What is the effect of hypothyroidism on congestive heart failure?

Hypothyroidism Worsens Heart Failure and Should Be Treated

Hypothyroidism is a recognized precipitant of acute decompensated heart failure and should be identified and treated in all patients with congestive heart failure, as restoration of normal thyroid function may reverse abnormal cardiovascular function. 1

Mechanisms of Cardiovascular Deterioration

Hypothyroidism causes multiple hemodynamic derangements that directly worsen heart failure:

• Systemic vascular resistance increases by up to 50%, creating increased afterload that the failing heart must overcome 2
• Bradycardia reduces cardiac output through decreased heart rate, compounding the already compromised cardiac function 2
• Diastolic relaxation and filling are significantly slowed, impairing ventricular filling and reducing stroke volume 2
• Decreased cardiac contractility further reduces the heart's pumping capacity 2
• Myocardial fibrosis develops as hypothyroidism stimulates fibroblasts, leading to structural cardiac damage 2
• Loss of coronary arterioles and impaired blood flow occur in chronic hypothyroidism, causing maladaptive changes in myocyte shape 2

Clinical Impact on Heart Failure Outcomes

The prognostic significance of hypothyroidism in heart failure patients is substantial:

• Hypothyroidism increases all-cause mortality by 44% (RR 1.44,95% CI: 1.29-1.61) in patients with established heart failure 3
• Cardiac death and/or hospitalization increase by 37% (RR 1.37,95% CI: 1.22-1.55) when hypothyroidism is present 3
• The ACC/AHA guidelines explicitly list endocrine abnormalities including hypothyroidism as common precipitants of acute decompensated heart failure 1

Screening and Diagnosis

• Thyroid function tests (TSH) are recommended in all patients presenting with heart failure due to the potential contribution of thyroid dysfunction 2
• The ACC recommends measuring TSH in all newly diagnosed hypertensive patients as hypothyroidism is a remediable cause of hypertension that commonly coexists with heart failure 2
• Screening is particularly important in patients treated with amiodarone, where thyroid disturbances should be suspected 1

Treatment Approach

Levothyroxine replacement therapy should be initiated for documented hypothyroidism with cardiac symptoms, but requires careful dosing in heart failure patients:

Initiation Strategy

• Start at low doses (25-50 mcg daily) in patients with cardiovascular disease, rather than full replacement doses 4
• Treatment must be initiated cautiously as minimal TSH elevations may not require aggressive dosage adjustment in patients with cardiac disorders 2
• Aim for TSH in the range of 2.5-5.0 mIU/L initially rather than aggressive normalization, particularly in elderly patients or those with significant cardiac disease 2

Monitoring

• Recheck TSH and free T4 in 6-8 weeks after initiating or adjusting levothyroxine 4
• Adjust levothyroxine by 12.5-25 mcg increments if TSH remains above reference range 4

Expected Benefits

• Treatment with levothyroxine can normalize blood pressure in patients with hypothyroid-induced hypertension 2
• Patients with thyroid hormone deficiency and heart failure should receive replacement doses to improve their prognosis and prevent worsening of cardiovascular function 5
• Restoration of normal thyroid function may reverse abnormal cardiovascular function 1

Critical Pitfalls to Avoid

• Do not withhold thyroid replacement in heart failure patients due to concerns about cardiac stress—untreated hypothyroidism worsens heart failure outcomes 3
• Avoid aggressive normalization of TSH in elderly or cardiac patients; maintaining TSH in the upper half of the reference range is acceptable 2
• Do not overlook hypothyroidism as a reversible cause of heart failure decompensation, particularly when other precipitants are not evident 1
• Overtreatment with levothyroxine can cause angina and arrhythmias, so careful dose titration is essential 2