This document provides an overview of electrocardiography (ECG) analysis. It discusses the electrical conduction system of the heart, including the sinoatrial node, atrioventricular node, and Purkinje fibers. It explains the three phases of the ECG wave - polarization, depolarization, and repolarization. Key aspects of interpreting ECG strips such as the P, QRS, and T waves are covered. Common cardiac rhythms like sinus rhythm, sinus bradycardia, sinus tachycardia, atrial fibrillation, atrial flutter, and ventricular fibrillation are also summarized.

1. Electrocardiography
Analysis
Maggie Cornish

2.  Electrical conduction system of the heart
 ECG
 Phases: polarization, depolarization,
repolarization
 Electrode Placement
 Interpreting ECG strips & waves
 Cardiac Rhythms
 Rhythm Quiz
Agenda

3.  Most important aspect heart’s anatomy & physiology
to master in ECG analysis
 Composed of myocardial tissue
 ECG supplies information how well
conduction system of the heart is
functioning
 Neurons serve conduction function
for the rest of the body
 Myocardial tissue has 2 advantages over nerve tissue
Electrical Conduction System

4.  Sinoatrial node, “pacemaker” of the heart
 Small concentration of myocardial tissue
 Initiates impulses that depolarize the rest of the
heart
 Located in upper portion of the right atrium
 Electrical impulse that triggers each heartbeat
 Spreads through the atria
 Muscle tissue to contract in a coordinated
manner
 Inherent rate of 60-100 beats per minute
SA Node

5.  Atrioventricular node
 Large bundle of myocardial tissue
 Internodal tracts connect SA node to AV node
 2 pathways: beat & alpha
 Delays impulses from SA node to allowing atria to
complete their contraction and empty completely
 Atrial kick
 Prevents extra beats from being conducted
 Distal portion of AV node is the bundle of His that
splits into two branches: left & right bundle branches
AV Node

6.  Spread across respective ventricles and become
purkinje fibers
 Ventricles contract
 Electrical signal having passed through both atria and
ventricles making them contract = one heart beat
AV Node

7.  Records the electrical activity of the heart
 Detected by electrodes
 Electrical activity of myocardial cells result in complex
electrical reaction occurring in each fiber of myocardium
 Millions of fibers of the myocardium react electrically to an
impulse creating a wave of energy detected by the ECG
 ECG pattern: characteristic wave forms produced by
electrical activity
 Painless
 Three phases of electrochemical activity: polarization,
depolarization, and repolarization
ECG

8.  Cells ready to contract
 SA node ready to initiate impulse
 Extracellular ions: Na and Ca strong positive electrical
charge
 Intracellular ion: K weak positive electrical charge
 Difference of strength of electrical charges create a
positive charge on outside of the cell membrane &
negative charge on the inside
Polarization

9.  “Action phase”
 Shift in ion concentrations
 Na ions rush into the cell, followed by slower Ca ions
 K ions pushed out of the cell creating polarity of cell
to become reversed
 Negative charge along outside of the cell membrane
& positive charge inside the cell membrane
 Shortens fibers producing contractions
 Contraction increases pressure, pushing blood out of
heart chambers “systole”
Depolarization

10.  “Recovery phase”
 Sodium Potassium pump
 Pump out Na and Ca and pump in K reestablishing
electrical charge along cell membrane
 Muscle fibers of myocardium are relaxing returning to
preconstraction state
 Relaxation decreasing pressure, heart chambers fill
“diastole”
Repolarization

11.  1) cleanse skin removing: oils, sweat, dirt and hair
 2) place electrode sticky side down and begin placing on
one corner, avoiding touching sticky side
 3) smooth electrode to skin in circular motion and connect
monitor wire
 5 lead ECG:
-white: RA second intercostal space (right side)
-brown: chest (middle)
-green: RL (right side)
-red: LL (left side)
-black: LA second intercostal space (left side)
Electrode Placement

12. Electrode Placement
Smoke over fire, snow over grass, brown in the middle

13. Interpreting ECG Strips
Each small box= 0.04 seconds, 1mm
Each large box= 0.20 seconds, 5mm
25mm/second papers

14.  Atrial depolarization
 Time for electrical impulse from SA node to spread
through the atrial muscle
 Amplitude: 2-2.5 mm in height
 Duration: 0.06-0.11 seconds
 P-R interval:
-time takes an impulse to travel from the atria through
the AV node, bundle of his, and bundle branches to the
Purkinje fibres
-beginning of p wave to beginning of QRS complex
-duration: 0.12-0.20 seconds
P wave & P-R interval

15. P-R Interval

16.  Ventricular depolarization
 3 waves: Q,R,S
 Q wave: beginning, sometimes not present
 R wave: positive deflection
 S wave: negative deflection
 Duration: no longer than 10 seconds
QRS Complex

17.  T wave: repolarization of ventricles
 S-T segment: end of ventricular depolarization and
beginning of ventricular repolarization
 QT interval:
-time necessary for ventricle depolarization &
repolarization
-beginning of QRS complex to end of T wave
T wave, Q-T interval, S-T segment

18. Sinus Rhythm
• Normal
• Electrical stimuli initiated in SA node, conducted through AV
node, bundle of His, bundle branches, and Purkinje fibers
• Depolarization and repolarization of atria and ventricles

19. Sinus Bradycardia
• HR: <60 bpm
• Rhythm unchanged
• Normal sinus slowed down
• Waves further apart

20. Sinus Tachycardia
• HR: >100 bpm
• Sinus rhythm greater than 100 bpm
• Waves closer together

21. Atrial Fibrillation
• No P wave since SA node isn’t functioning
• Atria generates up to 600 stimuli/min
• Instead seeing P wave, number of small waves of different sizes
“fibrillatory waves” (F waves)
• Stimuli not strong enough to depolarize the AV node, rhythm is
irregular since number of stimuli being generated in atria
• Fast rhythm: 110-140 bpm
• QRS normal since abnormality above the ventricles

22. Atrial Flutter
• Similar to atrial fibrillation
• Abnormality of conduction of atria
• Flutter waves bombard Av node but more organized and regular
fashion
• “saw-tooth” pattern

23. Ventricular Fibrillation
• Life threatening
• Chaotic depolarization of ventricles
• No clear P waves or QRS complexes

24. Myocardial Infarction
• Heart attack
• 1st hyperacute T wave: taller and pointed
• 2nd ST segment elevation: when heart muscle is being injured by lack of
blood flow and oxygen

25. NAME THAT
RHYTHM
QUIZ TIME!!

27. Atrial Fibrillation

29. Sinus Bradycardia

31. Ventricular fibrillation

33. Normal Sinus

35. Atrial flutter

37. Sinus Tachycardia

38.  Ambulance Technician Study. (2006). ECG basics. Retrieved from
http://www.ambulancetechnicianstudy.co.uk/ecgbasics.html#.UKu1b4aA8uc
 Catalano, J.T. (2002). Guide to ECG analysis (2nd ed.).Philadelphia, PA: Lippincott
Williams & Wilkins
 Lewis, S.L., Heitkemper, M.M., Dirksen, S.R, O’Brien, P.G., & Bucher, L. (2010).
Medical-surgical nursing in canada (2nd ed.) Toronto, ON: Elsevier Canada
 Perry, P.A. & Potter, A.G. (2009). Canadian fundamentals of nursing (4th ed.)
Toronto, ON: Elsevier Canada
 University of Nottingham School of Nursing. (2012). Beginners guide to normal
heart function, sinus rhythm & common arrhythmias. Retrieved from
http://www.nottingham.ac.uk/nursing/practice/resources/cardiology/index.php
References