ECG Theory Flashcards
Where on the chest should V1 be placed?
Right sternal edge, 4th intercostal space
Where on the chest should V2 be placed?
Left sternal edge, 4th intercostal space
Where on the chest should V3 be placed?
Midway between V2 and V4
Where on the chest should V4 be placed?
Mid-clavicular line, 5th intercostal space
Where on the chest should V5 be placed?
Anterior axillary line, same level as V4
Where on the chest should V6 be placed?
Mid axillary line, same level as V4
Which colour of limb lead corresponds to each of the bony prominences?
Right arm red, left arm yellow, left leg green, right leg black
One small box on an ECG is equal to what amount of time? One large box is equal to what amount of time?
0.04 secs / 0.2 secs
How is the rate calculated from an ECG of a person with a regular pulse?
300 divided by the number of large boxes between two R waves
How is the rate calculated from an ECG of a person with an irregular pulse?
The number of QRS complexes in 30 large squares multiplied by 10
What 5 questions should you ask yourself to ascertain the rhythm of an ECG?
- Is there electrical activity present? 2. Is the rhythm regular or irregular? 3. Are P waves present? 4. What is the relationship between the P waves and QRS complexes? 5. What is the QRS duration?
How can you tell if the axis of an ECG is normal?
The QRS complex in leads I and aVF will both be positive
How can you tell if the axis of an ECG is deviated to the left?
The QRS in lead I will be positive but in aVF will be negative
How can you tell if the axis of an ECG is deviated to the right?
The QRS in lead I will be negative but in aVF will be positive
What does left axis deviation suggest?
LVH or damage to the right ventricle
What does right axis deviation suggest?
RVH or damage to the left ventricle
What is the PR interval?
The time from the onset of the P wave to the onset of the QRS complex
What does the PR interval represent in the cardiac cycle?
The beginning of atrial depolarisation to the beginning of ventricular depolarisation
What is the normal value of the PR interval?
120-200ms (3-5 small squares)
The duration of the QRS complex is considered normal when?
It is < 120ms (3 small squares)
What is the QT interval?
The beginning of the QRS until the end of the T wave
What does the P wave represent in the cardiac cycle?
Atrial depolarisation
What does the QRS complex represent in the cardiac cycle?
Ventricular depolarisation
What does the T wave represent in the cardiac cycle?
Ventricular repolarisation
The T wave should not be more than how high?
Half the height of the QRS
Supraventricular rhythms originate where? Describe their QRS complexes?
From the AV node or above / narrow QRS complexes
What are the two main features of sinus rhythm?
A P wave for every QRS and QRS for every P wave / PR interval < 200ms (one large box)
What is a sinus arrhythmia?
When an ECG meets all the criteria of sinus rhythm, but the rhythm itself is irregular
What are the two main features of atrial fibrillation on ECG?
No P waves / Irregularly irregular QRS
What causes atrial fibrillation?
Disorganised activity in the atria
What causes atrial flutter?
Re-entry circuit within the atria
What are the 3 main features of atrial flutter on ECG?
Saw-tooth baseline / F waves / Ventricular rate divisible by 300
Retrograde P waves are a sign of what?
Junctional rhythm
What causes junctional rhythm?
Electrical impulses originate at the AV node instead of the SA node
What are the main features of a supra ventricular tachycardia on ECG?
Regular, narrow complex tachycardia / Often no clear P waves
How should a supra ventricular tachycardia be treated?
Vagal manoeuvres, then adenosine if these fail
If an ECG shows sinus rhythm with a differing P wave morphology every 3 beats, what does this suggest?
Supraventricular ectopic beats
What happens to the QRS complex in ventricular rhythms?
Broad complex
Polymorphic ventricular tachycardia is often associated with what ECG feature?
QT prolongation
Describe what is meant by aberrancy?
An underlying BBB causes a broad QRS which leads to difficulty diagnosing a supraventricular rhythm
What is a good predictor of SVT with aberrancy?
Known pre-existing BBB
If in doubt about an ECG with possible aberrancy, should you treat the patient?
Yes, if in doubt treat as VT
Describe what happens to an ECG in 1st degree heart block?
Prolonged PR interval
Describe what happens to an ECG in Mobitz 1 heart block?
Progressive PR prolongation until the occurrence of a dropped beat
Describe what happens to an ECG in Mobitz 2 heart block?
Random beats are missed
Describe what happens to an ECG in 3rd degree heart block?
No relationship between the P waves and QRS complex
Defibrillation can be used to treat which cardiac arrest rhythms?
VF and VT
What is pulseless electrical activity?
Cardiac arrest alongside any rhythm which would normally be associated with a pulse
What is asystole?
The total cessation of electrical activity from the heart
Leads II, III and aVF correspond to which vascular territory, and which specific artery?
Inferior, right coronary artery
Leads I, aVL, V5, V6 correspond to which vascular territory, and which specific artery?
Lateral, left circumflex artery
Leads V1-V4 correspond to which vascular territory, and which specific artery?
Anterior, left anterior descending artery
What happens to the T wave in ischaemia?
Tall, biphasic, inverted
What are the criteria for thrombolysis?
ST elevation > 1mm in two contiguous limb leads OR > 2mm in two contiguous chest leads
Pericarditis is an important differential of what ECG change? What is it secondary to?
An important cause of ST elevation, usually secondary to an MI or viral infection
How should pericarditis be treated if not contraindicated?
NSAIDs
As well as ST elevation, what are some other signs of pericarditis?
Widespread changes, PR depression
How can you tell if an ECG shows RBBB?
M shape in V1, W shape in V6
How can you tell if an ECG shows LBBB?
W shape in V1, M shape in V6
Left anterior hemiblock will show what type of axis deviation?
Left axis deviation
Left posterior hemiblock will show what type of axis deviation?
Right axis deviation
What is a normal QT interval?
< 440ms (11 small boxes, just over 2 large boxes)
