Common ECG Abnormalities Flashcards
When is a PR interval prolonged?
When it is more than 1 large box
When is the QRS complex prolonged?
When it is more than 3 small boxes
When is the Corrected QT interval (QTc) prolonged?
When more than 44 small boxes
What criteria must be met for the ECG to be in sinus rhythm?
- Rhythm must be regular
- Heart rate between 60 - 100 bpm
- P waves are present
- P waves must be upright in leads I,II
- PR interval should be 3-5 boxes (normal)
- QRS complex should be under or equal to 3 small boxes
- Every P wave must be followed by a QRS complex
- Every QRS is preceded by a P wave.
What is an atrioventricular conduction block?
This is a delay / failure of conduction of impulses from atrium to ventricles via AV node and bungle of His.
What causes AV conduction block?
Acute MI
Degenerative change (fibrosis as people age - changes electrical conduction)
What are the types of AV conduction block?
First degree heart block
Second degree heart block (Mobitz type 1 and Mobitz type 2)
Thrid degree heart block
What is 1st degree heart block?
Impulses get through but takes longer.
PR interval is prolonged to over 0.2 seconds (5 small boxes)
What is 2nd degree heart block - Mobitz type 1?
Also called Wenkebach type.
Successively longer PR intervals until one QRS is dropped then the cycle starts again.
What is 2nd degree heart block - Mobitz type II?
PR intervals do not lengthen but, suddenly dropped QRS complex.
This is dangerous as there is a high risk of progression to complete heart block.
What is 3rd degree heart block?
This is complete failure of AV conduction.
This means Atria and Ventricles are depolarising independently.
Ventricular pacemaker takes over (Ventricular escape rhythm).
Usually wide QRS complexes.
Ventricular rate is very slow (30-40bpm), often too slow to maintain BP.
Urgent pacemaker insertion usually required.
Ventricle doesn’t conduct through His Purkinje system so slower conduction.
In 3rd degree heart block, P-P intervals are regular and R-R intervals are regular but, there is no relationship between P waves and QRS complexes (The PR interval is completely variable from beat to beat)
What is a bundle branch block?
- Delayed conduction in the branches of the bundle of His (right or left bundle)
- P waves and PR interval normal
- Wide QRS complex (>3 small squares) - since ventricular depolarisation takes longer.
Where can abnormal impulses form from?
- These are also called supraventricular rhythms as they arise above the ventricles.
- Sinus node
- Atrium
- AV node
- Ventricular rhythms.
- Ventricle
What happens in a supraventricular rhythm?
SVT Normal (narrow) QRS complex.
What happens in ventricular rhythm?
Wide and bizarre QRS complexes.