Atrial Fibrillation ECG Interpretation #312


  • Atrial Fibrillation (afeb) occurs when multiple electrical impulses occur within the atria. This chaotic electrical activity results in a chaotic wave form between the QRS complexes. P waves are absent. They are replaced by lower case "f" waves. No P waves means there is no PR interval measurement.
  • This rapid electrical activity overwhelms the AV node causing impulses to enter the ventricular conduction system at irregular points. This results in irregular R to R intervals.


  • Not all fibrillatory waves are created equal. The "f" waves can be coarse (majority measure 3 mm or more) or can be fine (majority of waveforms measure less than 3 mm) to almost absent. Regardless always report your observations. Many times when a patient has "new onset" Atrial Fibrillation the patient will report with a heart rate of 160 bpm or more.


a fib ECG strip
  • When a patient experiences A-fib, the atria are not contracting as they normally would. They are just quivering. This absence of contraction of the atria can result in a loss of cardiac output anywhere from 15 - 30% due to the absence of "atrial kick". This is why the heart rate is so high. The body is trying to maintain homeostasis.
  • It will be impossible to determine the atrial rate. You will only be able to analyze and report the ventricular rate.
  • Atrial Fibrillation with a ventricular response in excess of 100 bpm is commonly referred to as Atrial Fibrillation with “rapid ventricular response” or "uncontrolled A-fib".

Practice Strip

afib rhythm strip

Analyze this tracing using the five steps of rhythm analysis.

Show Answer
  • Rhythm: Irregular
  • Rate: Ventricles - 90, Atria - Unable to determine (UTD)
  • P wave: "f" waves
  • PR interval: absent
  • QRS: 0.08
  • Interpretation: Atrial Fibrillation

Authors and Sources

Authors and Reviewers


? v:3 | onAr:0 | onPs:2 | tLb:0 | pv:1
uStat: False | db:0 | cc: | tar: False
| cDbLookup # 0 | pu: False | pl: System.Collections.Generic.List`1[System.String]

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