Repolarization Abnormalities - LQTS

Our family has a preliminary diagnosis of LQTS based on myself and my children, my sister and her children having borderline Long QTc and that my 20 year old son had a cardiac arrest while running after taking several puffs of his ventolin inhaler just over a year ago. He was successfully revived by paramedics.
My question is what exactly is the added risk of having repolarization abnormalities involving the T waves.
I realize that without seeing our ECGs you would just be guessing. But our t waves are very low amplitude and have a prominent U wave after them in the V leads especially. This seems to be troubling the doctors a bit and I haven't received any definite answers yet. We have doctors in Europe that specialize in LQTS analyzing our ECGs and they have agreed to genetically test us.
My second question is should we consider ICDs. My other 2 children have had dizzy spells during exercise but have not fainted. I have fainted several times and have been having more frequent near-fainting spells.
My third and final question is, is 137/bpm low for a 9 year old to have during peak exercise. His resting heart rate is around 73.
Thank you very much.

[Michael J. McWilliams, M.D.]

Hi SW,

I am very sorry you are in this situation -- I understand it must weigh heavily on your mind.

1. My question is what exactly is the added risk of having repolarization abnormalities involving the T waves.

The honest is answer is that we don't know the answer yet.  The QT interval reflects repolarization of the ventricular myocardium and the T wave component is thought to be caused by differences in repolarization time of the outer portion of your ventricular heart muscle (epicardium) and the inner layer (endocardium).  There is later component sometimes seen in normal and abnormal repolarization called a U wave.  In general we do not use the U wave to measure the QT interval, but sometimes the difference between T wave and U wave is difficult to distinguish.  In these situations, we sometimes consider the whole QTu (QT interval plus U wave) interval.

The morphology or shape of the QT interval is shown to correlate with the type of long QT syndrome (1-3).  This is sometimes helpful to determine what subtype your family may have, although genetic testing is more definitive when it is positive.  A negative genetic test does not mean that you do not have the syndrome – we haven’t found all the genetic abnormalities yet.  In general, syncope and sudden death with exercise is most often associated with Long QT type 1.  Venolin should not be used with long QT syndrome.

I think it is also important to mention that beta blockers are recommended for most subtypes of long QT syndrome.

2. My second question is should we consider ICDs. My other 2 children have had dizzy spells during exercise but have not fainted. I have fainted several times and have been having more frequent near-fainting spells.

The risk of sudden death events correlates with the duration of the QT interval.  QTc (corrected QT interval for heart rate) is shown to correlate with the risk of sudden death with QTc greater than 500 msec equating with higher risk.  That being said, if you have a family history of sudden death (your son), a long QTc on EKG, and a syncopal episodes, I would strongly consider an ICD.  You should talk to your doctor about this – I imagine you already have and they have probably recommended one.

Two things that would sway me to place an ICD for similar circumstances would be:
a. an exercise stress test that shows prolonging of the QTc or not shortening of the QTc with exercise and having a QTc that is abnormally high or
b. A rhythm strip showing a dangerous arrhythmia


3. My third and final question is, is 137/bpm low for a 9 year old to have during peak exercise. His resting heart rate is around 73.

I am not a pediatrician and haven’t worked a lot with children since medical school. I agree that a 9 year old should be able to increase their heart rate to greater than 137, but remember this is effort dependent and it may not have been a max effort.

I hope this helps.  I wish the best to you and your family.

[tickertock]

Just want to say glad to see you will still be answering our most posted questions on PVCs/PACs and various arrhythmias. Your kind and compassionate answers and follow up responses were very much appreciated by all on the regular heart forum. May you be blessed in every way.

[stevie_wonder]

Thank you very much for your opinion. It helps to hear it from more than one source. My 20 year old does not want an ICD but I definitely would feel safer if he would get one. I think that maybe if I got one that would help his decision. But I have to admit being as scared to get one almost as much as I am scared to not have one... if that makes any sense. We are all on Betablockers and even though my son had his cardiac arrest while running, the doctors are swaying towards LQT2 because of our t wave shapes. He takes the ventolin because of his asthma. His doctor will only allow him 2 puffs a day or he has to go the ER. He also takes a daily preventer (Flovent). My son who just turned 10 is very athletic and maybe that is why his heart rate didn't get too high but all the articles I have read on children's heart rates show them much higher during exercise.
Again thank you so much for helping.

[Michael J. McWilliams, M.D.]

Thanks for the comments. I really do enjoy this forum and learn a lot from it.

SW, I have to be careful sometimes of what we say for medical legal reasons.  If it were my family, I would recommend an ICD.

Please take care.