Phasic Aberrant Conduction in AF: Ashman’s Phenomenon

Report:

Atrial fibrillation with ventricular response 108/min

Ashman’s phenomenon

Nonspecific inferior T wave changes

Comment:

The chest discomfort could be ascribed to AF.

In 1947 Gouaux and Ashman published a report of RBBB aberration mimicking VT during AF14. The occurrence of RBBB is predicated on long-short sequences, frequently engendered by the AF. The importance of distinguishing this innocuous aberrancy from ventricular ectopic activity is obvious. The term Ashman’s phenomenon has come to comprise all phasic aberrant conduction – in rhythms other than AF and morphologies other than RBBB. The refractoriness of any conducting tissue is proportional to the length of the preceding cycle – the long pause makes the next short cycle likely to be terminated by an aberrant QRS. Usually it is the RBBB which fails, as it normally has longer refractory period than the left; but many cardiac patients have a tendency to develop LBBB as phasic aberrancy (below), rate dependent or permanent LBBB. Both the original ECG and the one below (Fig 25a) show an important clue that the broad complexes are aberrant, rather than VEBs: they are not followed by an attempted pause.

The ECG below (Fig 25a) demonstrates yet again how bad lead 2 is for rhythm strips where ventricular conduction is important. One could not tell LBBB from RBBB there. Anyway, this is an example of phasic aberrancy with LBBB.

Fig 25a. Another patient, with hypertensive heart disease. AF with two LBBB-aberrant complexes. There is also LVH with ST/T changes.

Fig 26. 84 year old man with normal coronary arteries and large cerebral hæmorrhage.