Atrial fibrillation quiz

A biphasic 100J shock has an estimated reversion rate of 85%.

Spontaneous reversion by 48 hours would be expected in approximately 60% of patients, and in 90% of patients treated with amiodarone.

Ischaemic heart disease is thought to be responsible for approximately 40% of cases, with hypertension the next most common cause. Lone fibrillators comprise 5% of cases. Clinical hyperthyroidism is only seen in 1% of cases, although approximately 5% of cases have an elevated TSH. Hypokalaemia alone is a rare cause of atrial fibrillation.

Cardiac conditions with reduced left ventricular compliance (eg aortic stenosis, hypertension) are the most likely to be associated with haemodynamic compromise from atrial fibrillation. The reduction in ventricular filling is likely to be greater than the 25% that occurs in normally compliant hearts.

The ventricular rate becomes slower and the amplitude of the fibrillation waves usually become finer with time after onset. Digoxin therapy makes the ventricular rate more regular.

Although a variety of recommendations regarding anticoagulation in atrial fibrillation exist, it is usually accepted that males <75 years of age and females < 65 years of age without other risk factors for stroke can be managed with aspirin alone. Patients who have had a previous stroke are the greatest potential beneficiaries of anticoagulation, with a number needed to treat of approximately 12.

This represents a relative reduction in stroke incidence of 60%. The baseline stroke incidence is 0.3% in patients in sinus rhythm. 

Mitral stenosis has a 25% lifetime incidence of fatal embolism associated with atrial fibrillation and is the highest risk lesion. Patients with AFib and a structurally normal heart have an annual incidence of stroke of 5%, those with rheumatic heart disease have an incidence of 10%. 

It is estimated that aspirin alone confers approximately 1/3 of the benefit of full anticoagulation in patients with atrial fibrillation, however the relative benefits of anticoagulation become greater in higher risk and older patients. Aspirin is generally not recommended as a result, but can be an option in younger patients who do not want to be anticoagulated.

50% are likely to revert within 24 hours – sometimes just observing or rate controlling works quite well too! 

An INR of 2-3 is recommended in this age group, decreasing to 2.0 as the target for patients ≥ 75 years of age. However most patients would be started on a DOAC unless there were contra-indications. 

A left atrial diameter of 3.5cm is normal, so is not associated with a decreased likelihood of reversion. 

Dofetilide at this dose is associated with a conversion rate of approximately 90%. A 70J biphasic cardioversion will work in 50% (same as waiting 24 hours) whilst sotalol is poorly effective. Flecainide at 200-300mg oral (or 2mg/kg IV) doses is as effective as Dofetilide, but not with a dose of only 100mg orally.

The aim is to have a relatively fast heart rate to shorted diastole and minimise the effects of regurgitation. This is balanced with the risk of shortening diastole too much and reducing ventricular filling. Patients with stenotic valvular and coronary artery disease are thought to benefit from a slower heart rate (and a longer diastole).

A ventricular rate of < 90bpm in new onset AFib suggests that there is significant disease of the cardiac conduction system. Rate control medications in this situation carry a significant risk of inducing high degrees of heart block and should usually be avoided.