ventricular end (= end of the A3 window); VP = ventricular pacing.

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  Figure 2. Intentional prolongation of the A3 window. A: Pacemaker setting and manual atrial mechanical test after intentional prolongation of the A3 window. The A3 window end was intentionally prolonged to 1000 ms. Although no VE marker was observed, the atrial signal was correctly sensed (AM) and atrioventricular (AV) synchronous pacing could be performed. B: The surface electrocardiogram (lead II), mechanical sensing signal, and intracardiac cardiac recording (EGM) during isoprenaline injection. Isoprenaline (2 μg) was injected to confirm atrial sensing during a high heart rate after prolongation of the A3 window in this patient. AV synchronous pacing was correctly performed after atrial mechanical sensing within the A3 windows even at a high heart rate (95 beats/min), suggesting A4 sensing within the A3 window. AM = atrial mechanical signal; EGM = intracardiac electrogram.

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  Figure 3. Schema of the comparison of pacemaker settings and atrial mechanical sensing between the normal setting and our novel method. A–C: Conventional setting of atrial mechanical sensing with the Micra AV (Medtronic, Inc, Minneapolis, MN). At a normal heart rate, small A3 (= ventricular filling) and large A4 signals (= active atrial contraction) are observed. The A3 signal is not sensed by a higher A3 threshold, although the A4 signal is correctly sensed. At an intermediate heart rate, the interval between A3 and A4 decreases. The A3 window is automatically shortened and the A4 signal can be sensed within the advanced A4 window. A3 and A4 signals fuse (and this fusion is called the A7 signal) at the higher heart rate. This duration of the A3 window is automatically changed in 15-ms steps based on observation of 8 consecutive beats. Therefore, there is a slight delay in adaptation of sensing of the atrial signal. D–F: Simplified A3 method by prolonging the A3 window setting. The atrial signal is promptly sensed by intentional prolongation of the A3 window irrespective of heart rate. There is no delay in sensing of the atrial signal.