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Approaching the ECG:
Read Right In A Minute
February 3, 2011
BGSMC Cardiology Study Group
Nick Sparicino, DO
Mohamad Lazkani, MD
Tomas Rivera-Bonilla, MD
History of the ECG/EKG
• During the late 1800’s and early 1900’s, Dutch physiologist Willem
Einthoven developed the early electrocardiogram He won the Nobel
prize.
• Hubert Mann first uses the electrocardiogram to describe
electrographic changes associated with a heart attack in 1920
• Electrocardiograms must be viewed in the context of demographics,
health history, and other clinical test correlates. They are especially
useful when compared across time to see how electrical activity of
the heart has changed (perhaps as the result of some pathology).
• Why PQRST and not ABCDE? The choice of P is a mathematical
convention dating from Descartes by using letters from the second
half of the alphabet. N has other meanings in mathematics and O is
used for the origin of the Cartesian coordinates. P is simply the next
letter. (For more on Descartes see Henson JR. Descartes and the
ECG lettering series. J Hist Med Allied Sci. April 1971;181�186)
Electrocardiography
• A recording of the electrical activity of the heart over time
• Gold standard for diagnosis of cardiac arrhythmias
•Helps detect electrolyte disturbances (hyper- &
hypokalemia), arrhythmias, myocardial ischemia and
infarction, pericarditis, chamber hypertrophy, drug toxicity
(i.e. digoxin and drugs which prolong the QT interval)
• Allows for detection of conduction abnormalities
• Screening tool for ischemic heart disease during stress
tests
• Helpful with non-cardiac diseases (e.g. pulmonary
embolism or hypothermia)
Electrocardiogram (ECG/EKG)
• Is a recording of electrical activity of heart conducted through
ions in body to surface
ECG Rules
• Wave of depolarization traveling towards a
positive electrode causes an upward
deflection on the ECG.
• Wave of depolarization traveling away
from a positive electrode causes a
downward deflection on the ECG.
Vectors: directions and amplitude
• Vector 1 – depolarization
of atrium(corresponds to P
wave)
• Vector 2 – Ventricular
Septum (1st deflection of
QRS)
• Vector 3 – Bulk of
ventricular muscle
• Vector 4 – Repolarization
of ventricular muscle
Approach to the ECG
• Systematic Approach
• rhythm, rate, intervals, axis, morphology
RRIAM: Read Right In A Minute
RHYTHM
• Locate the P wave
• Establish the
relationship between
P waves and QRS
complex
• If no P wave analyze
the QRS morphology
• Search for other
clues
• Interpret the rhythm
in the clinical setting
RATE
• Determining rate:
– Regular rhythm:
• Big box: 300, 150, 100,
75, 60, 50
– Irregular rhythm:
• # cycles in a 6 second
strip x10
• # cycles in a 12 second
strip x5
• remember to use
halves if half a cycle is
present in the strip
10mm = 1mV
1mm = 0.1mV
RATE: Intrinsic rates of pacing cells
(transmits the
impulses through
the inter-atrial
septum)
•
•
•
•
•
•
•
SA node
Atrial cells
AV node
His bundle
Bundle branch
Purjkinje cells
Myocardial cells
60-100 BPM
55-60 BPM
45-50 BPM
40-45 BPM
40-45 BPM
35-40 BPM
30-35 BPM
ATRIAL COMPONENTS
• P wave – atrial depolarization
– Duration 0.08 to 0.12 sec
• PR interval - impulse
initiation, atrial depol, atrial
repol, AV/His/BB/Purkinje
stimulation
– 0.12 to 0.20 seconds (>0.20
seconds = PR prolongation;
Heart Block discussed later)
VENTRICULAR COMPONENTS
• QRS complex - ventricular
depolarization
– 0.06 to 0.12 seconds
• Q wave Significance
– “pathological/MI” >0.03s or
>1/3 height of R wave
VENTRICULAR COMPONENTS
QT Interval - all the events of
ventricular systole
• Beginning of QRS to end of T wave
• Duration varies with heart rate, age,
sex but should be less than half the
RR interval
• Correction formulas exist to
balance HR, a major variable (as
HR decreases, QT interval
increases)
– Fridericia Correction (QTf):
• QTf = QT interval / cubed
root of the RR interval (in
sec)
– Bazett’s formula (QTc):
• QTc = QT interval / square
root of the RR interval (in
sec)
VENTRICULAR COMPONENTS
• ST segment - electrically
neutral period between
ventricular depol and repol
(time myocardium is
maintaining contraction in
order to push the blood out
of the ventricles)
• T wave - ventricular
repolarization
– Should be asymmetrical
with a slow upstroke and
a fast downstroke
AXIS - Quadrant Graphing Method
I (+)
I (+)
I (-)
I (-)
aVF (+)
aVF (-)
aVF (+)
aVF (-)
=normal
=LAD
=RAD
=extreme LAD or RAD
AXIS - Isoelectric Method
1
2
1. Find isoelectric lead
2. Find perpendicular lead
3. If QRS positive, vector towards lead, if negative, away
MORPHOLOGY
• Hypertrophy (atrial & ventricular)
• Bundle branch blocks and hemiblocks
• Segment depressions & elevations
– PR segment, ST segment
•
•
•
•
•
U waves
T wave morphologies
Delta wave
Osborne wave
ST – T changes
Hypertrophy Criteria
•
Left atrial enlargement
– Terminal negative P wave deflection in V1 > 0.04s and the amplitude of “same” P wave
in V1 > 0.10mV
– P-mitrale in lead II (notched P wave) Duration b/w peaks of P wave notches >0.04s
– Max p wave duration >0.11s
– Ratio of P wave duration to PR duration > 1:1.6
•
Right atrial enlargement
– P wave amplitude >2.5 mm in II and/or >1.5 mm in V1 (these criteria are not very
specific or sensitive)
– Better criteria can be derived from the QRS complex; these QRS changes are due to
both the high incidence of RVH when RAE is present, and the RV displacement by an
enlarged right atrium.
