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

TSH Testing in Cardiac Murmurs

TSH testing is not routinely indicated in the evaluation of cardiac murmurs unless there are specific signs or symptoms suggestive of thyroid dysfunction or other concerning features of the murmur that warrant further cardiac evaluation.

Evaluation of Cardiac Murmurs

Initial Assessment

• The approach to a patient with a heart murmur depends on the timing of the murmur in the cardiac cycle, location, radiation, and response to physiological maneuvers 1
• Cardiac murmurs are graded on intensity scales (1-6 for systolic murmurs, 1-4 for diastolic murmurs) 2

Echocardiography Indications

• Echocardiography is recommended for patients with:

  • Diastolic murmurs, continuous murmurs, holosystolic murmurs, or late systolic murmurs 1
  • Murmurs associated with ejection clicks or murmurs that radiate to the neck or back 1
  • Heart murmurs accompanied by symptoms or signs of heart failure, myocardial ischemia/infarction, syncope, thromboembolism, or infective endocarditis 1
  • Grade 3 or louder midpeaking systolic murmurs 1

• Echocardiography is not recommended for patients with grade 2 or softer midsystolic murmurs identified as innocent or functional by an experienced observer 1

Thyroid Function and Cardiac Manifestations

Subclinical Hyperthyroidism and Cardiac Effects

• Subclinical hyperthyroidism (particularly with TSH <0.1 mIU/L) is associated with:
  • Increased heart rate and cardiac contractility 1
  • Increased risk of atrial fibrillation (3-fold increased risk over 10 years in individuals ≥60 years) 1
  • Diastolic dysfunction and changes in myocardial velocities 3

Subclinical Hypothyroidism and Cardiac Effects

• Severe subclinical hypothyroidism (TSH ≥10.0 mIU/L) is associated with:
  • Greater incidence of heart failure compared to euthyroid individuals (adjusted hazard ratio: 1.88) 4
  • Increased left ventricular mass over time 4
  • Resting left ventricular diastolic dysfunction 5

Laboratory Testing in Cardiac Evaluation

• There are no guidelines specifically recommending routine TSH testing in the evaluation of cardiac murmurs 1
• Laboratory testing should be directed toward specific diagnoses when clinically suspected 1
• Thyroid function tests are appropriate when thyroid dysfunction is suspected based on clinical presentation 1

Clinical Decision Making

When to Consider TSH Testing in Patients with Murmurs

• Consider TSH testing when the cardiac murmur is accompanied by:
  • Signs or symptoms of hyperthyroidism (tachycardia, weight loss, heat intolerance, tremor) 1
  • Signs or symptoms of hypothyroidism (bradycardia, weight gain, cold intolerance, fatigue) 1
  • Unexplained atrial fibrillation, especially in older adults 1
  • Heart failure without obvious etiology 4

Pitfalls to Avoid

• Do not routinely order TSH for all cardiac murmurs, especially grade 1-2 midsystolic murmurs with otherwise normal cardiac examination 1
• Remember that innocent murmurs in asymptomatic adults typically have grade 1-2 intensity at the left sternal border, systolic ejection pattern, normal intensity and splitting of S2, and no other abnormal sounds 1
• Avoid attributing significant cardiac murmurs to thyroid dysfunction without appropriate cardiac imaging evaluation 1

Summary

• For most cardiac murmurs, especially innocent murmurs, TSH testing is not routinely indicated 1
• TSH testing should be considered when there are clinical features suggesting thyroid dysfunction or when the murmur is associated with unexplained cardiac abnormalities 1, 4
• The primary evaluation of significant murmurs should focus on appropriate cardiac imaging, particularly echocardiography 1