ECG basics Flashcards
PR interval
3-5 small squares (120-200ms)
QRS complex length
120ms (3 small squares)
1st degree heart block - how long is the PR interval?
Longer than 1 big square i.e. >6 small squares, or bigger than 220ms
Mobitz type 1 - ecg findings
PR interval steadily gets longer, then you drop a QRS complex
Another name for mobitz type 1
Wenchebach = Weird ONE = type ONE
ECG for Mobitz type 2
Constant PR interval but occasional dropped QRS complex
What is a fixed block?
Two p waves per QRS complex / three fixed p waves per qrs complex
Sometimes the T wave looks like an M because it’s super imposed with a p
type of mobitz 2
Is first degree heart block worrying?
Apparently not
Second degree is worrying
What might cause heart block?
Coronary artery disease
Drugs
Electrolyte abnormalities
What happens in complete heart block (third degree)?
No relationship between p wave and qrs complex so ventricles decide to autonomously depolarise,
QRS in complete heart block
QRS is wide (more than 120ms)
What do we call the trigger that causes a wide QRS complex?
Supraventricular trigger
Causes of complete heart block
Acute MI
Fibrosis of bundle branch/atria
Blockage of both bundle branches
What is the rate of the p wave/qrs complex in complete heart block?
QRS rate is actually really slow
P wave is usually faster
Overall bradycardia
How do you look for axis deviation?
Look at leads 1, 2 and 3
Right axis deviation
QRS complex in l3 pointing up
l1 pointing down like ‘reaching’
What happens to the QRS complex in branch blocks?
QRS widens because it takes forever to depolarise due to the bundle branch block
Also, you end up with TWO qrs complexes because the ventricles are depolarising out of sync
What are the causes of a widened QRS complex?
Bundle branch block OR
if ventricles are depolarising of their own accord
What does the QRS complex look like in certain leads in RBBB?
RBBB - Marrow
M in V1 - positive deflection in lead V1
W in V6
What does the QRS complex look like in certain leads in LBBB?
LBBB - William
W in V1 - negative deflection in lead V1
M in V6
Causes of RBBB
Can be normal !!
Atrial septal defect
Right side heart problm
Causes of LBBB
If asymptomatic, no problem
If chest pain, MI
What happens in WPW?
No AV node so no delay in conduction, so preexcitation occurs via bundle of Kent, so left ventricle depolarises early
What can WPW lead to?
Paroxysmal (on and off) tachycardia
also reentry tachycardia
