Cardiac Action Potential Duration Question

  • #1
What does the APD (Action potential duration) determine in a cardiac cell and how can it be changed (do I need to effect any of the phases of the AP)?

For example, if the vagal nerve releases acetylcholine here are its effects:

Inhibits Atrial Muscle Contraction- Negative inotropic effect (contract less vigorously)
Why- We lost Ca++ which causes weak muscle contractions

Inhibits SA Node Pacemaker activity- slows heart rate, lengthens R-R interval and P-P interval; Negativie Chronotropic
Why- We hyper-polarized and now it takes more time to get up to the threshold!

Inhibits AV Node Conduction (not Pacemaker it’s not firing): lengthens P-R internal; Negative Dromotorpic
Why
- Any tissues that uses Ca++ for AP will now have a slower conduction as we have decreased the amount of Ca++ going through the L-type channels (decreased upstroke slope)

So did this effect increase the APD in all these cases therefore increasing the refractory time so that AP could not be fired at fast rates?
 

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