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ECGs. AFMAMS Resident Orientation March 26 2012. Lecture Outline. ECG Basics Importance of systematically reading ECGs Rate Rhythm Axis Hypertrophy Intervals and Segments Ischemia / Infarction. ECG Basics. Measurements on ECG paper. Identify ECG Landmarks. Introduction.

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AFMAMS Resident Orientation

March 26 2012

lecture outline
Lecture Outline
  • ECG Basics
  • Importance of systematically reading ECGs
  • Rate
  • Rhythm
  • Axis
  • Hypertrophy
  • Intervals and Segments
  • Ischemia / Infarction
ecg basics
ECG Basics
  • Measurements on ECG paper
  • Be systematic
    • Rate
    • Rhythm
    • Axis
    • Chamber Hypertrophy
      • Atrial
      • Ventricular
    • Intervals
    • Ischemia/ Infarction
  • Read Every ECG the same way!
how to determine rate
How to Determine Rate
  • Rhythm Strip
    • 10 seconds
    • Count QRS complexesthen multiply by 6
  • Count Big Blocks between QRS complexes
      • 300-150-100-75-60-50-43-37
determining rhythm
Determining Rhythm
  • Look for the P wave
    • Leads II and V1
  • Present vs. Absent
  • Regular vs. Irregular
  • Symmetric vs. Asymmetric
  • Normal Sinus Rhythm is most common
normal p wave morphology
Normal P wave morphology
  • P wave represents atrial activation
  • The atria activate from right to left, so the first half of the P wave usually represents right atrial activation and the second half represents the left atrium.
  • The sinus node is the usual sight of atrial activation.
definition of sinus rhythm
Definition of Sinus Rhythm
  • NOT “A P wave before every QRS”


  • Normal P wave axis
  • Uniform P wave morphology
  • Regular P-P interval
  • P waves: normal sinus (NSR), sinus bradycardia, sinus tachycardia, multifocal atrial tachycardia (MAT), atrial flutter
  • No P waves: atrial fibrillation, junctional rhythm, ventricular fibrillation, ventricular tachycardia
  • Regular: normal sinus, sinus bradycardia, sinus tachycardia, atrial flutter, junctional rhythm, ventricular tachycardia
  • Irregular: atrial fibrillation, multifocal atrial tachycardia, ventricular fibrillation
normal p wave morphology1
Normal P wave morphology
  • Normal P wave duration: 0.08 – 0.11 seconds
  • Normal P wave amplitude: limb leads < 2.5mm; V1 positive deflection < 1.5mm and negative deflection < 1mm
  • Normal P wave axis: 0-75 degrees
  • Normal morphology: upright in I, II, aVF
normal p wave morphology2
Normal P wave morphology
  • P wave duration (seconds): measured from the beginning of the P wave to the end of the P wave.
  • Amplitude (mm): measured from the baseline to the top (or bottom). Positive and negative deflections are determine separately.
  • Refers to the direction of the movement of depolarization spreads through the heart
  • Since left ventricle is the largest and thickest chamber of the heart it undergoes most depolarization
  • Therefore, normal direction of depolarization is from middle of the chest towards the left hip
  • Important in determining
    • Prior myocardial infarction
    • Ventricular Hypertrophy
    • Intraventrcicular Conduction Delay
  • Two methods to calculate axis
    • Isoelectrical
    • Short-cut
isoelectrical calculation
Isoelectrical Calculation
  • Find the isoelectrical QRS complex
  • Axis is perpendicular to isoelectrical axis
  • Use other leads to determine if positive or negative
short cut method
Short Cut Method
  • Look at Lead I and II
  • If QRS positive in Leads I and II
    • Normal axis
  • If QRS negative in I and positive in II
    • Right Axis Deviation
  • If QRS positive in I and negative in II
    • Left Axis Deviation
  • If QRS negative in Leads I and II
    • Far Right Axis Deviation
atrial abnormalities
Atrial Abnormalities
  • Left Atrial Enlargement
    • Terminal negative P wave in lead V1 >1mm deep and 0.04sec in duration
    • Notched P wave with a duration >0.12sec in limb leads (I, II)
    • Seen in: MS, MR, LVH
  • Right Atrial Enlargement
    • Tall P wave in inferior leads - >2.5mm
    • Can be seen in: COPD, PE, Pulmonary HTN
Cornell Criteria

R in AVL + S in V3 > 28mm (>20mm in females)

Voltage Criteria

S in V1 + R in V5/V6 > 35mm

R in AVL > 11mm

Largest R in limb leads >20

Supporting Criteria



Prolonged QRS

Strain pattern

  • Right axis deviation (>+90)
  • R V1 >7 mm
  • R V1 + S V5 or V6 >10 mm
  • R/S ratio in V1 >1
  • S/R ratio in V6 >1
  • Incomplete right bundle branch block
  • ST-T wave abnormalities ("strain") in inferior leads
  • Right atrial hypertrophy (P pulmonale)
  • S1- S2 - S3 pattern (particularly in children
  • PR interval
  • QRS Complex
  • QT Interval
the pr interval
The PR interval
  • Normal interval: 0.12 – 0.20 seconds in length
  • Short PR interval: < or = 0.11 seconds
  • Long PR interval: > 0.20 seconds
  • Diffuse ST segment depressions
  • PR depression
  • Notching of the S wave
wolf parkinson white
Wolf Parkinson White
  • Short PR interval
  • Wide QRS complex
  • Presence of a delta wave
  • ST-T wave changes or abnormalities
  • Clinical association with paroxysmal tachycardias
qrs complex
QRS Complex
  • Normal QRS duration
    • 80 – 120 ms
  • Widened QRS
    • RBBB
    • LBBB
    • Electrolyte abnormalities
  • Asynchronous activation of the two ventricles increases the QRS duration (0.13 sec).
  • Terminal forces are rightward and anterior due the delayed activation of the right ventricle,
  • Results in an rsR\' pattern in the anterior-posterior lead V1 and a wide negative S wave in the lead V6 and Lead I
  • No significant association with risk factors for or the presence of ischemic heart disease, myocardial infarction, or cardiovascular deaths
rbbb criteria
RBBB Criteria
  • QRS > 120 ms
  • rSR’ or rsR’ in V1
  • Wide S in I, V5 or V6
lbbb criteria
LBBB Criteria
  • QRS duration > 120 ms
  • QS or rS complex in V1
  • RsR’ in V6
  • T wave deflection should be opposite QRS complex (Discordance)
qt interval
QT Interval
  • Normal
    • Male < 440 ms
    • Female < 460 ms
  • Calculated
    • QTc = QT / RR
  • Prolonged
    • Electrolytes
    • Inherited
  • Shortened
    • Hypercalcemia
  • ECGs are a cheap and readily available diagnostic test
  • ECGs provide a tremendous amount of information
  • Properly interpreting ECGs requires a lot of practice
second degree av block
Mobitz Type I

Progressive prolongation of the PR interval until a P wave is blocked

RR interval containing the nonconducted P wave is less than two PP intervals

Usually narrow QRS (block at the level of AV node)

Mobitz Type II

Intermittent nonconducted P waves

Constant PR interval

RR interval containing the nonconducted P wave is equal to two PP intervals

Often a wide QRS complex

Second Degree AV Block
third degree av block
Third Degree AV Block
  • Atrial and ventricular rhythms are independent of one another
  • PP and RR intervals are constant
  • Atrial rate > ventricular rate