Correlation between AV synchrony and device collected AM-VP sequence counter in atrioventricular synchronous leadless pacemakers: A real-world assessment

Abstract

Introduction: Micra atrioventricular (AV) provides leadless atrioventricular synchronous pacing by sensing atrial contraction (A4 signal). Real-world operation and reliability of AV synchrony (AVS) assessment using device data have not been described. The purposes of this study were to (1) assess the correlation between AVS and atrial mechanical sensed-ventricular pacing (AM-VP) percentages in patients with permanent high-degree AV block and (2) report on the real-world effectiveness of Micra AV.

Methods: The correlation between ECG-determined AVS in-clinic and device-collected %AM-VP was assessed using data from 40 patients with high-degree AV block enrolled in the Micra Atrial tRacking using a Ventricular AccELerometer (MARVEL) 2 study. A retrospective analysis to assess continuously-sampled %AM-VP since last session, device programming, and electrical parameters was performed using Micra AV transmissions from the Medtronic CareLink database. Patients with transmissions ≥180 days postimplant were included.

Results: Among the 40 MARVEL 2 AV block patients with a median %VP of 99.7%, AVS was highly correlated with AM-VP (median AVS 87.1%, median AM-VP 79.1%; R² = 0.764, p < .001). The CareLink cohort included 4384 patients programmed to VDD mode. The mean A4 amplitude was 2.3 ± 1.8 m/s² at implant and 2.3 ± 1.6 m/s² at 28 weeks. In patients with %VP >90% (n = 1662), the median %AM-VP was 74.7%. For the full cohort, median %VP was 65.6% and median projected battery longevity was 10.5 years.

Conclusion: In patients with a high pacing burden, %AM-VP provides a reasonable estimation of AVS. The first large real-world analysis of Micra AV patients with >90% VP showed stable atrial sensing over time with a median %AM-VP, a correlate of AVS, of 74.7%.

Keywords: AV synchrony; Micra AV; VDD pacing system; leadless pacemaker.

Figure 1

Association between AV synchrony and sequence counter (AM‐VP) in complete heart block patients from MARVEL 2. Light gray line is the line of unity while the dark blue line is the least squares regression line. The shaded region a difference of ≤10%. AM‐VP, atrial mechanical sensed‐ventricular pacing; AV, atrioventricular; MARVEL 2, Micra Atrial tRacking using a Ventricular AccELerometer.

Figure 2

Bimodal distribution of ventricular pacing percentage (left) and level of %AM‐VP in patients paced at least 90% (right) at last CareLink transmission. Right panel displays boxplots of %AM‐VP by ventricular pacing percentages ranging from 90% to 100%. AM‐VP, atrial mechanical sensed‐ventricular pacing.

Figure 3

Stability of A4 amplitude over time. Left panel displays monthly mean ± SD AV amplitude following implant while right panel displays the change in AV amplitude from last follow up to implant. AV, atrioventricular.

Figure 4

Influence of pacing mode and pacing burden on projected battery longevity. Estimated battery longevity is standardized from time of implant. Points indicate median projected longevity based on use conditions for each patient cohort.

Figure 5

Relationship between paced tracking index and heart rate for patients paced >90%. Points are median paced tracking index which is defined as the (%AM‐VP/%VP) × 100%. N represents the number of patients with at least 1 h of heart rate measurements since their prior CareLink transmission. “% Time” is the percentage of time since the prior transmission patients spent in each heart rate. Error bars represent the interquartile range. Horizontal dashed red line indicates median tracking rate across all patients and heart rates. AM‐VP, atrial mechanical sensed‐ventricular pacing.

Figure 6

(A) Rate histogram and device tracings for patient with high %AM‐VP and good AV synchrony. The rate histogram is normally distributed with a high percentage of AM‐VP events. The device tracing shows an accelerometer deflection representing a clear atrial contraction (A4) before the VP. (B) Rate histogram and device tracings for patient with high %AM‐VP indicative of atrial oversensing. Note that although the patient has high %AM‐VP, the AM‐VP events occur almost exclusively in 80−90 bpm bin. The device tracing below shows oversensing of the accelerometer signal shortly after the end of the A3 window. The A4 threshold in this example is set to a low value that oversenses the accelerometer not related to the atrial contraction. AM‐VP, atrial mechanical sensed‐ventricular pacing; AV, atrioventricular.