Hyperthyroidism refers to increased production and secretion of thyroid hormone from the thyroid gland.
Hyperthyroidism is not synonymous with thyrotoxicosis, the latter referring to a clinical syndrome of excess thyroid hormone.
Hyperthyroidism may be accompanied by the signs and symptoms of thyrotoxicosis (e.g. heat intolerance, weight loss, tremor). However, it is also possible to have subclinical hyperthyroidism (i.e. lacking thyrotoxicosis), but this is less common .
- sinus tachycardia
- high voltage QRS complexes
- atrial fibrillation
Thyrotoxicosis predisposes patients to a variety of tachydysrhythmias, as well as atrial and ventricular ectopy :
- paroxysmal supraventricular tachycardia (PSVT)
- non-specific ST segment and T wave changes
- elderly patients may have rate-related ischemia
- premature ventricular complexes (PVCs)
Numerous causes of hyperthyroidism exist :
- increased thyroid gland stimulation
- independent thyroid function
- TSH receptor gene activating mutations (e.g. functioning adenoma, multinodular goiter)
- thyroid tissue inflammation and subsequent release of stored thyroid hormone
- extrathyroid source
- iodine exposure
- iatrogenic (e.g. iodine contrast, iodine-containing drugs)