Symptoms and Signs of Atrial Fibrillation (AFib) vs. Ventricular Fibrillation (VFib)

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Medically Reviewed on 5/3/2019

Doctor's Notes on Atrial Fibrillation (AFib) vs. Ventricular Fibrillation (VFib)

An ECG (electrocardiograph or EKG) is a graphic display or measure of the electrical activity (heart rhythm) of the heart.

  • Atrial fibrillation (AFib) is a type of abnormal heart rhythm (arrhythmia), usually with a very fast heart rate, that is caused by irregular contractions of the upper chambers of the heart (the atria).
  • Ventricular fibrillation (VFib) also is a type of abnormal heart rhythm in which the heart rate that is irregular, and usually fast due to irregular contractions of the lower chambers of the heart (ventricles).

ECG similarities are usually a rapid irregular tracing.

  • In AFib, abnormal p waves precede the QRS signal on the ECG. In VFib, there is a rapid irregular tracing but p waves and the QRS signal are unidentifiable.
  • In most ECG's, AFib results in a rapid irregular pulse (QRS signal), while VFib results in no pulse (no clear QRS signal) so the ECG's are quite different.

AFib vs. VFib Causes

  • The ECG of AFib is caused by rapid irregular multifocal electrical signals from the atria, some of which get through to the ventricles to allow a heartbeat (evidenced by a QRS).
  • VFib is caused by multiple erratic ventricular signals that originate in the ventricles that do not allow the ventricles to contract (evidenced by no QRS signal).

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Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.