00:00:00
foreign
00:00:00
[Music]
00:00:05
of an electrocardiogram known as an ECG
00:00:08
or EKG is a skill in medicine that is
00:00:12
often overlooked in this video I'll
00:00:15
provide a systematic approach to help
00:00:17
you read them more confidently
00:00:19
the basics to remember are that each
00:00:22
component of the ECG represents
00:00:25
electrical activity within the heart
00:00:27
corresponding to different points in the
00:00:30
cardiac cycle for example the P wave
00:00:32
represents atrial depolarization and we
00:00:35
will look at each of these points in
00:00:38
more detail as part of the
00:00:39
interpretation
00:00:41
a normal 12 lead ECG is taken by using
00:00:44
four limb electrodes and six chest
00:00:47
electrodes each lead gives a slightly
00:00:50
different view of the heart with a
00:00:52
positive deflection when the activity is
00:00:54
towards that electrode and negative when
00:00:57
it is away from it leads 1 AVL V5 and V6
00:01:02
look at the lateral part of the heart
00:01:04
2 3 and avf the inferior part and V1 to
00:01:09
V4 give a septal and anterior View
00:01:13
the first step is to ensure the correct
00:01:15
patient information the date and the
00:01:18
calibration of the machine the date and
00:01:20
time are especially important because
00:01:23
you may be looking at one of a series of
00:01:25
ECGs looking for changes over time the
00:01:29
calibration is normally 25 millimeters
00:01:31
per second and 10 millimeters per
00:01:34
millivolt if these settings are adjusted
00:01:37
before the ECG is taken it can look
00:01:39
completely different so you need to
00:01:42
check it before you start interpreting
00:01:44
once they are confirmed I start by
00:01:47
looking at the axis because it is so
00:01:50
easy to overlook the overall direction
00:01:52
of the electrical activity gives the
00:01:55
axis and is normally between -30 and 90
00:01:59
degrees it could be normal deviated to
00:02:02
the left or to the right or extremely
00:02:05
deviated a quick way to assess it is the
00:02:08
quadrant method that allows you to
00:02:10
quickly place the axis in one of the
00:02:12
four quad just by looking at Lead 1 and
00:02:15
avf if both the positive the axis must
00:02:19
be in the lower right quadrant therefore
00:02:21
normal if Lead 1 is negative and avf is
00:02:24
positive there is right access deviation
00:02:27
if both the negative there is Extreme
00:02:30
axis deviation
00:02:32
the only one needing a further step is
00:02:34
if Lead 1 is positive and avf is
00:02:37
negative then the axis is in the upper
00:02:40
right quadrant and to distinguish left
00:02:43
axis deviation from normal you can look
00:02:46
at lead two if it is negative the axis
00:02:49
is deviated to the left
00:02:51
axis deviation can occur in many
00:02:54
different conditions and is not specific
00:02:56
but looking at it first can alert you
00:02:59
early that there could be further
00:03:01
abnormalities
00:03:02
next we look at the rate each small
00:03:05
square is one millimeter in width on the
00:03:09
standard speed of 25 millimeters per
00:03:12
second the small squares on the paper
00:03:14
represent 40 milliseconds and five of
00:03:17
these together form bigger squares
00:03:20
therefore with 200 milliseconds each
00:03:23
that means five of these big squares
00:03:26
make up one second so if one beat
00:03:29
happens every five big squares that's
00:03:31
one beat in one second so 60 beats in a
00:03:35
minute a shortcut is to divide 300 by
00:03:39
the number of large squares between each
00:03:41
QRS to get the approximate ventricular
00:03:44
rate this is easy if the rhythm is
00:03:47
regular if it's not then instead count
00:03:50
the number of QRS complexes over 10
00:03:53
seconds then multiply it by 6 forget the
00:03:56
number of beats in one minute
00:03:58
the normal rate is 60 to 100 beats per
00:04:02
minute with rates below that being
00:04:04
called bradycardia and above that being
00:04:07
tachycardia
00:04:09
that brings us nicely to Rhythm which
00:04:11
basically means do the Beats fall at
00:04:14
regular intervals to evaluate this look
00:04:17
at the gap between the QRS complexes
00:04:20
known as the RR interval is it the same
00:04:23
size each time or does it change this is
00:04:27
more obvious at normal heart rates but
00:04:29
can be tricky to distinguish at very low
00:04:32
or very high heart rates if the gap
00:04:35
