Transcript 8 - ER EKG Overview

EKG Overview
Heart
Walls
•
•
•
•
•
Inferior Wall
Septal Wall
Anterior Wall
Lateral Wall
Posterior Wall
Inferior Wall
• II, III, aVF
• View from Left Leg 
• inferior wall of left ventricle
I
aVR
V1
V4
II
aVL
V2
V5
III
aVF
V3
V6
Septal Wall
• V1, V2
• Along sternal borders
• Look through right ventricle &
see septal wall
I
aVR
V1
V4
II
aVL
V2
V5
III
aVF
V3
V6
Anterior Wall
• V3, V4
• Left anterior chest
•  electrode on anterior chest
I
aVR
V1
V4
II
aVL
V2
V5
III
aVF
V3
V6
Lateral Wall
• V5 and V6
• View from Left Arm 
• lateral wall of left ventricle
I
aVR
V1
V4
II
aVL
V2
V5
III
aVF
V3
V6
Lateral Wall
• I and aVL
• View from Left Arm 
• lateral wall of left ventricle
I
aVR
V1
V4
II
aVL
V2
V5
III
aVF
V3
V6
Key Principles of
Electrocardiography
There are 12 leads. The six
that reflect electrical activity in
the fontal plane are I, II, III, AVL,
AVR and AVF. The six
reflecting the horizontal plane
are V1 through V6.
Summary of EKG Leads
In summary, the 12 standard leads are:
Limb leads
I, from the right arm (-) toward the left arm (+)
II, from the right arm toward the left leg
III, from the left arm toward the left leg
Augmented Leads
aVR, augmented lead toward the right (arm)
aVL, augmented lead toward the left (arm)
aVF, augmented lead toward the foot
Summary of EKG Leads
In summary, the 12 standard leads are:
Chest Leads
• V1 through V6, starting over the right atrium with
V1, and placed in a semi-circle of positions
leftwards, to the left side of the left ventricle.
• V1 and V2, on the right and left sides respectively,
are placed just off the sternum at the 4th
intercostal spaces (the space between the 4th
and 5th ribs, which can be felt through the skin)
and the others travel around to V6 under the
armpit, as shown in the diagram.
Summary of EKG Leads
12 Lead Paper and
Measurements
• At one end of each ECG strip there is usually a
step-like structure called a calibration box. The
standard box is 10 mm high and 0.20 seconds
wide. The calibration box is there to confirm that
the ECG conforms to the standard format.
12 Lead Paper and
Measurements
• The easiest way to calculate the rate is to use the
method of separated boxes. Find a QRS complex
that starts on a thick line. The best is to use the tip
of the tallest wave on the QRS complex- R wave.
This will be a starting point. As a second step, find
the next QRS complex or any other spot- your end
point. Then just count the thick lines in between the
two spots, and calculate the rate from memorized
numbers 300, 150, 100, 75, 60, 50, where each
number represents one of the previous rates.
12 Lead Paper and
Measurements
12 Lead Paper and
Measurements
EKG Complex:
PQRSTU
12 Lead EKG Workshop
One of the most important reasons for obtaining an ECG is
to help evaluate the patient who presents with new-onset
chest pain. By doing so we hope to determine:
• If any acute changes are present.
• If there is evidence of prior infarction.
12 Lead EKG
Workshop
Specifically, we want to determine if the patient
being evaluated is acutely infarcting or ischemic. If
so, what area of the heart is involved, how
extensive is the involvement, are other
abnormalities present (i.e., AV block, conduction
defects, arrhythmias) and most importantly, is the
patient a candidate for acute intervention (i.e., with
thrombolytic therapy or angioplasty)?
Acute Infarction: What are the
Changes?
• There are 4 principal ECG indicators of acute
infarction:
• ST segment elevation
• T wave inversion
• Development of Q waves
• Reciprocal ST segment depression.
Acute Infarction: What are the Changes?
• A and B
show a normal QRS complex before any changes
develop.
Acute Infarction: What are the Changes?
• Picture C
shows the "hyperacute" stage, which is the earliest
change of Acute MI, in which the T wave becomes
broader and peaks (almost as if "trying" to lift the ST
segment). This change may be subtle (and easy to
miss!); it usually is short-lived.
Acute Infarction: What are the Changes?
• Picture D
shows conventional ST elevation follows (with ST
coving/"frowny" shape) and developing Q waves.
Acute Infarction: What are the Changes?
• Picture E and F
show Q waves becoming bigger, ST elevation is
maximal, and T wave inversion begins. T waves
evolve as ST segments return to baseline (in F).
Acute Infarction: What are the Changes?
• Picture G
shows ST-T wave abnormalities resolving (or nearly
resolving) but there is persistence of Q waves.
KEY Points regarding the
ECG with Acute MI:
• Not all patients with Acute MI develop ECG
changes. As many as 1/3 do not develop
changes, especially if MI occurs in electrically
silent areas of the heart.
• The A thru F sequence in the figure above
represents the "typical" evolution of Acute MI.
Variations on this theme are common (i.e., ST
depression or T wave inversion may be the only
change, Q waves don't always develop, Q waves
sometimes resolve with time, etc.).
Rhythm Identification:
P Waves
• Are there visible P waves?
• Does a QRS follow EVERY P wave?
• If not, how many P waves are before each
QRS?
• Is it a consistant number of P waves before
each QRS?
Rhythm Identification:
PR Interval
• Time interval
from start of P
wave to start of
QRS
• 0.12 - 0.20 sec.
In length
Rhythm Identification:
QRS (reg or irreg)
• Next, look at the QRS.
• Is it narrow or wide?
• Ask yourself again, do they occur at regular or
irregular intervals?
• If irregular, is the rhythm regularly irregular or
irregularly irregular?
Blocks
• The leads to look in first for right bundle branch block (RBBB for short) are
leads V1 & V2.
• In RBBB, the QRS complex has two R-waves which give the QRS a doublepeaked appearance. This is called the “R-S-R1” wave.
“R-S-R1” wave
• The leads to look in first for left bundle branch block (LBBB) are leads
V5, V6, and I.
• If the QRS is wide, mostly upright, and the T waves are inverted, then
you are most likely looking at LBBB.
Blocks
MI Identification
Inferior MI:
The leads to look in are leads II, III, & AVF.
MI Identification
Septal MI:
Look at leads V1-V2 for MI’s.
MI Identification
Anterior MI:
Look at leads V3-V4 for MI’s.
MI Identification
Lateral MI:
The leads to look in for lateral MI are leads I, AVL, V5, & V6.
MI Identification Posterior MI:
This one is tricky, and the EKG is not the definitive diagnostic tool
for this type of MI. Look for tall R waves and ST depression as
sign to suspect Posterior MI in V1 & V2.
MI Identification
Posterior MI:
If you suspect Posterial MI then need to perform a
“right sided EKG”
Obtaining the 18-Lead ECG
B) Posterior Leads
A) Right Ventricular Leads
Move V1 to V3R
Move V2 to V4R
Move V3 to V5R
Move V4 to V7
Move V5 to V8
Move V6 to V9
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MI Identification
Posterior MI:
Label the new leads that you changed to either V7, V8, V9 or
V4R, V5R, V6R.
Heart Walls and Lead Correlation
38
Lateral Wall
Septal Wall
Inferior Wall
Anterior Wall