Atrial fibrillation (AF) is a common tachyarrhythmia mainly occurring in older patients but paroxysmal form can occur in younger patients.
What is the basic pathology underlying AF?
Conditions that:
- Raise atrial pressure
- Increase atrial muscle mass
- Atrial fibrosis
- Atrial inflammation
can all cause AF
What are the causes of AF?
- Rheumatic heart disease
- Alcohol
- Thyrotoxicosis/hyperthyroidism
- Hypertension*
- Heart failure*
* Most common causes of AF in developed world - Idiopathic or lone AF
(genetic predisposition esp in young patients. 30-40% have at least one parent with AF. Genes assoc. with sodium, potassium channel, gap junction protein are implicated. Chromosomes 10, 6, 5 and 4 assoc with familial AF)
What happens to the atria in AF?
AF is maintained by continuous, rapid activation of the atria.
The atria responds electrically but there is no coordinated mechanical action and only some of the impulses are conducted to the ventricles.
The ventricular response depends on the rate and regularity of atrial activity.
What are the clinical features of AF?
Symptoms are highly variable.
- Incidental finding (30%)
- Emergency with rapid palpitations, dyspnoea and/or chest pain
- Deterioration in exercise with ongoing AF
- Irregularly irregular pulse
How is the pulse in AF characterised?
Irregularly irregular
What are the ECG changes seen in AF?
Absent p-waves
Irregular qrs complex
What are the 5 clinical classification of AF?
- First detected - irrespective of duration or severity of symptoms
- Paroxysmal - stops spontaneously within 7 days
- Persistent - continuous >7 days
- Longstanding persistent - continuous >1year
- Permanent
* Classification is helpful in choosing between rhythm restoration and rate control management.
What is the acute management for AF?
AF due to acute precipitating event i.e. alcohol toxicity, chest infection or hyperthyroidism => provoking cause should be treated.
For AF:
Ventricular rate control - by drugs that block AV node
Cardioversion electrically by DC shock or medically by IV anti-arrhythmic drug i.e. flecanide, amiodarone, propafenone
=> Conversion to sinus rhythm using DC cardio version achieved in 80%
=> Minimise risk of thromboembolism assoc. with cardioversion by giving anti-coagulant (warfarin) or direct acting oral anticoagulant for 3 weeks before cardioversion and 4 weeks after.
=> Urgent cardioversion with no time for anti-coagulant - guided by transoesophageal echocardiography to exclude atrial thrombus presence
There are 2 strategies used for long-term management of AF.
- Rate control (AV nodal slowing agents + oral anticoagulation)
- Rhythm control (anti arrhythmic drugs + DC cardioverson + oral anticoagulation)
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Rhythm control management:
- Describe the rhythm control management in younger, symptomatic and physically active patients.
- Describe the rhythm control management in patients with heart failure or left ventricular hypertrophy ;
coronary artery disease ;
paroxysmal atrial fibrillation or early persistent atrial fibrillation (atrial dilation)
- Any class of anti-arrhythmic drug can be given to young, symptomatic and physically active patients. Amiodarone should be kept as last resort due to its extra-cardiac adverse effects.
2i. Heart failure/LVH : Amiodarone only
ii Coronary artery disease : Sotalol or amiodarone
iii. Paroxysmal atrial fibrillation/early persistent atrial fibrillation : Left atrial ablation
- Ectopic trigger for atrial fibrillation found in pulmonary veins : radio frequency or cryothermal energy
Which group of patients is rate control therapy appropriate in?
- Patients with permanent form of the arrhythmia assoc with symptoms that can be improved by slowing down heart rate
- > 65yr old patients with recurrent atrial tachyarrhythmias
- Persistent tachyarrythmias and failed cardioversions
Which combination of drugs helps to achieve rate control?
Digoxin, beta-blockers or non-dihydropyridine calcium-channel blocker (verapamil or diltiazem)
*older patients with poor rate control with optimal medical therapy = AV node ablation and pacemaker implantation
HAS-BLED score used to identify patients at risk of bleeding. This is important to establish when putting patients on long-term anti-coagulation meds.
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Direct oral anti-coagulant (DOAC) blocks single step in coagulation cascade vs warfarin which blocks all vitamin K-dependent factors (II, VII, IX, X).
What are the two types of direct oral anti-coagulant?
- Direct thrombin inhibitors i.e. dabigatran
2. Direct factor Xa inhibitor i.e. rivaroxaban and apixaban
DOACs: rapid onset of action, shorter half-life and fewer food & drug interactions, does not require INR testing, equally as effective, safer than warfarin
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