ECG Theory (MI, Bradyarrhythmias and Blocks) Flashcards
What are the causes of ST elevation?
MI
Pericarditis* (widespread)
Early repolarisation
LBBB
*there should be no ST depression anywhere except for aVR or V1, don’t miss a massive STEMI
What are the causes of ST depression?
MI
Posterior STEMI
Left ventricular hypertrpohy + strain
Digoxin
What is the ECG criteria for LVH?
S wave in V1 + R wave in V5/6 greater than 35mm
OR
S wave in aVL greather than 11mm
What structure is affected in heart block?
AV node
Describe 1st degree heart block?
1st degree:
Inefficient AV node causing a prolonged PR interval
Describe 2nd degree heart block pathophysiologically and in terms of the ECG?
2nd degree:
Mobitz type 1 (wenckebach):
Tiring AV node; prolonging PR intervals followed by a dropped beat, it then resets with the PR interval normal again
Mobitz type 2:
AV node intermittently on and off in a 1:1, 2:1, 3:1 pattern
Describe 3rd degree heart block pathophysiologically as well as the ECG appearance?
3rd degree:
Complete AV node failure, normal atrial contraction with no beats conducted to ventricles.
Escape rhythm takes over:
- if from just under the AV node then it still is going down the bundle branches and it is narrow complex.
- if it is from elsewehere in the ventricles then it is broad complex as it is not a fast depolaristaion.
ECG appearance:
Appears as a very slow rate in the 30s/40s. No relationship between p & QRS complexes, find to consecutive p waves and count back.
Describe the treatment algorithim in bradycardia?
Are there any adverse features?
- Is the patient shocked?
- Are they unconscious?
- Are they in chest pain?
- What are there O2 sats?
Any of these features give Atropine 0.5mg IV
No adverse features, is there a risk of asystole?
- Recent asystole
- Mobitz type II
- 3rd degree heart block
- Ventricular pause more than 3 seconds
Yes to any of these:
-Give atropine 0.5mg IV up to 3mg and consider elective pacing
Or
-Transcutaneous pacing
Describe the pathophysiology and ECG appearance in bundle branch block?
One of the bundle branches wither left of right are blocked meaning there is fast conduction down one side of the ventricle and slow conduction down the other side.
ECG appearance
Wide QRS complex greater than 3mm
V1 mostly -ve then it is LBBB
V1 mostly +ve then it is RBBB
Other methods are William and Marrow
Or
Turn the page 90 degrees clockwise whichever way the main defelction is going in V1 is the direction of the branch block.
What is the normal axis range and describe a method for looking for axis deviation?
Normal axis is between -30 and 90 degrees.
Look at leads I II and III.
RAD: Lead III is the most +ve
LAD: Lead I is +ve and Lead II is mostly -ve
Any other combo is normal.
In any patient with RBBB on there ECG what should you look for?
Left axis deviation and prolonged PR interval.
RBBB + left axis deviation = Bifasicular block
RBBB + left axis deviation and heart block* = Trifasicular block
*Usually 1st degree (prolonged PR) but may 2nd degree or in a complete trifasicular block 3rd degree.
What are the fasicles?
The left bundle branch block splits off into 2 fasicles known as:
- the left anterior fasicle
- the left posterior fasicle
When one of these is blocked it is called fasicular block.
What is fasicular block?
Fasicular block is when either the anterior or posterior left fasicle is blocked.
If the anterior fasicle is blocked there will be: LAD
If the posterior fasicle is blocked there will be: RAD
What is bifasicular and trifasicular block and what will you see on an ECG?
Bifasicular block: RBBB and one of the left fasicles being blocked
ECG shows: RBBB and LAD
Trifasicular block: is when there is RBBB and both left fasicles are blocked.
ECG shows: RBBB, LAD and a type of heart block (most commonly 1st degree)
