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    EthanHunter is offline Permanently Banned 510 points
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    Hypercalcemia has short QT interval on EKG?

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    condition that cause hypercalcemia states like hyperPTH would cause short QT. Do u guys know why? I am not sure how to explain it using electrolytes. My thinking is hyperca causing phase 2 on the ventricular action potential to be longer due ca influx, but i dont know why it would cause shorten QT(mechanical contraction of the ventricle). Maybe because Ca influx cardiomyoctes causing contraction. My problem is i thought hyperCa would make cell less likely to depolarize according to Dr. *******-Pass Program-yet it cause short QT. Can someone explain the connection to me? Thank U.

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    IMG SURVIVOR is offline Moderator 536 points
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    Have in mind Im sleepy
    Tachycardia= short PR segment

    When the heart goes faster the PR segment gets smaller and it gets little time to fill up in Diastole.

    IMG going to
    Moderator: USMLE AND Residency Forums.

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    why even bother with the obvious. Just know where you are need it and where you can help the most.

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    Dr. X's Avatar
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    short QT interval signifies shorter ventricle depolarization and repolarization time. so you know that the heart is beating faster as there is an increase in contractility (ionotropy).

    contractility is based on intracellular ca concentration. After an upstroke by Na+ (inward current), the calcium comes in at phase2 (inward current). Remember that the calcium that comes in is bit more than the usual in hypercalcemia. Inward ca+ causes the release of ca+ from the SER, the famous ca+ induced ca+ release. Whether it be increased heart rate or sympathethic stimulation of the B1 receptor, more calcium causes an increase in contractility, aka positive ionotropism.

    In short, hypercalcemia causes an increase in contractility (you also see increased heart rate), which would show as shorter QT interval. your original thought seems right.

    In terms of depolarization, its better to keep your mind on Na than Ca, on ventricular action potential (at phase 0) or even when you are looking at SA node or AV node (at phase 4) where upstroke is by ca.

    some quickies:
    QT interval - controlled by heart rate.
    PR interval - controlled by conduction velocity.

    Increase in one means decrease in the other.
    eg. increase in HR means decreae in QT interval.
    SJSM.

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    EthanHunter is offline Permanently Banned 510 points
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    i know that phase 0 is ventricular depolarization using Na fast channel, which give the QRS complex on EKG, and SA/AV node only deplarize by CA slow channel P-wave on EKG. Ca influx trigger the actin/myosin contraction complex. But HyperCa causing less depolarize states in ventricle which seen to me would effect the QRS complex-widen and shorten it- instead of QT segment. Do u guys think Ca influx using Na/Ca channel? Ie Ca comes in and Na come out? Thanks for ur post it helps me clear up some issues.

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