heart arrythmia

  What is the difference between 1st or 2nd degree heart block and premature atrial contractions?  Thank you for your time.

[CCF CARDIO MD APS]

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Dear Dorothy,
A PAC is a premature atrial contraction and it is for the otherwise healthy
person a normal occurence, is not that frequent and usually is not noticed by
the patient when it occurs.  
First degree heart block is when the time it takes for the electrical signal to
get from the atria (upper chamber where the impulse originates) through the AV node
(connection between atria and ventricle that buffers the signals from atria
to ventricle)and into the ventricle (lower chamber) is delayed.  Keep in mind that
the electrical stimulus or signal has to get through the AVnode in order for the
heart to beat.  If for some reason the signal doesn't get through there is a
backup system in the ventricle themselves that will take over the responsibility
of stimulating a contraction(beat)of the heart however this can only occur at
a rate of about 40 beats per minute-this would represent third degree of complete
heart block.  Second degree heart block is in between 1st and 3rd degree. In
second degree heart block some of the signals (but not all) are getting through
the AVnode.  Of course there are different patterns of second degree, for instance
if there is simply a dropped beat for every three consecutive stimuli, this is much
different than if every other stimulus from the atria does not make it through.  The latter
example is of course more indicative of a sick conduction system and warrants
serious consideration of a pacemaker placement.  I hope this has been helpful.
Please write back if there are any further questions.
Information in the heart forum is intended for general medical informational
purposes only, actual diagnosis and treatment can only be made by your physician(s).