The underlying cause for AH should be kinown before there is an answer to your second question.
Usually, there is dilation due to intra heart pressures. Dilation can be a response to chronic volume overload (high blood pressure) or for example, in mitral valve regurgitation, the volume and pressure of the left atrium are greatly increased. The left atrium responds by undergoing chronic dilation, which enables it to accommodate the increased volume without as large an increase in pressure because of its increased compliance. Usually there is left ventricle dilatation as well.
The condition is deleterious because it increases the oxygen demand of the heart and decreases mechanical efficiency. Certain drugs, such as beta-blockers, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers have been shown to prevent or partially reverse remodeling (enlarged chamber) under pathologic conditions. Sometimes an athlete's heart chambers enlarge and that is not pathological, but beneficial and more efficient.
Volume from a leaky valve or pressure from high blood pressure normally.
And then it can cause atrial fibrillation which makes your atria into grapefruit.
Or, also likely, you were just born that way. Less likely though. When we see large atria in the echo lab. It's because of a leaky mitral valve which when the left ventricle squeezes, pushes blood back into the atria instead of forward. Stretches it out simply.
Atrial fibrillation is second. But which comes first, afib or the chicken or the egg? That is a long needless explanation.
So probably leaky valve, not the answer then, high blood pressure, then genetic, then well there is always this diastolic function stuff (an even longer needless explanation)
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