1. Chapter 1 for 12 Lead Training -RHYTHM BASICS-
Ontario Base Hospital Group
Education Subcommittee
2008
TIME IS MUSCLE

2. RHYTHM BASICS AUTHOR REVIEWERS/CONTRIBUTORS Tim Dodd, AEMCA, ACP
Hamilton Base Hospital
REVIEWERS/CONTRIBUTORS
Al Santos A-EMCA, ACP
Donna L. Smith AEMCA, ACP
Hamilton Base Hospital
2008 Ontario Base Hospital Group

3. Chapter 1 Overview Anatomy review Electrical impulse conduction
ECG paper constants
Limb placements
Heart rate determination
Steps to rhythm strip analyzes
ECG interpretations!

4. Chapter 1 Objectives
To gain a basic knowledge of cardiac electrophysiology
To understand the representations of the cardiac cycle on the ECG
To master techniques used for learning the characteristics of the different dysrhythmias
To learn measurement and count techniques essential for dysrhythmia interpretation

5. Cardiac Monitoring and Lead Placement

6. Lead Placement and ECG “View”
Our cardiac monitors have the ability to display ECG rhythms
In manual mode it is possible to capture various leads or “views” of the electrical activity
No matter which view is being displayed, the underlying rhythm does NOT change

7. 5 Lead Electrode Placement
RA (White): Place near right mid-clavicular line, directly below the clavicle
LA (Black): Place near left mid-clavicular line, directly below the clavicle
V (Brown): Place to Right of sternum at the 4th intercostal Space
LL (Red):Place between 6th & 7th intercostal Space on left mid-clavicular line
RL (Green): Place between 6th and 7th intercostal Space on right mid-clavicular line

8. Bipolar Leads or Limb Leads (I,II,III)

9. Einthoven’s triangle is composed of the standard (bipolar) limb leads:
Lead I: negative pole is right arm & positive is left arm
Lead II: negative pole is right arm & positive left leg
Lead III: negative pole is left arm & positive left leg

10. Lead Placement and Views
Lead I
Negative
Positive
Ground

11. Lead Placement and Views
Negative
Ground
Lead II
Lead II ECG cables are three colour coded cables, white, red, black (green)
White – right anterior chest, below clavicle
Red – mid axillary line below left nipple line – not on the hand… will be a continuation of left arm lead!!!
Black – left anterior chest, below clavicle
Factors affecting ECG quality:
ECG electrode directly over bone
dried out electrodes
loose connections
frayed cables
improper lead selection
Positive

12. Lead Placement and Views
Negative
Ground
Lead III
Positive

13. BiPolar Leads I, II & III
Lead I
Lead III
Lead II

14. Limb Leads -
Lead I
Lead II
Lead III
Left Arm
Right Arm
Left Leg +

15. Cardiac Conduction

16. Cardiac Conduction Essentially 2 pumps
Atria
Ventricles
Must operate in unison and in order
Three Primary Pacemakers
Sinoatrial Node
Atrio-Ventricular Junction
Purkinje System

17. Electromechanics Resting cells: negative interior, positive exterior
Changes in this resting state cause depolarization and repolarization

18. Electrical Flow
Towards negative electrode: downward deflection on paper
Towards positive electrode:
upward deflection on paper
As energy travels away from this axis amplitude on the ECG decreases

19. ECG “View” and Electrical Flow
Lead II offers the best “view”
The normal electrical axis travels the 11-5 o’clock vector which is degrees
Lead II is at 60 degrees

20. SinoAtrial Node Contraction of the Atria
Normally depolarizes times/min.
Can depolarize up to 300 times/min.
Follows special pathways – IntraAtrial:
Anterior, Middle, Posterior Internodal Tracts

21. AtrioVentricular Node
Pauses depolarization to allow ventricular filling
Capable of depolarizing times/min. (in the absence of the SA Node input)

22. Ventricular Pathways Bundle of His Left and Right Bundle Branches
Left bundle gives rise to anterior and posterior fascicles
Ends at the Purkinje fibers
Inherent depolarization rate < 40/min.

