Atrial flutter alone carried a lower stroke rate than atrial fibrillation

Design

Nationwide registry cohort with ECG-confirmed rhythm

Population

40,986 patients with new-onset atrial fibrillation or flutter, Finland 2007-2018

Primary outcome

Ischaemic stroke

Effect

Flutter only vs fibrillation only, adjusted IRR 0.60 (0.49-0.74)

This Finnish nationwide registry linked every patient with new atrial fibrillation or flutter from 2007 to 2018 to more than half a million digitally stored ECGs, so the rhythm diagnosis rests on the tracing rather than a code. Of 40,986 patients, 30,261 had fibrillation only, 2,409 flutter only and 8,316 both.

The crude ischaemic stroke rate was 1.1 per 100 patient-years with flutter only, 1.9 with fibrillation only and 2.1 with both. After adjustment, flutter alone carried a lower rate than fibrillation alone (IRR 0.60, 95% CI 0.49 to 0.74), and mixed rhythm slightly higher (1.11). The pattern held in untreated time, before ablation and across CHA2DS2-VA categories.

This is observational. It supports a lower absolute risk in pure flutter, but it does not test whether anticoagulation can be safely withheld, and guidelines still apply the same thresholds to flutter as to fibrillation.

• Continue to anticoagulate atrial flutter using the same risk score and thresholds as atrial fibrillation.
• Look for coexisting fibrillation on previous ECGs and monitoring; it was common and carried the higher risk.
• After flutter ablation, keep checking for new fibrillation, which often follows.
• Include the lower absolute risk of pure flutter in shared decisions for patients at the threshold for treatment.

Why it matters

It challenges the assumption that flutter and fibrillation share one stroke risk, which a future trial may need to test.

Don't overread it

This is a registry comparison; it does not show that withholding anticoagulation in flutter is safe.

The statistics, in plain English

An incidence rate ratio of 0.60 means the stroke rate in pure flutter was about 40% lower than in pure fibrillation after adjusting for measured differences. Because nobody was randomised, unmeasured differences between the groups could explain part of it.

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