Other Tests
- Ashman phenomenon is diagnosed using a surface ECG (all 12 leads are best). In difficult cases, electrophysiological studies are required to establish whether the arrhythmia is of supraventricular or ventricular origin. See the image below.
Ashman phenomenon illustrated by 12th and 15th beats, which follow a premature ventricular complex and long R-R cycle respectively. The underlying rhythm is atrial fibrillation. - Fisch[2] criteria for the diagnosis of Ashman phenomenon are as follows:
- A relatively long cycle immediately preceding the cycle terminated by the aberrant QRS complex: A short-long-short interval is even more likely to initiate aberration. Aberration can be LBBB and RBBB, and both patterns may be observed even in the same patient.
- RBBB-form aberrancy with normal orientation of the initial QRS vector: Concealed perpetuation of aberration is possible, such that a series of wide QRS supraventricular beats is possible.
- Irregular coupling of aberrant QRS complexes
- Lack of a fully compensatory pause (never seen in atrial fibrillation)
- QRS morphology is the most helpful clue in differentiating between a supraventricular and ventricular origin of wide QRS complexes. The morphologic features that favor ventricular origin of wide complexes include the following:
- LBBB morphology with slurred or notched downstroke in leads V1 or V2
- RBBB morphology with monophasic R, biphasic QRS, or rSR' (ie, "rabbit ear") pattern in V1
- QS pattern in V6
- QRS duration longer than 140 milliseconds in RBBB morphology and QRS duration longer than 160 milliseconds in LBBB morphology
- R-to-S interval longer than 100 milliseconds in a precordial lead
- Marked left axis (between -90° and 180°)
- Aberration may also be a sign of intermittent ventricular preexcitation via an accessory pathway, as may occur with Wolff-Parkinson-White syndrome.
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