ECG Flashcards
What leads are ECG changes in if anterior infarction?
V1-V4
ECG changes in leads V1-V4 show what type of infarction and what coronary artery is affected?
Anterior
Left anterior descending
What leads are ECG changes in if inferior infarction?
II, III, aVF
ECG changes in leads II, III, aVF show what type of infarction and what coronary artery is affected?
Inferior
Right coronary artery
What leads are ECG changes in if lateral infarction?
I, aVL, V5-6
ECG changes in leads I, V5-V6 show what type of infarction and what coronary artery is affected?
Left circumflex artery
What does P wave represent?
Atrial depolarisation
What does the PR interval (start of P to start of Q) represent?
Time for electrical activity to move between atria and ventricles
What does the QRS complex represent?
Depolarisation of ventricles
What does the ST segment (end of S to start of T) represent?
time between depolarisation and repolarisation of the ventricles (ventricular contraction)
What does the T wave represent?
Ventricular repolarisation
What is the RR interval?
One R wave to the end of the next R wave. Time between 2 QRS complexes
What is the QT interval?
Starts of QRS to end of T. Time taken for ventricles to depolarise and then repolarise.
Small square
0.04s
Large square
0.2s
How many squares is 1 second?
5 large squares
How many squares is 1 minute?
300 large squares
How many electrodes (conductive pad that records electrical activity) and how many leads (graphical representation of heart’s activity calculated by analysing the electrodes) are used in ECG?
12 leads so 12 separate graphs on 1 ECG paper.
10 electrodes that attach to pt to generate the 12 leads.
How many electrodes?
10
Name the chest electrodes?
V1-V6
V1 location?
4th intercostal space at the right sternal edge
V2 location?
4th intercostal space at the left sternal edge
V3 location?
Midway between the V2 and V4 electrodes
V4 location?
5th intercostal space in the midclavicular line
V5 location?
Left anterior axillary line at the same horizontal level as V4
V6 location?
Left mid-axillary line at the same horizontal level as V4 and V5
How many limb electrodes?
4
Name the limb electrodes
Red (RA)
Yellow (LA)
Green (LL)
Black (RL)
Red electrode location
Ulnar styloid process of the right arm
Yellow electrode location
Ulnar styloid process of the left arm
Green electrode location?
Medial or lateral malleolus of the left leg
Black electrode location?
Medial or lateral malleolus of the right leg
View of heart from V1 and V2?
Septal (Anteroseptal)
View of heart from V3 and V4?
Anterior
View of heart from V1, V2, V3, V4?
Anterior (anteroseptal)
View of heart from V5 and V6?
Lateral
What view of the heart does lead I show and how is it calculated?
Lateral (activity between RA and LA electrodes)
What view of the heart does lead II show and how is it calculated?
Inferior (activity between RA and LL)
What view of the heart does lead III show and how is it calculated?
Inferior (activity between LA and LL)
What view of the heart does aVL show and how is it calculated?
lateral (activity between RA+LL and LA)
What view of the heart does aVF show and how is it calculated?
Inferior (activity between RA+LA and LL)
One more lead that don’t really look at on ECG?
aVR (lateral view - activity between LA+LL and RA)
Why is each lead’s ECG recording slightly different in shape?
Each lead records heart’s activity from different direction (viewpoint)
When the electrical activity in the heart travels towards a lead, what do you get?
+ve deflection
When the electrical activity in the heart travels away from a lead, what do you get?
-ve deflection
What does each deflection (wave) on ECG represent?
Average direction of electrical travel (electrical activity in heart flows in many directions simultaneously)
What does the deflection height represent?
amount of electrical activity flowing in that direction (higher deflection, more activity towards the lead)
The lead with the most positive deflection is most aligned with what?
The direction the heart’s activity is travelling
R wave is greater than S wave?
Depolarisation is moving towards that lead
S wave greater than R?
Depolarisation is moving away from that lead
R wave and S wave equal size?
Depolarisation is exactly 90° to that lead
Electrical activity of the heart to cause ventricular contraction?
Electrical activity starts at sinoatrial node, spreads to the atrioventricular (AV) node. Then spreads down bundle of His and Purkinje fibres to cause ventricular contraction
What does the cardiac axis show?
Overall direction of electrical activity
In healthy individuals, where would you expect the cardiac axis to lie?
between -30°and +90º
If in healthy individuals, the cardiac axis lies between -30°and +90º, the overall direction of electrical activity is towards what leads?
I, II and III
(pointing towards 4&5 on a clock)
What lead shows the most positive deflection in healthy individuals whose cardiac axis lies between -30°and +90º?
