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Related Concept Videos

Electrocardiogram Fundamentals01:28

Electrocardiogram Fundamentals

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Introduction
An electrocardiogram (ECG) is a diagnostic tool for identifying cardiac conditions such as arrhythmias, conduction abnormalities, and myocardial ischemia.
Definition
An electrocardiogram (ECG) visualizes the heart's electrical activity by tracing the electrical movement associated with each heartbeat on a graph or monitor. As the heart beats, an electrical wave passes through it, correlating with the cardiac cycle events.
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Correlation between ECG and Cardiac Cycle01:25

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The electrical signals recorded on an electrocardiogram (ECG) occur before the mechanical processes of contraction and relaxation during the cardiac cycle.
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...
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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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Electrophysiology of Normal Cardiac Rhythm01:19

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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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Electrocardiogram01:29

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An electrocardiogram (ECG or EKG) is a critical diagnostic tool that records the electrical signals produced by the heart during each heartbeat. This recording is achieved through electrodes placed strategically on the arms, legs, and chest. The electrocardiograph amplifies these signals and produces 12 distinct tracings, offering a comprehensive understanding of the heart's electrical activity.
Three major waveforms are present in a typical ECG recording: the P wave, the QRS complex, and...
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Cardiac Action Potential01:30

Cardiac Action Potential

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Cardiac action potentials are essential for proper heart function, enabling the rhythmic contractions needed for adequate blood circulation. Nodal cells and Purkinje fibers, specialized for electrical conduction, generate these action potentials.
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Related Experiment Video

Updated: Feb 25, 2026

High-Resolution Endocardial and Epicardial Optical Mapping in a Sheep Model of Stretch-Induced Atrial Fibrillation
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Wavefront direction and cycle length affect left atrial electrogram amplitude.

Kazuki Iso1, Ichiro Watanabe1, Rikitake Kogawa1

  • 1Division of Cardiology, Department of Medicine, Nihon University School of Medicine, Oyaguchi-kamimachi, Itabashi-ku, Tokyo 173-8610, Japan.

Journal of Arrhythmia
|August 3, 2017
PubMed
Summary
This summary is machine-generated.

Atrial electrogram (EGM) voltage amplitude decreases with faster pacing rates, potentially explaining differences between sinus rhythm and atrial fibrillation. This study investigated left atrial EGM characteristics during different pacing conditions.

Keywords:
Atrial fibrillationAtrial pacingLeft atrial voltagePacing rate

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Area of Science:

  • Electrophysiology
  • Cardiac Arrhythmias
  • Atrial Electrophysiology

Background:

  • The relationship between atrial electrogram (EGM) characteristics during atrial fibrillation (AF) and sinus rhythm (SR) remains largely unexplored.
  • Activation rate and direction are hypothesized to influence EGM characteristics.
  • This study investigates left atrial (LA) EGMs recorded during pacing from various sites.

Purpose of the Study:

  • To examine the characteristics of left atrial (LA) electrograms (EGMs) during pacing from different sites.
  • To understand how pacing rate and location affect LA EGM amplitudes and conduction times.
  • To explore potential explanations for voltage discordance between sinus rhythm and atrial fibrillation.

Main Methods:

  • Ten patients undergoing pulmonary vein isolation for AF were included.
  • Atrial EGMs were recorded using a 64-pole basket catheter in the LA.
  • Pacing was performed at the high right atrium (HRA), proximal coronary sinus (CSp), and distal coronary sinus (CSd) at 600 ms and 300 ms cycle lengths.

Main Results:

  • When LA voltage in SR was ≥1.5 mV, bipolar voltages were consistently higher from HRA than CSp, and CSp than CSd, irrespective of pacing cycle length.
  • A shorter pacing cycle length (300 ms) reduced LA EGM voltage at sites with SR voltage ≥1.5 mV, but not at sites with SR EGM amplitude between >0.5 and <1.5 mV.
  • No significant differences in intra-basket conduction times were observed between the two pacing cycle lengths at any pacing site.

Conclusions:

  • The amplitude of atrial EGMs exhibits a rate- and direction-dependent reduction.
  • This phenomenon may partially account for the observed voltage discordance between SR and AF.
  • Findings contribute to understanding atrial electrophysiology during different rhythm states.