Ashman phenomenon in atrial fibrillation

Ashman phenomenon in atrial fibrillation

When there is short RR interval following a long RR interval, the QRS terminating the short RR interval is wide due to aberrant conduction with right bundle branch block pattern, known as Ashman phenomenon. This is because refractory period lengthens when RR interval increases. Aberrancy is more likely to occur in the right bundle than the left bundle. The aberrant beat can be mistaken for a ventricular ectopic beat.

Aberrancy may be sustained in subsequent beats due to concealed trans septal conduction. This will resemble a short run of ventricular tachycardia (VT).

The original description of Ashman phenomenon was in 1947 by Gouaux and Ashman.

Fisch C has proposed a few criteria for the diagnosis of Ashman phenomenon:

1. Long-short sequence terminating in the wide QRS. Occasionally a reverse sequence has also been reported. Though RBBB aberrancy is more common, LBBB aberrancy can also occur.
2. RBBB aberrancy has a normal initial QRS vector.
3. Varying coupling intervals of the aberrant QRS complexes
4. Full compensatory pause is not seen as the underlying rhythm is atrial fibrillation.

Bibliography

1. Surawicz B, Knilans TK. Chou’s electrocardiography in clinical practice. 6th edn Philadelphia: Saunders Elsevier, 2008: chapter 17, ventricular arrhythmias; 405–39.
2. Vivek Singla, Bhupinder Singh, Yadvinder Singh, Cholenahally Nanjappa Manjunath. Ashman Phenomenon: A Physiological Aberration. BMJ Case Rep. 2013 May 24;2013:bcr2013009660.
3. Fisch C. Electrocardiography of arrhythmias: from deductive analysis to laboratory confirmation–twenty-five years of progress.  J Am Coll Cardiol. 1983;1:306-16.