Download Poor R Wave Progression

Med 7500
ECG INTRO
1
This Section Includes:
Complexes: P, QRS,T waves and
miscellaneous waves
Intervals: PR, QRS, QT
Heart Rate Calculation
Axis determination
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Complexes and Intervals
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ECG Lead Placement
Limb leads
Precordial (V) leads
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Standard Leads
Limb Leads
Precordial Leads
A=”Augmented” leads
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P Waves
The P wave represents atrial depolarization.
It is normally upright in I, II, III aVF, V4-V6;
inverted in aVR, variable in others.
Best place to find P waves is in II and III
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P Waves
In V1, the p wave may be biphasic
(having an initial positive and terminal
negative deflection).
The initial positive deflection is the right atrium
component; the terminal deflection is the left
atrium.
Each component should be within 1 mm. This
becomes important when looking for atrial
enlargement.
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Biphasic P wave in V1
RA
LA
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PR Interval
Represents conduction through the atria
and AV node and into the his/purkinge
system prior to ventricular depolarization.
It is measured from the beginning of the P
wave to the beginning of the QRS complex.
Normal = 0.12-0.20 seconds
(3-5 small boxes).
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PR Interval
A major portion of the PR interval is the
normal delay through the AV node, which is
under the influence of the autonomic nervous
system.
PR is increased in: First degree AV block,
hyperthyroidism, coronary artery disease.
PR is shortened in: WPW, ectopic atrial rhythm,
or an occasional junctional rhythm.
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QRS Complex
Represents ventricular depolarization,
which occurs from endocardium to
epicardium.
Normal <0.10 sec
0.10-0.12 is borderline
>0.12 is prolonged.
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Measuring QRS Width
Measure the QRS
at its widest point,
usually right at
the baseline.
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QRS terminology
Q wave: the initial negative deflection of
the QRS-always occurs before an R wave
or alone.
R wave: the first positive deflection of the
QRS.
S wave: the terminal negative deflection
that occurs after the R wave.
R' wave: the second positive deflection
seen.
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QRS Morphologies
(Or Q wave)
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Causes of a Wide QRS
Conduction defects-bundle branch blocks
Left ventricular hypertrophy
Hyperkalemia
Ventricular or paced rhythms.
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R Wave Progression
The R wave normally increases across the
precordial leads, and should be
isoelectric (equally positive and negative)
by about V3-V4.
"Poor R wave progression" signifies a late
transition to a positive QRS; it may
suggest previous infarction, but is not
specific, and signifies rotation of the
heart along the axis representing the
transverse plane.
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Cross Sectional View
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Normal R Wave Transition
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Late Transition
(Poor R Wave Progression)
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Poor R Wave Progression
Anterior/Anteroseptal MI
LVH
Fascicular blocks(partial bundle branch
blocks)
Infiltrative or dilated cardiomyopathy
WPW
Chronic Lung Disease
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Early R Wave Progression
R waves too big in V1 and V2
Posterior MI
Right Ventricular Hypertrophy
Right Bundle Branch Block
Wolf Parkinson White
Miscellaneous
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RVH
Notice Large R waves in V1 and V2
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QT Interval
The QT interval measures time in ventricular
systole. It becomes shorter as the heart rate
goes up.
Normal is approx 0.3-0.4 sec for HR 60-100,
slightly longer for females.
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QT Interval
The QT interval should not be greater
than 1/2 the preceding R-R interval for HR
65-90.
The corrected QT interval (QTc) corrects
for heart rate, and can be calculated by
the formula:
QTc = QT + .00175(HR-60).
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Prolonged QT
QTc > 460 ms is generally considered
prolonged, but the cutoff isn’t absolute.
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Prolonged QT
The main risk to a long QT interval is
development of polymorphic ventricular
tachycardia, or torsades de pointes.
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Prolonged QT Interval
A prolonged QT is caused by:
hypocalcemia, hypokalemia, hypomagnesemia
type IA and type III antiarrhythmics,
procainamide, etc or amiodarone, sotalol, ibutilide,dofetilide
tricyclic antidepressants
antipsychotics
macrolide antibiotics-erythromycin, clarithromycin, azithromycin
quinolone antibiotics
methadone
congenital long QT syndrome
any cause of a widened QRS-less of a concern
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Short QTc
Short QTc:
Hypercalcemia, hyperkalemia, acidosis, ischemia,
increased vagal tone
Congenital (channelopathy assoc with sudden
death)
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ST Segment
The principal importance of
the ST segment is whether
it is elevated or depressed
compared to the baseline,
which is measured in the TP interval.
ST segment
Baseline
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ST Segment Changes
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ST Elevation
ST elevation is seen in acute injury/MI,
pericarditis, ventricular aneurysm,
prinzmetal's angina, myocarditis,
Brugada’s syndrome (ST elevation with
RBBB pattern).
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ST Depression
ST depression can be seen in myocardial
ischemia, ventricular hypertrophym
bundle branch blocks, paced or ventricular
beats, digoxin therapy.
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69 year old taking digoxin
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J Point
The J point is the intersection of the
beginning of the ST segment and the end
of the QRS. Normally there is a 90 degree
angle between the two, the ST segment
then proceeds horizontally, and
subsequently gently slopes into the T
wave.
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T Waves
Represent ventricular repolarization.
They are normally inverted in aVR, and
often V1 & V2.
Normal amplitude should not be greater
than 5 mm in limb leads or 10-15 mm in
precordial leads, but exceptions exist.
