Atrial Fibrillation, Hypothyroidism and T4

Atrial Fibrillation, Hypothyroidism and T4

How interesting to see a paper which suggests that thyroid hormone might have a very positive role in:

A situation other than an obvious thyroid disorder.

A heart issue where many doctors would run away from prescribing any thyroid hormone even if hypothyroidism were proved.

With a result which depends on fundamental structural changes.

Of course, this paper looks at rats - and there are many reasons to be careful bout transferring ideas from rats to humans.

J Card Fail. 2014 Oct 8. pii: S1071-9164(14)01226-3. doi: 10.1016/j.cardfail.2014.10.003. [Epub ahead of print]

Thyroid Hormone Replacement Therapy Attenuates Atrial Remodeling and Reduces Atrial Fibrillation Inducibility in a Rat Myocardial Infarction-Heart Failure Model.

Zhang Y1, Dedkov EI2, Lee B 3rd2, Li Y2, Pun K2, Gerdes AM2.

Author information



Heart failure (HF) is associated with increased atrial fibrillation (AF) risk. Accumulating evidence suggests the presence of myocardial tissue hypothyroidism in HF, which may contribute to HF development. Our recent report demonstrated that hypothyroidism, like hyperthyroidism, leads to increased AF inducibility. This study was designed to investigate the effect of thyroid hormone (TH) replacement therapy on AF arrhythmogenesis in HF.


Myocardial infarction (MI) was produced in rats by coronary artery ligation. Rats with large MIs (>40%) were randomized into L-thyroxine (T4, n=14) and placebo (n=15) groups 2 weeks after MI. Rats received 3.3 mg T4 (in 60-day release form) or placebo pellets in respective groups for 2 months. Compared with the placebo, T4 treatment improved cardiac function and decreased left ventricular internal diameters as well as left atrial diameter. T4 treatment attenuated atrial effective refractory period prolongation (45±1.5 ms in placebo group vs 37±1.6 ms in T4 group, P<0.01) and reduced AF inducibility (AF/atrial flutter /tachycardia were inducible in 11/15 rats, or 73% in placebo vs 4/14 rats, or 29% in the T4 treated group, P<0.05). Arrhythmia reduction was associated with decreased atrial fibrosis but was not associated with connexin 43 changes.


To our knowledge this is the first study demonstrating that TH replacement therapy in HF attenuates atrial remodeling and reduces AF inducibility post MI-HF. Clinical studies are needed to confirm such benefits in patients.

Copyright © 2014 Elsevier Inc. All rights reserved.


Arrhythmogenesis; Atrial fibrillation; Heart failure; Thyroid hormone

PMID: 25305503


9 Replies

  • Rod, that undermines one of the arguments for keeping hypothyroid patients undermedicated if it can be reproduced in clinical trials :-D

  • I'd go further than that! These rats weren't hypothyroid (as I read it) so we might conclude that giving them the T4 would actually have pushed them in the direction of being hyperthyroid (at least, over-treated).

    This thyroid hormone stuff simply is not understood. :-(

  • "This thyroid hormone stuff simply is not understood." AMEN to that statement. PR

  • Hi I have always known with permanent A.F , wrong thyroid up or down strongly affects mine.


  • I have read of specialists who prescribe T3 for heart patients and psychiatrists too. But not for thyroid patients, weird.....

  • I have AF and had thyroidectomy in February 2014. Currently taking T4 (Levo) 125mcg daily. I was briefly on T3 (March-April) but got violent episodes of AF. Since then only one mild episode, despite upping the dose from 100 to 125.

    I am feeling fine but probably due to the mix of medication (Fleccainide, Dilzem, Levo, Warfarin). So I am on the waiting list for ablation to reduce my intake of stuff, aiming to take just Levothyroxine for the rest of my life.

  • Best of luck getting there.

  • I've no idea what I AF

    3 Ecgs before op - & they didn't know either...

    1 Ecg kept me at docs waiting to see one for ages, he was just confused - I said I was fine.. they let me go.

    Beta blockers for heart rate before all this stuff... I think it's been ticking un-clock like for at least 10 years now...

    should I be worried? Well, I'm not.

  • I am just skimming the net for someone with hypo and transient af. Her cardio refuses to look at her thyroid as her TSH is suppressed but t3 and t4 in lower ranges. Thank for this.

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