ECG Flashcards
What can cause cardiac conduction disorders ?
HTN causing left ventricular hypertrophy
What are some cardiac conduction Disorders ?
What does an ECG show ?
Electrical activity within the heart
In particular, the depolarisation wave ( a wave of positive charge) which is dependent on which lead you’re looking at.
Explain what depolarisation is
Cells are negatively charged in comparison to the outside.
When they depolorise they become positively charged.
What is the right shouler lead called in an ECG ?
Augmented vector right (AVR)
What is the left shoulder lead called in an ECG ?
Augmented vector left (AVL)
What is the left foot lead called in an ECG ?
Augmented vector foot (AVF)
What do the leads detect in an ECG ?
any positive deflection coming towards them
Which leads are inferior leads?
Which coronary arteries supply here?
Leads 2, 3 and AVF
Because they are at the inferior aspect of the heart and receive blood from the right coronary artery?
Which leads are lateral leads?
Where are the supplies from?
Leads 1 and AVL (High lateral) Left circumflex
and , V5, and V6 - LAD, L circumflex or RCA
They are on the lateral side of the wall and receive blood from the left circumflex artery.
Which leads are considered septal leads ?
V1 AND V2
They are near the interventricular septum
Served by the left anterior descending
Which leads are anterior leads ?
V3 AND V4
Nearest the anterior wall of the heart
Served by the left anterior descending
Where are the ECG placements ?
What is the cardiac vector?
Which lead is this shown in ?
Average direction of all the myocardial cells is called the cardiac vector – runs from 11 o’clock to 5 o’clock position
Why do we have a 12 lead view
Lead I - Right arm to left arm - a measure of electrical activity across the chest.
Lead II - Right arm to feet , left leg
Lead III - left arm to left leg
What is the standard calibration for an ECG rhytm strip ?
25mm / second
What is the amplitude of an ECG rhythm strip?
10mm/mv
What is 1 small box equivalent to on an ECG rhythm strip ?
0.04 seconds
What is one large box equivelent to on the ECG rhytm strip ?
0.2 seconds
How many boxes would equate to 1 second on the ECG rhythm strip?
5 large box
During a flat line eg isoelectric phase does it mean there’s no activity?
Typically means no activity however
There can be some electricity in one direction and one in another and they can be cancelling each other out.
Explain the phases of the P QRST complex
Isoelectric phase
P wave:
Atrial depolarisation
Isoelectric phase
QRS:
Ventricular depolarisation
Isoelectric phase
T wave:
Repolarisation of ventricle
Why is the T wave a positive deflection?
Typically you see a positive reflection in depolarisation so do we see it in the depolarisation of the ventricles?
Repolarisation is a negative current wave because that negative current wave is going away from lead II It is a negative of a negative which then becomes a positive.
eg moving up towards the right shoulder
Explain the P wave
Normally:
- Relatively little muscle mass:
Duration < 2 small squares (<0.08 sec)
Height = <2.5 small squares (0.25mV)
- Upright in lead II
- Precedes the QRS complex
- Single hump (both atria depolarising together)
What is a bifid/biphasic p wave
when the atria aren’t contracting together
Why is there a deflection at the Q wave in lead II?
During ventricular activation, impulses are first conducted down the left and right bundle branches on either side the septum. This causes the septum to depolarize from left-to-right as depicted by vector 1 (Fig.1). This vector is heading slightly away from the positive electrode (to the right of a line perpendicular to the lead axis) and therefore will record a small negative deflection (Q wave of the QRS).
Explain the PR interval
Measured from start of P wave to start of QRS complex:
-Time taken for conduction to get through:
Atria
AVN and the bundle of His
- Normally 3-5 little squares (0.12 – 0.20 sec)
- Important area to check when considering “heart block” – i.e. atria & ventricles not synchronised
Explain ST segment
ST - ischemia - depression
ST - infarction - elevation
Measured from end of S and beginning of T waves
Phase when ventricular depolarisation is petering out
Important area to check as marker for myocardial ischaemia (depressed) or infarction (elevated)
Compared to TP segment which is the true baseline
What is this ?
ST depression - Ischaemia
What is this ?
ST elevation - Infarction
Explain the QT interval
QT interval:
Normal length 350- 450 ms
Total ventricular depolarisation & re-polarisation time
Equivalent to ventricular action potential duration
Duration dependent on HR
Prolongation puts the patient at risk for arrhythmias (Torsades de pointes)
What is a dangerous from of prolonged QT interval ?
Torsades de pointes (TdP)is a specific form of polymorphic ventricular tachycardia occurring in the context of QT prolongation; it has a characteristic morphology in which the QRS complexes “twist” around the isoelectric line.
Explain the U wave
U wave:
Last part of ventricular repolarisation (? Purkinje fibers)
? 10% incidence
Should be same as T wave polarity but <1/3 size
Can be seen in electrolyte disorder (particularly elevated K+)
What is the list of questions you should be asking when viewing a ECG ?
How is the patient?
Is there a cardiac arrest rhythm?
