Physiology of the heart 1 Flashcards
(22 cards)
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
How are antiarrhythmic drugs classed?
Vaughan williams classification 4 classes 1- sodium channel blocking agents 2- beta blockers 3-prolong the action potential 4- calcium channel blockers
Class 1 antiarrhythmic drugs
1a- disopyramide, quinidine, procainamide
1b- lidocaine, mexiliene
1c- flecainide, propafenone
2- propanol, nadolol, carvedilol, bisoprolol, meloprolol
3- amiodarone, sotalol
4- verapimil, diltiazem
What is digoxin and what are its main effects?
Used to treat atrial fibrillation and heart failure
part of the cardiac glycosides group
inhibits the Na/K pump
main effects on the heart:
bradycardia (increase vagal tone)
slowing of AV conduction [increase vagal tone)
increased force of contraction
problem- can cause ectopic activity- due to increased intracellular calcium
How does digoxin increase IC Ca?
inhibits Na/K pump
reduces gradient for inward movement of calcium
thus effecta Na/Ca pump which normally pumps calcium out of the cell
thus calcium builds up in the cell
Why has digoxin got a narrow therapeutic range?
Have to achieve a certain level in the bloodstream
anything above= nausea, vomiting, diarrhoea and confusion
What does the QT period represent? Whats a risk of increasing the QT period?
QT represents depolarisation and repolarization
drugs that prolong QT can trigger-
polymorphic ventricular tachycardia- widening and narrowing on the ECG
drugs that can prolong the QT interval:
amiodarone
sotalol
What are amiodarone’s adverse effects?
polymorphic ventricular tachycardia interstitial pneumonitis abnormal liver function hyper/hypo thyroidism sun sensitivity slate grey skin discolouration corenal microdeposits optic neuropathy
