Continuing Education Activity

The Ashman phenomenon was initially described by Dr Gouaux and Dr Ashman in 1947. They described that the earlier in the cycle, a premature atrial contraction (PAC) occurs, and the longer the preceding cycle is, the more likely the PAC will be conducted with aberration. The conduction deviates from the normal pathway. This activity discusses the etiology and the pathophysiology of the Ashman phenomenon and highlights the role of the interprofessional team in evaluating and treating patients with this condition.

Objectives:

• Identify the etiology and epidemiology of Ashman phenomenon.

• Determine the pathophysiology of the Ashman phenomenon.

• Evaluate the appropriate history, physical, and evaluation of the Ashman phenomenon.

• Communicate interprofessional team strategies for improving care coordination and communication to enhance the care of patients with the Ashman phenomenon.

Introduction

Dr Gouaux and Dr Ashman first described the Ashman phenomenon in 1947. In their initial description, they showed that the earlier in the cycle a premature atrial contraction (PAC) occurs and the longer the preceding cycle is, the more likely it is that the PAC is conducted with aberration and the conduction deviates from the normal pathway. However, this is an electrocardiogram (EKG) finding that does not impact mortality or morbidity.

Ashman phenomenon is often misinterpreted as a premature ventricular contraction (PVC) because of its appearance on the EKG as a single wide QRS complex and in patients with atrial fibrillation as narrow QRS complexes. It has also been seen in other supraventricular tachyarrhythmias. The Ashman phenomenon almost entirely causes single, wide QRS aberrant complexes. No symptoms are associated because the Ashman phenomenon is an EKG finding and not a disease process. Instead, any symptoms the patient would feel would be due to the underlying cardiac condition, which, in many cases, is atrial fibrillation.[1]

Etiology

The term Ashman phenomenon or Ashman beat is used when describing a particular occurrence on an EKG described as a wide QRS complex that follows a short RR interval preceded by a long RR interval. The QRS complex originates above the AV node and not at the right or left ventricle, and due to this, it presents as a right bundle branch block (RBBB) or left bundle branch block (LBBB).[2] This occurs because the refractory period of the myocardium is proportional to the length of the prior RR interval. A shorter RR is associated with a shorter action potential duration and vice versa. With a longer RR cycle, there is an increase in the refractory period, and if a short RR follows, the beat that terminates the cycle is likely to be conducted aberrantly.[3] Because the refractory period of the right bundle is longer than that of the left bundle, the right bundle remains in the refractory period when the supraventricular beat gets to the His-Purkinje system. This results in the blocked conduction through 1 bundle, leading to an electrocardiogram with bundle branch block morphology. 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 seen just less frequently. The RBBB pattern can be associated with left fascicular blocks.[4]

A practitioner can easily diagnose the Ashman phenomenon by using the Fisch criteria as first described by Dr Charles Fisch:

• A relatively long cycle immediately ahead of the cycle terminated by the aberrant QRS complex: A short-long-short interval is even more likely to initiate aberration. Aberration could be either LBBB or RBBB or both, and both patterns may be noticed even in the same patient.
• RBBB from aberrancy with a normal orientation of the initial QRS vector: The concealed propagation of aberration is possible, such that a series of wide QRS supraventricular beats is likely.
• Irregular coupling of aberrant QRS complexes
• Absence of a full compensatory pause[4][5]

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 heart block, and an Ashman beat is not seen.[6]

Ashman phenomenon is often confused with premature ventricular complexes due to EKG's similar appearance and subtle nature.[7] It is important to differentiate between premature ventricular complexes and the Ashman phenomenon, as they are often confused. While the Ashman phenomenon and premature ventricular complexes can have a widened QRS, subtle differences can be noted. Regularly coupling a widened QRS complex would support the diagnosis of premature ventricular complexes versus the Ashman phenomenon. Also, if the practitioner noted a full compensatory pause, this would favor a ventricular origin of the noted beat, while the lack of the compensatory pause favors aberrancy.[6] In summary, QRS morphology is the most crucial clue when distinguishing between a supraventricular or ventricular origin of wide QRS complexes.

Epidemiology

There have been no reported data on the geographic differences noted with the Ashman phenomenon. Ashman phenomenon is linked to the underlying pathology of the heart's conduction system and thus is nearly always linked to a conduction irregularity. Ashman beat is a common EKG finding in clinical practice; however, it is often misinterpreted.[5]

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 RR cycle length, leading to the opportunity for aberrant conduction.[6] The Ashman beat is caused by inconsistency in R-R interval length. Longer R-R intervals, such as those in bradycardia, have a longer refractory period. In contrast, shorter R-R intervals, such as those in tachycardia, have a shorter refractory period.[6] 

In the Ashman phenomenon, an elongated R-R interval followed by a shorter R-R interval is seen. During this time, the cardiac myocytes are still in the refractory period. The cardiac myocytes are still in the refractory period due to the initial extended/prolonged R-R interval. This electrical abnormality often causes a block to be noted on EKG, often a right bundle branch block pattern is noted, but left bundle branch block patterns can also be seen as discussed above.[8]

History and Physical

Clinically, the Ashman phenomenon is asymptomatic. However, a patient may experience symptoms of palpitations, shortness of breath, or lightheadedness due to an underlying baseline rhythm like atrial fibrillation or supraventricular tachycardia. However, this is not due to the PAC 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 EKG finding commonly observed in atrial fibrillation due to variability in the R-R interval, atrial tachycardia, and atrial ectopy.[7]

Evaluation

The workup would include a 12-lead electrocardiography. In cases where it is difficult to identify the baseline rhythm, electrophysiological studies may be needed. No related laboratory findings have been associated with the Ashman phenomenon.

Treatment / Management

No treatment is needed for isolated complexes. However, treatment of the underlying cardiac condition, such as controlling atrial fibrillation's heart rate and/or rhythm, may be necessary.

Differential Diagnosis

It is important to differentiate wide complex arrhythmias of ventricular origin from supraventricular arrhythmias with aberrancy to accurately treat the underlying rhythm.

Prognosis

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

Complications

No complications have been described in the literature due to the Ashman phenomenon.

Consultations

A consultation with a cardiologist or electrophysiologist may be needed to help identify and treat the underlying rhythm.

Deterrence and Patient Education

Patients who feel palpitations, chest pain, shortness of breath, dizziness, or syncope should be promptly evaluated. While not a common presentation of the Ashman phenomenon, this could represent a more serious problem, such as atrial fibrillation or other arrhythmias.

Enhancing Healthcare Team Outcomes

The Ashman phenomenon is an interesting incidental EKG finding with a benign course. When in doubt, a consultation with a cardiologist may be necessary to differentiate it from other wide QRS arrhythmias.