Anyone hear of Nocturnal A/V Block?

[Julie__0__0]

  I ran across the term Nocturnal A/V block in my readings.  Can anyone describe this condition?  

[CCF Cardio MD - MTR]

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Dear Julie, thank you for your question.  I think the term you mention relates to an overactive parasympathetic nervous system that slows down the electrical conduction of the heart during sleep.  The parasympathetic nervous system generally slows the body down and promotes resting activities like digestion and sleep.  Conversely, the sympathetic nervous system causes a "fight or flight" response by increasing alertness, heart rate, etc.  The vagus nerve innervates the heart and its conduction system and carries impulses from each nervous system.  At night, the parasympathetic fibers take over during sleep and the resting heart rate slows down.  However, there are some people who are overly sensitive to this response and the conduction through the heart tissue is dramatically slowed.  In this case, the normal sinus impulses are unable to transverse the atrioventricular node and AV block develops.  This signifies that certain sinus impulses are not being conducted to the ventricles.  If the heart rate gets too slow, fainting spells may result.  
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