ECG for Interns

1. ECG for Interns

UCI Internal Medicine Mini-Lecture

2. 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

3.

4. 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

5. ECG Interpretation

What is your approach to reading an ECG?
•Rate
•Rhythm
•Axis
•Hypertrophy
•Intervals
•P wave
•QRS complex
•ST segment – T wave

6. 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)

7. 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!

8. 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

9. 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.

10. 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

11. 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

12. 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

13. 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.

14. 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)

15. 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

16. Evolution of an MI: Patterns on EKG

17. First thing you should do when looking for ischemia: Group leads by region!

18. EKG “Grouped Leads” correspond to area of injury

19.

LET’S DO SOME
PRACTICE CASES

20. Case #1

70 year old male with history of diabetes mellitus and
hypertension occasionally feels lightheaded. He
recently fainted while standing.

21. Case #1 ECG

22. Case #2

58 year old female with no significant past medical
history presents with fatigue, lightheadedness and
shortness of breath.

23. Case #2 ECG

24. Case #3

78 year old female with history of HTN, DM, HL,
CAD admitted for syncope complains of palpitations
and lightheadedness.

25. Case #3 ECG

26. Case #4

67 year old male with history of diabetes,
hypertension, COPD presents with chest pain.

27. Case #4 ECG

28. Case #5

60 year-old man with history of HTN, HL, CAD
presents with nausea, shortness of breath and chest
pain.

29. Case #5 ECG

30. 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

31. 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