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QT interval/questions
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QT interval/questions

I have a form of SVT, therefore I have had a few EKG's over the last few years and they show that my QTc interval is approximately 440 - 450 (I am female).  I have asked my cardiologist and my internal medicice doctor if I have prolonged QT interval and they both said that I do not (one EKG computer print-out read: prolonged QT interval - but my doctor said that the machine was reading the p-waves and miscalculated it).  Well, from the research I have done I gather that my QTc interval is "borderline" long.  I have found a wealth of information telling people what they should do if they have prolonged QT interval (i.e. what medicines & activities to avoid, etc.).   What I cannot find anything about, is people that have "borderline" long QT interval.  Should we also be careful about the medicines we take?  Activities that we participate in?  Please just fill me in on what a person with borderline long QT interval should do.
    I should also mention that I do take a Beta Blocker for the SVT, but those EKG's I am referring to were performed before I was placed on Lopressor.
    Thanks so much for this wonderful service.  

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74076_tn?1189759432
Hello,

This can be a very confusing topic and the truth is that doctors don't always not the answers.

You QT interval varies depending you your heart rate (faster heart rate, short QT and vice versa) and electrolytes.  We tend to use the corrected QT interval or the QTc, which factors in heart rate.

The QTc read by the EKG machine is a good rough estimate of the QT interval.  It is always important to calculate it yourself.  Before you waste a lot of unnecessary time worrying, you may want to check to see if your doctor was right and the calculated QT was incorrect.

Another important factor is family history of sudden death.  If you have a history of premature, unexpected sudden death, this would highten my concern.

We have a lot yet to learn about the QT interval and who is at risk.  The best advice I can give is to look back at several EKGs and figure out if it is truly long or not.  I would not worry about a boarderline EKG and no family history.  You may want to mention your concerns to your doctor.  They might not know you are worried about this.

I hope this helps.

Good luck.
20 Comments
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84483_tn?1289941537

From what I understand .42 in men and .44 women is high end of the normal for the qtc interval, .43 in men is borderline and .45 in women is borderline, but does not usually mean that a diagnosis of LQTS from what I've read.

A high heartrate over 100 bpm makes the qtc interval confusing from what i gather also.

Computerized ECG machines are infamous for diagnosing left ventricular hypertrophy and long qt syndrome without either being present in a person, I would rely on what the doctor interpreted that looked over ECG, rather than computerized printout.

I understand your concerns though as I've had them before myself.
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Avatar_n_tn
Thanks tickertock, and actually on all my EKG's my heart was tachycardic at the time because I get so nervous when I am having an EKG for fear of what they will show.  So, maybe that was why the QTc was a little higher than normal - that makes me feel some better.  It seemed that I was the only one that was even remotely concerned about it.  My two Dr's were just like "No, you don't have it".  End of story. End of discussion.  And I was left to just worry about it.  I would have liked to have had an explanation as to why they thought I didn't have it, that would have given me more reassurance.  I go back to my Cardiologist in December and I will bring it up with her again and get an explanation this time.
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Avatar_n_tn
There are two measures of QT interval. QT and QTc. In fact, QTc is derived from QT. QT is the actual interval at the heart rate you had during the recording of the interval. The QTc is the interval that has been corrected (hence the "c") or normalised for the heart rate. In other words, once you convert to QTc the heart rate you had during the recording is irrelevant. This allows a normal range to be assigned to QTc irrespective of heart rate. I have also read the same limits that tickertock mentioned.
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Avatar_n_tn
Thanks Anacyde for your help and that was my original intention, to just be careful about what I take "just in case".  But when I brought this up to my internal medicine Dr., he said "there is no need to avoid those drugs, your QT length is not prolonged".  This is the Dr. that has followed me for 14 years.  He will be the one that prescribes antibiotics and so forth (just the thought of taking antibiotics scares me because I think most of them can cause QT prolongation).  So, I really just want to know for sure if a person that has borderline QT numbers needs to avoid certain drugs or if that is only reserved for the people that definitely have been diagnosed with LQTS......
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Avatar_n_tn
That is what I have read - that the QTc is supposed to be correct regardless of heart rate (hence the "c" in corrected).  But, I have also read a few articles stating that sometimes if a heart rate is too high that the EKG machine will not calculated it correctly and that is why you need to rely on your Dr's interpretation.  All of that sounds great and good except when it is happening to you.  When I saw that my report printed out "prolonged QT interval", I got so nervous.  It is easy for someone else to say "listen to what the Dr's say", but when you see it on black and white with your name on it - it scares you and you want reassurance.
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Avatar_n_tn
Actually I just checked my reports and my QTc is 420ms and no one has ever mentioned it. But I guess it is on the limit.
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Avatar_n_tn
Check this out ...

