Original source: eMedicine Medscape
Ashman Phenomenon
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]
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.
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]
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Longo D, Baranchuk A. Ashman phenomenon dynamicity during atrial fibrillation: the critical role of the long cycles. J Atr Fibrillation. 2017 Oct-Nov. 10 (3):1656. [QxMD MEDLINE Link]. [Full Text].
Sardar MR, Khaji A, Robert J, Bradley JT, Yan G. The Ashman phenomenon in patients with atrial fibrillation treated with an IKr blocker, dofetilide [abstract]. Circulation. 2013. 128:A10380. [Full Text].
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Gulamhusein S, Yee R, Ko PT, Klein GJ. Electrocardiographic criteria for differentiating aberrancy and ventricular extrasystole in chronic atrial fibrillation: validation by intracardiac recordings. J Electrocardiol. 1985 Jan. 18(1):41-50. [QxMD MEDLINE Link].
Roger Freedman, MD Director of Clinical Cardiology, Professor, Department of Internal Medicine, Division of Cardiology, University of Utah School of Medicine
Roger Freedman, MD is a member of the following medical societies: American College of Cardiology, American College of Physicians, American Heart Association, Heart Rhythm Society, Phi Beta Kappa, Sigma Xi, The Scientific Research Honor Society
Disclosure: Received grant/research funds from St. Jude Medical for other; Received consulting fee from St. Jude Medical for consulting; Received ownership interest from St. Jude Medical for other; Received grant/research funds from Boston Scientific for other; Received consulting fee from Boston Scientific for consulting; Received grant/research funds from Medtronic for other; Received consulting fee from Medtronic for consulting; Received consulting fee from Sorin for consulting.
Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Brian Olshansky, MD, FESC, FAHA, FACC, FHRS Professor Emeritus of Medicine, Department of Internal Medicine, University of Iowa College of Medicine
Brian Olshansky, MD, FESC, FAHA, FACC, FHRS is a member of the following medical societies: American College of Cardiology, American Heart Association, Cardiac Electrophysiology Society, European Society of Cardiology, Heart Rhythm Society
Disclosure: Nothing to disclose.
Jeffrey N Rottman, MD Professor of Medicine, Department of Medicine, Division of Cardiovascular Medicine, University of Maryland School of Medicine; Cardiologist/Electrophysiologist, University of Maryland Medical System and VA Maryland Health Care System
Jeffrey N Rottman, MD is a member of the following medical societies: American Heart Association, Heart Rhythm Society
Disclosure: Nothing to disclose.
Russell F Kelly, MD Assistant Professor, Department of Internal Medicine, Rush Medical College; Chairman of Adult Cardiology and Director of the Fellowship Program, Cook County Hospital
Russell F Kelly, MD is a member of the following medical societies: American College of Cardiology
Disclosure: Nothing to disclose.
Ram C Sharma, MD, MRCP Assistant Professor of Medicine, Division of Cardiovascular Medicine, Department of Internal Medicine, University of Louisville
Ram C Sharma, MD, MRCP is a member of the following medical societies: American Academy of Sleep Medicine, American College of Cardiology, and Royal College of Physicians of the United Kingdom
Disclosure: Nothing to disclose.
Source: eMedicine Medscape
This article is provided for informational purposes only and is not a substitute for professional medical advice. Always consult with a qualified healthcare provider for diagnosis and treatment.
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