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EKG Plain and Simple Third Edition CHAPTER 2 Electrophysiology EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Media Directory Slide 31 Inherent Rates Animation EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Depolarization • Change in the cardiac cell’s electrical charge from negative to positive • Accomplished by sodium and potassium ions changing place • Causes a wave of electrical charge to course from cell to cell, resulting in a discharge of electricity EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Repolarization • Return of the cardiac cell to its electrically negative charge • Accomplished by way of the sodiumpotassium pump, an active transport system EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-1 Depolarization and Repolarization EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Electrical vs. Mechanical • Depolarization and repolarization — myocardium’s electrical stimuli • Contraction and relaxation — mechanical response to that stimuli • Depolarization should result in heart muscle contraction • Repolarization should result in relaxation EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Electrical vs. Mechanical • Electrical stimulus precedes mechanical response • There will be NO HEART BEAT without first having had depolarization • But electrical stimulus does not guarantee mechanical response • There could be a mechanical problem making the myocardium incapable of pumping EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Action Potential • • • • • Phase 4: Cardiac cell at rest Phase 0: Depolarization Phases 1 & 2: Early repolarization Phase 2: Plateau phase Phase 3: Rapid repolarization EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-2 Action Potential EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Refractory Periods • Absolute: No stimulus can cause depolarization • Relative: Strong stimulus can cause depolarization • Supernormal period: Even a weak stimulus can cause depolarization EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-3 Refractory Periods EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. EKG Waves and Complexes • P wave: Atrial depolarization • Ta wave: Atrial repolarization. Not usually seen, as it occurs simultaneous with QRS • QRS complex: Ventricular depolarization • T wave: Ventricular repolarization • U wave: Late ventricular repolarization. Not usually seen EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-4 EKG Waves and Complexes EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. EKG Waves and Complexes • Each P-QRS-T sequence is one heart beat EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Segments • PR segment: Flat line between P wave and QRS complex • ST segment: Flat line between QRS complex and T wave EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Baseline • The flat line between the T wave of one beat and the P wave of the next beat • Also called isoelectric line EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Waves and Complexes Identification Practice 1 EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Waves and Complexes Identification Practice 2 EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Waves and Complexes Identification Practice 3 EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Waves and Complexes Identification Practice 4 EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Waves and Complexes Identification Practice 5 EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. QRS Nomenclature • Q wave: Downward wave preceding an upward wave • R wave: Any upward wave • S wave: Downward wave following an R wave • QS wave: Downward wave with no upward wave at all EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-5 Examples of QRS Complexes EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. QRS Nomenclature Practice EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Cardiac Conduction System • Pathway of specialized cells that create and conduct electrical impulses EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-6 Cardiac Conduction System EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Conduction Pathway • Sinus node interatrial tracts atrium internodal tracts AV node bundle of His bundle branches Purkinje fibers ventricle EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Characteristics of Cardiac Cells • Automaticity: Ability to create an impulse without outside stimulation • Conductivity: Ability to conduct an impulse to neighboring cells • Excitability: Ability to depolarize EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Characteristics of Cardiac Cells • Contractility: Ability to contract • Automaticity, conductivity, and excitability are electrical characteristics. Contractility is mechanical EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Pacemaker Cells • Pacemaker: Area of the conduction system that initiates the electrical impulses – Sinus node: Heart’s normal pacemaker. Inherent rate 60–100 beats per minute – AV junction: Backup pacemaker. Inherent rate 40–60 beats per minute – Ventricle: A lower backup pacemaker. Inherent rate 20–40 beats per minute EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Inherent Rates Animation Click on the screenshot to view an animation showing inherent rates. Click again to pause the animation. EKG Plain and Simple, Third Edition Karen M. Ellis Back to Directory Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-7 Normal Conduction EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-8 Sinus Fails, AV Junction Escapes EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-9 All Higher Pacemakers Fail, Ventricle Escapes EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved. Figure 2-10 Block in Conduction, AV Junction Escapes EKG Plain and Simple, Third Edition Karen M. Ellis Copyright ©2012 by Pearson Education, Inc. All rights reserved.
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