one particular supraventricular tachycadia is atrioventricular nodal reentry tachycardia, A V N R T. As you know, the S A node starts the electrical impulse travelling down the AV node & finally to the purkinje fibers. Now let's magnify the A V node, which reminds me of the fable, the tortoise & the hare. And that's because there's a slow and fast pathway in the A V node. And remember in the fable that the hare ran fast but took long naps. And that's significant because the fast pathway is fast but has a long sleep period called the refractory period, which is the time it will take to reset & start a depolarization. Now normally, we do use the fast pathway. And as the fast pathway depolarizes & moves to the next area, to the Purkinje fibers for a ventricular contraction, afterwards, the fast track will freeze up as the hare goes into its deep sleep during its long refractory period. Because it's in its refractory period, the fast pathway will extinguish the slow pathway's electrical stimulus right at the site of the common pathway. And that's normal. But some people are prone to a tachycardia called A V N R T. And this usually starts with a premature beat & this offbeat often occurs during the time when the fast track is in its frozen refractory state. And so the electrical impulse goes down the slow track, here marked with the tortoise. And as you know, the tortoise is slow & steady & the tortoise doesn't sleep often as his refractory period is very short & resets very easily. And since the tortoise is so slow, itl actually give time for the hare to wake up again. And by the time the tortoise eventually gets down to the bottom, the hare has finally woken up & ready to accept the electric impulse. And this will cause the fast hare to run back up to the top in a retrograde fashion and back at the top since the tortoise has a short refractory period, the hare easily passes the electrical stimulus to the tortoise walking down as the hare sleeps, the tortoise walks down slow & steady & the hare getting ample time to rest up from its refractory period and wake up again. Once again taking the electrical baton from the tortoise running fast up to the hill & once again passing off the electrical baton to the slow tortoise. And if you notice, this creates a vicious cycle or circuit & thus the name atrioventricular nodal reentry tachycardia as it is occuring in the A V node where the slow pathway is going antegrade & the fast pathway is going retrograde. As the most common scenario of A V N R T, the E K G shows a tachycardia going about 150 to 250 beats per minute with a narrow Q R S & hidden buried P waves that may be seen upside down since the fast track could go retrograde up to the S A node. If the valsalva does not break the electrical circuit in the emergency department, treatment in the Emergency department usually involves resetting the Atrioventricular node with adenosine.
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