Lead II as it is the most closely aligned to the overall direction of electrical spread (pointing towards 4&5 on a clock)
What lead shows the most negative deflection in healthy individuals whose cardiac axis lies between -30°and +90º?
aVR as it provides a viewpoint of the heart from the opposite direction
Cardiac axis leads in everyone?
horizontal= lead I
diagonal down to R= lead II (most + deflection)
diagonal down to L= lead III
vertical down= aVF
diagonal up to R= aVL
diagonal up to L= aVR (most -ve deflection)
What is right axis deviation (RAD)?
The direction of depolarisation is distored to the right (between +90º and +180º- like pointing to 7 on clock)
Most common cause of right axis deviation?
R ventricular hypertrophy- extra RV tissue generates stronger signal by R side of heart
Deflection in leads in right axis deviation?
Deflection in lead I becomes -ve and deflection in lead aVF/III to be more +ve
What is RAD associated with?
Pulmonary HTN as cause RV hypertrophy. Can be normal finding in very tall people.
What is left axis deviation?
Direction of depolarisation is distorted to the left (between -30° and -90°- like pointing towards 1 on a clock)
Deflection in leads in left axis deviation?
Deflection of lead III becomes -ve (only significant if deflection in lead II also becomes -ve)
What usually causes left axis deviation?
Conduction abnormalities
Normal adult HR?
60-100bpm
Tachycardia HR?
> 100bpm
Bradycardia HR?
<60bpm
How to calculate heart rate on ECG?
count number of large squares within 1 R-R interval then divide 300 by this number
eg. 4 large squares so 300/4= 75bpm
How to calculate heart rate on ECG if it is irregular (R-R interval differes throughout ECG)?
count number of complexes on rhythm strip (each strip typically 10secs long) then multiply by 6
eg. 6 complexes on rhythm strip so 10x6= 60bpm
Calculate heart rhythm on ECG?
mark out several consecutive R-R intervals on piece of paper then move them along the rhythm strip to check if subsequent intervals are similar
Irregular heart rhythms can be what?
regularly irregular (recurrent pattern of irregularity) or irregularly irregular (completely disorganised)
How to work out cardiac axis on ECG?
Look at leads I, II and III
Normal cardiac axis on ECG?
Lead II most +ve (R wave higher peak) compared to I and III
Right axis deviation on ECG?
Lead III most +ve (R wave higher peak) and lead I should be -ve (R wave low peak).
Lead II normal
Left axis deviation on ECG?
Lead I most +ve (R wave higher peak) and lead II and III are -ve (R wave trough not peak)
When looking at P waves what 4 questions do you ask?
1) Are P waves present?
2) If so, is each P wave followed by QRS complex?
3) Do the P waves look normal- duration, direction and shape?
4) If P waves are absent, is there any atrial activity?
P waves- sawtooth baseline shows what?
Flutter waves
P waves- chaotic baseline shows what?
Fibrillation waves
P waves- flat line shows what?
No atrial activity
What does absent P waves and an irregular rhythm suggest?
Atrial fibrillation
How long should the PR interval be?
120-200ms (3-5 small squares)
Prolonged PR interval is how long?
> 200ms (>0.2s) (more than 5 small squares)
What does a prolonged PR interval suggest?
atrioventricular delay (AV block)
Causes of 1st degree AV block?
Enhanced vagal tone: often seen in athletes (non-pathological)
Post myocardial infarction
Lyme disease
Systemic lupus erythematosus
Congenital
Myocarditis
Electrolyte derangements
Drugs: beta-blockers, calcium-channel blockers, digoxin and magnesium1
Thyroid dysfunction
First degree heart block (AV block) ECG findings?
Fixed prolonged PR interval (>200ms), P waves associated with QRS
How many types of second degree heart block are there?
2
Second-degree heart block type 1 is also known as what?
Mobitz type 1 AV block or Wenckebach phenomenon
ECG findings of Mobitz type 1 heart block?
Progressive prolongation of PR interval with occasional QRS dropping.
Explain the ECG findings of Mobitz type 1 heart block?
progressive prolongation of PR interval until QRS complex is dropped (not there)- when atrial impulse is not conducted. Av nodal conduction resumes with next bead and sequence repeats
Second degree heart block is also known as what?
Mobitz type 2 AV block
ECG findings of Mobitz type 2 heart block?
Consistent PR with occasional QRS dropping.
QRS dropping follows repeating cycle of every 3rd (3:1) or 4th (4:1 block) P wave.
Explain the ECG findings of Mobitz type 2 heart block?
Occasional QRS dropping due to failure of conduction
What is third-degree (complete) heart block?
No electrical communication between atria and ventricles due to complete failure of conduction.
ECG findings in third degree (complete) heart block?
