ECG1

16/12/2008 ECG Daig 1/ghazi �

Principles of ECG Diagnosis

Dr Ghazi Radaideh, MD, FRCP

Rashid HospitalDubai - UAE


Welcome to Principles of ECG Diagnosis

• The 12-lead electrocardiogram is the most powerful, least invasive, most cost-effective, and predictive tool in our diagnostic armamentarium.

• In recent years especially, the widely recognized benefits of early diagnosis and rapid revascularization of AMI have cast into focus the urgency of clinical competence in bedside electrocardiographic (ECG) assessment.


• This course about the principles of ECG diagnosis has been specifically designed to provide you with a practical approach to reading electrocardiograms (ECGs).

• The ECG (or EKG) will be broken into it’s individual components and their origins explained.

Objectives of this course

•Since ECG reading is a visual experience, typical examples of the various clinical situations for which ECGs are recorded constitute most of this course content


Part 1

Basic concepts ofThe Standard 12 Lead ECG


Basic concepts of The Standard 12 Lead ECG

This Part covers:1. The Conduction System2.Definition and the ECG recording 3.Orientation of the 12 Lead ECG 4. Protocol for ECG Interpretation5. Determining Heart Rate

6. Cardiac Axis


1.The Cardiac Conduction System

electrical pathway of an electrical impulse that causes a heart beat.


Action Potential of a Cardiac Cell5 Phases.

Ion flow into cell Ion flow out of cell

•Phase 0Rapid or upstroke depolarization with an influx of sodium ions into the cell

��

��

•Phase 2 –Plateau Phase: Continued Influx of Sodium & slow Influx of Calcium

•Phase 3 –Repolarization: Potassium outflow

Na+ andCa++•Phase 4

21

0

Ca++ K+

3

K+

4

Repolarization: Potassium outflow


Action Potential of a Cardiac Cell��

21

0 3

4

ERP RRPERP RRP

16/12/2008 ECG Daig 1/ghazi

Cardiac Conduction System

• It coordinates the production and pathway of the cardiac action potentials that cause the heart to beat.

• In order for normal depolarization and repolarization to occur, the electrical impulse within the cardiac cell must follow a specific pathway within the heart known as the conduction system.


Normal Cardiac Conduction System

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

16/12/2008 ECG Daig 1/ghazi ��

Impulse Conduction and Correlation with the ECG

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers


Accessory Pathways • Tiny bands of

myocardial tissue that most commonly insert in atrial muscle in one end and in ventricular muscle on the other end

•Affects 0,2% to 0,4% of population on routine screening


What is ECG (Electrocardiogram)?

• An ECG is the recording (“gram”) of the electrical activity (“electro”) generated by the cells of the heart (“cardio”) that reaches the body surface – ECG is a representation of the heart's

electrical activity recorded from electrodes on the body surface


The ECG Paper

1 small square = 1 mm = 0.1 mV

The horizontal axis represents time in secondsand helps to determine the heart rate and regularity.

An ECG is a two dimensional recording.

–1 sec=5 big boxes=15 small boxes

–1min=60sec=300big boxes=1500 small boxes

The vertical axis displays amplitude(voltage), measured in milli Volts.


•The normal calibration mark should be a full 10 mm for a 1 mV calibration (��

•� �� •! ��"��

If the ECG is half standard you MUST multiply all waves by 2 to normalize them#

If the ECG is double standard you MUST multiply all waves by 0.5 to normalize them


Skin Preparation• ECG electrodes contain conductive gel that

transmits the patients ECG signal.• Proper skin preparation and electrode placement

optimize ECG tracing and minimize artifact.

•Tips for Skin Preparation– Wash the site with soap and water.

– Dry the skin briskly, but do not abrade the skin.

– Make sure the electrode backing is moist. (Remember that electrodes can dry quickly)

–Placement is important - if you cannot obtain a goodt lead placement, you must start again with new electrodes, leads, etc.


Lead I: RA (-) to LA (+) (Right Left, or lateral)

Bipolar limb leads (frontal plane):

Lead II:

RA (-) to LF (+) (Superior Inferior)

Lead III

LA (-) to LF (+) (Superior Inferior)


Augmented unipolar limb leads

The signals are augmented (amplified) by 50%, hence the “a” in the lead names.

