ECG LEADS Chapter 3

introduction The heart produces electrical currents The body acts as a conductor of electricity

introduction An ECG is a recording of the electrical activity of the heart Different “views” of the heart can be recorded using different electrodes

INtroduction Electrodes are able to measure the voltages of the cardiac current

Electrodes

V1: Fourth intercostal space to the right of the sternum. V2: Fourth intercostal space to the Left of the sternum. V3: Directly between leads V2 and V4. V4: Fifth intercostal space at midclavicular line. V5: Level with V4 at left anterior axillary line. V6: Level with V5 at left midaxillary line. (Directly under the midpoint of the armpit)

Electrode placement

Electrode and Lead are not the same thing.

Leads 12 possible leads Six limb (extremity) leads Bipolar leads: I, II, and III Unipolar leads: aV R, aV L, aV F Six chest (precordial) leads

limb leads Electrodes Right arm Left arm Left leg Right leg (ground)

lead i LA = electrical voltages of the heart that are transmitted to the left arm RA = electrical voltages of the heart that are transmitted to the right arm The electrocardiograph sustracts RA from LA and the difference appears as lead I.

lead i Lead one ‘travels’ horizontally. Its left pole (LA) is postive and its right pole (RA) is negative. Therefore, lead I = LA minus RA Shows a positive wave when an impluses moves towards the left arm, negative wave when an impuse moves away from the left arm.

Lead II Lead II points downward diagonally Lower pole (LL) is positive and upper pole (RA) is negative. Lead II = LL minus RA

Lead III Lead III points downward diagonally Lower pole (LL) is positive and upper pole (LA) is negative. Lead III = LL minus LA

Bipolar Leads

Unipolar or Augmented limb leads Record the electrical voltages at one location rather than relative to the voltage at another electrode

limb leads aVR + aVL + aVF = 0

Bipolar leads & Unipolar (or augmented) leads Frontal plane Limb leads

chest leads V1 to V6 unipolar horizontal plane front to back

Chest Leads

ALL 12 leads Frontal Plane Horizontal Plane

Monitor leads 12 leads are not always necessary Sample of a monitor lead V1 (positive) Right shoulder (negative) Left shoulder (ground)

Holter Monitors