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Understanding EKGs A Practical Approach For the Dental Hygienist CHAPTER 4 The Electrical Conduction System Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The Electrical Conduction System • Objectives – Identify the location of the following SA node Internodal pathways Bachmann’s bundle AV node Bundle of His AV junction Bundle branches Purkinje network Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The Electrical Conduction System • Objectives (continued) – Relate the normal path of an impulse traveling through the electrical conduction system Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The Cardiac Conduction System Bachmann’s Bundle Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The SA Node • Sinoatrial (SA) node – Located in the upper posterior portion of the right atrial wall of the heart 50% actual pacemaker cells, remaining cells conduct electrical impulse – “Primary pacemaker” of the heart – Firing rate = 60-100 bpm Depolarization and myocardial contraction occur after impulse leaves SA node Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Internodal Pathways • Internodal pathways – Receive the electrical impulse as it exits the SA node – Pathways Distribute impulse throughout atria – Transmit the impulse from SA node to AV node Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Bachmann’s Bundle • Bachmann’s bundle – Also known as Wenckebach’s bundle and Thorel’s pathway – A group of interatrial fibers contained in the left atrium – Subdivision of anterior internodal tract – Conducts electrical activity from the SA node to the left atrium Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The AV Node • Atrioventricular (AV) node – Located on floor of right atrium above tricuspid valve – Electrical activity delayed 0.05 seconds – Allows for more complete filling of ventricles – Only pathway of atrial electrical impulses to ventricles Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The AV Junction • AV junction – SA node joins the bundle of His – If the SA node fails or slows below the normal rate, AV junctional tissues initiate electrical activity and thus the role of secondary pacemaker Accessory pathway: an irregular muscle connection between atria and ventricles that bypasses the AV node Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The Bundle of His • Bundle of His – Conduction pathway that leads out of AV node. – Receives blood from left anterior and posterior descending coronary arteries. – Lies at top of interventricular septum – Referred to as the common bundle Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The Bundle of His • Bundle of His – Ability to self-initiate electrical activity at intrinsic firing rate of 40-60 bpm – Connection between upper and lower chambers of the heart. Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Bundle Branches • Bundle of His – Divides into two main bundle branches Right bundle branch Left bundle branch – Conducts electrical activity from bundle of His to Purkinje’s network Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Purkinje’s Network • Purkinje’s network – Fibers that spread throughout the ventricles – Carries impulses directly to ventricular muscle cells – Intrinsic firing rate of 20-40 bpm Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Review of Electrical Conduction System of the Heart Bartender Bouncer Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Janitor Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electrical Conduction System Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley Copyright ©2010 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.