Monitoring and Guidance of Physical Activity During the Maintenance Phase of Cardiac Rehabilitation: the Antwerp Activity Index

Adopting and maintaining an active lifestyle after phase 2 cardiac rehabilitation (CR) is crucial for cardiac patients. Tools to provide an active transition from phase 2 CR to phase 3 CR are lacking, resulting in negative changes in physical activity (PA) behaviour, cardiovascular risk profiles and cardiorespiratory fitness (CRF) levels. The researchers developed a procedure that calculates a PA-score (Antwerp Activity Index; AAI) based on reliable heart rate (HR) data collected by commercially available heart rate monitors (HRMs), which is designed to reflect changes in CRF. This procedure could serve as a valuable tool to facilitate a more active transition from phase 2 CR to phase 3 CR. Ultimately, positively influencing CR patients' PA levels (and possibly) cardiovascular and overall health-related outcomes.

This study will collect HR data with the Fitbit Versa 4 smartwatch and Polar H10 chest strap with the aim of:

Goal 1. Assessing the effect of our AAI-score intervention on adherence towards physical activity maintenance of post-phase 2 CR patients during phase 3 CR.

Goal 2. Assessing the potential differences in the participants' self-experienced physical activity and objectively measured physical activity.

Goal 3. Investigating the correlation between adherence to our AAI score and changes in CRF.

Goal 4. Measuring the adherence to our AAI score intervention. Goal 5. For a subpopulation of AF patients, we will analyse whether the AAI score intervention influences AF recurrence and burden.

Goal 6. Analysing technical outcomes regarding the use of the AAI score and the accompanying application. This will include system performance as well as user interaction with different elements of the application.

Patients complying with the inclusion criteria who completed phase 2 CR of two large care facilities and who are interested will be randomised into one of two groups:

Group 1: Patients who, after following the standard multidisciplinary in-hospital phase 2 CR trajectory, receive a Fitbit Versa 4 and our application with our AAI-score and who receive regular feedback (intervention group).

Group 2: Patients who, after following the standard multidisciplinary in-hospital phase 2 CR trajectory, receive a Fitbit Versa 4 with blinded AAI data collection and no feedback (control group - standard care).

Participants start with a run-in period wherein their eligibility for continuous PPG-HR tracking will be objectively measured. Objective eligibility will be determined by correlation of the Fitbit HR with the Polar HR (Polar H10 chest strap). The eligibility assessment will take place in the three consecutive CR training sessions scheduled for the participant. If deemed ineligible, the participant's participation in the study ends. Participants deemed eligible during the run-in period will be randomised to the intervention or control group.

All included participants will use the Fitbit device for an average of four months. Patients are instructed to continuously wear the Fitbit Versa 4 smartwatch for the whole monitoring period, sync the data daily via the Fitbit application, and charge the device when needed. The intervention group has access to the generated AAI scores through a study application. During an initiation visit, participants will be informed about how the score works and its purpose. The intervention group will receive tailored targets to adhere to. This group will also receive semi-automatic feedback reports through the application. Feedback will be provided every two weeks for the first two months and once more at the end of the third month. No feedback will be given during the last month of follow-up. Feedback is solely based on the collected scores and not on the values used to calculate the score (heart rate). Feedback is limited to overviews of recent days and motivational messages aimed at maintaining or increasing their scores. The control group also receives the Fitbit device but does not have access to the scores generated by the AAI algorithm or receive feedback through the Cardio2U application. This simulates current standard care. The AF subpopulation of both groups will also receive a license to use the FibriCheck application for the duration of the study. An application of the same name will accompany this. These measurements are taken in the background without participant intervention. At the end of the 4-month follow-up period, both the intervention and control groups will perform an exercise stress test. At this moment, the study ends, and all related devices are returned to a study team member. During this visit, a study team member will assist participants in completing two IPAQ questionnaires, which will assess their PA levels over the last two weeks. Through a personal online link, participants will also be asked to complete a quality of life questionnaire (SF-36), a self-developed experience questionnaire (PREM) and a digital health readiness questionnaire (DHRQ). The use of the AAI score through the application will be monitored throughout the entire study period, which occurs automatically without participant intervention.