Complete dissociation of P waves and QRS complex (cannon waves); AVN fails depolarisation.
Atria and ventricles function independently.
Third degree heart block: where do narrow-complex escape rhythms originate (QRS <0.12s)?
Above bifurcation of bundle of His
Third degree heart block: where do broad-complex escape rhythms originate (QRS >0.12s)?
Below bifurcation of bundle of His
1st degree heart block CP and Mx?
Asymptomatic. Increased risk of AF.
Consider pacemaker if symptomatic.
Morbitz type 1 CP and Mx?
Usually asymptomatic, bradycardia, syncope
Consider pacemaker if symptomatic.
Causes of Mobitz type 1?
Increased vagal tone: often seen in athletes (non-pathological)
Drugs: beta-blockers, calcium channel blockers, digoxin, amiodarone
Inferior myocardial infarction
Myocarditis
Cardiac surgery (mitral valve repair, Tetralogy of Fallot repair)
Mobitz type 2 CP and Mx?
Palpitations, pre-syncope, syncope, regular irregular pulse
Cardiac monitor asap as risk of complete block; isoprenaline if haemodynamically compromised; permanent pacemaker.
Risk of asytole.
Mobitz type 2 AV block causes?
Myocardial infarction
Idiopathic fibrosis of the conducting system (Lenegre’s or Lev’s disease)
Cardiac surgery (especially surgery occurring close to the septum such as mitral valve repair)
Inflammatory conditions (rheumatic fever, myocarditis, Lyme disease)
Autoimmune (SLE, systemic sclerosis)
Infiltrative myocardial disease (amyloidosis, haemochromatosis, sarcoidosis)
Hyperkalaemia
Drugs (e.g. beta-blockers, calcium channel blockers, digoxin, amiodarone)
Thyroid dysfunction
3rd degree heart block CP and Mx
Palpitations, confusion, SOB, chest pain, fatigue, syncope, sudden cardiac death
QRS<0.12s= IV atropine or isoprenaline
QRS>0.12s= permanent junctional or ventricular pacemaker
Risk of sudden cardiac death due to ventricular arrhythmias
Causes of third degree AV block?
Congenital: structural heart disease (e.g transposition of the great vessels), autoimmune (e.g maternal SLE)
Idiopathic fibrosis: Lev’s disease and Lenegre’s disease
IHD: MI, ischaemic cardiomyopathy
Non-ischaemic heart disease: calcific aortic stenosis, idiopathic dilated cardiomyopathy, infiltrative disease (e.g. sarcoidosis, amyloidosis)
Iatrogenic: post-ablative therapies and pacemaker implantation, post-cardiac surgery
Drug-related: digoxin, beta-blockers, calcium channel blockers, amiodarone
Infections: endocarditis, Lyme disease, Chagas disease
Autoimmune conditions: SLE, rheumatoid arthritis
Thyroid dysfunction
Where does 1st degree heart block occur?
Between SA node and AV node (within atrium)
Where does Mobitz type 1 heart block occur?
IN the AV node
What is the AV node?
Only part of conductive tissue in heart which can conduct at different speeds
Where does Mobitz type 2 heart block occur?
AFTER AV node in bundle of His or Purkinje fibres
Where does 3rd degree heart block occur?
at or after AV node resulting in complete blockade of distal conduction
What can shortened PR interval mean?
1) P wave origninates somewhere closer to AV node so condution quicker (SA node not fixed location & some atria’s smaller than others)
2) atrial impulse getting to ventricle by faster shortcut instead of slow conduction across atrial wall. This accessory pathway can be associated with a DELTA WAVE.
What do you need to look at when assessing QRS complex?
Weight, height, morphology
How can width of QRS complex be described?
Narrow (<0.12s) or broad (>0.12s)
When does a narrow QRS complex occur?
GOOD.
When impulse conducted down bundle of His and Purkinje fibre to ventricles- results in well organised synchronised ventricular depolarisation;
When does a broad QRS complex occur?
ABNORMAL depolarisation sequence.
Broad QRS complex: what is a ventricular ectopic?
impulse spreads slowly across myocardium from the focus in ventricle so get broad QRS
What is an atrial ectopic?
Get narrow QRS as it would conduct down heart’s normal conduction system.
What could a broad QRS complex be due to?
- ventricular ectopic
- bundle branch block
Why does bundle branch block result in broad QRS?
impulse gets to one V rapidly down intrinsic conduction system then spreads slowly across myocardium to the other V
Bundle branch block ECG findings?
Broad QRS
LBBB ECG findings?
deep S wave in V1 which may be notched (“W”) and broad “M” shaped R wave in V6
RBBB ECG findings?
RSR’ pattern in V1 (“M”) and broad S wave in V6 (“W”)
Way to remember bundle branch block ECG findings?
