Ashman phenomenon (Ashman beat) occurs when a premature supraventricular beat occurs before the right bundle branch has recovered from it’s refractory period. This results in the premature beat displaying a right bundle branch block pattern.

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Frequently during premature atrial contractions, however atrial fibrillation can express Ashman phenomenon as the R-R interval varies in this arrhythmia.

There is no clinical significance to this finding and no treatment is necessary, although some patients feel palpitations from the premature beat.