Is located in the inferior aspect of the right 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; functions to slow the conduction speed to allow for atrial conductionOnce the SA node initiates an electrical impulse, the resulting electrical wave moves across the right and left atria. The atrial septum serves as an electrical insulator. Bachman’s Bundle tunnels through the atrial septum to continue the electrical wave across... prior to ventricular conduction (atrial kickThe contraction of the atria prior to ventricular contraction causes an increased volume and stretch to the ventricles – resulting in increased force of contraction and increased stroke volume (Starling’s Law); this extra stroke volume increases cardiac output by 10-35%....); also serves as a pacemakerAn electronic pulse generator that stimulates depolarization of the atria and/or the ventricles. 1. Six Second ECG Guidebook (2012), T Barill, p. 201 if the SA nodeThe SA node, usually the dominant pacemaker, 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... fails to fire.
The atrioventricular (AV) node is a rounded bulbar structure of specialized cells similar to the SA node. The AV node also has intrinsicCharacteristic or property natural to the heart and its structures. 1. Six Second ECG Guidebook (2012), T Barill, p. 198 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..., with the ability to serve as a pacemaker in case of SA nodalCommonly refers to the junction; for example, junctional rhythm is also known as nodal rhythm; may also refer to the sinoatrial node. 1. Six Second ECG Guidebook (2012), T Barill, p. 200 failure. The AV node usually does not initiate impulses, though, as its intrinsic firing 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. is normally 40-60 /minute, slower than the SA node. Remember, the fastest pacemaker site rules.
The AV node has a second important role. The AV node 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... slows impulse conduction to allow the atria time to contract prior to ventricular contraction. In other words, 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... provides the time delay for an atrial kick. The time taken to cross the small AV junctionConnects the atria to the ventricle and slows the impulse conduction speed sufficiently to allow for atrial kick; the junction consists of the AV node and the bundle of His; the junction is a supraventricular structure. 1. Six Second ECG... is 10-12/100 of a second (a significantly lengthy period for such a small structure).
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 atria, through the AV junction (the AV node and the bundle of His) 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, 56