Highlights
Research published in the European Heart Journal reveals a potent day-to-day association between plasma potassium levels and the occurrence of atrial fibrillation (AF) in at-risk individuals. The study, utilizing data from the LOOP trial, provides high-resolution temporal evidence of how electrolyte fluctuations influence cardiac rhythm.
- Hypokalaemia (p-potassium <3.5 mmol/L) was associated with a 2.24-fold increase in the incidence rate of daily AF compared to normal potassium ranges.
- Each 1 mmol/L decrease in plasma potassium was associated with a five-fold increase in the odds of experiencing AF episodes longer than 60 minutes.
- The association was most pronounced when potassium levels deviated from an individual’s usual baseline value, suggesting the importance of personalized electrolyte monitoring.
- Hypokalaemia was found in nearly 20% of days where AF episodes lasted longer than 240 minutes, indicating that low potassium may play a role in the persistence of arrhythmia.
Background: The Clinical Challenge of Paroxysmal AF and Electrolyte Imbalance
Atrial fibrillation (AF) remains a leading cause of stroke, heart failure, and cardiovascular morbidity worldwide. While established risk factors such as hypertension, obesity, and age are well-documented, the triggers for individual paroxysmal episodes often remain elusive. Potassium, a primary intracellular cation, is fundamental to cardiac electrophysiology. It governs the resting membrane potential and the repolarization phase of the action potential in atrial myocytes. Clinicians have long suspected that fluctuations in potassium levels—often driven by diet, medications like diuretics, or renal function—could trigger AF, yet empirical evidence linking day-to-day potassium variations to AF detected by continuous monitoring has been sparse.
Standard clinical care often relies on sporadic blood tests and intermittent ECGs, which may miss the transient nature of both hypokalaemia and paroxysmal AF. The advent of implantable loop recorders (ILRs) has revolutionized this field, allowing for years of continuous rhythm monitoring. By linking these high-fidelity rhythm data with routine blood test results, researchers can finally investigate the acute temporal relationship between electrolyte status and arrhythmic events.
Study Design: Leveraging Continuous Monitoring and Routine Clinical Data
This study represents a post hoc analysis of the LOOP study, a large-scale randomized controlled trial that evaluated the efficacy of ILR screening for AF in individuals with stroke risk factors (age 70–90 years with hypertension, diabetes, heart failure, or prior stroke). The analysis focused on 1,334 participants who received an ILR and had available plasma potassium (p-potassium) measurements from routine clinical care.
The researchers linked ILR raw data with blood test results, ensuring a strict temporal alignment where the potassium measurement and the heart rhythm monitoring occurred within the same 24-hour window. In total, the study combined over 1.6 million days of heart rhythm monitoring with 12,136 p-potassium measurements. The primary outcome was the occurrence of daily AF lasting more than 60 minutes. Secondary analyses examined different AF durations (240 min) and compared absolute potassium levels against individual “usual” values (calculated as the mean of all other potassium measurements for that participant).
Key Results: Quantifying the Link Between Potassium and Daily AF
The results provide a compelling quantitative link between low potassium and AF. The mean p-potassium was significantly lower on days when AF was detected compared to days without AF, with a mean difference of -0.21 mmol/L (95% CI: -0.25 to -0.18).
Incidence and Odds Ratios
Using self-controlled case analyses, the researchers found that the incidence rate ratio (IRR) for AF during periods of hypokalaemia (<3.5 mmol/L) versus the normal range (3.5–5.0 mmol/L) was 2.24 (95% CI: 1.29–3.88). When treated as a continuous variable, each 1 mmol/L decrease in p-potassium was associated with an adjusted odds ratio (aOR) of 0.20 (95% CI: 0.15–0.28). This effectively translates to a five-fold increase in the odds of AF for every 1 mmol/L drop in potassium.
Episode Duration and Persistence
One of the most striking findings was the correlation between potassium levels and the duration of AF episodes. Hypokalaemia was present in only 5.1% of days where AF lasted less than 60 minutes. However, this prevalence rose to 19.1% on days where AF lasted longer than 240 minutes. This suggests that while low potassium may trigger AF, it may be even more critical in sustaining the arrhythmia once it begins.
