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12 Lead ECG Interpretation: The Basics and Beyond

Cindy Weston, DNP, RN, CCRN, CNS‐CC, FNP‐BC

Assistant Professor

Texas A&M Health Science Center

Objectives

• Review the basics of 12 lead electrocardiogram

• Review when to order an ECG

• Identify the 12 most common rhythms and their treatment 

• Identify and initiate treatment for acute myocardial infarction

Disclosures

• No Conflicts

“I struggled with everything cardiac in nursing school.”

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My Tips

• Understand Anatomy

• Take a Systematic Approach

• Ask yourself “Is this clinically significant?”

• Know common arrhythmias

• Know what to do about them

Conduction System

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Action Potential

Intrinsic Rates

SA Node _______ beats/min

AV Node _______ beats/min

Bundle of HIS ____ beats/min

Purkinje Fibers ____ beats/min

60-100

40-60

20-40

20-40

Basic Rhythm 

Depolarization

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Waves & Intervals

• P wave• Atrial depolarization (right then left)

• Usually upright (positive)

• PR interval• 0.12‐0.20 seconds

• Measures start of atrial depolarization to start of ventricular depolarization

Waves & intervals

• QRS wave/interval• Q not always present, R first positive, S negative after R

• Ventricular depolarization

• < 0.10‐0.12

• T wave• Ventricular repolarization

• Usually upright

• May vary based on perfusion, electrolytes, meds

Waves and Intervals

• QT interval• < 0.40 seconds

• Corrected QTc (0.34‐0.43)

• Men <0.47; women < 0.48

• > 0.50  DANGER!!!

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Waves and Intervals

• U wave• Repolarization of Purkinje fibers

• Electrolyte imbalance: hypokalemia, hypercalcemia, digoxin toxicity, use of some antiarrhythmics, congenital long QTc

ST segment

ECG Graph paper

horizontalSm box 0.04 secLg box 0.20 secverticalLg box 0.5mVSm box 0.1mV

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My Systematic Approach

• Rate

• Regularity

• Waves: p,q,r,s,t,u

• Intervals: PR, QRS, QTc

• ST segments

• R wave progression

• Axis: lead I & AVF

RATE

• # QRS 6 second strip x 10

• Memorize: 300, 150, 100, 75, 60, 50 rule

• 1500 / #small boxes between R‐R waves

Regularity

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PQRST(U) waves

Intervals: PR, QRS, QTc

ST Segments

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12 LEAD ECG

12 snapshots of the electrical conduction in the heart

12 Views

• Limb leads give 6 views• I,II,III  (Bipolar)

• AVR, AVL, AVF (unipolar, augmented vector)

• Precordial leads give 6 views• V1, V2, V3, V4, V5, V6

Einthoven’s Triangle

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Precordial chest leads “v” leads

12 Lead ECG

• 3 limb leads (I, II, III)

• 3 Augmented Vector leads (AVR, AVL, AVF)

• 6 Precordial leads (V1‐V6)

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R wave progression

AXIS

Direction of electrical vector during ventricular depolarization

AXIS‐ NORMAL

Left- Wedding RingLead I

Right- Aggie RingLead AVF

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AXIS‐ LEFT Deviation

Left- Wedding RingLead I

Right- NO Aggie RingLead AVF

AXIS‐ RIGHT Deviation

Left- NO Wedding RingLead I

Right- Aggie RingLead AVF

AXIS‐ Extreme Right “no man’s land” 

Left- NO Wedding RingLead I

Right- NO Aggie RingLead AVF

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Hypertrophy: LVH

• Left Axis Deviation

• R wave in AVL exceeds 13 mm

• R wave in V5 or V6 PLUS S wave in V1 or V2 exceeds 35 mm

• “eye ball test”  QRS touch…

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RVH 

RVH

BBB:  Left

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BBB: Right

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12 Common Issues

• Acute Coronary Syndrome

• STEMI

• NSTEMI/Unstable angina

Contiguous Leads

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STEMI

Brown, H. (2014). Synopsis and review of the American College of Cardiology Foundation/American Heart Association 2013 ST-elevation myocardial infarction guideline. AACN Advanced Critical Care, 25(2), 142-150.

Contiguous leads

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Contiguous Leads

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STEMI

Brown, H. (2014). Synopsis and review of the American College of Cardiology Foundation/American Heart Association 2013 ST-elevation myocardial infarction guideline. AACN Advanced Critical Care, 25(2), 142-150.

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STEMI

Brown, H. (2014). Synopsis and review of the American College of Cardiology Foundation/American Heart Association 2013 ST-elevation myocardial infarction guideline. AACN Advanced Critical Care, 25(2), 142-150.

STEMI

Brown, H. (2014). Synopsis and review of the American College of Cardiology Foundation/American Heart Association 2013 ST-elevation myocardial infarction guideline. AACN Advanced Critical Care, 25(2), 142-150.

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ST depression

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T‐wave inversion

Q‐waves

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NPs treating suspected Acute Coronary Syndrome

• Give ASA 325 mg x1

• STEMI• If outpatient EMS transport to ED with notification

• If inpatient‐ prepare for reperfusion (STEMI protocol)

• ST depression/T‐wave inversion/CP• Serial cardiac enzymes

• Serial ECGs

12 Abnormal Rhythms

• Premature Beats

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12 Abnormal Rhythms

• Atrial Fibrillation

Atrial Fibrillation

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Treatment Guidelines• Antiarrhythmic

• Rate Control

• Rhythm Control

Anti‐arrhythmics

Top 12 Abnormal RhythmsAtrial Flutter

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12 Abnormal RhythmsSupraventricular Tachycardia

SVT

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Treatment

• Vagal• Adenosine• Calcium channel blockers

• Digoxin• Beta blockers• Cardioversion

12 Abnormal RhythmsWPW

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12 Abnormal Rhythms

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12 Abnormal Rhythms

12 Abnormal Rhythms

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12 Abnormal Rhythms

12 Abnormal Rhythms

12 Abnormal RhythmsComplete Heart Block