between beats changes throughout the ECG
00:04:38
then the rhythm is irregular but the
00:04:41
story doesn't end there the irregularity
00:04:44
can be present with no clear pattern
00:04:46
known as irregularly irregular like
00:04:49
atrial fibrillation or regularly
00:04:51
irregular such as in some second-degree
00:04:54
heart blocks
00:04:55
looking at the QRS complexes evaluates
00:04:58
the ventricular Rhythm but it's also
00:05:01
important to evaluate the atrial rate
00:05:03
and the communication between the Atria
00:05:06
and the ventricles which is why I also
00:05:08
include the P wave and PR interval when
00:05:11
looking at the Rhythm
00:05:13
the P wave represents atrial
00:05:15
depolarization
00:05:17
the normal P wave should be positive in
00:05:19
lead 2 have a duration of less than 120
00:05:23
milliseconds an amplitude of less than
00:05:26
2.5 millimeters and each P wave should
00:05:29
be followed by a QRS complex
00:05:32
some abnormalities can include an
00:05:34
increased duration or amplitude of the P
00:05:37
wave that may indicate left or right
00:05:39
atrial dilatation respectively or the
00:05:42
absence of p waves entirely such as in
00:05:45
atrial fibrillation
00:05:46
the electrical activity then normally
00:05:49
passes through the Atria ventricular
00:05:51
node just before being conducted down
00:05:54
into the ventricles and causing
00:05:56
ventricular depolarization and
00:05:58
contraction the PR interval is the time
00:06:00
between atrial depolarization and
00:06:03
ventricular depolarization and is
00:06:06
measured from the start of the P wave to
00:06:08
the start of the QRS complex its normal
00:06:11
duration is between 120 and 200
00:06:15
milliseconds a prolongation indicates
00:06:17
slowing of the conduction between the
00:06:19
Atria and ventricles for example a first
00:06:22
degree AV block a shortening may suggest
00:06:26
a condition with an accessory pathway
00:06:28
like wolf Parkinson White
00:06:30
a variable PR interval suggests other
00:06:33
forms of atrioventricular blocks I'll
00:06:36
leave a link to a video dedicated to
00:06:38
Heart blocks here
00:06:39
next up is the morphology of the
00:06:42
remaining components of the ECG there is
00:06:45
the QRS complex itself which represents
00:06:48
ventricular depolarization and is
00:06:51
generally divided into narrow or widened
00:06:54
normally the electrical activity moves
00:06:57
quickly through the conduction system
00:06:58
and goes more slowly through the muscle
00:07:00
tissue narrow complexes generally
00:07:03
suggest the origin of that beat is
00:07:06
supraventricular while a wider QRS
00:07:08
suggests either the activity is
00:07:11
originating in the ventricles or there
00:07:14
is a block in the conduction system
00:07:16
carrying the electrical signal to one of
00:07:18
the ventricles and so to get to the
00:07:21
other side must go through The
00:07:22
myocardium the latter is why left and
00:07:25
right bundle branch blocks have a wide
00:07:28
QRS morphology and pacemakers will also
00:07:31
traditionally have a morphology similar
00:07:34
to left bundle branch block
00:07:36
here is a comparison of left and right
00:07:38
bundle branch blocks and an easy way to
00:07:41
remember the morphology of each is the
00:07:44
mnemonic William marrow the voltage of
00:07:47
the QRS complexes can also indicate
00:07:49
pathology classically large amplitudes
00:07:53
in the precordial leads May point to
00:07:55
left ventricular hypertrophy while
00:07:58
alternating amplitudes could indicate
00:08:00
pericardial effusion
00:08:02
Q waves are the first negative
00:08:04
deflection in the QRS the r wave is a
00:08:08
following upwards deflection and S is
00:08:11
any negative deflection following that
00:08:13
pathological Q waves are defined as Q
00:08:16
waves greater than 25 percent of the QRS
00:08:19
complex with a width greater than 40
00:08:22
milliseconds they can indicate previous
00:08:25
ischemia there should be progression
00:08:28
from V1 to V6 where the S Wave is
00:08:31
initially greater than the r wave but
00:08:33
then at around V3 or V4 the r wave
00:08:36
becomes greater than the S Wave
00:08:38
poor progression can also indicate
00:08:41
previous ischemia
00:08:42
the ST segment is next representing the
00:08:46
interval between ventricular
00:08:47
depolarization and repolarization it
00:08:51
extends from the end of the S Wave to
