Ashman phenomenon

Ashman phenomenon is an ab2242ant ventricular conduction due to a change in QRS cycle length.

In atrial fibrillation, when a relatively long cycle is followed by a relatively short cycle, the beat with a short cycle often has right bundle-branch block (RBBB) morphology.

Findings cause diagnostic confusion with premature ventricular complexes (PVCs).

An intraventricular conduction abnormality caused by a change in the heart rate.

The process is dependent on the effects of rate on the electrophysiological properties of the heart.

The phenomenon can be modulated by metabolic and electrolyte abnormalities and drugs.

The ab2242ant conduction depends on the relative refractory period of the conduction system distal to the atrioventricular node.

The refractory period depends on the heart rate.

The action potential duration, which is the 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 a prolonged duration of action potential is associated with a long R-R interval.

A longer cycle lengthens the subsequent refractory period, and, if a shorter cycle follows, the beat ending it is likely to be conducted with ab2242ancy.

An ab2242ant conducted beat occurs when a supraventricular impulse reaches the His-Purkinje system while one of its branches is still in the relative or absolute refractory period: resulting in a slow or blocked conduction through this bundle branch and delayed depolarization through the ventricular muscles, causing a wide QRS complex on the ECG.

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.

An electrocardiographic manifestation of the underlying condition so that the morbidity and mortality associated is related to the underlying condition.

The diagnosis of Ashman phenomenon is made on ECG evaluation.

Symptoms, if present, are related to the premature complexes and are not related to whether the complexes are conducted ab2242antly.

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

Conditions causing an altered duration of the refractory period of the bundle branch or the ventricular tissue cause Ashman phenomenon.

Altered duration of the refractory period of the bundle branch or the ventricular tissue are seen in atrial fibrillation, atrial tachycardia, and atrial ectopy.

Diagnosed using an ECG, but electrophysiological studies are required to establish whether the arrhythmia is of supraventricular or ventricular origin.

QRS morphology helps to differentiate between a supraventricular and ventricular origin of wide QRS complexes.

ECG features that suggest ventricular origin of wide complexes include: LBBB morphology with slurred or notched downstroke in leads V1 or V2, RBBB morphology with monophasic R, biphasic QRS, or rSR’ pattern in V1, QS pattern in V6, QRS duration longer than 140 milliseconds in RBBB pattern and QRS duration longer than 160 milliseconds in LBBB pattern, R-to-S interval longer than 100 milliseconds in a precordial lead and marked left axis (between -90° and 180°).

Ab2242ation may also be a sign of intermittent ventricular preexcitation via an accessory pathway, as with Wolff-Parkinson-White syndrome.

No treatment is needed for isolated complexes.

The underlying cardiac condition is treated as possible.

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