Introduction:

The Micra™ leadless intracardiac pacing system is widely used in clinical routine now with proven feasibility, implantation safety and beneficial mid-term electrical performance. An important issue is still the rate adaptive right ventricular stimulation. Because implanted in the permanently moving right ventricle, the challenge is to detect movement caused by physical patient activity apart from the normal heart movement. One aspect regarding the R-mode-sensor is the long-established ADL-concept (Activities of Daily Living). That means stimulating between intervention rate and ADL-rate, thus responding to the rate-requirements during normal everyday physical activity of elderly patients. We analyzed our data to understand if this concept is supported by the modified sensor (3-axis-sensor) of the Micra system. 

Methods:

In 35/150 patients successfully treated with intracardiac leadless pacemaker, we analyzed the ventricular pacing rate from stored histograms in those patients in VVIR mode to understand if the paced rate reflects the rate-band between interventional rate and ADL-rate as it is suggested by the ADL-concept. An activity test was performed in 24/35 patients to confirm that the selected vector was sufficient. Only rate histograms covering a minimum of 20 days were included in the analysis in order to avoid periods of recovery after implantation and / or other procedures performed during hospital stay.

Results:

In the subgroup of 35 patients, ventricular rate diagrams for a period of more than 20 days were shown (93±65 days; 61%male ; average age 80 ± 4 years). They had a high rate of right ventricular pacing (96.3 ± 15.7%). During an average of 27% ± 13% of ventricular pacing, the frequency met the ADL criteria (intervention rate: 60 bpm; ADL-rate 95 bpm). This translates into 5.3 hours pacing time per day within the ADL-range.
In 24 of 35 patients (68.8%) an activity test was performed. Vector 1 was programmed as the most useful vector.

Conclusion:

In this real life setting, the rate adaptive right ventricular stimulation of the leadless Micra™ system demonstrated a good working three–axis accelerometer, resulting in chronotropic competence and pacing time in ADL compared to transvenous pacemakers working with the same concept.