Arrythmias (pathophysiology)

Question 1

Pacemaker cells (SA/AV node)

Answer 1

Specialized, non-contractile cells

Depolarized

High automaticity

Ca dependent spikes

Question 2

Ventricular myocytes

Answer 2

Contractile cells

hyperpolarized

low automaticity

Na dependent spikes

PLATUE PHASE

Question 3

Re-entry arrhythmia

Answer 3

ischemic damage on one of the sides causes no signal from that side leading to no cancellation

during the relative refractory period, this lack of cancellation can create another trigger signal to fire again without the SA/AV node

Question 4

Re-entry requirements

Answer 4

multiple parallel pathways

unidirectional block

conduction time > than ERP

Question 5

Class 2: BB

Answer 5

slow pacemaker and Ca currents in SA/AV node

increase refractories in SA/AV node

increase PR interval

Question 6

Indications of BB

Answer 6

arrhythmias involving catecholamines

atrial arrhythmias–> protects ventricular rate

post MI prevention of ventricular arrhythmias

prophylaxis in long QT syndrome

Question 7

Graphs for class 2 and 4

Answer 7

BB no reduction in peak shift to the right

CCB has a reduction in the peak

Question 8

Class 4: CCB

Answer 8

Selective block for channels opening more frequently

Increase refractoriness of AV node
Increase PR interval

Block reentrant arrhythmias involving AV node
Atrial arrhythmias–>protect ventricular rate

Question 9

Class 1A

Answer 9

Mix block of Na and K channels

Blocks open state

Moderate, incomplete dissociation

ECG effects: widen QRS, prolonged QT

Question 10

Class 1A products

Answer 10

Quinidine: antimuscarinic activity, 2-8% risk of TdP

Procainamide: lupus-like syndrome, ganglionic block

Disopyramide: antimuscarinic activity

Question 11

Class 1B

Answer 11

Na channel block

Blocks open state and inactivated state

Rapid, complete dissociation

Slight narrowing of action potential

ECG effects: no effects

Question 12

Class 1B products

Answer 12

Lidocaine (IV): only ventricular arrhythmias (VF)

Phenytoin

Mexiletine

Tocainide

Question 13

Class 1C

Answer 13

Strong Na block

Blocks open state

Very slow, incomplete dissociation

ECG effects: widens QRS

Question 14

Class 1C products

Answer 14

Flecainide: ventricular and supraventricular

Propafenone: ventricular and supraventricular
SOME BB ACTIVITY

Moricizine

Question 15

Class 3: K channel blockers

Answer 15

Blocks Ikr channel

Prolonged action potential duration

Increases ERP to prevent reentrant arrhythmias

Acts on the Ikr hERG channel resulting in increased risk of TdP by: inducing EADs and trigger upstrokes leading to multifocal and polymorphic VT

ECG effects: prolonged QT

Question 16

Class 3 products

Answer 16

Amiodarone: all 4 antiarrhythmic mechanisms with highest in Ikr

Dronedarone: prevent AFIB

Ibutilide: converts AFIB into NSR

Sotalol: ventricular arrhythmias and maintain NSR

Dofetilide: atrial arrhythmias