ECG Review Flashcards
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?
How do you manually calculate heart rate from an ECG
Number of R waves in 15 large grid squares * 20
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
What does the P wave represent
Atrial depolarisation
How long should P waves be
No longer than 2 small squares (0.08s/ 80ms)
What time period is represented by one square on an ECG
0.04
What is represented by the PR interval
- Time to cross the AV node and propogate via bundle of His to the ventricles
How long should the PR interval be
120-200ms
What does a PR interval of >200ms indicate?
A form of heart block
Hypokalaemia
Acute rheumatic fever
Carditis
What does QRS complex indicate
Synchronisation of the contraction of ventricular muscles
How long should QRS complex be
<120ms in duration
Describe how a normal ECG would appear (5)
60-100bpm Regular rhythm P wave <80ms PR interval <200ms QRS duration <120ms
Define sinus bradycardia
A heart rate <60bpm
What may cause sinus bradycardia (4)
1- Healthy, athletic person
2- Drug abuse
3- Hypoglycaemia
4- Brain injury
What medication commonly causes sinus bradycardia
Beta blockers
Define sinus tachycardia
A heart rate >100bpm
Where does sinus tachycardia originate from
SA node
Describe how ventricular tachycardia appears
Rate= 180-190bpm
Prolonged QRS
P wave not seen
‘Just looks wrong- dips downwards kind of into V shapes’
What can cause ventricular tachycardia
MI, Coronary artery disease, poor heart structure
Abnormal tissues in ventricular generate rapid and irregular heart rate
How may ventricular tachycardia lead to cardiac arrest
Poor cardiac output leads to cardiac arrest
Describe how ventricular fibrillation appears on an ECG
Irregular rhythm, rate >300bpm
Disorganised, no recognisable QRS, P wave not seen
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
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
What do all forms of heart block have in common
PR interval >200ms
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
