ECGs 2 Flashcards by Callum Donoher

What is meant by the overall axis of the heart/ECG?

The overall direction of depolarisation of the heart

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How can you imagine the layout of axis in the human body?

Imagine a stick man

Left arm = 0 degrees and is lead I
Feet = +90 degrees and is avF lead
Right arm = 180 degrees
Head = -90 degrees

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What part of the ECG determines the axis of the ECG?

QRS complexes

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What part of the ECG determines the axis of the ECG?

QRS complexes

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Which 2 leads of the ECG determines the axis of the heart/ECG?

Lead I
AvF lead.

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What is considered a normal axis of the heart?

Between -30 and 90 degrees
So generally in the left lower quadrant

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How do you determine the axis of the heart using lead I and avF lead?

Lead I determines the horizontal axis of the vector

avF lead determines the vertical axis of the vector

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How do you interpret lead I to determine the horizontal part of the vector to determine the axis?

Lead 1 the current normally runs to the left, this is the positive direction, to the right is the negative direction

So if the QRS in lead I is more positive than negative (more squares in the upward deflection than the downward deflection) it means the electrical current is going in the normal positive direction so to the left

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How do you interpret avF to determine the vertical part of the vector to determine the axis?

In lead avF, the current normally runs downwards, so this is the positive direction

So if the QRS in lead avF is more positive than negative (more squares in the upward deflection than the downward deflection) the current is flowing in the positive direction so is going down the avF lead.

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What degrees is considered left axis deviation?

Between -30 and -90 degrees

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What degrees is considered right axis deviation?

+90 and 180 degrees So generally

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What is the likely axis in this scenario:
-lead I QRS positive
-avF lead QRS is negative

+ Lead I means horizontal vector is left
- lead avF means upward vertical vector

So going top left quadrant so is left axis deviation

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What is the likely axis in this scenario:
-lead I QRS negative
-avF lead QRS is positive

-ve lead I means depolarisation happening in opposite direction than normal so horizontal vector is right

+ve avF means depolarisation happening in normal direction so vertical vector is downwards

So overall depolarisation is going bottom right quadrant (+90 to +180) so is RIGHT AXIS DEVIATION

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What can cause Right Axis Deviation?

Right ventricular strain likely due to a Massive PE

Left posterior fasicular block

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What causes Left Axis Deviation?

Left ventricular strain

Left anterior fasicular block cause right

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What are the 3 types of P waves?

Normal
P-mitrale
P-pulmonale

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What does a p-mitrale wave look like?

Biphasic p wave (on first slide of notes)

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What generally causes p-mitrale (biphasic p wave)?

What can cause this?

Left atrial enlargement

Mitral stenosis

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What is p-pulmonale?

Tall peaked p wave where the p wave is greater than 2.5 small squares high

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What generally causes p-pulmonale?

What can cause this?

Right atrial enlargement

Pulmonary hypertension, COPD, left sided heart failure causing right sided heart failure

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What are the characteristic ECG findings of a massive pulmonary embolism?

S1Q3T3
Right Axis Deviation (Due to right ventricular strain)

Can get p-pulmonale but not always (due to right atrial enlargement)

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What is meant by the characteristic S1Q3T3 seen on an ECG with a massive pulmonary embolism (PE)?

Deep S wave in lead I
Q wave in lead III
Inverted T wave in lead III

What type of patients do you commonly see p-pulmonale in?

COPD patients

What is the PR interval?

Time between the start of the P wave till the start of the QRS complex

What is represented by the PR interval?q

Time taken from the initiated depolarisation from the SAN to reach the AVN and travel down the bundle branches and the Purkinje fibres to the first ventricular depolarisation/contraction

When are there issues with a long PR interval?

When the PR is very long There’s other conducting disease Infective endocarditis on aortic valve (abscess in area where AVN is)

What causes a short PR interval/what does a short PR interval represent?

Short PR = very quick time between initial depolarisation of atria reaching the ventricles (means there’s an alternate pathway that is by passing the AVN) An accessory pathway (Wolff Parkinson White Syndrome)

What type of wave will be visible on an ECG if theres an accessory pathway causing a shortened PR interval? How does this look?

Delta wave Slow upstroke/slurring of a wave before the QRS complex (top of page 2 in notes)

What is suggest if there is the presence of a Q wave in the QRS complex?

Patient has had a full thickness MI

What is the criteria for there being a Q wave?

Very first deflection must be down Must be at least 1/4 of the depth of the subsequent R wave The Q wave exists outside of leads III, II or avF since it’s normal to have Q. Waves here

How should the R wave change as you move through the chest leads?

R wave should progress so should get bigger and bigger

What is the voltage criteria for classifying left ventricular hypertrophy?

Need all 3 criteria: -Count the squares of the S-wave in V1 or V2 (whichever is bigger) THEN count squares of R wave in V5 or V6 (whichever is bigger) then add the number of squares together. If its >35mm meets criteria -any S or R waves on chest leads that are greater than 30mm -R wave in lead I and avL > 14mm

What is indicated by a broad QRS?

Bundle Branch Block

What is a normal QRS complex?

Less than 3 squares

How do you assess whether a bundle branch block is either left or right?

Look at the chest leads V1-V6 at the Broad QRS complexes

What is the saying used to help determine the direction of bundle branch block?

WILLIAM MARROW

What does WILLIAM MARROW mean?

You look at the QRS complexes in leads V1 to to V6 V1 to V3 will either look like a W or M V4 to V6 will either look like a W or M (opposite to V1 to V3)

Which name is used to show Left Bundle Branch block when looking at the chest leads?

WILLIAM

Which name is used to show Right Bundle Branch block when looking at the chest leads?

MARROW

How do you determine left bundle branch block using WILLIAM?

W.I.LL.IA.M Look at the broad QRS complexes in V1-V3 it will look like a W Look at the broad QRS complexes in V4-V6 it will look like an M The way you can remember that WILLIAM is for LBBB is the 2 LLs in the middle

How do you determine right bundle branch block using MARROW?

M.A.RR.O.W Look at the broad QRS complexes in V1-V3 it will look like an M Look at the broad QRS complexes in V4-V6 it will look like an W The way you can remember that MARROW is for RBBB is the 2 RRs in the middle

What are the 3 types of ST segments?

Normal Elevated Depressed

What are the 3 causes of ST elevation?

-MI (acute myocardial injury) -pericarditis -brugada syndrome

How does an ST elevation caused by an MI/acute myocardial injury?

Tombstone look to it Regional to the area of damage with reciprocal changes in other leads

How does the ST elevation cased by pericarditis appear?

Saddle shaped elevated ST segment with pr depression

What is the difference between ST elevations caused by MI/acute Myocardial injury and pericarditis?

MI/myocardial injury: -tombstone look that is specific to the area of damage Pericarditis: -saddle shaped ST segment with PR depression

What are the 2 types of ST depression that are dangerous/indicate coronary artery disease?

Horizontal ST depression Downsloping ST depression

What are some types of pathological T waves that indicate an MI?

Biphasic T wave Symmetrical T wave inversion T wave triangular inversion Asymmetrical T wave inversion is not dangerous

What is the QT interval?

How long it takes ventricles to repolarise

How do you identify the QT interval on an ECG?

Start of the Q wave to the end of the T wave (Look at last page of notes if unsure)

What can QT prolongation cause?

Leads to torsades de pointes

What is the equation for working out QTc?

QT / square root of RR interval Units = m/s

What is the RR interval?

Distance between the 2 peaks of the QRS (Look at last page of notes if unsure)