1. 5
The Electrocardiogram

2. The Electrocardiogram
Objectives
Define the term electrocardiogram
Describe the basics of EKG monitoring
List the types of EKG leads
Discuss the relevance of Einthoven’s
triangle
Identify and explain the grids and markings on a representative strip of EKG graph paper

3. The Electrocardiogram
Objectives (continued)
Describe the relationship of the following EKG waveforms to the electrical events in the heart
P wave
PR interval
QRS complex
ST segment
T wave

4. The Electrocardiogram
Graphic representation of the electrical activity of the heart
Electrocardiograph
Machine used to record the electrocardiogram, or EKG machine
EKG
Graphic tracing of electrical activity of the heart, not mechanical activity

5. The Electrical Basis of the EKG
Electrical activity is sensed by electrodes placed on the skin surface
Recorded in the form of an electrocardiogram
Cardiac monitor depicts electrical impulses on monitor screen or oscilloscope

6. The Electrical Basis of the EKG
Electrical impulses present on the skin surface are very low voltage; impulses are amplified by an EKG machine
The printed record of the electrical activity of the heart is called a rhythm strip or an EKG strip

7. EKG Leads Electrode Leads
An adhesive pad that contains conductive gel and attaches to patient’s skin
Leads
How electrodes are connected to the cardiac monitor
3 leads must have a positive, a negative, and a ground

10. EKG Leads

11. EKG Leads

12. EKG Leads

13. EKG Leads Einthoven’s triangle
Imaginary inverted triangle formed around heart by proper placement of bipolar leads
Top formed by lead I, right side formed by lead III, and left side formed by lead II
Each lead represents a different look at, or view, of the heart

14. EKG Graph Paper Leaves the machine at constant speed of 25 mm/s Time
Measured on horizontal line
Amplitude or voltage
Measured on vertical line on graph paper

15. EKG Graph Paper Electrocardiographic Paper divided into small squares
1 mm in width
Time interval of 0.04 seconds

16. EKG Graph Paper Electrocardiographic paper
Darker lines divide paper every fifth square
Vertically and horizontally
Large squares measure
5 mm in height and width
Represents time interval of 0.20 seconds
Five small squares in each large square

17. EKG Waveforms
Wave or waveform refers to movement away from the baseline or isoelectric line (beginning and ending of all waves)
Positive deflection
Above isoelectric line
Negative deflection
Below isoelectric line

18. EKG Waveforms
Electrical impulse leaves SA node, produces waveform on graph paper
One complete cardiac cycle = P, Q, R, S, (QRS complex) and T wave

19. P Wave First wave produced by electrical impulse from SA node
Smooth, rounded upward deflection
Depolarization of left and right atria
0.10 seconds in length

20. PR Interval
Time impulse travels from SA node through internodal pathways in atria toward ventricles
Time interval from start of P wave to start of QRS
seconds in length

21. QRS Complex Consists of Q, R, and S waves
Represents conduction of impulse from bundle of His through ventricular muscle
Ventricular depolarization

22. QRS Complex Q wave R wave S wave
First downward deflection
R wave
First upward deflection
Largest deflection seen in lead I and II
S wave
Downward deflection after R wave
Measures less than 0.12 seconds (3 small boxes)

23. ST Segment
Time interval during which ventricles depolarized and repolarization of ventricles begin
Isoelectric or consistent with baseline

24. T Wave Follows ST segment Represents ventricular repolarization
Slightly rounded, positive deflection
Resting phase of cardiac cycle

25. Summary of EKG Waveforms
P wave
Atrial depolarization
QRS complex
Ventricular depolarization, atrial repolarization
T wave
Ventricular repolarization