12 Lead Basics

Objectives

• Coronary Artery Anatomy• What the Leads See• Lead Placement• Skin Preparation

Coronary Artery Anatomy

• The 12 lead shows which area of the heart is ischemic or damaged

• This corresponds to the artery that is occluded

Coronary Artery Anatomy

• Right Coronary Artery

• Supplies• Right ventricle,

inferior and posterior wall

• SA and AV nodeRight Coronary Artery

Right Ventricle

Inferior Wall

Coronary Artery Anatomy• Left Main

Coronary Artery• Left Anterior

Descending and Circumflex arteries branch off the Left Main

• Occlusion of the left main has very poor prognosis

Left Main Coronary Artery

Left Anterior Descending

Coronary Artery Anatomy

• Left Anterior Descending

• Supplies• Anterior and

Septal wall of the left ventricle

Left Anterior DescendingAnteroseptal

Coronary Artery AnatomyPosterior view of heart and arteries

Posterior wall

Lateral wall

• Left Circumflex Artery

• Supplies• Posterior wall• Lateral wall• Inferior wall –

in 10% of the population

Normal 12 Lead

• This an example of a 12 lead that the Zoll E series will generate• The 12 lead only provides a view of the left ventricle, the right ventricle

and posterior wall is not seen with a 12 lead• To view the right ventricle or posterior wall a 15 lead ECG would need

to be done – we are not covering this or doing this in the field at this time

12 Lead ECG• Limb Leads (I, II, III, aVR, aVL, aVF)

• 3 bipolar leads (I, II, III)• 3 unipolar leads (aVR, aVL, aVF)• Place electrodes on the limbs if there is a 12

lead in the patient’s future – highly preferable to torso placement

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

12 Lead ECG• Chest Leads (V1, V2, V3, V4, V5, V6)

• 6 unipolar electrodes• Electrodes are placed on the chest• Preparing the skin improves tracing (more about

that later)

V1

V2

V3

V4

V5

V6

I aVR

aVL

aVF

II

III

Limb Lead Placement

• Place leads on limbs

• Away from major muscles or arteries

• Have patient remain still during 12 lead acquisition (to reduce artifact)

Chest Lead Placement• V1 is placed in the 4th

intercostal space to the right of the sternal boarder– To find the 4th intercostal

space feel for the clavicle – Just below the clavicle is the

2nd rib, then the 3rd and 4th

rib – Between the 4th rib and the

5th rib is the 4th intercostal space

• V2 is placed to the left of the sternal boarder in the 4th intercostal space

Chest Lead Placement

• V4 is placed next in the 5th

intercostal space in the mid-clavicular line– Find the half way mark on

the left clavicle and move down one rib so V4 is between the 5th and 6th ribs

• V3 is placed after V4 and is simply placed in between V2 and V4 either on the 5th rib or in the 5th

intercostal space

Chest Lead Placement

• V5 is placed in the 5th

intercostal space and the anterior axillary line– To find the anterior axillary

line lay the patient’s left arm at their side and follow the crease line in their armpit down the front of their chest

• V6 is placed in the 5th

intercostal space in the mid-axillary line

Chest Lead Placement

V1 V2

V3

V4 V5 V6

V1: 4th intercostal space to the right of the sternumV2: 4th intercostal space to the left of the sternumV3: directly between V2 and V4V4: 5th intercostal space at the left mid-clavicular lineV5: level with V4 at the anterior axillary lineV6: level with V5 at the mid-axillary line

Skin Prep

• Dry moist skin

• Clip or shave excess hair

• Abrade dead skin with skin prep tape or dry 4x4 gauze

• These measures improve the 12 lead tracing

Inferior Wall

• II, III, aVF– View from Left Leg ⊕– inferior wall of left ventricle

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Inferior Wall

Inferior Wall

• Posterior View– portion resting on diaphragm– ST elevation in leads II, III, aVF

suspect inferior injury

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Lateral Wall

• I and aVL– View from Left Arm ⊕– lateral wall of left ventricle

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Lateral Wall

• V5 and V6– Left lateral chest– lateral wall of left ventricle

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Lateral Wall

• I, aVL, V5, V6– ST elevation

suspect lateral wall injury

Lateral Wall

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Anterior Wall• V3, V4

– Left anterior chest– ⊕ electrode on anterior chest

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Anterior Wall

• V3, V4– ST segment elevation

suspect anterior wall injury

Anterior Wall

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Septal Wall

• V1, V2– Along sternal borders– Look through right ventricle &

see septal wall

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Septal

• V1, V2– ST segment elevation

suspect septal wall injury– septum is left ventricular

tissue

Septal Wall

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Remember to SAIL through it!

Septal leads: V1 and V2

Anterior leads: V3 and V4

Inferior leads: II, III, aVF

Lateral leads: I, aVL, V5 and V6

What about aVR?

• aVR does not face the epicardial surface so it does not provide information regarding ischemia

• aVR is therefore not used for identification of STEMI

I aVR

aVL

aVF

II

III

V1

V2

V3

V4

V5

V6

Thank You for participating in Sunnybrook – Osler Centre for

Prehospital Care online education!

If you have any questions please bring them with you to class!