1. BASICS OF ECG
PHYSIOTHERAPY IN CARDIOPULMONARY CONDITIONS (BPT402)
JAMIA MILLIA ISLAMIA
New-Delhi
Submitted to- Dr. JAMAL ALI MOIZ (PhD)
Submitted by- SHOAA MAHMOOD
Enrollment no.- 17BPT035
BPT 4th YEAR
2020-2021
CPRS
2. Introduction:
• ECG is the recording of the electrical activity of the heart.
• Traditionally this is in the form of a transthoracic (across the thorax or chest) interpretation of the electrical
activity of the heart.
• Over a period of time, as detected by electrodes attached to the surface of the skin and recorded or displayed
by a device external to the body. The recording produced by this non-invasive procedure is termed an
electrocardiogram (ECG).
• An ECG is used to measure the heart’s electrical conduction system.
• It picks up electrical impulses generated by the polarization and depolarization of cardiac tissue and translates
into a waveform. The waveform is then used to measure the rate and regularity of heartbeats, as well as the
size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices
used to regulate the heart, such as a pacemaker.
3. General symptoms indicatinguse of electrocardiographyinclude:
• Symptoms of myocardial infarction
• Symptoms of pulmonary embolism
• Cardiac murmurs
• Syncope or collapse
• Seizures
• Perceived cardiac dysrhythmias
• It is also used to assess patients with systemic disease, as well as monitoring during anesthesia and critically
ill patients.
Function:
• An ECG produces a pattern reflecting the electrical activity of the heart and usually requires a trained
clinician to interpret it in the context of the signs and symptoms the patient presents with.
• It can give information regarding the rhythm of the heart (whether or not the electrical impulse consistently
arises from the part of the heart where it should and at what rate), whether that impulse is conducted normally
throughout the heart, or whether any part of the heart is contributing more or less than expected to the
electrical activity of the heart.
4. • It is one of the key tests performed when a heart attack (myocardial infarction) is suspected; the ECG can
identify whether the heart muscle has been damaged in specific areas, though not all areas of the heart are
covered.
• The output of an ECG recorder is a graph (or sometimes several graphs, representing each of the leads) with
time represented on the x-axis and voltage represented on the y-axis.
• A dedicated ECG machine would usually print onto graph paper that has a background pattern of 1-millimeter
squares (often in red or green), with bold divisions every 5 mm in both vertical and horizontal directions.
• Faster paper speeds can be used, for example, to resolve finer detail in the ECG. At a paper speed of 25 mm/s,
one small block of ECG paper translates into 40 ms. Five small blocks make up one large block, which
translates into 200 ms. Hence, there are five large blocks per second. A calibration signal may be included
with a record. A standard signal of 1 mV must move the stylus vertically 1 cm, that is, two large squares on
ECG paper.
Fig. 1- ECG graph paper
5. Layout:
• By definition, a 12-lead ECG will show a short segment of the recording of each of the twelve
leads. This is often arranged in a grid of four columns by three rows, the first column being the
limb leads (I,II, and III), the second column the augmented limb leads (aVR, aVL, and aVF), and
the last two columns being the chest leads (V1-V6).
• Each column will usually record the same moment in time for the three leads and then the
recording will switch to the next column, which will record the heart beats after that point.
• Each of these segments is short, perhapsone to threeheart beats only, dependingon the heart rate,
and it can be difficult to analyze any heart rhythm that shows changes between heart beats.
Fig. 2- Correct ECG layout
6. Placementof electrodes:
Ten electrodes are used for a 12-lead ECG. The electrodes usually consist of a conducting gel, embedded in the
middle of a self-adhesive pad onto which cables clip. Sometimes the gel also forms the adhesive. They are
labeled and placed on the patient's body as follows:
Fig. 3- Proper placement of the limb electrodes, color-coded Fig. 4- Placement of precordial leads
as recommended by American Heart Association
7. Table 1: 12 leads
Electrode lebel (in the USA) Electrode placement
RA On the right arm, avoiding thick muscle
LA On the same location where RA was placed, but on
the left arm
RL On the right leg, lateral calf muscle
LL On the same location where RL was placed, but on
the left leg
V1 In the fourth intercostal space, just to the right of the
sternum
V2 In the fourth intercostal space, just to the left of the
sternum
V3 Between leads V2 and V4
V4 In the fifth intercostal space in the left mid-
clavicular line
V5 Horizontally even with V4, in the left anterior
axillary line
V6 Horizontally even with V4 and V5, in the left mid-
axillary line
8. Limb leads:
• In both the 5 and 12-lead configurations, leads I, II and III are called limb leads.
• The electrodes that form these signals are located on the limbs—one on each arm and one on the left leg.
• The limb leads form the points of what is known as Einthoven's triangle.
Fig. 5- Einthoven’s triangle
9. • Lead I is the voltage between the (positive) left arm (LA) electrode and right arm (RA) electrode:
I = LA – RA
• Lead II is the voltage between the (positive) left leg (LL) electrode and the right arm (RA) electrode:
II = LL – RA
• Lead III is the voltage between the (positive) left leg (LL) electrode and the left arm (LA) electrode:
III = LL - LA
Augmented limb leads:
• Leads aVR, aVL, and aVF are called augmented leads. They measure electrical activity between one limb and
a single electrode.
