QTC

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Specializes in Med-Surg/Oncology, Psych.

Hi all!

I'm looking for some help understanding the QTC or corrected QT interval. A friend of mine has started working on a tele unit and on that unit they are starting to look to the QTC as a really important indicator of how the pt is faring. I'm dying to get into cardiac nursing (already signed up for basic dysrhythmia class, ACLS, etc), and I want to have a thorough understanding of this concept. Can someone offer some reputable sources for a good explanation on what the QTC is and why it's becoming so important? Thank you in advance!

-Erin:heartbeat

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The QT interval is the time between ventricular depolarization and repolarization. Drugs (in particular antiarrhythmics) can prolong the QT interval. The longer the interval gets, the higher the risk for ventricular arrhythmias, the most notable being torsades de pointes (polymorphic VT).

Pts with cardiac disease, CT surgery pts, or those on offending drugs should be monitored with daily EKGs. Haldol is a common ICU drug which prolongs QT as well. Congenital QT prolongation is also a known entity but less common in the ICU/CCU.

The "c" means the QT interval is "corrected" for the heart rate with Bazett's formula. As the HR increases, QT should decrease. To correct, take the measured qt and divide it by the square root of the R-R interval.

You should measure the QT on the 12 lead, and count it out yourself. It starts at the beginning of the QRS and runs until the end of the t wave.

Small box 40 msec, large box 200 msec (5 small boxes).

QTc is normally 430-450 (varies w/ gender).

Greater than 500 msec creates significant increase risk for TdP and needs to be addressed (stop drugs, cardiology eval etc).....

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Specializes in Med-Surg/Oncology, Psych.

Thank you for this great reply! To be sure that I understand, what you're saying is that if the QTc falls between 430 and 450, then that means that the QT interval is an appropriate length relative to the patient's heart rate?

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It's average.

For nuts and bolts purposes, if the QT is going up or over 500, it needs to be addressed.

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Specializes in Cardiovascular.

I recently had a pt admitted for recurrent Firing of AICD. This was his third admit for same reasons. Last admission his pacer was interrrogated and he was loaded on amio gtt, transitioned to po and dc. Within the same day of dc, he returned back to ED because his ICD fired 6 times on him. So this admit, he was started on an amio bolus AGAIN. EKG prior to gtt QTc 485ms. Prior EKG's from past showed his longest QTc at 545ms. During monitoring of gtt, his QTc slowing trending up, reaching 545-552, and at one pt 566 nst. ED labs = Mg 2.0 with K+ 4.8...Tele SR/SA w 1degree avb, bbb, rate 46-50's, BP stable, pt NAD. I called cards in concern for QTc, Cards MD oncall stated that he was not concerned with his QTc and that he needed his antiarrhthmics and pt had a pacer anyway. I asked him when should I be concered w this pt, he stated if his QTc >550 and sustained.

What do you guys think of this QTc in this situation? Also pt receving another amio load with in 24hr of last admit!? Im thinking its his prolonged QTc that is triggering torsades or PVT and ultimately firing his ICD.

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