An implantable cardioverter defibrillator (ICD) is a prophylactic treatment for patients with ventricular fibrillation, ventricular tachycardia secondary to structural heart disease, who are at high risk of sudden cardiac death because medication alone is inadequate to prevent it, and for patients who have been resuscitated from or are at high risk of sudden cardiac death (SCD) [1].

Sudden cardiac death is when a person who is normally asymptomatic develops symptoms of heart disease and dies suddenly within one hour [2]. The most common cause of sudden cardiac death is cardiac arrest, which is 90% due to various arrhythmias, including myocardial infarction, and 10% due to malfunctioning of the heart pump [2]. As a treatment to prevent these sudden deaths, implantable cardioverter defibrillator is a non-drug treatment that can save the patient's life by detecting dangerous arrhythmia and delivering an electric shock when it occurs, and patients at high risk of cardiac arrest are targeted for such treatment [3].

Health-related quality of life (HRQoL) focuses on aspects directly related to health. The World Health Organization (WHO) defined health as "not merely the absence of disease but a state of complete physical, mental, and social well-being" [4]. Health-related quality of life (HRQoL) is a concept that focuses on the impact of health, disease, disability, and impairment on an individual's quality of life and emphasizes the individual's subjective experience [5].

Although implantable defibrillators can reduce mortality by preventing sudden cardiac death, they can have physical, psychological, and social impacts on the recipient, as permanent implantation of the device requires adaptation to a new way of life and ongoing care [6]. In particular, recipients experience various physical discomforts and negative psychological states such as depression, anxiety, and decreased health-related quality of life [7], which can lead to decreased physical functioning, decreased hospital utilization, and increased risk of mortality [7].

Defibrillator implantation patients experience discomfort with sleep disturbances, weakness [8], fatigue, and dizziness [9] and vague symptoms such as pain at the implant site, foreign body sensation, palpitations, and chest discomfort, which negatively impact their activities [10]. Similarly, defibrillator implantation patients experience arrhythmia symptoms, pain, complications, electric shocks, fear of death, worry about the defibrillator itself, and vague fears about the future [10]. These negative experiences are associated with uncertainty [9], and negative psychological states, such as fear of electric shocks and midrange sounds, contribute to a decreased quality of life for AED patients [10,11].

Uncertainty is a variable that affects recovery from illness and refers to a cognitive state in which an individual lacks cues and is unable to assign meaning to or interpret an illness in a way that accurately predicts outcomes, which can negatively impact a patient's HRQoL and recovery from illness [12]. In addition, uncertainty can lead to assessments of risk rather than opportunity, resulting in negative emotions such as anxiety, depression, anger, and fear [13], which can also negatively impact HRQoL [14]. The uncertainty associated with living with an ICD leads to psychosocial adjustment problems [15] and reduced HRQoL [16].

Psychological distress and decreased HRQoL are associated with adverse outcomes such as increased rates of sustained fatal arrhythmias and increased risk of sudden cardiac death [8]. Therefore, ICD implant patients must accept the life change of living with an implanted device for the rest of their lives, and the process of adapting to the device and accepting it as part of their lives is necessary [7]. Therefore, based on the uncertainty of the disease, self-care competencies that enable patients with implantable cardioverter-defibrillators to evaluate the uncertainty as an opportunity rather than a crisis, to reduce the uncertainty, to help them adapt to the changed life, and ultimately to improve their HRQoL, with active support from family, friends, and medical staff, are important.

Self-care is the activity and performance of one's life and functioning in a healthy manner, and humans are capable of self-care, and self-care competence is an integral acquired ability of an individual that is developed through a learning process based on intellectual curiosity, education and guidance from others, and experience in performing self-care [17]. Therefore, self-care competence to understand and manage one's illness is an important variable to reduce uncertainty about the prognosis of patients with implantable cardioverter-defibrillators. Mishel [10] found that the best way to reduce uncertainty is through information provision and that adaptation occurs through self-care such as emotion management, cognitive support, and direct action.

Fillion's [18] study found that empowering defibrillator implantation patients with self-management skills through continuity of information, continuity of care, continuity of relationships, and active management can reduce uncertainty and improve HRQoL through the crisis-to-opportunity process [12] as a coping mechanism.

Self-care competence is an even more critical issue for chronic disease patients who must live with their illness for life, managing and controlling it. Research targeting chronic disease patients is also being conducted domestically. Between uncertainty and HRQoL, self-care competence was reported as a complete mediating variable, indicating its importance when aiming to improve HRQoL in uncertain situations [19]. Studies involving hemodialysis patients [20] and stroke patients [19] showed that higher self-care competence improved HRQoL within the uncertainty-quality of life relationship. Conversely, both hemodialysis [20] and stroke [19] patient studies found that higher uncertainty levels correlated with lower HRQoL. The HRQoL measurement tool used in the hemodialysis patient study was the same as the one used in this study. This result indicates that self-care competence, as a mediating variable to reduce uncertainty in chronic disease patients, can influence HRQoL. Significant factors affecting quality of life in patients with ICDs included gender, age, underlying disease, ejection fraction (EF), and whether an electrical shock had been delivered [21,22].

