Patients with heart disease have diverse risks associated with their lifestyle. Therefore, there is a need to enhancing their motivation to adhere to an appropriate lifestyle through the acquisition of knowledge about disease management and lifestyle improvement to prevent the recurrence of disease after discharge. Cardiac rehabilitation (CR) is a multidisciplinary program including education for risk factors; it significantly reduces the mortality of patients with myocardial infarction, ischemic heart disease, and heart failure [12]. In addition, CR reduces the burden on the healthcare system by maximizing the physical, psychological, and social condition of patients and encouraging behavior that can reduce or prevent further events [34]. Although CR may improve the mortality and morbidity rates of heart disease, low utilization remains a problem to be solved. Globally, CR participation rates are low, ranging from 14% to 43%, with high dropout rates after enrollment [5]. Factors associated with participation in CR include patient, medical, and healthcare-oriented characteristics, as well as availability, affordability, and accessibility of a program, and the limitation of a participant's time and location in relation to a CR center are considered major factors that can negatively affect CR participation [6]. To overcome these barriers, cardiac telerehabilitation was introduced based on the use of smartphone [7].

Mobile health (mHealth) applications and cardiac telerehabilitation have developed fast and have potential for cardiovascular disease prevention and management [78]. mHealth is defined as healthcare supported by mobile devices, such as mobile phones, patient monitoring devices, interactive websites, and other wireless devices to support health objectives and behavior change [910]. Mobile phone ownership was reported to be 95% in the United States; in particular, smartphone ownership was 77% among adults in 2018 [11]. Currently, about 2 billion people own smartphones, which is an increase of 42% in comparison to 2011 [12]. South Korea has had the highest smartphone ownership among all countries, and smartphone penetration reached 88% in 2016 [13].

Mobile technology has advanced rapidly, along with the popularization of smartphones, while various software applications have been developed. The introduction of various types of applications provides enormous opportunities for the delivery of healthcare services. Personalized care based on the characteristics of the individual has become possible, thereby enhancing the efficiency of such services [14]. Moreover, by enabling communication between providers and patients regardless of spatio-temporal limitations, more people can provide necessary care, leading to higher satisfaction than that for conventional interventions [15]. Recently, using monitoring sensors and sending feedback to providers and patients has provided new areas of treatment and development. Technology for engaging in and monitoring physical activity is becoming more readily available and can affect current CR provision. Some evidence has shown that cardiac telerehabilitation as a solution for cardiac patients is more feasible and effective than conventional center-based CR [16]. Various mHealth and telerehabilitation services have been developed and used so far, but more research and development is needed [7]. Furthermore, there are still major difficulties in integrating mHealth into daily clinical practice. One problem is that the development of mHealth is focused on the technological part, not on the patient's needs and expectations to use the technology [8].

It is believed that developing and applying programs that meet the interests and needs of the patients are important. A pilot study evaluated the phone usage and needs of patients with coronary artery diseases with regards to an mHealth healthy eating program [17]. It found that mobile phone usage was high among participants, and the participants were interested in receiving the program through mobile technology. Another study documented patients' current technology usage, interests in, and preferences for telerehabilitation, and their relationship with age, gender, and other characteristics [18]. Although the characteristics and preferences of telerehabilitation subjects were investigated through those studies, it differences between diagnoses should be identified. A previously developed app called AnSim (Hanmi Healthcare, Seoul, Korea) for cardiac patients, specifically focuses on coronary artery disease patients after percutaneous coronary intervention. CR programs are offered to patients with various cardiac diseases. Specified disease management is required for patients with coronary artery disease, post-operation and after heart failure (HF) or after heart transplantation (HT) according to their diagnosis. In particular, HF is a subtle and complex disease. Because HF patients have a high risk of an arrhythmic event, they require more attention, even in center-based CR programs [1]. If a smartphone-based cardiac telerehabilitation program could be tailored to each diagnosis, it would be able to provide more effective and efficient management.

This study aimed to identify the current smartphone usage status of selected patients with HF and HT and to describe their needs for smartphone-based disease education through a home health monitoring system.

This study documented the use of current technology by cardiac patients and their interest in smartphone-based CR. The significance of this study is that it identified the needs of participants regarding smartphone application-based disease education and home health monitoring systems.

