1 Electrophysiology of the Heart

Question 1

What is the view of the heart called when you open it in the chest?

Answer 1

Anatomical position of the heart

Question 2

What arteries supply blood to the heart?

Answer 2

Coronary arteries

Question 3

What is the LAD?

Answer 3

Your left anterior descending (LAD) artery is one of two branches of your left main coronary artery.

Anterior means the artery supplies blood to the front portion of your heart. It’s the biggest supplier of oxygenated blood to your heart’s lower left pumping chamber or ventricle.

Question 4

Why are the coronary arteries on the surface of the heart?

Answer 4

So they are not affected by the heart’s contraction

Question 5

How are the atrium and ventricles described as pumps?

Answer 5

Atrium = priming pump
Ventricles = main pump

Question 6

How many pulmonary veins are there and what do they do?

Answer 6

There are 4 altogether = 2 from each lung

The blood is oxygenated in the lungs and returned to the heart by the pulmonary veins

Question 7

What is the role the electrical signal?

Answer 7

Initiates and synchronizes the contraction of the atria and ventricles

Question 8

Can the pump output be varied?

Answer 8

Yes, this is important if the blood flow needs to be changed depending on acitivty

Question 9

What cells are electrically excitable?

Answer 9

Nerves and muscle cells (cardic muscle cells too)

Question 10

What does the ATPase pump do?

Answer 10

Pumps 2K+ in and 3Na+ out of the cell using ATP as energy source because they are moving against conc grad

Inside of the cell becomes negatively charged

Question 11

Define action potential

Answer 11

Depolarization followed by repolarization of cell membrane

Question 12

What is the resting membrane potential of a cardiac cell v nerve cell?

Answer 12

Cardiac cell = -85-95mV
Nerve cell = -70mV

Question 13

What is the difference between an atrial and ventricular action potential

Answer 13

VENTRICLE has a longer plateau phase because of the voltage-gated calcium channels

All cardiac cells have the plateau phase but the duration changes

Question 14

What joins cardiac cells and what happens because of this?

Answer 14

Gap junctions are channels between the cells allowing cardiac AP to propagate from cell to cell through low reistance pathway

Question 15

How is the heart contraction initiated and synchronized?

Answer 15

Signal starts from SA node and ripples outward across ATRIUM causing atriums to contract at same time

Fibrous tissues do not have gap junctions so electrical signal cannot cross to the ventricles = DELAY

AV node = embedded within fibrous tissue allows signal to be passed to Bundle of HIs, bundle branches and then purkinje fibres

Question 16

Can the heart beat outside the body?

Answer 16

Yes, heart does not require nerve or hormonal input to beat

Because of autorhythmicity, some cells have prepotential/PACEMAKER potential to trigger AP

Question 17

What is the heirarchy of pacemakers?

Answer 17

SA node = 90-100 bpm
AV node = 40-60 bpm
Bundle of His = 15-30bpm

Question 18

What is overdrive suppression?

Answer 18

Fastest pacemaker normally drives the heart and suppresses other pacemakers

Question 19

What is an ectopic beat and what is the location of that beat called?

Answer 19

Heartbeat generated outside the normal pacemaker

Ectopic focus/pacemaker = site that generates an ectopic beat

Question 20

What are agents that alter heart rate called?

Answer 20

Chronotropic

Question 21

What are positive chronotropic agents?

Answer 21

Adrenaline and noradrenaline = act on β-adrenergic receptors on heart

Increase heart rate

Question 22

What are negative chronotropic agents?

Answer 22

Acetylcholine = acts on muscarinic cholinergic receptors on the heart

Slows heart rate

Question 23

At rest what system controls heart rate?

Answer 23

Heart is under parasympathetic tone, which slows the natural rhythm of the heart

Question 24

What system increases heart rate?

Answer 24

Sympathetic nervous system needed to adjust heart rate = NOT initiate it

Question 25

How does ANS affect SA node? ***

Question 26

What are the leads needed in an ECG?

Answer 26

12 leads = 3 bipolar limb leads, 3 augmented limp unipolar leads and 6 precordial unipolar leads

Leads 1-3
aVR, aVL and aVF
V1-V6

Question 27

Difference between bipolar ad unipolar leads?***

Question 28

Which leads measure vertical axis and which measure horizontal axis?

Answer 28

Vertical = bipolar limb and augmented limb
Horizontal axis = precordial /chest leads

Question 29

How does the flow of electrical signal produce the recordings we see in the ECG?

Question 30

P wave

Answer 30

Atrial depolarization

Question 31

QRS complex

Answer 31

Ventricular depolarization

Question 32

T wave

Answer 32

Ventricular repolarization

Question 33

P-R interval

Answer 33

Time between atrial depolarization and ventricular depolarization

0.12-0.20 seconds if greater than 0.20s then AV conduction block

Question 34

ST segment

Answer 34

Isoelectric period following QRS = time the entire ventricle is depolarized

Roughly corresponds to plateau phase of ventricular AP

Question 35

What is ST segment important for?

Answer 35

Diagnosis of ventricular ischaemia or hypoxia

Question 36

What can diagnose ventricular ischaemia or hypoxia?

Answer 36

ST segment

Question 37

Q-T interval

Answer 37

Time for both ventricular depolarization and repolarization to occur

Rough estimate of duration of average ventricular AP