However, no studies have validated the mediating effect of self-care competence on the relationship between uncertainty and HRQoL in patients with ICDs, and only fragmentary causal relationships have been identified, such as factors affecting HRQoL in patients with ICDs [23]. Therefore, improving the HRQoL of implantable cardioverter-defibrillator patients can reduce the incidence of ventricular arrhythmias and subsequent mortality [24,25].

Therefore, this study aimed to identify the relationship between uncertainty, self-care competence, and HRQoL, and to identify the mediating effect of self-care competence on the relationship between uncertainty and HRQoL to provide a basis for establishing a systematic support system to promote the HRQoL of implantable cardioverter-defibrillator patients. The purpose of this study is to determine the extent of uncertainty, self-care competence, and HRQoL in patients with implantable cardioverter defibrillators and to examine the mediating effect of self-care competence on the relationship between uncertainty and HRQoL.

This study was conducted to determine the extent of uncertainty, self-care competence, and HRQoL in patients with ICDs, and to identify the mediating effect of self-care competence on the relationship between uncertainty and HRQoL, and to provide a basis for intervention programs to improve the HRQoL of patients with ICDs.

We found that the mean uncertainty score for ICD patients was 2.84±0.33 out of 5, which is moderate. This is lower than the score of 3.08±0.50 measured with the same tool in the study by Bangchoy (2021) [28] for patients with ICDs. This result is likely due to the difference in fear of electric shocks, with 37.4% of the subjects in Bangchoy's study having experienced electric shocks and 50.0% of the subjects in our study having experienced electric shocks. Illness uncertainty is related to ambiguity and unpredictability of disease prognosis, and studies have supported that ICD patients experience illness uncertainty due to the unpredictable nature of symptoms such as arrhythmia symptoms, cardiac arrest experience, and electric shock [29]. Therefore, to reduce uncertainty in ICD implant patients, it is necessary to apply nursing interventions in the clinical setting that consider not only physical symptoms but also psychological problems.

The self-care competence scores of ICD patients in this study were 4.29±0.71 out of 6 points, differing from the 3.96±0.07 points reported by Chae et al.[20] using the same tool in hemodialysis patients. This difference likely stems from the distinct self-management demands of each condition: hemodialysis patients face complex, ongoing requirements spanning strict dialysis schedules, dietary restrictions, and fluid management across daily life, whereas ICD patients primarily focus on psychological anxiety regarding the risk of electrical shocks, device monitoring, and symptom tracking. Therefore, a simple score comparison is limited due to the differing disease characteristics and may alter the inherent meaning of the self-care competence scores themselves. This difference is thought to arise because the moderating factors influencing self-care competence differ between the two conditions.

The subjects in this study were 43.5% aged 60 or older and 78.7% male, whereas in Chae et al.'s [19] study, 52.7% were aged 60 or older and 56.2% were male. This variation is likely due to the diverse moderating factors of self-care competence, such as gender and age [18]. Age can significantly influence the performance of self-care competence. Self-care theory posits that self-care competence is closely linked to cognitive capacity, learning ability, and health literacy. Older adults are more likely to experience natural declines in these abilities, which can act as limitations to self-care competence. Furthermore, studies on elderly ICD patient populations have reported anxiety and reduced HRQoL associated with shock events, confirming a correlation between disease understanding and self-care competence [30]. Therefore, tailored educational strategies for different age groups are required.

Gender differences are also an important interpretive variable. The high proportion of male participants and high employment rate in this study suggest that differences in self-care attitudes can be interpreted in relation to social role factors. Maintaining employment and a sense of social responsibility can strengthen motivation to engage in self-care competence, which may lead to disease adaptation and health care behaviors. This context should be understood not as a gender generalization but as a variable interacting with social role and economic factors [31].

Therefore, it is thought that the self-care competence of ICD patients will be strengthened if the moderating factors to improve self-care competence are identified and customized programs are developed and intervened. According to a study by Grady et al (2014) [32], chronic patients such as ICD patients can improve self-care through knowledge of the disease, symptom monitoring, lifestyle changes, medication adherence, and regular hospital visits, so it is necessary to develop intervention programs that take this into account.

