Optimizing Digital Cardiac Rehabilitation Using the Multiphase Optimization Strategy: Mixed Methods Feasibility Study

Cardiac rehabilitation (CR) is an evidence-based, multicomponent intervention. However, participation in and reach of CR remain suboptimal globally. Digital CR is a promising alternative to traditional center-based CR, with the potential to increase intervention reach and efficiency. However, efforts to increase the efficiency of digital CR require an understanding of the relative effectiveness of the components of CR, which is currently lacking. The Multiphase Optimization Strategy provides a framework to evaluate the effects of individual components within complex interventions.

This mixed methods study explored the feasibility and acceptability of implementing the procedures of a factorial design and delivering multiple intervention components in preparation for an optimization randomized controlled trial of a digital CR intervention.

Patients attending CR in a community setting were randomized to 1 of 8 experimental conditions in a 2 × 2 × 2 (2³) factorial trial design. Each condition received a different combination of three intervention components over a 6-week study period (1) goal setting and self-monitoring, (2) education, and (3) feedback messages. Feasibility was assessed through intervention fidelity (eg, usage statistics) and outcome measure data completeness. Acceptability was measured using the System Usability Scale, a questionnaire, and semistructured interviews based on the Theoretical Framework of Acceptability.

A total of 8 participants were recruited and retained in the study. The mean age was 75 (SD 5.6) years, and the majority were female (5/8, 62.5%). The digital CR intervention demonstrated good usability (System Usability Scale score 72.1, SD 19.1), and 83.3% (5/6) of participants found the digital technology acceptable. However, only half (2/4, 50%) found the feedback messages acceptable. Fidelity was high for goal setting/self-monitoring and feedback but lower for education. Qualitative findings indicated that participants held positive attitudes toward the intervention and reported improvements in physical activity, although many expressed a preference for more tailored feedback and 2-way communication. Of the 3 prespecified progression criteria, usability met the "Go" criterion, whereas intervention fidelity, acceptability, and outcome measure data completeness met the "Amend" threshold.

This study demonstrated the feasibility of implementing a factorial design and delivering multiple intervention components within a digital CR intervention. While the intervention was generally acceptable, modifications to the education and feedback components are necessary prior to conducting a pilot optimization randomized controlled trial.