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The Basics of EKG Interpretation and Rhythm Recognition: Atrial Fibrillation

Updated on June 14, 2015

Recognizing Arrhythmias: Atrial Fibrillation

Atrial Fibrillation is one of the more common heart arrhythmias, and becomes more common as you age. Atrial Fibrillation, also known as "A-Fib" is a condition where the normal pacemaker (the sinus node) of the heart is no longer in control of depolarization of the atria (the top two chambers of the heart). Instead, the atria quiver and shake, similar to how jello jiggles. They no longer pump blood into the ventricles. This is called fibrillation.

There are a few hallmarks of recognizing atrial fibrillation on a monitor that I will cover below.

EKG Atrial Fibrillation vs Sinus Rhythm
EKG Atrial Fibrillation vs Sinus Rhythm

Atrial Fibrillation

Unless there is prior damage, the QRS should still be narrow similar to Normal Sinus Rhythm. The rate of a-fib is extremely variable. Usually you will see atrial fibrillation at rates of 60 and above. Occasionally rates will reach dangerously high levels and require immediate medication attention. This is most frequent with new onset atrial fibrillation, but will occasionally happen with already diagnosed patients. I have also seen low rates with atrial fibrillation, but less frequently.

EKG work of JHeuser, wikimedia commons

Atrial Fibrillation EKG baseline
Atrial Fibrillation EKG baseline

Absent P Waves

and a wavy baseline

Because the atria are quivering instead of pumping normally, you won't see a distinct P wave. The activity in the atria is a disorganized quivering which will appear as a coarse baseline, though at times can appear as a fine baseline.

In the picture, the top EKG (with the red arrow) shows a wavy baseline very typical for atrial fibrillation. The bottom EKG (with the purple arrow) shows a smooth baseline and a P wave, more typical of Normal Sinus Rhythm,


If you compare the two rhythms in the picture, you will see that each QRS complex (the spike) is the same distance from the other ones. The rate is about 70 beats per minute and you can predict accurately when the next beat will occur, based on prior beats. This rhythm is called normal sinus rhythm, and it is said to be regular.

The top rhythm appears to have no particular rhyme or reason when the beats occur. Each beat is a different distance from the other beats. This EKG is atrial fibrillation, and is said to be irregularly irregular. This distinction of irregularly irregular is important because some cardiac rhythms are regularly irregular.

Be careful: Sometimes a sinus rhythm with ectopy (early beats) can look like atrial fibrillation. Look for P waves; Atrial fibrillation never has P waves.

Blood Thinners

aka anticoagulants

Blood thinners are frequently prescribed to people with atrial fibrillation. People with A-Fib have a higher chance of developing clots in their atria. If these clots dislodge, they can migrate to the heart, lungs, or brain, causing tissue beyond the clot to lose blood flow (a migrating clot is called an embolism). This loss of blood flow is calledas ischemia. If the clot goes to the heart can cause a heart attack (myocardial infarction). A clot that goes to the brain is called an ischemic stroke and/or cerebrovascular accident (CVA). A clot in the lungs is called a pulmonary embolism. All are potentially life threatening emergencies.

The reason for this is that people with a-fib have a higher chance of forming clots and "throwing an embolism" is because the atria are not pumping properly, and blood can clot in one of the many sinuses in the atria.

Blood thinners (anticoagulants) decrease the chances of these clots forming. I have seen Coumadin (AKA Warfarin) used most frequently, though I am starting to see Pradaxa and Xarelto as well. Aspirin is less commonly used, and seems to be used only when Coumadin is not well tolerated.

Because the blood is less able to clot, people on blood thinners frequently get bruises. Additionally, active bleeding may not stop on its own, and frequently will require medical attention to stop.

Atrial Fibrillation is not a death senteance

People with atrial fibrillation can live long, fulfilling lives. Adjustments have to be made, and their doctor will probably want them to be seen to have blood drawn regularly, especially when they first start.

A good portion of my elderly patients have atrial fibrillation and are still very active and healthy. My father in law was diagnosed not too long ago. His initial symptom was weakness, almost lethargy, and inability to hold his head up. Chest pain, shortness of breath/trouble breathing, and heart palpitations are also common for new onset patients.

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