I'm looking for information about the Bundle of Histawara, aka the AV
Bundle, aka the Bundle of Hist.  Specifically, I'm looking for
information about the number of neurons, the number of connections,
and observations of patients who have had their Bundle removed,
perhaps in conjunction with a heart replacement or artificial heart
surgery.

Hi -

I'm unable to provide you with a good estimate for the number of
myocardial cells (it is special myocardial cells, not neurons, that
make up the bundle of His) or the number of connections which these
cells make, so I won't be providing this as an answer.

There are lots of observations of patients with damage to their AV
bundle - these are categorized according to the amount of damage done
to the bundle, which is reflected in how the heartbeat is affected.

1st degree block is simply a prolongation of the time for an impulse
to traverse the bundle (leads to a prolongation of the P-R interval -
the time from when the atria contract until the ventricles contract).

2nd degree block involves a continuously prolonging P-R interval until
a beat is dropped (depending on the pattern of drops, this is further
categorized).

3rd degree block is a complete block between the contraction of the
atria and the ventricles.  Both the atria and the ventricles keep
beating, just not synchronously.  This produces a ~10% drop in the
cardiac output due to decreased ventricular filling due to loss of the
atrial 'kick'.  This is a common cause of bradycardia (slow heartrate)
and is associated with fainting with exertion.  This is correctable
with a pacemaker.

The AV node is not damaged (usually) during a heart replacement - and
would not be necessary in an artificial heart as it would have it's
own method of coordinating the pumping action of its chambers.

synarchy

Try these links for an overview:

http://radiology.uchc.edu/code/26.htm

http://www.heartcenteronline.com/myheartdr/common/artprn_rev.cfm?filename=&ARTID=483

http://www.naspe-patients.org/patients/the_normal_heart/electrical_system.html