Cardiac conduction velocity is the velocity at which a depolarization wave moves through the myocardium, the muscular middle layer of the heart, and it’s measured in meters per second.
The depolarization wave travels through the sinoatrial node, or SA node, through both atria, down the atrioventricular or AV node, through the Bundle of His and the Purkinje fibers, and finally to all of the parts of the ventricles, all in about 220 milliseconds, which is less than a quarter of a second!
If we zoom in on the myocardium, the depolarization waves move across neighboring cells. It moves from one cell to the next when ions like calcium and sodium slip through gap junctions and trigger voltage-gated sodium channels in that cell over to open up, allowing a rush of more sodium into the cell and causing an action potential to occur.
That then results in more sodium and calcium leaking through to the next cell, triggering an action potential, which goes on to the next, and so on.
Ultimately these cellular processes determine how fast or slow a depolarization wave will move across different types of tissues.
More sodium channels and gap junctions speed up the depolarization wave, Fewer gap junctions and fewer sodium channels slow down the depolarization wave.
Alright so let’s break down the conduction velocities in the different parts of the heart, starting at the SA node,i the depolarization wave moves through the myocytes in the atria at about 1 meter per second, then goes through the AV node really slowly, roughly between 0.01 and 0.05 meters per second.