Electrical conduction of the heart Flashcards
describe the pathway of transduction
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
what is an action potential
transient depolarisation of a cell as a result of activity of ion channel
what are the two types of cardiac action potential
non pace maker and pacemaker
draw a non-pacemaker action potential
check home screen
what are the phases of non-pacemaker action potential
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
what is pacemaker activity
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
what is the definition hierarchy of pacemakers
the primary pacemaker is defined as the tissue with the highest firing frequency - the fastest pacemaker sets heart rate and overrides slower ones
what are the specific components of the hierarchy of pacemakers
SAN - 100 beats per min - primary
AVN - 40 beats per min - secondary
purkinjie fibres - 20 beats per min
why is the intrinsic ability higher than the normal frequency of the heart
SAN is under constant vagal stimulation which suppresses its intrinsic frequency to around 60 bpm
draw and describe a pacemaker action potential
check home screen
draw a comparison of a ventricular muscle fibre vs a sinus nodal fibre
check home screen
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
check table on home screen
what are the 4 classes of drugs affecting the cardiac action potential
class 1 - Na+ channel blocker class 2 - B blocker (K+ rectifier) class 3 - K+ channel blocker class 4 - Ca2+ channel blocker
give examples of class one blockers
1a - (moderate strength) quinidine
1b (weak) phenytoin
1c (strong) flecanide, propafenone
give examples of class 4
verapamil, ditiazem
give examples of class 3 drugs
amiodarone
sotalol
give examples of class 2 drugs
propranolol, metoprolol
how does conduction of action potentials in the heart occur
depolarising currents pass through GAP Junctions located at intercalated disks
how much does the AVN delay the impulse by
100 ms
what are the conduction velocities at these points atrial muscle av node bundle of HIS left and right bundle branches ventricular muscle purkinjie muscles
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
what is the lead placement on the chest for an ECG
anterior to lateral left
V1 - V6
what is the lead placement on the limbs for an ECG
LA - +/-
RA - -/-
LL - +/+
what is the lead one vector and what does it measure
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
what is the lead 2 vector and what does it measure
from the RA to the LF
from the centre of this lead to the top left side on the LA shows aVL
what is the lead 3 vector and what does it measure
from LA to LF
from the centre of that lead to the top right corner of RA measure aVR
on an ECG what is the relationship between direction of electrical activity and electrode
electrical activity towards an electrode results in a positive deflection (up)
electrical activity away from an electrode results in a negative deflection (down)
on an ECG what do the small boxes show
- 04 seconds
0. 1 mV high and 0.1 mm
on an ECG what do the large boxes show
- 2 seconds
0. 5 mV high
what shows atrial depolarisation on an ECG
p wave
after the p wave there is a pause what is that
AV node delay
what is the PQ interval
travel from SAN to AVN and bundle of HIS
what is ventricular contraction on the ECG
R wave
what is the ST segment on an ECG
represents the time between full ventricular depolarisation and repolarisation
what is the T wave
ventricular repolarisation
what is atrial fibrillation on an ECG
absence of P wave an irregularly irregular ventricle depolarisation
what is atrial flutter
caused by re-entrant rhythm
shark teeth pattern of p waves
more P waves occur than ventricular waves
what does ventricular fib look like on an ECG
no regularity at all and completely messy line
what does ventricular tachycardia look like
wide QRS complex
big mountain look
what does first degree heart block look like on an ECG
prolonged PR interval more than 200 seconds
ie p wave then break then QRS
what are the differences in degree of 1st to 3rd AV block
1 p wave then phase then QRS
2 p waves then QRS
3 p waves then QRS
