12-Lead 12-Lead ElectrocardiographyElectrocardiography

a comprehensive course

Adam Thompson, EMT-P, A.S.Adam Thompson, EMT-P, A.S.

Lesson

5

The 6-Step MethodThe 6-Step Method

• 1. Rate & Rhythm1. Rate & Rhythm

• 2. Axis Determination2. Axis Determination

• 3. Intervals3. Intervals

• 4. Morphology4. Morphology

• 5. STE-Mimics5. STE-Mimics

• 6. 6. Ischemia, Injury, & InfarctIschemia, Injury, & Infarct

Lesson FiveLesson Five

• STEMISTEMI– ST-Segment Elevated Myocardial InfarctionST-Segment Elevated Myocardial Infarction– ST-Segment Elevation of > 1mm in two contiguous ST-Segment Elevation of > 1mm in two contiguous

leads. leads. – In V2 & V3, ST-Segment elevation must be at least In V2 & V3, ST-Segment elevation must be at least

2mm.2mm.

*The smaller the QRS complex, the more significant minimal ST-*The smaller the QRS complex, the more significant minimal ST-

Elevation is.Elevation is.

Objectives

• Learn how to identify a STEMI

• Learn how to localize the infarcted area

• Apply everything learned thus far

What are Contiguous Leads?What are Contiguous Leads?

• Contiguous leads are leads that look at Contiguous leads are leads that look at the same area of the heart. the same area of the heart.

• They show up on the 12-lead proximal They show up on the 12-lead proximal to each other.to each other.

Lead I

lateral

aVR V1

septal

V4

anterior

Lead II

inferior

aVL

high lateral

V2

septal

V5

low lateral

Lead III

inferior

aVF

inferior

V3

anterior

V6

low lateral

Coronary Circulation

Left Main

Circumflex(LCx)

Left Anterior Descending(LAD)

Right Coronary Artery(RCA)

Coronary Circulation

Right Coronary Artery

(RCA)

Left Circumflex Artery

(LCx)

Left Anterior Descending

(LAD)

•Right Atrium•Inferior Wall•Inferior-Right Ventricle

•Posterior Wall - 85% of population

•Inferior Wall•Isolated Right Ventricle

•Posterior Wall - 15% of population

•Anterolateral•Inferolateral•Posterolateral

•Anterior•Anteroseptal•Anteroseptal-lateral

*Nicknamed “Widow-maker”

Coronary Occlusion

Heart Anatomy

Lateral Wall

Septal

Inferior

Anterior

Heart Anatomy

Epicardium

Endocardium

Myocardium

Ischemia, Injury, Infarct

ST-Elevation

• The most common cause of ST-elevation is not myocardial infarction.

• Less than 50% of STEMI alerts called by paramedics are actually Acute Coronary Syndrome (ACS) patients

ST-Elevation

• ST-Elevation is elevation of the J-Point which causes elevation of the following ST-Segment.

• Elevation is defined as anything above the isoelectric line.

• Find the isoelectric line by locating the TP-Segment.

T P

TP-Segment

ST-Elevation

• The J-Point is where the QRS complex and the ST-Segment meet.J-Point

ST-Segment Morphology

Concave Convex

J-Point J-Point

Evolution of MI

• Insufficient blood supply to the myocardium.– Ischemia, injury or infarction, or all three.

• The branches of coronary arteries arising from the aortic root are distributed on the epicardial surface of the heart.

• These in turn provide intramural branches that supply the cardiac muscle.

• Myocardial ischemia generally appears first.

Evolution of MI

InfarctionIschemia

Injury

Needs O2 Damage from Irreversible lack of O2 damage

Ischemia

• Subendocardial ischemia– Ischemia in this area prolongs local recovery time.

Since repolarization normally proceeds in an epicardial-to-endocardial direction, delayed recovery in the subendocardial region due to ischemia does not reverse the direction of repolarization but merely lengthens it.

