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Conduction System of the Heart01:20

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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.
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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.
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Mechanism of Cardiac Arrhythmias01:28

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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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Dysrhythmias IV: Characteristics of Bradyarrhythmias01:18

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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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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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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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Acidosis slows electrical conduction through the atrio-ventricular node.

Ashley M Nisbet1, Francis L Burton1, Nicola L Walker1

  • 1British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, University of Glasgow Glasgow, UK.

Frontiers in Physiology
|July 11, 2014
PubMed
Summary
This summary is machine-generated.

Acidosis significantly prolongs atrio-ventricular node (AVN) delay and can cause AVN block, leading to brady-arrhythmias. This study investigated the electrical effects of acidosis on heart function, specifically the AVN.

Keywords:
acidosisatrio-ventricular blockatrio-ventricular nodebradycardiaoptical mappingright atrium

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Area of Science:

  • Cardiology
  • Electrophysiology
  • Acid-Base Physiology

Background:

  • Acidosis impacts cardiac mechanical and electrical activity, but its effects on the atrio-ventricular node (AVN) are not well understood.
  • The AVN plays a critical role in regulating heart rhythm by controlling conduction between the atria and ventricles.

Purpose of the Study:

  • To investigate the electrophysiological effects of acidosis on the atrio-ventricular node (AVN) in mammalian hearts.
  • To determine if acidosis-induced AVN dysfunction contributes to cardiac arrhythmias.

Main Methods:

  • Utilized optical mapping techniques on isolated Langendorff-perfused rabbit hearts and isolated right atrial preparations.
  • Exposed cardiac tissue to hypercapnic (low pH) Tyrode's solutions to simulate acidosis.
  • Measured parameters including time of earliest activation (Tact), atrial-Hisian (AH) interval, and refractory periods.

Main Results:

  • Hypercapnic acidosis significantly prolonged Tact and the AH interval, indicating delayed conduction through the AVN.
  • Acidosis increased AVN effective and functional refractory periods and Wenckebach cycle length.
  • Complete AVN block occurred in a significant proportion of preparations under acidic conditions, especially at shorter pacing cycle lengths.

Conclusions:

  • Acidosis dramatically prolongs AVN conduction delay.
  • Acidosis-induced AVN dysfunction, particularly in conjunction with rapid heart rates, can lead to partial or complete AVN block.
  • These findings implicate acidosis in the development of brady-arrhythmias during conditions of local or systemic acidosis.