Prolonged S-T segment

[mobey]

God I hope this isn't a dumb question.

A co-worker showed me a strip from a 3 lead which had a very prolonged st segment. I can't remember exactly what the measurements were but it was definatly > than .20 between ths end of the QRS and the start of the T wave.

I am wondering what causes such an anomoly?

BTW I have no idea what her history is other than she is 104 yr old. (the Pt. not my co-worker)

[AnthonyM83]

Is that what Long QT Syndrome would present as?

[mobey]

Is that what Long QT Syndrome would present as?

I have never heard of that before today. I googled it and didn't get much smarter!!

Could someone simplify this syndrome and it's significance for us??

[fiznat]

.20 seconds from end of the S to the start of the T is kinda borderline I think. Someone correct me if I'm wrong but I THINK the QT interval should be no longer than .40 or so. Assuming this patient has a normal QRS (less than .20 sec), we are looking at borderline extended QT intervals.

In any case, lots of things can cause this. It can be baseline (an inherited pathology or benign sign), or due to medications that influence ion channels and repolarization. I believe, although I am not sure, that digoxin is one of the prime suspects for pathological extended QT.

I believe the real danger with extended QT is R on T syndrome (a T wave landing on top of an R wave), which can trigger all kinds of nasty rhythms like VT (more common) and VF (less common). I did a little reading and I guess Torsades is also fairly popular with extended QTs. As you might imagine, the closer the T wave is to the QRS, and the more tachy the rhythm, the more danger. By itself though, a QT interval like one it sounds like you are describing is usually not too much to worry about.

[AnthonyM83]

Like Fiznat touched on, it's a problem with the ion channels in your heart that are used during repolarization. Inherited genetic variabilities (defects) may change their structure so they don't work like they should or not as well as they should. Basically, they aren't regulating ion flow (which allows depolarization/repolarization) like they should (staying open or closed for too long, sending ions wrong direction at wrong times, etc).

And apparently, a lot of medications, like Fiz said, can cause it too...but I don't know as much about how they do that.

[AZCEP]

The QT interval is going to change with the patient's heart rate. A rule of thumb is it should not be longer than half the previous R-R. This works for rates from 70+ beats per minute. Once the rate is faster than about 140/min, you really begin to split hairs on where the half way point should be.

Faster rate = shorter QT

Slower rate = longer QT

As for the ST segment, unless the QT is lengthened with it you shouldn't worry too much about it.

[PatrickW]

IIRC, a long QT can be due to electrolyte imbalances as well as what others have mentioned above.

Long QT with a U wave: Hypokalemia (Also, flat T waves)

Long QT without a U wave: Hypocalcemia.

[gvandellen]

Read This:

http://www.emedicine.com/med/topic1983.htm

I used this for a paper on LQTS...

G

[mylesblock]

The biggest item that needs to be worried about is the prolonging of the relative refractory period. This is what causes those arrhythmias stated above (VT and VF) when another cell in the Atria other then the SA node fires during that period. There are meds that cause a prolonged QT and others that make it worse.