• Lead aVR provides no specific view of the heart. Lead aVL shows electrical activity coming from the heart‘s
lateral wall. Lead aVF shows electrical activity coming from the heart’s inferior wall.
Precordialleads:
• The electrodes for the precordial leads (V1, V2, V3, V4, V5 and V6) are placed directly on the chest. Because
of their close proximity to the heart, they do not require augmentation.
10. Wavesand intervals:
Fig. 6- Normal ECG wave
Normal P wave
• Location—before the QRS complex
• Amplitude—2 to 3 mm high
• Duration—0.06 to 0.12 second
• Configuration—usually rounded and upright
• Deflection—positive or upright in leads I, II, aVF, and V2 to V6; usually positive but may vary in leads III and
aVL; negative or inverted in lead aVR; biphasic or variable in lead V1
11. Normal PR interval
• Location—from the beginning of the P wave to the beginning of the QRS complex
• Duration—0.12 to 0.20 second
Normal QRS complex
• Location—follows the PR interval
• Amplitude—5 to 30 mm high but differs for each lead used
• Duration—0.06 to 0.10 second, or half the PR interval
• Configuration—consists of the Q wave, the R wave, and the S wave
• Deflection—positive in leads I, II, III, aVL, aVF, and V4 to V6 and negative in leads aVR and V1 to V3
Normal ST segment
• Location—from the S wave to the beginning of the T wave
• Deflection—usually isoelectric; may vary from – 0.5 to + 1 mm in some precordial leads
12. Normal T wave
• Location—after the S wave
• Amplitude—0.5 mm in leads I, II, and III and up to 10 mm in the precordial leads
• Configuration—typically round and smooth
• Deflection—usually upright in leads I, II, and V3 to V6; inverted in lead aVR; variable in all other leads
Normal QT interval
• Location—from the beginning of the QRS complex to the end of the T wave
• Duration—varies; usually lasts from 0.36 to 0.44 second
Normal U wave
• Location—after T wave
• Configuration—typically upright and rounded
• Deflection—upright
13. Interpreting a rhythm strip: 8-step method
Step 1: Determine the rhythm
Step 2: Determine the rate
Step 3: Evaluate the P wave
Step 4: Measure the PR interval
Step 5: Determine the QRS complex duration
Step 6: Examine the T waves
Step 7: Measure the QT interval duration
Step 8: Check for ectopic beats and other abnormalities
Normal sinus rhythm
Normal sinus rhythm is the standard against which all other rhythms are compared.
Characteristics
• Regular rhythm
• Normal rate
• P wave for every QRS complex; all P waves similar in size and shape
• All QRS complexes are similar in size and shape
• Normal PR and QT intervals
• Normal T waves
14. Axis:
Fig. 7- Diagram showing how the polarity of the QRS complex in leads I, II, and III can be used to estimate the
heart's electrical axis in the frontal plane.
• With a healthy conducting system, the cardiac axis is related to where the major muscle bulk of the heart lies.
Under normal circumstances, this is the left ventricle, with some contribution from the right ventricle.
• It is usually oriented in a right shoulder to left leg direction, which corresponds to the left inferior quadrant of
the hexaxial reference system, although −30° to +90° is considered to be normal.
15. Table 2: Axis of heart
Normal -30° to +90° Normal Normal
Left axis deviation -30° to -90° May indicate left
anterior fascicular
block or Q waves
from inferior MI
Left axis deviation
is considered normal
in pregnant women
and those with
emphysema
Right axis deviation +90° to +180° May indicate left
posterior fascicular
block, Q waves
from high lateral MI
or a right ventricular
strain pattern
Right deviation is
considered normal
in children and is a
standard effect of
dextrocardia
Extreme right axis
deviation
+180° to -90° Is rare, and
considered an
‘electrical noman’s
land’
16. Fig. 8- Hexaxial Diagram
• The hexaxial reference system showing the orientation of each lead: For example, if the bulk of heart muscle
is oriented at +60 degrees with respect to the SA node, lead II will show the greatest deflection and aVL the
least.
17. Summary:
• Electrocardiography is the examination of choice for diagnosis of a normal cardiac rhythm and arrhythmias
and for monitoring the effect of antiarrhythmic therapy.
• An electrocardiogram records the depolarization and repolarization process in atria and ventricles during the
cardiac cycle.
• Electrocardiography is used to evaluate cardiac rate and rhythm. It allows the diagnosis of the nature of a
dysrhythmia.
18. References:
• Donna Frownfelter and Elizabeth Dean, Principles and practice of Cardiopulmonary Pulmonary Therapy,
Third edition.
• PatricaA. Downie, Cash’s textbook of chest, heart and vascular disorders for physiotherapists, 4th edition.
• Francis W.K. SmithJr. et al, Electrocardiography, in Saunders Manual of Small Animal Practice (Third
Edition) , 2006
