Flashcards in CVS 7.2 - ECG Abnormalities Deck (19):
What causes ventricular ectopic beats?
Ventricular cells gain pacemaker activity
What happens as a result of ventricular ectopic beats?
- Causes premature ventricular contraction
- Happens every other beat etc or in couplets, triplets etc
How does a ventricular ectopic beat change the ECG wave?
Gives a wide QRS complex due to a slower depolarisation of the ventricle as the purkinje fibres aren't being used
What is atrial fibrillation?
A quivering and irregular heartbeat due to the muscles contracting in an uncoordinated way
How does the ECG wave differ during atrial fibrillation?
- P waves are absent as there is no coordinated spread of depolarisation
- Has irregularly irregular fibrillation waves instead
What causes atrial fibrillation?
- Many points in the atria behaving like pacemakers
- Overwhelms AVN (has a refractory period)
- No coordinated spread of depolarisation due to multiple depolarisation points
Why is the QRS complex unchanged during atrial fibrillation?
QRS = in ventricles where activity is normal so still contracts
What is ventricular fibrillation?
Uncoordinated contraction of the ventricular myocardium causing the muscle to quiver
How does the ECG wave differ during ventricular fibrillation?
- Abnormal waves due to chaotic and fast ventricular depolarisation
- Looks like shit
What happens as a result of ventricular fibrillation?
- No contraction
- No cardiac output, no pulse
What is heart block?
A communication problem between the atria and ventricles
How does the ECG wave differ during 1st degree heart block?
- Prolonged P wave (longer than 0.2s)
- Indicates that the AVN is holding the impulse for too long
- Still has ventricular contraction because electrical signals still reach the ventricles
How does the ECG wave differ during mobitz 1 second degree heart block?
- Erratic P-R interval
- P-R elongates until QRS complex is dropped
- Indicates AVN is taking longer in the refractory period
How does the ECG wave differ during mobitz 2 second degree heart block?
- Regular P-R interval
- Leads to dropped QRS complexes
- Indicates that excitation isn't passing through the AV node/bundle of His = not all atrial contractions result in ventricular contractions
What does mobitz 2 second degree heart block lead to?
- Third degree heart block
- Sudden death
How does the ECG wave differ during third degree heart block?
- Inverted QRS complex
- Indicates no AVN conduction = no excitation to the ventricles
- No ventricular contraction but atria are fine
Can the ventricles contract during third degree heart block? Why?
- Yes due to ectopic pacemaker cells
- Beats are usually slow
What is a bundle branch block?
A delay/obstruction of the electrical excitation in the bundle branches/fascicles