Heart & Cardiology/Borderline QTc


28 year old female 5'8" 178 lb and blood pressure 101/74 (suffer from orthostatic hypotension a, so Bp varies).  
Medications: Flonase, zoloft 12.5 mg (just starting), and lorazepam .5 mg x3 daily.

I have a question in regards to EKG reading.  I have a history of SVT, PVCs and have had 3 ablations for SVT.

I recently had two EKGs done at my doctors before starting Zoloft.  For my first EKG my qtc was 470.  The following week my qtc was 444 with pulse rate of 85.  I asked the dr about the 470 qtc reading because I know that is prolonged and he wasn't sure why it was high.  He said my heartrate was elevated during the EKG so the machine may have misread it.  The following week my EKG was done and the qtc was 444.  My dr said its fine to take the Zoloft, because I have has two prior qtc readings of 440 and 444.  The 470 qtc seems to be a one time thing.

Here are my questions:

What is your opinion?  Is it possible the machine over corrected my qtc at one point?  I thought that during elevated heartrate a the qtc decreases..?  Should the zoloft be fine to take?  I can't find any info. About how much of a qt prolongation zoloft may cause.  Is the qt prolongation dependant upon dose?

Thank you for your assistance.

Hello Jacquie,

The EKG probably read your QT correctly, but the formula for calculating QTC isn't very accurate for fast heart rates.  470 is the upper limit of normal for QTC, and is probably okay with a fast heart rate.  Zoloft doesn't affect QT.  I think it's safe for you to take Zoloft.

Please write back if this note doesn’t answer all your questions.

David Richardson

Heart & Cardiology

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David Richardson


Adult heart function and disease. Not very good about children lesss than 12. Hypertension is o.k. Heart rhythm a special interest.


Certified in cardiology by the American Board of Internal Medicine. Was chairman of division of cardiology at the Medical College of Virginia. Am now mostly retired.

Fellow of American Heart Association and American College of Cardiology and member of American Physiological Society..

Circulation, American Heart Journal, Hypertension.

M.D. from Harvard Medical School. Residency training at Yale Uhniversity School of Medicine and Medical College of Virginia.

Awards and Honors
Gold Heartt Award from American Heart Association in 1995.

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