EKG Plain Simple Plain and Simple CHAPTER Third Edition Copyright ©2012 by Pearson Education, Inc. All rights reserved. EKG Plain and Simple, Third Edition.

EKGEKGPlain Plain and SimpleSimple

CHAPTER

Third Edition

Copyright ©2012 by Pearson Education, Inc.All rights reserved.

EKG Plain and Simple, Third EditionKaren M. Ellis

Electrophysiology

2



Media DirectoryMedia Directory

Slide 31 Inherent Rates Animation



DepolarizationDepolarization

• 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



RepolarizationRepolarization

• Return of the cardiac cell to its electrically negative charge

• Accomplished by way of the sodium-potassium pump, an active transport system



Figure 2-1 Depolarization and Repolarization



Electrical vs. MechanicalElectrical 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



Electrical vs. MechanicalElectrical 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



Action PotentialAction Potential

• Phase 4: Cardiac cell at rest• Phase 0: Depolarization• Phases 1 & 2: Early repolarization• Phase 2: Plateau phase• Phase 3: Rapid repolarization



Figure 2-2 Action Potential



Refractory PeriodsRefractory Periods

• Absolute: No stimulus can cause depolarization

• Relative: Strong stimulus can cause depolarization

• Supernormal period: Even a weak stimulus can cause depolarization



Figure 2-3 Refractory Periods



EKG Waves and ComplexesEKG 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



Figure 2-4 EKG Waves and Complexes



EKG Waves and ComplexesEKG Waves and Complexes

• Each P-QRS-T sequence is one heart beat



SegmentsSegments

• PR segment: Flat line between P wave and QRS complex

• ST segment: Flat line between QRS complex and T wave



BaselineBaseline

• The flat line between the T wave of one beat and the P wave of the next beat

• Also called isoelectric line



Waves and Complexes Waves and Complexes Identification Practice 1Identification Practice 1















QRS NomenclatureQRS 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



Figure 2-5 Examples of QRS Complexes



QRS Nomenclature PracticeQRS Nomenclature Practice



Cardiac Conduction SystemCardiac Conduction System

• Pathway of specialized cells that create and conduct electrical impulses



Figure 2-6 Cardiac Conduction System



Conduction PathwayConduction Pathway

• Sinus node interatrial tracts atrium internodal tracts AV node bundle of His bundle branches Purkinje fibers ventricle



Characteristics of Cardiac CellsCharacteristics 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



Characteristics of Cardiac CellsCharacteristics of Cardiac Cells

• Contractility: Ability to contract• Automaticity, conductivity, and excitability

are electrical characteristics. Contractility is mechanical



Pacemaker CellsPacemaker 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



Inherent Rates AnimationInherent Rates Animation

Click on the screenshot to view an animation showing inherent rates.Click again to pause the animation.

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Figure 2-7 Normal Conduction



Figure 2-8 Sinus Fails, AV Junction Escapes



Figure 2-9 All Higher Pacemakers Fail, Ventricle Escapes



Figure 2-10 Block in Conduction, AV Junction Escapes

EKG Plain Simple Plain and Simple CHAPTER Third Edition Copyright ©2012 by Pearson Education, Inc. All rights reserved. EKG Plain and Simple, Third Edition.

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depolarization slide

ellis electrical

ellis ekg waves

mechanical depolarization

relaxation slide