Download - 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
Leads Anatomical
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
Anterior LAD
Septum LAD
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
Lead I Positive
Negative
Positive
Lead II Positive
Positive
Negative
Lead III 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
lead V1 • Best seen in leads II
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
– instead of the rS complex normally seen in lead V1
– 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
for tachyarrhythmias, pacing for bradyarrhythmias
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