Interpretation of ECG Flashcards
Name the parts that make up the ECG
- P wave
- QRS
- T wave
What does the P wave signal
atrial depolarisation
What does the QRS complex signal
- ventricle depolarisation
What does the T wave signal
- Ventricular repolarisation
What should the first thing in an ECG should you look at
- to make sure you are looking at the right person ECG - check the name, date of birth and hospital number
- its calibration - 1mV = 10mm
What are the two calibration numbers that you should remember
- Paper speed should be 25mm/sec
- calibration should be 1mV = 10mm
- these are at the bottom of most ECG
What should the paper speed in an ECG be
25mm/sec
Where should the chest leads go
6 of them
- V1 - 4th intercostal space on the right sternum
- V2 - 4th intercostal space on the left sternum
- V4 - 5th intercostal space midclavicular line (apex beat)
- V3 between V4 and V2
- V6 - mid axillary line
what does the chest lead allow you to do
- Look at the QRS complex from different planes
describe how the QRS becomes positive
- It becomes positive by the time you reach V4
name the 6 limb leads
I II III aVR aVF aVL
Out of the limb leads which should be positive and negative
I - QRS is meant to be positive II - QRS is meant to be positive III- QRS is meant to be positive aVR - should always be negative aVF - QRS is meant to be positive aVL - halfway between the right direction so half and half
when is QRS positive
QRS is positive when ventricular depolarisation is in the right direction
Name the chest leads
V1-V6
Name the normal ECG wave forms and what is normal
- PR = 120-200 msec (3-5 small Sq)
- QRS < 120 msec (< 3 small Sq)
- QTc < 440 msec
what does 1 small sequence and 1 big sequence in msec
1 small Sq = 40 msec
1 big square= 200 msec
How do you work out the QTc
QT/ square root of RR
what is the QTc dependant on
- it is dependant on the heart rate
How do you read an ECG
– Rhythm – Rate – Axis – P waves – PR interval/ heart block – QRS morphology/ ST segments/ T waves – QT interval
How do you assess Rhythm
- are the QRS regular complexes
- is there a P wave before every QRS
What is the definition of sinus rhythm
- there is a P wave before every QRS
- requires an ECG to know
What is sinus arrhythmia
- variation of RR interval with respiration
- normal variant
Why is lead II used to look at the P wave and thus used in rhythm
one of the best leads to look at the p wave
- atrial depolarisation is in the same direction
What are ectopics
When you heart throws up some extra beats
- ectopics above the AV node are called supraventricular ectopics
- ectopics below the AV node are called ventricular ectopics
What is the difference between supra-ventricular and ventricular ectopics
Supraventricular
- ectopics above the AV node are called supraventricular ectopics
- narrow QRS complex
Ventricular
- ectopics below the AV node are called ventricular ectopics
- Broad QRS complex
What is the normal heart rate
50-100bpm
How do you calculate heart rate
- look at the RR interval
- count the number of squares between the QRS complex
- number of big squares and then divide 300 by the number of big squares
who can you not calculate heart rate in
- Patients who have an irregular heart rhythm
What is the axis
Axis is the net electrical vector of the heart
- gives an overall idea of the direction of depolarisation
in what direction does the heart depolarise
- from the top of the right shoulder and down
- from aVR to II
What is the normal electrical axis
-30 to +120
what is the axis in left axis deviation and right axis deviation
Left axis deviation is when the axis is greater than -30
right axis deviation is when the axis is greater than +120
if lead II is positive then
the axis is likely to be normal
If lead II is not positive then
then the axis is likely to be abnormal - have to work out if it is right and left deviation
What do you do if lead II is not positive
- If lead II is not positive you have to work out if it is right or left axis deviation
- then you look at lead III
- if lead III is negative then it is left axis deviation
- if lead III is positive then look at lead I
- if lead I is negative then you have right axis deviation
right axis deviation can be a…
normal variant whereas left axis deviation is always abnormal
What can cause right axis deviation
– children and tall thin adults
– RVH
– chronic lung disease/ pulmonary embolus
– left posterior hemiblock
– atrial septal defect/ ventricular septal defect
– Wolff-Parkinson-White syndrome - left sided accessory pathway
What can cause left axis deviation
– LVH
– LBBB and left anterior hemiblock
– Q waves of inferior myocardial infarction
– Wolff-Parkinson-White syndrome - right sided accessory pathway
What leads is it best to look at P wave morphology
Leads I and II
What causes P pulmonale
- peaked P wave
- Right atrial hypertrophy (tall and thin)
What causes P mitrale
- Bifid P wave
- Left atrial hypertrophy (M shape)
What is the normal PR length
- Normal PR = 120-200 msec
* Normal 3-5 small Sq
What are the types of heart block
– 1st degree
– 2nd degree (Mobitz I and II)
– 3rd degree or Complete heart block
what does the ECG look like in bundle branch block
- PR normal
- QRS > 120 msec
- LBBB and RBBB
describe 1st degree heart block
PR interval is longer than 120msec
Describe 2nd degree heart block
