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Ventriculophasic Reflex

2 bytes removed, 22:39, 27 January 2010
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Ventriculophasic reflex is a phenomenon that can be seen during AV block or during ventricular extrasystoles in bigemini. It describes the sinus arrhythmia that exists during a irregular rhythm. The phenomenon has been described by Erlanger and Blackman in 1910 <cite>Erlanger</cite>. Different theories have been postulated to explain the phenomenon (a.o. by Wenkebach), but the theory published by Rosenbaum and Lepeschkin in 1955 <cite>Rosenbaum</cite> is the most accepted.
A positive chronotropic (accelerating) effect on the ventricular contraction is probably caused by stretch on the right atrium by contraction of the ventricles. A negative chronotropic effect (slow downslowing) is probably caused by a vagal reflex caused by stimulation of the carotid arterial baroreceptors by the pressure wave. The result of these two effects determines whether the P-P interval that surrounds the extra beat is shorter or longer than the P-P interval that surrounds the missing beat.
The baroreflex influences both the sinus node and the AV node and thus both sinus rate and atrioventricular conduction can be influenced.
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