6/7-ECGs Flashcards
What is the normal conduction pattern in the heart?
- electrical activity starts at Sino Atrial Node
- impulse spreads across atria
- impulse delayed at atrio ventricular node to allow complete atrial contraction
- conduction spreads to bundle of His-right/left bundle branch-purkinje fibres to stimulate myocardial contraction
Name the colours and locations of the limb leads
Right upper limb lead - red - right shoulder
Left upper limb lead - yellow - left shoulder
Right lower limb lead - black - right ankle
Left lower limb lead - green - left ankle
Name the colours and locations of the chest leads
V1 - red - 4th right intercostal space
V2 - yellow - 4th left intercostal space
V3 - green - 5th left intercostal space (closest to sternum)
V4 - blue - 5th left intercostal space
V5 - orange - 5th left intercostal space
V6 - purple - 5th left intercostal space (closest to mid clavicular line)
Where can the QRS complex normally be seen?
aVL, I, II, aVF
Which is between -30 and +90 degrees
What is left axis deviation?
Where the QRS complex is present at less than -30 degrees
What causes left axis deviation?
Inferior wall MI
LV hypertrophy
Left anterior bundle block
What is right axis deviation?
Where the QRS complex is found above 90 degrees
What causes right axis deviation?
RV hypertrophy
Acute right heart strain (e.g. Pulmonary embolism)
Left posterior bundle block
What is the standard recording speed of ECGs?
25mm per second
How many seconds are equivalent to big and small squares?
Big square = 0.2 seconds
Small square = 0.04 seconds
Where is the P-R interval measured from and what is the normal range?
Measured from start of p to start of q
Normally 3-5 small squares
What does a long P-R interval indicate?
Indicates a slow atria ventricular conduction, 1st degree heart block
Where is QRS width measured from and what is the normal range?
Measured from start of q to end of s
Normally 2-3 small squares
What does a wide QRS complex indicate?
Indicates abnormal conduction for ventricular depolarisation
Where is Q-T interval measured from and what is the normal range?
Measured from start of q to end of t
Normally 0.35-0.43 seconds
What does a prolonged Q-T interval indicate?
Indicates prolonged repolarisation of ventricles leading to arrhythmias e.g. prolonged QT syndrome
Where is S-T segment measured from?
End of s to start of t
What does a raised or depressed S-T segment indicate?
Should be equal to baseline (isoelectric), raised/depressed indicates ischaemia/MI
What is the equation to calculate a regular heart rate?
No of small squares per minute / no of small squares between peeks
=1500/x
What is needed to be classed as sinus rhythm?
Identical round P waves
Followed by QRS complex every time
Regular rhythm
Why are the depolarisation/repolarisation waves orientated in the same direction?
Repolarisation occurs in opposite direction so usually inverted deflections orientated in same direction
What differences are there between the depolarisation and repolarisation waves?
Repolarisation waves are more prolonged and lower amplitude
What are the features of atrial fibrillation?
Wavy baseline
No p waves
Irregularly irregular rhythm
What causes atrial fibrillation?
Hypoxia Hypertension Sepsis Alcohol Ischaemic heart disease
What are the consequences of untreated atrial fibrillation?
Clot leading to stroke
Rapid ventricular rate leading to hypertension/angina/ heart failure
How is atrial fibrillation treated?
Rate control - digoxin/ beta blockers
Anti-arrhythmics- amiodrone
Anti-thrombotics - warfarin/ dabigatron
What causes ventricular fibrillation?
Ischaemic heart disease
Hypoxia
Post MI
Prolonged QT arrhythmia
How is ventricular fibrillation treated?
Implanted cardiac defibrillator
Anti-arrhythmics - amiodorone
Describe the features of first degree heart block
Prolonged P-R interval greater than 0.2 seconds
Sinus rhythm
Describe the features of 2nd degree heart block, mobitz type 1
Progressive p-r elongation until QRS is not conducted
Describe the features of 2nd degree heart block, mobitz type 2
Fixed PR interval until sudden dropped QRS complex
Which mobitz type has a high risk of developing into third degree heart block?
Mobitz type 2
Describe the features of 3rd degree heart block
No relationship between atrial and ventricular activity
Wide QRS complex (from escape rhythm)
Bradycardic 30-40 bpm
How is heart block treated?
Anticholinergics - atropine
Beta agonist - isoprenaline
Pacemaker if severe
What causes heart block?
MI Rheumatic fever Calcium channel blockers Beta blockers Sarcoid
Describe the features of ventricular ectopic beats
Wide, abnormally shaped QRS complexes as impulse is spread slower by abnormal conduction system to ventricles
Describe the stages of a STEMI on an ECG over several weeks
Acute - ST elevation in leads facing injured area
Hours later - ST elevation, depressed R wave, Q wave begins
1/2 days later - t wave inversion p, Q wave deepens
Days later - ST normalises, T wave still inverted
Weeks later - T wave normalises, Q wave persists
What effect does hyperkalaemia have on ECGs?
RMP less negative, so voltage gated Na channels inactivated making heart less excitable, causing conduction issues leading to ventricular fibrillation
What effect does hypokalaemia have on ECGs?
RMP more negative, leading to
Low t waves
High u wave (after t wave)
Low ST segment
What are the differences between atrial and ventricular fibrillation?
Atrial has coordinated ventricular contraction, ventricular doesn’t
Atrial has cardiac output, ventricular doesn’t
Atrial has a pulse, ventricular doesn’t
Atrial has an irregularly irregular heart rate, ventricular has no heart beat
