Electrical conduction of the heart

Question 1

describe the pathway of transduction

Answer 1

SAN pacemaker cells
goes to both internodal pathway and bachman’s bundle (left atrium)
internodal pathway across right atrium to AVN
AVN goes down bundle of HIS which separates into two branches down to the apex of the heart
then then travel back up via purkinjie fibres around the ventricles

Question 2

what is an action potential

Answer 2

transient depolarisation of a cell as a result of activity of ion channel

Question 3

what are the two types of cardiac action potential

Answer 3

non pace maker and pacemaker

Question 4

draw a non-pacemaker action potential

Answer 4

check home screen

Question 5

what are the phases of non-pacemaker action potential

Answer 5

phase 0 - Na+ channels open 
phase 1 - Na+ channels close 
Phase 2 - Ca2+ open and fast K+ close 
Phase 3 - Ca2+ channels close and fast K+ open 
phase 4 - resting potenital

Question 6

what is pacemaker activity

Answer 6

the intrinsic, spontaneous time dependant depolarisation of a cell membrane that leads to an action potential
any cell with pacemaker ability can initiate a heart best

Question 7

what is the definition hierarchy of pacemakers

Answer 7

the primary pacemaker is defined as the tissue with the highest firing frequency - the fastest pacemaker sets heart rate and overrides slower ones

Question 8

what are the specific components of the hierarchy of pacemakers

Answer 8

SAN - 100 beats per min - primary
AVN - 40 beats per min - secondary
purkinjie fibres - 20 beats per min

Question 9

why is the intrinsic ability higher than the normal frequency of the heart

Answer 9

SAN is under constant vagal stimulation which suppresses its intrinsic frequency to around 60 bpm

Question 10

draw and describe a pacemaker action potential

Answer 10

check home screen

Question 11

draw a comparison of a ventricular muscle fibre vs a sinus nodal fibre

Answer 11

check home screen

Question 12

what is the difference between pace maker and non-pacemaker cardiac action potential in these variables 
membrane potenital 
events leading to action potential 
rising phase 
repolrisation phase 
hyperpolarisation 
duration of action potential 
refractory period

Answer 12

check table on home screen

Question 13

what are the 4 classes of drugs affecting the cardiac action potential

Answer 13

class 1 - Na+ channel blocker 
class 2 - B blocker (K+ rectifier) 
class 3 - K+ channel blocker 
class 4 - Ca2+ channel blocker

Question 14

give examples of class one blockers

Answer 14

1a - (moderate strength) quinidine
1b (weak) phenytoin
1c (strong) flecanide, propafenone

Question 15

give examples of class 4

Answer 15

verapamil, ditiazem

Question 16

give examples of class 3 drugs

Answer 16

amiodarone

sotalol

Question 17

give examples of class 2 drugs

Answer 17

propranolol, metoprolol

Question 18

how does conduction of action potentials in the heart occur

Answer 18

depolarising currents pass through GAP Junctions located at intercalated disks

Question 19

how much does the AVN delay the impulse by

Answer 19

100 ms

Question 20

what are the conduction velocities at these points
atrial muscle 
av node
bundle of HIS 
left and right bundle branches 
ventricular muscle 
purkinjie muscles

Answer 20

atrial muscle - 0.5 m/sec 
av node - 0.05 
bundle of HIS - 2
left and right bundle branches - 2
ventricular muscle - 0.5 
purkinjie muscles - 4

Question 21

what is the lead placement on the chest for an ECG

Answer 21

anterior to lateral left

V1 - V6

Question 22

what is the lead placement on the limbs for an ECG

Answer 22

LA - +/-
RA - -/-
LL - +/+

Question 23

what is the lead one vector and what does it measure

Answer 23

from the RA to the LA across the upper chest
from the centre of that lead to the bottom tip of the triangle LF
aVF

Question 24

what is the lead 2 vector and what does it measure

Answer 24

from the RA to the LF

from the centre of this lead to the top left side on the LA shows aVL

Question 25

what is the lead 3 vector and what does it measure

Answer 25

from LA to LF

from the centre of that lead to the top right corner of RA measure aVR

Question 26

on an ECG what is the relationship between direction of electrical activity and electrode

Answer 26

electrical activity towards an electrode results in a positive deflection (up)
electrical activity away from an electrode results in a negative deflection (down)

Question 27

on an ECG what do the small boxes show

Answer 27

0. 04 seconds

0. 1 mV high and 0.1 mm

Question 28

on an ECG what do the large boxes show

Answer 28

0. 2 seconds

0. 5 mV high

Question 29

what shows atrial depolarisation on an ECG

Answer 29

p wave

Question 30

after the p wave there is a pause what is that

Answer 30

AV node delay

Question 31

what is the PQ interval

Answer 31

travel from SAN to AVN and bundle of HIS

Question 32

what is ventricular contraction on the ECG

Answer 32

R wave

Question 33

what is the ST segment on an ECG

Answer 33

represents the time between full ventricular depolarisation and repolarisation

Question 34

what is the T wave

Answer 34

ventricular repolarisation

Question 35

what is atrial fibrillation on an ECG

Answer 35

absence of P wave an irregularly irregular ventricle depolarisation

Question 36

what is atrial flutter

Answer 36

caused by re-entrant rhythm
shark teeth pattern of p waves
more P waves occur than ventricular waves

Question 37

what does ventricular fib look like on an ECG

Answer 37

no regularity at all and completely messy line

Question 38

what does ventricular tachycardia look like

Answer 38

wide QRS complex

big mountain look

Question 39

what does first degree heart block look like on an ECG

Answer 39

prolonged PR interval more than 200 seconds

ie p wave then break then QRS

Question 40

what are the differences in degree of 1st to 3rd AV block

Answer 40

1 p wave then phase then QRS
2 p waves then QRS
3 p waves then QRS