This study was designed in line with Strengthening the Reporting of Observational studies in Epidemiology (STROBE) methodology for cross-sectional studies.17 The population distribution was analysed for prevalence by gender, exposure to CVD risk factors, and number of risk factor counts. Statistical associations were tested between independent variables and risk factors, and the direction of association was determined.
This study does not require ethical approval or subject consent. However, approval for use of anonymised data was required. This was received from the office of the Caldicott Guardian, NHS Highland. The NHS Scotland guidance and regulation on the use of anonymised data of patients does not require recourse to patients on the use of data for the purpose of clinical research inputs meant for hospital benefits.
Retrospective data from patients who had undergone PCI at Raigmore Hospital in Inverness, NHS Highland from 4th of January 2016 to 31st of December 2019 were included in the study. Eligible patient’s demographic and clinical data were collected at the point of admission for a PCI.
Patients who have had at least one elective or emergency PCI.
Demographic details include age, gender, geographic deprivation groups, economic deprivation ranks, family history of coronary artery disease, and risk factor counts; procedural, administrative, and clinical details such as body mass index, total cholesterol concentration, blood sugar concentration, blood pressure status and smoking status.
Data source and measurements
Age at the time of the data collection was grouped into four ranges: below 40, 40–59, 60–79, and 80 and above years.18 Geographic deprivation groups were derived from postcode data-match with the Scottish Index of Multiple Deprivation, SIMD 2019.19 The SIMD 2019 defines geographical location postcodes in Scotland as six groups: ‘accessible rural’, ‘remote rural’, ‘accessible small towns’, ‘remote small towns’, ‘large urban areas’ or ‘other urban areas’ - these groups were re-classified into ‘SIMD groups’ and expressed as ‘urban’, ‘accessible’ and ‘remote’. Economic deprivation ranks were derived from postcode data-match with the Scottish Index of Multiply Deprivation, SIMD 2020.19 The SIMD 2020 defines geographical location postcodes in Scotland as economic rank 1 (most economically deprived data zone) to rank 6976 (least economically deprived data zone) and classified as ‘SMID ranking’ in quintiles from one to five. BMI ranges were defined using the WHO adults’ BMI classification: underweight (below 18.5), normal weight (18.5–24.9), pre-obesity (25.0–29.9), obesity class I (30.0–34.9), obesity class II (35.0–39.9), obesity class III (above 40).20 These were grouped into ‘low or normal weight’ (≤24.9) and ‘elevated BMI’ (≥25.0) to capture the preventive and corrective nature of intervention. Cholesterol concentration was defined using the BHF measurement and grouped ≤5mmol/L as healthy and >5mmol/L as high.21 Blood sugar and blood pressure were qualitatively defined from the original dataset.
Body mass index (BMI) was derived from patients’ weight and height data and measured in kg/m2. All dependent variables (BMI, total cholesterol, blood sugar concentration, and blood pressure) used the National Health Services, NHS Scotland measurement units.22 These variables were grouped based on exposure as high cholesterol and healthy cholesterol (cholesterol concentration), diabetic and not diabetic (blood sugar concentration), hypertensive and not hypertensive (blood pressure), elevated BMI and not obese (BMI group), smoking and not smoking (smoking group). Units are available in appendices.
The study data has a few repeat patient PCI visits resulting in point duplicates. This was noted and reported in the results section. The study data did not provide sufficient detail of collection for the cholesterol variable (for hyperlipidaemic exposure), resulting in missing data >50%. Fitness analysis was conducted to measure the effect of this bias on concerned variable. Goodness of fit was tested to measure the representativeness of the data.
The distribution of the population by gender was presented in tables. Tests for differences in means (Welch two sample t-tests) and equality of proportions (3-sample prop-tests) were conducted to check for variance between groups. The prevalence of each risk factor by exposure within the population was analysed by proportions. Risk factor counts proportions were reported for each risk factor within the population.
Missing data were checked (missing compare test) for fitness as missing completely at random (MCAR) to validate the nature of missingness in variables with >10% missing data e.g. hyperlipidaemic variable, for exposure to cholesterol. Goodness of fit (Pearson's Chi-squared test) was conducted to ascertain the representativeness of the data in the general population.
A test of association was performed (Pearson's chi-square test) to detect if there was any significant relationship (1) across independent variables (population’s age, gender, deprivation groups, deprivation ranks, and risk factor counts) and CVD behavioural risk factor determinants (for all identified behavioural risk factors), and (2) within CVD behavioural risk factor determinants using a dependent variable of interest as a potential predictor based on initial association and prevalence scores. A unit score was assigned for overall level of prevalence and association significance across all CVD behavioural risk factor determinants. Unit scores were added to ascertain a preferential determinant of choice.16,18
Finally, the direction of risk in association was analysed for a preferred CVD risk factor determinant (general logistics modelling: odds ratio and co-efficient estimates) among notable predictors with significant association scores in order to inform a suggestive clustering for the purpose of targeting intervention design in the whole population.
Continuous data analysis was presented as means ± standard deviations (SD) while categorical data was presented in percentages. Data wrangling and analyses was done using the R Studio Version 1.3.1056 software.23 All tests were two-tailed with level of significance set at P<0.05, and 95% Confidence Interval (CI).
Role of funding source
The sponsors, as acknowledged in this text were not involved in study design; the collection, analysis and interpretation of data, the writing of the report or the decision to submit this paper for publication.