Can a decreased Thyroid-Stimulating Hormone (TSH) level cause palpitations?

Decreased TSH Levels and Palpitations

Yes, decreased TSH levels can cause palpitations. Subclinical hyperthyroidism, characterized by low TSH with normal thyroid hormone levels, is associated with increased heart rate, cardiac arrhythmias (particularly atrial fibrillation), and cardiovascular symptoms including palpitations. 1, 2

Pathophysiology of Low TSH and Cardiac Effects

• Exogenous and endogenous subclinical hyperthyroidism increase heart rate, left ventricular mass, and cardiac contractility, which can manifest as palpitations 1
• Low TSH leads to increased cardiac output and decreased systemic vascular resistance, contributing to the sensation of palpitations 1
• Even subclinical hyperthyroidism (low TSH with normal T3/T4) can cause cardiac symptoms before overt hyperthyroidism develops 2
• The cardiac effects are more pronounced when TSH is severely suppressed (<0.1 mIU/L) compared to mildly suppressed (0.1-0.45 mIU/L) 1

Clinical Evidence Linking Low TSH to Palpitations

• Multiple studies have found more hyperthyroid-type symptoms, including palpitations, in individuals with subclinical hyperthyroidism compared to euthyroid individuals 1
• Successful treatment of endogenous subclinical hyperthyroidism has been shown to decrease heart rate and cardiac output, reducing palpitations 1
• Among patients with exogenous subclinical hyperthyroidism (from excessive levothyroxine), decreasing the dose normalized heart rate 1
• Beta-blockers have been shown to decrease atrial premature beats and improve diastolic filling in patients with subclinical hyperthyroidism and palpitations 1

Risk Stratification for Cardiac Complications

• The risk of cardiac arrhythmias is significantly higher when TSH is <0.1 mIU/L 1
• Older adults (>60 years) with low TSH have a 3-fold increased risk of atrial fibrillation over 10 years 1
• Untreated hyperthyroidism increases cardiovascular risk (OR = 1.25), while treated hyperthyroidism shows normalized risk (OR = 1.04) 3
• The duration of decreased TSH correlates with increasing cardiovascular risk, with each 6-month period of low TSH increasing risk by approximately 9-10% 3

Clinical Approach to Palpitations with Low TSH

• A single low TSH measurement is insufficient for diagnosis; multiple tests should be performed over a 3-6 month interval to confirm abnormal findings 2
• Follow-up testing of serum T4 levels in persons with persistently abnormal TSH levels can differentiate between subclinical and overt thyroid dysfunction 2
• For mild/asymptomatic hyperthyroidism with palpitations, beta-blockers (e.g., atenolol or propranolol) can provide symptomatic relief 4
• Treatment is generally recommended for patients with TSH <0.1 mIU/L, particularly those with overt Graves' disease or nodular thyroid disease 2

Important Clinical Considerations

• Palpitations may be the presenting symptom of hyperthyroidism before other classic symptoms develop 5
• Common causes of low TSH include Graves' disease, toxic nodular goiter, thyroiditis, and medication effects 2
• Untreated hyperthyroidism can progress to more serious cardiovascular complications including atrial fibrillation, heart failure, and increased mortality 5, 3
• The early recognition and effective treatment of thyroid dysfunction in patients with arrhythmia is mandatory because the long-term prognosis may be improved with appropriate treatment 6

Pitfalls to Avoid

• Failure to consider non-thyroidal causes of low TSH, especially in hospitalized or acutely ill patients, can lead to misdiagnosis 2
• Overdiagnosis of hyperthyroidism based on a single low TSH measurement without confirmatory testing should be avoided 2
• Transient thyroiditis can cause temporary hyperthyroidism with palpitations that resolves spontaneously, so careful monitoring is essential before initiating long-term treatment 4
• Close monitoring of thyroid function every 2-3 weeks is necessary to detect potential transition to hypothyroidism, which is common in thyroiditis 4