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ECG BasicsECG Basics

By :Dr Harith Abdulkadir sh. Mohamoud

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What is the ECG What is the ECG

An electrocardiogram (ECG or EKG) is a recording of the electrical activity of the heart over time produced by an electrocardiograph,

A noninvasive machine recording via skin electrodes.

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First, First,

consider depolarization and consider depolarization and

repolarization of a repolarization of a singlesingle cellcell

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Single Cell

The “PQRST”The “PQRST”

P wave - Atrial depolarization

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• T wave - Ventricular repolarization

• QRS - Ventricular depolarization

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ECG shapeECG shape

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Chest (Precordial) LeadsChest (Precordial) Leads

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Chest (Precordial) LeadsChest (Precordial) Leads

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The hexaxial reference systemThe hexaxial reference system

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Arrangement of Leads on the EKGArrangement of Leads on the EKG

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Principles of heart ECG recordingPrinciples of heart ECG recording

(1) An electrical force directed twoards the (+) pole of a lead results in an upward deflection on the EKG recording of that lead

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Toward Toward

   - + =  

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(2) forces that head away from the (+) electrode result in a downward deflection

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Head awayHead away

- + =

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(3) an elcterical forces directed perpendicular to ECG lead does not register any activity by that lead, or it can be bi-phasic ( equi-phasic )

( a “ flat line on the recording )

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Perpendicular Perpendicular

 

- + =

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(4) The magnitude of the deflection either upward or downward , reflects how parallel the electrical forces is to the axis of the lead being examined .

The more parallel to the lead the greater the magnitude of the deflection

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The electrical impulse actuallyproceeds by radial spread.

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Normal conduction.leads aVL and aVF

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Sequence of conduction,Precordial leads

Always memorize Always memorize V1 + v2 = Sr = S>R

v3+ v4 = SR or S=R

v5 + v6 = Rs or R>S

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Varieties of QRS complexesVarieties of QRS complexes

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ECG interpretation ECG interpretation

1. Heart rhythm 2. Heart rate 3. Intervals ( PR , QT , ST )4. Mean QRS axis 5. P wave abnormalities 6. Abnormalities of QRS 7. ST and T wave abnormalities

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1) Heart rhythm 1) Heart rhythm Sinus rhythm every P wave is

followed by a QRS every QRS is

preceded by a P wave

P wave is upward in lead I , II , III

if not Arrhythmia

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The ECG PaperThe ECG PaperHorizontally

◦ One small box - 0.04 s◦ One large box - 0.20 s

Vertically◦ One large box - 0.5 mV

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2) Heart rate 2) Heart rate Heart rate = 25mm/sec times 60sec/min No of mm b/w beats

If the distances are regular, count the number of "little boxes" from the beginning of one QRS to the beginning of the next QRS complex.

Divide the number of "little boxes" (which each represent 0.04 seconds) into 1500 to obtain the heart rate in beats per minute.

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Heart Rate = 

1500

No. small boxes

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Rule of 300Rule of 300

Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300.

The result will be approximately equal to the rate

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Rule of 300Rule of 300

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Rule Rule 66 Seconds Seconds

Every 3 seconds (15 large boxes) is marked by a vertical line.

9 * 10 = 90 beat /min

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3 sec 3 sec

3) Intervals 3) Intervals

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(Learn the normal PR, QRS and QT intervals)

4) Mean QRS Axis4) Mean QRS Axis

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5) Abnormalities of P wave5) Abnormalities of P wave

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6) Abnormalities of QRS complex 6) Abnormalities of QRS complex

Ventricular hypertrophy Bundle branch block

Myocardial Infarction

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Memorize these principles Memorize these principles In right ventricular hypertrophy

there is always inversion of the normal

In the left ventricular hypertrophy there is exaggeration of the normal

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Bundle branch block Bundle branch block Right bundle

branch block ( RBBB)

Left bundle branch block ( LBBB )

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RBBBRBBB

RBBB RBBB

RBBB is seen in :- Occasional normal

subjects Pulmonary embolus Coronary artery

disease ASD Active carditis RV diastolic

overload.

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LBBBLBBBLBBB is seen in :-

Always indicative of organic heart disease

Found in ischaemic heart disease

Found in hypertension

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Bundle branchblocks

Myocardial infarction Myocardial infarction

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Lateral MI, Recorded in aVL

2

Transmural and Non-transmural Transmural and Non-transmural

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ECG evolution of MI

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MI locations: II, III, aVF = Inf MIV1-2 = Septal MIV4-5 = Ant MI

I, aVL, V5-6 = Lateral MIV1-6 = Extensive Ant MI

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Localization of MIs

7) ST segment and T Wave 7) ST segment and T Wave Abnormalities Abnormalities Drug effects Electrolyte disturbance Myocardial ischemiapericarditis Infarction Transmural MI ST deviate to upward Nontransmural MI ST deviate downward

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Repolarizationabnormalities

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Thank you all for listeningThank you all for listening

THE END

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