ECG

Question 1

What is the basic passage of electrical conduction through the heart?

Answer 1

1) SAN → spontaneously active cells- conducts current down atria and internodal pathways. P wave on ECG

2) Atrioventricular node → current slows down between atria and ventricles- this allows atrial muscle to finish contracting to expel blood into ventricles

3) Septum & His-Purkinje system → current travels through septum and His-Purkinje system. Rapid conduction through left and right bundles to Purkinje fibres leading to ventricular contraction. QRS complex of ECG

4) Cardiac muscle relaxes & membrane potential recovers/repolarises. T wave on ECG

Question 2

What do the different ECG leads do?

Answer 2

Read the electrical current through the heart in different directions so each have different looking ECG graphs

e.g. lead 2 goes top left to bottom right and shows the biggest QRS wave of all the leads

Question 3

What happens to the ECG if we tilt the heart slightly clockwise?

Answer 3

Heart configuration is different and the nodes are no longer parallel to the lead 2- this means less deflection of the QRS wave

Question 4

What is the above thing called?

Answer 4

Axis deviation- can be a change in heart position (seen in taller people) OR a change in position of electrical conduction e.g. if right bundle branch gets damaged then current in left branch becomes more prominent which changes the conduction

Question 5

What would changes to atrial conduction (with examples) do to the ECG?

Answer 5

Change p wave
Eg atrial fibrillation causes loss of p wave
Atrial flutter gives saw tooth pattern

Question 6

• What is this aberrant activity is caused by?

Answer 6

caused by other cells in heart forming pacemaker potentials

• Sometimes these little fluttery currents may not be big enough to pass through AV node to form ventricular contraction
• NOTE: atrial fibrillation and atrial flutter are the names of the conditions/arrhythmias, whilst a loss of p-wave and saw tooth pattern are what can be seen in these conditions (respectively) on an ECG

Question 7

What would happen to the ECG if there was a barrier/problem at the AV node (e.g. cell destruction)?

Answer 7

• It would cause a longer PR interval- bigger gap between P wave and QRS complex initiation
• PR also means between start of P wave and start of QRS complex, not the peaks

Question 8

How do we calculate heart rate

Answer 8

300/Large squares
RR interval

Question 9

How would RR interval change during tachycardia and bradycardia

Answer 9

reduced RR interval (tachycardia)

increased RR interval (bradycardia)