An electrocardiogram uses electrical conductors placed on the arms and legs to detect cardiac potential differences between sites. The standard 12-lead electrocardiogram records voltage changes from 12 different leads, including bipolar limb leads and unipolar chest leads. It provides a record of voltage changes occurring on the body surface as the heart's electrical impulse propagates through the cardiac cycle, following standardized conventions.

1. Electrocardiogram Leads

2. Goedemorgen:

3. Introduction
• An electrocardiographic lead is pair of electrical
conductors
• For detecting cardiac potential differences.
• Bipolar leads will make potential differences at
different sites.
• It is a routine diagnostic procedure.
• It is standardised and has universal conventions

4. What are leads?
• Leads I, II, and III are bipolar leads
• Leads aVR, aVL, and aVF are unipolar leads
• Leads V1–V6 are unipolar leads
• ♥ Clinical Tip: Patients should be treated according to
their symptoms, not merely their ECG.

5. Basic Electrocardiographic Conventions
• Placed on both arms and the left leg
• Called Einthoven's triangle
• Example: lead II electrocardiogram measured between
right arm & left leg .
• upward deflection in a lead II electrocardiogram =
an electrical polarity exists between left leg and right
shoulder electrodes >>> left leg electrode being positive.

6. Downward deflection in a lead II record > the left leg electrode
being negative.

7. How to measure the dipoles?
» The net dipole is determined by:
(1) how extensive the wavefront is?
(2) the consistency of orientation between individual dipoles
at different points in the wavefront

8. How to measure the dipoles?
The net dipole makes:
lower portion (+) in contrast
to
upper portion of body.
Postive voltages exists on
three sides.
from Einthoven's triangle by
observing that the net dipole
has the arrows point positive
direction of leads I, II, and III.
Note: dipole is most parallel to lead II.
Thus, it has a large component in the lead II
direction. >> create a larger voltage on lead II than
on leads I or III.
Small component on lead III >>oriented nearly
perpendicular to lead III.

9. The Standard 12-Lead Electrocardiogram
• Recorded from 12 different leads.
• leads I, II, and III > bipolar leads
• nine leads > unipolar leads.
• Three leads are generated by using the limb electrodes.
• Two electrodes > indifferent electrode.
• Third limb electrode is made the positive pole of the pair.
[augmented unipolar limb leads]
• The voltage record between the electrode at the right arm
and the indifferent electrode = aVR
• recorded on left arm and lead = aVL
• recorded from the electrode on left leg = aVF

11. Chest leads
• six specified positions on the chest wall.
• precordial or chest leads and are designated
as V1 through V6.
• when positive electrode is in position 1 and
wave of ventricular excitation sweeps away
from it > deflection downward.
• When electrode is in position 6 and the wave
of ventricular excitation sweeps toward it, >
deflection upward.

12. Recap
It is a record of
the voltage
changes that
occur on the
surface of the
body as a result
of the
propagation of
the action
potential
through the
heart during a
cardiac cycle.
There are
standardized
conventions
used for
recording
electrocardio
grams.
The magnitude
and direction
of the net
dipole formed
by the
wavefront of
the action
potential at any
instant in time
can be deduced
from the
magnitude and
orientation of
the
electrocardiogr
aphic
deflections.
The mean
electrical axis
describes the
orientation of the
net dipole at the
instant of
maximum
wavefront
propagation
during
ventricular
depolarization
and normally
falls between 0
degrees and +90
degrees on a
polar coordinate
system.
The standard
12-lead is
widely used to
evaluate
cardiac
electrical
activity and
consists of a
combination of
bipolar and
unipolar
records from
limb & chest

13. La fin
• The End
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• El final