General Medicine

ASHMAN PHENOMENON 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. initial initial; background-repeat: initial initial;">The aberrant conduction depends on the relative refractory period of the components o 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 Epidemiology Frequency United States No geographic variations occur. Ashman phenomenon is related to the underlying pathology and is a common ECG finding in clinical practice. Mortality/Morbidity Ashman phenomenon is simply an electrocardiographic manifestation of the underlying condition; therefore, the morbidity and mortality is related to the underlying condition