Ashman Phenomenon

Etiology

The term Ashman phenomenon or Ashman beat is used when describing a particular occurrence on an ECG, which is defined as a wide QRS complex that follows a short R-R interval preceded by a long R-R interval. The QRS complex originates above the AV node and not within the right or left ventricle, usually as a partial or complete right bundle branch block (RBBB).[3] This occurs because the refractory period of the conduction system increases with the length of the prior R-R interval.[4]

A shorter R-R cardiac cycle induces a shorter refractory recovery period, and a longer R-R induces a longer recovery period. With a longer R-R cycle, there is an increase in the refractory period; if a subsequent short R-R triggers ventricular activation during the relative refractory period before the conduction system has recovered sufficiently to conduct normally, the conduction will be aberrant.[5] Since the refractory period of the right bundle branch is longer than the left bundle branch block, a right bundle branch block pattern is more common, but a left bundle branch pattern can still be observed, albeit less frequently. Additionally, an RBBB pattern can be associated with a left fascicular block.[6] (See Image. Atrial Fibrillation With a Wide QRS Complex).

Additionally, the degree of aberrant conduction may vary from beat to beat and patient to patient. While a right bundle branch block pattern is more common, a left bundle block pattern or combined block pattern may sometimes be observed in the same patient. In situations where both LBBB and RBBB are noted, the patient likely has an underlying conduction defect.[7]

Epidemiology

Data on the geographic differences noted with the Ashman phenomenon have not been reported. Ashman phenomenon is linked to the underlying pathology of the cardiac conduction system and thus is nearly always associated with a conduction irregularity. Ashman beat is a common ECG finding in clinical practice that is frequently misinterpreted.[8]

Pathophysiology

Ashman phenomenon has most widely been associated with atrial fibrillation, which has been noted to occur secondary to the chaotic impulses from the atrium. These chaotic impulses cause variability in the R-R cycle length, allowing aberrant conduction.[7] The Ashman beat is caused by inconsistency in R-R intervals. The refractory period of the cardiac conduction system (His-Purkinje system) depends on the preceding cycle length. Thus, a longer R-R interval is followed by a longer refractory period, while a shorter R-R interval is followed by a shorter refractory period.[9] 

In the Ashman phenomenon, an elongated R-R interval followed by a shorter R-R interval is seen. As mentioned earlier, the longer R-R interval stretches the refractory period of the His-Purkinje system. If a shorter R-R interval follows that long interval, the cardiac conduction system may be found in the refractory period.[5] This electrical abnormality is often observed as a block on ECG; a right bundle branch block pattern is noted frequently as the right bundle branch has a relatively longer refractory period.[10]

History and Physical

Clinically, the Ashman phenomenon is asymptomatic. However, a patient may experience palpitations, shortness of breath, or lightheadedness due to an underlying baseline arrhythmia such as atrial fibrillation or supraventricular tachycardia. However, this is not due to the PVC itself, which is conducted with an aberration. An irregularly irregular rhythm is found on examination if associated with atrial fibrillation. Ashman phenomenon is a benign ECG finding commonly observed in atrial fibrillation due to variability in the R-R interval, atrial tachycardia, and atrial ectopy.[11]

Evaluation

Electrocardiography Evaluation

The workup would include a history, clinical examination, and a detailed evaluation of 12-lead electrocardiography during sinus rhythm and comparing it with the presenting ECG. In essence, evaluating the Ashman phenomenon involves understanding its context, like atrial fibrillation, excluding differential diagnoses, and addressing any underlying cardiac conditions. Tailoring the investigation and management to the individual patient is crucial for optimal outcomes.[12]

A clinician can diagnose the Ashman phenomenon using the Fisch criteria:

• Relatively long cycle immediately preceding the cycle terminated by the aberrant QRS complex
  • A consistent pattern of a relatively long preceding R-R cycle immediately ahead of the short R-R cycle results in a wide QRS complex.
• A short-long-short interval is even more likely to initiate aberration
  • Finding an example of a shorter-longer-shorter R-R cycle pattern with less QRS width is contrary to the Ashman phenomenon, and that would argue for other causes of at least some of the wide complexes. 
• RBBB-form aberrancy with the normal orientation of the initial QRS vector (a series of wide QRS supraventricular beats is possible)
  • The aberration is usually RBBB morphology with a normal initial force because the right bundle normally has the longest recovery time after a long preceding cycle length. However, the wide complex could be either LBBB or RBBB or a combination, and different patterns may be noticed even in the same patient.
  • Concealed propagation is possible, such that a series of wide QRS supraventricular beats may occur.
• Irregular coupling of aberrant QRS complexes
  • Irregular coupling of aberrant QRS complexes is common with Ashman phenomena and uncommon with PVCs, which typically have a fixed coupling interval between the preceding QRS and the wide premature QRS.
• Lack of fully compensatory pause
  • The absence of a full compensatory pause is common in the Ashman phenomenon, even with a regular underlying rhythm. In contrast, a PVC in a regular underlying rhythm typically blocks the presentation of a supraventricular beat without resetting the supraventricular pacing source, so then the next narrow beat occurs at double the normal R-R interval, known as a "compensatory pause."[6][8][13]

Premature Ventricular Complexes and Ashman Phenomenon

The Ashman phenomenon is often confused with PVCs due to their similar appearance on ECG.[11] However, differentiating between PVCs and the Ashman phenomenon is crucial, as they have different clinical implications. While the Ashman phenomenon and PVCs can have a widened QRS, subtle differences can be noted. Regular coupling to a widened QRS complex would support the diagnosis of PVCs versus the Ashman phenomenon. Also, if the clinician observes a full compensatory pause, a ventricular origin of the noted beat is suggested. However, the lack of a compensatory pause favors aberrancy.[7] A long rhythm sequence should be reviewed to compare R-R sequences that lead to each wide complex and to assess that all wide complexes are consistent with the Ashman phenomenon. If a shorter-longer-shorter sequence does not result in the observed widening, that would be inconsistent with the Ashman phenomenon. In summary, QRS morphology is the most crucial clue when distinguishing between a supraventricular or ventricular origin of wide QRS complexes.

Treatment / Management

Management of the Ashman phenomenon primarily involves addressing the underlying arrhythmia and associated conditions rather than the phenomenon itself. Proper control of atrial arrhythmias while monitoring and managing associated cardiac conditions is crucial for ensuring effective treatment and improving patient outcomes.[8](B3)

Differential Diagnosis

The following differentials should be considered before confirming the diagnosis of the Ashman phenomenon:

• The baseline right bundle branch should be excluded before diagnosing the Ashman phenomenon.
• PVCs during atrial fibrillation or supraventricular arrhythmias usually do not present as a typical bundle branch block and are followed by a compensatory pause.[13][14]
• Intermittent preexcitation during supraventricular tachycardia can be identified by manifest ventricular preexcitation in delta waves.
• Artifacts due to movement or poor electrode contact can sometimes cause misleading QRS changes that could be mistaken for the Ashman phenomenon.[15][16]

In clinical practice, distinguishing the Ashman phenomenon from these differentials typically involves careful analysis of the ECG, including looking at the baseline ECG, QRS morphology during sinus rhythm and tachycardia, and the context of the heart rate.

Prognosis

Ashman phenomenon is a benign condition with no known impact on the mortality or morbidity of a patient.

Complications

No complications associated with the Ashman phenomenon have been described in the literature.