Chapter03

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Chapter 3 : 

Chapter 3 Individual Vectors

Vectors : 

Vectors A vector is a diagrammatic way to show:  Strength of electrical impulse  Direction of electrical impulse Each cell gives rise to its own electrical impulse. Each varies in intensity and direction. The heart has a few million individual vectors.

Adding and Subtracting Vectors : 

Adding and Subtracting Vectors Vectors:  Represent amounts of energy and direction  Add up when going in same direction    Cancel each other out if they point in opposite directions   > At an angle, they add or subtract energy and change directions when they meet

Electrical Axis of the Heart : 

Electrical Axis of the Heart The final vector: Sum of all ventricular vectors = electrical axis of the heart Each wave and segment has its own respective vector: P wave vector T wave vector ST segment vector QRS vector ECG: Measurement of vectors as they pass under an electrode

Electrodes and Waves : 

Electrodes and Waves Positive impulse moving away from electrode is converted into downward wave Positive impulse moving toward electrode is converted into upward wave An ECG shows positive deflection for energy coming toward it, negative deflection for energy moving away from it

Leads: Pictures of the Heart : 

Leads: Pictures of the Heart  Electrodes placed at certain angles to the main axis give: Multiple pictures of the heart 3-D perspective Information about where pathologic processes occur

Lead Placement (1 of 2) : 

Lead Placement (1 of 2) Limb leads (extremity leads) Right arm (RA) Left arm (LA) Right leg (RL) Left leg (LL) Placed at least 10 cm from heart Insert fig 3-7 left-hand part only

Lead Placement (2 of 2) : 

Lead Placement (2 of 2) Precordial leads (chest leads) V1 and V2—Each side of sternum at 4th intercostal space V3, V4, V5, and V6 * Follow diagram for placement

How the Machine Manipulates Leads : 

How the Machine Manipulates Leads ECG reads positive and negative poles of limb electrodes Produces leads I, II, and III Insert fig 3-8

Hexaxial System (1 of 2) : 

Hexaxial System (1 of 2) A system of analyzing vectors Coronal cut: Cuts the center of the heart along a plane, creating a front half and a back half Gives rise to the six limb leads: I, II, III, aVR, aVL, and aVF Leads are 30° apart

Hexaxial System (2 of 2) : 

Hexaxial System (2 of 2) Leads are 30° apart

Precordial System : 

Precordial System Precordial leads are on a plane perpendicular to the limb leads. This is called a transverse plane. Result is cross-section: six leads produced by six chest electrodes

The Heart in Three Dimensions : 

The Heart in Three Dimensions Cutting the heart in both coronal and transverse planes gives a 3-D picture of the heart.

Leads in Three Dimensions : 

Leads in Three Dimensions Leads that face the bottom of the heart: II, III, and aVF V3 and V4 are most anterior I, aVL, V5, and V6 are lateral leads

Localizing an Area: Inferior Wall : 

Localizing an Area: Inferior Wall Leads II, III, and aVF represent the inferior wall of the heart

Localizing Other Areas : 

Localizing Other Areas Insert fig 3-15

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