How to read ECG
ECG
Representation of Electrical activity of heart
ECG Leads
12 lead ECG 6 limb leads: Lead I, II, III
aVL, aVR, aVF
6 Chest Leads: V1, V2,V3, V4, V5, V6
ECG paper
Speed 25mm/s 1 large square= 5 small square [5mm] Voltage 10mm =1mV
Appearance of waves
Positive deflection [upward] If electrical impulses flowing towards that lead
Negative deflection [downward]
If electrical impulses flowing away from that lead
Origin of waves
P wave PR interval
Atrial depolarization
Atrial depolarization to start of ventricular depolarization QRS complex Ventricular depolarization
T wave
QT interval U wave
Ventricular repolarization
Ventricular depolarization & repolarization ? Interventricular septal repolarization
Systematic approach
The following 14 points should be analyzed carefully in every ECG: Standardization Heart rate Rhythm P waves PR interval QRS voltages QRS interval QT interval Mean QRS axis Precordial R-wave progression Abnormal Q waves ST segments T waves U waves
Standardization
Heart Rate
1500/RR
If HR is irregular Count no. of QRS complexes in 30 large squares= 6 sec Multiply it with 10 HR [per min]
Rate calculation
Memorize the number sequence: 300, 150, 100, 75, 60, 50
ECG machines: print out HR
DO NOT RELY ON IT!!!! Always Calculate yourself.
Bradycardia: <60/min
Tachycardia: >100/min
Rhythm
Rhythm strip: prolonged recording of Lead II Sinus rhythm ? Each QRS complex preceded by P wave
Regular/ irregular?
Regular Sinus rhythm
Irregular
QRS AXIS
Indicator of overall direction that wave of depolarization takes when passing through ventricles Also called ANGLE Measured in degrees
Photo
Right axis deviation [RAD] Beyond +90
Left Axis Deviation [LAD]
Beyond -30
Method 1
Most precise method Use of vectors Measure overall height of QRS in lead I & aVF Plot in graph paper Measure the ANGLE of vector
Method 2
Quick method
Identify limb lead in which QRS complex
is isoelectric
[with equal positive & negative
deflection]
Implies: electric flow is at Right angle to
this lead
Method 3
For quick assessment Look at QRS complexes in lead I & II
Predominantly
positive QRS in
lead I
Axis between
-90 to +90
Excludes RAD
Predominantly positive QRS in lead II Axis between -30 to +150 Excludes LAD
Lead I
QRS Positive QRS Positive
Lead II
QRS Positive
Cardiac Axis
Normal Axis
QRS Negative Left Axis Deviation Right Axis Deviation
QRS Negative QRS Positive
LAD WPW syndrome LBBB Inferior wall MI
RAD RVH WPW syndrome Anterolateral MI Dextrocardia
P wave
Present or not? Sinus rhythm If completely absent
Atrial Fibrillation
Hyperkalemia
If intermittently absent
Sinus arrest
Inverted P waves?
Incorrect positioned electrodes
Dextrocardia
Abnormal atrial depolarization
Height of P waves
> 2.5 mm: tall
Indicative of Right Atrial enlargement P Pulmonale
P PULMONALE
P MITRALE
Width of P waves >2mm width: abnormal Bifid P wave
Indicates Left Atrial enlargement
P Mitrale
PR Interval
From start of P wave to start of R wave Normally Not <3 small squares Not > 5 small squares Consistent
Short PR Interval
AV junctional rhythm WPW syndrome
Lown Ganong-Levine syndrome
Long PR Interval
Denotes delay in conduction through AV node First Degree Block PR prolonged, constant
Second degree Block Mobitz Type I PR progressively increase until one P
wave fails to produce QRS complex
Mobitz Type II
PR interval normal & fixed, But occasional P waves fail to produce QRS
Third Degree Block [Complete AV Block] No relationship between P waves & QRS complex
2:1 Block Alternate P waves are not followed by QRS complex
Q WAVE
First negative deflection in QRS complex ? Pathological Q waves If >2 small squares deep >1 small square wide >25% of height of the following R wave in depth
QRS complex
Appearance of QRS Complex vary from lead to lead
Width: Narrow/ wide
Wide QRS:
> 3 small squares
Bundle branch block Ventricular arrhythmia
Size of QRS complex Small: Pericardial effusion
?incorrect calibration
Big QRS complex
Ventricular hypertrophy: R/L
WPW syndrome
Progression of R wave
V1: small R wave , large S wave, Gradually R wave increases, S wave decreases
V6: small Q wave, large R wave
V3 and V4 : located midway between V1 and V6, QRS complex nearly isoelectric in one of these leads
Progression of R wave
Left ventricular Hypertrophy
R Wave in V5 or V6 >25mm S Wave in V1 or V2 > 25mm Sum of R wave in V5 Or V6 & S wave in V1 or V2 >35mm
LVH
Right Ventricular Hypertrophy
Right axis deviation Deep S Waves in leads V5 & V6 R>S in V1 RBBB
RBBB
Right Bundle Branch Block Broad QRS complex Small r wave in V1, small Q wave in V6 S wave in V1, R wave in V6 R wave in V1, S wave in V6
LBBB
Left Bundle Branch Block Broad QRS Small Q wave in V1, Small r wave in V6 R wave in V1, S wave in V6
S wave in V1, R wave in V6
WILLIAM MORROW William: W in V1 & M in V6: LBBB
Morrow: M in V1 & W in V6: RBBB
LBBB Ischemic Heart Disease Cardiomyopathy LVH
RBBB
Ischemic heart
disease
Cardiomyopathy
ASD
Massive pulmonary
Fibrosis
embolism
ST Segment
From end of S wave to start of T Wave Normally: Isoelectric ? Depressed/ elevated
Elevated ST segment Acute MI Prinzmetals angina Pericarditis LV aneurysm High take off
Depressed ST segment Myocardial ischemia Posterior MI Ventricular hypertrophy with Strain Drugs: Digoxin
Ventricular Hypertrophy with strain pattern
Tall R waves Deep S waves ST segment depression T wave inversion
T Wave
T wave
Inverted? Normal in aVR V1,V2, III Size Normal: not > size of preceeding QRS complex Too small? Too large?
Tall T waves
Hyperkalemia Acute MI
Too small T Waves
Hypokalemia Pericardial effusion
hypothyroidism
Inverted T waves
Normal in few leads: aVR, V1, V2, III MI Myocardial ischemia Ventricular hypertrophy with strain Digoxin toxicity
QT Interval
From start of QRS complex to end of T wave Varies with HR
Corrected QT interval
QTC QTC =QT/RR Normal: 0.35-0.43 sec
Prolonged QTc
If 0.44 sec Hypocalcemia Acute myocarditis Torsades de pointes
U waves
Mostly in anterior chest leads Difficult to identify clearly
Prominent U Waves Hypoklemia Hypercalcemia
Hyperthyroidism
Common ECG Problems
ACUTE MI
Ischemia
HYPERKALEMIA
LVH WITH STRAIN
PERICARDITIS