Lead aVL: LA (+) to [RA & LF] (-)

(Leftward)

Lead aVF: LF (+) to [RA & LA] (-)

(Inferior)

Lead aVR: RA (+) to [LA & LF] (-)

(Rightward)


Orientation of the The V Leads

• V1 and V4 - display the electrical activity of the anterior wall of the heart.

• V5and V 6 - display the lateral wall electrical activity.

V1V2V3

V4

V5

V6


The 12-Leads

3 Limb leads (I, II, III)

3 Augmented leads(aVR, aVL, aVF)

6 Precordial leads (V1- V6)


Right chest (or anterior) leads

• Right chest leads are V1, V2; and aVR.

If additional right chest leads need to be seen, (e.g., to diagnose a RV MI) do another 12 lead ECG but move 4 electrodes to these positions:

V3R , V4R ,V5R,V6R .


4Protocol for ECG Interpretation


Reading 12-Lead ECG step-by-step (RAWIHI)

1. Rate, Rhythm and Regularity2. Determine the QRS Axis3. Evaluate the Waves (P,QRS,T ),

Intervals (PR,ST,QT)4. Evaluate for chamber Hypertrophy5. Look for myocardial Infarction and Ischemia6. Interpret the ECG


Determining Heart RateMethod I

• If the RR distances are regular -• count the number of "small boxes" from R to the next R Then divide 1500 by

the number of "small boxes" to obtain the heart rate in beats per minute.

Heart Rate = 1500 /No. small boxes

•If large boxes used then divide by 300

•Heart Rate = 300/No. large boxes


Method I• If the distances are irregular,

– count the number of QRS complexes within 20 large boxes and multiply this number by 15 OR ( 30 large boxes and multiply this number by 10) to obtain the heart rate in beats/minute.

(1min = 60sec = 300big boxes)

Or

• within 50 large boxes and multiply by 6


The EKG grid used to rapidly estimate the heart rate

Normal sinus rhythm

Start300 150 75100


RRhythm

Rhythm:• Is it sinus? Or not?• If not what could be?

» Atrial» Junctional» Ventricular

Sinus Rhythm:•The P wave is upright in leads I and II . Each P wave is usually followed by a QRS complex•. If the P wave in lead II is not upright, then sinus rhythm is not present (unless there is dextrocardia or lead reversal).


Determine regularity

– Regular (are they equidistant apart)? – Occasionally irregular? – Regularly irregular? – Irregularly irregular?

Interpretation? Regular

R R

•Look at the R-R distances (using a caliper or markings on a pen or paper).

R R R


Irregular heart beat

Determine regularityR R R R


Cardiac axis• The cardiac axis refers to

the mean direction of the electrical activity during ventricular depolarisation.

It is measured from a zero reference point. The zero reference point looks at the heart from the same viewpoint as lead I.


Determining QRS axisSeveral methods can be used to calculate the

cardiac axis, though occasionally it can prove extremely difficult to determine:

1. by inspection of leads I, II, and III2. Equiphasic lead (equal voltages in the R

and the S waves ) method3. Vector method for QRS axis


QRS Axis by Inspection Methodleads I and II

Negative PositivePositiveLead II

PositiveNegative PositiveLead I

Left axis deviation

Right axis deviation

Normal axis


2.Equiphasic lead method for QRS axis:

1. Locate a lead that has the smallest total QRS complex and/or is equiphasic.

2. Now look at the lead that is 90 degrees from the equiphasic lead.

- If this lead’s QRS complex is positive, the axis is in the direction of that lead. If negative, the axis is 180 degrees opposite.

The QRS axis should be at 90 degrees to this lead.


3.Vector method for QRS axis• Leads I and aVF are at 90 degrees to each other

and so form good bases for vector analysis .


What is the axis in this ECG?

aVF

I


Conditions for which determination of the axis is helpful in diagnosis

• Conduction defects ( LAFB…)• Ventricular enlargement ( RVH..)• Broad complex tachycardia • Congenital heart disease (ASD..)• Pre-excited conduction (WPW…)• Pulmonary embolus,• myocardial infarction.


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