In the HRQoL of this study, the physical HRQoL score was 59.57±15.58 and the mental HRQoL score was 56.75 ±15.10. In a previous study of ICD implantation patients (Bang, 2021) [28] was physical HRQoL score 58.93±17.0 and the mental HRQoL score of 59.82±18.74. In this study, physical HRQoL scores were higher than mental HRQoL scores, whereas in Bang's (2021) [28] study, physical HRQoL was slightly lower than mental HRQoL. This difference may be due to the fact that our study had more NYHA Class I (76.9%) patients than NYHA Class II (23.1%) patients, whereas Bang [28] et al. had more Class II (56.4%) patients than NYHA Class I (32.5%) patients.

It is thought that unpredictable electrical shocks and device-related complications (Flemme et al., 2011) [33] and negative emotional states (Rosman et al., 2015) [34] associated with ICD implantation affect mental HRQoL. Therefore, it is necessary for healthcare providers in clinical settings to improve the quality of life by forming a psychological support system to provide a sense of mental stability in addition to physical symptoms.

The factors that made a significant difference in uncertainty in our study were shock experience and time since defibrillation. This is similar to a previous study [11] that found that patients who had never been shocked had higher levels of uncertainty due to the mental challenge of not knowing when they would be shocked. It was suggested that they were expressing uncertainty about death rather than just the event of a shock [11]. Therefore, it is thought that ICD patients have high uncertainty because their negative evaluation of their health status leads to anxiety about their prognosis. Therefore, psychological counseling programs that can reduce uncertainty are needed. In addition, in terms of the number of months since ICD implantation that had a significant effect on uncertainty, 60 months or less had significantly higher uncertainty than 121 months. A previous study [9] showed that there was no difference between the immediate post-implantation period, 6 months, and 12 months, and Lee [35] showed that psychological adjustment was different depending on the order of time at 1 month, 6 months, and 1 year after the procedure, but there is no long-term study after the procedure, so repeated studies are needed to confirm the uncertainty of ICD timing.

The factors that showed significant differences in self-care competence in this study were education, occupational status, and NYAH class. In this study, high school and university graduates had higher self-care competence than elementary school graduates and below. Lee [35], who investigated the anxiety and depression levels of patients after implantation of an implantable cardioverter defibrillator (ICD), found that the higher the level of education, the more efficiently they could acquire information about and manage the ICD. In addition, the higher the education level of the subjects, the higher the self-care capability. This suggests that subjects with higher education have a better understanding of the disease, so it is necessary to provide differentiated education programs by education level to improve self-care capabilities.

The finding that those with jobs had higher self-care competence than those without jobs in this study is in the same vein as the finding that those with better economic conditions are better adapted to the treatment process and self-care [36], and it is thought that those with jobs make persistent efforts to manage their disease in order to maintain their jobs. NYAH Class I patients had higher self-care competence than NYAH Class II patients. In a study of ICD implantation patients, Yoon [37] reported that the higher the NYHA stage, the more severe the experience of symptoms such as severe dizziness, shortness of breath, palpitations, chronic fatigue, and pain. This is likely due to the fact that subjects with NYAH Class 1 did not have severe physical symptoms. Therefore, careful nursing care is needed to identify the NYAH class stage and identify physical symptoms.

In this study, factors showing differences in physical HRQoL were employment status, diabetes, cerebrovascular disease, NYHA class, and ICD type, EF, while factors showing differences in mental HRQoL were employment status, NYHA class, and ICD type. Particularly, having employment was associated with significantly higher physical and mental HRQoL. These results align with previous studies reporting that employed individuals reported higher levels of physical and mental HRQoL [6,37,38]. However, employment status should be interpreted not merely as an indicator of economic capability, but as a concept encompassing various factors such as maintaining social roles, performing activities of daily living, physical functional level, and social interaction. That is, the very fact of maintaining employment likely reflects a relatively good functional status and level of social participation, and these factors may be associated with improved HRQoL. Meanwhile, ICD recipients require long-term medical management, including device checks, follow-up monitoring, and battery replacement procedures. Some studies report that this ongoing treatment process can act as a psychological burden factor [35,36]. However, since this study did not directly measure economic burden, there are limitations to interpreting the relationship between occupational status and HRQoL as directly linked to medical cost burden. Therefore, future studies need to comprehensively analyze the impact on HRQoL by considering financial factors such as ICD-related medical cost burdens, economic stress, and insurance coverage levels.

In this study, patients with NYHA class I had higher physical and mental HRQoL than patients with class II. In a study by Yoon [37] also reported that the lower the NYHA class, the higher the physical and mental HRQoL because of the better daily activity status. These results suggest that the lower the stage of NYAH class, the higher the physical and mental HRQoL because patients experience fewer symptoms and can be more active in daily life. Therefore, it is necessary to repeat the study in a larger group of patients with various NYAH classes in the future.