type 1
- PR interval gradually gets longer until it is no longer followed by a QRS complex
type 2
- PR interval is randomly not followed by a QRS complex
Describe 3rd degree heart block
- When the P wave doesn’t correspond with the QRS wave at all
- AV dissociation
what is wolf parkinson white syndrome associated with
- pre excitation through an accessory pathway
What does an ECG of wolf parkinsons white syndrome look like
- Short P-R interval
- delta wave
- Wide QRS complex
What does supra-ventricular tachycardia look like on an ECG
- Regular
- Narrow complex tachycardia
- No P waves or atrial activity
What is the normal QRS duration
Normal range < 120 msec/ 3 small Sq
How do you tell left and right bundle branch block
WiLLiaM morphology
- William - if you get a W pattern around V1/V2 and an M pattern around V5/V6 then it is left bundle branch block
MaRRoW
- if you get a M around V1/V2 and W around V5/V6 then it is a right bundle branch block
What does left ventricular hypertrophy look like on an ECG
- Large QRS voltages
- Any V or S > 25mm
- Combined R and S > 35mm
- aVL or I > 13 mm
What is left ventricular hypertrophy associated with
- Strain pattern of ST depression and T wave inversion
what leads look at which part of the wall
- inferior
- anterior
- lateral
- inferior - II/III/aVF
- anterior - V2-4
- lateral - V5-6/I/aVL
What are the ECG changes with myocardial infarction
- Peaked T waves (minutes before)
- ST elevation ( minutes-hours after)
- ST depression
- Q waves (hours after to a few days - can persist but may resolve)
- inverted T waves - hours may reverse or may be permanent
What do you divide MI into
STEMI
NSTEMI
Wellens syndrome
Antero-lateral T wave inversion
- anterior NSTEMI pending troponin
- LAD syndrome - LAD can involve the lateral wall as well as the anterior wall
- this patient should be treated as an MI
- Sign of an LAD lesion
How do you define Atrial Fibrillation
disordered electrical activity
What does an ECG look like in atrial fibrillation
- Irregularly irregular ventricular rhythm
- No P waves
Define what happens in atrial flutter
Re-entrant circuit in RA Flutter rate 300 bpm
describe what an ECG looks like in atrial flutter
- flutter waves
- regular rate
- V rate depends on the degree of transmission of F waves
What is the flutter rate in atrial flutter
300bpm
describe atrial tachycardai
- abnormal focus of atrial depolarisation -
abnormal P wave morphology - Unexplained tachycardia
name a type of SVT
- AVNRT - atrio ventricular node re-entrant tachycardia
describe an SVT
- Accessory pathway in AV node
- Leads to SVT
a broad complex tachycardia is a
VT until proven otherwise
define atrial flutter waves
Saw tooth P wave
What do you do when someone has ventricular fibrillation
- disorder ventricular depolarisation
- person in cardiac arrest
- perform CPR, give
- need a defibrillator
What ECG changes happen in hypokalaemia
- small T waves
- Prominent U waves
- Peaked P waves
What ECG changes happen in hyperkalemia
- Tall Tented T waves
- wide QRS complex
- Absent P waves
- Sine wave appearance
What ECG changes happen in hypercalcaemia
- short QT interval
What ECG changes happen in hypocalcaemia
- long QT interval
- small T waves
What can cause a prolonged QT interval
- Congenital – Romano-Ward syndrome, Jervell and Lange-Nielsen syndrome
- Cardiac – MI, ischaemia, mitral valve prolapse
- HIV – direct effect of virus or protease inhibitors
- Metabolic – hypokalaemia, hypomagnesaemia, hypocalcaemia, starvation, hypothyroidism, hypothermia
- Toxic – organophosphates
- Anti-arrhythmic drugs – quinidine, amiodarone, procainamide, sotalol
- Antimicrobials – erythromycin, levofloxacin, pentamide, halofantrine
- Antihistamines – terfenadine, astimazole
- Motility drugs – domperidone
- Psychoactive drugs – haloperidol, risperidone, TCAs, SSRIs
- Connective disease disorders – Anto-RO/SSA Abs
- Herbalism – Chinese folk remedies (arsenic), cocaine, quinine, artemisinins (antimalarials)
What can cause a short QT interval
hypercalcaemia
When is a T wave peaked
hyperkalameia
When is a T wave flattened
hypokalaemia
What can cause AF
- IHD
- thyrotoxicosis
- hypertension
- obesity
- CCF
- alcohol
What are the causes of 1st and 2nd degree heart block
- normal variant
- athletes
- sick sinus syndrome
- IHD
- acte myocarditis
- drugs - digoxin and beta blockers
What are the causes of 3rd degree heart block
- IDH
- idiopathic (fibrosis)
- congenital
- aortic valve calcification
- cardiac surgery/trauma
- digoxin toxicity
- infiltration (abscesses, granulomas, tumours, parasites)
What does digoxin look like
- Down-sloping ST depression
- T wave inversion in V5-V6
- any arrhythmia may occur
What does right bundle branch block look like
- QRS >0.12s
- V1: ‘RSR’ pattern, dominant R
- V1-V3 or V4: T-wave inversion
- V6: wide, slurred S-wave
What does left bundle branch block look like
- QRS > 0.12s
- V5 - M pattern
- V1 - dominant S
- I, aVL, V5-V6: T wave inversion
What is bifasciular block
LBBB+RBBB: manifests as an axis deviation
What is trifascicular block
bifasciular block + 1st degree Heart block
What does left ventricular hypertrophy look like
R-wave in V6 >25mm OR sum of S-wave in V1 and R-wave in V6 >35mm
What does right ventricular hypertrophy look like
Dominant R-wave in V1, T-wave inversion in V1-V3 or V4, deep S-wave in V6, RAD
