Ashman Phenomenon 

Updated: Dec 22, 2020
Author: Roger Freedman, MD; Chief Editor: Jeffrey N Rottman, MD 

Overview

Background

Ashman phenomenon is an aberrant ventricular conduction due to a change in QRS cycle length, and it can be seen in any supraventricular arrhythmia.[1]  It is gnerally described as a wide QRS complex that follows a short R-R interval preceded by a long R-R interval.[2]

In 1947, Gouaux and Ashman[2] reported that in atrial fibrillation, when a relatively long cycle was followed by a relatively short cycle, the beat with a short cycle often has right bundle-branch block (RBBB) morphology,[3, 4]  although left BBB (LBBB) morphology can also occur.[1, 2] This causes diagnostic confusion with premature ventricular complexes (PVCs) or, rarely, ventricular tachycardia.[1] If a sudden lengthening of the QRS cycle occurs, the subsequent impulse with a normal or shorter cycle length may be conducted with aberrancy.

No geographic variations occur.[2] Ashman phenomenon is related to the underlying pathology of the cardiac conduction system and is a common electrocardiographic (ECG) finding in clinical practice.

No treatment is needed for isolated complexes.[2] Treat the underlying cardiac condition as appropriate.

As Ashman phenomenon is simply an ECG manifestation of the underlying condition, not a disease process itself, morbidity and mortality is related to the underlying condition (often, atrial fibrillation).[2]

Pathophysiology

Ashman phenomenon is an intraventricular conduction abnormality caused by a change in the heart rate. This is dependent on the effects of rate on the electrophysiological properties of the heart and can be modulated by metabolic and electrolyte abnormalities and the effects of drugs.

The aberrant conduction depends on the relative refractory period of the components of the conduction system distal to the atrioventricular node. The refractory period depends on the heart rate. Action potential duration (ie, refractory period) changes with the R-R interval of the preceding cycle; shorter duration of action potential is associated with a short R-R interval and prolonged duration of action potential is associated with a long R-R interval. A longer cycle lengthens the ensuing refractory period, and, if a shorter cycle follows, the beat ending it is likely to be conducted with aberrancy.

Aberrant conduction results when a supraventricular impulse reaches the His-Purkinje system while one of its branches is still in the relative or absolute refractory period. This results in slow or blocked conduction through this bundle branch and delayed depolarization through the ventricular muscles, causing a bundle-branch block configuration (ie, wide QRS complex) on the surface ECG, in the absence of bundle-branch pathology. A RBBB pattern is more common than a left bundle-branch block (LBBB) pattern because of the longer refractory period of the right bundle branch.

Several studies have questioned the sensitivity and specificity of the long-short cycle sequence. Aberrant conduction with a short-long cycle sequence has also been documented.

Etiology

Conditions causing an altered duration of the refractory period of the bundle branch or the ventricular tissue cause Ashman phenomenon. These conditions are commonly observed in atrial fibrillation, atrial tachycardia, and atrial ectopy.

A study by Sardar et al indicated that dofetilide, a delayed rectifier potassium current (IKr) blocker used to treat atrial fibrillation, can promote the development of Ashman phenomenon, possibly through a reverse use-dependence effect associated with prolongation of the ventricular refractory period.[5] The study involved 10 patients with atrial fibrillation who underwent dofetilide loading, receiving 250-500 micrograms of the drug every 12 hours. The investigators found that the total number of Ashman beats rose from 42±24 prior to the administration dofetilide to 93±79 after the first dose of the drug and 133±101 after the second dose.[5]

 

Presentation

History and Physical Examination

History

The diagnosis of Ashman phenomenon is made using electrocardiographic (ECG) evaluation findings. Patients may be asymptomatic, or they may have symptoms of the underlying cardiac condition.[2]

Ashman phenomenon, per se, causes no symptoms. Symptoms, if present, are related to the premature complexes and are not related to whether the complexes are conducted aberrantly.

Physical examination

No specific physical examination findings are described for Ashman phenomenon.

Pulse findings may include an irregular pulse, tachycardia, and/or pulse deficit in atrial fibrillation.

 

DDx

Diagnostic Considerations

Understanding Ashman phenomenon is useful in differentiating wide complex arrhythmias of ventricular origin from supraventricular arrhythmias with aberrancy, because the prognosis and treatment of these conditions are different.[1, 2]

A supraventricular impulse with aberrant conduction is confused with a premature ventricular contraction (PVC), and a series of consecutive aberrantly conducted supraventricular impulses may appear to be ventricular tachycardia.

Intermittent ventricular preexcitation, as in Wolf-Parkinson-White syndrome, should also be considered in the differential diagnosis of Ashman phenomenon.

It is important to diagnose and appropriately treat disease entities associated with Ashman phenomenon as well as to diagnose ventricular tachycardia.

Fisch criteria

The Fisch criteria for diagnosing Ashman phenomenon is as follows[2, 6] :

  • A relatively long cycle immediately ahead of the cycle terminated by the aberrant QRS complex: A short-long-short interval is particularly likely to initiate aberration, which could be either left or right bundle branch block (LBBB, RBBB) or both. Both patterns may be occur in the same patient.
  • RBBB from aberrancy with a normal orientation of the initial QRS vector: oncealed propagation of aberration is possible, such that there is a likelihood of a series of wide QRS supraventricular beats.
  • Irregular coupling of aberrant QRS complexes
  • Absence of a full compensatory pause

Differential Diagnoses

 

Workup

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 o 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] :

  • 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.

  • 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°)

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.