The SA node, usually the dominant pacemakerAn electronic pulse generator that stimulates depolarization of the atria and/or the ventricles. 1. Six Second ECG Guidebook (2012), T Barill, p. 201, is located in the right atrium at the opening of the superior vena cava. The SA (sinoatrial) node is a clump of hundreds of specialized cardiac cells that have the ability to self-initiate an electrical impulse. This pacemaking ability, called automaticityA cardiac cell’s (usually pacemaker cells such as the SA node, AV node or His-Purkinje network) ability to self-initiate an impulse; note that abundant catecholamines and/or ischemia enhances automaticity – non-pacemaker cells may become pacemaker cells. The SA node, usually..., makes the SA node a pacemaker site in the heart.
As a general rule, the site in the heart that is able to self-generate the quickest rateHeart Rate; calculated by counting the number of QRS complexes in six seconds and multiplying by 10; rate is also determined by measuring the number of large squares between two R waves; i.e. –1 large square = heart rate of 300/minute., RULES the heart. This site is almost always the sinoatrial node (SA node)Located in the upper right atrium near the inlet for the superior vena cava, serves as the predominant pacemaker for the heart with rates usually of 60-100/minute. The SA node, usually the dominant pacemaker, is located in the right atrium.... Thus, the SA node is often called the dominant pacemaker. If an ectopicA depolarizing wave that originates anywhere outside of the SA node. 1. Six Second ECG Guidebook (2012), T Barill, p. 196 site (site other than the SA node) begins to fire faster than the SA node, the ectopic site tends to drive the heart.
The SA node initiates an electrical impulse at a rate faster than other pacemaker sites. In the heart, the pacemaker which fires at the quickest pace takes control of heart rateThe number of QRS complexes per minute; note that HR may not equal perfused pulse rate. See also: - Step 1 Heart Rate - Rate - Rule of 300s (Triplicate Method) - Six Second Count - The Caliper Method 1..... This is why the SA node is the “dominant pacemaker”. A cardiac rhythmOften refers to a discernible pattern in time or distance between QRS complexes and/or P waves. that originates from the SA node is called a sinus rhythmAlso known as regular sinus rhythm or sinus rhythm, this cardiac rhythm is not a dysrhythmia; sinus rhythm originates in the sinoatrial (SA) node with a rate of 60-100/minute; P waves are upright in most leads and the QRS is....
The SA node normally generates electrical impulses at 60-100 /minute. This rate tends to increase with sympathetic stimulationIschemia and sympathetic stimulation can enhance a ventricle’s automaticity, stimulating the ventricle to initiate an impulse before a sinus initiated wave reaches the ventricles. This solitary wave doesn’t ride the Autobahn. Rather, this one wave must traverse both ventricles. The... (norepinephrine and epinephrine) and slows with parasympathetic stimulation (acetylcholine and the Vagus nerve). Therefore, Vagal stimulation can slow the SA node to rates below 60/minute causing a sinus bradycardiaA heart rate slower than a pacemaker’s regular intrinsic rate – commonly thought as less than 60/minute for sinus rhythms; less than 40/minute for junctional rhythms. The term ‘bradycardia’ describes a heart rate less than the normal rate expected of.... Sympathetic stimulation can cause rapid sinus rhythms called sinus tachycardias.
A wave of depolarizationThe rapid influx of positive ions (sodium and/or calcium) into a cell – depolarization is necessary for contraction to occur. A depolarizing wave moves through the myocardium on average along a trajectory or vector. A vector is a force moving... normally begins with the SA node. This electrical wave from the SA node passes quickly across the atriaRight and left atria (1/3 volume and muscle mass of the ventricles) pump blood to the ventricles. Chambers and Layers of the Heart 1. Six Second ECG Guidebook (2012), T Barill, p. 190, through the AV junctionConducts the impulse through the fibrous plate that separates the atria and the ventricles; consists of the AV node and the bundle of His; functions also to slow the conduction speed to allow for atrial conduction prior to ventricular conduction... (the AV nodeIs located in the inferior aspect of the right atria; functions to slow the conduction speed to allow for atrial conduction prior to ventricular conduction (atrial kick); also serves as a pacemaker if the SA node fails to fire. The... and the bundle of HisPart of the AV junction, the bundle of His conducts the impulse through the fibrous plate that separates the atria and the ventricle; the bundle of His is also a pacemaker, firing at 40-60/minute. The bundle of His serves as...) then across the ventriclesThe larger chambers of the heart (3 times the volume and muscle thickness than the atria), responsible for the pumping of blood to the lungs and the rest of the body. via the bundle branchesThe bundle of His terminates in the right and left bundle branches, insulated rapidly conducting electrical pathways that connect with the Purkinje network and thus begin depolarizing waves across the ventricles; the left bundle branch splits into three smaller branches... and the Purkinje networkA matrix of fibres located throughout the myocardium that connects the impulse from the bundle branches to the myocardial tissue. The bundle branches and the Purkinje network facilitate rapid depolarization throughout the ventricles. The Purkinje network also creates a typical....
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 46-48, 109, 116