Approach Considerations
Electrocardiography
Ashman phenomenon is diagnosed using a surface electrocardiogram (ECG) (all 12 leads are best). In difficult cases, electrophysiological studies are required to establish whether the arrhythmia is of supraventricular or ventricular origin. [2] See the image below.
Ashman Phenomenon. Ashman phenomenon illustrated on electrocardiograpm by the 12th and 15th beats, which follow a premature ventricular complex and long R-R cycle, respectively. The underlying rhythm is atrial fibrillation.
Fisch criteria for the diagnosis of Ashman phenomenon are as follows [2, 6] :
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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 left or right bundle branch block (LBBB, RBBB); both patterns may be observed in the same patient.
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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.
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Irregular coupling of aberrant QRS complexes
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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:
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LBBB morphology with slurred or notched downstroke in leads V1 or V2
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RBBB morphology with monophasic R, biphasic QRS, or rSR' (ie, "rabbit ear") pattern in V1
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QS pattern in V6
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QRS duration longer than 140 milliseconds in RBBB morphology and QRS duration longer than 160 milliseconds in LBBB morphology
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R-to-S interval longer than 100 milliseconds in a precordial lead
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Marked left axis (between -90° and 180°)
Several studies by Marriott et al [7] and Gulamhusein et al [8] have analyzed His electrogram findings with simultaneous surface ECG findings and found low sensitivity and specificity of Ashman phenomenon for helping diagnose aberrancy versus ventricular rhythm.
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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Ashman Phenomenon. Ashman phenomenon illustrated on electrocardiograpm by the 12th and 15th beats, which follow a premature ventricular complex and long R-R cycle, respectively. The underlying rhythm is atrial fibrillation.