Ischemia

• Transmural ischemia

– is said to exist when ischemia extends subepicardially. This process has a more visible effect on recovery of subepicardial cells compared with subendocardial cells. Recovery is more delayed in the subepicardial layers, and the subendocardial muscle fibers seem to recover first.

Ischemia

• Hyperacute T-Waves– Results from subendocardial ischemia– Symmetrical & tall– Wide with blunt peak (unlike Hyperkalemia)– Present for about first 30 min. of AMI

• Inverted T-waves– Results from transmural ischemia

Ischemia

Asymmetrical

Symmetrical

Ischemia

Ischemia-Mimic

Peaked T-Waves

Inverted T-Waves

Hyperkalemia STE-Mimic

Injury

• Injury to the myocardial cells results when the ischemic process is more severe.

• In patients with coronary artery disease, ischemia, injury and myocardial infarction of different areas frequently coexist, producing mixed and complex ECG patterns.

Injury

• ST-Depression– Subendocardial

• ST-Elevation – Subepicardial– Transmural.

Injury

Injury

ST-Depression

ST-Elevation

Injury-Mimic

ST-Elevation

Hyperkalemia STE-Mimic

Infarct

• The term infarction describes necrosis or death of myocardial cells.

• Atherosclerotic heart disease is the most common underlying cause of myocardial infarction.

• The left ventricle is the predominant site for infarction; however, right ventricular infarction occasionally coexists with infarction of the inferior wall of the left ventricle.

Infarct

• During acute myocardial infarction, the central area of necrosis is generally surrounded by an area of injury, which in turn is surrounded by an area of ischemia.

• Various stages of myocardial damage can coexist.

• The distinction between ischemia and necrosis is whether the phenomenon is reversible.

Infarct

• Pathological Q-waves– Wider than 0.04sec / 40ms (1 small box)– Deeper than 25% the height of R-Wave

Reciprocal Changes

• ST-Depression found in leads opposite of those with ST-Elevation is considered to be a reciprocal change. – This is caused by a view from the opposite

direction.

Site Facing Reciprocal

Septal V1, V2 V7, V8, V9

Anterior V3, V4 None

Lateral I, aVL, V5, V6 II, III, aVF

Inferior II, III, aVF I, aVL

Posterior V7, V8, V9 V1, V2

Reciprocal Changes

QuickTime™ and a decompressor

are needed to see this picture.

Inferior Injury

Reciprocal ST-Depression

Location of MI

Inferior Wall

Anterior Wall

Lateral Wall

Septal

Location of MI

Left Ventricle

Right Ventricle

Antero-Septal Wall

• Leads V1 & V2 view the septal wallLeads V1 & V2 view the septal wall

• Leads V3 & V4 view the anterior wallLeads V3 & V4 view the anterior wall

LV

RV

V1 V2 V3V4

V5

V6

Septal Wall

Anterior Wall

• Leads V3 & V4 view the Anterior Wall

LV

RV

V1 V2 V3V4

V5

V6

Anterior Wall

Lateral Wall

• Leads I, aVL, V5 & V6 view the lateral wall

LV

RV

V1 V2 V3V4

V5

V6

Lateral Wall

Inferior Wall

Inferior Wall

Inferior Wall

Inferior Wall

Right Ventricular Wall

• With a proximal occlusion of the RCA, a right ventricular infarct is possible.– Hypotension is most common finding.– Right-sided placement of V3 & V4 can be used to

view the right ventricle for ST-Elevation.• V4R is most sensitive lead for right-sided changes. • QRS complexes and ST-Elevation may be of much

lesser amplitude in right-sided leads.

Right Ventricular Wall

• Hypotension is most common assessment finding with RV-Infarction.– NTG should be used very conservatively– Fluids should be administered if unstable

• ST-Elevation in lead III > than STE in lead II is very specific for RV-Infarction

Right Ventricular Wall

V4V3

Move V3 & V4 to mirrored position on right side of chest to obtain V3R & V4R.

