Study design and setting
This was a longitudinal survey involving a multi-ethnic Asian cohort of adult outpatients with known CVD in National University Hospital, Singapore, a 1200-bed tertiary hospital and a major referral center. Recruitment took place between 29th April to 19th June 2020, commencing approximately 4 weeks after partial lockdown was imposed, till the end of Phase 1 Safe Re-opening.
Study population
Asian patients with known CVD were eligible if they were at least 21 years of age, had completed a HRQoL questionnaire prior to the COVID-19 outbreak, and agreed to participate. Asian was defined as a person having origins in any of the original peoples of the Far East, Southeast Asia, or the Indian subcontinent, for example, Cambodia, China, India, Japan, Korea, Malaysia, Singapore, Pakistan, Philippines, Thailand and Vietnam[13]. The diagnosis of CVD (coronary artery disease, heart failure, arrhythmias, others) was based on internationally accepted criteria, and performed by their managing cardiologists. In addition, these patients were part of previous research projects which collected data on HRQoL [Survey on Heart Disease Patients’ Health-related Quality of Life and Preferences (CIRB Reference: 2017/2125), Improving Outcomes in Acute Myocardial Infarction Through Reversal of Early and Late Cardiac Remodelling Study (DSRB Ref: 2014/00793) and Nitrates In Combination with Hydralazine in Cardiorenal Syndrome Study (DSRB Ref: 2014/00790)] and were referred by their managing cardiologists for participation during outpatient consultations. Patients were recruited consecutively with no restrictions on type and stage of CVD.
Patients were excluded if they were illiterate or refused to provide consent.
Verbal consent for participation was obtained over the phone, prior to follow-up survey. This study was approved by the Domain Specific Review Board (NHG DSRB Ref: 2020/00436) and conducted according to the World Medical Association Declaration of Helsinki.
Assessments
Our study used EQ-5D questionnaires for HRQoL assessments. The EQ-5D is one of the most commonly used generic preference-based health status questionnaires [14]. Three-level EQ-5D (EQ-5D-3L) contains five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression, each with three response levels (no problems, some/moderate problems or severe/extreme problems). It also has a visual analog scale (EQ-VAS) measuring health on the scale of 0 to 100, with a higher score indicating better health. A five-response level version was later developed (EQ-5D-5L) to enhance its sensitivity and reduce ceiling effect [15]. Both the versions have been psychometrically validated in a large number of diseases and conditions, including cardiovascular health [16].
Our study used official English and Chinese versions of EQ-5D-3L and EQ-5D-5L questionnaires. The utility scores for EQ-5D-3L and EQ-5D-5L were derived from the Singapore value set for EQ-5D-3L and its crosswalk algorithm, respectively [17]. Utility scores range from -0.769 to 1, with higher scores indicating better health. Dimension-specific sum score was calculated as the mean of each dimension-specific item responses. Dimension-specific score range from 1 to 3 for EQ-5D-3L and 1 to 5 for EQ-5D-5L, with a higher score indicating worse health.
The EQ-5D-3L and EQ-VAS were administered to all study participants. In addition, a subset of participants also administered the EQ-5D-5L. EQ-5D-3L and EQ-5D-5L were administered in random order to avoid sequence effect on the responses. The pre-pandemic questionnaires were self-administered by the participants during physical outpatient visits. However, due to restrictions in face-to-face visits during the pandemic, the follow-up assessments were conducted remotely, either via the phone or through the mail.
In addition to EQ-5D questionnaires, the study collected sociodemographic and clinical information on patient CVD diagnosis, comorbidities and New York Heart Association (NYHA) functional class. Clinical information was recorded from patients’ medical records available at the hospital. NYHA functional class was assessed during both pre- and during pandemic visits.
Sample size
We anticipated that pandemic might have a mild-to-moderate impact on patients’ HRQoL. The sample size for the study was estimated to detect a change of one-third of standard deviation (SD) (paired difference divided by SD = 0.33 standardized effect size) based on dimension-specific scores[18]. A sample size of 75 participants was required to detect the desired change in a dimension-specific score of 0.33 standardized effect size with 80% power at a 5% two-sided level of significance using the paired t-test[19]. The sample size was not adjusted for multiplicity due to the exploratory nature of this study. The sample size was calculated using PASS 2020 Power Analysis and Sample Size Software (2020). NCSS, LLC, US.
Statistical analysis
The mean (SD) of pre-pandemic and pandemic, as well as change in dimension-specific scores were calculated for all EQ-5D dimensions. Two-sided paired t-tests were used to assess the statistical significance of the change in the scores. The changes in scores were also presented with the standardized effect size (SES) estimated as the mean paired difference of during and pre-pandemic assessments divided by the standard deviation of pre-pandemic assessment. SES was considered small (0.2), medium (0.5), and large (0.8) according to Cohen’s recommendation [18].
Dimension-level item responsiveness was evaluated using a percentage of participants in each of the severity level at pre- and during-pandemic assessments. The distribution of participants between the two assessments was compared using the McNemar-Bowker exact test of symmetry.
EQ-VAS and utility scores for EQ-5D-3L and EQ-5D-5L were analyzed similarly to dimension-specific scores.
The analysis based on the EQ-5D-3L and EQ-5D-5L data were considered as the primary analysis and sensitivity analyses, respectively, as EQ-5D-5L was administered to only a subset of participants. Sensitivity analyses were also performed on the EQ-5D-3L and EQ-5D-5L data using the Wilcoxon signed-rank test to evaluate the robustness of the paired t-test results.