Title: The Basics of ECG Interpretation
1The Basics of ECG Interpretation
2Summary
- Cardiac conducting system and the ECG waveform
- The normal ECG
- Abnormalities of conduction
- Heart Rhythms
- QT prolongation
- Normal Variants
3Cardiac Depolarisation
- Originates in pacemaker cells (automaticity).
- Spreads along defined pathways.
- Causing co-ordinated muscular contraction.
- Electrical signal from depolarisation detectable
at body surface. (1 mV cf. 90 mV _at_ cell) - This is the ECG.
4The Cardiac Conducting System
5Anatomy of the ECG
6The Limb Leads
- I, II, VL - L lateral surface
- VF, III - Inferior surface
- VR - R atrium
- Cardiac Axis
- Lead II often used for rhythm strips.
7The Chest Leads
- V12 - R Venticle
- V34 - Septum
- V56 - L Ventricle
- Bundle Branch Blocks
- Ischaemia (esp. V5)
8The Normal ECG
9Characteristics of the Normal ECG
- Rate 50-100 bpm
- Sinus rhythm
- Cardiac Axis -30º to 90º
- P lt120 ms
- PR lt200 ms
- QRS lt120 ms
- QT Male lt0.43 s Female lt0.45 s
- ST isoelectric
10Calculating Heart Rate
- Standard ECG speed is 25 mm.s-1
- Heart Rate 300/ big squares
300/3.879 bpm
11Cardiac Axis (Einthovens Triangle)
- Average direction of depolarisation in the
ventricles
12Cardiac Axis (at a glance)
First look at lead I and aVF
Then look at lead II...
13Abnormalities of conduction
- At the AVN Heart Block
- 1st degree
- 2nd degree
- 3rd degree
- In the His/Purkinje system Bundle Branch Block
- LBBB
- RBBB
14First Degree Heart Block
- Prolonged PR interval gt200 ms (5 small sq.)
- Slow conduction through the AVN
- Not itself important
- May indicate disease
- RA
- IHD
- Dig. Toxicity
15Second Degree Heart Block
- Mobitz Type I (Wenkebach)
- Increasing PR interval preceding unconducted P.
- Does not usually cause symptoms.
- May indicate disease (RA, IHD, Dig.).
- Usually benign
16Second Degree Heart Block
- Mobitz Type II
- Fixed PR interval with some unconducted P waves.
- May occur with fixed ratio eg. 21 block
- Indicates underlying disease.
- May cause symptoms/precede complete block.
17Third Degree (Complete) Heart Block
- No relationship between P QRS
- QRS often wide
- Atrioventricular dissociation
- Impairs cardiac performance.
18Left Bundle Branch Block
- Characteristic, widened QRS in chest leads
- Will not cause symptoms itself
- Always indicates underlying heart disease
- Makes ECG interpretation difficult or impossible
W i LL ia M
19Right Bundle Branch Block
M a RR o W
- Characteristic, widened QRS in chest leads
- May indicate right heart disease
- Can occur in normal individuals
- Partial RBBB is always normal.
20Heart Rhythm
- Always ask
- What is the QRS width?
- lt120ms gt Supraventricular source
- gt120 ms gt Ventricular source (or BBB)
- Is there a P wave?
- Is the rhythm regular/irregular/irregularly
irregular?
21Supraventricular Rhythms (1)
22Supraventricular Rhythms (2)
Inspiration
Expiration
- (Respiratory) Sinus Arrhythmia
23Supraventricular Rhythms (3)
24Supraventricular Rhythms (4)
25Supraventricular Rhythms (5)
26Supraventricular Rhythms (6)
27Supraventricular Rhythms (7)
28Supraventricular Rhythms (8)
29Ventricular Rhythms (1)
- Ventricular Ectopic and Couplet
30Ventricular Rhythms (2)
31Ventricular Rhythms (3)
32Ventricular Rhythms (4)
33QT Prolongation
- QT represents the ventricular refractory period
- Normal lt450 ms (ish)
- Risk of prolongation...
Torsades de Pointes - potentially lethal.
34QT Prolongation
- ? How long is too long
- Affected by temperature, gender, heart rate
- Diurnal variation up to 70 ms
- Numerous drugs
- Cisapride
- Terfenadine
- Total of 48 listed as causing TdP by FDA
35Normal Variants
- Always normal
- Sinus Arrhythmia
- Supraventricular Extrasystoles
- Partial RBBB
- Often normal
- Sinus Bradycardia (and pauses in athletes)
- First Degree Heart Block
- Ventricular Extrasystoles
- Left/Right Axis Deviation
- RBBB
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