Electrocardiography BIOLOGY

1. G H Raisoni College of Engineering ,Nagpur
Department of First Year
Engineering
Subject: Bio Systems In
Engineering
TAE II: Technical
Presentation Topic:
Electrocardiography

2. What is
Electrocardiography?
Electrocardiography (ECG or EKG)
is the process of recording the electrical activity of the heart
over a period of time using electrodes placed on a patient's
body. These electrodes detect the tiny electrical changes on
the skin that arise from the heart muscle
depolarizing during each
heartbeat.

3. Willem Einthoven
 He was a Dutch doctor
and physiologist. He
invented the first
practical
Electrocardiogram in
1903 and received the
Nobel Prize in Medicine
in 1924 for it.

5. Electro
de
name
Electrode placement
RA On the right arm, avoiding thick muscle.
LA
In the same location where RA was placed, but on the left
arm.
RL On the right leg, lateral calf muscle.
LL
In the same location where RL was placed, but on the left
leg.
V1
In the fourth intercoastal space (between ribs 4 and 5)
just to the right of the sternum (breastbone).
V2
In the fourth intercoastal space (between ribs 4 and 5)
just to the left of the sternum.
V3 Between leads V2 and V4.
V4
In the fifth intercostal space (between ribs 5 and 6) in
the mid clavicular line.
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. The names and correct locations for each
electrode are as follows:

6. RA, LA, RL, LL – Limb Leads
RA/LA - Lead I
RA/RL - Lead II
LA/LL - Lead III
V1, V2, V3, V4, V5, V6 - Precordial Leads

7. Preparation before recording ECG:
A] Patient’s Prepation:
1)
 Place the patient in a
supine or semi-Fowler’s
position. If the patient
cannot tolerate being
flat, you can do the ECG
in a more upright
position.
 Instruct the patient to
place their arms down
by their side and to
relax their shoulders.
 Make sure the patient’s
legs are uncrossed.
 Move any electrical
devices, such as cell
phones, away from the
patient as they may
interfere with the
machine.


8. B] Skin Preparation
 Dry the skin if it’s moist or diaphoretic.
 Shave any hair that interferes with
electrode placement. This will ensure a
better electrode contact with the skin.
 Rub an alcohol prep pad or benzoin
tincture on the skin to remove any oils
and help with electrode adhesion.


9. C] Electrode
Application
Check the electrodes to make sure
the gel is still moist.
Do not place the electrodes over
bones.
Do not place the electrodes over
areas where there is a lot of muscle
movement.

10. How does ECG machine
works?
 In a 12-lead EKG, six electrodes are attached to the skin on
the chest around the heart. Four more electrodes are
added, one on each arm and leg. The ten electrodes
combine in twelve different ways to read twelve different
angles on the heart. When the heart depolarizes with each
heartbeat, the electrodes sense the tiny electrical impulses
on the skin that are created as a result. The impulses travel
back to the machine where they are interpreted and
printed on a graph.
 Each heart muscle cell has a negative charge at rest, but
moves closer to a neutral charge with each beat, called
depolarization. Each pair of electrodes records the changes
in voltage created between the two when the heart
depolarizes with each beat. A healthy heart will print out
an orderly wave of progression with each heart beat, while
a heart with diseased or damaged tissue will show certain
irregularities in the heart’s rhythm, size, or position.

11. Current moving away from +ve electrode Negative Deflection
 Current moving towards +ve electrode
Positive Deflection
The Principle
+
+

12. Intervals and Segments
An interval is a portion of the baseline and at least one
wave. We measure an interval on the horizontal axis in
seconds. The PR, QRS, and QT are the intervals which
should be routinely scanned on each ECG.
A segment in an electrocardiogram is the region between
two waves.

13. PR Interval
 The PR Interval is calculated from the
beginning of the P wave to the beginning of
the QRS complex. It represents the time it
takes the heart’s electrical impulse to travel
from the atria through the AV node, bundle of
His, and left/right bundle branches.
 Normal Duration: 0.12-0.20 seconds (120-
200 ms)
 Prolonged PR Intervals represent a
conduction delay through the atria or AV
node.

14. QRS Complex
 The QRS complex follows the P wave and
represents the depolarization (contraction)
of the ventricles.
 Normal Duration: 0.06-0.12 seconds
(60-120 ms)
 Prolonged QRS complexes represent a
conduction defect at the Bundle of His or
in the bundle branches.

15. QT Interval
 The QT interval represents the depolarization
and repolarization of the ventricles.
 Normal Duration: 0.36-0.44 seconds (360-
440 ms)

16. Recording on machine as the
heart pumps

17. What Does an Electrocardiogram Show?
Many heart problems change the heart's electrical
activity in distinct ways. An electrocardiogram (EKG)
can help detect these heart problems.
EKG recordings can help doctors diagnose heart
attacks that are in progress or have happened in the
past. This is especially true if doctors can compare a
current EKG recording to an older one.
An EKG also can show:
• Lack of blood flow to the heart muscle (coronary
heart disease)
• A heartbeat that's too fast, too slow, or irregular
(arrhythmia)
• A heart that doesn't pump forcefully enough (heart
failure)
• Heart muscle that's too thick or parts of the heart
that are too big (cardiomyopathy)
• Birth defects in the heart (congenital heart defects)
• Problems with the heart valves (heart valve disease)
• Inflammation of the sac that surrounds the heart
(pericarditis)
An EKG can reveal whether the heartbeat starts in the
correct place in the heart. The test also shows how

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