Ashman Phenomenon in A F and Fish Criteria

Transcript of the video: Now I am going to describe Ashman Phenomenon in atrial fibrillation, which is responsible for a long and short sequence followed by a wide QRS, in atrial fibrillation noted on ECG, which may resemble a ventricular ectopic beat.

This is the diagrammatic representation of Ashman phenomenon. You have sequences of AF beats, and a long cycle occurs, followed by a short cycle. So this QRS is aberrant, having rSR’ pattern, resembling right bundle branch block pattern. This was described by Richard Ashman, from Lousiana State University School of Medicine in New Orleans. This is the long cycle. During long cycle, there is lengthening of refractory period of the ventricle so that, when a short cycle occurs immediately after that, the right bundle is refractory. That is why, incomplete or complete right bundle branch block pattern can occur, during a long-short sequence, which is known as Ashman phenomenon and this can be mistaken for a ventricular ectopic beat. Sometimes, the aberrancy produced by Ashman phenomenon, may be sustained a few more cycles, resembling exactly like a ventricular tachycardia, run of ventricular tachycardia. Long cycle followed by short cycle. But this is not due to Ashman phenomenon. This is called concealed transseptal activation. Aberrancy due to concealed transseptal activation. The impulse is activating the other bundle from the opposite side through the interventricular septum, so that, the bundle becomes refractory for the next cycle. For this cycle is due to Ashman phenomenon, all subsequent cycles, aberrancy is due to concealed transseptal activation, making the bundle refractory for a period of time. That is known as ventricular tachycardia like pattern, due to concealed transseptal activation in atrial fibrillation, after a cycle which has caused Ashman phenomenon.

Ashman phenomenon was described in 1947. The Fisch criteria for diagnosis of Ashman phenomenon, were proposed in 1983. Why these are needed, because, it will resemble ventricular tachycardia or ventricular ectopics and we need some differentiating features. So these are the Fisch criteria:

Long-short sequence terminating in the wide QRS. We have already seen. Occasionally, a reverse sequence has also been reported. Though right bundle branch block aberrancy is more common, LBBB aberrancy can also occur. What I have shown is right bundle branch block aberrancy and RBBB aberrancy has a normal QRS vector. That is, the initial r is still there in Ashman phenomenon, which we have already seen. In LBBB aberrancy, of course the initial r will not be there. That is why they have put it as RBBB aberrancy has a normal initial QRS vector. The intial vector is always abnormal when there is left bundle branch aberrancy. Then, varying coupling intervals of the aberrant QRS complexes. Ashman phenomenon can occur recurrent in an ECG and the coupling intervals are varying, basically because of the underlying atrial fibrillation. You know that ventricular ectopic beat has a full compensatory pause, which is not seen in Ashman phenomenon, because underlying rhythm is atrial fibrillation. Full compensatory pause is possible only in sinus rhythm, because the sinus cycle is not reset by the ventricular ectopic beat. But this cannot occur in atrial fibrillation as there are plenty of impulses coming from the atria in atrial fibrillation. So that is why full compensatory pause is not seen in Ashman phenomenon. These are the Fisch criteria, which have been proposed in 1983, by Fisch, while Ashman phenomenon was described in 1947.