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ECG Findings

  • Irregularly irregular narrow-complex tachycardia

  • Absence of P-waves, but fibrillatory atrial activity may be seen


  1. Atrial fibrillation is typically a narrow-complex rhythm, but in presence of underlying bundle branch block, aberrant conduction, or accessory pathway, it may be wide complex.

  2. Most “irregularly irregular” rhythms are due to atrial fibrillation, but other rhythms may produce similar findings. These include multifocal atrial tachycardia, atrial flutter with variable AV block, and frequent premature ventricular contractions.

  3. Hemodynamically stable patients are treated with chemical rate or rhythm control with a goal heart rate of < 120 bpm. In hemodynamically unstable patients, synchronized cardioversion is the treatment of choice. Risks of cardioversion include subsequent stroke.

  4. When a very fast (>200 bpm) irregular tachycardia is seen with changing QRS shape and morphology, suspect atrial fibrillation with Wolff-Parkinson-White syndrome (WPW) and avoid AV nodal blocking agents as this can promote conduction over the accessory pathway and lead to ventricular tachycardias and death.


Atrial Fibrillation. (ECG contributor: R. Jason Thurman, MD.)


R-to-R interval varies in an “irregularly irregular” pattern (double arrows). The baseline “rumble,” representing “F waves,” may be very fine or even indiscernible.


The baseline “rumble” may be very coarse, resembling atrial flutter waves.

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