Please explain QT/QTS and P-R-T axes?

Question

What are the norms values for these?
QT/QTS: 340/438 s
P-R-T axes: 242 31
What are the norms for the above?


I understand the QRS interval if prolonged indicates (ventricular?) ischemia (heart block). Been trying to get the norms for the above. Just trying to understand very basics and the meaning of the cited values.

Answer 1

QT is the length of time from the q wave (or r wave if there is no q) to the end of the t wave.

Count it in number of small squares (on your ECG there are small squares and every 5 small squares you get a big square).

On the time axis, one small square = 0.04 sec = 40 ms

So if your QT is 340ms that means it would be 8 to 9 small squares long. However, the actual QT varies a little with heart rate so there is a QTc or corrected QT. I'm not sure what your QTS is all about, but I think that may be the way corrected QT is represented on your ECG machine.

You can find the QTc by counting the R-R interval

QTc = QT / SQRT(RR)

This is a pain to do so I usually look at the number that the ECG machine supplies. It gets it right much more often than I do.

QTc < 450ms is normal

Long QTc (>480ms) has been associated with sudden cardiac death from arrhythmia. See the wiki page on long qt syndrome, but don't worry cos that ECG does not demonstrate it. Just be aware.

P-R-T axis: I usually ignore the P wave axis and look to see if it is morphologically normal. If there is an abnormality of the P wave, then I think about its axis. I don't use the computer generated numbers for the P wave as I find the computer can sometimes be a little dumb about what constitutes a P wave. We often see ECG's reported as Atrial Fibrillation (ie No P waves) when there plainly are, and vice versa.

For the R axis - this is the one that is most important. It represents the general overall direction of electrical flow in each heartbeat. The easiest way to look at the axis is to look at leads I, II and III - and particularly leads I and III.

If the waves are up in I, II and III the axis is normal.

If the III is down and I is up (they point "outwards") this indicates Left Axis Deviation

If I is down and III is up (they point "inwards") this indicates Right Axis Deviation

"Left Out - Right In"

Left Axis Deviation (LAD) is important in the context of RBBB morphology, representing bi-fascicular block and being a potential explanation of a patient's syncope.

The t axis is likewise unimportant. It is more important to go and look at the morphology of the t-waves and to see if there is ST-segment elevation or depression anywhere. The various patterns of this can lead to ANY form of t-wave axis calculated by the ECG machine.

Answer 2

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RE:
Please explain QT/QTS and P-R-T axes?
What are the norms values for these?
QT/QTS: 340/438 s
P-R-T axes: 242 31
What are the norms for the above?


I understand the QRS interval if prolonged indicates (ventricular?) ischemia (heart block). Been trying to get the norms for the above. Just trying to understand very basics and the...

Answer 3

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