2. ecg basics leads

Basics of ECG Leads - Simplified approach

1. ELECTROCARDIOGRAM EASY LEARNING APPROACH Dr. Harshil J. Shah Resident of Medicine Department of General Medicine P.D.U. Medical College, Rajkot

2. ECG Basics: Leads

3. Understand the basic concept of an ECG lead, Learning Objectives: Know the 12 conventional ECG leads, and the angles from which each lead views the heart’s electrical activity, Know the proper location of the 10 conventional ECG electrodes. Correlate specific groups of leads with anatomic regions of the heart.

4. A lead is a view of the voltage between two points (known as poles) as a function of time. The positive pole for each lead is marked by a single recording electrode on the body. The negative pole for each lead is marked by either a single recording electrode, or a virtual electrode known as a “central terminal” which averages input from multiple other electrodes. A lead is not the same as an electrode. What is a Lead?

5. STANDARD OR BIPOLAR LIMB LEADS (LEAD I, II, III)

6. AUGMENTED OR UNIPOLAR LIMB LEADS (aVR, aVL, aVF)

7. PRECORDIAL LEADS (V1 – V6)

8. RHYTHM STRIPS Usually V1, Lead II, V5

9. Willem Einthoven invented the first practical ECG in 1903. Attached recording electrodes to the right arm, left arm, and left leg to create the three standard limb leads. Standard Limb Leads The right leg is used to ground the system. I + III = II EINTHOVEN’S RULE

10. To increase the number of directions from which the heart can be viewed, the ECG machine also uses a “central terminal” . The central terminal is made by connecting the right arm, left arm and eft leg electrodes together. This results in a virtual negative terminal that is composed of the average of the electrical potentials from the 3 limbs. Augmented Limb Leads

11. aVR + aVL + aVF = 0 The ‘a’ stands for augmented . The “ V ” is listed in any lead that uses the central terminal . Augmented Limb Leads

12. aVR + aVL + aVF = 0 The Hexaxial system I + III = II EINTHOVEN’S RULE

13. The Hexaxial system

14. The Hexaxial system III = II - I aVR = - ½ (I + II) aVL = I – ½(II) aVF = II – ½(I) Modern ECG machines only directly measures leads I and II, and calculate the four others.

15. There are 6 leads which examine the heart’s electrical activity in the transverse plane. The positive pole for each is at a location on the anterior or left lateral chest wall. The negative pole for each is the central terminal. The leads are named V1 – V6. V1 V2 V3 V4 V5 V6 PRECORDIAL LEADS

16. PRECORDIAL LEADS V1 V2 V3 V4 V5 V6 POSITION V1 4 th ICS, just right to sternum V2 4 th ICS, just left to sternum V3 Halfway between V2 and V4 V4 5 th ICS, in midclavicular line V5 Halfway between V4 and V6 V6 5 th ICS, in mid axillary line V1 V2 V3 V5 V4 V6

17. Spatial Relationship between leads Frontal plane Transverse plane

18. ANATOMICAL CORRELATIONS Inferior Leads II, III, aVF Septal Leads V1, V2 Anterior Leads V3, V4 Lateral Leads I, aVL, V5, V6 No grouping aVR

19. Inferior Leads II, III, aVF No grouping aVR Septal Leads V1 - V2 Lateral Leads I, aVL, V5-V6 Anterior Leads V3 – V4