First of all, please peruse the drawing linked below. It's
not good but it gives you the idea.
This is an ECG with two traces on the oscilloscope. The
upper trace is an ordinary-looking ECG. The lower trace
is
a heart shape traced as in the image. The different
parts
of the ECG are
scaled up and down as appropriate and an
average of one cycle is shown on the high-persistence
phosphor CRT at a time (probably out of date but there
you
go). I've considered Lissajous figures but want to keep
it
simple. On the other hand, if there's a way of producing
a
cardioid using ECG readings and an oscilloscope, that
would be very interesting indeed, if also a complete
mindfsck.
OK, one caveat: I'm a herbalist, not a cardiologist and i
seldom get to read ECGs, though it occasionally comes
up. When it does, i look things up in my nice shiny
wipe-clean hospital cardiology book.
Therefore, any mistakes i make in the following are
unlikely to result in me killing anyone by mistake.
A healthy heart produces a trace which looks like a
heart:
symmetrical, good aspect ratio, two upper semicircular
humps separated by a curved valley along with a V-
shaped
lower half. There will be some variations between
adults,
children, resting, exercise and so on, physiologically.
Tachycardia produces a narrower heart-shape.
Bradycardia produces a wider heart-shape.
In atrial fibrillation, the start of the left heart hump,
which
happens to be an atrium, disappears, the heart-shape
looks lopsided in the middle and it constantly shifts
around. This can be seen easily because of the
persistence of the phosphor.
Nodal rhythm: Starts in the middle of the left hump.
Leftmost side completely absent.
First degree block: Heart stretched out to the left.
Second degree block: Middle of heart can vanish.
Wenkebach phenomenon: Heart stretches and shrinks in
the middle.
Wolff-Parkinson-White &c: Left and part of right side
narrow.
Conduction defects: Wide in the middle.
Flat-topped, no valley: Ventricular hypertrophy.
Sharp right-hand edge: hypokalaemia.
Right hump higher than left: hyperkalaemia.
Wide middle: hypercalcaemia.
Narrow middle: hypocalcaemia.
As i say, the normal-looking trace is still there at the
bottom, allowing someone who is used to looking at
them
to diagnose as normal, but also, the heart-shaped trace
makes differences easier to spot with less experience,
and
in at least one case actually gives a direct visual hint of
what's going on.