In the present study, the mean physical HRQoL according to ICD type was statistically significantly higher for Double cavity (64.27 points) than CRT-D (50.00 points). In a study by Yoon [37], there was no statistical difference in physical HRQoL scores by ICD type, and in a study of Chinese people [39], the mean physical HRQoL scores by ICD type were 44.72 for single cavity, 42.60 for double cavity, and 42.11 for CRT-D. Therefore, it is necessary to repeat the study to confirm and compare the differences including physical HRQoL scores by ICD type. Based on this study alone, the physical HRQoL score was highest for Double cavity 64.27, but there was no difference in uncertainty and mental HRQoL by ICD type. Therefore, it is necessary to identify the degree and frequency of physical symptoms to improve the physical HRQoL of ICD implantation patients by ICD type and manage symptoms accordingly.

The findings that physical HRQoL was higher in the absence of diabetes and cerebrovascular disease were similar to the findings of Yoon [37], who reported higher physical and mental HRQoL in the absence of diseases other than rhythm disorders. It is thought that the absence of underlying medical conditions may have contributed to higher physical and mental HRQoL due to positive effects on self-management in daily life. Based on these results, comprehensive self-management through lifestyle management, psychological support, and information sharing about ICD implantation should be provided after ICD implantation to prevent the development of underlying diseases in ICD implantation patients.

The results of this study showed that the physical and mental HRQoL of the Participants were negatively correlated with uncertainty and positively correlated with self-care competence, and the relationship between uncertainty and self-care competence was negatively correlated, and physical and mental HRQoL were positively correlated. It can be seen that the lower the uncertainty and the higher the self-care competence of ICD implantation patients, the higher the physical and mental HRQoL. This is consistent with the findings of Jo et al. [19]. It can be seen that the higher the uncertainty, the lower the HRQoL [10,12], and the higher the self-care competence, the higher the HRQoL [23], which is characterized by negative emotions such as arrhythmia symptoms and electric shocks in ICD patients. Therefore, a comprehensive self-management empowerment strategy involving healthcare providers, counselors, and family members is needed to reduce uncertainty and increase self-care competence.

In this study, self-care competence was found to partially mediate the relationship between uncertainty and HRQoL. The study found that uncertainty had a direct negative impact on physical and mental HRQoL, and self-care competence was identified as a key mechanism partially mediating this relationship. This suggests that uncertainty not only directly negatively impacts HRQoL but also indirectly lowers it by diminishing self-care competence. Self-care competence comprises not only knowledge but also complex behavioral elements such as symptom recognition and monitoring ability, decision-making ability, and self-regulation ability. For ICD patients, unpredictable electrical shock experiences and physical changes can be linked to psychological distress, leading to reduced HRQoL. Previous studies have also confirmed that increasing uncertainty leads to a decline in self-care competence [30]. This means that uncertainty affects HRQoL through self-care competence, and when uncertainty is low and self-care competence is high, HRQoL is high. This is consistent with the findings of studies that mediated the relationship between uncertainty and HRQoL through self-care competence [19,20]. These results suggest that self-care competence is important for improving HRQoL in uncertain situations such as ICD implant patients’ various symptoms and electric shock experiences.

This suggests that the HRQoL of ICD patients is not solely determined by disease severity or demographic characteristics but can be structurally influenced by cognitive interpretations of the disease situation and self-care competence. Notably, self-care competence demonstrated the potential to function as an adaptive resource capable of buffering the decline in HRQoL during periods of uncertainty. Therefore, nursing care for ICD patients needs to expand beyond a device-management-centered approach to a multidimensional management system integrating uncertainty reduction strategies and interventions to enhance self-care competence. This study is significant in that it simultaneously provides theoretical grounds and practical directions for improving the HRQoL of ICD patients. Therefore, to improve the HRQoL for ICD patients, strategies to enhance self-care using digital tools—such as step-by-step education programs tailored to the disease characteristics, symptom monitoring training, and self-care program should be implemented alongside psychological interventions that simply reduce uncertainty. Such strategies can serve as interventions that strengthen patients’ self-care competence and simultaneously improve both physical and mental HRQoL.

The study participants were middle-aged, employed, and had high EF. They were classified as NYHA Class I. While uncertainty, self-care competence, and both physical and mental HRQoL associated with ICD were at moderate levels, mental HRQoL was lower than physical HRQoL. The results of this study showed that self-care competence had a direct effect on both physical and mental HRQoL in the relationship between uncertainty and HRQoL in patients with ICDs. Therefore, self-care competence was identified as a mediating variable that positively influences HRQoL in uncertain situations, indicating that the implementation of self-care competence enhancement programs is crucial for improving participants’ HRQoL. To reduce uncertainty and improve HRQoL, it is necessary to assess the degree of uncertainty and strengthen self-care competence by utilizing self-care competence apps that enable continuous self-care. Additionally, nursing intervention strategies are required to enhance psychological support, including professional counseling to strengthen emotional support systems.