What is the rate?
What is the rhythm?
Are there any P waves?
Are there any odd P waves?
Is there heart block?
Are there any odd QRS complexes?
Is the T wave abnormal?
Is the QT the correct duration?
What would the rhythm be if the patient has no pulse but you see this?
Pulseless electrical activity
What are the cardiac arrest rhythm
Astole
VF
PEA
Pusle ventricular tachycardia
What is this ?
Asystole
What is this ?
Ventricular Fibrillation
How do you calculate the Heart rate on an ECG ?
HR = 300/ RR interval
(count the big squares)
What is Bradycardia ?
HR < 60 bpm
What is Tachycadria ?
HR > 100 bpm
What is the heart rate for this rhythm?
What rhythm is it ?
Sinus Bradycardia
What is the heart rate for this rhythm?
What rhythm is it ?
Sinus Tachy cardia
What is a Premature Atrial Contraction? (PAC)
Premature atrial contractions (PACs) are extra heartbeats that begin in one of your heart’s two upper chambers (atria).
This can be normal and happens in healthy patients induced by stress, alcohol, caffiene.
What does this show ?
PAC
What type of rhytm is this ?
Irregular Irregularity
NO PATTERN WHATS SO EVER
What is Sinus Arrhythmia
Sinus arrhythmia is a normal physiological phenomenon, most commnonly seen in young, healthy people.
The heart rate varies due to reflex changes in vagal tone during the different stages of the respiratory cycle.
Inspiration increases the heart rate by decreasing vagal tone.
With the onset of expiration, vagal tone is restored, leading to a subsequent decrease in heart rate.
The incidence of sinus arrhythmia decreases with age, presumably due to age-related decreases in carotid distensibility and baroreceptor reflex sensitivity.
What are typical signs of AF ?
No P waves
Irregular iregularity
Typically quick
What is this ?
AF
What is this ?
Junctional Rhythm
The SA node not working and the AV node has taken charge.
AV fired at 40- 60
What are causes of First degree heart block ?
Causes of First Degree Heart Block
Increased vagal tone
Athletic training
Inferior MI
Mitral valve surgery
Myocarditis(e.g. Lyme disease)
Electrolyte disturbances (e.g.Hyperkalaemia)
AV nodal blocking drugs (beta-blockers,calcium channelblockers,digoxin, amiodarone)
May be a normal variant
What is this ?
First-degree heart block
P -wave precedes each QRS-complex but interval is >0.2s
What is this ?
A-V block
Second degree (Mobitz Type I)
Prolonging PR interval then a drop in PQRST.
What is this ?
A-V block
Second degree (Mobitz Type II)
No Lengthening of the PR
No pattern
What causes 2nd degree heart block ?
2nd degree heart block:
Mechanism
Mobitz I is usually due to reversible conduction block at the level of the AV node.
Malfunctioning AV node cells tend to progressively fatigue until they fail to conduct an impulse. This is different to cells of the His-Purkinje system which tend to fail suddenly and unexpectedly (i.e. producing a Mobitz II block).
What is complete heart block ?
Mechanism
Complete heart block is essentially theend pointof eitherMobitz IorMobitz IIAV block.
It may be due to progressive fatigue of AV nodal cells as perMobitz I(e.g. secondary to increased vagal tone in the acute phase of an inferior MI).
Alternatively, it may be due to sudden onset of complete conduction failure throughout the His-Purkinje system, as perMobitz II(e.g. secondary to septal infarction in acute anterior MI).
The former is more likely to respond to atropine and has a better overall prognosis.
Patients with third degree heart block are at high risk of ventricular standstill and sudden cardiac death.
They require urgent admission forcardiac monitoring, backup temporary pacing and usually insertion of a permanent pacemaker.
What is this ?
Complete heart block
Nothing is communicating !!!
One of the hardest ones to pick up !
What is this
Premature ventricular contraction
CAN BE NORMAL
But potentially needs investigating if happens more frequently
How much time is one large box in an ECG ?
0.2 seconds
What process does the QRS complex relate to
ventricular depolarisation
When does atrial repolorisation happen ?
During the QRS however, it is hidden.
What do you see with ischema in the heart?
ST depression
What is an important area to check when considering heart block ?
PR interval
Whats the difference between segment and interval?
PR becomes longer, longer and longer and then drop of QRS what is this?
Type 2 Heart block: Mobitz 1
What is the major hallmark of A fib ?
No p waves
Irregularly irregular
No gradual prolongation of PR wave however drop of QRS
Type 2 heart block: Mobitz 2
Which type 2 heart block is worse mobitz 1 or 2?
What would you give these patients?
Mobitz 2
Has high potential to complete heart block
Pacemaker
What presenting complaints would you do an ECG for ?
- Chest pain
- Palpitations
- SOB
- Fainting
What lead looks at right arm to left arm ?
Lead 1
What lead looks at Right arm to Left Leg
Lead 2
What lead looks at Left arm to LL
Lead 3
What definition should you see in Lead I and II?
What does this mean?
