Thyroid disorders are common endocrine system diseases that can cause a wide range of symptoms. These symptoms may sometimes overlap with those of heart conditions, leading to diagnostic confusion. In this article, we will explore the link between thyroid disorders like hypothyroidism and hyperthyroidism and heart problems.
How do thyroid hormones affect the heart?
Thyroid hormones like triiodothyronine (T3) and thyroxine (T4) play an important regulatory role in the body. They affect the metabolism, growth and development of tissues, including the heart muscle.
T3 is the more active hormone that actually binds to receptors in the heart cells. This influences the contraction force and heart rate. T3 also impacts cholesterol levels and blood pressure, which affect heart health.
Therefore, when thyroid hormone levels are too high (hyperthyroidism) or too low (hypothyroidism), it disrupts the normal regulatory mechanisms of the cardiovascular system.
Can hypothyroidism mimic heart disease?
Yes, hypothyroidism can sometimes present with symptoms similar to various heart conditions. This includes:
Congestive heart failure
In hypothyroidism, reduced metabolism and heart contractions can reduce cardiac output. This leads to fluid congestion, fatigue, shortness of breath and peripheral edema. These are classical symptoms of congestive heart failure.
Cardiac tamponade
Fluid accumulation around the heart, called pericardial effusion, may compress heart chambers. This tamponade effect causes chest pain, dyspnea, dizziness and fainting episodes.
Heart attack
Due to cholesterol deposits, coronary blood flow is impaired in hypothyroidism. Sometimes, complete blockage may occur, cutting off blood supply and causing myocardial infarction. Typical chest pain, ECG changes and cardiac enzyme rise is seen.
However, the underlying pathophysiology is different from classic heart disease. Management involves thyroid hormone replacement, not clot-busting or revascularization procedures.
Atherosclerotic disease
High cholesterol levels and blood pressure in hypothyroidism accelerate the development of atherosclerosis. This causes angina, carotid bruits, peripheral vascular disease, etc. These manifestations can easily be confused with primary cardiovascular illnesses.
Can hyperthyroidism mimic heart disease?
Yes, hyperthyroidism can also mimic certain cardiovascular disorders. These include:
Atrial fibrillation
Excess thyroid hormones increase heart rate and atrial arrhythmias. Palpitations, irregular pulse, dyspnea, reduced exercise tolerance are seen in thyrotoxic atrial fibrillation.
Heart failure
High output cardiac failure may occur due to the increased metabolic demands. Tachycardia, wide pulse pressure, pounding heart, cardiomegaly and pulmonary congestion develop.
Angina
Despite lack of atherosclerosis, angina can occur due to the mismatch between myocardial oxygen demand and supply. Chest pain, ST-T changes are seen during exertion.
| Manifestations | Hypothyroidism | Hyperthyroidism |
|---|---|---|
| Heart rate | Bradycardia | Tachycardia |
| Blood pressure | Diastolic hypertension | Systolic hypertension |
| Heart failure | Low output failure | High output failure |
| Chest pain | Atherosclerotic angina | Hyperdynamic angina |
| Arrhythmias | Bradyarrhythmias | Tachyarrhythmias |
How to differentiate cardiac and thyroid disorders?
Distinguishing between primary heart disease and thyroid-related cardiac manifestations can be challenging at times. However, certain clinical features and tests can provide clues:
Age and sex
Cardiac illness peaks in older men around 45-65 years. Thyroid disorders are more common in middle-aged women.
Symptom duration
Cardiac symptoms in thyroid imbalance are often subacute in onset over weeks to months. Primary heart disease tends to be more acute or chronic.
Risk factors
Lack of cardiovascular risk factors like smoking, obesity, diabetes favors thyroid origin. Dyslipidemia and hypertension can occur in both scenarios.
Physical signs
Goiter, Graves’ ophthalmopathy, tremor, temperature changes point towards hyperthyroidism. Dry skin, cold intolerance, delayed reflexes suggest hypothyroidism.
Thyroid function tests
TSH, T3 and T4 levels confirm thyroid hypo/hyperactivity. Normal levels do not completely exclude thyroid dysfunction though.
Cardiac biomarkers
Troponin rise excludes demand-supply mismatch angina of hyperthyroidism. But mild elevation may be seen in hypothyroid acute coronary events.
ECG changes
Low voltage, flattened T waves favor hypothyroidism. Left axis deviation, AF, tachycardia suggest hyperthyroidism. Q waves, ST elevation indicate MI.
Echocardiography
Hyperdynamic circulation in hyperthyroidism and pericardial effusion in severe hypothyroidism can be detected. Regional wall motion abnormalities are seen in CAD.
Thyroid antibody testing
Presence of anti-TPO antibodies indicates autoimmune thyroid disease like Hashimoto’s or Graves’.
Conclusion
Thyroid hormone excess or deficiency can mimic heart disease in many ways. However, a combination of clinical evaluation, cardiac and endocrine lab testing, imaging studies can accurately pinpoint the etiology. Prompt diagnosis allows early treatment of the underlying thyroid disorder, greatly improving cardiac outcomes.
Treating the cardiac manifestations with medications or interventions without addressing the thyroid imbalance often leads to suboptimal results. A multidisciplinary approach with endocrinologists and cardiologists working together yields the best patient outcomes.
Public awareness about the thyroid-heart link is crucial for timely diagnosis and management. Patients presenting with cardiac symptoms should be screened for thyroid dysfunction and vice versa. Addressing this important mimic can help prevent inappropriate interventions and significant morbidity.