Is Thyroid-Stimulating Hormone (TSH) evaluation indicated in patients with cardiac murmurs?

TSH Testing in Cardiac Murmur Evaluation

TSH testing is not routinely indicated in the standard evaluation of cardiac murmurs unless there are specific signs or symptoms of thyroid dysfunction. The ACC/AHA guidelines for valvular heart disease do not include TSH testing in their recommended diagnostic algorithm for cardiac murmurs 1.

Standard Evaluation of Cardiac Murmurs

The appropriate diagnostic approach for cardiac murmurs depends on several factors:

• Echocardiography is recommended for asymptomatic patients with diastolic murmurs, continuous murmurs, holosystolic murmurs, late systolic murmurs, or murmurs associated with ejection clicks 1, 2
• Echocardiography is indicated for patients with heart murmurs and symptoms/signs of heart failure, myocardial ischemia, syncope, thromboembolism, or infective endocarditis 1, 2
• Asymptomatic patients with grade 3 or louder midpeaking systolic murmurs should undergo echocardiography 1, 2
• Echocardiography can be useful for murmurs associated with abnormal cardiac physical findings or abnormal ECG/chest X-ray 1
• Echocardiography is not recommended for patients with grade 2 or softer midsystolic murmurs identified as innocent or functional by an experienced clinician 1

Thyroid Disease and Cardiovascular Manifestations

While TSH is not part of routine murmur evaluation, thyroid dysfunction can affect the cardiovascular system in ways that might produce or alter cardiac murmurs:

• Hyperthyroidism (including subclinical) is associated with increased risk of atrial arrhythmias and can increase heart rate, left ventricular mass, and cardiac contractility 1, 3
• Subclinical hyperthyroidism with TSH <0.1 mIU/L is associated with a 3-fold increased risk of atrial fibrillation in individuals over 60 years 1, 4
• Hypothyroidism can affect cardiovascular function through mechanisms including dyslipidemia, hypertension, and myocardial dysfunction 3, 5
• Even subclinical thyroid dysfunction may contribute to cardiovascular disease progression if left untreated 3

When to Consider TSH Testing with Cardiac Murmurs

TSH testing should be considered in patients with cardiac murmurs when:

• There are clinical features suggestive of thyroid dysfunction (e.g., tachycardia, tremor, weight changes, heat/cold intolerance) 1, 3
• New-onset atrial fibrillation is detected, particularly in older adults 1, 4
• There are unexplained changes in cardiac function or murmur characteristics that aren't accounted for by primary cardiac pathology 3, 6
• The patient has risk factors for thyroid disease along with cardiovascular symptoms 1, 5

Clinical Pearls and Pitfalls

• Subclinical hyperthyroidism (particularly with TSH <0.1 mIU/L) may increase cardiovascular risk even when T3 and T4 levels are normal 1, 4
• Patients with treated hyperthyroidism may show improvement in cardiac parameters including heart rate and cardiac output 1
• Cardiac troponin T remains a reliable marker of cardiac injury even in hypothyroid patients, despite the fact that CK and CK-MB may be elevated in hypothyroidism without cardiac damage 7
• In subclinical hypothyroidism, TSH elevation may be a risk factor for atherosclerosis through mechanisms including endothelial dysfunction and insulin resistance 5

In conclusion, while TSH testing is not part of the standard evaluation algorithm for cardiac murmurs according to ACC/AHA guidelines, it should be considered when clinical features suggest possible thyroid dysfunction that could be contributing to or complicating cardiovascular findings.