Module title = Tutorial: Chamber Sizes

Lesson title = Right atrial enlargement

Right atrial enlargement is abbreviated RAE. Leads II and V₁ show the P waves the best. We will focus on these leads.

When the right atrium enlarges the electrical signal becomes stronger in the direction of the axis of lead II:
   


As a result, the P wave in lead II is taller. A P wave that is > 2.5 mm in lead II is diagnostic of RAE.  These P waves are taller than 2.5 mm. R

  

The P wave shape is often pointy. This is another finding of RAE.

The enlarged RA will also create a stronger electrical signal toward V₁ as seen in the diagram. This will result in a taller P wave in V₁, but only for the first half of the P wave.


A P wave that is 1.5 mm tall in V₁ is suggestive of RAE. This finding however, is not required to make the diagnosis.
Red arrow = P wave     Blue arrow = QRS


If the RA gets really big, it can grow toward the left. (see diagram below). If it does this, then the final part RA depolarization will be away from V₁ and cause an inverted waveform. This is similar to LEFT atrial enlargement, but it does not mean the LA is enlarged.


In contrast to LEFT atrial enlargment, the P wave duration is normal (< 120 ms or 3 little squares) with RAE. Check the ECG above to see that even though there is a biphasic P wave in V₁ (suggesting LAE), the P wave width is < 120 ms.

Of course, you can have RAE and LAE at the same time, so a wide P wave does not rule out RAE.

Summary of diagnostic criteria for RAE:  (in brackets = minor criteria)

• P wave taller than 2.5 mm in lead II
• P wave is usually pointy
• (P wave taller than 1.5 mm in lead V₁)
• (P wave duration < 120 ms)