Systolic blood pressure drops slowly over the final two years of life in individuals older then age 80. This terminal sBP decline most likely is a marker rather than cause of mortality.
Background: Clinical trials show benefit from lowering systolic blood pressure in people aged ≥80 years but epidemiological studies suggest lower systolic blood pressure may be associated with higher mortality. This study aimed to evaluate associations of SBP with all-cause mortality by frailty category over 80 years of age and to evaluate SBP trajectories before death.
Methods: A population-based cohort study was conducted using electronic health records of 144,403 participants aged 80 and older registered with family practices in the United Kingdom from 2001-2014. Participants were followed for up to five years. Clinical records of systolic blood pressure (SBP) were analysed. Frailty status was classified, using the e-Frailty Index, into the categories of 'fit', 'mild', 'moderate' and 'severe' frailty. All-cause mortality was evaluated by frailty status and mean SBP in Cox proportional hazards models. SBP trajectories were evaluated using person months as observations, with mean SBP and antihypertensive treatment status estimated for each person month. Fractional polynomial models were used to estimate SBP trajectories over five years before death.
Results: There were 51,808 deaths during follow-up. Mortality rates increased with frailty level and were greatest at SBP <110 mmHg. In 'fit' women, mortality was 7.7 per 100 person years at SBP 120-139 mm Hg, 15.2 at SBP 110-119 mmHg and 22.7 at SBP <110 mmHg; for women with 'severe' frailty, rates were 16.8, 25.2 and 39.6 respectively. SBP trajectories showed an accelerated decline in the last two years of life. The relative odds of SBP<120 mmHg were higher in the last three months of life than five years previously both in treated (odds ratio 6.06) and untreated patients (6.31). There was no evidence of intensification of antihypertensive therapy in the final two years of life.
Conclusions: A terminal decline of SBP in the final two years of life suggests that epidemiological associations of low SBP with higher mortality may be accounted for by reverse causation, if participants with lower blood pressure values are closer, on average, to the end of life.