23-24: Ashman Phenomenon

ECG Findings

• Aberrant ventricular conduction, usually with RBBB pattern.

• Altered durations of the refractory period of the bundle branch or ventricular tissue are present, commonly due to atrial fibrillation, atrial ectopy, and atrial tachycardia.

Pearls

1. After depolarization, tissue repolarizes during its refractory period. Refractory period changes with the preceding cardiac cycle, with longer R-R intervals producing longer refractory periods and shorter R-R intervals producing shorter refractory periods.

2. A longer R-R interval lengthens the following refractory period. When an early or premature (ectopic) depolarization reaches the ventricular conduction system before it has completely repolarized, aberrant conduction may occur and be manifest on the ECG with a bundle branch block pattern.

3. Ashman phenomenon most commonly appears with an RBBB pattern, since the right bundle has a longer refractory period than the left bundle.

4. Ashman phenomenon is often seen in atrial fibrillation, when a long R-R interval is followed by a much shorter R-R interval.

5. In the setting of a premature atrial beat (as seen in this example), the earlier in the cycle the premature atrial contraction occurs and the longer the preceding R-R interval is, the more likely aberrant conduction of the beat will occur.