Anti-arrythmics Flashcards
What are the possible underlying causes of arrhythmias?
Disorders of impulse formation:
Automaticity
Triggered activity
Disorder on impulse conduction:
reentry
Combination of both
What is automacity?
Ability of the cardiac cell to initiate an impulse without need a prior stimulation:
–> For sinus node and other focal pacemaker cells this is normal but can be enhanced and lead to an accelerated rate.
Cells that do not normally initiate an impulse can do so:
–> Multiple possible mechanisms (changes in K channels, increased Ca release from SR activating different Ca or N channels, etc)
What is triggered activity?
Impulse initiation in cardiac fibres caused by depolarizing oscillations within in membrane voltages (after depolarization). They are the consequence of preceeding action potential(s):
Early afterdepolarization (EAD) Delayed afterdepolarization (DAD)
When large enough to reach threshold, will trigger an action potential.
What are the classes in Vaughn-Williams classification?
Class 1: Na channel blockers
- Membrane stabilising. Slow the rate of depolarization and may inhibit the arrhythmia by decreasing the cells responsiveness to excitation
Class 2: Cathecholamine blockade (b-blockers)
Class 3: K channel blockers
- Increasing in refractory period
Class 4: Calcium channel blockade
-Depress inward Ca current, prolonging conduction and refractoriness.
Some block potassium channels
How many subgroups are there for Class 1?
Class 1A - quinidine, procainamide Class 1B - lidocaine, (being replaced by amiodarone ie. class 3) Class 1C - propafanone, fleicainide
What is procainamide?
Class 1A drug
How does procainamide work?
Prolongs the action potential duration and refractoriness of atrial and ventricular tissue.
What is procainamide used for?
Used in both supraventricular and ventricular arrhythmias.
–> Atrial fibrillation in WPW
What is a side effect of procainamide?
Prolonged QT/Torsades de pointes
Hemolytic anemia, thrombocytoepnia, neutropenia
Hypotension
SLE like syndrome
How does lidocaine work?
Increases the stimulation threshold and leads to suppression of automaticity (esp in Purkinje fibres)
Shortens the action potential duration and also can shorten QT in diseased tissues
- -> Used commonly for VF in ACS
- -> NOT GOOD FOR SUPRAVENTRICULAR
- -> good for post-MIs
What are side effects of lidocaine?
Hypotension, bradycardia
Neurological (confusion, headache, tremor, somnolence)
Seizure
What is Flecainide/Propafenone used in?
Used mainly for Atrial fibrillation. Also may have a use in PVCs.
What additional drud needs to be coadminitered with Flecainide/Propafenone?
Needs to be used with a B-blocker. (1:1 atrial flutter causing increased ventricular rate)
What are some risks using class 1C drugs?
Increases mortality in post MI patients, therefore not used in patients with ischemic heart disease. Also not used if any structural heart disease.
Increased risk of ventricular arrhythmias in chronic atrial fibrillation
What are class 2 drugs work?
Beta-blockers:
1) Blocks the sympathomimetic amine effects on Ifunny currents (phase 4) of nodal tissues. SA node: slowing HR AV node: prolonging refractory period. Terminating SVT (re-entry) Decrease ventricular response
2) Attenuation of sympathetic electrophysiological consequences Shortening of action potential duration Augmenting ventricular conduction Increasing vent. Automaticity Decreasing VF thresholds Reversal of anti-arrhytmic drugs