Chow et al. [7] reported that, due to the recent increase in the number of smartphone users, smartphone applications have become an important tool in disease management. Accordingly, mHealth and cardiac telerehabilitation have been established as a new form of disease management and have advanced greatly [915]. Varnfield et al. [19] reported that, since applications can be easily built into smartphones, cardiac patients can use them at any time or place, and as a result, these applications can be effective tools for realizing mobile education and health management. Currently, many applications use monitoring sensors and provide feedback about the user's biological information. Healthcare providers are able to monitor patients' heart rate, blood pressure, and other health parameters [2021], and there is growing interest in how to remotely manage heart failure patients using monitoring sensors and mobile applications [22].

Patients in this study showed a high interest in both smartphone-based education and monitoring systems. One of the difficulties in applying mHealth is the lack of scientific evidence of efficiency [23]. Some interventions have been started to provide evidence to support mHealth's effectiveness, such as the Mobile Applications Rating Scale (MARS), a tool to assess the quality of health applications, and the United States Agency for International Development (USAID) site that collects evidence regarding mHealth [2425]. The effectiveness of these interventions need to be verified to establish the confidence of both clinicians and patients and to facilitate engagement with these technologies. Moreover, inclusion of medical staff members in the development of smartphone-based cardiac telerehabilitation applications and active participation in patient care can be a solution to address the issues of the validity and reliability of these applications.

When participants search for health-related information through their smartphones, high rates (50.0%) of internet browsing and low rates (3.1%) of hospital website use were reported. On the Internet, there is a huge amount of information available; thus, the amount of inaccurate data is considerable [26]. Among these inaccurate data, healthcare providers should gather and provide high-quality health-related information for patients' healthcare. It is necessary to provide exact information without time and space limitations through validated smartphone-based CR applications.

Various heart diseases can progress to HF, and the end of treatment for HF is HT surgery [27]. In HT patients that have undergone a worsening HF process for a considerable period of time, although the left ventricle ejection fraction can be higher than in the HF group, the comorbidities can be higher and general condition can be lower than in HF patients. HF patients are treated to prevent progression of their disease, whereas the care of patients after HT is more focused on organ rejection and prevention of infection. Besides HF or HT, other heart diseases also have different focuses of disease management. For example, it was reported that monitoring of weight and symptoms was recommended to avoid hospital admission of HF patient [28]. In heart transplantation patients, taking of immunosuppressive medication is important as well as avoiding behaviors that may cause infection and monitoring the signs of infection [29]. Patients with coronary artery disease need to change their behavior to prevent further recurrent events [30]. Those previous study's results are in line with the findings of our study, showing high demands for home health monitoring of blood pressure and body weight in HF patients, while body temperature is of greatest importance for the HT group. The comparison of HF and HT conducted in this study showed that the needs for smartphone-based educational programs and home health monitoring systems were different for each disease. Also, the frequency of searching for health-related information using smartphones was higher in the HF group. This preference currently warrants a technology-based CR intervention tailored to the patient's needs and usage [8]. Smartphone-based CR has low participation of healthcare providers, but more enhanced accessibility and utility than center-based CR [16]. It is expected that smartphone-based CR can be developed in a patient-centric manner by reflecting the reported needs of the patients. Then higher participation of patients based on their needs may be facilitated.

This study had several limitations. First, our results were collected from a small group in a single center. Second, the sample was limited to people who had experienced heart failure and/or had undergone heart transplant surgery who participated in a phase II (outpatient) CR program. Consequently, the study could not identify any differences according to other cardiac disease, such as coronary artery or valvular diseases. We suggest further studies of diverse cardiac patients with a greater number of subjects.

In conclusion, the objective of this study was to provide basic information needed for the development of smartphone application-based disease education and home health monitoring systems for the management of heart diseases. This study documented a high usage rate and interest in mobile health technology among heart failure and post-heart-transplantation patients. Based on the demands and interest, a smartphone-based cardiac telerehabilitation program including disease education and an exercise program should be developed. This study found differences patients' needs regarding smartphone-based disease education and home health monitoring systems according to principal diagnosis. It will be necessary to consider both the generality of heart disease and the specificity of each principal diagnosis to develop and support the utilization of a smartphone-based cardiac telerehabilitation program.