antiarrhythmia drugs

Question 1

what are the 3 broad types of arrythmia

Answer 1

1. rate = tachycardia, bradycardia
2. rhythm: fibrillation (uncoordinated contraction of chambers) - ineffective pumping
3. abnormal automacity

Question 2

types of conduction block - 2 broad types

Answer 2

1. AV conduction block - subclassification
   - most extreme: complete AV block: AP not conducted from A to V, ventricle has own rhythm (ventribular escape)
2. re-entry: due to unidirectional block
   - re-entry circuit created

Question 3

describe the formation of afterdepolarisation

Answer 3

these happen at NON-NODAL tissues

1. Early afterdepolarisation
   - due to prolonged repolarisation phase
   - more cells enter relative refractory period = excitable during repolarisation phase
   - due to reduced K conductance / increase Na Ca conductance
   - increases risk of torsades de pointe
2. delayed afterdepolarisation
   - due to increased intracellular Ca (Ca overload)
   - AP can be initiated before the next impulse arrive from nodal tissue

Question 4

what are the 4 classes of antiarrhythmic drug

Answer 4

class I: Na blocker
ClassII: B blocker
ClassIII: K blocker
ClassIV: Ca channel blocker

Question 5

which class blocks DAD (x2)
which class can only be used in supraventrricular origin

Answer 5

1. Ca channel blockers and B blockers prevent Ca overload = block DAD
2. Ca channels are mostly used in supraventricular oorigin

Question 6

what are the mechanism of action of class I drug

Answer 6

1. Na blocker: use dependent, binds to the inner channel of the Na fast gate (activated or opened state)
   - reduced AV conduction velocity, reduced tachycardia

Class IB: rapid kinetic - LIDOCAINE
- blocks premature beat, selective for refractory state: prevent

Class Ic
slow kinetic - marked reduction of rate