ECG or EKG
António Mesquita
Definition
An electrocardiogram (ECG or EKG)
is a test that records the electrical
activity of the heart.
ECG is 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).
How does it works…
The heart is a muscle with well-
coordinated electrical activity, so the
electrical activity within the heart can be
easily detected from outside of the body.
After the appropriate leads are attached
to the body, a heated stylus moves
upward with positive voltage and
downward for negative voltage.
• On the moving heat-sensitive paper,
voltage is traced out.
• The test takes about five minutes,and it
is fairly painless.
Types of ECG lead
There are two basic types of ECG
leads. Bipolar leads (standard
limb leads) utilize a single positive
and a single negative electrode
between which electrical
potentials are measured.
Unipolar leads (augmented leads
and chest leads) have a single
positive recording electrode and
utilize a combination of the other
electrodes to serve as a
composite negative electrode.
Lead Position
A typical ECG report shows the cardiac cycle from 12
different vantage points (I, II, III, aVR, aVL, aVF, V1-
V6), like viewing the event electrically from 12
different locations (like a 3D perspective).BUT only
10 electrodes are used.
Lead I represents activity that is going from the right
arm to the left arm
Lead II represents activity that is going from the right
arm to the left leg
Lead III represents activity that is going from the left
arm to the left leg
aVL is placed on the left arm (or shoulder)
aVF is placed on the left leg (or hip)
aVR is placed on the right arm (or shoulder)
V1- 4th intercostal space to the right of sternum
V2- 4th intercostal space to the left of sternum
V3- halfway between V2 and V4
V4- 5th intercostal space in the left mid-clavicular line
V5- 5th intercostal space in the left anterior axillary
line
V6- 5th intercostal space in the left mid axillary line
Electrical vectors and how they
apply to the heart
The inferior leads (leads II, III and aVF) look at
electrical activity from the vantage point of the
inferior region (wall) of the heart. The lateral
leads (I, aVL, V5 and V6) look at the electrical
activity from the vantage point of the lateral wall
of the heart. The anterior leads, V1 through V6,
and represent the anterior wall of the heart. aVR
is rarely used for diagnostic information, but
indicates if the ECG leads were placed correctly
on the patient.
The inferior leads record events from the apex
of the left ventricle. The lateral and anterior
leads record events from the left wall and front
walls of the left ventricle, respectively. The right
ventricle has very little muscle mass. It leaves
only a small imprint on the ECG, making it more
difficult to diagnose than changes in the right
ventricle.
ECG waves and intervals
QT interval: duration of ventricular
depolarization and repolarization
RR interval: duration of ventricular cardiac
cycle (an indicator of ventricular rate)
PP interval: duration of atrial cycle (an
indicator or atrial rate)
PR interval: time interval from onset of
atrial depolarization (P wave)
QRS duration: duration of ventricular
muscle depolarization
P wave: the sequential activation
(depolarization) of the right and left atria
QRS complex: right and left ventricular
depolarization (normally the ventricles are
activated simultaneously)
Examples of Waves
ECG with atrioventricular block (due to ischemia, nodal compression and
inflamation and extreme stimulation).
Normal ECG
ECG with ventricular tachicardia
Normal ECG
ECG during ventricular fibrilation
(due to ischemia or electric shock)
Normal ECG
The End
