Conduction blocks Flashcards
What is first degree heart block
occurs where there is delayed atrioventricular conduction through the AV node
ECG for first degree heart block
pr interval is greater than 0.2 seconds
5 small or 1 big square
What is second degree heart block
where some of the atrial impulses do not make it through the AV node to the ventricles. This means that there are instances where p waves do not lead to QRS complexes
names of the three types of second degree heart block
Mobitz1
Mobitz2
2:1 BLOCK
What happens in mobitz type 1
- atrial impulses becomes gradually weaker until it does not pass through the AV node.
- After failing to stimulate a ventricular contraction the atrial impulse returns to being strong
- cycle repeats
ecg for mobitz 1
- increasing PR interval until the P wave no longer conducts to ventricles
- This culminates in absent QRS complex after a P wave.
- This cycle repeats itself.
what occurs in mobitz type 2
- intermitted failure or interruption of AV conduction
- Normal pr intervals
ecg for mobitz type 2
- pr intervals are the same
- missing qrs complexes
what is 2:1 block
2 p waves for each qrs complex , every second p wave is not a strong enough atrial pressure to stimulate a QRS complex
what is third degree heart block
- COMPLETE HEART BLOCK
- no observable relationship between p waves and QRS complexes
treatment for stable av node blocks
observation
treatment for unstable or risk of asystole
- first line- atropine iv 500mcg
- no improvement:
- atropine repeated up to 6 doses
- other inotropes
- transcutaneous cardiac pacing
What occurs in left bundle branch block
right ventricle contracts before the left
define bundle branch block
a block in the conduction of one of the bundle branches , so the ventricles don’t receive impulses at the same time
describe normal cardiac conduction
- The sino-atrial node acts as the initial pacemaker
- Depolarisation reaches the atrioventricular node
- Impulses travel simultaneously down the bundle of His via the left and right bundle branches. The septum is depolarised from the left.
- Both the left and right ventricular walls are depolarised simultaneously
diagnostic criteria for RBBB
- QRS- > 120 ms
- RSR pattern in V1-V3
- Wide , slurred S wave in lateral leads
Explain MaRroW for RBBB
Complexes in V1 resemble M and V6 resembles W
Describe the steps in right bundle branch block
- The sino-atrial node acts as the initial pacemaker
- Depolarisation reaches the atrioventricular node
- Depolarisation through the bundle of His occurs only via the left bundle branch. The left branch still depolarises the septum as normal.
- The left ventricular wall depolarises as normal.
- The right ventricular walls are eventually depolarised by the left bundle branch, this occurs by a slower, less efficient pathway.
Diagnostics for LBBB are
- QRS duration > 120ms (3 small squares)
- Dominant S wave in V1
- Broad, monophasic R wave in lateral leads – I, aVL, V5-V6
- Absence of Q waves in lateral leads
- Prolonged R wave > 60ms in leads V5-V6
WiLliaM mnemonic for LBBB
Complexes in v1 resemble W
Complexes in v6 RESEMBLE m
Why might LBBB occur
- conduction system degeneration
- myocardial pathologies
- after cardiac procedures
- STEMI - rare
What does the left bundle branch split into
anterior and posterior fasicles
anterior fasicle block may cause ….?
left axis deviation
posterior fasicle deviation causes …. r
right axis deviation
