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Thyroid UK
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Intermittent slow heart beat

I am finding that every now and then, usually between 10am and 1.30pm, I have episodes when my heart rate slows to the low 50s. My breathing tends to get light and I struggle not to fall asleep. This is pretty embarrasing when I am in a meeting at work. These episodes last maybe half an hour. My blood oxygen levels become low too, a fact I only realised when playing around with a friend's pulse oximeter and set the alarm off. I am pretty sure I am not under-medicated because my TSH is very low and although my FT4 and FT3 are in range (towards the top of the range) my doctor would really like me to lower my dose, something I am resisting because I need to be able to function properly at work.

I take Vitamin D and B12, which I find helpful. I am changing GP soon and moving house, so will try to get my vitamins checked when I have a GP organised.

I was wondering whether anyone else gets these episodes, and whether I can do anything about them. At the moment the one thing that helps is forcing myself to breathe more often, but it's an uphill struggle. The first time I noticed this happening I had an ECG which was normal.

5 Replies

It sounds to me, and I'm not medically qualified, is that you are on insufficient thyroid hormone replacements.

You need a blood test, the earliest possible, fasting (you can drink water) and allow a gap of 24 hours between last dose of levothyroxine and the test and take afterwards.

TSH, T4, T3, Free T3, Free T4 and thyroid antibodies. B12, Vit D, iron, ferritin and folate.

If GP or lab wont do all of these you can get a private blood test from one of our labs.

T3 runs our whole metabolism, and heart and brain require the most and we have millions of T3 receptor cells in our body. Too low a dose of T4 gives us additional problems and breathing can also be affected.


If levo is too low, we cannot produce sufficient T3.

Low temps and pulse indicates too low a dose of thyroid hormones to me, and I am not medically qualified.


Your FT3 is definitely towards the top of the range? I was just looking at a post of yours from 8m ago (don’t worry, I’m not a creepy post stalker - just looking for clues :) :) ) where you said you were fighting to keep your levo dose high because your doctor didn’t like that your TSH is suppressed. But you didn’t mention an FT3 reading then - have you had one since?

It is entirely normal for TSH to be suppressed when on levothyroxine and means nothing at all. Doctors often don’t seem to understand how TSH works. It isn’t a thyroid hormone, it’s a pituitary hormone that signals the thyroid to make thyroid hormones. When there’s levothyroxine in your system, even if it’s not enough, the brain sometimes stops bothering with producing TSH.

Now. Your FT4 was overrange then. That makes it possible that you’re making RT3 out of some of the levothyroxine. RT3 acts like a drain - it’s the body’s way of getting rid of excess T4. But unfortunately, that means that you’re probably not getting enough T3 going into your cells. You really need to know what your FT3 levels are - and a doctor who understands that suppressed TSH is meaningless in a patient treated with levothyroxine. You may well need some liothyronine adding to your levo dose, which is going to require you finding a doctor who isn’t a numpty on thyroid issues.

You mention Vit D and B12 - what about ferritin? I’m wondering whether you might be iron deficient as well (often the case when other vits and minerals are low).


Oh, and another thought. The low pulse oximeter reading - 2 potential causes:

One, you’re not breathing deeply enough for some reason. Are you stressed in those meetings? Do you find you’re holding your breath when you read and write emails (I do sometimes - it’s surprisingly common to get stressed by that!)

Two - is there any possibility your workplace or home has high carbon monoxide levels? Are your gas appliances safe? If that’s a possibility, the haemoglobin levels in your blood may be low and simply can’t carry enough oxygen. Might be worth checking out...


I do that aswell jazzw-holding my breath particulary if im a little stressed and sometimes my nose aswell, its only since having a thyroid problem.strange!!😊



I doubt it is to do with thyroid levels if it happens between 10am - 1.30am. Could it be low blood sugar? Perhaps you need a snack in between breakfast and lunch.

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