ECG Flashcards
PR interval
Start of P to start of Q
3-5 boxes
PR segment
End of P to start of Q
QT interval (idea and number)
Start of Q to end of T
9-11.5 boxes
ST segment
End of S to start of T
QRS complex (number)
2-3 boxes (30-120ms)
Number of leads
3 bipolar leads - I, II, III (frontal plane)
3 augmented leads
6 precordial leads
Where is Lead II put
Positive electrode on left leg
Negative electrode on right arm
Ground on right leg
Speed of contraction in different cells
AV node: 0.05m/s Purkinje fibres: up to 5m/s Conduction via bundles: 1m/s AV node delays signal by 0.1-0.2 seconds Slower conduction between contractile myocytes (0.5m/s)
What is happening at each part of an ECG
P wave: depolarisation of the atria
PR segment: delay of AV node
QRS complex: depolarisation of ventricles
T wave: repolarisation of ventricles
ST segment - beginning of repolarisation in the ventricles
Calculate Rate
300 divided by the number of big boxes
Or if irregular - number of P waves in a 10 second interval, and times this by 6 - bpm
First Degree Heart Block
PR interval is more than 5 little boxes
usually asymptomatic
In young people
Delayed AV node transmission
Mobitz type 1 (Wenckebach)
PR interval gets longer and longer until a QRS fails to follow P wave
Cause: AV node damage
Mobitz Type II (Hay)
Some P waves are blocked and not followed by a QRS
PR interval remains the same
Likely cause: problem with bundle of His
Implant pacemaker
Third degree Heart Block
Atrial signals consistently fail to arrive at the ventricles
Ventricular rate is consistent - 30-40 bpm
Time between atrial and ventricular beats is variable
PR interval varies rapidly
Narrow-complex escape rhythms >40bpm
or Broad-complex escape rhythms - slower HR
Respiratory sinus arrhythmia
Benign
When a person breathes in, heart beat increases
When a person breathes out, heart beat decreases
Escape beats and premature beats
Premature beats triggered by irritable tissue
Escape beats triggered by natural rhythmicity of non-atrial tissue
Triggered in ventricular tissue or by AV node
Premature Ventricular Contractions
Unusually wide and weird looking ventricular contractions
the 2 ventricles are electrically unsynchronised
No S wave, and a negative dip where the T wave should be
Atrial Fibrillation
Disorganised electrical activity in atria - no P wave/wiggly line
Ventricular rate is fast and irregular
Very common in elderly
Can lead to thrombus formation in atria
What is the ECG best for
Excellent for rate (Holter monitor 24/7)
Seeing when something is wrong, but is not a one stop diagnosis
Fast and affordable
What are deep, large Q waves a sign of
Dead tissue - old MI
What does 1 big/little box represent
1 big box: 200ms
1 small box: 40 ms
