ECG Review Flashcards by Alice Scholfield

When interpreting an ECG, which order would you address the various aspects in

Rate
Rhythm
Atrial activity
One p wave before each QRS?
P wave normal duration
PR interval normal duration
QRS normal duration
ST segment normal (elevated/ depressed?

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How do you manually calculate heart rate from an ECG

Number of R waves in 15 large grid squares * 20

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How can you see if RR intervals are the same

Marks where the R ares on piece of paper and move along to see if they’re the same

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What does the P wave represent

Atrial depolarisation

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How long should P waves be

No longer than 2 small squares (0.08s/ 80ms)

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What time period is represented by one square on an ECG

0.04

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What is represented by the PR interval

Time to cross the AV node and propogate via bundle of His to the ventricles

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How long should the PR interval be

120-200ms

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What does a PR interval of >200ms indicate?

A form of heart block
Hypokalaemia
Acute rheumatic fever
Carditis

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What does QRS complex indicate

Synchronisation of the contraction of ventricular muscles

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How long should QRS complex be

<120ms in duration

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Describe how a normal ECG would appear (5)

60-100bpm
Regular rhythm
P wave <80ms
PR interval <200ms
QRS duration <120ms

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Define sinus bradycardia

A heart rate <60bpm

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What may cause sinus bradycardia (4)

1- Healthy, athletic person
2- Drug abuse
3- Hypoglycaemia
4- Brain injury

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What medication commonly causes sinus bradycardia

Beta blockers

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Define sinus tachycardia

A heart rate >100bpm

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Where does sinus tachycardia originate from

SA node

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Describe how ventricular tachycardia appears

Rate= 180-190bpm
Prolonged QRS
P wave not seen
‘Just looks wrong- dips downwards kind of into V shapes’

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What can cause ventricular tachycardia

MI, Coronary artery disease, poor heart structure

Abnormal tissues in ventricular generate rapid and irregular heart rate

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How may ventricular tachycardia lead to cardiac arrest

Poor cardiac output leads to cardiac arrest

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Describe how ventricular fibrillation appears on an ECG

Irregular rhythm, rate >300bpm

Disorganised, no recognisable QRS, P wave not seen

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What happens to patient in ventricular fibrillation

Disorganised electrical signals cause the ventricles to quiver instead of contract
Patient will be unconcious as blood not pumped to brain- DEFIB

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How can you distinguish ventricular tachycardia and ventricular fibrillation on an ECG

In VT rhythm and amplitude of QRS are normal, just a lot faster

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What do all forms of heart block have in common

PR interval >200ms

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What is first degree heart block, and is it a problem

- PR interval is fixed, constant duration >200ms - Regular rate - Rarely causes problems, common amongst athletes

What is second degree heart block type 1

- Each successive impulse from atria finds more difficult to pass AVN - PR interval gets progressively longer until P wave is not followed by QRS - After this, system resets

What is second degree heart block aka

Wenkenbach

What happens in second degree heart block type 2?

AVN randomly fails to respond to some atrial impulses | Rate is irregularly irregular

What is third degree heart block

Impulses from atria do not connect with ventricles | Ventricular rhythm independent from atrial

What rate is usually present in third degree heart block and why

Bradycardia - Ventricles generate their own signal from a focus somewhere in the ventricle - Ventricular escape beats are slow

What symptoms are often present in atrial fibrillation

- Palpitations - Fainting - Chest pain - Congestive heart failure - May be asymptomatic

What is the underlying mechanism of atrial fibrillation

- Many sites within the atria, not just the SAN, generate electrical impulses - This leads to irregular conductions to ventricles

How will an ECG of somebody with atrial fibrillation appear?

- Rate: 100-160bpm - Rhythm: irregularly irregular - QRS: normal - P wave: absent

What is the underlying mechanism of atrial flutter

- Re-excitation of electrical impulses causes high frequency bombardment of AVN - High but regular rhythm

Describe how an ECG of somebody with atrial flutter would appear

110bpm Regular rhythm P waves replaced with flutter waves P wave rate= 300bpm

What is junctional rhythm

Damage to SAN/ blockage on conduction pathway causes the AVN to take over as the pacemaker

Describe how an ECG appears if junctional rhythm is occuring

- 40-60bpm - Regular rhythm - Normal QRS complex - P wave ratio 1:1. Inverted in lead 2 - P-R interval is the same

What is happening in supraventricular tachycardia

- Abnormality in or near the AVN | - High frequency of impulses at the AVN

Describe how an ECG appears for supraventricular tachycardia

140-220bpm Regular rhythm QRS duration is normal P wave is absent or buried in preceding T wave P-R interval differs depending on the site of the pacemaker

What is the most common form of supraventricular tachycardia

AV nodal reentrant tachycardia

What % of cases of AVNRT occur in women and what is the main symptoms

75% | Palpatations

Describe the underlying mechanism of AVNRT

- Occurs when reentry circuit forms within on just next to AVN - Atrial impulses go around in a circle instead of dying away causing repeated activation of AVN after a short time

What 2 anatomical pathways are involved in AVNRT and where are they located

Fast and slow pathways | Both located in the right atrium

What is the main difference seen on an ECG of somebody with bundle branch block

Widening of the QRS complex | Notch on the R wave

What does RBBB indicate

Problems with the right side of the heart

What does LBBB indicate

Heart disease

How can you distinguish between left and right bundle branch block?

WiLLiaM MaRRoW LBBB--> There is a 'w' shape in v1 and an 'm' in v6 RBBB--> There is an 'm' in v1 and a 'w' in v6

What does the ST segment represent

Time where both the ventricles are fully depolarised

How long should the ST segment be?

80-120ms

How should the ST segment appear and why

It should be flat or isoelectric because if both ventricles are working correctly their voltage will cancel out

What is indicated by a downsloping ST segment

Coronary ischaemia | Hypokalemia

What does STEMI stand for

ST elevation myocardiac infarct

What must the ECG show for a person to qualify as a STEMI

new ST elevation in 2 or more adjacent ECG leads

What leads should you be looking at to determine electical axis

Leads 1 and aVF

What does it mean if the QRS complexes are overall positive in both leads 1 and aVF

Normal electrical axis

What is the normal quadrant for the electrical axis of the heart to be in

0-90 degrees

What would you see if the electric axis for the heart is left axis deviated

Lead 1 positive | aVF negative

What would you see if the electrical axis for the heart is right axis deviated

Both negative

What quadrant/ degrees would the electrical axis of the heart be in if lead 1 was positive but avf was negative? What could this indicate

Left upper quadrant 0--90 degrees Possible LAD

What quadrant/ degrees would the electrical axis of the heart be in if lead 1 was negative but avf was positive? What could this indicate

Right lower quadrant 90-180 degrees Possible RAD

What quadrant/ degrees would the electrical axis of the heart be in if both Lead 1 and avf were negative? What could this indicate

Right upper quadrant -90-180 degrees Extreme axis deviation

ECG Review Flashcards

(61 cards)