V1. V6
W. iLLia M
M. aRRo W
Height of QRS complex can be what?
Small or tall
Small QRS complex meaning?
<5mm in limb leads or <10mm in chest leads
Tall QRS complex meaning?
Ventricular hypertrophy (or tall slim people)
To assess the morphology of QRS complex what should you look for/at?
?delta wave
Q-waves
R & S waves
J point segment
What does a delta wave look like on ECG?
QRS complex’s upstroke is slurred
What does a delta wave indicate?
ventricles are being activated earlier than normal from a point distant from AV node, early activation then spreads slowly across myocardium.
Presence of delta wave could mean what?
Delta wave AND tachyarrhytmias= Wolff-Parkinson-White syndrome.
Presence of just delta wave does NOT diagnose
Can isolated Q waves be normal?
Yes
Pathological Q wave?
> 25% the size of the R wave that follows it or > 2mm in height and > 40ms in width.
A single Q wave is not a concern, but what could you look for for evidence of previous MI?
The Q waves in an entire territory
Where should you assess R wave progression?
Across the chest leads (from small in V1 to large in V6)
The transition from S>R wave to R>S wave should occur where?
In V3 or V4
Poor progression in R waves (S>R through to leads V5 and V6) can be a sign of what?
Previous MI or in very large people due to poor lead position.
What is the J point segment?
where s wave joins ST segment
What can a raised J point segment result in?
The ST segment that follows being raised (“high take off”).
“High take off” (benign early repolarisation) is where ST segment is raised just because the J point is elevated. Is this bad?
Normal variant but confusing as it LOOKS like ST elevation
Key points for J point segment?
- benign early repolarisation occurs mostly <50yrs (so >50yrs suspect ischaemia)
- J point is raised with widespread ST elevation in multiple territories so ischaemia less likely
- T waves also raised (STEMI= T wave normal and ST elevated)
- the ECG abnormalities DON’T change (STEMI= changes will evolve)
What is the ST segment in a healthy individual?
Isoelectric line (neither elevated nor depressed)
What is ST-elevation?
> 1mm (1 small square) in 2 or more contiguous (next to eachother) limb leads or >2mm in 2 or more chest leads
What is ST-elevation most commonly caused by?
acute full-thickness MI
What is ST depression?
≥ 0.5 mm in ≥ 2 contiguous leads
What does ST depression indicate?
Myocardial ischaemia
What do T waves represent?
repolarisation of ventricles
What 4 things can T waves be?
tall, inverted, biphasic or flattened
When are T waves considered to be tall?
> 5mm in the limb leads AND
10mm in the chest leads (the same criteria as ‘small’ QRS complexes)
Tall T waves can be associated with what?
Hyperkalaemia (tall tented T waves)
Hyperacute STEMI
When are T waves normally inverted? (NORMAL variant)
V1 and lead III
Inverted T waves are a nonspecific sign of what conditions?
- ischaemia
- LBBB (V4-6)
- RBBB (V1-3)
- PE
- LV hypertrophy (lateral leads)
- hypertrophic cardiomyopathy (widespread)
- general illness
What must you do when looking at T wave inverion?
Observe the distribution of T wave inversion (anterior, lateral, posterior leads). 50% ITU pts will have T wave inversion.
What are bisphasic T waves and what can they indicate?
2 peaks.
Ischaemia and hypokalaemia.
Flattered T waves are non-specific sign that may represent what?
Ischaemia or electrolyte imbalance.
Are U waves a common finding?
No
What the a U wave?
> 0.5mm deflection after the T wave best seen in V2 or V3.
U waves become larger…
the slower the bradycardia
When are U waves seen?
electrolyte imbalance, hypothermia, secondary to antiarrhythmic therapy
Overview of how to read ECG? (10 steps)
1) HR: 300/?
2) Rhythm: R-R intervals (?sinus rhythm-normal) look at lead II
3) Cardiac axis: most +ve in lead II if normal; if not ?R or L axis deviation
4) P waves: 4 questions (present; followed by QRS; normal duration direction & shape; absent-?atrial actvity)
5) PR interval: prolonged?(AV block) or shortened?
6) QRS complex: width (broad= BBB), height, morphology (?delta wave, Q wave, R wave progression)
7) ? J point segment
8) ST segment: elevation (infarction) or depression (ischaemia)
9) T waves: tall, inverted, biphasic or flattened
10) U waves (rare)
Most commonly used lead?
Lead II
ECG findings in Wallen’s syndrome? (ECG pattern causes by high-grade stenosis in the left anterior descending coronary artery)
biphasic or deep T wave inversion in V2-3
minimal ST elevation
no Q waves
