Independent predictors of physical health in community-dwelling patients with coronary heart disease in Singapore

Coronary heart disease (CHD) is one of the leading causes of death and disability among adults worldwide, even in Singapore [1]. It has been well documented that patients with CHD experience poor health-related quality of life (HRQoL) [2, 3]. The HRQoL is a complex and multidimensional construct including physiological, emotional, and psychosocial components [4]. In particular, the physical health component of HRQoL was an important outcome measure for patients with CHD [5]. Poor physical health was found to be associated with higher hospital readmission rates and increased mortality [5]. Numerous studies have identified the determinates of physical health in patients with CHD, and many factors have been reported to contribute to the poorer physical health of patients with CHD. These include: (1) socio-demographic factors: age, gender, race, and social economic status (including education, income, and occupation) [6‐8]; (2) clinical factors: cardiac-related comorbidities such as hypertension and diabetes, type of diagnosis, revascularization therapies, and severity of the disease [7, 9]; (3) psychosocial factors: anxiety and depression, social support, and stress [4, 10]. However, our recent systematic literature review indicated that there is limited knowledge of the Asian CHD population with regards to their perceptions of the HRQoL and the influencing factors [1]. A deeper understanding of the independent predictors of physical health for Singaporean patients with CHD may help health professionals to develop effective interventions to address the key issues.

We adapted the Revised Wilson and Cleary model of HRQoL as the conceptual framework in guiding this study [11]. The Revised Wilson and Cleary model of HRQoL combined the paradigms of biomedical and social science, and posited HRQoL was influenced by both individual and environmental characteristics such as clinical, psychological, social and demographic status. We recently conducted a randomized controlled trial for community-dwelling patients with CHD in Singapore (Trial Registration Number: ISRCTN15839687). This report is the analysis of the baseline data of the trial, and the aim of this short report is to identify the independent predictors of physical health of Singaporean patients with CHD.

HRQoL is the subjective evaluation of the impact of an illness and its related treatment on patient’s life [19]. It is an important outcome that has been widely used to measure treatment satisfaction and efficacy [3]. Past evidence has shown that patients with CHD tended to have a poor HRQoL compared to the healthy population [20]. Results from the current study revealed that the participants’ HRQoL in the current sample is similar to the previous studies conducted in Hong Kong and mainland China [4, 5]. However, when compared to the recent study done locally [1], the participants in the current sample reported a poorer HRQoL in both physical and mental aspects. In addition, there was a higher percentage who reported high levels of anxiety or depression.

Anxiety and depression are the two psychological factors that are commonly identified as strong predictors to a poorer HRQoL among patients with CHD [20‐23]. Both were found to be associated with recurrent heart attacks and risks of death [24‐26]. In the current study, anxiety, depression, and perceived stress were found to be negatively correlated to physical health. Such finding is not surprising, as patients with CHD often have symptoms like chest pain and breathlessness which give rise to the sense of impending doom and aggravate patients’ fear of another heart attack. Because of the fear and the sense of uncertainty, many patients have altered their lifestyle with the goal of preventing the attack [27, 28] and become apprehensive in returning to their normal routines [28]. On the other hand, while grappling with new changes, the inability to fulfil one’s role (social, familial, or professional) may further distort their self-images and contribute to their mounting anxiety [29]. In the current sample, the majority of the participants were from a lower social economic class, with 67.4 % still working and 53.5 % earning a monthly household income of equal to or less than SGD3,000, much lower than the median household income (SGD8,290) in Singapore [18]. Barbareschi and Sanderman [30] argued that a low-SES individual possessed limited resources to promote wellbeing and had higher psychosocial stress. Many of our participants faced the stress to make ends meet, thus engaging in secondary prevention behaviours may become less of a priority. Consequently, the reduced engagement in health behaviours results in an accelerated disease progression and a poorer HRQoL.

