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ECG Interpretation of Arrhythmias I: Sinus Arrhythmias

ECG Interpretation of Arrhythmias I: Sinus Arrhythmias

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, and...

Electrophysiology of Normal Cardiac Rhythm

Electrophysiology of Normal Cardiac Rhythm

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 of...

Dysrhythmias IV: Characteristics of Bradyarrhythmias

Dysrhythmias IV: Characteristics of Bradyarrhythmias

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...

Conduction System of the Heart

Conduction System of the Heart

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...

Conduction System of the Heart

Conduction System of the Heart

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:...

Mechanism of Cardiac Arrhythmias

Mechanism of Cardiac Arrhythmias

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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Related Experiment Video

Updated: Jul 13, 2026

Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

Published on: July 5, 2021

[Sinus rhythm: mechanisms and function].

Guy Lerebours¹

¹Institut de recherches internationales Servier, 6, place des Pléiades, 92415 Courbevoie, France.

Medecine Sciences : M/S

|July 17, 2007

Summary

The sinus node generates the heart's normal rhythm through electrical impulses. Neural regulation by neurotransmitters like acetylcholine and catecholamines adjusts heart rate for metabolic needs, impacting exercise capacity.

Area of Science:

Cardiology
Electrophysiology
Cardiac Physiology

Context:

The sinus node, a specialized cardiac tissue, initiates and regulates normal heart rhythm.
Pacemaker cells within the sinus node exhibit spontaneous diastolic depolarization, crucial for automaticity.
Cardiac rhythm is influenced by ion channel currents, including I(f), Ca2+, K+, and Na/Ca exchange currents.

Purpose:

To elucidate the mechanisms of normal cardiac rhythm generation by the sinus node.
To explain the role of various ionic currents in pacemaker cell depolarization.
To describe the neural regulation of heart rate by adrenergic and cholinergic neurotransmitters.

Summary:

Normal cardiac rhythm originates in the sinus node via spontaneous diastolic depolarization, influenced by multiple ionic currents.

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Published on: February 17, 2015

Optocardiography and Electrophysiology Studies of Ex Vivo Langendorff-perfused Hearts

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Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

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Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection

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Optocardiography and Electrophysiology Studies of Ex Vivo Langendorff-perfused Hearts

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Autonomic neurotransmitters modulate sinus node activity: acetylcholine slows heart rate, while catecholamines increase it.

Sinus rhythm optimizes heart rate for metabolic demands, supporting exercise capacity and quality of life.

Impact:

Understanding sinus node function is key to managing heart rate and addressing arrhythmias.
Neural regulation of heart rate is vital for adapting cardiac output to physiological demands.
Maintaining normal sinus rhythm is fundamental for optimal physical performance and overall well-being.