Low SBP predicts all-cause death in patients with atrial fibrillation

Individuals with atrial fibrillation (AF) and a systolic blood pressure (SBP) of <110 mm Hg appear to be at higher risk of all-cause death, suggests a study, noting however that SBP is not significantly associated with renal (dys)function.

"This may reflect general poor health and/or excessive antihypertensive therapy, which should be avoided,” the investigators said.

A total of 1,580 patients (mean age 71 years, 60 percent male) were included in the analysis and had their baseline SBP recorded. They were then categorized as follows: 120–129 mm Hg (n=289, reference group), <110 mm Hg (n=165), 110–119 mm Hg (n=254), 130–129 mm Hg (n=321), 140–159 mm Hg (n=385), and ≥160 mm Hg (n=166).

The investigators conducted Cox regression analysis, adjusted for age, oral anticoagulation (OAC), and CHA2DS2-VASc score, to establish the impact of SBP, renal function, and their interaction on 1-year outcomes. They compared the SBP cohorts using ANOVA and chi-square tests.

Use of OAC was 84 percent and comparable across SBP groups. Nearly one in four (24 percent) participants had renal dysfunction (estimated baseline glomerular filtration rate [eGFR] <60 ml/min), with significantly lower eGFR values in the SBP 110–119 mm Hg group. [J Hypertens 2024;42:2148-2154]

A history of heart failure was more common among individuals with SBP <110 mm Hg, which was independently predictive of all-cause mortality on univariate (hazard ratio [HR], 2.36, 95 percent confidence interval [CI], 1.20–4.64) and adjusted analysis (adjusted HR, 9.71, 95 percent CI, 1.73–54.5).

Of note, SBP showed no statistically significant interaction with eGFR and no associations with either haemorrhagic or thromboembolic events.

“The ‘paradox’ of higher mortality in people with lower SBP likely reflects poor overall health,” the investigators said. “The lack of effect of SBP categories for cerebrovascular and thromboembolic events supports this but shows that other health issues were likely driving the higher mortality among people with low SBP.”

Causality

Nevertheless, this study showed associations, but not direct causation, between lower BP and death, as opposed to the effects of multimorbidity, polypharmacy, and frailty on outcomes seen in other studies. [Thromb Haemost 2022;122:142-150; Thromb Haemost 2023;doi:10.1055/s-0043-1770724; Thromb Haemost 2024;124:69-79]

"This is important given the clinical complexity associated with AF patients, with implications for treatments and outcomes,” the investigators said. “This is evident by the higher proportion of patients with heart failure and the corresponding higher use of digoxin and diuretics in the group with the lowest SBP.” [Thromb Haemost 2024;124:135-148; Thromb Haemost 2022;122:2030-2041]

Establishing causality would require a treatment intervention and is beyond the scope of the current study, according to the investigators, noting that their findings suggest avoiding excessive BP reduction in individuals with adequately anticoagulated AF regardless of renal function.

“Our study further indicates that ongoing monitoring of BP is needed to avoid low systolic BP in people with AF,” they said.