– QR, Qr, qR, or qRs morphology in lead V1 (in absence of coronary heart disease)
– QRS voltage in V1 is <5 mm and V2/V1 voltage ratio is >6
•
Biatrial enlargement
– Features of both RAE and LAE in same ECG
– P wave in lead II >2.5 mm tall and >0.12s in duration
– Initial positive component of P wave in V1 >1.5 mm tall and prominent P-terminal force
Hypertrophy Criteria
Hypertrophy Criteria
Other LVH Criteria
•Sokolow-Lyon Criteria
–S wave in V1 + R in V5 or V6 >= 3.5mV
–Or R wave in V5 or V6 >2.60mV
•Cornell Voltage Criteria
–Female: R in aVL + S in V3 >2.0 mV
–Male: R in aVL + S in V3 > 2.8 mV
•Hypertrophic Cardiomyopathy
–LVH (tall R in V2-V5)
–Deep narrow Q in aVL and V6
–LAE (increased negative terminal p wave in V1)
•Other Criteria (quick glance)
–I = R >14mm
–aVR = S >15 mm
–aVL = R > 12 mm
–aVF = R >21 mm
–V5 = R > 26 mm
–V6 = R >20 mm
Hypertrophy Criteria
RVH Criteria
–Right ventricular hypertrophy
• Any one or more of the following (if QRS duration <0.12 sec):
–Right axis deviation (>90 degrees) in presence of disease capable of
causing RVH
–R in aVR > 5 mm, or
–R in aVR > Q in aVR
•Any one of the following in lead V1:
–R/S ratio > 1 and negative T wave
–qR pattern
–R > 6 mm, or S < 2mm, or rSR' with R' >10 mm
•Other chest lead criteria:
–R in V1 + S in V5 (or V6) 10 mm
–R/S ratio in V5 or V6 < 1
–R in V5 or V6 < 5 mm
–S in V5 or V6 > 7 mm
•ST segment depression and T wave inversion in right precordial leads
is usually seen in severe RVH such as in pulmonary stenosis and
pulmonary hypertension.
Hypertrophy Criteria
•
Biventricular Criteria
– 1. High voltage, biphasic RS complex in midprecordial leads (also common in LV
septal defect)
– 2. LVH criteria in precordial leads with RAD in limb leads
– 3. Low amplitude S in lead V1 combined with deep S wave in lead V2
– 4. LVH criteria in left precordial leads combined with prominent R waves in right
precordial leads
– 5. LAE as sole criteria for LVH combined with any criteria suggestive of RVH
•
Left or right strain pattern Criteria
– ST-T wave changes associated with abnormal repolarisation secondary to increased
ventricular tension have classically referred to as "strain" pattern.
• Left ventricular hypertrophy is often associated with ST depression and deep T
wave inversion. These changes occur in the left precordial leads, V5 and V6. In
the limb leads the ST-T changes occur opposite the main QRS forces. Therefore,
if the axis is vertical, the ST-T changes are seen in II, III and aVF. If the axis is
horizontal the ST-T changes are seen in I and aVL.
• Right ventricular hypertrophy can be associated with ST depression and T wave
inversion in the right precordial leads, V1 - V3. Leads II, II and aVF may also show similar
ST - T wave changes.
Put it all together
• Try to come up with a common theme to the differential
diagnosis based on the list of abnormalities you’ve
created
• Do not overlook anything
• Practice, Practice, Practice (look at many ECGs,
especially normal ones in the beginning, developing
good habits using RRIAM and calculate intervals
committing normal values to memory)