Normal for females is about 2/3 of that.
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70 y/o with a cerebral
bleed
Deeply inverted T
waves
Thought to be
caused by autonomic
changes induced by
increased intracranial
pressure
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T Waves
T wave inversion: myocardial ischemia,
repolarization change from LVH or RVH,
BBBs, paced or ventricular beats, digoxin
therapy.
Tall, or hyperacute T waves can be from
hyperkalemia, early MI, CVA, occ.
antipsychotic drugs.
Flattened or biphasic T waves are nonspecific.
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60 y/o dialysis patient
K=6.8
Tall, or hyperacute T waves-think hyperkalemia or very early MI.
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Miscellaneous
Waves
39
66 year-old taking Lasix, ate
too many prunes and got
diarrhea.
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U Waves
U waves follow the t wave and are small
upright waves from an unknown cause.
They can be a normal variant, especially with
bradycardia, or be seen in hypokalemia.
They are usually about 10% the height of the T
wave, and are most visible in V2 and V3
Their presence can cause an artifactual
increase in the QT interval. ECG machines can
sometimes make this mistake.
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Calculating
Heart Rate
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Heart Rate
The normal paper speed is 25mm/sec.
Each small box is 1mm, thus each small box
= .04 seconds (1/25)
There are 5 small boxes between large hash
marks, so each large box = 0.2 seconds.
There are then 300 large
boxes in one minute.
(60/0.2).
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For Regular Rhythms:
If there were a beat every large box the
heart rate would be 300. If every other
large box, it would be 150; every third
100 and so on.
To rapidly calculate the heart rate for
regular rhythms, find a QRS on a dark
line, and use the same permutation of
300-150-100-75-60-50-43-38… or divide
the number of large boxes between R
waves into 300.
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Rate with Regular
Rhythm
300 150 100 75
60
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Irregular Rhythms
For irregular rhythms, you must count out
an interval, usually 3-6 sec (15 or 30 large
boxes and count the number of QRS
complexes in that interval.
Then multiply appropriately to get 60
seconds.
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Rate Calculation for
Irregular Rhythms
1
2
3
4
5
6
7
8
30 large boxes=6 seconds
8 complexes in 6 seconds so rate = 8x10 or 80
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Axis
Determination
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Normal Axis
The normal axis is from approx –29 to
105-110 degrees, depending on the source
of info.
The patient’s age should, however be taken
into account.
As people age, the axis tends to shift leftward,so an
axis of 90+ degrees may be normal in a younger
patient, but abnormal in an elderly patient.
Similarily an axis of 0 to -15 may be abnormal in a
younger patient.
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Axis Deviation
RAD is an axis > 105 degrees
LAD is an axis of –30 degrees to -90
-90 to +/- 180 is usually denoted extreme
axis deviation
EAD
RAD
LAD
Nl
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Causes of Right Axis
Deviation
COPD
RVH or acute overload
RBBB
Arm lead reversal
Dextrocardia
Occ. normal variant
Left posterior hemiblock
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Causes of Left Axis
Deviation
LVH
LBBB
Left Anterior Hemiblock
Pregnancy, Ascites (elevates diaphragm)
Inferior MI
Advanced age
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Lead Directions
Arrows point to the positive pole of each lead
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Calculating Axis with
Isoelectric Lead
If the axis of depolarization is going
toward the positive pole of a lead, a net
positive deflection in the QRS will result.
If the axis is going away from the lead, a
net negative QRS will result.
If the axis is perpendicular to a lead, the
QRS will be isoelectric (equally positive
and negative).
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Axis Direction
Lead III is negative so the axis is pointing away
from its positive pole.
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Calculating AxisIsoelectric Lead
Note leads and perpendiculars.
I and aVF
II and aVL
III and aVR
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Find an Isoelectric Lead
To determine the axis, first try and find an
isoelectric QRS in the limb leads. The axis
will then be along its perpendicular;
towards it if the QRS is positive; away if
the QRS is negative.
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Axis with isoelectric lead
Lead aVF is isoelectric
It’s perpendicular is I,
which is positive.
perp
end
ar
icul
Therefore the axis is
at O degrees
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Axis?
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If No Isoelectric
QRS Is Present
First isolate axis to a quadrant using leads I and aVF.
Remember that if a lead is positive, the axis lies within 90
degrees of either side.
So if I is positive, the axis is between -90 and +90. If I were
negative, the axis would be from +90 to -90 on the other
side.
Once you know the quadrant, determine which leads go
through that quadrant.
Using the perpendicular leads, you can tell which side of
the leads crossing the quadrant the axis lies.
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1. I is (+) and aVF is (-), so
axis is between 0 and -90.
2. III and aVL cross
this quadrant.
3. The perpendicular to aVL is
II, which is positive, so axis
must be more (+) than aVL.
4. Axis is between 0
and -30, therefore -15,
or the midpoint.
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Shortcut: You can also take the smallest lead and find
the perpendicular. Then check to see on which side of
that lead the axis lies, depending on whether the
smallest lead is + or -.
smallest
*
*
*
perpendicular
*
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AXIS
If a lead is close to isoelectric, the axis can
be estimated by adding or subtracting
5-10 degrees
If multiple leads are isoelectric, making
the axis difficult if not impossible to
determine, it is sometimes denoted as
“indeterminate”
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www.anwresidency.com
Click “student” tab
Go to lectures and under ECG you ewill
find ECGs to download under each
section.
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