1. Electrocardiogram (ECG/EKG)
Is a recording of electrical activity of heart conducted thru ions in body to surface
Fig 13.22a
13-60

2. Normal conduction pathway:
SA node -> atrial muscle -> AV node -> bundle of His -> Left and Right Bundle Branches -> Ventricular muscle

3. Types of ECG Recordings
Bipolar leads record voltage between electrodes placed on wrists & legs (right leg is ground)
Lead I records between right arm & left arm
Lead II: right arm & left leg
Lead III: left arm & left leg

4. Fig b

5. ECG Leads The standard ECG has 12 leads: 3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the viewpoint from which it looks at the heart.

6. The 12-Lead System
The most commonly used clinical ECG-system, the 12-lead ECG system, consists of the following 12 leads, which are:

7. Standard Limb Leads

8. Augmented Limb Leads

9. Precordial Leads
Adapted from:

10. All Limb Leads

11. Elements of the ECG: P wave: Depolarization of both atria;
Relationship between P and QRS helps distinguish various cardiac arrhythmias
Shape and duration of P may indicate atrial enlargement
PR interval: from onset of P wave to onset of QRS
Normal duration = sec ( ms) (3-4 horizontal boxes)
Represents atria to ventricular conduction time (through His bundle)
Prolonged PR interval may indicate a 1st degree heart block
QRS complex: Ventricular depolarization
Larger than P wave because of greater muscle mass of ventricles
Normal duration = seconds
Its duration, amplitude, and morphology are useful in diagnosing cardiac arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc.
Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are abnormal and may represent MI

12. ST segment:
Connects the QRS complex and T wave
Duration of sec ( msec
T wave:
Represents repolarization or recovery of ventricles
Interval from beginning of QRS to apex of T is referred to as the absolute refractory period
QT Interval
Measured from beginning of QRS to the end of the T wave
Normal QT is usually about 0.40 sec
QT interval varies based on heart rate

13. P wave Elements of the ECG:
Depolarization of both atria;
Relationship between P and QRS helps distinguish various cardiac arrhythmias
Shape and duration of P may indicate atrial enlargement

14. QRS complex: Represents ventricular depolarization
Larger than P wave because of greater muscle mass of ventricles
Normal duration = seconds
Its duration, amplitude, and morphology are useful in diagnosing cardiac arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc.
Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are abnormal and may represent MI

15. PR interval: From onset of P wave to onset of QRS
Normal duration = sec ( ms) (3-4 horizontal boxes)
Represents atria to ventricular conduction time (through His bundle)
Prolonged PR interval may indicate a 1st degree heart block

16. T wave: Represents repolarization or recovery of ventricles
Interval from beginning of QRS to apex of T is referred to as the absolute refractory period

17. ST segment: QT Interval Connects the QRS complex and T wave
Duration of sec ( msec
QT Interval
Measured from beginning of QRS to the end of the T wave
Normal QT is usually about 0.40 sec
QT interval varies based on heart rate

19. Fig b

20. Fig c

21. Fig d

24. Fig g

25. The normal electrocardiogram