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Tutorial in ECG Dr. Chew Keng Sheng Emergency Medicine Universiti Sains Malaysia http://emergencymedic.blogspot.com

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This is the lecture notes that I have been giving to the medical students (2nd, 3rd, final year) for the last two years (updated 2008).

### Transcript of Tutorial in Basic ECG for Medical Students

Tutorial in ECG

Dr. Chew Keng ShengEmergency Medicine

Universiti Sains Malaysia

http://emergencymedic.blogspot.com

The Basics• Standard calibration

– 25 mm/s– 0.1 mV/mm

• Electrical impulse that travels towards the electrode produces an upright (“positive”) deflection relative to the isoelectric baseline

Vertical and horizontal perspective of the ECG Leads

II, III, aVF Inferior surface of heart

V1 to V4 Anterior surface of heart

I, aVL, V5, and V6

Lateral surface of heart

V1 and aVR Right atrium

Location of MI and Affected Coronary Arteries

Location of MI Affected Artery

Lateral Left circumflex

Inferior RCA

Posterior RCA

Right Ventricle RCA

Right Sided & Posterior Chest Leads

Sinus Rhythm

• The P wave is upright in leads I and II• Each P wave is usually followed by a Q• The heart rate is 60 99 beats/min

Normal Sinus Rhythm

Instant Recognition of Axis Deviation

Cardiac AxisNormal Axis

Right Axis deviation

Left Axis Deviation

Negative

Positive

Positive

Negative

Calculating Cardiac Axis

P wave• Always positive in lead

I and II in NSR• Always negative in lead

aVR in NSR• < 3 small squares in

duration• < 2.5 small squares in

amplitude• Commonly biphasic in

Right Atrial Enlargement• Tall (> 2.5 mm), pointed P waves (P

pulmonale

Left Atrial Enlargement• Prominent terminal P negativity (biphasic)

in lead V1 (i.e., "P-terminal force") duration >0.04s, depth >1 mm

• Notched/bifid (‘M’ shaped) P wave (P ‘mitrale’) in limb leads with the inter-peak duration > 0.04s (1 mm)

Left Atrial Enlargement

P Pulmonale and P Mitrale

RAH and LAH

Right Atrial HypertrophyLeft Atrial Hypertrophy

Short PR Interval• WPW (Wolff-

Parkinson-White) Syndrome

• Accessory pathway (Bundle of Kent) allows early activation of the ventricle (delta wave and short PR interval)

QRS Complexes• Non pathological Q waves are often

present in leads I, III, aVL, V5, and V6• The R wave in lead V6 is smaller than the

R wave in V5• The depth of the S wave, generally, should

not exceed 30 mm• Pathological Q wave > 2mm deep and >

1mm wide or > 25% amplitude of the subsequent R wave

QRS In Hypertrophy

RVH Changes• A tall positive (R) wave

– an R wave exceeding the S wave in lead V1– in adults the normal R wave in lead V1 is

generally smaller than the S wave in that lead• Right axis deviation (RAD)• Right ventricular "strain" T wave inversions

Conditions with Tall R in V1

Right Atrial and Ventricular Hypertrophy

COPD

Left Ventricular Hypertrophy• Sokolow & Lyon Criteria (Am Heart J,

1949;37:161)– S in V1+ R in V5 or V6 > 35 mm

• An R wave of 11 to 13 mm (1.1 to 1.3 mV) or more in lead aVL is another sign of LVH

• Others: Cornell criteria (Circulation, 1987;3: 565-72)– SV3 + R avl > 28 mm in men– SV3 + R avl > 20 mm in women

Hypertrophy Strain Pattern vs ACS

ST Segment

• Normal ST Segment is flat (isoelectric)– Same level with subsequent PR segment

• Elevation or depression of ST segment by 1 mm or more, measured at J point IS ABNORMAL

• “J” (Junction) point is the point between QRS and ST segment

Variable Shapes Of ST Segment Elevations in AMI

Goldberger AL. Goldberger: Clinical Electrocardiography: A Simplified Approach. 7th ed: Mosby Elsevier; 2006.

T wave• The normal T wave is asymmetrical, the

first half having a more gradual slope than the second half

• The T wave should generally be at least 1/8 but less than 2/3 of the amplitude of the corresponding R wave

• T wave amplitude rarely exceeds 10 mm• Abnormal T waves are symmetrical, tall,

peaked, biphasic or inverted.

T wave• As a rule, the T wave follows the direction

of the main QRS deflection. Thus when the main QRS deflection is positive (upright), the T wave is normally positive.

• Other rules– The normal T wave is always negative in lead

aVr but positive in lead II. – Left-sided chest leads such as V4 to V6

normally always show a positive T wave.

QT interval• QT interval decreases when heart rate increases• A general guide to the upper limit of QT interval.

