1. The Standard 12-ECG System
CHAPTER 13
The Standard 12-ECG System

2. Consists of four limb electrodes and six chest electrodes
Standard 12-ECG System
Consists of four limb electrodes and six chest electrodes
Collectively, view the heart from 12 different positions
Six standard limb leads
Six precordial (chest) leads

3. ECG Lead Systems

4. Standard 12-ECG System Each lead:
Views the electrical activity of the heart from a different angle
Has a positive and negative component
Monitors specific portions of the heart from the point of view of the positive electrode in that lead

5. STANDARD LIMB LEADS

6. Standard Limb Leads
Fig The standard limb leads—leads I, II, III, aVR, aVL, and aVF. Each of the standard limb electrodes can function as either a positive or negative electrode.

7. Einthoven’s Triangle
Fig Leads I, II, and III axes form Einthoven’s triangle.

8. Einthoven’s Triangle Around the Heart
Fig Einthoven’s triangle around the heart.

9. Einthoven’s Triangle Around the Heart
Fig In the normal heart, the dominant electrical current in the heart flows from the base to the apex in a right to left direction.

10. Frontal Plane and Limb Leads
Fig The frontal plane and the limb leads.

11. PRECORDIAL (CHEST) LEADS

12. Electrodes and Precordial Leads
Fig (A) The position of the electrodes on the rib thorax, and (B) the precordial leads as they reflect the surface of the myocardium.

13. Axis of Six Precordial Leads
Fig The axis of the six precordial leads.

14. Horizontal Plane and Its Leads
Fig The horizontal plane and its leads.

15. Electrodes for the Monitoring System MCL
Fig The position of the electrodes for the monitoring system MCL.

16. THE ECG PAPER

17. ECG Monitoring Paper
Fig The ECG monitoring paper, with the blocks enlarged to illustrate the minimum units of measurement.

18. Large square = 5 sm. Sq. = 0.20 sec. Speed = 5 lg. Sq./sec.
ECG Paper
Small square = 0.04 sec.
Large square = 5 sm. Sq. = 0.20 sec.
Speed = 5 lg. Sq./sec.
Vertical portion of sm. Sq. =
Amplitude (voltage) of 0.1 millivolt (mV)
1 millimeter (1mm) in distance

19. ECG Monitoring Paper
Fig The ECG monitoring paper, with the blocks enlarged to illustrate the minimum units of measurement.

20. ECG Monitoring Paper
Fig ECG monitoring paper showing markers indicating 3- and 6-second intervals. There are 15 blocks in 3 seconds and 30 blocks in 6 seconds.

21. Normal ECG Configurations
Fig Normal ECG configurations.

22. ECG Configuration
Fig The duration of the normal ECG configuration.

23. The P Wave
Represents atrial depolarization
Usually symmetrical and upright

24. The PR Interval
Represents the total atrial electrical activity

25. The QRS Complex
Represents the ventricular depolarization

26. The QRS Complex
Fig (A) Q waveform of the QRS. (B) R waveform of the QRS complex. (C) S waveform of the QRS complex.

27. The ST Segment
Represents the time between ventricular depolarization and repolarization

28. ST Segment Highlighted within Cardiac Complex
Fig (A) The ST segment highlighted within cardiac complex. Note variation. (B) ST above the baseline. (C) Shows 3 mm ST segment increase. (D) shows 3 mm ST segment decrease.

29. The T Wave
Represents ventricular repolarization, rest, and recovery

30. The T Wave
Fig (A) T wave shows ventricular depolarization. (B) The T wave with ST segment elevation. (C) Measuring an inverted T wave and with ST segment depression.

31. Its origin and mechanism are not known Often prominent in certain
The U Wave
Its origin and mechanism are not known
Often prominent in certain
Electrolyte disturbances
Medications
Heart diseases

32. The U Wave
Fig The U wave highlighted (arrow) within the cardiac complex.

33. Summary of Normal ECG Configurations and Heart Activity

34. Summary of Normal ECG Configurations and Heart Activity
Table 13-2