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Monday, October 10, 2011

Heart Rhythms Part 3: Junctional Rhythms

The human heart has several redundant systems. If an electrical impulse is not started in the atria within a certain amount of time, the AV node starts one. This is a junctional beat. Picture the AV node as being the electrical junction box between the upper and lower sections of the heart.

The AV node has an intrinsic rate between 40 and 60 beats a minute. Since the sinus node cranks along at 60-100 the AV node normally does not have to do anything. But if the atria fails to send down an electrical impulse, the AV kicks in.

The are only a couple of real medical issues with this heart beat. First, it is indicative of something else going wrong. You should figure out why the sinus node is failing. Second, you lose the atrial kick. Basically the heart functions less efficiently.

On the ECG a junctional rhythm can have several different appearances. It will have a narrow QRS complex just like a sinus rhythm. The variation comes with the P wave. It can appear closer to the QRS complex, be missing, appear upside down or appear behind the QRS complex. Think of the heart as a long electrical line. If you add a charge to it in the middle, the electricity will flow to both ends. So when the AV node fires, the electrical impulse goes to the ventricles and the atria.

If it gets to the atria first, you'll see a P wave first (PR interval less than .12 sec).

If it gets to both areas of the heart simultaneously then the P wave will be buried behind the QRS complex.

If the the impulse gets to the ventricles first, the P wave will come after the QRS complex.

Also, depending on the route the electrical impulse takes through the atria, the P wave may be inverted.

So now that you recognize the rhythm as junctional the rate comes into play.
  • Heart rates <40 - Junctional Bradycardia Rhythm
  • Heart rates 40 to 60 - Ideojunctional Rythym
  • Heart rates 60 to 100 - Accelerated Junctional Rhythm
  • Heart rates 100 to 160 - Junctional Tachycardia Rhythm
  • Heart rates 160 to 250 - SVT (I'll cover this in a later post)

Heart Rhythms Part 1: Basic Anatomy
Heart Rhythms Part 2: Sinus Rhythms
Heart Rhythms Part 3: Junctional Rhythms
Heart Rhythms Part 4: Ventricular Rhythms
Heart Rhythms Part 5: Premature Beats
Heart Rhythms Part 6: Heart Blocks
© FireMedic and Firefighter/Paramedic Stories, 2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to FireMedic and Firefighter/Paramedic Stories with appropriate and specific direction to the original content.

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