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Related Concept Videos

Dysrhythmias IV: Characteristics of Bradyarrhythmias01:18

Dysrhythmias IV: Characteristics of Bradyarrhythmias

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Bradyarrhythmias are cardiac rhythm disorders characterized by a slower-than-normal heart rate, typically defined as fewer than 60 beats per minute. Some of which are discussed here:Sinus BradycardiaSinus bradycardia presents a heart rate lower than 60 beats per minute, with a regular rhythm originating from the SA node. The ECG typically shows normal P waves preceding each QRS complex, a normal PR interval (0.12 to 0.20 seconds), and a normal QRS duration (0.06 to 0.10 seconds).First-Degree AV...
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Disturbances in Heart Rhythm01:29

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Arrhythmia or dysrhythmia refers to an abnormal heart rhythm caused by a defect in the heart's conduction system. It can cause the heart to beat irregularly, too quickly, or too slowly, leading to symptoms like chest pain, shortness of breath, and fainting. Factors such as stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte abnormalities can trigger arrhythmias.
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Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers01:12

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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...
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Decreased pulse rate01:14

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Bradycardia is a medical condition in which the heart rate is slower than normal. It occurs when the heart's natural pacemaker, the sinus node, generates slower electrical impulses than the standard rhythm. In adults, bradycardia is diagnosed when the pulse rate falls below 60 beats per minute, indicating a deviation from the normal heart rate range.
There are specific risk factors that can elevate the likelihood of developing bradycardia. Advanced age is a significant factor, with...
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ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias01:25

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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...
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Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers01:20

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Class IV antiarrhythmic drugs, such as verapamil and diltiazem, block calcium channels. They primarily affect the heart, slowing the conduction in calcium-dependent tissues like the SA and AV nodes. These drugs manage reentrant supraventricular tachycardia (SVT) and reduce ventricular rate in atrial flutter/fibrillation.
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Complete Atrioventricular Block Presenting With Syncope Caused by Severe Hypothyroidism.

Sang-Hoon Seol1, Doo-Il Kim1, Bo-Min Park1

  • 1Division of Cardiology, Department of Internal Medicine, Inje University College of Medicine, Haeundae Paik Hospital, Busan, Korea.

Cardiology Research
|March 29, 2017
PubMed
Summary

Severe hypothyroidism can cause complete atrioventricular block and syncope. Thyroxine replacement therapy effectively resolved these cardiac issues in a 75-year-old male patient, highlighting the link between thyroid function and heart rhythm.

Keywords:
Atrioventricular blockHypothyroidismSyncope

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Area of Science:

  • Cardiology
  • Endocrinology
  • Internal Medicine

Background:

  • Complete atrioventricular block and syncope can present with various underlying causes.
  • Thyroid dysfunction, particularly hypothyroidism, can have significant cardiovascular manifestations.

Observation:

  • A 75-year-old male presented with syncope due to complete atrioventricular block and severe bradycardia (minimum heart rate 22 bpm).
  • Initial laboratory results indicated high thyroid-stimulating hormone (TSH) and low free thyroxine (fT4) levels, suggestive of hypothyroidism.

Findings:

  • Treatment with thyroxine for several days led to the resolution of the atrioventricular block.
  • Follow-up electrocardiogram demonstrated a normalized heart rate without evidence of atrioventricular block, confirming the efficacy of thyroid hormone replacement.

Implications:

  • Severe hypothyroidism is a reversible cause of complete atrioventricular block and syncope.
  • Thyroid hormone replacement therapy is crucial for managing cardiovascular complications associated with hypothyroidism.