Participants
Patients from three medical centers in the Shanxi province of China were enrolled according to predefined inclusion and exclusion criteria. The inclusion criteria were: age ≥18 years; diagnosed with HF according to current guidelines [3]; New York Heart Association (NYHA) functional class II-IV; and receipt of HF therapy in the past month. Patients who experienced acute cardiovascular events in the past 2 months, had a life expectancy of < 1 year, could not understand or complete the questionnaire due to language barriers or intellectual disabilities, and those who refused to participate in this project were excluded.
Procedure and data collection
The present investigation was a multicenter, prospective cohort study performed from May 2017 to May 2019. Information regarding baseline data, self-administered questionnaire, and CHF-PRO scores were collected during hospitalization. Self-management advice, which included medication use, regular schedule, keeping warm, dietary instructions, health education, smoking cessation, temperance, and exercise, was provided in written form to the participants at discharge. Dietary instructions included a low-sodium diet (LSD), low-fat diet, and the avoidance of over-eating. Among these strategies, a regular schedule was defined as maintaining relatively fixed sleep and wake times, and LSD intake < 5 g of salt per day. All participants were followed-up at 1, 3, and 6 months after discharge in face-to-face consultations or telephone follow-up to obtain information regarding the self-administered questionnaire and CHF-PRO scores [9]. To ensure quality, all questionnaires were administered by professionally trained individuals.
Baseline information included patient age, sex, height, weight, marital status, education, annual income, family history of cardiovascular disease, NYHA functional class, blood pressure, and complications. The Charlson comorbidity index was applied to assess complications.
The self-administered questionnaire was developed to assess self-management. The questionnaire contained all strategies provided at discharge as mentioned above, with responses scored on a 5-point Likert, as follows: 0 (never happens); 1 (happens occasionally); 2 (happens half of the time); 3 (happens often); and 4 (happens every day).
The CHF-PRO was developed by the authors’ research group and adopted in this study. This questionnaire contains 57 items, 12 subdomains, and 4 domains, which consisted of physical, psychological, social, and therapeutic domains [9]. Patients responded to each item on a 5-point Likert scale to reflect how often they had experienced each issue.
Statistical analysis
Continuous variables are expressed as mean ± standard deviation (SD) or median (interquartile range). Univariate analysis of variables and calculation of MCID were performed using SPSS version 25.0 (IBM Corporation, Armonk, NY, USA). The backward method was used for statistically significant variables (P < 0.1). Further multilevel model assumptions were confirmed through analysis of residuals generated by MLwiN version 3.0 software (Centre for Multilevel Modelling, University of Bristol, Bristol, United Kingdom).
Multilevel model
The multilevel model, which can handle repeated measures data, was applied to assess the effect of self-management strategies to the overall summary (OS) of CHF-PRO. The main concept of this model is to estimate variance at each level and consider the effect of the explanatory variables on the variance to estimate the regression coefficient effectively [11]. The model was constructed as follows:
Yij represents OS of CHF-PRO taken from the ith person; eij is the residual of the first level; β0j is the coefficient variable, which could be formulated by equation 2; β0 and βj stand for fixed parameters representing the average of the intercept and slope, respectively; and u0j and uij represent interindividual variability in intercepts and slopes via random effects. Maximum likelihood estimates can be computed from the covariance matrix.
Multivariate multilevel model
The multivariate multilevel model was fitted to assess self-management strategies on physical scores (PHYS), psychological scores (PSYS) [11]. The multivariate variance components model was constructed as follows:
In the equation above, Yitk represents the vector of two outcome measurements, taken from the i th person at time t; Dk is a pseudo variable, with a unique pseudo variable for each outcome; the k response variable, β0ik is the overall intercept for person i; β1ik denotes a patient-specific slope; and eitk is residual error at time t for person i.
In the present study, model 1 was the null model. Time was added to model 1 as an explanatory variable to establish model 2, which was used to study the effect of time on variables. Model 3 was constructed when baseline information and self-management situation of participants were included in model 2.
MCID
Although P < 0.05 is often considered to be the criterion for evaluating the effectiveness of an intervention in PRO or QoL, the P value merely represents statistical significance. In our study, MCID was introduced to analyze its clinical significance to determine more effective self-management strategies. ES of the distribution method was applied to calculate MCID according to characteristics of the current CHF-PRO data [10, 12]. ES was formulated as follows:
In the equation above, x0 represents baseline scores of patients. represents the average baseline scores of individuals, and is the average follow-up scores of individuals. In our study, a moderate effect of 0.5 was used as the effect size statistics to estimate MCID.
Finally, β values of the multi-level model were compared with MCID. The first level of the variables was considered “0”, and multiplied the β value by the grade of levels minus “1”. The corresponding grade of variables up to MCID was defined as reaching clinical significance.