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Color-Coded Cables

Placement• Black and white on front limbs– Placed at the elbow region

• Green and Red on back limbs– Placed at the stifle region

• Alcohol, electrode gel, or ECG pads can be used as conduction agents for more accurate readings. If your patient has long hair, it should be shaved at the site of cable placement in order to achieve adequate conduction

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Red/OrangeLeftBackLeg

GreenRightBackLeg

WhiteRightFront

Leg/arm BlackLeft

FrontLeg/arm

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What is a Lead?

• Lead systems allow you to look at the heart from different angles

• Each lead has a positive and negative pole attached to the surface of the skin, which can be used to measure the spread of electrical activity within the heart

• The leads or cables read the electrical activity of the heart between two points

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Leads• Lead I: causes right forelimb to

become a negative pole and left forelimb to become a positive pole

• Lead II: causes right forelimb to become negative and left rear limb to become positive

• Lead III: the left hind limb become a positive pole and the left forelimb becomes a negative pole

• The cables read the electrical activity of the heart between two points

• Selecting specific leads on the ECG machine will cause specific cables to become negative or positive poles

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Leads

• Upward deflection on the ECG-produced when electrical impulses travel towards a positive electrode

• Downward deflection on the ECG-produced when impulses travel toward a negative electrode

• Flat line-produced when there is no electrical spread through the heart

• We only need to use lead II to assess arrhythmias in animals

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ECG Technique Position: Right lateral recumbency;

but the patient may be placed in a natural position (sitting, standing, or resting) in critical cases or for routine monitoring

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Wave Forms

• Connection of the amplifier to selected body parts (usually the limbs) with wires (known as leads) and to a recorder (electrocardiograph), provides a characteristic wave form. The wave form is a recording of the electrical activity of the heart. This wave form recording is the electrocardiogram (ECG)

• Each event has a distinctive waveform

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What are these so called waves and what do they mean?

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P waveThe first upward pulse of the ECG; the P wave is formed

when the atria (the 2 upper chambers of the heart)contract to pump blood into the ventricles.

This is known as Atrial depolarization.Stimulated by the SA Node

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P-R intervalReflects the activation of the

AV node.– Measured from the

beginning of the P wave to the beginning of the Q wave

– Flat portion is due to delay of depolarization at the AV node (allowing time for the ventricles to fill)

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QRS waves (QRS complex)Formed when the ventricles (the two lower chambers of the heart)

are contracting to pump out blood.Q wave is the 1st negative deflectionR wave is the 1st positive deflection

S wave is the negative deflection that follows the R wave

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The ventricles contract (ventricular depolarization) and the atrium expands (atrial repolarization)

QRS Wave Complex

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ST segmentMeasures the end of the contraction of the ventricles to the

beginning of the rest period (this is a pause) before the ventricles begin to contract for the next beat

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T waveThe next slight rising section, the T wave, measures

the resting (relaxation or ventricular repolarization) period of the ventricles. T waves can be positive, negative or

Biphasic (having 2 distinct phases)

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The T Wave is the last wave for each heart beat; it represents ventricular repolarization (relaxation)

The interval between waves is measured in milliseconds

T Wave

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QT Interval• The summation of

ventricular depolarization and repolarization

• Represents ventricular systole– Q-T interval is measured

from the onset of the Q-wave to the end of the T-wave

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RR Interval is used to measure HR

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Calculating Heart Rate

• Use a ruler to determine set length of tracing• Determine how many seconds are

represented in that tracing• Count R-R intervals in that set amount of

tracing and multiply by the time• This will give you the heart rate