Can hypothyroidism cause bradycardia?

Hypothyroidism and Bradycardia

Yes, hypothyroidism can cause bradycardia, which is one of the most common cardiovascular manifestations of this condition. 1

Pathophysiological Mechanism

• Hypothyroidism leads to a low metabolic state that directly causes bradycardia through decreased chronotropic effects on the heart 1
• The hemodynamic changes in hypothyroidism are characterized by:
  • Increased systemic vascular resistance (up to 50% higher than normal) 2, 1
  • Slowed diastolic relaxation and filling 2, 1
  • Decreased cardiac contractility 2
  • Overall reduction in cardiac output 1

Clinical Presentation

• Bradycardia is often accompanied by mild hypertension (particularly diastolic) and a narrowed pulse pressure 2
• Despite significant bradycardia, clinical heart failure is relatively rare in hypothyroidism because the reduced cardiac output is usually sufficient to meet the lowered systemic metabolic demands 2, 1
• In severe, long-standing hypothyroidism, patients may develop:
  • Pericardial effusions 2, 1
  • Nonpitting edema (myxedema) 2, 1
  • Rarely, atrioventricular blocks 3, 4

Diagnosis and Management

• Thyroid function tests are recommended in all patients presenting with bradycardia of unclear etiology 2
• According to the 2018 ACC/AHA/HRS guideline on bradycardia management, hypothyroidism is recognized as a reversible cause of sinus bradycardia 2
• Cardiovascular abnormalities from hypothyroidism respond well to replacement therapy with thyroxine (T4) 2
• The guideline recommends that patients presenting with symptomatic sinus bradycardia secondary to hypothyroidism should first be managed by treating the underlying thyroid condition rather than proceeding directly to permanent pacing 2

Clinical Pearls and Pitfalls

• Although bradycardia is typical in hypothyroidism, there are rare case reports of tachyarrhythmias associated with severe hypothyroidism 5, 6
• Severe bradycardia or AV blocks due to hypothyroidism may initially be misdiagnosed as requiring permanent pacemaker implantation, but often resolve with thyroid hormone replacement 7, 3
• In pediatric patients with severe AV block and bradycardia, hypothyroidism should be considered as a possible cause to avoid unnecessary interventions 4
• Dilated cardiomyopathy is not a characteristic feature of hypothyroidism, but there are case reports of cardiomyopathy improving with thyroid hormone replacement 2, 1

Treatment Approach

• For symptomatic bradycardia due to hypothyroidism:
  • Initiate thyroid hormone replacement therapy with levothyroxine 2
  • Monitor heart rate response to treatment 3
  • Permanent pacing should be considered only if bradycardia persists despite achieving euthyroid state 2
• Temporary supportive measures may be needed in severe cases while awaiting the effects of thyroid hormone replacement 4