ECG Flashcards
In which position should a patient be before taking an ECG
semi-recumbant position at a 30-40 degree angle
Where should limb leads be placed
On the bony prominences of the wrist and ankle
Where should the chest leads be placed
V1 - 4th ICS RHS V2 - 4th ICS LHS V3 - between V2 + 4 V4 - 5th ICS left mid clavicular line V5 - 5th ICS left anterior axillary line V6 - 5th ICS left mid axillary line
What could mistakenly be identified if the patient is sitting upright whilst having an ECG
ST elevation
How do you calculate the HR if the tracing is regular
300 divided by the number of large squares between 2 R waves
How do you calculate the HR if the tracing is irregular
count the number of QRS complexes in 30 large squares and times that by 10
What does the P wave represent
Atrial depolarisation
What does the PR interval represent
AV node conduction
What is the normal PR interval
0.12-0.20 seconds
What does the QRS complex represent
Ventricular depolarisation
What is the normal QRS complex duration
<0.12 seconds
How do you calculate the QTc
square root of R-R interval (sec) / QT interval (ms)
what is the R wave
the first positive deflection of QRS complex
what does the cardiac axis tell you
the overall direction of travel of electrical activity
How do you assess the horizontal cardiac axis
look at R wave progression across the CHEST leads
Which leads do you look at to determine vertical cardiac axis
leads I and aVF
Look at the most pointy part of the QRS complex
lead I: positive
aVF: positive
What is the cardiac axis?
normal
lead I: positive
aVF: negative
What is the cardiac axis?
left axis deviation
lead I: negative
aVF: positive
What is the cardiac axis?
right axis deviation
Causes of left axis deviation
Left anterior hemiblock Expiration LBBB WPW emphysema hyperkalaemia
Causes of right axis deviation
Normal Inspiration Right ventricular hypertrophy RBBB left posterior hemiblock dextrocardia Ventricular ectopic WPW
What is heart block
specific set of conditions related to conduction between the atria and ventricles through the AV node
ie AVN dysfunction
What are the types of heart block
First degree
Second degree Mobitz I
Second degree Mobitz II
Third degree
What is first degree heart block
Prolonged PR interval (>0.20s)
Fixed and stable rhythm
What is second degree Mobitz type I heart block
PR interval gets progressively longer until it drops a beat
Progressive PR prolongation leads to eventual missed beat
What is second degree Mobitz type II heart block
Constant prolonged PR interval but then you drop a beat
Every so often there is no QRS following a P wave
Which is more worrying, Mobitz I or II
Mobitz II is always abnormal and needs intervention
may progress into asystole
What is third degree heart block
No relationship between atria and ventricles (ie P waves and QRS complexes)
QRS complexes are fixed but P waves are random
Always abnormal and needs intervention
How do you define tachycardia
HR >100bpm
You can use regular/irregular to define rhythm, true or false
FALSE
You should say, sinus rhythm, VT, VF, SVT, AF…
What is sinus tachycardia
tachycardia in sinus rhythm
HR varies with inspiration, expiration and pain
Will not be fixed
Describe atrial fibrillation
Chaotic atrial activity
Irregularly irregular
Absent P waves
Ragged baseline
Irregularly irregular = AF until proven otherwise, true or false
True
If there is a noisy baseline in lead II, where can you look for P waves
V1
Causes of atrial fibrillation
Coronary artery disease mitral stenosis or regurgitation hypertrophic cardiomyopathy pericarditis pneumonia lung cancer PE sarcoidosis Holiday heart syndrome - alcohol Hyperthyroidism CO poisoning Genetics
Describe atrial flutter
Re-entry circuit involving the whole atrium
Regular rhythm usually 300bpm or divisible
Sawtooth baseline - F waves
If the HR is too fast, what can you give to identify underlying flutter waves in atrial flutter
adenosine to block the AVN
Which drug interacts with adenosine to inhibit its breakdown and should therefore be avoided
dipyridamole
Describe junctional rhythm
Electrical impulse starts in the AVN instead of the SAN causing the electrical impulse to simultaneously move to the atria and ventricles
You see an inverted P wave after the QRS complex
Define a narrow complex tachycardia
Originates above the AVN
ie within the AVN itself or the atria
His-Purkinje system still activates the ventricles giving a narrow QRS complex
What are the types of narrow complex rhythms/SVTs
AVNRT
AVRT including WPW
Atrial tachycardia
Supraventricular ectopics
What is AVNRT
AV node re-entry tachycardia
Occurs within the AVN itself
commonest cause of SVT
ectopic beat causing a re-entry circuit around the AVN
What is AVRT
AV re-entry tachycardia
Conduction happens normally but when they reach the ventricles it finds an accessory pathway and creates another circuit
How do you manage SVTs?
