Atrial Fibrillation Management Notes

Atrial Fibrillation (AF)

• Described as an emerging epidemic.
• Affects approximately 5% of the population aged over 65 years in Australia.
• Associated with increased long-term risk of stroke, heart failure, and mortality.
• Clinicians need a reliable approach to diagnosis and management.

Diagnosis

• May be asymptomatic.
• Detected by irregular pulse and typical electrocardiogram (ECG) changes.

Associations

• Frequently seen as a sequela of:
  • Hypertension
  • Coronary artery disease
  • Valvular heart disease
  • Congestive cardiac failure
• Development of AF can reduce cardiac function and exacerbate underlying cardiac disease.
• Also commonly associated with:
  • Infections
  • Pulmonary disease including pulmonary emboli
  • Endocrine disorders (most commonly thyrotoxicosis)
  • Electrolyte disturbances
  • Renal failure
  • Postoperatively during convalescence
• Primary goal in these situations is diagnosis and treatment of the underlying condition.

Management

• Dependent on the clinical context.
• Most cases can be managed on an outpatient basis.
• Two important principles:
  • Assessment of thromboembolic risk
  • Rate control; rhythm control may not always be necessary

Assessment of Thromboembolic Risk

• Morbidity and mortality associated with AF results from thromboembolism.
• Discoordinate atrial contraction can lead to thrombus formation in the left atrial appendage.
• This may embolize and enter the systemic circulation, causing infarction in the brain, kidney, gastrointestinal tract, or limbs.
• Evaluation of thromboembolic risk should be performed in all patients with AF, including paroxysmal and chronic AF.
• Following reversion to sinus rhythm, atrial stunning increases the risk of emboli for 4 weeks.
• Anticoagulation should be continued in sinus rhythm for at least 1 month and may be continued if there is suspicion of further paroxysmal events.
• Symptoms are unreliable as episodes of AF are frequently silent.

Benefits of Anticoagulation

• Warfarin reduces stroke risk by approximately 70% with a target INR of 2.0–3.0.
• Aspirin reduces stroke risk by approximately 20% at a dose of 325 mg.
• Warfarin carries a bleeding risk of approximately 0.5–1.5% per year.
• Patient stratification into low, medium, and high risk of embolic complications enables rational decision-making regarding anticoagulation.

Risk Stratification and Antithrombotic Therapy

• High Risk:
  • History of suspected embolic stroke and mitral valve disease, especially mitral stenosis (10–15% annual risk).
  • Require warfarin unless major contraindication (e.g., recent intracranial hemorrhage or recurrent falls).
• Intermediate Risk:
  • History of hypertension (even if normotensive on treatment), left ventricular dysfunction or heart failure, diabetes mellitus, or age over 65 years (3.5–5.0% annual embolus risk).
  • Risk factors are additive.
  • Warfarin is appropriate in most cases, but risks and benefits should be carefully considered.
• Low Risk:
  • Less than 65 years of age with none of the above risk factors (0.5–1.0% per year).
  • Aspirin is the most appropriate agent.

Interruption of Warfarin Therapy

• For surgical or dental procedures, it is reasonable to cease anticoagulation for up to 1 week without substituting unfractionated or low molecular weight heparin (expert opinion).
• These guidelines do not apply to patients with prosthetic valves.

Ceasing Anticoagulation After Reversion to Sinus Rhythm

• Reasonable to consider, but fibrillation is likely to recur unless there has been a clear precipitating event.
• Patients in whom a rhythm control strategy has been employed and who have anticoagulation ceased have an increased risk of emboli.
• Decision needs careful consideration of the ongoing risk of recurrent AF.

Rate Control

• Loss of coordinated atrial contraction in AF can result in an accelerated ventricular rate.
• Can contribute to symptoms of shortness of breath or palpitations, and can also cause hypotension, congestive cardiac failure, or myocardial ischaemia.
• Goal of rate control is preventing symptoms and complications.
• Can be achieved with drugs or AV nodal ablation and pacing.

Pharmacologic Rate Control

• Efficacy of pharmacological rate control is about 80%.
• Agents act to slow atrioventricular nodal conduction and thus slow the ventricular rate.
• If monotherapy is unsuccessful, then a second or third agent can be introduced cautiously due to increased risk of symptomatic bradycardia or heart block.
• Beta Blockers:
  • Metoprolol or atenolol are suggested as first-line therapy.
  • Target rate is a resting heart rate of 60–80 bpm.
  • Depress myocardial contractility and must be used with caution if there are signs of decompensated heart failure or hypotension.
  • Avoid in patients with asthma.
• Calcium Channel Antagonists:
  • Nondihydropyridine calcium channel antagonists (diltiazem and verapamil) are commonly used.
  • Second line for patients in whom beta blockers are contraindicated or not tolerated.
  • Act to depress ventricular function and should be used with caution if there is a history of left ventricular failure.
• Digoxin:
  • As effective as a rate control agent at rest, but alone it fails to adequately control exercise-induced tachycardia.
  • Best used in combination with another agent, although in predominantly sedentary elderly patients it is suitable as monotherapy.
  • Indicated for use in patients with hypotension or left ventricular failure as it does not lower blood pressure and may offer slight inotropy.
  • Renally excreted, so care should be taken to adjust the dose for patients with impaired renal function; drug levels can be used to monitor this in the medium to long term.

