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QT correction methodology

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LessValuableNinja has 8 years experience and specializes in Cardiac (adult), CC, Peds, MH/Substance.

5,490 Profile Views; 754 Posts

[h=1]Hey All,

While many articles and studies tout the importance of correcting the QT interval for either R-R or rate, there seems to be little consensus on what this means. In fact, many educational materials discuss this concept, then provide (potentially) outdated methods that may not have great evidence behind them supporting their use versus other methods. Additionally, many resources do not address evidence, or pros and cons of different methods. I've done a bit of research, and am having little success finding any sort of professional consensus on what formula to use in different situations.

I'd like to solicit opinions and information on the subject. Key questions include:

1) Are there any professional organization recommendations on QTc correction formulas? This could be either nursing or physician organizations.

2) Do you have a personal opinion on the subject? If so, what is your opinion, and why?

3) Is there a standard where you work? If so, what is the standard? What information or evidence has been given to you supporting the standard? How do you feel about the standard?

4) Any great articles/studies on the subject? I have an entire folder of studies and articles on the subject numbering in the hundreds, but don't have a single article or study that addresses professional consensus or provides a good overview of the pros and cons of many methods, or provides a recommendation of one method over many others (some address one versus a few others). Anything that you've read that makes you say, "Yeah, this'll work, and I feel good about using this method based on their evidence?"

Thanks so much for your time, experience, and brain.[/h]

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1: No idea.

2: Not really. I'm open to new data. As I'll explain below, I haven't really been a party to at-work discussions or debates about the best correction formula, and the QTc is not emphasized as one of the more important monitored values in many of our patients.

3: We primarily use the QTc provided for us by either our monitors or our 12 lead EKGs. I believe (though I'm not certain) that both devices apply Bazette's formula to calculate the QTc, which is the QT interval divided by the square root of the RR interval. Some of GE's published materials reference Bazette's formula. And though I don't know what formula our 12 lead EKGs use, they are a bit older and so Bazette's formula also seems like a safe bet.

We have been given no particular evidence that I'm aware of that this is the best formula to use. I suspect most of our nurses do not actually know the formula to correct QT intervals, and so rely on the the one provided by the monitors when needed.

4: I tend to doubt a professional consensus exists, though I'd be curious to hear your thoughts since it appears you've devoted more time to the subject than I have. I'm familiar with the following study comparing different QTc formulas:

Which QT Correction Formulae to Use for QT Monitoring?

...though I'm reluctant to put too much weight on it, due to concerns about sample size and pool as well as a perhaps unjustified assumption that QTc is more closely related to all-cause mortality than it actually is. I'm no expert on the subject though. Do you know of better studies?

In truth, I most often see QTc ignored except when it is way off of normal limits or else when we are using a drug or treating a condition in which we expect and anticipate QTc abnormalities in the first place. For whatever it's worth, the QTc doesn't get a whole lot of attention where I work otherwise, and different formulas that might be used to correct it get even less.

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