ECG (foundations)

Question 1

Define depolarization

Answer 1

-90mV at start, Membrane potential is negative, influx of Na+, this causes the membrane to become more positive (+30mV)

Question 2

Define repolarization

Answer 2

+20mV–> -90mV, huge efflux of K+, leave the cell, as well as sodium ions leaves, membrane potential become more negative

Question 3

What is the refractory period?

Answer 3

A period where a new action potential cannot be produced

Question 4

Describe and explain the conduction of the heart

Answer 4

1. SAN found in the wall of RA, stimulates the contraction of heart, and releases a wave of excitation that travels across both atria, causing them to contract simultaneously. (septum blocks transmission to ventricles)
2. This wave passes over the AVN node located in the interatrial septum, ensuring a 0.1 second delay, to ensure atria have fully contracted and emptied before releasing a wave of excitation which travels down the interventricular septum towards the apex
3. The wave travels down the bundle of his which splits into left and right branches, the wave continues to travel along Purkinje fibres which split and spread through R & L side of the heart, this triggers ventricular contraction at the apex, allowing efficient emptying of the heart

Question 5

What causes the P, QRS and T wave on an ECG?

Answer 5

P wave is atrial systole (contraction)
QRS wave is when ventricular systole occurs, atria’s repolarize during this time
T- wave ventricular repolarization

Question 6

What is the S-T interval,

Answer 6

The interval between ventricular depolarization and repolarization

Question 7

How is HR controlled?

Answer 7

The autonomic nervous system regulates it via sympathetic & parasympathetic pathways
Sympathetic NS increases HR, BP & CO
Parasympathetic NS decreases HR, BP & CO

Question 8

Define ectopic focus

Answer 8

The site that generates the ectopic HB

Question 9

Define the characteristics of a myocardial infarction

Answer 9

An MI is a heart attack, caused by reduced blood flow to heart tissue,
- ST segment is elevated over the damaged area
-ST segment has a depression in opposite ECG leads
-Reduced R wave
- Inverted T wave
- Pathological Q waves

Question 10

Define plateau phase

Answer 10

Influx of calcium ions occur, some Na+ is leaking back out, membrane starts to become more negative.