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CHAPTER 13

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  1. CHAPTER 13 The Standard 12-ECG System

  2. 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. 13-1. 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. 13-2. Leads I, II, and III axes form Einthoven’s triangle.

  8. Einthoven’s Triangle Around the Heart • Fig. 13-3. Einthoven’s triangle around the heart.

  9. Einthoven’s Triangle Around the Heart • Fig. 13-4. 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. 13-5. The frontal plane and the limb leads.

  11. PRECORDIAL(CHEST) LEADS

  12. Electrodes and Precordial Leads • Fig. 13-6. (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. 13-7. The axis of the six precordial leads.

  14. Horizontal Plane and Its Leads • Fig. 13-8. The horizontal plane and its leads.

  15. Electrodes for the Monitoring System MCL • Fig. 13-9. The position of the electrodes for the monitoring system MCL.

  16. THE ECG PAPER

  17. ECG Monitoring Paper • Fig. 13-10. The ECG monitoring paper, with the blocks enlarged to illustrate the minimum units of measurement.

  18. 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. 13-10. The ECG monitoring paper, with the blocks enlarged to illustrate the minimum units of measurement.

  20. ECG Monitoring Paper • Fig. 13-11. 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. 13-12. Normal ECG configurations.

  22. ECG Configuration • Fig. 13-13. 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. 13-14. (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. 13-15. (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. 13-16. (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. The U Wave • Its origin and mechanism are not known • Often prominent in certain • Electrolyte disturbances • Medications • Heart diseases

  32. The U Wave • Fig. 13-17. 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

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