Read on Twitter
1/ QT/ √ RR is wrong?
Today’s @CPSolvers case was phenomenal and while I won’t ruin it for anyone, I will say that the corrected QT came up in the chat and as promised here’s a brief @MedTweetorial on QT correction formulae and the nuance involved in correcting.
Today’s @CPSolvers case was phenomenal and while I won’t ruin it for anyone, I will say that the corrected QT came up in the chat and as promised here’s a brief @MedTweetorial on QT correction formulae and the nuance involved in correcting.
2/ First, check out @cardionerds video on the QTc, why it matters, various formulae, nuance in manually finding the end of the T wave as well as what to do in bundle branch blocks and A-fib. My planned thread is much shorter thanks to this epic video
3/ Brief summary of the video relevant to us:
-QT is a measure of ventricular depol and repol
-QT changes with HR and we correct to a normalized HR of 60
-Automated EKG read has <50% sensitivity to catch long QTc
-Prolonged QT assoc. w/ life-threatening polymorphic VTach
-QT is a measure of ventricular depol and repol
-QT changes with HR and we correct to a normalized HR of 60
-Automated EKG read has <50% sensitivity to catch long QTc
-Prolonged QT assoc. w/ life-threatening polymorphic VTach
4/-Use lead II, v5 or v6 when manually measuring
- Many formulae exist
- Special circumstances for bundle branch blocks and A-fib
But really, watch the @cardionerds video!
- Many formulae exist
- Special circumstances for bundle branch blocks and A-fib
But really, watch the @cardionerds video!
5/ Which formula do you use?
If none of these or something else, comment below!
If none of these or something else, comment below!
6/ Some history:
Bazett in 1920 produced a marvelous and elegant paper and derived the formula of QTc = QT/ √ RR from a sample size of 39 young pts
But we now know that it overcorrects at higher HR and undercorrects at lower HR https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1542-474X.1997.tb00325.x
Bazett in 1920 produced a marvelous and elegant paper and derived the formula of QTc = QT/ √ RR from a sample size of 39 young pts
But we now know that it overcorrects at higher HR and undercorrects at lower HR https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1542-474X.1997.tb00325.x
7/ Also in 1920 Fridericia found that QT divided by cube root of RR helped derive the QTc (again elegant and full of incredible mathematics). Find a translated reprint from 2003 below:
https://onlinelibrary.wiley.com/doi/full/10.1046/j.1542-474X.2003.08413.x?sid=nlm%3Apubmed
Both Bazett and Fridericia's formulae are population-derived
https://onlinelibrary.wiley.com/doi/full/10.1046/j.1542-474X.2003.08413.x?sid=nlm%3Apubmed
Both Bazett and Fridericia's formulae are population-derived
8/ So which should you use?
Well, Charbit et al found in a 108 patient study that Bazett had a sensitivity of 54% and Fridericia had a sensitivity of 100% in detecting QT prolongation
https://pubmed.ncbi.nlm.nih.gov/16436843/
So we should all use Fredericia’s formula then? Maybe.
Well, Charbit et al found in a 108 patient study that Bazett had a sensitivity of 54% and Fridericia had a sensitivity of 100% in detecting QT prolongation
https://pubmed.ncbi.nlm.nih.gov/16436843/
So we should all use Fredericia’s formula then? Maybe.
9/ The FDA acknowledges that both of them have issues but recommends submitting uncorrected QT and RR interval data, heart rate data, as well as QT interval data corrected using Bazett’s and Fridericia’s for study in new meds
https://www.fda.gov/media/71372/download
https://www.fda.gov/media/71372/download
10/ However, there have been advocates for application of linear regression techniques and Hodges in 1983 and the Framingham group in 1992, came up with their own formulae that relate QT interval linearly to the RR interval and to the heart rate. https://www.ajconline.org/article/0002-9149(92)90562-D/pdf
11/ A good review of all of this can be found here in this JAHA 2016 article by Vandenberk et al where they found that Fridericia and Framingham showed the best rate correction and improved 30 day and 1 year mortality.
https://www.ahajournals.org/doi/10.1161/JAHA.116.003264
https://www.ahajournals.org/doi/10.1161/JAHA.116.003264
12/ @mdcalc actually gives you all 4 now (though what I love about Hodge's is that you can do it in your head) https://www.mdcalc.com/corrected-qt-interval-qtc
13/ So what should I use in clinical practice? I don’t know! Plenty of studies have shown that Bazett’s which is the most-widely used probably shouldn’t be used.
Whatever you do, manually correct it and don’t rely on the automated read!
Hoping for some cards or EP help here!
Whatever you do, manually correct it and don’t rely on the automated read!
Hoping for some cards or EP help here!
14/ If you use another formula for correction, document which formula you used as most people still use Bazett and consistency is probably more important than anything else.
15/ Summary:
-Watch the @cardionerds video
-QT correction should be done manually given how bad the automated read can be and risks assoc with prolonged QT
-Bazett can be inaccurate and Fridiericia, Framingham and Hodge’s are more accurate but consistency is key
-Watch the @cardionerds video
-QT correction should be done manually given how bad the automated read can be and risks assoc with prolonged QT
-Bazett can be inaccurate and Fridiericia, Framingham and Hodge’s are more accurate but consistency is key
CC: @RosenelliEM @medrants @DxRxEdu @rabihmgeha @AnandJag1 @Anand_88_Patel @sargsyanz (I know I am missing many more people who were present today)
@cardionerds with Bazett's being so widely-used and as inaccurate studies say, what should we all be doing in practice?
@cardionerds with Bazett's being so widely-used and as inaccurate studies say, what should we all be doing in practice?
Also @haematognomist @joshmedpeds @fzghyer
Feel free to share or tag with anyone else who was present today! I still don't know everyone in the wonderful @CPSolvers community or follow them on Twitter though I would love to!
Feel free to share or tag with anyone else who was present today! I still don't know everyone in the wonderful @CPSolvers community or follow them on Twitter though I would love to!
