Hypokalaemia and atrial fibrillation detected by implanted loop recorders.

Background And Aims: Potassium levels influence cardiac electrophysiology, yet their day-to-day association with atrial fibrillation (AF) remains unclear. This study investigated the association between plasma potassium (p-potassium) and daily AF in at-risk individuals undergoing continuous electrocardiographic monitoring.

Methods: This is a post hoc analysis of the LOOP study randomizing participants with stroke risk factors to implantable loop recorder (ILR) screening for AF (n = 1501) or usual care. The ILR raw data were linked to p-potassium measurements collected in routine care allowing for 1-day time difference. Associations between p-potassium and daily AF > 60 min (main outcome) were analysed using generalized and linear mixed effect models.

Results: The ILR data and blood tests results were available for 1334 participants combining >1.6 million days of heart rhythm monitoring (including 50 746 days with AF) with 12 136 p-potassium measurements. P-potassium was lower on days with AF [mean difference -.21 mmol/L (-.25; -.18)]. Self-controlled case analyses comparing AF incidence during hypokalaemia (p-potassium <3.5 mmol/L) vs in normal range yielded an incidence rate ratio of 2.24 (1.29-3.88). Hypokalaemia was present in 5.1% of days with AF lasting <60 min and 19.1% with AF lasting >240 min. Each mmol/L decrease in p-potassium was associated with a five-fold increase in odds of AF [adjusted odds ratio (aOR) .20 (.15-.28)], more strongly when p-potassium deviated from the individual's usual value [aOR .15 (.10-.24); P-interaction = .001], and less in participants receiving diuretics [aOR .28 (.17-.47); P-interaction < .0001].

Conclusions: This exploratory study found that low p-potassium was associated with day-to-day AF occurrence, particularly for longer episodes and when deviating from the individual's usual level.