ECG Revisted Flashcards
What can ECGs helps see?
- Conduction abnormalities
- Structural abnormalities
- Perfusion abnormalities
Why are ECGs helpful?
- Relatively cheap and easy to undertake
- Reproducible between people and centres
- Quick turn around on results/report
- Leads are views of the heart
What is a vector?
A quantity that has both magnitude and direction
How is a vector usually shown?
by an arrow in the net direction of movement, whose size reflects the magnitude
What does an isoelectric line represent?
no net change in voltage I.e. vectors are perpendicular to the lead
What does the width of of the deflection show?
‘duration’ of the event
Which direction are upward deflection?
towards the cathode (+)
Which direction are downward deflection?
towards the anode (-)
What is each wave composed of?
both the up and downstrokes
What is the P wave?
electrical signal that signifies relaxation of the ventricles
What is the QRS complex?
electrical signal that stimulates contraction of the ventricles (ventricular systole)
What is the T wave?
electrical signal that stimulates contraction of the atria
What happens at the SAN? What does it look like on a ECG?
- Auto-rhythmic myocytes (sponateanously depolarising)
- Atrial depolarisation
- Wide as slow and not high as small and going more towards positive then negative vector
(P)
What happens at the AVN?
- AVN depolarisation
2, Isoelectric ECG - Slow signal transduction
- Protective
What happens at the bundle of his?
- Rapid conduction
- Insulated
What happens at the bundle branches?
Septal depolarisation (S)
What happens at the purkinje fibres (1)?
Ventricular depolarisation (R)
What happens at the purkinje fibres (2)?
Late ventricular depolarisation (S)
What does the fully depolarised ventricles look like on ECG?
Isoelectric line
What is ventricular repolarisation?
T wave
Where is lead I placed?
- Right Arm to Left Arm
- One L
Where is lead II placed?
- Right Arm to Left Leg
- Two L’s
Where is lead III placed?
- Left Arm to Left Leg
- Three L’s
How do you read electrode placement?
- English is read left to right and top to bottom, polarity does that too
- Drawn as a triangle and reading left to right and top to bottom, the first electrode of each pair you reach is the anode (-ve)
Where is V1 placed?
- Right sternal border
- In the 4th intercostal space
Where is V2 placed?
- Left sternal border
- In the 4th intercostal space
Where is V3 placed?
-Halfway between V2 and V4
Where is V4 placed?
- Mid-clavicular line
- 5th intercostal space
Where is V5 placed?
- Anterior axillary line
- At level of V4
Where is V6 placed?
- Mid-axillary line
- At level of V4
What is the bottom of the ECG reading?
Rhythm strip
What does sinus rhythm look like?
- Each P wave is followed by a QRS complex (1:1)
- Rate is regular (even R-R intervals) and normal (83bpm)
- Otherwise unremarkable
What does sinus bradycardia look like?
- Each P wave is followed by a QRS complex (1:1)
- Rate is regular (even R-R intervals) and slow (56bpm)
- Can be healthy, caused by medication or vagal stimulation
What does sinus tachycardia look like?
- Each P wave is followed by a QRS wave (1:1)
- Rate is regular (even. R-R intervals) and fast (107bpm)
- Often a physiological response (I.e. secondary)
What does sinus arrhythmia look like?
- Each P wave is followed by a QRS wave
- Rate is irregular (variable R-R intervals) and normal-ish (65-100mph)
- R-R interval varies with breathing cycle
What does atrial fibrillation look like?
- Oscillating baseline - atria contracting asynchronously
- Rhythm can be irregular and rate may be slow
- Turbulent flow pattern increases clot risk
- Atria not essential for cardiac cycle
What does atrial flutter look like?
- Regular saw tooth pattern in baseline (II,III, avF)
- Atrial to ventricular beats a 2:1 ratio, 3:1 ratio or higher
- Saw-tooth not always visible in all leads
What does first-degree heart block look like?
- Prolonged PR segment/interval caused by slower AV conduction
- Regular rhythm 1:1 ratio of P-waves to QRS complexes
- Most benign heart block, but a progressive disease of ageing
What does secondary degree heart block (Mobitz I) look like?
- Gradual prolongation of the PR interval until beat skipped
- Most P-waves followed by QRS; but some P waves are not
- Regular irregular: caused by a diseased AV node
- Also called Wenckebach
What does secondary degree heart block (Mobitz II) look like?
- P waves are regular but only some are followed by QRS
- No P-R prolongation
- Regular irregular: success to failures (e.g. 2:1) or random
- Can rapidly deteriorate into third degree heart block
What does third degree (complete) heart block look like?
- P waves are regular, QRS are regular, but no relationship
- P waves can be hidden within bigger vectors
- A truly non-sinus rhythm - back-up pacemaker in action
What does ventricular tachycardia look like?
- P waves hidden: dissociated atrial rhythm
- Rate is regular and fast (100-200bpm)
- At high risk of deteriorating into fibrillation (Cardiac arrest)
- Shockable rhythm - defibrillators widely available
What does ventricular fibrillation look like?
- Heart rate irregular and 250 bpm and above
- Heart unable to generate an output
- Shockable rhythm - defibrillators widely available
What does ST elevation look like?
- P waves visible and always followed by QRS
- Rhythm is regular and rate is normal (85bpm)
- ST-segment is elected >2mm above the isoelectric line
- Caused by infarction (tissue death caused by hypo perfusion)
What does ST depression look like?
- P Waves visible and always followed by QRS
- Rhythm is regular and rate is normal (95bpm)
- ST-segment is depressed >2mm below the isoelectric line
- Caused by myocardial ischaemia (coronary insufficiency)
