From:
Claire Curtis
Date: 2002-06-28 20:33:00 UTC
Subject: Re: Here is most of Seven of Six's EKG/ECG report
Hi Sukie et al --
I'm not a vet, but I was a defibrillator-certified EMT at one time.
An EKG is a picture of the electrical (not the physical) activity of the
heart. For humans, the P wave shows the electrical wave going through
the atria, which usually means the atria are stimulated to contract.
Then the electrical impulses travel up and down and around the
ventricles; the changes in direction of electrical travel create the
shape of the QRS complex, and this electrical stimulation usually
results in ventricular contraction. After the physical contraction of
the ventricles, there is a "refractory period" during which time ions
move around to prepare for the next contraction; in effect this is an
electric flow, and is as the T bump on an EKG.
(Go to
http://endeavor.med.nyu.edu/courses/physiology/courseware/ekg_pt1/EKGseq.html
and click on "4. The Sequence of Cardiac Depolarization and
Repolarization" for a nice interactive animation)
The heart muscle _can_ continue to contract even without external
electrical stimulation (think of the infamous chickenheart). But
effective pumping requires coordination, and in the absence of a steady
external electrical stimulation (a pacemaker), the heart is apt to
become disorganized to the point that it no longer pumps effectively.
Think of the heart muscle cells as a crowd of people all trying to sing
a song -- works well if there is someone leading it, but the singing
tends to get ragged if the conductor sits down.
A "block" occurs when the electrical signal is stopped somewhere along
the way. It doesn't mean the heart is not pumping, just that the
coordinating signal is not getting through. This will often cause
bradycardia, since the "natural" rhythm of an unstimulated heart is
quite a bit slower -- about half the speed -- of a normally stimulated
heart. A "complete block" means that the heart is depending entirely on
its natural rhythm, which is too slow. Also, since the movement of blood
from the atrium to the ventricle depends on good timing, and that timing
is no longer being coordinated properly, there is apt to be some back
eddies in blood flow which will reduce the effectiveness of the pumping
that does occur.
In Seven's case we are just all hoping that the crowd keeps on singing,
and that the conductor is just sitting down for a rest and will return
shortly.
Our prayers are with you.
Claire; Sam, Franklin, and Missy.