00:08:53
the start of the T wave this is a famous
00:08:55
part of the ECG as elevation of this
00:08:59
segment May indicate an st elevation
00:09:01
myocardial infarction as well as other
00:09:04
conditions like pericarditis in cases of
00:09:07
St elevation it's important to look for
00:09:10
reciprocal changes in opposite leads for
00:09:13
example St elevation in anterior or
00:09:16
lateral leads may have reciprocal St
00:09:19
depressions in the inferior leads
00:09:22
depressions of this portion generally is
00:09:24
an abnormal finding that can also
00:09:26
indicate ischemia it's worth noting that
00:09:29
it's difficult to interpret the ST
00:09:31
segment in people with bundle branch
00:09:33
blocks therefore more specific criteria
00:09:36
are needed
00:09:37
another feature to be aware of is the
00:09:39
jpoint which is where the S wave ends
00:09:42
and the ST segment begins as it can be
00:09:46
raised causing the appearance of St
00:09:48
elevation this is also known as benign
00:09:51
early repolarization and tends to happen
00:09:54
in people under the age of 60. it's also
00:09:57
likely to be present in multiple leads
00:09:59
not corresponding to a specific
00:10:01
territory and will not have reciprocal
00:10:04
changes and will not change over time as
00:10:07
you would expect with acute ischemia
00:10:09
T waves indicate repolarization of the
00:10:12
ventricles and can be described as tall
00:10:14
flat inverted or even biphasic in most
00:10:18
cases they will be positive and
00:10:20
concordant with the QRS complex but in
00:10:23
cases where they are negative they are
00:10:25
known as t-wave inversions this is
00:10:28
normal in V1 AVR and Lead 3 and can also
00:10:32
persist from childhood in some people in
00:10:34
V2 and V3 inverted T waves in the
00:10:38
absence of St changes can indicate a
00:10:41
historic ischemic event
00:10:43
the classic example of tall T waves is
00:10:45
hyperkalemia and biphasic T waves
00:10:48
meaning T waves that have both a
00:10:50
positive and negative components are
00:10:53
usually due to ischemia or hypokalemia
00:10:57
the interval between the start of the Q
00:10:59
wave and the end of the T wave is the QT
00:11:02
interval and it represents the time
00:11:04
taken from the start of ventricular
00:11:07
depolarization to the end of
00:11:09
repolarization
00:11:11
it gets shorter with faster heart rates
00:11:13
and longer with slower heart rates so it
00:11:16
needs to be corrected for the heart rate
00:11:18
for interpretation classically this is
00:11:21
using bezet's formula its normal value
00:11:24
is generally above 360 milliseconds and
00:11:27
less than 440 milliseconds in males or
00:11:31
less than 460 milliseconds in females
00:11:33
it's important to remember this as
00:11:36
prolongation can predispose to
00:11:38
potentially lethal arrhythmias like
00:11:40
ventricular tachycardia or torsads
00:11:43
U waves are other waves that
00:11:46
occasionally appear after the T waves
00:11:48
most commonly as a result of electrolyte
00:11:51
imbalances or hypothermia using all of
00:11:54
this information you can categorize the
00:11:56
ECG tachycardia is generally divided
00:12:00
into broad or narrow complex and then
00:12:02
further into regular or irregular
00:12:04
bradycardia can be divided based on the
00:12:07
presence or absence of p waves then
00:12:09
further into if every P wave is followed
00:12:12
by a QRS complex or not this is not an
00:12:15
exhaustive list but covers some general
00:12:17
arrhythmias
00:12:18
overall the ACG is a snapshot of the
00:12:22
activity of the heart at the time it was
00:12:24
captured therefore it needs to be
00:12:26
correlated with the history of how the
00:12:28
patient presented and why the ECG was
00:12:31
indicated in the first place you also
00:12:33
need to consider changes over time for
00:12:36
example in myocardial ischemia another
00:12:39
good example is syncope or palpitations
00:12:41
due to an arrhythmia unless the
00:12:44
patient's heart was in an arrhythmia at
00:12:46
the time of the ECG it won't necessarily
00:12:49
be seen therefore longer monitoring with
00:12:52
a halter monitor may be used for further
00:12:55
reading and practice I would recommend
00:12:57
using the Life in the Fast Lane website
00:12:59
which is the main reference for this
00:13:01
video as they have a comprehensive
00:13:03
resource to improve your ECG reading
00:13:06
skills