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Long QT, help please
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Long QT, help please

I recently had a ECG that showed that I have long QTc of around 440. I've had about 20 ECG's in the past that all came up normal and no where near 440 or even above 400. Multiple stress tests, holters, and echo's come back normal as well. No one in my family has any heart problems and or has fainted.
Any one have any possible reason as to why I could have developed Long QT? I should also add that I'm on 12.5mg of atenolol and no other medication, and I had my potassium levels checked about 3 months ago at which point they were right in the middle of normal. Also, my heart was elevated during the monitoring if this makes a difference.

Any tips, insights, or advice would be wonderful and very much appreciated.
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Avatar_m_tn
It may make a difference that your heart rate was elevated, but only if it was much lower during all your other normal EKG's. LQT1 is heart rate mediated, with higher heart rates producing a longer QTc, which is why passing out or cardiac arrest occur during exercise in this substrate of the disease. In LQT2 a sudden shot of adrenaline and increase in HR will cause the rise in QTc, which is why alarm clocks and such are the triggers for that one. LQT3 is the opposite way, as lower heart rates, and thus sleep are the triggers.
      Here are a few other things to consider though: Long QT Type 1 predominately affects children, so if you are 27 and are still alive your phenotype would be extremely mild, likely never killing you, even if this is what you have. The same is true of LQT2 and both LQT1 and LQT2 tend to hit adult females not males if they do strike in an adult. You definetely do not have LQT3 if an elevated HR made the QTc go up.
     Furthermore, there is a huge overlap of people with LQT Syndrome and normal, healthy people. The average QTc is about 390-400ms, but up to 5% of all people have a QTc above 440ms, 2% above 450ms, and 1% above 460ms. Meanwhile, although the average QTc in LQT Syndrome is about 480ms, there are a good 40% of them who are in the 450ms and below range. Considering how rare LQT Syndrome actually is (less than 1% of the whole population) 40% of well less than 1% is a lot less people than 5% of everyone, so a great many more people have an EKG at 440ms every time out of 20, not just once, and still don't have this rare disease.
         Finally, checking your potassium levels will not really show if you have a LQT problem, because in LQT1 and LQT2 it's a potassium ion channel gating function issue, which simply means that not enough potassium is getting into the heart when it needs to. It has nothing to do with how much potassium is in your blood overall. This is mediated by a genetic mutation. In LQT3 it is a problem of too much sodium being allowed in, as the sodium ion channels have incomplete inactivation. The potassium ion channels have incomplete and slowed activation in LQT1-2. Your atenolol will not contribute to QTc prolongation. However, if you are on a beta blocker like this, I should tell you that there is an unspecific correlation between diastolic dysfunction and QT interval length, with diastolic dysfunction occurring in up to 50-80% of all hypertensive patients. This would be an essentially benign finding, but perhaps a sign that you need to take further steps to lower your BP.
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3198987_tn?1349078636
Thanks for the reply, it was very informative.
I'm taking the beta blocker for tachycardia so my blood pressure is usually around 105/65, and I've had multiple tests before this that showed no diastolic dysfunction. I'm really confused by my QTc result. In the past it's always been 370. I've never even felt dizzy before from any heart related issues, and my last stress test was one year ago and all was fine. Infact I had another ECG 3 months ago that was normal. Could it be just something. I talked to my cardiologist on the phone today and he said "Not to worry about it and it's nothing urgent" what ever that means.
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Avatar_m_tn
   Over the course of any 24 hour period our QTc interval has a range that can be up to 100ms wide for a lot of people. I had a lot of EKG's done when I first started having my palpitations and I've had a QTc interval as low as 392ms and as high as 448ms. I don't have LQT Syndrome,  My palpitations are benign, and yours most likely are as well. The amount of time you will spend worrying about this number, if you are anything like me, will not be worth it in the end. LQT Syndrome is a genetic disorder and you have no family history. Like I said earlier if every person with some PVC's and one EKG that had a QTc of 440ms had LQT Syndrome, then LQT Syndrome would be the new cancer that was the biggest disease in the world. I'm 99.99% sure your doctor is right for not being worried about this. Something you may want to consider pursuing, if it will help give you some reassurance, is a 24 hour Holter that monitors QT intervals. They normally only monitor PR and QRS duration, but some new ones can show your min max, hour by hour and overall QT/QTc averages. I would bet good money that you would show an average of 390ms or something, but have a min and max of like 350ms and 450ms. Think of it like HR. Most times a resting HR is like 65-70BPM, but at some point in your day it gets really high and really low. QT intervals are kind of the same way.
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Avatar_f_tn
A QTc of 440 is right at the border of being normal/slightly borderline high and this value is not alarming.

As mentioned above, QTc will change throughout the day so you could ask for a Holter monitor if you want additional testing.

The QTc value should be calculated by an experienced EP - computer generated values are not always accurate.  Also, several formulas are available for calculating QTc and should be used in different situations, eg some formulas tend to overcorrect more than others at heart rates of over 100bpm.   So, this is something to consider.

Finally,  drugs/medications (including albuterol, caffeine, decongestants etc), electrolyte imbalances (calcium, magnesium, potassium), and even hypothermia can result in prolongation of the QTc interval.

So..... Several things can cause a prolongation of the QTc interval, measurement of the QTc can be very difficult and thr values are not always accurate, and your value of 440 ms is not in a concerning range.  Do follow up with your doctor if you are concerned.
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3198987_tn?1349078636
Thank you, that does put my mind at ease. I was pretty worried at first, but I'm starting to accept that it could just be computer error or some benign reason that may have caused this.
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