ECG Tutorial Flashcards
what are the features to cover when analysing a 12 lead ECG
Rate Rhythm Axis P wave PR interval QRS Complex ST segment T wave
Rate, rhythm, axis > Then work through each segment in order (e.g. P > PR > QRS etc.)
How to calculate the rate for regular rhythm traces?
inc. for a tachycardia
300/ no. of large squares between R waves
tachycardia: 1500/ small squares between R waves
How to calculate the rate for irregular rhythm traces?
number of QRS complexes x 6
What are 6 key questions to ask in order to determine the rhythm?
- is EA present
- are p waves present
- what is the QRS rate
- is the QRS regular/ irregular
- is the QRS narrow/ broad
- what is the relationship between the p and QRS
p > QRS > relationship
what is meant by ‘the cardiac axis’?
it is an expression of the direction of sum electrical activation in the heart
as electrical signals travel towards a lead they are POSITIVE/ NEGATIVE
What about when they travel away from a lead?
Or when they travel perpendicular to a lead?
travel towards > positive
travel away > negative
travel perpendicular > isoelectric
What is Einthoven’s triangle?
demonstrates the angle of orientation of the bipolar leads (I, II, III)
what are the bipolar leads
Record the difference in voltage between 2 extremities
I: LA and RA
II: LL and RA
III: LL and LA
What is wilson’s central terminal
Demonstrates the angle of orientation of the bipolar leads
Is this not the same as Einthoven’s? confused.
which 2 leads can be used to help determine cardiac axis and how?
Look at QRS complex in leads I and avF
normal: both +
left axis deviation: I +, avF -
right axis deviation: I -, avF +
indeterminate: both -
What is a
1) normal axis range
2) RAD range
3) LAD range
1) -30 to +90
2) +90 to +180
3) -30 to -180
State what a small and large box represent, time-wise, on the ECG paper
1 small box = 0.04s
1 large box = 0.2s
5 large boxes = 1 s
What acts as the gatekeeper to the ventricles?
The AVN - accepts input from the atria and subsequently conducts, incorporating a delay, to the ventricles.
Why does the AVN incorporate a delay when conducting from the atria to ventricles?
This delay acts to protect the ventricles from rapid rates and also to allow for ventricular filling.
Which section of the ECG strip represent the AVN delay? How long should this section be?
the PR interval
normal = 0.12 - 0.2s (3-5 small squares)
NB: measured from the start of the P wave to the start of the QRS complex
How long should QRS be?
Considered normal if <0.12s (3 small squares)
Prolonged QRS may indicate..?
May be aberrant conduction
Where is the start and end of the QT interval? How long should it be
Start of the QRS to the end of the T wave.
Varies with HR, as it represents ventricular repolarisation
How to correct the QT interval?
Bazetts formula (to calculate the QTc)
There should be an upright, rounded P-wave in leads __, __ and ___ and an inverted P-wave in ___
II, III and aVF
aVR
In the QRS complex, if the initial deflection is downward it is termed a __ wave. The first upward deflection is termed an __ wave
Q
R (whether preceded by a Q or not)
NB: first downward deflection after an R wave is termed the S wave
The R wave amplitude should DECREASE/ INCREASE from V1 to V6
increase
T/F: the T wave (ventricular repolarisation) is normally in the same direction as the QRS
true
NB: no clearly defined range but generally shouldn’t be more than 1/2 the height of the preceding QRS
6 questions to ask when determining the cardiac rhythm
- is there electrical activity
- is the rhythm regular or irregular
- what is the heart rate
- are there p waves present
- what is the relationship between the p waves and the QRS complexes
- what is the QRS duration
(EA > regularity > HR > p > pQRS > QRS)
What is a supraventricular rhythm?
any rhythm which originates above the AVN, whether conducted through or not
In supraventricular rhythms, the QRS complex is usually NARROW/ BROAD
narrow
examples of supraventricular rhythms?
