Heart structure and valve problems
Atrial fibrillation is more likely when the atria are stretched or irritated. Several heart conditions do this by changing pressure and flow inside the heart.
Valve problems
The heart’s valves act like one-way doors. If a valve is narrowed or leaky, pressure can build up behind it and stretch the atria. The mitral valve is especially important because it sits between the left atrium and the left ventricle.
- Mitral regurgitation (leaky valve): can enlarge the left atrium over time.
- Mitral stenosis (narrow valve): increases left atrial pressure and AF risk.
- Aortic stenosis: can stiffen the ventricle and raise left atrial pressures indirectly.
Heart failure and a “stiff heart”
Some people have a heart that pumps “normally” but is stiff and doesn’t relax well. This can raise pressures that stretch the atrium. AF can sometimes be the first obvious sign of this.
Scarring and previous heart procedures
Scarring in the atria can occur after heart surgery or inflammation. Scar tissue can disrupt the normal spread of electrical signals.
How doctors look for structural causes
The most common test is an echocardiogram (ultrasound of the heart). It can show:
- Atrial size (enlarged atria suggest long-term strain)
- Valve function
- Pumping function
- Evidence of high pressures or heart stiffness