AV Nodal Ablation and Pacing

• Ablation of the AV node and insertion of a permanent pacemaker provides highly effective heart rate control.
• Best used for patients who have failed treatment with pharmacologic agents or cannot tolerate them due to hypotension.
• Useful in patients with tachycardia-induced cardiomyopathy.
• Limitations include the persistent need for anticoagulation (due to persistent AF), loss of AV synchrony, and lifelong pacemaker dependence.
• There is some concern over the long-term effects of right ventricular pacing, and this procedure is best avoided in young patients.

Rhythm Control

• Cardioversion of AF is not essential. Many patients will tolerate AF with only minimal or no symptoms.
• In these cases, management should consist of only rate control and anticoagulation as required.
• In some cases, AF can cause significant symptoms and reversion to sinus rhythm is required.
• This can be achieved by either drug therapy or direct current reversion (DCR).

Amiodarone

• The most effective antiarrhythmic agent currently available.
• Effective due to prolongation of the action potential and refractory period of cardiac conducting tissue.
• Can be used either in the acute setting with recent onset of AF or for patients in chronic fibrillation.
• In the acute setting, either intravenous regimens with a loading bolus and infusion or oral treatment are reasonable options.
• Trials have shown reversion rates of up to 95%, particularly with intravenous regimens.
• Patients with a shorter duration of AF, smaller left atrial size, and who receive higher doses of amiodarone are more likely to revert.
• In chronic AF, the chance of successful reversion is lower.
• At 28 days, it can be expected that 15–40% of patients will be in sinus rhythm.
• Associated with significant adverse effects, including bradycardia, hypotension, nausea, constipation, thyroid abnormalities(hypo- or hyper- thyroidism).
• Widely distributed in body tissues and has an extraordinarily long half-life of 60–90 days.
• Serious potential complications must be taken into account before commencing a patient on amiodarone.

Flecainide

• Effective agent in AF, acting to revert and maintain sinus rhythm.
• Significant side effect profile limiting its usefulness clinically.
• Causes significant reduction in cardiac conduction and contractility and is also proarrhythmic.
• Contraindicated in patients with coronary artery disease or left ventricular dysfunction, and should only be used if these conditions have been excluded.
• May also act to increase AV nodal conduction, actually accelerating the ventricular rate.
• Therefore, it is often used in conjunction with an AV nodal blocking agent such as beta blockers or verapamil.

Sotalol

• A beta blocker with extended antiarrhythmic properties.
• Conflicting evidence regarding its ability to revert patients to sinus rhythm but it has been proven to assist in maintaining sinus rhythm.
• Not currently recommended for pharmacologic cardioversion but can be useful following DCR for maintenance of sinus rhythm.
• A popular agent because it does not have the broad adverse effect profile of the agents described above.
• The only serious adverse event, apart from those associated with other beta blockers, is QT prolongation.

Electrical Cardioversion (Direct Current Reversion - DCR)

• Immediate DCR is indicated acutely for AF or flutter associated with a rapid ventricular rate associated with hemodynamic compromise or symptoms of myocardial ischemia.
• Also indicated for patients with AF of less than 48 hours.
• In stable, symptomatic patients, it can be attempted after at least 4 weeks of therapeutic anticoagulation.
• If the patient has significant symptoms or hemodynamic compromise with an unknown duration of AF, a transoesophageal echocardiogram (TOE) may be performed immediately before DCR.
• The immediate success rate of DCR is 70–99%.
• Maintenance of sinus rhythm is more likely to be achieved on antiarrhythmic medication.
• DCR should not be attempted for patients with relatively short periods of sinus rhythm between cardioversions (designated as having permanent AF).
• Rate control and anticoagulation is the most appropriate strategy in this setting.

Catheter Ablation

• Early techniques attempted to scar the atrium to terminate fibrillation, but enthusiasm was tempered by prohibitive complication rates.
• Recent advances concentrate on the pulmonary veins with higher success rates and lower complications.
• Best reserved for younger patients with paroxysmal AF that have failed treatment with at least one antiarrhythmic drug.
• In patients without significant structural heart disease, success rates of up to 90% are achieved, although multiple procedures may be required.

Conclusion

• Successful treatment of AF is dependent on careful assessment of the risks and benefits of potential treatment options for each patient.

Tables

Table 1. Contraindications to Warfarin Therapy

Table 2. Antithrombotic Therapy for Patients with AF