Measures and analysis. The primary outcome measure was the difference in systolic BP at 12-month follow-up between the intervention and usual care groups (adjusting for baseline BP, practice, BP target levels, and sex). Secondary outcomes included systolic and diastolic BP at 6 and 12 months, weight, modified patient enablement instrument, drug adherence, health-related quality of life, and side effects from the symptoms section of an adjusted illness perceptions questionnaire. At trial, registration participants and general practitioners were asked about their use of self-monitoring in the usual care group.
The primary analysis used general linear modelling to compare systolic BP in the intervention and usual care groups at follow-up, adjusting for baseline BP, practice (as a random effect to take into account clustering), BP target levels, and sex. Analyses were on an intention-to-treat basis and used multiple imputation for missing data. Sensitivity analyses used complete cases and a repeated measures technique. Secondary analyses used similar techniques to assess differences between groups. A within-trial economic analysis estimated cost per unit reduction in systolic BP by using similar adjustments and multiple imputation for missing values. Repeated bootstrapping was used to estimate the probability of the intervention being cost-effective at different levels of willingness to pay per unit reduction in BP.
Main results. The intervention and usual care groups did not differ significantly – participants had a mean age of 66 years and mean baseline clinical BP of 151.6/85.3 mm Hg and 151.7/86.4 mm Hg (usual care and intervention, respectively). Most participants were White British (94%), just more than half were men, and the time since diagnosis averaged around 11 years. The most deprived group (based on the English Index of Multiple Deprivation) accounted for 63/622 (10%), with the least deprived group accounting for 326/622 (52%).
After 1 year, data were available from 552 participants (88.6%) with imputation for the remaining 70 participants (11.4%). Mean BP dropped from 151.7/86.4 to 138.4/80.2 mm Hg in the intervention group and from 151.6/85.3 to 141.8/79.8 mm Hg in the usual care group, giving a mean difference in systolic BP of −3.4 mm Hg (95% CI −6.1 to −0.8 mm Hg) and a mean difference in diastolic BP of −0.5 mm Hg (−1.9 to 0.9 mm Hg). Exploratory subgroup analyses suggested that participants aged 67 years or older had a smaller effect size than those younger than 67. Similarly, while the effect sizes in the standard and diabetes target groups were similar, those older than 80 years with a higher target of 145/85 mm Hg showed little evidence of benefit. Results for other subgroups, including sex, baseline BP, deprivation, and history of self-monitoring, were similar between groups.
Engagement with the digital intervention was high, with 281/305 (92%) participants completing the 2 core training sessions, 268/305 (88%) completing a week of practice BP readings, and 243/305 (80%) completing at least 3 weeks of BP entries. Furthermore, 214/305 (70%) were still monitoring in the last 3 months of participation. However, less than 1/3 of participants chose to register on 1 of the optional lifestyle change modules. In the usual care group, a post-hoc analysis after 12 months showed that 112/234 (47%) patients reported monitoring their own BP at home at least once per month during the trial.