- sinus rhythm
- AF
- AVNRT (WPW)
- sinus arrhythmia
- atrial flutter
- wandering atrial pacemaker
- “SVT”
Which supraventricular rhythm is this describing:
‘A p wave for every QRS. PR <200ms’
sinus rhythm
What is sinus arrhythmia
Occurs when the ECG meets all the criteria of sinus rhythm but the rhythm itself is irregular.
The irregularity is caused by physiological changes in the cardiac timing caused by respiration. Is considered a normal variant.
What causes AF?
- occurs due to disoragnised EA in the atria
- impulses no longer travel from the SA node through the atrial myocardium to the AV node
- the AV node receives continuing electrical impulses and conducts some of these to the ventricle
How is AF identified on ECG?
Irregularly irregular QRS complexes and absent P waves. Ragged baseline
What is atrial flutter
a regular, usually narrow complex tachycardia
Is usually division of 300
How is atrial flutter seen on ECG?
F waves, regular QRS complexes, ‘saw tooth’ baseline
What causes atrial flutter
A reentry circuit within the atria. Usually results in an atrial rate of 300bpm. As the AVN filters the ventricular rate and this usually results in a ventricular rate which is a division of 300 e.g. 150, 100, or 75
Can the ventricular rate be irregular in atrial flutter?
Yes - not uncommon.
Due to so called variable AV block, however each R-R interval is a multiple of the others.
What is a junctional rhythm?
The electrical impulse starts in the AV node instead of the SA node. This results in electrical impulse travelling simultaneously to the atria and ventricles. Often causes an inverted p wave seen just after the QRS complex.
How does a junctional rhythm appear on ECG?
Retrograde P waves can be seen in the ST segment.
Regular. May be normal, brady or tachy
In junctional rhythm the QRS complex is usually NARROW/ BROAD
narrow - unless there’s co-existant left or right bundle branch block.
What is a supraventricular tachycardia?
a tachycardia that originates above or involves the AV node
Two broad causes of SVT?
generally involves with
- an accessory pathway i.e. WPW
- or the AV node itself i.e. AVNRT
SVT
- regular or irregular?
- narrow or broad complex tachy?
regular, narrow complex tachycardia
how to recognise a supraventricular ectopic on ECG?
- sinus rhythm but then every so often a P wave comes early and with a differing morphology
- causes varying PR intervals and RR intervals
T/F: ventricular rhythms (rhythms that originate in the ventricle) are always pathological
true
ventricular rhythms are always NARROW/ BROAD complex
broad (QRS > 120ms)
examples of ventricular rhythms?
- ventricular premature complexes
- VT (monomorphic)
- polymorphic VT
- ventricular escape rhythm
- VF
what is a ventricular premature complex (VPC)
a premature beat arising from an ectopic focus within the ventricles
VPCs can occur in different patterns e.g. ?
- bigeminy (1 sinus beat: one VPC)
- trigemeny (1 sinus beat: 2 VPCs)
how does monomorphic VT appear on ECG?
- regular broad complex tachycardia (QRS >120ms)
T/F: monomorphic VT is often self resolving and requires no treatment
false - may be associated with haemodynamic compromise. Always abnormal and must be acted upon.
how does VF appear on ECG?
- irregular, random baseline
- no clear discernable waveforms
how does VF appear clinically?
- always ass. with LOC
- if in doubt > shock them!
what is a capture beat? (a type of ventricular rhythm)
occurs when a sinus beat is conducted through the AV node and beats the next VT beat > EARLY narrow complex beat
what are fusion beats?
fusion between a sinus beat and the next VT beat
NB: both capture and fusion beats are proof of independent rhythms in the atria and ventricles
What is the hallmark of a rhythm that originates in the ventrcle?
that the QRS complex is broad
this is also the case in pts with LBBB and RBBB
There are various discriminating factors to determine whether a rhythm is ventricular in origin or not
1) if in doubt treat as what?
2) a good predictor of SVT with aberrancy is what?
3) a good predictor of VT is what?
