ECG Flashcards
What waves are seen on an ECG?
P QRS T
What is the complex seen on an ECG?
QRS complex
Why cant you see atrial repolarisation on an ECG?
Atrial repolarisation happens at the same time as ventricular depolarisation. Ventricular depolarisation involves much more tissue depolarising much faster so it swamps any signal from atrial repolarisation
What happens at the Q of the QRS complex?
The interventricular septum depolarises from L to R
What happens at the R of the QRS complex?
The bulk of the ventricle depolarises from the endocardial to the epicardial surface
What happens at the S of the QRS complex?
Upper part of the interventricular septum depolarises
What is the left leg in relation to?
Right arm
Which direction does a wave of repolarisation go in?
AWAY from the electrode
What direction does a wave of depolarisation go in?
TOWARDS the electrode
Why is the R wave bigger in the SLL II than in the SLL I or SLL III?
Because the main vector of depolarisation is in line with the axis of recording from t he left leg with the respect to the right arm
What is the P wave caused by?
Atrial depolarisation
What is the QRS complex caused by?
Ventricular depolarisation
What is the T wave caused by?
Ventricular repolarisation
Why is the T wave positive?
The AP is longer in the endocardial cells than in the epicardial cells, so the wave of repolarisation runs in the opposite direction to the wave of depolarisation i.e. a wave of repolarisation moving away from the recording electrode produces another positive going blip
What is the PR interval?
Time from atrial depolarisation to ventricular depolarisation
What is the PR interval mainly due to?
Transmission through the AV node
What is the QRS interval?
Time for the whole of the ventricle to depolarise
Normal time of QRS interval
0.08 seconds
What is the QT interval?
Time spent while the ventricles are depolarised
What does the QT interval vary with?
HR
Normal QT interval
0.42 seconds at 60 bpm
What does a wave of depolarisation cause on an ECG?
Upward going blip
Are fast events or slow events transmitted better?
Fast
How to work out the HR from an ECG?
- Measure R-R interval and work out how many in 60 seconds
2. Count how many R waves in 30 large squares (6 seconds) and multiple by 10
Normal HR
60 - 100
Name for < 60 bpm
Bradycardia
Name for > 100 bpm
Tachycardia
What else would you look at on an ECG?
HR
Is each QRS complex preceded by a P wave?
Is the PR interval too short (<0.12 sec) or too long (>0.2s)
Is the QRS complex too wide (>0.12 sec)
Is the QT interval too long (>0.42 s at 60bpm)?
What does STEMI stand for?
ST elevated myocardial infarction
What does NSTEMI stand for?
Non elevated myocardial infarction
Which of STEMI or NSTEMI is worse?
STEMI
What are the limb leads?
aVR aVF aVL SLL III SLL II SLL I
Does AVF give a positive or a negative blip?
Positive
Does AVR give a positive or a negative blip?
Negative
Which precordium leads flip over?
V3/V4
What plane do the limb leads look at?
Frontal plane
What plane do the precordial leads look at?
Transverse plane
What is a downward QR wave?
1st deflection
What is a downward sR wave?
Subsequent deflection
What does more voltage on the ECG indicate?
The more the muscle
Max QRS width
3 little boxes
What interval is very difficult to determine on the ECG due to all of the influencing variables?
QT interval
What does prolonged P-R interval indicate?`
1st degree heart block
Which Mobitz type of type II heart block is more pathological?
Mobitz type II
What determines the atrial rate?
Between the P waves
Causes of atrial dissociation
Complete heart block
VT
Pacemaker
Does VT have to be >100bpm?
No, can be whatever speed it determines
What type of BBB is always abnormal?
LBBB
Signs on ECG of LBBB
V1 downward
V6 upright and notched
Is RBBB always abnormal?
Can be a variant of normal
Signs on ECG of RBBB
V1 smaller R waves and larger R prime
V6 slurred S wave
How much of the myocardium does the left main stem artery cover?
2/3rds
Causes of ST depression
Occlusion
Severe hypotension
Severe anaemia
Why does troponin rise and fall in ischaemia?
Due to the dynamic features and nature of ischaemia
Is P : QRS relationship is 1;1, what does this mean?
Sinus rhythm
What wall of the heart is not looked at on the ECG? What can be looked at and where to try and identify this?
Posterior wall
Can look like ST depression on the anterior leads
What artery supplies the sinus node?
Right coronary artery
VF vs VT on ECG
VF - big amplitude, not same shape or frequency
VT - same waveform
Does adenosine treat atrial tachycardia and why?
No - as does not needing the AV node
What is used to treat SVT?
Cardioversion
What kind of treatment is SVT?
An umbrella term
Examples of Cardioversion
Valsalva
Carotid sinus massage
Adenosine
Features of adenosine
Blocks AV node
Half life 10 seconds
Patients feel like they will die
Cannulas placed as proximal as possible
What is given after adenosine?
Saline
Treatment of VT
Anaesthetist put patient to sleep - then Defibrillator
If comes back
- amiodarone
What are little bumps on ECG usually? What do they usually confirm?
P waves
Confirms VT due to more ventricular activity
Is there atrial activity in AF?
Yes, but all fluttered/fibrillating
What do irregular QRS complexes represent?
AV nodal function in AF