By contrast, CSS-CS and CSS-MF were found to be positively correlated with PCS in the current study. These findings are consistent with evidences from the literature supporting the association between self-efficacy and physical health [31‐33]. Low cardiac self-efficacy was found to be associated with a poorer health status even after it was adjusted for disease severity and depressive symptoms [34]. LaPier and Cleary [33] reported that older patients reported higher levels of cardiac self-efficacy, suggesting that life experiences and coping skills may help increase a patient’s confidence in self-management behaviours. Furthermore, while lower cardiac self-efficacy was associated with poorer physical function and less physical activities, patients with low physical function may actually have the greatest improvements in self-efficacy after engaging in physical activities [33]. These findings suggest that self-efficacy is an important and perhaps more easily modified factor that influences the physical health component of patients with CHD.

In this study, depression and CSS-MF were identified as the independent predictors for the PCS. In addition, CHD family history was found to be a significant predictor for the PCS after adjusting other variables. These three predictors accounted for 42 % of the variance. The results suggested that a high level of depression predicted poorer physical health, while a higher level of CSS-MF predicted better physical health. Interestingly, after adjusting other variable, no family history of CHD predicted better physical health. Depression has been consistently identified as the factor that has a major impact on the HRQoL of CHD patients worldwide, including in Asian patients [1, 4, 5, 10]. Depression impairs the patients’ engagement in secondary prevention behaviours such as exercise and medication adherence, which are crucial in delaying disease progression [2]. Lee et al. [5] added that many individual risk factors (modifiable and non-modifiable) that influence the physical component of the HRQoL of CHD patients were mediated by psychological distress. Therefore, providing interventions to mitigate the psychological distress for this group of patients may be more helpful and effective in enhancing treatment outcome [5]. Similarly, CSS-MF could be another modifiable factor that is important in maintaining patients’ physical health. Like depression, CSS-MF probably affects a patient’s physical health through its association with an individual’s engagement in secondary preventive behaviours. Oka and Gortner [35] noted that self-efficacy was a strong mediating factor that influences patients’ activity levels, and that it was a better predictor of physical activity than peak oxygen consumption. Many studies have also reported that there was a strong connection between self-efficacy and exercise behaviour, and functional status and quality of life in patients with CHD [36, 37]. Lastly, family history of CHD became one of the significant predictors after adjusting other variables. This finding gave us a heads-up that we might have missed out on significant findings if we only included the significant univariates into the multivariate analysis. Nevertheless, the presence of family history of CHD may indicate a genetic predisposition that links to poorer physical health.

Several factors must be considered when interpreting the results of this study. First, this was a cross-sectional analysis of the baseline data from the randomised controlled trial study, therefore caution must be exercised when extrapolating these results to CHD patients in other settings. Second, the use of self-reported questionnaires may result in social desirability responses. Third, despite we had recruited a total of 129 participants, it is still possible that current study may be under power as there were more than ten independent variables in the final multivariate linear regression analysis. Nevertheless, the current study has shed some light on the key factors influencing the physical health component of the HRQoL in patients with CHD in Singapore. Healthcare practitioners may have started to recognize that patients with a poorer physical health component in their HRQoL not only have a poorer overall quality of life, but also impaired physical function. In this sample, we identified depression and CSS-MF as the independent predictors for the physical health component of the HRQoL. This finding suggests tailored interventions that target mitigating one’s psychological distress and promote self-efficacy may be helpful in improving patients’ physical health and quality of life. Healthcare professionals may incorporate routine screenings for symptoms of depression and provide early intervention. This study also emphasizes the importance of going beyond brief discharge instructions and equipping patient coping skills in dealing with life changes arising from CHD. These measures will better prepare patients to deal with the challenges related to CHD, improve self-efficacy and eventually improve HRQoL.

BMI, body mass index; CHD, coronary heart disease; CSS, cardiac self-efficacy scale; CSS-CS, self-efficacy for controlling symptoms; CSS-MF, self-efficacy for maintaining function; HADS, hospital anxiety and depression scale; HRQoL, health-related quality of life; MCS, mental component summary; PCS, physical component summary; PSS, perceived stress scale; SF-12v2, short form 12-item health survey version 2