文档介绍：Electrocardiogram, ECG
Blood circulation
Cardiac electrical activity
Electrocardiogram (EKG or ECG)
What is it?  An electrocardiogram – abbreviated as EKG or ECG – is a test that measures the electrical activity of the heartbeat.  With each beat, an electrical impulse (or “wave”) travels through the heart.  This wave causes the muscle to squeeze and pump blood from the heart.
The Heart
is a pump
has electrical activity
(action potentials)
generates electrical
current that can be measured
on the skin surface (the EKG)
What is the function of ECG
In an ECG test, the electrical impulses made while the heart is beating are recorded and usually shown on a piece of paper. This is known as an electrocardiogram, and records any problems with the heart's rhythm, and the conduction of the heart beat through the heart which may be affected by underlying heart disease.
Currents and Voltages
At rest, Vm is constant
No current flowing
Inside of cell is at constant potential
Outside of cell is at constant potential
++++++++++++++++++
------------------------------
A piece of cardiac muscle
outside
inside
0 mV
+
-
Currents and Voltages
During AP upstroke, Vm is NOT constant
Current IS flowing
Inside of cell is NOT at constant potential
Outside of cell is NOT at constant potential
++++------------------------
------++++++++++++++
A piece of cardiac muscle
outside
inside
Some positive
potential
+
-
current
AP
An action potential propagating
toward the positive ECG lead
produces a positive signal