Hypercalcemia and heart rate

Published

Hello everyone!

Could anyone possibly help me to understand the mechanism of the effect of hypercalcemia on the heart rate?

I know that normally excess in extracellular Ca++ has a ''sedative effect'' on the Na+ channels. It actually raises the threshold potential by making Na+ channels more difficult to activate by depolarising currents. If this is true then it would be much more difficult for the heart muscle fiber to depolarize and reach an action potential.

But we doe see in cases of hypercalcemia a smaller Q-T segment which means a quicker depolarization and repolarization.

How can this be explained?

Up Vote Up Vote ×
Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

Welcome to allnurses! The largest online nursing community!

We are happy to help....what semester are you? What has your research revealed to you? hint....Calcium is different on the heart

Up Vote Up Vote ×

Hello Esme12,

Thank you very much for your reply! Well I think in the heart muscle the main depolarizing current is created by the Ca++ ions. Because the heart muscle fibers are organized in syncitiums and when one one of these cells becomes excited the action potential spreads to all of them.

The depolarizing current open further the Na+ channels but in the case of hypercalcemia maybe not so easy. After a very small period (I think smaller than milliseconds) open also the Na+/Ca++ channels and we have an influx of Ca++ (plateau phase). The plateau phase stabilizes the depolarization of the membrane (it becomes longer).

In the case of hypercalcemia I think that the delayed Na+/ Ca++ channels do open but the fast Na+ channels open more difficulty. Because of the greater concentration in Ca++ ions the Ca++ influx is more intense and quicker.(maybe also because of the little activation of the Na+ channels the cell membrane hasn't still reached the ''desirable'' depolarization state -> quicker Ca++ influx). The intense Ca++ influx decreases then the duration of the plateau phase -> action potentials become shorter -> tachycardia -> shorter Q-T segment.

Some of these are just assumptions that I make but discussing it with people who have experience in this field can make it more clear to me :)

I have finished my studies since 2009. I have only 2 years of work experience but I like learning new things and become better :)

Up Vote Up Vote ×

Any arguments???

Up Vote Up Vote ×
+ Join the Discussion