www.long-qt-syndrome.com/ekg_readout.html

Seems that even with a QTc of 460ms, you only have a 5% chance of actually having LQTS
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Avatar_n_tn
Thanks Jeff.  That all makes me feel better.  I hope the good doc that answers my question is reassuring also.
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84483_tn?1289941537

My QTc is also 420ms on my last couple of ECG printouts and it always reads Sinus rhythm within the normal limits. Interpretation : Normal , nothing else on the ECG. Before the computerized printout it was almost always calculated by the doctor as 40 or 41 ms.
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21064_tn?1309312333
I ran into a similar situation when EKG printouts showed "prolonger QT" intervals.  I had reading that were over 500, and the Dr. said it was not LQTS.  My EP specialized in the disorder and in fact, has done lots of research on the topic.  I figure if she says I don't have it, I'll settle for that : )

I believe the "mis"calculations also were derived from computer generated data and computer generated diagnoses.  Could be you had the same thing happen...

Hope you get the answers you are looking for.  Have a great weekend!

connie
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Avatar_n_tn
I was always a believer in doctors interpertations of EKG's when the machine would print out positive heart problems. This went on for 3 years and lo and behold the doctors were wrong and now I am paying for their mistakes.  I know it is a lot of work going from various doctors for second. third opnions but it may save your life if there is something serious wrong like in my case and also will save your sanity. But, make sure you go to cardio doctors that have no interest whatsoever in your previous cardiologist or else the answers will be the same...

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Avatar_n_tn
It amazes me the doctors can be accurate measuring off the strips.  I was looking at my strip and you obviously need to measure to time intervals - RR and QT.  RR is easy due to the abrupt ramping either side of the R. The QT is a different story as both points can be hard to find. I have ready it is best measured I think in lead 2, but it is not always easy to find the point where the EKG begins the small notch prior to ramping abruptly to the R point.  Same goes for the T. The T point is meant to be where there is a clear transition from the end of the T wave back to the baseline. You only have to be 1mm out (and QT is normally around say 8mm) and you can have a 40ms error in the QT! I checked mine a few times and the equipment calculated QTc of 420ms is pretty spot on. I thought it was out until I realized the Q point is not actually the start of the ramp up to the R point (need to include little notch). The thing to remember is that QTc is meant to translate the QT interval from what was measured at your heart rate during the test to what the interval would be if your heart rate was actually 60.  It has been shown that QTc increasingly over-estimates as your heart rate increases above 60. Hence, if you have a QTc of 420ms at HR of 90, then in reality your QT would be lower than this if your heart rate had actually been 60!
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21064_tn?1309312333
Hi Jeff,

I don't have a clue as to how to interpret the EKG strips.  I've read some articles and such, but still don't really get it. Your explanation of the difference between QT and QTc was great.  Am I correct in assuming that even though the "numbers" can be indicative of LQTS, there are other factors to consider? I have four of my EKG printouts with the following results:

82 BMP, QT/QTc  432/505*
60 BMP, QT/QTc  460/460
75 BMP, QT/QTc  456/509*
73 BMP, QT/QTc  468/516*

The readings with the * all had the computer generated statement as follows:

"Prolonged QT interval or TU fusion, ocnsider myocardial disease, electrolyte imbalance, or drug effects"

I had just started on Tambacor at the time and it is thought to have possible effects on the QT interval.  Dr. said, not a problem.  I'm assuming the interval was prolonged by the medicine.  Make sense?

Thanks for any input.

Connie

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Avatar_n_tn
Your most accurate reading is the one where your HR was 60 since in this case you are already at the QTc normalised heart rate of 60, so no translation is required and therefore no error is introduced. You were 460ms which I believe is the high end of normal for a female. The other thing is, I suspect the EKG comment about TU fusion means that the long QT may have been because it was not possible to identify the end of the T wave due to the presence of a U wave after the T wave. This could lead to an incorrect QT measurement and hence the comment. Has your doctor measured it manually and if so what was it?

I am not a doctor, so my comments are based upon my reading.
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21064_tn?1309312333
THANKS!!!  Those readings, all taken within 48-72 hours of one another, were when I had just been started on Tambacor for frequent pvcs.  I was in the hospital and monitored 24/7 so there was tons of data read, and interpreted.  My EP actually researches and specializes in LQTS so I feel very comfortable that if she says I don't meet the criteria, that I don't.  I was just wondering how to explain the numbers.

