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Steps in Rhythm Analysis
• Evaluation of ECG requires systematic
approach to analyzing given rhythm
– Numerous methods can be used for rhythm
interpretation
– Text uses method that first looks at QRS complex
• Most important observation in life-threatening
dysrhythmias
• Followed by P waves and relationship between P
waves and QRS
• Rate
• Rhythm
• P-R interval
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Steps in Rhythm Analysis
• Questions paramedic must ask in any
rhythm analysis to determine presence or
potential for life-threatening rhythm
disturbances
– Is the patient sick?
– What is the heart rate?
– Are there normal looking QRS complexes?
– Are there normal looking P waves?
– What is the relationship between the P waves
and QRS complexes?
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Analyze the QRS Complex
• Analyze QRS complex for regularity and
width
– QRS complexes ≤ 0.10 second wide (less
than three small squares) are supraventricular
in origin
• These complexes are normal
– Complexes ≥ 0.12 second wide may indicate
conduction abnormality in ventricles
• May indicate that focus originates in ventricles and
is abnormal
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Analyze the P Waves
• Normal P wave in lead II is positive and
smoothly rounded and usually precedes each
QRS complex, indicating that pacemaker
originates in SA node
– Paramedic should observe the following five
components when evaluating P waves
• Are P waves present?
• Are P waves occurring at regular intervals?
• Is there one P wave for each QRS complex, and is
there a QRS complex following each P wave?
• Are P waves upright or inverted?
• Do they all look alike? (P waves that look alike and are
regular are likely from same pacemaker.)
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Analyze the Rate
• Analysis of heart rate may be done in a
number
of ways
– Methods for calculating heart rate
•
•
•
•
Heart rate calculator rulers
Triplicate method
R-R method
6-second count method
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Analyze the Rate
• Determined by analyzing ventricular rate
(QRS complex)
– Normal adult heart rate is between 60 and 99
beats/minute
• If ventricular rate is less than 60 beats/minute,
considered bradycardia
• If rate is greater than or equal to 100 beats/minute,
considered tachycardia
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Take a poll of your
classmates. How many have a
resting
heart rate less than
60 beats/minute?
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Heart Rate Calculator Rulers
• Available from number of manufacturers
– Follow directions that come with rulers
– Are reasonably accurate if rhythm is regular
– Mechanical device or tool should not be relied
on solely to determine heart rate
• There will be occasions when device or tool is not
readily available
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Triplicate Method
• Accurate only under two circumstances
– Rhythm is regular
– Heart rate greater than 50 beats/minute
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Triplicate Method
• Requires memorizing two sets of numbers
– 300-150-100
– 75-60-50
• Numbers are derived from distance between heavy
black lines (each representing 1/300 minute)
• Two 1/300-minute units = 2/300 minute = 1/150
minute, or heart rate of 150 beats/minute
• Three 1/300-minute units = 3/300 minute = 1/100
minute, or heart rate of 100 beats/minute
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Triplicate Method
• Using triplicates, the paramedic can calculate
heart rate as follows
– Select an R wave that lines up with dark vertical
line
– Number next six dark vertical lines consecutively
from left to right as 300-150-100 and 75-60-50
– Identify where next R wave falls with reference to
six dark vertical lines
• If R wave falls on 75, heart rate = 75 beats/minute
• If R wave falls halfway between 100 and 150, heart rate
is about 125 beats/minute
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R-R Method
• May be used several different ways to
calculate
heart rate
– Rhythm must be regular to obtain accurate
reading
– Method works equally well for slow rates
• Method 1. Measure distance in seconds
between peaks of two consecutive R
waves
– Divide this number into 60 to obtain heart rate
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R-R Method
• Method 2. Count the large squares
between the peaks of two consecutive R
waves
– Divide this number into 300 to obtain heart
rate
• Method 3. Count small squares between
peaks of two consecutive R waves
– Divide this number into 1500 to obtain heart
rate
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6-Second Count Method
• Least accurate method of determining heart
rate
– Useful for quickly obtaining an approximate rate in
regular and irregular rhythms
• Short vertical lines at top of most ECG graph
papers are divided into 3-second intervals
when run at standard speed of 25 mm/second
– Two of these intervals = 6 seconds
– Heart rate is calculated by counting number of QRS
complexes in 6-second interval
• This number is multiplied by 10
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Which of these rate
calculation methods is
fastest? Which is most
accurate?
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Step 4: Analyze the Rhythm
• To analyze ventricular rhythm, compare R-R
intervals on ECG tracing in systematic way
from left to right
– Measurement may be taken using ECG calipers
or pen and paper
– Using calipers, place one tip of caliper on peak of
one R wave and adjust other tip so that it rests on
peak of adjacent R wave
– Use caliper to map distance of R-R interval to
evaluate evenness and regularity
• P waves may be mapped for regularity in this same
way
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Step 4: Analyze the Rhythm
• In absence of calipers, use similar method
of evaluating R-R interval using pen and
paper
– Place straight edge of paper near peaks of R
waves and mark off distance between two
other consecutive
R waves
– Compare this R-R interval with other R-R
intervals in ECG tracing
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Step 4: Analyze the Rhythm
• If distances between R waves are equal or
vary by
less than 0.16 second (four small
squares), rhythm
is regular
– If shortest and longest R-R intervals vary by
more than 0.16 second, rhythm is irregular
– Irregular rhythms may be classified further
– May be classified as regularly irregular
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Step 4: Analyze the Rhythm
• In this case, irregularity has pattern, also
called “group beating”
• Irregular rhythms also may be occasionally
irregular
– In this case, only one or two R-R intervals are
unequal
• Irregular rhythms may be irregularly
irregular
– In this case, rhythm is totally irregular
– No relationship is seen between R-R intervals
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Step 5: Analyze the P-R Interval
• P-R interval indicates time it takes for
electrical impulse to be conducted through
atria and AV node
– Interval should be constant across ECG
tracing
– Prolonged P-R interval (greater than 0.20
second) indicates delay in conduction of
impulse through AV node or bundle of His
– Delay is called atrioventricular block
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Step 5: Analyze the P-R Interval
• Short P-R interval (less than 0.12 second)
indicates impulse progressed from atria to
ventricles through pathways other than AV
node
– Known as accessory pathway syndrome,
most common of which is Wolff-ParkinsonWhite syndrome
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Using Five Steps to
Analyze Rhythm
• Normal sequence of atrial and ventricular
activation as it relates to ECG tracing is as
follows
– Each P wave (atrial depolarization) is followed by
normal QRS complex (ventricular depolarization)
and T wave (ventricular repolarization)
– All QRS complexes are preceded by P waves
– P-R interval is within normal limits, and R-R
interval is regular
– Five steps in ECG rhythm interpretation can be
applied to rhythm
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