Related Experiment Video
Updated: Jun 10, 2026
14:39
Isolation and Functional Characterization of Human Ventricular Cardiomyocytes from Fresh Surgical Samples
Published on: April 21, 2014
Changes in autonomic regulation and ventricular repolarization induced by subclinical hyperthyroidism.
F Galetta1, F Franzoni, P Fallahi
1Department of Internal Medicine, University of Pisa, Pisa, Italy.
Summary
Subclinical hyperthyroidism (SHT) disrupts cardiovascular autonomic function, leading to increased sympathetic activity and reduced vagal tone. This condition also elevates QT dispersion, indicating uneven ventricular repolarization and potential cardiovascular risk.
Area of Science:
- Cardiology
- Endocrinology
- Autonomic Nervous System Research
Background:
- Subclinical hyperthyroidism (SHT) is characterized by suppressed TSH with normal thyroid hormone levels.
- Cardiovascular complications are a concern in SHT, but autonomic function and repolarization effects are not fully understood.
Purpose of the Study:
- To investigate the impact of SHT on cardiovascular autonomic function.
- To assess the effect of SHT on ventricular repolarization.
Main Methods:
- Thirty SHT patients and 30 controls underwent 12-lead ECG and 24-hour ambulatory ECG monitoring.
- Evaluated QT interval dispersion (ventricular repolarization inhomogeneity) and heart rate variability (HRV; autonomic modulation).
Main Results:
- SHT patients exhibited significantly higher QT dispersion (p<0.001) compared to controls.
- SHT patients demonstrated significantly lower HRV measures (0.01>p<0.001) than controls.
- A significant inverse correlation was found between QT dispersion and HRV in SHT patients (r=-0.47, p<0.01).
Conclusions:
- SHT is associated with sympathovagal imbalance, marked by increased sympathetic and decreased vagal tone.
- SHT leads to increased inhomogeneity of ventricular recovery times.
- Assessing HRV and QT dispersion may aid in monitoring cardiovascular risk in SHT patients.
Related Concept Videos
01:27Hyperthyroidism II: Pathophysiology
Hyperthyroidism is a hypermetabolic state caused by elevated levels of thyroid hormones, triiodothyronine (T3) and thyroxine (T4). It results from dysregulation at the thyroid, pituitary, or immune system level and affects multiple organ systems.PathophysiologyThe most common cause of hyperthyroidism is Graves’ disease, an autoimmune disorder in which antibodies, specifically thyroid-stimulating antibodies (TSAb), a subtype of TSH receptor antibodies (TRAb), bind to and activate TSH receptors...
01:25Hyperthyroidism I: Introduction
Hyperthyroidism is a type of thyrotoxicosis characterized by the thyroid gland's overproduction of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). This hormone excess increases the basal metabolic rate and enhances sensitivity to catecholamines.DiagnosisDiagnosis is based on clinical features and biochemical testing. It typically shows suppressed thyroid-stimulating hormone (TSH) levels below 0.4 mIU/L, with elevated free T3 and/or T4. Additional tests, including thyroid...
01:24Graves Disease II: Pathophysiology
Graves’ disease is an autoimmune disorder characterized by the production of thyroid-stimulating immunoglobulins (TSI) that activate TSH receptors, leading to excessive synthesis and release of thyroid hormones (T3 and T4) and resulting in hyperthyroidism.Among all causes of hyperthyroidism, Graves’ disease is the most common and can happen at any age, though it is more frequent in women. It produces a hypermetabolic state with features such as weight loss, tachycardia, tremor, and heat...
01:23Hypothyroidism II: Pathophysiology
Hypothyroidism is a disorder characterized by insufficient production of thyroid hormones, which regulate metabolism, energy balance, and multiple organ systems.TypesHypothyroidism is classified based on the level of dysfunction. Primary hypothyroidism results from intrinsic thyroid gland dysfunction, causing reduced hormone production despite normal or increased stimulation. Secondary hypothyroidism arises from inadequate thyroid-stimulating hormone (TSH) secretion by the pituitary. Tertiary...
01:28Graves' Disease I: Introduction
Graves' disease is an autoimmune disorder that causes hyperthyroidism, or overactivity of the thyroid gland. It results from autoantibodies called thyroid-stimulating immunoglobulins (TSIs), which bind to thyroid-stimulating hormone (TSH) receptors, leading to overstimulation of hormone production and a hypermetabolic state.EtiologyAlthough considered idiopathic, Graves’ disease has well-established contributing factors. There is a strong genetic component, with increased prevalence in...
01:31Regulation of Heart Rates
The regulation of heart rate is a complex process controlled by the autonomic nervous system (ANS), hormonal influences, and intrinsic cardiac mechanisms. The ANS has two main components: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).
The SNS increases heart rate through the release of norepinephrine and epinephrine, which act on beta-1 adrenergic receptors in the heart. This action increases the rate of depolarization in the sinoatrial (SA) node, the heart's...
The SNS increases heart rate through the release of norepinephrine and epinephrine, which act on beta-1 adrenergic receptors in the heart. This action increases the rate of depolarization in the sinoatrial (SA) node, the heart's...