CSB601 Chap.7 Atrial Fibrillation, Anticoagulants and Antiplatelets
Atrial Fibrillation, Anticoagulants and Antiplatelets
Rhythm, rate and clot prevention
This chapter covers the Week 5 material on arrhythmias, centred on atrial fibrillation, and the medicines that prevent clots.
It compares beta blockers, diltiazem, verapamil, digoxin and amiodarone for slowing the ventricle or restoring rhythm, explains how stroke risk is scored, and sets warfarin, heparins and direct oral anticoagulants against aspirin and clopidogrel on the clotting pathway.
What Week 5 cases probe
Cases look for dangerous combinations such as verapamil with a beta blocker, unsafe tablet splitting, warfarin brand changes, food and drink effects on INR, and the trade-offs of moving from warfarin to dabigatran.
Matching questions test drug classes and mechanisms.
What this chapter covers
- 01
AF Rate Control Agents
- 02
Rhythm Control and Amiodarone
- 03
Stroke Risk Scoring
- 04
Warfarin and INR Monitoring
- 05
Direct Oral Anticoagulants
- 06
Aspirin and Clopidogrel
Worked example · free
Fast AF with a weak left ventricle
- 2The resting rate target is below 110 bpm, or below 90 bpm if symptoms persist. With an LVEF of 35%, diltiazem is avoided because non-dihydropyridine calcium channel blockers depress contraction, so a heart-failure beta blocker becomes the first-line choice.
- 2If rate control stays suboptimal, digoxin can be added, with renal function and electrolytes checked first. Amiodarone is not used first-line for chronic rate control because of thyroid, lung, liver, skin and eye toxicity.
- 2Reversible triggers such as electrolyte or thyroid problems are checked, and her CHA2DS2-VA score is calculated: a score of 2 or more favours an oral anticoagulant, while HAS-BLED highlights modifiable bleeding risks.
Key terms
- CHA2DS2-VA Score
- A stroke risk tool for non-valvular atrial fibrillation in which a score of 2 or more favours an oral anticoagulant.
- International Normalised Ratio
- A standardised blood clotting measure used to adjust warfarin, with a target of about 2 to 3 in atrial fibrillation.
- Direct Oral Anticoagulant
- An oral anticoagulant such as apixaban, rivaroxaban or dabigatran that directly inhibits factor Xa or thrombin without routine INR testing.
- Ventricular Rate Control
- A treatment strategy in atrial fibrillation that slows conduction through the AV node so the resting heart rate falls below 110 bpm.
Atrial Fibrillation, Anticoagulants and Antiplatelets FAQ
Why is digoxin not used to convert atrial fibrillation back to normal rhythm?
Digoxin slows conduction through the AV node by increasing vagal tone, which lowers the ventricular rate at rest, but it does not convert AF to sinus rhythm or stop it returning after cardioversion. It also works poorly during exercise, when sympathetic tone is high, so it suits patients at rest and those who also have heart failure.
Do people taking apixaban or rivaroxaban need regular INR tests?
No routine INR monitoring is needed, because these drugs inhibit factor Xa directly and give predictable anticoagulation. Their short half-lives make adherence critical: a missed dose quickly reduces protection. Kidney function still matters, since impaired clearance calls for caution, and bleeding remains a risk that patients should be able to recognise.
Why is aspirin stopped several days before surgery?
Aspirin permanently disables COX-1 in each platelet it reaches, cutting thromboxane A2 production for the rest of that platelet's life, roughly 7 to 10 days. Its antiplatelet effect only wears off as new platelets are made, which is why teaching materials expect it to be stopped several days ahead rather than on the eve of an operation.
What foods and drinks matter for someone taking warfarin?
Vitamin K intake, mostly from green leafy vegetables, should stay fairly constant rather than be avoided, because sudden changes shift the INR. Alcohol and cranberry juice should be limited since both increase bleeding risk. Brand consistency matters as well, because the two warfarin brands sold in Australia are not bioequivalent.
Exam move
Treat this chapter as three linked questions and revise them in order. First, rate control: build a four-row card for beta blockers, diltiazem or verapamil, digoxin and amiodarone with mechanism, one key number and the main catch, including the LVEF rule and the danger of combining verapamil with a beta blocker.
Second, stroke prevention: rehearse the CHA2DS2-VA action bands and what HAS-BLED is for, and practise writing the score name correctly. Third, clot biology: sketch the platelet lane and the coagulation lane from memory, then place aspirin, clopidogrel, warfarin, heparins, apixaban, rivaroxaban and dabigatran on it. Matching questions in the study guide test exactly these class and mechanism links.
Finish with one counselling script for a warfarin patient covering brand consistency, vitamin K, alcohol and cranberry, and one comparing warfarin with a direct oral anticoagulant.
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