The document describes the electrocardiogram (ECG or EKG), which measures electrical activity of the heart. It notes that the ECG waveform consists of P waves from atrial depolarization, QRS complex from ventricular depolarization, and T waves from ventricular repolarization. It explains that the ECG represents both depolarization and repolarization waves generated by the heart during each heartbeat. It provides details on normal ECG intervals and how to analyze ECG rhythms.

1. The electrocardiogram
 ECG or EKG
 The ECG is a measurement of the sum total of
electrical activity generated by the heart
measured from the surface of the body
 An electrical record of the heart’s activity
 It is one of the most valuable diagnostic tools for
the recognition of a large variety of cardiac
disorders

2. Characteristics of the normal electrocardiogram
 The normal electrocardiogram is composed
of:
 P wave: is caused by electrical potentials
generated when the atria depolarize before
atrial contraction begins
 QRS complex: is caused by potentials
generated when the ventricles depolarize
before contraction
The P wave and the components of the QRS
complex are depolarization waves

3.  T wave: is caused by potentials generated as
the ventricles recover from the state of
depolarization. the T wave is known as a
repolarization wave
 The electrocardiogram is composed of both
depolarization and repolarization waves.

4. The atrial repolarization wave, known as the
atrial T wave, is usually obscured by the much
larger QRS complex. For this reason, an atrial T
wave seldom is observed in the
electrocardiogram

5. The “PQRST”
 P wave - Atrial
depolarization
• QRS - Ventricular
depolarization
• T wave - Ventricular
repolarization

6. Depolarization Waves Versus Repolarization Waves
In figure (A) depolarization,
The first half of the fiber has
already depolarized, while
the remaining half is still
polarized
The left electrode on the
outside of the fiber is in an
area of negativity, and the
right electrode is in an area
of positivity, this causes the
meter to record positive
When depolarization has
reached half way mark the
record risen to maximum
positive value

7. Depolarization Waves Versus Repolarization Waves
In figure (B) depolarization
has extended over the entire
muscle fiber, and the
recording to the right has
returned to the zero baseline
because both electrodes are
now in areas of equal
negativity. The completed
wave is a depolarization wave
because it results from spread
of depolarization along the
muscle fiber membrane

8. Depolarization Waves Versus Repolarization Waves
In figure (C) shows halfway
repolarization of the same
muscle fiber, with positivity
returning to the outside of
the fiber. At this point, the
left electrode is in an area
of positivity, and the right
electrode is in an area of
negativity
Consequently, the
recording, as shown to the
right, becomes negative

9. Depolarization Waves Versus Repolarization Waves
In figure (D) the muscle
fiber has completely
repolarized, and both
electrodes are now in areas
of positivity, so that no
potential difference is
recorded between them
This completed negative
wave is a repolarization
wave because it results
from spread of
repolarization along the
muscle fiber membrane

10. Relation of ventricle action potential to the
QRS and T waves in the electrocardiogram
 No potential is recorded in the
electrocardiogram when the
ventricular muscle is either
completely polarized or completely
depolarized
 Only when the muscle is partly
polarized and partly depolarized
does current flow from one part
of the ventricles to another
part, and therefore current also
flows to the surface of the body
to produce the electrocardiogram

11.  The time of the onset of the P wave to the onset
of the QRS complex is termed as PR interval. It
represent the conduction time from the atrial to
the ventricle
 The time from the beginning of the Q wave to
the end of the S wave is called the QRS interval.
It indicates the time taken by the impulse to
separate to the two ventricles

12.  The time from the beginning of the Q wave to
the end of T wave is called the QT interval. It
represent the total electrical activity of
ventricles
 The line between the QRS complex and T wave
is called ST segment. It represent the time
between completion of depolarization and onset
of repolarization

13.  The time interval from the apex of one R
wave to the next R wave is called R-R interval
 R-R interval is related to the heart rate or rate
of ventricular contraction
 The time interval from the beginning of one P
wave to the beginning of the next P wave is
called P-P interval

14. Vertical Axis = Voltage
 Vertical axis represents voltage on the EKG
 One small box (1 mm) represents 0.10 mV

15. Horizontal Axis = Time
 1 small (1 mm) box = 0.04 seconds (40 ms)
 1 large (5 mm) box = 0.20 seconds (200 ms)
 5 large (5 mm) boxes = 1 second (1000 ms)
 15 large (5 mm) boxes = 3 seconds and is
marked on EKG paper

16. The ECG Paper
 Horizontally
 One small box - 0.04 s
 One large box - 0.20 s
 Vertically
 One large box - 0.5 mV

17. The ECG Paper
3 sec 3 sec
 Every 3 seconds (15 large boxes) is marked by
a vertical line.
 This helps when calculating the heart rate.
NOTE: the following strips are not marked
but all are 6 seconds long.

18. Rhythm Analysis
 Step 1: Calculate rate.
 Step 2: Determine regularity.
 Step 3: Assess the P waves.
 Step 4: Determine PR interval.
 Step 5: Determine QRS duration.

19. Step 1: Calculate Rate
3 sec 3 sec
 Option 1
 Count the # of R waves in a 6 second rhythm
strip, then multiply by 10.
Interpretation?
9 x 10 = 90 bpm

20. Step 1: Calculate Rate
R wave
 Option 2
 Find a R wave that lands on a bold line.
 Count the # of large boxes to the next R wave. If
the second R wave is 1 large box away the rate is
300, 2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc.
(cont)

21. Step 1: Calculate Rate
3 1 1
0 5 0 7 6 5
0 0 0 5 0 0
 Option 2
Interpretation?
Approx. 1 box less than
100 = 95 bpm

23. What is the heart rate?

24. Step 2 : Determine Regularity
 Regular: If the difference between the longest
R-R interval in the ECG and the shortest R-R
interval is less than 0.12 second
 Irregular: If the difference between the
longest R-R interval in the ECG and the
shortest R-R interval is greater than 0.12
second

25. Step 2: Determine regularity
R R
 Look at the R-R distances (using a caliper or
markings on a pen or paper).
Interpretation?
Regular

26. Step 3: Assess the P waves
 Are there P waves?
 Do the P waves all look alike?
 Do the P waves occur at a regular rate?
 Is there one P wave before each QRS?
Interpretation?
Normal P waves with 1 P
wave for every QRS

27. Step 4: Determine PR
interval
 Normal: 0.12 - 0.20 seconds.
(3 - 5 boxes)
Interpretation?
0.12 seconds

28. Step 5: QRS duration
 Normal: 0.04 - 0.12 seconds.
(1 - 3 boxes)
Interpretation?
0.08 seconds

29. Rhythm Summary
 Rate 90-95 bpm
 Regularity regular
 P waves normal
 PR interval 0.12 s
 QRS duration 0.08 s
Interpretation?
Normal Sinus Rhythm