Longstanding hyperthyroidism is associated with normal or enhanced intrinsic cardiomyocyte function despite decline...

Area of Science:

• Cardiology
• Endocrinology
• Physiology

Background:

• Thyroid hormones (THs) are crucial for cardiac homeostasis.
• Imbalances in THs can lead to cardiac dysfunction.
• Chronic hyperthyroidism presents risks including arrhythmia, impaired exercise capacity, and heart failure.

Purpose of the Study:

• To investigate the long-term effects of chronic hyperthyroidism on left ventricular (LV) remodeling and function.
• To assess changes in LV myocyte function, chamber function, and tissue remodeling in a hamster model.

Main Methods:

• F1b hamsters received 10 months of thyroid hormone (TH) treatment.
• Echocardiography monitored LV chamber remodeling and function over 10 months.
• Terminal assessments included echocardiography and LV hemodynamics.

Main Results:

• Hyperthyroid hamsters developed cardiac hypertrophy, myocyte lengthening, chamber dilatation, and increased wall stress.
• Significant LV interstitial fibrosis was observed in hyperthyroid hamsters.
• Despite global cardiac decline, isolated cardiomyocytes showed enhanced function.

Conclusions:

• Long-term hyperthyroidism leads to deleterious cardiac remodeling and impaired global LV function.
• Increased interstitial ventricular fibrosis appears to be a key factor in cardiac dysfunction.
• Intrinsic cardiomyocyte function may be preserved or enhanced even with impaired global heart function.