ECG LEADS

introduction The heart produces electrical currents The body acts as a conductor of electricity Electrodes are able to measure the voltages of the cardiac current

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

Inroduction 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 I + III = ?

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

Einthoven’s triangle Lead I = Difference in voltage between LA and RA Lead II = LL minus RA Lead III = LL minus LA RALA LL

lead i The LA electrode detects electrical voltages of the heart that are transmitted to the left arm The RA electrode detects 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 points horizontally. Its left pole (LA) is postive and its right pole (RA) is negative. Therefore, lead I = LA minus RA

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

Limb leads Add the voltage in lead I to that in lead III and you get the volatage in lead II. I = +2 III = +5 II = +7

Augmented limb (extremity) leads Record the electrical voltages at one location rather than relative to the voltage at another electrode

Augmented limb leads aVR + aVL + aVF = 0

Limb leads

Frontal plane Limb leads

Electrode and Lead are not the same thing.

chest leads V1 to V6 unipolar horizontal plane

Electrode placement 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.

Chest 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