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CHAPTER 13

CHAPTER 13. The Standard 12-ECG System. 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. ECG Lead Systems. Standard 12-ECG System. Each lead:

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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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