Lecture 2 Flashcards
cardiac action potential - phase 0
Rapid depolarisation
all or nothing
Rapid Na+ influx
cardiac action potential - phase 1
Partial depolarisation
Rapid Na influx deactivated
cardiac action potential - phase 2
Platau
slow inward Ca current
initial fall in outward K
heart contracts
cardiac action potential - phase 3
Repolarisation
deactivation of inward Ca current
increasing outward K current
ready for another activation
cardiac action potential - phase 4
Pacemaker potential Gradual depolarisation in diastole (relaxation) Found in nodal and conducting tissue increasing inward Na/Ca Decreasing outward K
Function of the AV node
conduction tissue to the ventricles
causes delay - so atria dont contract at same time as ventricles
instant activation of ventricles following this
Features of nodal tissue
drives pacemaker
no rapid depolarisation - no fast Na current, fast Ca current instead`
Features of abnormal impulse propagation
o Re entry – trail of refractoriness – circus movement – go back to cells
o Heart block – AV block – block at AV node – 200milliseconds – PR interval
o 2nd degree – transient –
o 3rd degree – complete block – atria contract independently – ventricles rely on backup pacemaker
Features of abnormal impulse generation
triggered activity - delayed after depolarisation
increased automaticity - ectopic activity
Tachycardia
faster heart rate
Bradycardia
Slowed heart rate
Atrial tachycardia
faster heart rate - due to atria
multiple p waves
atria contract too quickly
ventricles dont contract at same speed due to AV
Ventricular tachycardia
Ventricles contract quicker
slower passage through the ventricles
wide complex ventricular rhythm
atrial fibrillation
- Atria act as passive channels for blood flow
- Not contracting
- Irregular chaotic
- Just P waves
- Heart rate fast
- Can get atrial thrombus – anticoagulants
ventricular fibrillation
cardiac arrest no defined rhythm or outfit wide complex irregular ventricular response use defibrilator to trigger heart back to normal rhythm
Sympathetic stimulation of heart
o Increased heart rate (positive chronotropic effect – affects heart rate)
o β-1 adrenoceptors (cAMP)
o Increased slope of pacemaker potential
o Increases automaticity – intrinsic capacity of the heart to fire off APs
Parasympathetic stimulation of heart
o Reduces heart rate o Muscarinic (M2) acetylcholine receptors o M2 mainly in nodal and atrial tissue o Decreased slope of pacemaker potential o Decreased automaticity o Inhibits atrioventricular conduction
what are the 4 classes of Vaughan Williams classification
• Class I: Sodium channel blockers
o Ia - disopyramide, quinidine, procainamide
o Ib - lidocaine, mexilitene
o Ic - flecainide, propafenone
• Class II: Beta adrenceptor antagonists –
o propranolol, nadolol, carvedilol (non-selective)
o bisoprolol, metoprolol (β1-selective)
• Class III: Prolong the action potential
o amiodarone, sotalol
• Class IV: Calcium channel blockers
o verapamil, diltiazem
What are the features of digoxin
• Cardiac glycoside
• Inhibit Na/K pump
• Can get increased intracellular Ca
• Main effects are on the heart:
o Bradycardia (increased vagal tone)
o Slowing of atrioventricular conduction (increased vagal tone)
o Increased ectopic activity
o Increased force of contraction (by increased intracellular Ca) – important
• Narrow therapeutic range
o Nausea, vomiting, diarrhoea, confusion
• Used in atrial fibrillation (AF) to reduce ventricular rate response
• Use in severe heart failure as positively inotropic
what are the adverse affects
• Has iodine in – thyroid
• Causes QT prolongation and Polymorphic ventricular tachycardia
• Goes everywhere in the body:
o Interstitial pneumonitis – lungs
o Abnormal liver function
o Hyperthyroidism / Hypothyroidism – iodine metabolism – overactive or underactive
o Sun sensitivity
o Slate grey skin discolouration
o Corneal microdeposits
o Optic neuropathy – v serious
• Multiple drug interactions
o Esp coagulants – warfarin – patient becomes over anti-coagulated
• Very large volume of distribution
o If u stop it will stay in system for 3 months