Personalized Deviations vs. Absolute Values
The study also introduced the concept of the individual’s “usual” potassium value. The association between low potassium and AF was significantly stronger when the potassium level deviated from the participant’s own average (aOR 0.15; P-interaction = 0.001) than when simply comparing absolute values across the population. This implies that a potassium level within the “normal” laboratory range might still be pro-arrhythmic if it represents a significant drop for that specific patient.
The Role of Diuretics
Interestingly, the association between low potassium and AF was less pronounced in participants receiving diuretics (aOR 0.28 vs. 0.14 in non-users; P-interaction < 0.0001). While counterintuitive at first glance—since diuretics often cause hypokalaemia—this may reflect a degree of clinical "pre-conditioning" or more frequent monitoring and intervention in patients known to be taking these medications.
Mechanistic Insights: Why Potassium Matters
From an electrophysiological perspective, hypokalaemia increases the chemical gradient for potassium efflux but paradoxically decreases the conductance of certain potassium channels (such as the inward rectifier potassium current, IK1). This leads to hyperpolarization of the resting membrane potential and a prolongation of the action potential duration in some tissues, while potentially shortening it in others due to effects on the sodium-potassium pump. These changes increase the likelihood of early and delayed afterdepolarizations (EADs and DADs), which serve as triggers for AF. Furthermore, hypokalaemia can increase automaticity and slow conduction velocity, creating the ideal substrate for reentry—the primary mechanism behind sustained AF.
Expert Commentary and Clinical Implications
The findings from the LOOP analysis suggest that the current clinical threshold for “concerning” potassium levels may need to be re-evaluated for patients at risk of AF. While 3.5 mmol/L is the traditional cutoff for hypokalaemia, this study suggests that even levels in the low-normal range (e.g., 3.6–3.8 mmol/L) could be problematic if they represent a downward shift for the patient.
Study Limitations
As an exploratory post hoc analysis of an observational nature within a randomized trial, this study cannot definitively prove causality. The p-potassium measurements were taken during routine care, which introduces potential selection bias (i.e., blood tests may have been ordered because a patient felt unwell). Additionally, while the study controlled for many variables, residual confounding from factors like magnesium levels or acute illness cannot be entirely ruled out.
Practice Gaps
For clinicians, these data reinforce the need for meticulous electrolyte management in patients with known AF or those at high risk for it. Specifically, in patients undergoing AF ablation or those with high paroxysmal burdens, maintaining potassium in the higher end of the normal range (e.g., >4.0 mmol/L) may be a simple, low-cost strategy to reduce the frequency and duration of episodes.
Conclusion
This study provides robust evidence that low plasma potassium is a significant day-to-day predictor of atrial fibrillation occurrence and duration. By utilizing continuous ILR monitoring, the researchers have shown that hypokalaemia more than doubles the incidence of AF and that the risk is particularly high when potassium levels fall below a patient’s personal baseline. These findings advocate for a more personalized and proactive approach to electrolyte monitoring in cardiovascular care, potentially using potassium stability as a tool for rhythm control.
Funding and ClinicalTrials.gov
The LOOP study was supported by the Innovation Fund Denmark, the Danish Council for Independent Research, the John and Birthe Meyer Foundation, and Medtronic. The study is registered at ClinicalTrials.gov (NCT02039284).
References
- Hessellund AK, Kongebro EK, Haugan KJ, et al. Hypokalaemia and atrial fibrillation detected by implanted loop recorders. Eur Heart J. 2025;46(47):5129-5139. doi:10.1093/eurheartj/ehaf623.
- Diederichsen SZ, Haugan KJ, Kronborg C, et al. Strategies for maintenance of sinus rhythm and the role of potassium: A systematic review. Europace. 2020;22(11):1622-1631.
- Skogestad J, Aronsen JM. Hypokalemia-induced arrhythmias and the importance of maintaining a high-normal serum potassium level in heart failure. Front Physiol. 2018;9:1457.
