1. ecg basics sammy

1
samueldebassu@gmail.com
BASICS OF
ELECTROCARDIOGRAPHY

Objectives
 Review of the conduction system & Action Potential
 ECG leads and recording
 ECG waveforms ,segments and intervals
 Normal ECG and its variants
 Basic Interpretation Steps of ECG 12 lead ECG
 Arrhythmias
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HISTORY
 1842- Italian scientist Carlo Matteucci realizes
that electricity is associated with the heart beat
 1876- Irish scientist Marey analyzes the electric
pattern of frog’s heart
 1895 - William Einthoven , credited for the
invention of EKG
 1906 - using the string electrometer ECG, William
Einthoven diagnoses some heart problems
samueldebassu@gmail.com 3

Cont…
 1924 - the noble prize for physiology or medicine is
given to William Einthoven for his work on ECG
 1938 -AHA and Cardiac society of great Britan
defined and position of chest leads
 1942- Goldberger found Augmented leads

ACTION POTENTIAL OF CARDIAC CELL

Phases
 0: depolarisation
Na+ influx
 1: short
repolarisation K+
efflux, Cl- influx
 2: plateau phase
(Ca++ influx
 3: repolarisation
(K+ efflux
 4: resting

7
Action Potential with the ECG

Normal Impulse Conduction
Sino atrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
9

Impulse Conduction & the ECG
Sino atrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
10

The “PQRST”
 P wave – Atrial depolarization
 QRS - Ventricular
depolarization
 T wave – Ventricular
repolarization
11

The PR Interval
Atrial depolarization
+
delay in AV junction
(AV node/Bundle of His)
(delay allows time for
the atria to contract
before the ventricles
contract)
12

Pacemakers of the Heart
 SA Node - Dominant pacemaker with an intrinsic rate
of 60 - 100 beats/minute.
 AV Node - Back-up pacemaker with an intrinsic rate
of 40 - 60 beats/minute.
 Ventricular cells - Back-up pacemaker with an
intrinsic rate of 20 - 45 bpm.
13

WAVE FORMS

P WAVE
Denotes Atrial depolarization
 Shape-Rounded, neither peaked nor notched
 Width/Duration-2.5 small sq
 Height-2.5 small sq
 Better seen in Lead II/Lead V1
 Upright in every lead except aVR

PR INTERVAL
 Distance between onset of P wave to the beginning of Q
wave(in absence of Q wave beginning of R wave)
 Denotes time interval impulse travelling from SA node
to Ventricular muscle through AV node
 Normal Range:3 to 5 small Sq
 Short if <3 small sq and long if >5 small sq

NORMAL QRS COMPLEX
 Denotes Ventricular depolarization
 Normal width of QRS-2 to 3 small sq
 Narrow complex if less than 2 small sq and Broad
Complex if more than or equal to 3 small sq

T WAVE
 Same direction as the preceding QRS complex
 Blunt apex with asymmetric limbs
 Height < 5 small sq in limb leads and <10 small square in precordial leads
 Smooth contours
 May be tall in athletes
ST SEGMENT
 Merges smoothly with the proximal limb of the T wave
 No true horizontality

QT INTERVAL
 Distance between beginning of QRS to the end Of T wave
 Reciprocal relation with heart rate
 Normal 8-11 small sq
 If arrhythmia is present( HR less than 60 or more than 100
bpm) then QT interval should be corrected.
Corrected QT(QTc)=QT/√RR

U WAVE
• Best seen in midprecordial leads
• Height < 10% of preceding T wave
• Isoelectric in lead aVL (useful to measure QTc)
• Rarely exceeds 1 small sq in amplitude
• May be tall in athletes (2 small sq)

WHAT IS AN ECG?
• An ECG is the recording of the electrical activity
generated by the cells of the heart that reaches the
body surface.
•

ECG USED IN DIAGNOSIS OF…
Cardiac Arrhythmias
Myocardial ischemia and infarction
Pericarditis
Chamber hypertrophy
Electrolyte disturbances

ECG LEADS
• Leads are electrodes which measure the
difference in electrical potential between either:
1. Two different points on the body (bipolar leads)
2. One point on the body and a virtual reference
point with zero electrical potential, located in
the center of the heart (unipolar leads)

