Arrhythmia - Heart Block Flashcards
What is normal sinus rhythm?
60-100 bpm
What is the conduction pathway for electrical signals in heart?
SA node
AV node
Bundle of His
Purkinje fibres
What is the PR interval?
Time taken for depolarisation to go from SA node to AV node
What is heart block?
Bradycardia
Causes of heart block?
Scarring/fibrosis of hearts electrics via aging
MIs
IE
Rate limiting meds - Bblockers/CCBs
Digoxin toxicity
What is 1st degree heart block?
A delay in the conduction pathway from SA node to ventricles
How does 1st degree HB show on ECG?
Prolonged PR interval
Is 1st degree HB a problem?
Not really
What is 2nd degree heart block?
A series of increasing delays in the time it takes for the AV node to transmit signal to ventricles
What are the 3 sub types of 2nd degree HB?
Mobitz type 1 and 2
2:1/3:1/4:1 conduction
What is mobitz type 1?
Occurs in the Av node
PR interval gets progressivly longer and it takes longer for signal to go from SA node to ventricles
Eventually results in a skipped beat
Cycle of PR shortening starts over again
Not as serious and doesn’t need treatment - mild dizziness
What is mobitz type 2?
Occurs below the AV node
Not cycle bases - most beats have a constant PR interval
Some beats just do not have ventricular depolarisation - a missed beat
Light-headed, dizzy and fainting
This is more serious and needs treatment
What is2:1/3:1/4:1 conduction?
A rotation of conducted and non-conducted atrial beats into ventricles
Number depends on how many skipped beats follow a normal beat
So 1 normal beat and 3 skipped beats is 3:1 - 3 to 1 beat
What is 3rd degree heart block?
Complete block of signal transmission
How do ventricles pump in 3rd degree heart block if all transmission has stopped?
They are excited by a slow escape mechanism from depolarising focus in ventricular cardiac muscle
