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Normal Sinus Rhythm
Lancashire & South Cumbria Cardiac Network
ECG Interpretation
• A mystery?
• An enigma?
• Confusing?
• Difficult?
Criteria - P wave
• P Wave represents atrial depolarisation.
• An upright rounded P-wave in leads II, III and
AVF, and an inverted P-Wave in AVR which
precede each QRS Complex.
• The P wave does not exceed 2.5mm in height.
• It does not exceed 3mm in width.
• A biphid P wave is seen in lead V1.
Criteria - PR interval
• PR Interval
• 0.12 - 0.20seconds.
• Delay at AV node
» Protect ventricles
» Allow for ventricular filling
Criteria QRS complex
• QRS Complex represents ventricular
depolarisation.
•
•
•
•
Should not exceed 0.12 seconds in duration.
Should not exceed 27mm in height.
Sharp narrow complex
RS in V1, QRS in V6
Criteria T wave
• The deflection produced by repolarisation
of the ventricles.
• No clearly defined range
• General rule - T wave should not be more
than 1/2 the height of the preceding QRS
Criteria - QT interval
• QTc Interval
• Should not exceed 0.42 seconds
(QTc).
• QT interval corrected to the heart
rate.
Correction Calculation
QTc
=
measured Qt interval
√ cycle length
Criteria U wave
• The origin is uncertain
• May represent repolarisation if the IVS
• May represent slow conduction of
ventricular myocardium
• Prominent U waves are abnormal
• Usually most visible in V1-V4
Nomenclature - QRS
• The 1st negative deflection - Q
• The 1st positive deflection - R
• The 2nd negative deflection or If a negative
follows a positive - S
Nomenclature -QRS
Nomenclature - QRS
Nomenclature - QRS
• Waves > 0.5mv (5mm) high
• Capital letters e.g. QRS
• Waves < 0.5mv (5mm) high
• Lower case e.g. qrs
Intervals
• P wave duration measured?
• PR interval measured?
• QRS interval measured?
• QT interval measured?
Amplitudes
• P wave height measured?
• QRS height measured?
Segments
• PR segment measured?
• ST segment measured?
1mm =
0.1mv
1mm = 0.04s
Paper
speed
P
QRS
segments
Pr Int
QT Interval
Limb leads
• Measurements - lead II
• QRS Axis
• P wave Axis
Chest Leads
• Progression of R waves throughout the
chest leads
• Transitional Zone
• Phases of Activation
Depolarisation Stages
1
2
3
Typical complexes in the Precordial leads
RV
V1
RV
V2
IVS
V3
IVS
V4
LV
V5
LV
V6
Progression of R waves
throughout the chest leads
• Size of the R wave should increase from V1
to V6.
• V4 Usually at the Apex (Transitional Zone
where the first negative wave appears).
Normal Rhythms
• Sinus Bradycardia: Same findings as for
Normal Sinus Rhythm except
– Heart Rate less than 60 bpm
Normal Rhythms
• Sinus Tachycardia: Same findings as for
Normal Sinus Rhythm except
– Heart Rate greater than 100 bpm
Normal Rhythms
• Sinus Arrhythmia: Same findings as for
Normal Sinus Rhythm except
– The R - R Interval is Irregular
Normal Rhythms !!!
• *Sinus Arrest*
• Considered a ‘Sinus rhythm’ but is
abnormal
Summary
• Checklist
• Criteria
ECG INTERPRETATION
• If the normal ECG is
known then
interpretation of
abnormals becomes
easier
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