The goal of this mixed prospective observational and qualitative studies is to evaluate the usability of a newly developed application (App) and the feasibility and perception of a 12 weeks tele-cardiac rehabilitation (tele-CR) program. The main question it aims to answer is: Does tele-CR program intervention a acceptance feasibility in coronary heart disease patients? The findings will guide subsequent intervention design studies.

CHD is one of the leading causes of death in worldwide and Taiwan. While tele-CR holds the potential to reduce the readmission and improve the quality of life of patients with CHD, there is currently a paucity of research on this technology in Taiwan. Currently, traditional cardiac rehabilitation is the main method in Taiwan. However, the problem of under-usage in traditional cardiac rehabilitation after discharge persists. Literature shows that tele-CR may be a safe and effective supplement or alternative strategy. Therefore, we plan to develop a feasible tele-CR Program to optimize the quality of continuing care for CHD patients. The purpose of this study includes: 1. Develop App and management platform. 2. Understand the usability of the App in the 4th and 12th weeks. 3. Understand tele-CR program recruitment rates. 4. To understand the engagement rate of tele-CR program in the 1st, 4th, 8th and 12th weeks. 5. To understand the retention rate of tele-CR program at 1, 4, 8 and 12 weeks. 6. Understand the experience of receiving tele-CR program (qualitative).

A mixed methods approach will be used, including prospective observational and qualitative research designs. The study will be conducted in the cardiology ward of a medical center in the Northern District. A purposive sampling of patients admitted to the hospital with a primary diagnosis of CHD will be conducted. We estimate that we will recruit 45 cases (quantitative).

This study was reviewed and approved by the Institutional Review Board (IRB) of the study hospital. Research assistants provided detailed explanations of the study's purpose and procedures to potential participants who met the inclusion criteria. Any questions or concerns raised by the participants were addressed before obtaining written informed consent. Data collection was conducted only after consent was secured. Questionnaire data were obtained either through self-administration or via research assistants, who posed the questions individually based on the participants' needs. All data collection took place in a quiet and undisturbed environment to ensure accuracy and comfort.

All participants will undergo tele-CR for 12 weeks after completing the basic characteristics assessment. After discharge, the researchers monitored App usage and conducted four follow-up sessions via LINE or telephone at 1, 4, 8, and 12 weeks post-discharge. These follow-ups, lasting approximately 5-15 minutes each, aimed to assess patients' living conditions, resolve any issues promptly, and provide encouragement or praise based on their engagement with the App.

To evaluate the App's acceptance and usability, the Technology Acceptance Model Scale (TAMS) and System Usability Scale (SUS) were administered during the 4th and 12th weeks. Data collection methods included telephone or in-person sessions, allowing participants to complete the questionnaires either independently or through a question-and-answer format according to their preference. At the 8th-week telephone follow-up, participants were invited to engage in one-on-one semi-structured in-depth interviews. These interviews were scheduled at the participants' convenience and conducted in a quiet, private setting. With participants' consent, the interviews were audio-recorded, and researchers documented non-verbal behaviors for additional insights. If participants could not be reached via telephone, follow-up appointments were coordinated during outpatient visits to ensure data integrity and minimize participant attrition or data discrepancies. This approach was designed to enhance the reliability of the study findings. The recruitment, engagement, and retention rates will also be calculated. Data analysis will be performed using SPSS 26.0 software. A two-tailed test with statistical significance set at p < 0.05 will be adopted.

Inclusion Criteria:

1. The main diagnosis at admission of CHD.
2. Age ≥20 years.
3. Owns an iOS or Android smartphone and can use it.
4. Conscious, clear and can communicate.
5. Agrees to participate in the research after explanation and is willing to use the App.

Exclusion Criteria:

1. Level IV on the New York Heart Association Functional Classification.
2. Left ventricular ejection fraction≦40%.
3. Have a history of severe arrhythmia (e.g., ventricular tachycardia, ventricular fibrillation, complete atrioventricular block).
4. Combined with other serious heart diseases (e.g., congenital heart disease, cardiomyopathy).
5. Mental disorders, end-stage renal disease and other systemic diseases diagnosed by a physician.
6. Severe infection, injury, surgery (e.g., coronary artery bypass graft) or cancer treatment has occurred in the past three months.
7. Physical activities are affected by neurological, respiratory, skeletal, or peripheral vascular diseases.
8. Restricted use of the App due to sensory or cognitive impairment.
9. Already participated in other clinical trials.
10. Planning to receive surgery (e.g., coronary artery bypass graft).

Patients admitted to the hospital with a primary diagnosis of CHD will be conducted. We plan to recruit a group of patients to receive the tele-CR program and evaluate the usability of the App perceived by patients at 1 and 3 months after discharge. Therefore, we use the t-test (one sample case) statistical method and set the effect size to a moderate 0.5, power is 0.8, alpha is 0.05 (two-tailed), and the number of samples required after calculation using G*power 3.1 software is 34. Considering the 20% attrition rate, we estimate that we will recruit 45 cases (quantitative). The number of samples for qualitative research is mainly to achieve data saturation, and according to the literature, it is recommended to have at least 12 people.

The anonymized datasets and study protocols will be available upon reasonable request for academic purposes following the study's conclusion.