Because my situation was so weird (PVCS leading to CM), my file and test results were reviewed and studied by many docs around the country.  I imagine that everything calcuable (if that's a word) has been measured and quantified over and over again.  I'm thinking the interval was off b/c of the Tambacor.  I'll have to remember to ask for a more recent copy of an EKG report to compare the data.  It will be interesting to see what's going now that the frequency of the pvcs is so diminished.  Thanks again!!  That stuff is so difficult to understand : (

Oh, I do not have any manual measurements.
Connie
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84483_tn?1289941537

Jeff you done your homework concerning cardiac isssues, reminds me of myself. Qtc interval usually decrease with increasing heartrate , though it can also increase , it does not mean you have LQTS.

Many factors have to be considered before diagnosing someone with LQTS, in can be a difficult diagnosis from all what i have read concerning this syndrome.

The most concerning issues is syncope, torsades and family history of sudden cardiac death usually before age 35, this usually with a repeated long qt interval is usally strongly suggestive of LQTS. Manually calculated Qtc intervals are the most accurate when done correctly from what I gather.

Connie, flecainide can prolong the qt interval and lead to torsades that is why its use is almost always initiated in a hospital for a few days, that could have contributed to your Qt interval being prolonged. Your EP sounds as though he/her know their stuff. Do you know how many cases in which frequent PVCs 15,000 to 30,000 daily have contributed to cardiomyopathy? I understand there are only a few rare documented cases and it has to persist for years.

Like Jeff I am not a medical doctor, just searching for answers to the many cardiac issues that i am still ignorant to and probably always will be.

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21064_tn?1309312333
Hello,

I do not know how many case have been documented, but I do know that it is very rare. Had my pictures been better (I was not meant for stardom...hahaha), my case was going to be written up. I feel very fortunate to have such a thorough and understanding EP.  I am moving to NC soon and hope I can find someone just as competent and caring.  I will continue to have my serial checks for MVR in Cleveland, but want to find a local doc just in case.  

As you may recall, I had two ablations for the pvcs.  I am SO happy to report that my latest echo (April 05) showed even further improvement in EF and normal sinus rhythm during the entire test!! It has been nearly 2 years since the first procedure, and about 18 months since the second procedure and my EF has steadily been increasing.  Latest echo showed 60%!!!  The doctor and I were very, very happy!  She couldn't wait to tell me at my checkup.

I do think that the RX played a role in the QT interval. Despite the somewhat elevated QT interval, my history and other exam results do not clinically correlate to LQTS (thank goodness).

Hope you are well : 0

Connie
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21064_tn?1309312333
I thought you might be interested in this article:

http://circj.jstage.jst.go.jp/cgi-bin/rs.cgi?SID=141149936f2e4bb8f71c0c44a27303e3

If the link does not work, the article is from the Japanese Circulation Journal, Vol. 66 (2002) , No. 11 1065-1067

"A Case of Cardiomyopathy Induced by Premature Ventricular Complexes"

Hirokazu Shiraishi1), Kazuya Ishibashi1), Norifumi Urao1), Masaki Tsukamoto1), Masayuki Hyogo1), Natsuya Keira1), Satoshi Hirasaki1), Takeshi Shirayama2) and Masao Nakagawa2)

The abstract:

Tachycardia-induced cardiomyopathy is a well-known and reversible condition, but the left ventricular dysfunction caused by frequent isolated premature ventricular complexes (PVCs) has been rarely reported. Apparent dilated cardiomyopathy was resolved in a patient after the focal source of PVCs was eliminated by radiofrequency catheter ablation. Echocardiography showed progressive improvement of the abnormal wall motion. Frequent PVCs could be the cause of left ventricular dysfunction in a subset of patients with dilated cardiomyopathy and radiofrequency ablation should be the choice of therapy in those patients. (Circ J 2002; 66: 1065 - 1067)
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Avatar_n_tn
I WAS DIAGNOSED WITH SVT ABOUT TWO-YEARS AGO AND HAVE BEEN ON A BETA-BLOCKER EVER SINCE.  I AM A 36YR. OLD FEMALE.
DO I NEED TO ASK MY DOCTOR ABOUT LONG QT?
ANY INFORMATION WOULD BE GREATLY APPRECIATED.
I AM VERY CURIOUS ABOUT THE CONNECTION.
THANX, llllorilea
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