4) __ and __ beats are almost always diagnostic of VT
5) __ __ should ALWAYS by confirmed by 12 lead ECG if patient not in cardiac arrest
1) VT
2) pre-existing LBBB or RBBB
3) pre-existing coronary disease
4) capture and fusion
5) VT
What is heart block?
a term given to a block in conduction between the atria and ventricle (not to be confused with BBB)
What is heart block due to?
AV nodal dysfunction
- drugs
- ischaemia
- age
How does 1st degree heart block appear on ECG?
- PR interval >0.2s (1 big square)
- no progressive lengthening
- stable rhythm
(need to consider possibility or high degrees of block)
reason behind 2nd degree heart block?
Two types
In both, a P wave is blocked from initiated a QRS complex
2nd degree heart block - Mobitz type 1 vs type 2?
Type 1: progressive PR prolongation followed by eventual ‘missed beat’
Type 2: no such pattern
Which is considered to be more benign - type 1 or type 2 second degree heart block?
type 1 (where there’s progressive lengthening of PR interval followed by a dropped QRS)
why is there progressive PR prolongation before the missed beat in type 1 second degree heart block?
due to the time taken for the AV node to repolarise in order to ‘accept’ the next impulse
NB: may be a normal finding
T/F: mobitz 1 second degree heart block doesn’t always receive treatment
true - not treated unless severe or accompanied with collapse or haemodynamic compromise
how does mobitz 2 second degree heart block appear on ECG?
- constant PR interval
- subsequent missed beat
T/F: mobitz 2 second degree heart block may be a normal finding
false - always abnormal
- may deteriorate into CHB/ asystole
- needs intervention
How does 3rd degree heart block occur and appear on ECG?
- no relationship between P and QRS
- no communication between atria and ventricle
- broad QRS (ventricular escape rhythm)
T/F: 3rd degree HB is always abnormal
true - unstable, requires intervention
There are ‘automatic’ pacemarkers at different stages in the heart
1) normally rate is controlled by what?
2) T/F: all cells in the heart are capable of automaticity
3) what has the highest rate?
1) by the SA node
2) true - if electrically isolated they will continue to deploarise at a given rate
3) the SA node, followed by the AV node, then the his bundle and then the ventricular myocardium
what is the escape phenomenon
Because all cells in the heart are capable of automaticity, this provides a ‘backup’ for patients with disruption of the electrical conducting system e.g. complete heart block.
A ventricular escape rhythm occurs at __-__ bpm and is NARROW/ BROAD, REGULAR/ IRREGULAR and dissociated from atrial activity if present
30-40
broad
regular
Fasicular block - what are the ‘fasicles’?
- AV node
- LAHB
- LPHB
- Rt bundle branch
Bifasicular vs trifasicular heart block?
blockage of two fasicles = bifasicular block
blockage of 3 = trifasicular
T/F: bifasicular block always requires intervention
fase - doesn’t require direction intervention, however beware it may herald the onset of trifasicular or complete heart block
Features of bifasicular block on ECG?
2 of:
- PR > 0.2s
- left axis deviation
- RBBB
Features of trifasicular block on ECG?
- PR > 0.2s
- left axis deviation
- RBBB
OR alternating RBBB and LBBB
What are the shockable cardiac arrest rhythms?
- pulseless VT
- VF
Which cardiac arrest rhythm is being described
1) broad complex tachycardia requiring prompt defib to restore sinus rhythm
2) chaotic and irregular. No QRS complexes can be seen. Prompt defib required to restore sinus rhythm.
1) VT
2) VF
Complete AV block may be associated with circulatory collapse - in which case do what?
IV atropine and isoprenaline may be indicated as stabilising measures until transvenous pacing wire insertion can be undertaken.
what are the non-shockable cardiac rhythms?
PEA and asystole
what is pulseless electrical activity (PEA)
cardiac arrest occurring with any rhythm which would usually be associated with a pulse
PEA management?
prompt CPR and identify a potential reversible cause
if left untreated ventricular tachy-arrhythmias can deteriorate from __ __ to __ __ then ___
VT to VF then asystole
