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Interpreting an ECGStudent led tutorial 1
Tim Jackson [email protected]
Chris Pavitt [email protected]
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What is an ECG?
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Depolarisation of the heart
Relating the ECG wave form to electrical activity within the heart
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ELECTRICAL ACTIVITY
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PQ
RS
T
ECG
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`
PQ
RS
T
ECG
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PQ
RS
T
ECG
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PQ
RS
T
ECG
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Normal ranges for ECG intervals
PR interval
QRS
QT interval
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Remember these values!
Interval Normal range (per ms) Pathology
P-R 120-200 Long – heart block (drugs, electrolytes)
QRS 80-120 Long – conduction abnormalities e.g. bundle branch block
QT (varies with heart rate) >450 can lead to ventricular tachycardia
Long – repolarisation abnormalities, ion channelopathies e.g. long QT syndrome
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Working out your intervals
LEARN THIS!
TASK – Work out the PR interval in this ECG
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Remember these values!
Interval Normal range (per ms) Pathology
P-R 120-200 Long – heart block (drugs, electrolytes)
QRS 80-120 Long – conduction abnormalities e.g. bundle branch block
QT (varies with heart rate) >450 can lead to ventricular tachycardia
Long – repolarisation abnormalities, ion channelopathies e.g. long QT syndrome
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Rate Normal range: 60 – 100 bpm
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Working out the rate (bpm)
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Rhythm
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Rhythm
The heart pumps blood at a fixed rate (feel your own pulse)
This maintains a constant cardiac output
Recall that each P-QRS-T cycle = systole (one beat)
Rhythm
Regular pulse
Irregular pulse
Irregularly-Irregular pulse
Regularly-Irregular pulse
Sinus arrhythmia
2nd Degree Heart block
(Wenkebach)
Atrial fibrillation
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Rhythm example
Atrial fibrillation
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Heart Block
Heart blockA blocking of the depolarisation wave spreading through the heart
Heart block
Mobitz type 2Some P waves not conducted, PR interval fixed
Type 3 / CompleteP wave and QRS dissociationType 2
Mobitz type 1/ WenkebachProgressive PR prolongation, then dropped beat
Type 1PR interval > 0.2 seconds
Advanced BlockFixed ratio of P: QRS complex
student ledtutorials
Interpreting an ECGStudent led tutorial 1
Tim Jackson [email protected]
Chris Pavitt [email protected]
student ledtutorials
Appendix 1 – Rate calculations
22
The simple method:1. Find a QRS complex2. Find the next QRS complex along3. Find the R wave in both 4. Count how many big boxes there are in between each
R wave5. With a calculator do:
• 300 / (number of big boxes)
6. You can make this exact as you like ie 3.4 boxes
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Appendix 2 – Rhythm
23
Method:1. Grab a piece of paper
2. Line it up horizontally across ECG lead 2 tracing
3. Make sure you can see the tips of each R wave
4. Make a vertical mark on the paper for the first 2 R waves
5. Line up 1st mark with 2nd R wave
6. Does the 2nd mark line up with 3rd R wave?
7. Carry on repeating this.
Interpretation If the heart rate is regular then the distance between each QRS should be
regular, and thus your marks will line upIf the heart rate is irregular, then the distance between each QRS will
vary, and your marks will not always line up
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Appendix 3 – Clinical information heart block
Aetiology:CongentialAcquired
1. Idiopathic fibrosis2. Myocardial infarction3. Inflammatory process
1. Acute2. Chronic
4. Drugs
Clinical featuresType 1 – Rarely symptomsType 2 –
• Wenkebach usually not a problem and may be normal in athletes/ asleep• Mobitz 2 usually a sign of severe disease and syncope may occur. Treated with
a pace makerType 3/complete – Syncope or stokes-adams attacks may occur. Also treated
with pacemaker
