EKG Tutorial: Atrial Rhythms

Electrocardiography

Atrial Rhythms

It is possible for the the atria to depolarize a bit earlier than normal. This is actually quite common (in the sense that it happens to a lot of people, not that one person does it all the time!). If you're willing to go back to the toilet analogy, it would be like your toilet flushing by itself right before you pushed the handle... Yeah, I know it's a stretch but we were on a roll!

P.A.C. If the premature impulse falls in the relative refractory period or later, an atrial contraction may occur. This, logically, is called a Premature Atrial Contraction (PAC).

Examine the PAC and notice some characteristics of atrial complexes:

Upright normal P-wave
Narrow QRS complex (0.04 - 0.12 ms)

If the SA node or the internodal pathways suffer stress or damage, the atria can frequently initiate impulses from other portions of the atrial tissue. PACs are one possible outcome. Other rhythms which may arise in atrial tissue are fibrillation and flutter.

A Fib Atrial Fibrillation describes a condition in which the atrial tissue randomly generates action potentials from many different regions. Physically, the atrial muscle appears to quiver (it looks like Jell-o). There are no noticable p-waves, and the overall rhythm is irregularly irregular.

The reason you cannot see P-waves is that the atrial activity is about as scrambled as a breakfast omelette. The key to recognizing A-fib are the narrow QRS's and the irregularly irregular rhythm.

4:1 A Flutter Atrial Flutter is recognized by the distinct "saw tooth" pattern of P-waves.

The QRS complexes can appear at different intervals and frequencies. Naming conventions for A-flutter depend on these relations.

Atrial Flutter, 2:1 Block

The 2:1 block indicates there are 2 P-waves followed by 1 QRS.

Atrial Flutter, Variable Block

This is extremely common among A-flutter patients. There can be as few as a single P-wave or as many as 6 or more P-waves between each QRS complex.

The clinical significance of A-fib and A-flutter is two fold:.

First, because the atria generally don't have time to fill completely, the preload to the ventricles is reduced and cardiac output suffers.
Perhaps even more dangerous is the erratic and turbulent blood flow caused by the erratic contraction and relaxation of the atrial walls. In the turbulence, blood can form small clots which may lodge in small vessels. If a clot (or thrombus) is released into the cerebral vessels, it can cause a stroke (often called CVA, cerebrovascular accident).

Electrocardiography

Atrial Rhythms

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