Patients with a normal axis should have a positive deflection in leads I and II.
When would you see right Axis deviation ?
What would you see on an ECG ?
Salson colour will have a negative deflection (Lead I) because deflection is not going towards the left side. Lead II remains normal.
Causes:
- RV hypertrophy
- LV infarction
- Pulmonary emboli (RV outflow blocked)
- Dextrocardia
The points will point towards each other they are RIGHT for each other (RIGHT DEVIATION).
When would you see Left Axis deviation ?
What would you see on an ECG ?
Left axis deviation:
I biggest positive
II negative
Lead III will follow same as Lead II and show a negative.
Causes:
Left ventricular hypertrophy
Conduction defects
Inferior MI
LBBB
ECG leads will point away from each other.
They have LEFT each other they dont want each other anymore. (LEFT deviation).
What does a wide QRS suggest ?
Problems in the ventricle
Sudden change in Axis is always worrying
Is this true ?
YESS
What patients are at risk of left ventricle hypertrophy ?
Those with long-standing HTN !!
also
Causes:
Aortic valve stenosis
Systemic hypertension
Co-arctation
Cardiomyopathy
What would you expect to see on an ECG in left ventricular hypertrophy ?
lateral v5, v6 higher than normal R wave in the lateral leads
R wave < 25mm (5 big squares)
V1 and V2 will get negative defelction because the axis is towards the letft.
S wave < 25mm (5 big squares)
What would you see on an ECG in right ventricular hypertrophy?
(A lot less common to see than left ventricular hypertrophy)
Tall r waves in v1 and v2
Here the QRS is too small. What would cause this?
!!Pericardial effusion !!
We are increasing the distance between the heart and the chest wall, also the fluid within the heart will dampen the electrical conduction.
Could potentially be normal for the patient if they have barrel chest, breast, or obesity because electrodes are further away. Equally could see large QRS is a person is particularly thin because the chest is so close to the heart.
QRS too wide, What could this be ?
Bundle branch block
Explain right Bundle Branch Block
Where will you see changes in ECG ?
Indicates depolarisation is taking an abnormal route. One bundle will be slower than the other so you will see two R waves.
ECG:
- Two R waves in V1 and V2.
- Wide QRS
Causes:
“Normal”
Ischaemic Heart Disease
Cardiomyopathy
Congenital (ASD)
Massive PE
Explain William Morrow in RBBB
Explain William Morrow in LBBB
What is the J point ?
J Point:
First bend on the upstroke of the S wave or downstroke of R wave
Transition of QRS to ST segment
Where was the ST measured from?
Where is it compared against to see if it’s elevated or depressed?
Measured from end of S to start of T wave
Isoelectric reference is TP segment
How would you define ST elevation ?
Limb leads> 1mm at J point
V leads >2mm at J point
What can cause ST elevation ?
STEMI
Pericarditis ( here you will have ST elevation perufsily not just in some leads)
Printzmetal Angina
High take off / Bening Early Repolarisation
When would you see ST depression ?
1- Myocardial ischaemia
2- Ventricular hypertrophy with strain
3- Reciprocal to ST elevation in opposing leads (e.g. anterior leads with acute posterior MI)
4 - Drugs (e.g. digoxin; quinidine)
What are the new Definitions for ST elevation?
Explain the zones of infarction in relation to the electrophysiology of a STEMI.
Zone of ischemia - ST depression +/- T inversion (altered repolarisation)
Zone of injury - ST elevation +/- loss of R wave
Zone of infarction - Pathological Q (no depolarisation of affected area)
What is the first thing to change on ECG during a STEMI?
Elevated T wave
RCA supplies which part of the heart ?
Inferior
2, 3 avf
Which part does the circumflex supply ?
1 avl v5 v6
Lateral
Left anterior descending supplies what part of the heart?
What leads?
anterior
v1, v2, v3, v4
What does this ECG show
anterior lateral STEMI
In the LCA
THIS IS BAD !!! Supplies the entire left side of the heart?
What does this ECG show
Inferior STEMI
RCA
What are the two signs of mitral stenosis on ECG ?
Bifid P waves
No p waves
Patients with mitral stenosis are often in atrial fibrillation so there may be no P waves. A bifid P wave or P mitrale reflect left atrial enlargement and are sometimes seen before atrial fibrillation
What do Peaked P waves Suggest ?
Peaked P waves suggest P pulmonale or right atrial enlargemen
What do Delta waves suggest
Wold-Parkinsons-White syndrome
What is this ?
NSR w/ a Premature atrial complex
What is this ?
VENTRICULAR FIBRILLATION
What is this?
What does the ECG what leads have changed ?
Widespread concave ST elevation and PR depression throughout most of the limb leads (I, II, III, aVL, aVF) and precordial leads (V2-6).
Reciprocal ST depression and PR elevation in lead aVR (± V1).
Sinus tachycardia is also common in acute pericarditis due to pain and/or pericardial effusion.
What is this ?
Left axis deviation (LAD) and left ventricular hypertrophy (LVH)