vagal manoeuvres: valsalva, carotid massage, head in cold water
adenosine
What is the function of adenosine
very short acting drug that blocks the AV node temporarily to break the re-entry circuit
What is the management of a clinically unstable SVT
defibrillation (stops all cardiac cells)
What is WPW syndrome
presence of an accessory pathway causes the ventricles to immediately depolarise instead of having the delaying mechanism of the AVN
What is a delta wave caused by and in which condition is it seen
delta wave - pre-excitation of the ventricles
WPW
What is a supraventricular ectopic
sinus rhythm but the morphology of the P waves differs
define broad complex tachycardias
originates within the ventricular myocytes
or
SVT with aberrancy
Broad complex arrythmias are always abnormal, true or false
true
What is a PVC
Premature Ventricular Complex = premature beat arising from an ectopic focus within the ventricles
what is bigemy
1 sinus beat with a VPC
what is trigemy
1 sinus beat couples with 2 VPCs
What are the types of ventricular tachycardia
monomorphic
polymorphic
describe monomorphic VT
regular broad complex tachycardia
QRS >0.12s
describe polymorphic VT
broad complex tachycardia that looks like its twisted
“forth rail bridge”
torsades de pointes
what is torsades de pointes usually associated with
Long QT interval
hypomagnesaemia
describe ventricular fibrillation
irregular random baseline
broad complex tachycardia
it is BAD
what is a capture beat
when a sinus beat conducted through the AVN beats the next VT beat resulting in an early narrow complex beat
what is a fusion beat
fusion between a sinus beat and the next VT beat
What are the differentials of a broad complex tachycardia
VT
SVT with aberrancy
What is the pathology behind a VT
rhythm originates in the ventricles and does not use the His-Purkinje system causing broad complexes
Re-entry circuit within the ventricle often involving scarred myocardium
How is VT defined
> =3 beats of ventricular origin at >120bpm
sustained VT needs >30s of tachycardia
What is idioventricular rhythm
VT less than <100bpm
what is accelerated idioventricular rhythm
VT between 100-120bpm
What can SVT with pre-existing L/RBBB look like on ECG
broad complex tachycardia
Who is more likely to get SVT with aberrancy
younger patients
how can you differentiate between SVT with aberrancy or VT
vagal manoeuvres or adenosine
what is aberrancy
conduction not over the usual conducting system
What are almost always diagnostic of VT
capture and fusion beats
What are the shockable rhythms
VF
Pulseless VT
What are the non-shockable rhythms
asystole
PEA
How do you manage complete AV block
IV atropine and isoprenaline
what is PEA
Pulseless electrical activity = cardiac arrest occurring with any rhythm that would usually be associated with a pulse
Which parts of an ECG trace are important to look at in the context of ischaemia/infarction
ST segment
T waves
Q waves
which leads are associated with an inferior MI
Leads II, III, aVF
which leads are associated with a lateral MI
Leads I, aVL, V5, V6
which leads are associated with an anterior MI
Leads V1-4
what are ECG markers of ischaemia
tall T waves –> biphasic –> inverted –> flattened
ST depression
What are the strict criteria for thrombolysis
ST elevation:
- > 1mm in 2 contiguous limb leads
- > 2mm in 2 contiguous chest leads
What are Q waves and why are they pathological
Q waves indicate septal depolarisation but are usually masked so when present, something is abnormal
suggests myocardial necrosis
Criteria for pathological Q waves
any Q waves in leads V1-3
>= 0.03s in remaining leads
D.Dx of ST elevation
MI pericarditis LBBB left ventricular hypertrophy coronary vasospasm Brugada syndrome SAH ventricular aneurysm
What should be considered in patient with NEW LBBB
MI
what is a hallmark of BBB
Prolonged QRS
in which direction is the septum normally activated
left to right
what happens to septal depolarisation in LBBB
it reverses and goes from right to left
Causes of LBBB
MI aortic stenosis IHD HTN dilated cardiomyopathy hyperkalaemia digoxin toxicity
What are signs of a posterior MI on ECG
ST depression in leads V1-3
What is pericarditis
inflammation of the pericardium secondary to MI or viral infection
Symptoms of pericarditis
pleuritic chest pain
fever
pericardial rub
eases upon sitting forward
ECG signs of pericarditis
saddle ST elevation
changes do NOT evolve
widespread changes involving >1 vascular territory
PR depression
what can the left bundle branch be divided into
left anterior and posterior hemi-bundle
what is non-specific interventricular conduction delay
broad QRS that does not display L/RBBB
what is BBB
delay in conduction in either one of the bundle branches
what happens to the QRS complex in BBB
QRS duration >0.12s (>3 small squares)
What does RBBB look like on ECG
QRS >0.12s
M shaped complex in V1
(RSR wave)
MaRRoW
What does LBBB look like on ECG
QRS >0.12s
W shaped complex in V1 and M shaped complex in V6
WiLLiam
What happens in RBBB
the right ventricle is stimulated by an impulse from the left ventricle
What happens in LBBB
the left ventricle is stimulated by the right bundle
damage has occurred to both the left anterior + posterior hemi-bundles
what is hemi-block
defect in conduction along one of the 2 hemi-fascicles of the left bundle branch
what are the types of hemi block
LAHB
LPHB
LAHB causes left/right axis deviation?
left axis deviation
LPHB causes left/right axis deviation?
right axis deviation
define sinus rhythm
there is a P wave for every QRS complex and a QRS complex for every P wave with a normal PR interval
what is sinus arrhythmia
meets all the criteria for sinus rhythm except for the rhythm itself which is irregular caused by physiological changes in respiration
