Enlargement of left atrium but pressure's normal

Doctor heard a murmur and sent me for an echo.  The results were normal, but MD noted that I have a borderline abnormality in that the left atrium is enlarged, but the pressure is normal.  I am obese and was seeking routine guidance from the MD for diet/exercise and to have someone to be accountable to!  MD states that she feels the enlargement is due to the weight I've been carrying and that over time it has put increased stress on my heart and caused an enlargement in the left atrium.

My questions are:
1.  Is this reversible with weight loss and continued diet/exercise?
2.  Why would only one chamber be enlarged and not all four?

Thanks!

[erijon]

You have to understand the limitations of echocardiography in assessing left atrial size: although they are telling you that it is dilated with the upper limit of normal is 4 cm, it may actually not be dilated at all. This measurement was most likely obtained on a single 'slice' of the atrium and may not be representative of actual left atrial size. For instance if you slice a banana perpendicular to its long axis you may get a small value, but if you cut it at a 45 degree angle you may get a larger value: simply because you were not perpendicular to its main axis. Often patients, especially patients who may be heavy or have been heavier in the past do not have the standard  orientation in the chest and may be rotated to the left, causing the standard echocardiographic views to be off axis and the consequent inaccuracies in measurements. The most accurate way to measure the left atrial size is to report atrial volumes,  but this is difficult to assess in most patients, and in general has very little prognostic value in most patients. The exception are patient with atrial fibrillation whose likelihood of responding to treatment depends on the left atrial size.

If there is an underlying cause to an actual enlarged atrium such as hypertension or obesity, then the LA can remodel itself if the underlying cause us resolved. In any case, an enlarged LA is not too significant however it can result in a greater risk of stroke and Afib as blood is allowed to pool. Also, I have an enlarged LA as well and my cardiologist told me it may just be normal for me and was not concerned at all, just a thought.

Good luck, I hope this helps.