Did AF screening have a greater effect at higher blood pressure?

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Hypertension is a known risk factor for atrial fibrillation (AF) and stroke, but evidence on how systolic blood pressure (SBP) interacts with the effects of AF screening has been lacking.

The LOOP Study randomized people aged 70–90 who had no prior AF and had additional stroke risk factors to screening with an implantable loop recorder (ILR), with anticoagulation started if an AF episode lasting at least 6 minutes was detected, or to usual care. This substudy included 5,997 participants with baseline SBP measurements. Outcomes were analyzed by time to first event using cause-specific Cox models.

The hazard ratio for stroke or systemic arterial embolism with ILR screening versus usual care decreased as SBP increased. Among participants with SBP of at least 150 mm Hg, ILR screening produced a 44% reduction in the risk of stroke or systemic arterial embolism versus usual care (adjusted hazard ratio 0.56 [0.37–0.83]). Within the ILR group, SBP of at least 150 mm Hg was associated with a higher incidence of AF episodes lasting at least 24 hours than lower SBP (adjusted hazard ratio 1.70 [1.08–2.69]), but not with the overall occurrence of AF (adjusted P >0.05).

The researchers concluded that the impact of AF screening on thromboembolic events increased with blood pressure. SBP of at least 150 mm Hg was associated with a more than 1.5-fold increased risk of AF episodes lasting at least 24 hours and an almost 50% reduction in stroke or systemic arterial embolism with ILR screening, with a greater screening effect than at lower blood pressure. They said the findings should be considered hypothesis-generating and require further study.

The study was registered at https://www.clinicaltrials.gov, identifier NCT02036450.