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Related Concept Videos

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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ECG Interpretation of Arrhythmias I: Sinus Arrhythmias01:16

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Arrhythmias are disturbances in the heart's rhythm that lead to abnormal heartbeats. These irregularities can originate from different parts of the heart and are classified based on their origin and nature.
Types of Arrhythmias
Sinus Node Arrhythmias
Sinus Bradycardia: Originating from the sinoatrial (SA) node, sinus bradycardia involves slower impulses, resulting in a heart rate of less than 60 beats per minute (bpm). Causes include sleep, vagal stimulation, beta-blockers, hypothyroidism,...
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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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Conduction System of the Heart01:19

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Autorhythmicity is a term that refers to the heart's inherent ability to generate electrical signals and instigate muscle contractions. This self-regulating conduction system within the heart consists of two key components: the pacemaker cells and specialized conducting cells.
The pacemaker cells are located in two primary nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node pacemaker cells can autonomously depolarize, triggering an action potential that leads to the...
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Conduction System of the Heart01:20

Conduction System of the Heart

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The cardiac conduction system produces and transmits electrical impulses that prompt myocardial contraction, ensuring efficient heart function. This intricate system ensures that the heart beats in a coordinated and efficient manner, beginning with the atria and then the ventricles. The conduction system optimizes cardiac output by maintaining this precise sequence, which is crucial for adequate blood circulation.
This system relies on the unique properties of nodal and Purkinje cells:...
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Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers01:24

Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

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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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Updated: Jan 9, 2026

Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection
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PITX2 dosage-dependent changes in pacemaker cell state underlie sinus node dysfunction and atrial arrhythmias.

Lieve E van der Maarel1, M Ridwane Mungroo1, Otto J Mulleners1

  • 1Department of Medical Biology, Amsterdam Cardiovascular Sciences, Amsterdam Reproduction and Development, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, the Netherlands.

Nature Communications
|December 5, 2025
PubMed
Summary
This summary is machine-generated.

Genomic deletions increase PITX2 gene expression, causing heart rhythm disorders. This study links PITX2 dosage to pacemaker cell identity loss and atrial arrhythmias in mice and human cells.

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Methods for the Isolation, Culture, and Functional Characterization of Sinoatrial Node Myocytes from Adult Mice
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Area of Science:

  • Cardiovascular Biology
  • Developmental Biology
  • Genetics

Background:

  • Physiologically relevant increases in transcription factor dosage are underexplored in development and disease.
  • Genomic deletions upstream of the Paired-like homeodomain transcription factor gene (PITX2) are linked to sinus node dysfunction and atrial fibrillation.

Purpose of the Study:

  • To investigate the role of increased PITX2 expression in sinus node development and function.
  • To establish a mechanistic link between genetic variation, PITX2 dosage, and cardiac arrhythmias.

Main Methods:

  • Utilized a mouse model (delB) with genomic deletions affecting PITX2 expression.
  • Analyzed embryonic sinus node development and cardiomyocyte identity in delB mice.
  • Examined ectopic PITX2c expression in human induced pluripotent stem cell-derived pacemaker cardiomyocytes.

Main Results:

  • Ectopic PITX2 expression in delB mouse embryonic sinus nodes occurred in a heterogeneous pattern at physiological dosages.
  • Discrete subdomains within the delB sinus node showed PITX2 dosage-dependent loss of pacemaker cardiomyocyte identity.
  • Severity of sinus node dysfunction and atrial arrhythmia susceptibility correlated with PITX2 dosage.
  • Ectopic PITX2c in human cells mimicked delB mouse findings, showing dosage-dependent transcriptional and electrophysiological changes.

Conclusions:

  • Spatiotemporally defined increases in transcription factor dosage, specifically PITX2, can lead to developmental defects in the heart.
  • Genetic variations affecting PITX2 dosage provide a mechanistic link to sinus node dysfunction and atrial arrhythmogenesis.
  • This study highlights the importance of transcription factor dosage in cardiac development and disease predisposition.