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Updated: Jan 23, 2026

Transesophageal Atrial Burst Pacing for Atrial Fibrillation Induction in Rats
Published on: February 14, 2022
Alterations in atrial ion channels and tissue structure promote atrial fibrillation in hypothyroid rats
Jianqiang Li1, Zhaorui Liu1, Hongwei Zhao1
1Department of Cardiology, The First Affiliated Hospital of Harbin Medical University, Harbin Medical University, Harbin, China.
Purpose:
It is well known that hyperthyroidism is associated with atrial fibrillation (AF); however, the relationship between hypothyroidism and AF remains controversial.
Methods:
Hypothyroidism was established in rats by two methods: methimazole-induced (MMI) and thyroidectomy (TX). MMI model includes control (n = 10), MMI (n = 10), and MMI + L-thyroxine (T4, n = 10). Methimazole was given intragastrically in MMI and MMI + T4 for 12 weeks, and T4 was added intragastrically in MMI + T4 at week 5. TX model includes sham (n = 10), TX (n = 10), and TX + T4 (n = 10). Four weeks after surgery, rats in TX + T4 received T4 for 8 weeks. Triiodothyronine (T3), T4, and thyroid-stimulating hormone (TSH) were measured. Electrophysiology, tissue structure and function, and protein levels of potassium and L-type calcium channels were assessed in the atria.
Results:
Severe changes in the atrial structure of hypothyroid rats were observed. Compared with euthyroid rats, atrial effective refractory period (AERP) in hypothyroid rats was significantly shortened; accordingly, inducibility and duration of AF were considerably increased. Protein levels of minK, Kv1.5, Kv4.2, Kv4.3, Kv7.1, and Cav1.2 were upregulated in hypothyroid rats, whereas there was only a tendency toward increased Kir2.1. Kv11.1 was statistically upregulated in the MMI model and had an increasing tendency in the TX model. Conversely, Kir3.1 and Kir3.4 were downregulated in hypothyroid rats. The above changes could be partially inhibited by T4 treatment.
Conclusions:
AERP shortening due to altered protein levels of ion channels and atrial structural changes increased the susceptibility to AF in hypothyroidism. Thyroid replacement therapy could prevent electrical and structural remodeling under hypothyroid condition.
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