Cardiac electrophysiology and ECG

Question 1

why is it important that the coronary arteries are on the surface of the muscle

Answer 1

so they are not compressed upon contraction

Question 2

what structures drain blood from the upper and lower body into the right atrium

Answer 2

upper - superior vena cava
lower - inferior vena cava

Question 3

what does it mean that the heart has variable pump output

Answer 3

flow is not always the same

Question 4

how many pulmonary veins are there

Answer 4

4
2 from each lung that converge before the heart

Question 5

what allows cardiac action potentials to propagate from cell to cell

Answer 5

gap junctions

Question 6

what is the duration of a normal cardiac action potential
what mediates this

Answer 6

250 ms
voltage gated Ca2+ channels allowing leading to a plateau phase of the AP

Question 7

what is the resting membrane potential of cardiac muscle cells

Answer 7

-85 mV

Question 8

what structures form gap junctions
what happens if there are genetic deformities of these proteins

Answer 8

connexons
mutations are incompatible with life

Question 9

what are the specialised conductive tissues in the heart (in order)

Answer 9

SA node
AV node
bundle of His
left and right bundle branch
Purkinje fibres

Question 10

automaticity of heart cells

Answer 10

ability to generate a heart beat without nervous system input

Question 11

what electrically isolates the atria and ventricles

Answer 11

annulus fibrosus ?
hearts fibrous skeleton - fibrous rings

Question 12

where does electrical activity normally originate in the heart
what is the pacemaker potential of these cells

Answer 12

SA node
-70mV

Question 13

why does the SA node depolarise before the AV node

Answer 13

it has a higher pacemaker potential (less negative)

Question 14

what forms the only site of electrical connection between the atria and ventricles

Answer 14

AV node

Question 15

what is the rate of SA pacemaker potential
why is heart rate different to this

Answer 15

~90 - 100 bpm
parasympathetic tone slows natural rhythm

Question 16

chronotropic agents

Answer 16

agents that alter heart rate

Question 17

examples of positive chronotropic agents and their receptors

Answer 17

adrenaline and noradrenaline
beta-adrenergic receptors

Question 18

examples of negative chronotropic agent and its receptors

Answer 18

acetylcholine
muscarinic cholinergic receptors

Question 19

effect of ANS on the membrane potential of the SA node

Answer 19

sympathetic: increases the potential (more rapid depolarisation)
parasympathetic: decreases the potential

Question 20

what controls the movement of electrolytes through gap junctions

Answer 20

free movement only controlled by concentration gradients

Question 21

what is an ECG

Answer 21

recording of electrical activity of the heart from the body surface using electrodes to allow a spatial perspective of electrical events

Question 22

why do an ECG

Answer 22

• suspect disturbances in rhythm and conduction
• localise and assess extent of ischemic damage
• assess size of chambers
• assess effects of changes in electrolyte concentrations

Question 23

how does the flow of electrical signals provide the recording we see in the ECG

Answer 23

electrical vectors parallel to the axis of the lead result in maximal deflection
vectors perpendicular to axis result in 0 deflection
vectors travelling towards the exploring electrode (+) result in a +ve deflection
vectors travelling away from + electrode result in -ve deflection

Question 24

p wave

Answer 24

atrial depolarisation

Question 25

QRS complex

Answer 25

ventricular depolarisation

Question 26

t wave

Answer 26

ventricular repolarisation

Question 27

P-R interval

Answer 27

time between atrial and ventricular depolarisation due to AV node conduction block

Question 28

ST segment

Answer 28

plateau phase of ventricular action

Question 29

what part of an ECG is important in diagnosis of ventricular ischemia or hypoxia

Answer 29

ST segment

Question 30

Q-T interval

Answer 30

time for both ventricular depolarisation and repolarisation roughly estimates the duration of an average ventricular AP

Question 31

what does ST elevation indicate

Answer 31

myocardial infarction think "STEMI"

Question 32

what does ST depression indicate

Answer 32

myocardial ischemia

Question 33

what does a sinus dysrhythmia ECG show

Answer 33

varied R-R intervals with normal sinus rhythm

Question 34

what does a atrial fibrillation ECG show

Answer 34

irregularly irregular, often rapid, absent P waves, and erratic, fibrillatory waves between QRS complexes.

Question 35

what does left ventricular hypertrophy ECG show

Answer 35

increased QRS voltage, particularly in the left precordial leads (V5, V6) may also display signs like a left axis deviation and ST-T wave abnormalities.