Rhythm of the heart Flashcards
Major ions in cardiac myocytes:
Ca2+
Na_
K+
Phase 4 of AP cardiac myocyte:
RMP - K+ is moving out of the cell.
What causes the rapid depolarisation
Opening of fast voltage Na+ channels
What causes plataeu phase?
K+ and voltage gated Ca2+ open
How do pacemaker potentials differ?
Slow Ca2+ and Na+ influx. Then L-type Ca2+ open to rapidly let Ca2+ in.
Intrinsic rate of SAN
60-100 bpm
Bachmann’s bundle =
SAN to atria
What spreads electrical impulse rapidly and synchronously though LV and RV
His-Purkinje system
What happens when PNS increases?
Slows HR
When does PNS increase?
Sleep
Vasovagal syncope
fittness
When does PSN decrease?
First seconds of exercise
Heart failure
Atropine
First seconds of exercise vs after
First seconds = PSN decrease
After = SNS increases
When does SNS increase?
After first min of exercise
Fear
Adrenaline
Salbutamol
When does SNS decrease?
Rest and sleep
Beta blockers
Vasovagal syncope
P wave =
depolarisation of atria
QRS =
depolarisation of venticles
PR intervals =
Conduction through AV node
PR segment =
time taken to get signal from SAN and AVN
Q is depolarisation of
Interventricular septum
R is depolarisaiton of
Mass of ventricles
S is depolarisation of
Apex
QT interval =
Reflects repolarisation of ventricular myocardium
Normal PR interval is
<200 m sec
< 200msec is equivalent to
<5 small squares
1 small square =
0.04 msec
40 sec
1 large square =
0.2 msec
200 sec
Normal QRS complex =
<120 msec
<120 msec is equivalent to
<3 small squares
QT interval is dependent on
Rate
QTc =
Qt interval adjusted for rate
QTc = QT interval at
60 bpm
How to work out rate of regular ECG
300/RR interval (num of large squares)
Bradycardia =
< 60 bpm
Regular QRS
P wave in front of each
Normal AV delay
<60 bpm
Sinus bradycardia