S6: antiarrhythmics, antiplatelets & fibrinolytics Flashcards
What is an arrhythmia?
Heart condition where there are disturbances in:
1) Pacemaker impulse
2) Contraction impulse conduction
3) Combination of the two
Results in rate and/or timing of contraction of heart muscle that may be insufficient to maintain normal cardiac output
Describe the mechanism of action of class 1 drugs
Block Na+ channels
Marked slowing conduction in tissue (phase 0)
Minor effects on action potential duration
Describe the mechanism of action of class 2 drugs
Beta-blockers
Diminish phase 4 depolarisation and automaticity
Describe the mechanism of action of class 3 drugs
Block K+ channels
Increase action potential duration
Describe the mechanism of action of class 4 drugs
Calcium channel blockers decrease inward Ca+ currents resulting in decrease of phase 4 spontaneous depolarisation
Effect plateau phase of action potential
Describe Wolf-Parkinson-White syndrome
Accessory pathway in the heart connecting atrium to ventricle
Present only in small populations – leads to pre-excitation
Describe Vaughan-Williams classification
1B: no change in phase 0 (eg. lidocaine)
1C: marked phase 0 (eg. flecainide)
II: beta-adrenergic blockers (eg. bisoprolol, metoprolol)
III: prolong repolarisation (eg. amiodarone, sotalol)
IV: calcium channel blockers (eg. verapamil, diltiazem)
V: variable (eg. adenosine, digoxin, atropine, ivabradine)
Describe class 1B agents
Decrease phase 0 conduction in fast beating or ischaemic tissue
Uses: acute ventricular tachycardia
Side effects: CNS effects (dizziness, drowsiness) & abdominal upset
Describe class 1C agents
Substantially decreased phase 0 in normal, decreased automaticity, increased refractory period & APD
Uses: supraventricular arrhythmias, PVCs, Wolff-Parkinson-White syndrome
Side effects: pro-arrhythmia and sudden death in chronic use, CNS & gastrointestinal effects
Describe class II agents
Increases APD & refractory period in AV node to slow AV conduction velocity, decreases phase 4 depolarisation
Uses: sinus and catecholamine dependent tachycardia, stable heart failure
Side effects: bronchospasm, hypotension
Describe amiodarone (class III)
Increases refractory period & APD, decreases phase 0 conduction, increases threshold, decreases phase 4, decreases speed of AV conduction
Uses: very wide spectrum, effective for most arrhythmias
Side effects: pulmonary fibrosis, hepatic injury, photosensitivity
Describe sotalol (class III)
Increases APD & refractory period, slow phase 4, slow AV conduction
Uses: wide spectrum, supraventricular and ventricular tachycardia
Side effects: proarrhythmic, fatigue, insomnia
Describe class IV agents
Slow conduction through AV, increases refractory period in AV node, increases slope of phase 4 in SA to slow HR
Uses: control ventricles during supraventricular tachycardia, convert supraventricular tachycardias
Side effects: constipation, caution when partial AV block is present (can get asystole)
Describe adenosine
Natural nucleoside that binds A1 receptors and blocks adenylyl cyclase thus reducing cAMP which is turn activates K+ currents in AV and SA node causing hyperpolarisation – reduces HR
Also reduces Ca2+ currents, increasing refractory period in AV node
Uses: convert re-entrant supraventricular arrhythmias
Describe ivabradine
Slows the sinus node by blocking funny channels
Uses: reduce inappropriate sinus tachycardia, reduce HR in heart failure and angina
Side effects: flashing lights, teratogenicity not known