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Hyperthyroidism II: Pathophysiology

Hyperthyroidism II: Pathophysiology

Hyperthyroidism is a hypermetabolic state caused by elevated levels of thyroid hormones, triiodothyronine (T3) and thyroxine (T4). It results from dysregulation at the thyroid, pituitary, or immune system level and affects multiple organ systems.PathophysiologyThe most common cause of hyperthyroidism is Graves’ disease, an autoimmune disorder in which antibodies, specifically thyroid-stimulating antibodies (TSAb), a subtype of TSH receptor antibodies (TRAb), bind to and activate TSH receptors...

ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias

ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias

Arrhythmia is a condition characterized by an irregular heart rhythm, with ECG changes that differ based on its origin and nature. The types of arrhythmias discussed below include atrial, junctional, and ventricular arrhythmias.Atrial ArrhythmiasPremature Atrial Complexes (PACs): PACs are early atrial beats caused by stress, caffeine, alcohol, electrolyte imbalances, hypoxia, hyperthyroidism, or certain medications (e.g., bronchodilators and decongestants). The ECG shows early P waves with an...

Dysrhythmias II: Classification of Tachyarrhythmias

Dysrhythmias II: Classification of Tachyarrhythmias

Tachyarrhythmias are a type of dysrhythmia where the heart rate exceeds 100 beats per minute. Here are some common types of tachyarrhythmias:Sinus TachycardiaSinus tachycardia originates from increased impulses from the sinus node, leading to an elevated heart rate. It is often triggered by stress, fever, or exercise.Patients may experience palpitations, a sensation of a racing heart, dizziness, and chest discomfort.Causes and Risk Factors: Common causes include physical exertion, emotional...

Hyperthyroidism I: Introduction

Hyperthyroidism I: Introduction

Hyperthyroidism is a type of thyrotoxicosis characterized by the thyroid gland's overproduction of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). This hormone excess increases the basal metabolic rate and enhances sensitivity to catecholamines.DiagnosisDiagnosis is based on clinical features and biochemical testing. It typically shows suppressed thyroid-stimulating hormone (TSH) levels below 0.4 mIU/L, with elevated free T3 and/or T4. Additional tests, including thyroid...

Mechanism of Cardiac Arrhythmias

Mechanism of Cardiac Arrhythmias

Arrhythmias are irregular heart rhythms occurring when the heart's electrical impulses become abnormal. These disturbances can lead to various symptoms, depending on their severity and the underlying cause. Some common factors contributing to arrhythmias include hypoxia, ischemia, electrolyte imbalances, excessive catecholamine exposure, drug toxicity, and muscle overstretching. Arrhythmias can be classified into two main types based on the rate and site of origin of abnormal heart rhythms.

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

Class III antiarrhythmic drugs are a group of medications that can prolong action potentials in the heart. They achieve this by blocking potassium channels or enhancing inward currents from sodium channels. However, these drugs have a unique property of "reverse use-dependence," which is most pronounced at slower heart rates and can lead to torsades de pointes—a specific type of arrhythmia. However, it is essential to note that excessive QT interval prolongation—a measure of the heart's...

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Thyrotoxicosis-induced ventricular arrhythmias.

Powlimi J Nadkarni¹, Meeta Sharma, Bruce Zinsmeister

¹Department of Endocrinology, Washington Hospital Center, Washington, District of Columbia 20010, USA. powlimi@gmail.com

Thyroid : Official Journal of the American Thyroid Association

|September 26, 2008

Summary

Thyrotoxicosis can cause ventricular tachycardia, especially in patients with existing heart disease. Achieving a euthyroid state resolved these arrhythmias, suggesting a link between thyroid hormone levels and cardiac rhythm disturbances.

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Area of Science:

Cardiology
Endocrinology
Thyroid Disease

Background:

Thyrotoxicosis commonly causes supraventricular arrhythmias like atrial fibrillation.
Ventricular arrhythmias are infrequently linked to thyrotoxicosis and typically indicate underlying cardiac pathology.

Observation:

Three patients with thyrotoxicosis and coronary disease presented with ventricular tachycardia as their primary arrhythmia.
These ventricular arrhythmias resolved upon achieving a euthyroid state.

Findings:

The thyrotoxic state may contribute to the development or lower the threshold for ventricular arrhythmias.
This case series highlights a potential etiological role of hyperthyroidism in ventricular tachycardia.

Implications:

Urgent management of thyrotoxicosis is crucial in patients with pre-existing heart conditions.
Early intervention can prevent potentially life-threatening cardiac arrhythmias associated with hyperthyroidism.