Thursday, September 1, 2011

What is the rhythm? Answer at the bottom.

An elderly woman presented with abdominal pain.  Here is her ECG:
























This is easily mistaken for atrial flutter because the waves have a fluttering, wavy, sawtooth appearance.  However, 3 things make atrial flutter impossible, 2 are related:
1) the rate of the waves is > 400
2) the QRS does not appear at the same part of the atrial wave cycle each time (which it must do in flutter)
3) the ventricular rate is irregularly irregular.  In atrial flutter, the ventricular rate can be regular if there is a constant ratio (2:1 block, 3:1 block etc).  It can also be regularly irregular, in which every QRS comes at a multiple of the atrial wave rate (if atrial wave rate is 300, it happens every 200 ms, and every R-R interval must be a multiple of 200ms)

2) and 3) are related: since 2) is true, 3) must also be true.

The woman had atrial fibrillation.  It was misdiagnosed as flutter, and this may have contributed to a delayed diagnosis of mesenteric embolism.

2 comments:

  1. Is it surprising that you have such well formed, large p-waves in atrial fibrillation? Doesn't this suggest that she is having organized activity in the atrium and thus organized atrial contractions rather than quivering?

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  2. I think that if it were truly organized, the "p" waves would all be identical and the QRS would occur at the same time on each cycle. So appearances are deceiving.

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