Cause page

Illness and temporary triggers

AF can start during a temporary stress on the body — even in people who have never had AF before. This does not mean the episode is meaningless: it can still reveal underlying vulnerability.

Infections and inflammation

Chest infections, severe flu, and other infections can trigger AF via fever, inflammation, and stress hormones.

After surgery

AF can occur after surgery because of pain, inflammation, fluid shifts, and changes in electrolytes. It is commoner after major operations and in older patients.

Dehydration and electrolyte changes

Low potassium or magnesium can make the heart more prone to rhythm problems. Dehydration can worsen this, especially if you are unwell or taking diuretics.

Thyroid overactivity

An overactive thyroid can trigger AF by increasing the body’s “speed setting.” Thyroid tests are commonly checked when AF is newly diagnosed.

What happens after a trigger-related episode?

Sometimes AF resolves when the illness resolves. Even then, it is still worthwhile to look for underlying contributors (blood pressure, sleep apnea, weight, heart structure).

Key point: a trigger often explains “why today,” but not necessarily “why me.” Both pieces matter.