S6: antiarrhythmics, antiplatelets & fibrinolytics Flashcards

1
Q

What is an arrhythmia?

A

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

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2
Q

Describe the mechanism of action of class 1 drugs

A

Block Na+ channels
Marked slowing conduction in tissue (phase 0)
Minor effects on action potential duration

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3
Q

Describe the mechanism of action of class 2 drugs

A

Beta-blockers

Diminish phase 4 depolarisation and automaticity

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4
Q

Describe the mechanism of action of class 3 drugs

A

Block K+ channels

Increase action potential duration

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5
Q

Describe the mechanism of action of class 4 drugs

A

Calcium channel blockers decrease inward Ca+ currents resulting in decrease of phase 4 spontaneous depolarisation
Effect plateau phase of action potential

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6
Q

Describe Wolf-Parkinson-White syndrome

A

Accessory pathway in the heart connecting atrium to ventricle
Present only in small populations – leads to pre-excitation

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7
Q

Describe Vaughan-Williams classification

A

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)

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8
Q

Describe class 1B agents

A

Decrease phase 0 conduction in fast beating or ischaemic tissue
Uses: acute ventricular tachycardia
Side effects: CNS effects (dizziness, drowsiness) & abdominal upset

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9
Q

Describe class 1C agents

A

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

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10
Q

Describe class II agents

A

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

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11
Q

Describe amiodarone (class III)

A

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

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12
Q

Describe sotalol (class III)

A

Increases APD & refractory period, slow phase 4, slow AV conduction
Uses: wide spectrum, supraventricular and ventricular tachycardia
Side effects: proarrhythmic, fatigue, insomnia

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13
Q

Describe class IV agents

A

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)

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14
Q

Describe adenosine

A

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

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15
Q

Describe ivabradine

A

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

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16
Q

Describe digoxin

A

Inhibition of Na+/K+ ATPase
Leads to rise in intracellular sodium, leads to decreased NCX, increased intracellular calcium, more stored in SR, increased force of contraction
Enhances vagal activity -> slows AV conduction and slows HR
Uses: treatment to reduce ventricular rates in atrial fibrillation and flutter

17
Q

Describe atropine

A

Selective muscarinic antagonist
Blocks vagal activity to speed AV conduction and increase HR
Uses: vagal bradycardia

18
Q

Define thrombus and embolus

A

Thrombus – clot adhered to vessel wall

Embolus – intravascular clot distal to site of origin

19
Q

Compare venous and arterial thrombosis

A

Venous thrombosis associated with stasis of blood and/or damage to the veins
-high red blood cell and fibrin content, low platelet content
Arterial thrombosis usually forms at site of atherosclerosis following plaque rupture
-lower fibrin content and much higher platelet content

20
Q

Describe prevention of platelet aggregation in healthy endothelium

A

Prostacyclin (PGI2) produced and released by endothelial cells – inhibits platelet aggregation
PGI2 binds to platelet receptors -> increased [cAMP] in platelets
Increased [CAMP] - > decreased calcium – prevents platelet aggregation
Decrease in platelet aggregatory agents, stabilises inactive GPIIb/IIIa receptors

21
Q

Describe aspirin (cyclo-oxygenase inhibitor)

A

Potent platelet aggregating agent thromboxane A2 formed from arachidonic acid by COX-1
Aspirin – inhibits COX1 and reduces platelet aggregation (irreversible)
Low non-analgesic doses (75mg), loading doses of 300mg used in ACS
Higher doses inhibit endothelial prostacyclin (PGI2)

22
Q

What are the adverse effects, warnings, contraindications & important drug interactions of aspirin?

A

Adverse effects: GI irritation, GI bleeding, haemorrhage, hypersensitivity
Warnings, contraindications: Reye’s syndrome (avoid under 16s), hypersensitivity, 3rd trimester (premature closure of ductus arteriosus)
Important drug interactions: caution other antiplatelets and anticoagulants

23
Q

List aspirin indications

A

Some AF patients post stroke
Secondary prevention of stroke and TIA
Secondary prevention of ACS
Post PCI and stent to reduce ischaemic complications
NSTEMI/STEMI
Gastric protection required for long term use in at risk patients

24
Q

Describe the mechanism of action of ADP receptor antagonists

A

Inhibit binding of ADP to P2Y12 receptor -> inhibit activation of GPIIb/IIIa receptors
Clopidogrel and prasugrel are irreversible inhibitors of P2Y12 (prodrugs)
Clopidogrel – slow onset of action without a loading dose, others have more rapid onset of action
Ticagrelor acts reversibly at different site to clopidogrel and has active metabolites

25
Q

What are the adverse effects, warnings, contraindications & important drug interactions of ADP receptor antagonists?

A

Adverse effects: bleeding, GI upset, thrombocytopenia rarely
Warnings, contraindications: caution in high bleed risk patients with renal and hepatic impairment
Important drug interactions: clopidogrel requires CYPs for activations (CYP inhibitors – omeprazole, ciprofloxacin, erythromycin, some SSRIs); ticagrelor can interact with CYP inhibitors and inducers

26
Q

List ADP receptor antagonist indications

A

Second agent in ‘dual antiplatelet therapy’
Ischaemic stroke
Where aspirin is contraindicated
Age, coronary anatomy and bleed risk dictate which agent added to aspirin

27
Q

Describe phosphodiesterase inhibitors

A

Dipyridamole inhibits cellular reuptake of adenosine -> increased [adenosine] -> inhibits platelet aggregation via adenosine A2 receptors
Also acts an phosphodiesterase inhibitor -> prevents cAMP degradation -> inhibit expression of GPIIb/IIIa
Uses: secondary prevention of ischaemic stroke and TIAs, adjunct for prophylaxis of thromboembolism following valve replacement, stroke

28
Q

What are the adverse effects and important drug interactions of phosphodiesterase inhibitors?

A

Adverse effects: vomiting, diarrhoea, dizziness

Important drug interactions: antiplatelets, anticoagulants, adenosine

29
Q

Describe glycoprotein IIb/IIIa inhibitors

A

Blocks binding of fibrinogen and vWF, target is final common pathway
Abciximab – blocks GPIIb/IIIa receptors
Administered IV
Specialist use in high risk percutaneous transluminal coronary angioplasty patients with other drugs

30
Q

What are the adverse effects and important drug interactions of glycoprotein IIb/IIIa inhibitors?

A

Adverse effects: bleeding

Important drug interactions: caution with other antiplatelet and anticoagulant agents

31
Q

Describe fibrinolytic agents

A

Fibrinolytics dissolve the fibrin meshwork of thrombus
Alteplase in acute ischaemic stroke <4.5 hours from symptoms, following STEMI diagnosis acutely vs primary PCI
Streptokinase can only be used once as antibodies develop
Tranexamic acid – stops bleeding (opposite effect)

32
Q

What are the adverse effects and important drug interactions of fibrinolytic agents?

A

Adverse effects: bleeding

Important drug interactions: antiplatelets and anticoagulants

33
Q

Compare thrombolysis and primary PCI following MI

A

Offer primary PCI if indicated, as the preferred coronary reperfusion strategy for people with acute STEMI if:
-presentation is within 12 hours of onset of symptoms
-AND primary PCI can be delivered within 120 minutes of the time when fibrinolysis could have been given
Reperfusion injury is a negative consequence of PCI
NSTEMI patients may also be candidates for PCI

34
Q

Describe secondary prevention of ACS

A
Once haemodynamically stable:
-ACEi
-B-blocker
-dual antiplatelet therapy (75mg + ADP receptor antagonist)
-statin 
PLUS cardiac rehabilitation