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Related Concept Videos

Mechanism of Cardiac Arrhythmias01:28

Mechanism of Cardiac Arrhythmias

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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.
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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.
Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart...
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ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias01:25

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

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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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Electrophysiology of Normal Cardiac Rhythm01:19

Electrophysiology of Normal Cardiac Rhythm

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The normal cardiac rhythm is a synchronized electrical activity that facilitates the regular and coordinated contraction of the heart muscle. This process is essential for efficient blood circulation throughout the body. The fundamental elements involved in establishing and maintaining this rhythm include the unique electrical properties of cardiac muscle cells, the sinoatrial (SA) node's pacemaker function, the specialized conducting system, and the ionic mechanisms underlying each phase...
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Dysrhythmias I: Introduction01:15

Dysrhythmias I: Introduction

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Dysrhythmias refers to abnormalities in the heart's rhythm. They result from disruptions in the heart's electrical conduction system, which includes the sinoatrial(SA)node, atrioventricular(AV) node, the bundle of His, bundle branches, and Purkinje fibers.Definition and PathophysiologyDysrhythmias result from disorders of impulse formation, impulse conduction, or both. The heart contains specialized cells in the sinoatrial node, atrioventricular node, and the bundle of His and Purkinje fibers...
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Dysrhythmias III: Characteristics of Dysrhythmias01:29

Dysrhythmias III: Characteristics of Dysrhythmias

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Dysrhythmias, also known as arrhythmias, are irregular heart rhythms that result from abnormal electrical activity in the heart, affecting its ability to circulate blood efficiently. Tachyarrhythmias, a subset of dysrhythmias, are characterized by abnormally fast heart rates exceeding 100 beats per minute. Here are some types of tachyarrhythmias with their distinct ECG features:Sinus Tachycardia:Sinus tachycardia presents a regular heart rhythm with an increased rate of 101-180 beats per...
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Related Experiment Video

Updated: Mar 13, 2026

Dual-Dye Optical Mapping of Hearts from RyR2R2474S Knock-In Mice of Catecholaminergic Polymorphic Ventricular Tachycardia
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Cardiac dynamics: Alternans and arrhythmogenesis.

Gary Tse1, Sheung Ting Wong2, Vivian Tse3

  • 1School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong.

Journal of Arrhythmia
|October 21, 2016
PubMed
Summary

Cardiac repolarization alternans, beat-to-beat changes in heart action potentials, arise from tissue heterogeneities and dynamic factors beyond restitution. Understanding these mechanisms is key to preventing arrhythmias.

Keywords:
AlternansCardiac arrhythmiaDynamicsRe-entryRestitution

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Area of Science:

  • Cardiology
  • Biophysics
  • Computational Biology

Background:

  • Cardiac tissue heterogeneities are vital for normal heart function.
  • Repolarization alternans, beat-to-beat action potential alternations, can arise from exacerbated heterogeneities or dynamic factors.
  • While restitution was a traditional explanation, cardiac memory, calcium dynamics, and mechano-electric feedback are now recognized as key contributors.

Approach:

  • Reviewing the fundamental mechanisms driving cardiac repolarization alternans.
  • Analyzing the transition from spatially concordant to arrhythmogenic spatially discordant alternans.
  • Discussing the role of alternans in generating clinical arrhythmias and identifying future therapeutic targets.

Key Points:

  • Cardiac heterogeneities and dynamic factors beyond restitution contribute to repolarization alternans.
  • Mechanisms driving alternans include cardiac memory, calcium handling, refractory period restitution, and mechano-electric feedback.
  • Alternans can transition from spatially concordant to spatially discordant forms, increasing arrhythmogenicity.

Conclusions:

  • Understanding alternans mechanisms is crucial for developing anti-arrhythmic therapies.
  • Targeting factors like calcium handling and mechano-electric feedback may offer new therapeutic avenues.
  • Further research into alternans is needed to effectively manage cardiac arrhythmias.