Nope, qtc does not shorten or lengthen with heart rate.
Qt interval changes.. However 'corrected' qt or 'qtc' is your qt interval after a formula has been applied to it to negate the heart rate.
QTc is not problematic unless over 500ms.
Long Qtc is caused by genetics or severe electrolyte abnormalities. It would appear neither is the case for you. That change is very much within normal limits and healthy.
Thanks for your advice mate. Im pretty sure that the interval shortens when the rate gets higher? As QRS narrows? On some of my old ecgs, I did see one of them at 66bpm and it spat out a QT of 368ms and a QTc of 385ms. Following that was one with a rate of 85bpm and it spat out a QT of 342ms and a QTc of 406ms ?? I must be reading them wrong perhaps? I did already have a stress test in 2015 on a treadmill @ 201bpm and the e.p said everything was fine.
I've tried to learn the manual by hand way of it but evrytime I try I can't get the hang of it. Are you any good at it? If I was to supply you with the information on one of my ecgs?
So the margin of error is usually 40 ms or so in either direction.
For example i measured 2 qt intervals today, one interval was 40 higher then the machine one was 40 lower.
Remember each small red box on the ecg paper = 40ms... That box is 1mm wide..
So a 1 mm error in where the machine "thinks" the t wave ends can cause a huge (40 ms) shift in qt.
And yes you are absolutely correct, the higher the heart rate the more difficult it is for the machine to get a qti/qtc. This is because the p wave begins to distort the terminal aspect of the t wave as they move closer together.
As for qtc.. Im sure the machine got the formula right to convert qti to qtc, however its the qt interval input that gets messed up.
Garbage in garbage out as they say..
In terms of measuring, honestly a magnifying glass (or extremely,good eyesight), a pen, calipers and a straight ruler are key here.
As for being good at it, im decent.. But unfortunately i cant just use the numbers, id need to actually see an image sorry.
Ok I understand, I just was baffled to see one come out at 449 and 30 minutes later when I requested them to repeat it, it had dropped to around 420, that quickly! But that probably backs your theory of saying the machine was wrong in the correcting department. I probably already know the answer to this lol, but I suppose if a reputable E.P has went through my treadmill test and holter monitor overnight, it pretty much makes it a almost impossibility to have it.