ECG for Interns
UCI Internal Medicine Mini-Lecture
Learning Objectives
• Basics of EKG
• Establish Consistent Approach to Interpreting ECGs
• Rate, rhythm, axis, identifying ischemia
• Review Essential Cases for New Interns
• Provide Additional Resources for Future Learning
Basics of EKG: Einthoven’s Triangle and
Vectors
+AVR
Why is lead II often so
important?
->you can see the heart’s
depolarization vector is in
the same axis as lead II!
->this means that in normal
conduction, the QRS
should be upright in lead II
+AVL
+AVF
ECG Interpretation
What is your approach to reading an ECG?
•Rate
•Rhythm
•Axis
•Hypertrophy
•Intervals
•P wave
•QRS complex
•ST segment – T wave
Rate
Square Counting: 300-150-100-75-60-50-42A
Count QRS in 10 second rhythm strip x 6  use this method to
determine rate when rhythm is irregular (e.g., atrial fibrillation)
Rhythm
Look at the rhythm strip below and answer the questions
•
Are P waves present?
• yes
•
Is there a P wave before every QRS complex and a QRS complex after
every P wave?
• yes
•
Are the P waves and QRS complexes regular?
• yes
•
Is the PR interval constant?
• yes
Yes to all these
questions, so this is
normal sinus rhythm!
Axis
•Axis is the general flow of electricity as it passes through
the heart
 Look at the main direction of the QRS complex in leads I and AVF
I
AVF
Axis
+
+
normal
+
-
LAD
-
+
RAD
QRS Duration
• Normal QRS is < 120 ms
• Prolonged QRS duration (>120ms) is seen in bundle
branch blocks (BBB).
• This is a result of abnormal conduction through the
bundle branches or fascicles in the electrical conduction
system
• Different criteria for left and right bundle branch blocks
but know the general morphology of each.
Left and right bundle
branch blocks
Left BBB –
•
• Dominant S wave in V1 (‘W’-shaped)
• Broad, notched (‘M’-shaped) R wave in V6
•
Right BBB –
• Tall R wave in V1 (‘M’-shaped)
• Wide, slurred S wave (‘W’-shaped) in V6
QRS complex
Poor R Wave Progression in V1 to V6: suggests prior anterior MI
•Pathologic Q wave = previous MI.
-Q wave amplitude 25% or more of the subsequent R wave OR
- Q wave > 0.04 s in width + > 2 mm in amplitude in more than one lead
Hypertrophy
LVH: 2 commonly used criteria (use either)
1. Sokolow criteria:
S in V1 or V2 + R in V5 or V6 ≥ 35 mm.
2. Cornell criteria:
S in V3 + R in aVL > 28 mm (men)
S in V3 + R in aVL > 20 mm (women)
RVH:
V1 R/S ratio >1
OR
V6 S/R ratio >1
Intervals
What is the normal PR interval?
•0.12 to 0.20 s (3 - 5 small squares).
•Short PR – Look for Wolff-Parkinson-White.
•Long PR – 1st Degree AV block
What is the normal QRS?
•< 0.12 s duration (3 small squares).
•Long QRS - look for bundle branch block, ventricular pre-excitation, ventricular
pacing or ventricular tachycardia
What is the normal QTc (QT/square root of RR)?
•< 0.42 s.
•Long QTc can lead to torsades to pointes.
P Waves
•Left atrial enlargement (P mitrale) = wide, bifid P wave: >0.12s in
lead II or biphasic P in lead V1 with largely negative terminal portion
•Right atrial enlargement (P pulmonale) = peaked P: amplitude
>2.5mm in inferior leads (II, III, avF) or >1.5mm in V1, V2
•If multiple morphologies  Wandering pacemaker or
Multifocal atrial tachycardia (common in COPD)
ST segment and MI
ST elevation may indicate STEMI if the following are met:
• At least 1 mm (0.1 mV) elevation in the limb leads (I, II, III, AVL, AVR)
• At least 2 mm elevation in the precordial leads (V1-V6)
• Elevation must be in at least 2 anatomically contiguous leads (see upcoming slides on
“grouping leads”)
ST depression may indicate NSTEMI if the following are met:
• Downsloping ST depression ≥ 0.5 mm
• Must be in at least 2 anatomically contiguous leads
Evolution of an MI:
Patterns on EKG
First thing you should do when looking
for ischemia: Group leads by region!
EKG “Grouped Leads” correspond
to area of injury
LET’S DO SOME
PRACTICE CASES
Case #1
70 year old male with history of diabetes mellitus and
hypertension occasionally feels lightheaded. He
recently fainted while standing.
Case #1 ECG
Case #2
58 year old female with no significant past medical
history presents with fatigue, lightheadedness and
shortness of breath.
Case #2 ECG
Case #3
78 year old female with history of HTN, DM, HL,
CAD admitted for syncope complains of palpitations
and lightheadedness.
Case #3 ECG
Case #4
67 year old male with history of diabetes,
hypertension, COPD presents with chest pain.
Case #4 ECG
Case #5
60 year-old man with history of HTN, HL, CAD
presents with nausea, shortness of breath and chest
pain.
Case #5 ECG
Additional Resources
Websites:
•http://en.ecgpedia.org/
•http://ecg.utah.edu
•http://ecg.bidmc.harvard.edu/maven/
Apps:
•ECG Guide by QxMD (iPad and iPhone)
•ECG Interpret (iPhone)
Books:
•12-Lead ECG: The Art of Interpretation, Tomas Garcia (perhaps
the best book on ECGs with detailed explanations and
physiology.)
•Arrhythmia Recognition, Tomas Garcia
Summary
• Learned the basics of EKG
• Learned how to have a consistent approach to EKGs
• Reviewed essential cases for new interns
• Equipped with resources for continued learning