For HR = 70 bpm, QT<0.40 sec. – For every 10 bpm increase above 70 subtract 0.02

sec. – For every 10 bpm decrease below 70 add 0.02 sec

• As a general guide the QT interval should be 0.35 0.45 s, and should not be more than half of the interval between adjacent R waves (R R interval).

QT Interval

Long QT Syndrome

QT Interval• The QT interval increases slightly with age

and tends to be longer in women than in men.

• Bazett's correction is used to calculate the QT interval corrected for heart rate (QTc): QTc = QT/ Sq root [R R in seconds]

U wave• Normal U waves are small, round, symmetrical

and positive in lead II, with amplitude < 2 mm (amplitude is usually < 1/3 T wave amplitude in same lead)

• U wave direction is the same as T wave direction in that lead

• More prominent at slow heart rates and usually best seen in the right precordial leads.

• Origin of the U wave is thought to be related to afterdepolarizations which interrupt or follow repolarization

Calculation of Heart Rate• Method 1: Count the number of large (0.2-

second) time boxes between two successive R waves, and divide the constant 300 by this number OR divide the constant 1500 by the number of small (0.04-second) time boxes between two successive R waves.

• Method 2: Count the number of cardiac cycles that occur every 6 seconds, and multiply this number by 10.

Calculation of Heart Rate

Question• Calculate the heart rate

RBBB and LBBB

• RBBB = MaRroW• LBBB = WiLLiaM

Rhythm Disturbances

Cardiac Arrest & Peri-arrest Rhythms

• Cardiac Arrest– Shockable

• VF, Pulseless VT– Non Shockable

• Asystole, PEA

• Peri arrest rhythms– Tachyrrhythmias – Bradyarrhythmias

Drugs to control rate

Drugs to revert the rhythms

Note that by this time, if 3rd shock is required, it is the DRUG →SHOCK→ CPR sequence. It is the same sequence thereafter

The drugs to be given at this stage are vasopressors

Cardiac Arrest

After the 3rd sequence and giving adrenaline/vasopressin, consider giving antiarrhythmics like amiodarone for VF or magnesium for torsades de pointes. The sequence is still the same DRUG→SHOCK→ CPR. At any time, if rhythm becomes non-shockable, follow the non-shockable algorithm

Cardiac Arrest

For cardiac arrest, the first thing to know is whether the rhythm is shockable or not shockable. In periarrest rhythms (bradyarrhythmias and tachyarrhythmias, the first thing to know is whether it STABLE or NOT STABLE

When The Arrhythmias Is Unstable

Four main signs1. Signs of low cardiac output – systolic

hypotension < 90 mmHg, altered mental status

2. Excessive rates: <40/min or >150/min3. Chest pain4. Heart failure• If unstable, electrical therapy: cardioversion

Atropine 0.5 mg each bolus up to 3 mg. Atropine as temporizing measure only.Needs transcutaneous/transvenous pacing

Four Rhythms At Risk Of Developing Asystole

1. Recent asystole2. Mobitz II 2nd degree AV Block3. Complete Heart Block (especially with

broad QRS or initial heart rate <40/min)4. Ventricular standstill more than 3 sec

For these, consider also electrical therapy– Only mentioned in European Resuscitation Council

Guidelines 2005

Bradyarrhythmias• 2nd degree Mobitz type 1• the block is at AV Node• Often transient• Maybe asymptomatic• 2nd degree Mobitz type 2• Block most often below AV node, at

bundle of His or BB• May progress to 3rd degree AV block

* For polymorphic VT – if patients become unstable, perform defibrillation rather than cardioversion. If ever in doubt whether to perform cardioversion or defibrillation, then perform DEFIBRILLATIONRule of thumb – if your eye cannot synchronize to each QRS complex, neither can the machine!

Tachyarrhythmias• For stable tachyarrhythmias, we need to further

decide whether it is NARROW QRS or WIDE QRS• For each type, further divide into

– Regular– Irregular

Tachyarrhythmias• Narrow QRS tachyarrhythmias

– Regular• Sinus Tachycardia, PSVT, atrial flutter with regular AV

conduction

– Irregular• Atrial Fibrillation, Atrial flutter with variable AV Block

• Wide (Broad) QRS tachyarrhythmias– Regular

• Ventricular Tachycardia, SVT with BBB

– Irregular• Polymorphic VT, AF with BBB

Narrow complexes and regular – attempt vagal maneuver and adenosine;Narrow complexes but not regular- likely AF. Don’t give adenosine. May attempt rate control using beta blocker or diltiazem

Amiodarone can be given for both regular and irregular broad complexes

Recommended Resources• ABC of Clinical Electrocardiography

– www.bmj.com• Goldberger: Clinical Electrocardiography:

A Simplified Approach, 6th edition.– Access via www.mdconsult.com

• ECG Learning Center– http://medstat.med.utah.edu/kw/ecg/index.html

• ECG Library– http://www.ecglibrary.com/ecghome.html

Thank You

Contact me:Dr. K.S. Chew

[email protected]://emergencymedic.blogspot.com