1. UCI Internal Medicine Mini-Lecture
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
The purpose of this mini-lecture is to teach the fundamentals of reading ECGs. This is to help beginning interns establish a consistent approach to interpreting the ECG. The ECGs that will be reviewed here are fundamental ECGs that will be seen over and over again during the course of the intern year. While some interns may readily recognize the pathology represented on the ECG, the instructor should help the intern go through the ECG in a methodological fashion. The mini-lecture is designed in a way so that each slide could be a quick lesson in itself that can be quickly squeezed into a free moment during the day. The instructor should start with the fundamentals of ECG interpretation, then proceed with interpreting individual cases using a consistent method as time permits through the course of the block.

3. This is another diagramatic to get an idea of how the heart sits relative to the view each of these leads “looks at”

4. Basics of EKG: Einthoven’s Triangle and Vectors
+AVR
+AVL
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
Lead II is a great lead (especially when looking at tele monitor) to get an idea of what is going on in the heart because depolarization is in the same direction! This means you should expect an upright P and QRS in lead II
+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
SLIDE STARTS WITH QUESTION ONLY
Ask interns about their method for interpreting an ECG.
Emphasize the importance of interpreting an ECG always in the same order so that nothing is missed.
Question will appear first in presentation, then answers.

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)
Rate — Ask interns to define normal rate, bradycardia and tachycardia. Square counting: or count number of QRS complexes in rhythm strip and multiply by 6 (especially for 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?
Are the P waves and QRS complexes regular?
Is the PR interval constant?
1st Example: Normal sinus rhythm
2nd Example: Third degree heart block
No P waves – atrial fibrillation
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
Left Axis Deviation (LAD)
Right Axis Deviation (RAD)
The cardiac axis refers to the mean direction of the wave of ventricular depolarization in the frontal plane, measured from a zero reference point. Normal is anywhere from -30 degrees to +90 degrees

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
Is there good R wave progression?
Normal R wave progression: around V3 or V4, QRS transitions from predominately negative to predominately positive and R/S ratio becomes>1.
Poor R wave progression suggests anterior MI, but not diagnostic
Are Q waves present, suggestive of infarction?

12. Hypertrophy RVH: V1 R/S ratio >1 OR V6 S/R ratio >1
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)
Hypertrophy – Can use either sokollow or cornell criteria to diagnose LVH. There are many different criteria but these are the simplest and most commonly used.
RVH:
V1 R/S ratio >1 OR
V6 S/R ratio >1

13. Intervals What is the normal PR interval? What is the normal QRS?
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.
Questions and Responses will appear with each forward button.
What are the normal PR, QRS, QT intervals?
Short PR – Look for Wolff-Parkinson-White.
Long PR - 1st degree AV block.
Long QRS – look for bundle branch block, ventricular preexcitation, ventricular pacing, or ventricular tachycardia.
Normal QTc varies. Males < Females.
Prolonged QTc (QT/square root of RR) can lead to torsades de pointes.
Prolonged QTc can be caused by MI, myocardial disease, hypocalcaemia, hypothyrodism, intracranial hemorrhage, drugs (e.g. sotalol, amiodarone), hereditary

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
Septal wall – v1, v2
Lateral – 1, avL, v5, v6
LAD occlusion – V1-V6
Cx occlusion – 1, avl, possibly v5, v6
RCA occlusion – II, III, avf

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 Ask interns to go through all the steps of interpretation:
Rate: Emphasize counting boxes between R-R interval. Divide 300 by # large boxes or count QRS complexes x 6. HR: 45 bpm. Bradycardia
Rhythm: Regular.
Axis: Normal
Hypertrophy: LVH
Intervals: Prolonged PR interval 240 ms – 1st degree AV block. This may be difficult to count.
P waves: Normal morphology.
QRS complex: Good R wave progress. No pathologic Q waves.
ST segment – T wave: Normal.
Answer: Sinus bradycardia with 1st degree heart block causing symptomatic syncope.
Next Step? Ask the patient if he takes anti-hypertensive medications that cause bradycardia. If not, the patient should be evaluated for symptomatic bradycardia with a Holter monitor. He may need a pacemaker.

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 Ask interns to go through all the steps of interpretation:
Rate: Count QRS complexes and multiply by 6. HR 120. Tachycardia.
Rhythm: Any P-waves present? None, so A fib.
Axis: Normal
Hypertrophy: LVH
Intervals: Normal
P waves: None. Atrial fibrillation.
QRS complex: Normal.
ST segment – T wave: Normal.
Answer: Atrial fibrillation with rapid ventricular response. Symptoms are often vague. Palpitations are not always felt.
Next Step? Treatment for rate control with CCB, BB, digoxin or amiodarone.

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
Ask interns to go through all the steps of interpretation even if answer may be obvious.
Rate: HR 150. Tachycardia.
Rhythm: Any P-waves present? Not a supraventricular rhythm.
Axis: Unable to determine.
Hypertrophy: Unable to determine.
Intervals: QRS > 120 ms indicates wide complex tachycardia from ventricular pacing.
P waves: None.
QRS complex: Unable to determine R wave progression or Q waves.
ST segment – T wave: Unable to determine.
Answer: Monomorphic V Tach. Interns should recognize this immediately as a life threatening emergency.
Next step? ACLS algorithm for unstable tachycardia. Call rapid response code and get ready to cardiovert.

26. Case #4
67 year old male with history of diabetes, hypertension, COPD presents with chest pain.

27. Case #4 ECG Ask interns to go through all the steps of interpretation.
Rate: HR 116
Rhythm: irregular.
Axis: right axis
Hypertrophy: RVH
Intervals: Normal
P waves: multiple P-wave morphologies
ST segment – T wave: Non-specific ST, T-wave changes.
Answer: Multifocal atrial tachycardia

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 Rate: HR 55 Rhythm: Regular. Axis: Normal Hypertrophy: LVH
Intervals: Normal
P waves: Normal morphology and size.
QRS complex: Good R wave progression.
ST segment – T wave: ST elevations in the inferior (II, III, aVF) and apical/lateral (V5-V6) leads. ST depressions consistent with reciprocal changes are seen in leads aVL and V1-V2.
Answer: STEMI
Where? Inferolateral MI
Which vessel is most likely occluded? Right coronary artery +/- left circumflex
Next step? Give ASA. Order 15 lead ECG to check for right ventricular MI. Call cardiology to activate the cath lab.

30. Additional Resources Websites: http://en.ecgpedia.org/
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