ECG LEADS
• The standard ECG has 12 leads:
3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the
viewpoint from which it looks at the heart

STANDARD LIMB LEADS

EINTHOVEN’S TRIANGLE

PRECORDIAL LEADS
Placement of precordial leads.
V 1 - 4th intercostal space , right of sternum.
V 2 - 4th ICS left of sternum V 4 - 5th ICS midclavicular line
V 3 - Midway between V2 and V4 V 5 - 5th ICS anterior axillary line
V 6 - 5th ICS mid axillary line

PRECORDIAL LEADS

SUMMARY OF LEADS
Limb Leads Precordial Leads
Bipolar
I, II, III
(standard limb leads)
-
Unipolar
aVR, aVL, aVF (augmented
limb leads)
V1-V6

ANATOMIC VIEW OF LEADS

Knowing about coronary blood flow
can help to predict which area of
the heart would be affected by a
blockage in particular coronary
artery!!!

Coronary circulation
• Originate at the base of the
aorta from openings called
the coronary ostia located
behind the aortic valve
leaflets.
– Right coronary artery
– Left main coronary artery

SPECIAL SITUATION
• Amputation or burns or bandages should be
placed as closely as possible to the standard
sites
Dextrocardia
• right & left arm electrodes should be reversed
pre-cordial leads should be recorded from
V1R(V2) to V6

ECG PAPER BASICS
• ECG graphs:
– Small Square -Height 1 mm and width 0.04 s
–Large Square -Height 5 mm and width 0.04X5=0.2s
• Paper Speed:– 25 mm/s( As 0.2 s=5 mm,1 s=25
mm)
• Voltage Calibration:– 1 mV= П 10 mm( 10 small
square)

The ECG Paper
 Horizontally
- One small box - 0.04 s
- One large box - 0.20 s
 Vertically
- One large box - 0.5 mV
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Normal Rhythm Analysis
 Step 1: Calculate rate.
 Step 2: Determine regularity.
 Step 3: Assess the P waves.
 Step 4: Determine PR interval.
 Step 5: Determine QRS duration.
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1. HEART RATE
DETERMINING THE HEART RATE
Rule of 300
10 or 20 times method

I. RULE OF 300
 Every 3 seconds (15 large boxes) is marked by a
vertical line.
Heart rate=300/large box
40
3 sec 3 sec

1. What is the heart rate?
2. What is the heart rate?

II. 10 TIMES RULE
 Count the number of R in large square with 10 second
and multiply it by 6 would become rate in 60 sec.
 If small strip-counting the number in 15 large square
(equivalent to 3 second) and multiply it by 20
 This method works well for irregular rhythms.

Step 1: Calculate Rate
– Count the # of R waves in a 6 second rhythm strip,
then multiply by 10.
– For irregular rhythms Interpretation?
– 9 x 10 = 90 bpm
43
3 sec 3 sec

What is the heart rate?
33 x 6 = 198 bpm

2. DETERMINING RHYTHM
Paper and pencil method
Caliper method

Determine regularity. cont.
 Look at the R-R distances (using a caliper or markings on a
pen or paper).
 Regular (are they equidistant apart)? Occasionally irregular?
Regularly irregular? Irregularly irregular?
 Interpretation? Regular
46
R R

Step 3: Assess the P waves
 Are there P waves?
 Do the P waves all look alike?
 Do the P waves occur at a regular rate?
 Is there one P wave before each QRS?
 Interpretation? Normal P waves with 1 P wave for every QRS
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Step 4: Determine PR interval
Normal: 0.12 - 0.20 seconds.
(3 – 5 small boxes)
Interpretation? 0.12 seconds
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Step 5: QRS duration
 Normal: 0.04 - 0.12 seconds.
(1 - 3 small boxes)
 Interpretation? 0.08 seconds
49

Normal Rhythm Summary
 Rate 90-95 bpm
 Regularity regular
 P waves normal
 PR interval 0.12 s
 QRS duration 0.08 s
 Interpretation? Normal Sinus Rhythm
50

Is it normal sinus rhythm??
Interpret?

52
Question ?

1. ecg basics sammy

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