The same can be done for V5 & V6.

Right Ventricular Wall

Always make sure to denote the leads you change.

I aVR V1 V4R

II aVL V2 V7

III aVF V3R V6

Posterior Wall

• Dominant RCA– When the RCA supplies the posterior descending

coronary artery– 85% of people have dominant RCA

• Dominant Circumflex– When LCx supplies the posterior descending

coronary artery– 15% of people have dominant circumflex

Posterior Wall

• The reciprocal leads are V1 & V2• ST-depression in V1 & V2 may actually be

representing ST-elevation of the posterior wall

• Tall R-waves in V1 & V2 may actually be representing pathological Q-waves of the posterior wall

Posterior Wall

V1/V2

To identify a posterior wall MI, a technique commonly taught is to pretend you are looking at the complex upside-down through a mirror

Posterior Wall

Move V4 to V7 - posterior axillary line Move V5 to V8 - midscapularMove V6 to V9 paraspinal

I aVR V1 V7

II aVL V2 V8

III aVF V3 V9

V7, V8, V9

LBBB With MI

Modified Sgarbossa’s criteria• Any concordant ST-Elevation!• ST-Elevation > 25% of depth of preceding S-

Wave = MI– This is an advanced skill, and is completely reliant

on the T-wave discordance found with a LBBB

• This same criteria may be used with paced rhythms

Sgarbossa’s Criteria

Sgarbossa’s Criteria

Other MI Findings

• If ECG print out does not read ***Acute MI***, it is highly unlikely that the capture meets STEMI criteria.– It is possible that the 12-lead is not a true STEMI even with

the “Acute AMI” reading.

• Wellen’s phenomenon - Biphasic or inverted T-waves (Most commonly in V2 & V3), precursor to AMI from LAD stenosis.

Practice

RBBB With MI

Practice

Antero-septal MI

Antero-septal MI

A

B

Practice

Anterior MI

Practice

A

B

Inferior MI

Practice

Inferior MI

Practice

Antero-septal MI

Practice

RBBB, Inferior MI

Practice

Practice

RBBB

No ST-Elevation!

Practice

29 y/o Male

WPW

29 y/o Male

Practice

B

A

Practice

Practice

A

B

R

R

Practice

A

B

R

R

Inferior-Posterior MI

A

B

R

R

Practice

Antero-septal MI

A

B

Practice

Bigeminy Anterior MI

Practice

Antero-septal-lateral MI

Practice Scenarios

“Always consider the company it keeps”

- Dr. Thomas Garcia

Practice Scenario 1

• You respond to an 87 year-old female who states that she awoke with “a fast heart rate”.

• She states that she has had this condition for over 50 years, and denies any pain or dyspnea.

• She has had heart surgery in the past.

Practice Scenario 1

• No abnormal physical exam findings• BP: 156/74 • HR: 124 irregularly irregular• O2 Sat:96% on room air

Practice Scenario 1

Practice Scenario 2

• You respond to a 51 year-old female who reportedly became unconscious and slumped over in a chair.

• Family states that she has been unconscious for 5 minutes.

• She has a history of hypertension and takes Xanax and hydrochlorothiazide.

Practice Scenario 2

• She is flushed and diaphoretic • She is awake but disoriented

• BP: 180/120• HR: 110 Regular • Respirations: 16 • O2 Sat: 95%

Practice Scenario 2

Practice Scenario 3

• You respond to a 94 year-old female in a nursing home.

• She had a syncopal episode per the LPN, and is currently complaining of unlocalized pain.

Practice Scenario 3

• She is pale but dry• BP: 142/57 • HR: 88 • Respirations: 24 • O2 Sat: 88% on High-flow O2

Practice Scenario 3

Practice Scenario 3

Practice

Trigeminal PVCs

Possible Antero-septal Infarct

Trigeminal PVCs

Trigeminal PVCs

Lesson 5

• This concludes lesson 5

• Please review the course materials