Left Atrial Enlargement

[00:00:00]If you are looking to master left atrial enlargement changes with my P waving lead V1, then this video is for you and we're going to do it by breaking down the anatomy of the P wave in lead V1.

[00:00:12]So, here is V1. It sits [snorts] on my right sternal border and these are my atria. This is my right atrium and my left atrium. And so, we're going to be focusing on left atrial enlargement, but let's just talk about depolarization in general across the atria. So, the sinus node fires off signal for my P waves for atrial depolarization. And it sits here in the posterior aspect of the right atrium. So, when it fires off and conducts signal, signal's first going to spread through the right atrium. Notice that the spread of signals heading towards V1. And so, V1 is going to initiate its atrial P wave with an upright deflection. Then signal travels across a special set of fibers, it's called the Bachmann's bundle. And when it travels across the Bachmann's bundle, it enters the left atrium and depolarizes in this direction. Notice the direction my vector of depolarization is heading away from lead V1. And so, subsequently, we're going to have a negative deflection in V1. And so, this is my biphasic P wave.

[00:01:14]And the negative portion of that is my left atrium. So, if I have left atrial enlargement, I should see enlarging of this left atrium.

[00:01:25]And I should therefore see enlarging of the negative component of my P wave. And sometimes my criteria for that is going to be the depth and width of this to be greater than 1 by 1 mm. So, this is 1 mm by 1 mm squared. Essentially, can we fit a small square inside of the P wave?

[00:01:46]The negative component specifically. So, in this case you look at lead V1, I look at this deep negative component and I say, I think I can fit a small box inside of that. I think I can fit a small box right here. I believe we have a some EKG criteria that meets left atrial enlargement and now you know exactly why.

[00:02:06]Hope that helps.