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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