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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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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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Adrenergic stimulation generally impacts cardiac rate and rhythm. Specifically, stimulation of the β-adrenoceptors triggers an increase in intracellular calcium ion influx and pacemaker currents, which may cause arrhythmias. Catecholamines like adrenaline also demonstrate β2-adrenoceptor-mediated hypokalemia, impacting cardiac action potential and disrupting the normal cardiac rhythm. Class II antiarrhythmic drugs are β-adrenoceptor antagonists or β-blockers, which...
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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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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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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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Reflex Atrioventricular Block.

Richard Sutton1

  • 1National Heart & Lung Institute, Imperial College, London, United Kingdom.

Frontiers in Cardiovascular Medicine
|April 21, 2020
PubMed
Summary
This summary is machine-generated.

Reflex atrioventricular block, though considered rare, is increasingly recognized in vasovagal and carotid sinus reflexes. Distinguishing it from other heart blocks and understanding its mechanism are crucial for clinical decisions like pacing.

Keywords:
adenosineatrioventricular blockcardiac conduction system diseasecardiac pacingcarotid sinus reflexvasovagal reflex

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Area of Science:

  • Cardiology
  • Autonomic Nervous System Function

Background:

  • Reflex atrioventricular block is a recognized but often underestimated cardiac phenomenon.
  • Recent evidence indicates it may be more prevalent than previously assumed.
  • It is associated with specific autonomic reflexes, namely vasovagal and carotid sinus reflexes.

Purpose of the Study:

  • To highlight the underappreciated incidence of reflex atrioventricular block.
  • To differentiate it from other causes of atrioventricular block, such as ventricular conduction tissue disease.
  • To discuss the potential role of adenosine in mimicking this condition and its mechanistic explanations.

Main Methods:

  • Review of existing literature and recent data on reflex atrioventricular block.
  • Analysis of its occurrence in vasovagal and carotid sinus reflex contexts.
  • Comparison with paroxysmal atrioventricular block originating from conduction tissue disease.
  • Consideration of adenosine's role in the pathophysiology.

Main Results:

  • Reflex atrioventricular block is less rare than previously thought.
  • It is observed in both vasovagal and carotid sinus reflex pathways.
  • Low chronic adenosine levels and adenosine release can present similarly to reflex atrioventricular block.
  • Mechanisms are becoming clearer with recent research.

Conclusions:

  • Reflex atrioventricular block warrants greater clinical attention due to its prevalence.
  • Accurate differentiation from other atrioventricular blocks is essential for appropriate management.
  • Understanding the role of adenosine and autonomic reflexes aids in diagnosis and treatment.
  • This condition may be an indication for cardiac pacing, particularly when considering the vasodepressor response.