Physiology of the heart 1 Flashcards
What are the phases of the cardiac action potential?
0= rapid depolarisation 1= partial repolarisation 2= plateau phase 3= repolarisation 4=pacemaker potential
Why is phase 2 important?
Maintaining a depolarised state slows down the action potential
need a period of time for the heart to fill with blood again
if the heart was like neurons- wouldnt have the mechanical impact- would not pump blood
What phase isn’t present in the SAN and AVN?
Phase 0
slow calcium causes depolarisation- no influx of sodium
What are the types of abnormal impulse generation?
Triggered activity- closer you bring the stimuli together- greater the after depolarisation becomes- go over critical threshold- fire an action potential
Increased automaticity
What is ‘after depolarization’
After a normal action potential theres a transient increase in the membrane
What are the types of abnormal impulse propagation?
Re-entry
Heart block
What are the types of heart block?
1st degree= delay at the AVN is longer (between p wave and the rest of the complex), but the beats get through
2nd degree= 3 impulses will get through- then get a p wave with no ventricular contraction- dropped a beat
3rd degree= atria are contracting- but there is no connection between the atria and ventricles-
p waves present but not synchrony to the ventricles
What is bradycardia?
Slower heart rate
origin from the sinus node
What is tachycardia?
Faster heart rate
origin from the sinus node
What is atrial tachycardia?
Atria are contracting very rapidly
but the contractions arent all getting to the ventricles
-see multiple p waves before the QRS complex
What is ventricular tachycardia?
Very serious condition
see a wide complex ventricular rhythm- duration beyond 120 milliseconds
Whats atrial fibrillation?
Atria fibrillate- uncoordinated contraction
no true p waves or atrial rhythm
irregular ventricular response makes the heart inefficient- heart is irregular and often fast
atrial thrombus can occur
Whats ventricular fibrillation?
No defined rhythm or output
ventricles fibrillating- no cardiac output
fatal
usually based on coronary heart disease
defibrillation can save their life- get them back into a normal rhythm
variable morphology on an ECG
What does sympathetic stimulation result in?
Increased heart rate- positive chronotropic effect
mediated by adrenaline & noradrenaline
binds to beta1 adrenoreceptors- increase heart rate and force of contraction
increases the slope of the pacemaker potential
increased automaticity
What does parasympathetic stimulation result in?
Reduces the heart rate
muscarinic acetylcholine receptors (m2)
m2 mainly found in nodal and atrial tissue
decreases the slope of the pacemaker potential