23. Any beat or rhythm not generated from the SA node is considered an escape beat
and/or escape rhythm

24. Conduction Pathways

25. Pathway – structure relationship
Slide courtesy of York Base Hospital

26. ECG Paper
Horizontal lines: distance in millimeters and time in seconds
Vertical lines: voltage (amplitude) in millimeters
Uses the Metric system
Is very good for accuracy

27. ECG Paper Light vertical lines are 0.04 second (1 mm) apart
Dark vertical lines are 0.20 second (5 mm) apart
5 dark squares is 1 second

28. Cardiac Conduction P Wave - Depolarization of the atria
- usually SA node
- upright
P-R Interval - impulse conduction through AV node
- from beginning of P wave to beginning of QRS complex
- delay results from tissue density increasing
to 0.20 seconds
QRS Complex - depolarization of the ventricle
to 0.12 seconds
- large amplitude due to increased mass of ventricle producing more activity
Q Wave - septal wall depolarization
- first negative deflection on ECG complex after P wave
R Wave - ventricular wall depolarization
- large mass of ventricle
S Wave - lateral wall depolarization
- downward deflection
T Wave - ventricular repolarization
U Wave - not well understood

29. Cardiac Conduction: P Wave
Atrial Impulse
Seconds

30. Cardiac Conduction: PR Interval
P Wave Sec.
PRI Sec.

31. Cardiac Conduction: QRS Complex
P Wave Sec.
PRI Sec.
QRS Sec.

32. Analyzing a Rhythm Strip

33. Dysrhythmia Interpretation: 5 Step Approach
Step 1: What is the rate?
Step 2: Is the rhythm regular or irregular?
Step 3: Is the P wave normal?
Step 4: P-R Interval/relationship?
Step 5: Normal QRS complex?
Listed are the 5 steps to ECG interpretation. When interpreting the ECG it is
important to follow the 5 steps to avoid what is known as “Pattern Recognition”
whereby the interpreter assumes a rhythm is of one type by just looking at it
whereas the rhythm would be identified correctly if the steps were followed.
Use this system repeatedly throughout this presentation and following practice to aid students comfort level in identifying ECG’s.

34. Step 1- Rate
Method 1
Count the number of R waves for a six second interval and multiply by ten.
6 sec
3 sec
3 sec
Points to consider:
reliable only when rhythm is regular
good for fast or slow rates
(can be used for regular & irregular)

35. Step 1 - Rate
Method 2: Count the number of 5mm squares and divide into 300 (or memorize)
300
150
100 75 60 50 43 37 33
30 … slow
Points to consider:
start count where QRS complex touches large line
reliable for regular rhythms only
-not recommended for bradycardic rhythms

36. Step 1 - Rate
RATE:
Tachycardia exists if the rate is greater than 100 beats/min.
Bradycardia exists if the rate is less than 60 beats/min.

37. Step 2 - Rhythm
RHYTHM:
Determine if the ventricular rhythm is regular or irregular (pattern to irreg.?)
R-R intervals should measure the same
P-P intervals should also measure the same

38. Step 2 - Rhythm REGULAR IRREGULAR
Measure the R to R intervals to determine if the rhythm is regular in nature.
It is acceptable to allow for a difference of + or – one small square when
determining regularity of the rhythm
Points to consider:
regular rhythms are produced by natural pacemakers
regularly irregular rhythms are significant of heart blocks
-fast rhythms are difficult to determine if a regular pattern exists
IRREGULAR

39. STEP 2 - Rhythm Example
Irregularly Irregular

40. STEP 3 – Is the P Wave Normal
Identify and examine P waves:
Present?
Appearance?
Consistency?
Relation to QRS?

41. Associated with a QRS Complex?
STEP 3 - Is the P Wave Normal
Normal
P wave with no QRS complex
Same Shape
P waves that appear to be the same shape indicate that the impulse which
generated them most likely came from the same place.
Associated with a QRS Complex?

42. PR Interval/Relationship
STEP 4 –
PR Interval/Relationship
Consistent PRI of <.20 secs is normal,
lengthened or variant PRI’s could indicate an AV block
Look for a marraige of P waves to QRS-T complexes. Normal complexes
will always have the components as in the diagram. Look for both P waves
with no corresponding QRS-T complexes as well as QRS-T complexes with no
associated P wave.
The P-R Interval is the time required for the impulse to travel through the AV
node. Impulses generated in the atria should take between 0.16 to 0.20 seconds
to travel through the AV node. Any delay of > 0.20 seconds is significant of a
conduction delay through the AV Node.

43. STEP FIVE –QRS DURATION
A narrow QRS complex (< 0.12), indicates the impulse has followed the normal conduction pathway
A widened QRS complex (> 0.12), may indicate the impulse was generated somewhere in the ventricles
Measure from the first deflection (+ve or –ve) to where the QRS complex
comes back to the isoelectric line. The normal range for the QRS width is
0.8 to 0.12 seconds or < 3 small squares
You can say with certainty that if the QRS complex is narrow the inpulse had
a supraventricular origin. If on the other hand the QRS comlex is wide, the
impulse was either generated in the ventricles or was aberrently conducted. In
either case, the normal specialiszed pathways where not used thus a widened
wave.

44. REMEMBER!!! Use a systematic approach Go through all the steps
Take your time!
Compare with your characteristics list
Interpret the dysrhythmia

45. QUESTIONS?

46. Education Subcommittee
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Well Done!
Education Subcommittee