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Old 06-03-2015
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Heart Short QT on ECG

Anything that decreases the duration of action potential (Ca channel blockers, Hyperkalemia) will decrease QT interval (Kaplan 2011 p.46)

Now I saw a question in USMLErx about Sarcoidosis and Hypercalcemia, Hypercalcemia causing shortened QT.

What causes Short QT and WHY?


Was surfing the internet, but couldn't find anything helpful

Can anyone expalin it to me?
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Last edited by MananaMD; 06-03-2015 at 04:52 AM.
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Old 06-04-2015
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The only thing I can think of is Class IB anti arrythmic (Lidocaine, Mexiletine, Tocainide, Phenytoin). Other than that, I do not know.
As to why, I do not have the slightest idea.
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Old 06-04-2015
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QT interval= electrical depolarization and repolarization of the ventricles.
Short QT interval= ventricles are depolarizing and repolarizing faster
Recall that during phase 2 of AV node Action Potential there's increase in Ca2+ into the cell and K+ out via there respective channels. Well the trick is here, when you pump Ca2+ into the cell, you're increasing the intracellular Ca2+. Recall that Ca2+ is an activator of many proteins and enzymes in the cytoplasm. Your cell has to remain in homoeostasis. So your cells says **** this ****, pumps into the SR or excretes via Ca2+to 3-Sodium exchanger(Leak currents). The more Ca2+ you have inside the cell, the more Ca2+ to 3Na+ exchanger has to work. So now your pumping more sodium(1ca:3na) into the cell. As result of your cell trying to maintain homeostasis via leak currents, there is an increased activity of 3Na-2K+ exchanger. Which pumps 3Na out and 2K+ into the cell. Now where the **** does all this increased intracellular K+ go? Out through the K+ Channels responsible for Re-polarization of ventricles during phase 2 and phase 3. So as a result of hypercalcemia, your increasing the velocity of depolarization of ventricles (directly via Ca2+ influx) and increasing the velocity of re-polarization (indirectly through the K+ current Channels ).
Well lets go back to what QT interval means;electrical depolarization and repolarization.
Short QT means: Depolarization and repolarization are occuring faster(increased velocity of these processes) (Short means short time, which means increased velocity(d/↓t=↑V)

Hopefully that explains that. Learn to read an ECG and extrapolate knowledge to basic physiological concepts.
http://i.imgur.com/Yj0gmr0.gif

Last edited by guru007; 06-04-2015 at 12:36 PM.
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Thank you !
That's helpful..
U did great job !

I am interested about ca channel blockers and short QT
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similar concept.

When you have hyperkalemia, your body overtime will naturally compensate by pumping it into cells via insulin, catecholamines, or hyperkalemia itself and will naturally try to correct it via renal mechanism.
Increased Potassium inside the heart cells, will leave through the potassium current channels. Making repolarization faster. You'll have a short QT, as your ventricles are repolarizing faster.

CCB's only block L-type voltage gates. This will cause a reduction of inward depolarizing current. Which mean repolarization will happen sooner. Shortened QT

Last edited by guru007; 06-04-2015 at 02:36 PM.
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