Micra AV Tracking During Exercise Testing

Participants will be screened and eligible participants who express informed consent will complete exercise testing and holter monitoring. For each participant, the tracking performance of the atrial mechanically sensed, ventricular pacing device will be assessed at rest and during exercise using exercise testing. For each test, the sinus rate trend will be recorded alongside the presence or absence of a mechanically sensed ventricular paced event (AM-VP) for each sinus beat. The average tracking index in each phase of exercise testing - rest, exercise, and recovery - and across the spectrum of achieved heart rates across the cohort will be calculated and reported. Holter monitoring will also be used to assess tracking index across the spectrum of heart rates achieved during routine daily activities across a 24 hour period.

After enrollment, the following baseline information will be assimilated from the medical record and will be collected if not already done based on routine clinical care: date of pacemaker implant, pacemaker implant location (high septum, mid septum, apex), cardiac disease history, and programmed pacemaker parameters.

Exercise testing will be performed between one week and six months after Micra AV implant. Participants will complete preparation for exercise testing according to institutional standards. Participants will be given instructions to take all prescribed medications, including antiarrhythmic drugs and AV nodal blocking agents, according to their usual schedule, including on the day of the test.

Participants will be provided with a holter monitor. Participants will begin wearing the monitor during the rest period at the start of the exercise testing protocol. Exercise testing will be completed using standardized Micra AV device programming settings: VDD mode with nominal maximal tracking rate. Auto programming will be used to initialize device parameter selection. Following completion of auto programming, a MAM test will be performed to assess atrial signal discrimination. A fixed A3 discrimination threshold will then be selected which is approximately 1.0 m/s2 greater than the isolated accelerometer A3 signal.10 Other sensing parameters will be adjusted as clinically indicated to optimize atrial signal discrimination. Each participant will undergo device monitoring accompanied by external telemetry for 20 minutes at rest, followed by a fitness level-appropriate standardized stress protocol (e.g., Bruce protocol, Naughton protocol, Eckland protocol) on the treadmill or recumbent bicycle. They will perform graded exercise until achieving a heart rate of 130 bpm, or until physical fatigue, limiting chest pain (or discomfort), marked ischemia, or a drop in blood pressure occur (if such symptoms develop prior to reaching the target heart rate), supervised by a clinician experienced in performing cardiac stress testing. Once reaching 130 bpm, participants will remain at the current stage on their exercise protocol until physical fatigue, limiting chest pain (or discomfort), marked ischemia, or a drop in blood pressure occurs, or up to a maximum of twenty total minutes of exercise. Participants will be asked to report level of perceived exertion and fatigue level at pre-determined intervals. Cardiac rhythm will be recorded using 12-lead telemetry throughout the rest, exercise, and recovery periods. If the tracking index during exercise is lower than 70%, atrial sensing will be optimized using a MAM test.

The following data will be collected during exercise testing: exercise protocol utilized, protocol stage achieved, baseline cardiac rhythm, characterization of atrial and/or ventricular tachyarrhythmias, resting heart rate, peak heart rate, peak blood pressure, perceived level of exertion and fatigue, total exercise time, total metabolic equivalents (METs) achieved, and reason for termination.

The following data will be abstracted from device interrogation and 12-lead telemetry following the test: total number of sinus atrial beats, total number of premature atrial complexes (PAC), total number of premature ventricular complexes (PVC), number of tracked events, number of non-tracked ventricular paced events, and number of ventricular beats resulting from native AV conduction. Participants will continue to wear the provided holter monitor for the remainder of the 24 hour period. The following data will be collected during holter monitoring: average heart rate, peak heart rate, minimum heart rate, characterization of atrial and/or ventricular tachyarrhythmias, total number of sinus atrial beats, total number of premature atrial complexes (PAC), total number of premature ventricular complexes (PVC), number of tracked events, number of non-tracked ventricular paced events, and number of ventricular beats resulting from native AV conduction. Patient charts will be reviewed at the time of study completion to report clinical outcomes including death, device extraction, and/or transition to a transvenous pacing system.