Atrial Fibrillation (af)

Atrial Atrial Fibrillation Fibrillation (AF) (AF) By Stephanie Chieng

Introduction • AF is a cardiac arrhythmia (abnormal heart rhythm) that involves the two upper chambers (atria) of the heart. • It is a loss of atrial contribution to ventricular filling (inefficient movement of blood to ventricles due to incomplete filling of atria)

Introduction (cont’) • In AF, the normal electrical impulses (by the SA node) are overwhelmed by disorganized electrical impulses that originated in the atria and pulmonary veins, leading to conduction of irregular impulses to the ventricles that generate the heartbeat. • The result is an irregular heartbeat which may occur in episodes lasting from minutes to weeks, or it could occur all the time for years.

Signs & Symptoms • Often asymptomatic, and is not in itself generally life-threatening • Common Sx: chest palpitations, dyspnoea on exertion (DOE) • Light headedness, dizziness, reduced exercise tolerance (due to reduced CO and inadequate cerebral blood flow) • Reduced CO results in signs of HF ( JVP, ankle oedema, fluid in the lungs)

Causes • Most commonly associated with CVD, IHD, CHF, CVA • Valve diseases, atrial septal defect • HTN, COAD, pulmonary embolism, hyperthyroidism • Excessive alcohol intake; an alchoholic cardiotoxicity caused by an episode of binge drinking

Types of AF • The American College of Cardiology (ACC), American Heart Association (AHA), and the European Society of Cardiology (ESC) recommend in their guidelines the following classification system based on simplicity and clinical relevance AF Category

Defining Characteristics

1st detected

Only 1 diagnosed episode

Praroxysmal

recurrent episodes that self-terminate in less than 7 days

Persistent

recurrent episodes that last more than 7 days

Permanent

An on-going long term episode

Diagnosis • Clinical history, physical examination • Evaluation of ECG- check rhythm • Echocardiogram; trans-thoracic or transoesophageal (more invasive,but not as much tissue top penetrate to achieve visualisation)

Types of Treatments (i) Rhythm control i.e reversion to normal sinus rhythm (NSR) (ii) Rate control i.e administration of medications to control ventricular rate, followed by maintenance of NSR and (iii) Prevention of systemic emolization with anticoagulant (or antiplatelet in selected patients)

• Paroxysmal- rate control alone maybe appropriate for brief or minimally symptomatic recurrences • Persistent/permanent- control of ventricular rate is commonly the initial strategy. • Principle: slow HR, then restore NSR • Reduce risk of stroke • Tx any underlying disorder that’s causing or raising the risk of AF—for example, hyperthyroidism.

• Initial Tx is up to whether major goal of therapy is control of ventricular rate, or whether attempts are to be made to obtain and maintain sinus rhythm. • The AFFIRM trial ('rate control' vs 'rhythm control') showed no statistically significant difference in mortality or in quality of life between the two options.

Rhythm control

• Rhythm control allows the atria and ventricles to work together again to efficiently pump blood to the body. • Electrical cardioversion (CD): a jolt of electricity delivered to the heart to "convert" the rhythm from AF back to a normal heart rhythm. • Medicines (pharmacological CD) used to control a person’s heart rhythm include amiodarone,flecainide, sotalol etc; occasionally older medicines such as quinidine, procainamide, and disopyramide.

• Electrical CD is preferred when patient is haemodynamically unstable. • Patients with left atrail size of <4.5-5c, AF of recent onset, little or not HF, and an underlying reversible cause such as hyperthyroidism, MI have higher chance of successful cardioversion. • Chronic AF is difficult to manage, so may have to resort to other approaches to control rhythm: implantable devices or AV node ablation.

Pharmacological CD • Amiodarone: Initially 200mg TDS for 1wk, reduce to 200mg BD for a further wk. Maintenance: 200mg/day or lowest effective dose. • Flecainide: 200-300mg as single dose • Quinidine: 0.75-1.5g in divided dose over 6-12hrs • Propafenone: 450-600mg as single dose

Maintaining sinus rhythm

• The main indication for antiarrhythmic drug therapy to maintain sinus rhythm after CD are the persistent Sx despite rate control strategy (palpitations,weakness,dizziness,HF) & patient preference for rhythm control. • Satolol: Initially, 80 mg daily as a single or in 2 divided doses, increased gradually every 2-3 days. Maintenance: 160-320mg daily in 2 divided doses. Max: 640 mg daily. • Monitor for excessive QT prolongation; cease if QT increases by >20% from baseline; use low doses or not at all in patients with impaired renal function

• Flecainide: 50-100mg BD. Max: 400mg/day • Disopyramide: 400-750mg in 4 divided doses. (as conventional capsules every 6hr; as extended-release capsules every 12hr) • Amiodarone is also effective in sinus rhythm control. However, caution need to be exercised due to its long term adverse effects profile.

Rate Control • Rate control in AF usually achieved by slowing AV conduction with IV/oral beta-blockers, diltiazem,verapamil or in patients with HF, digoxin is used as single agent or in combination. • Aim for ventricular rate <80b/min at rest & 180b/min on exercise. Some patients have controlled ventricular rate & hence do not require specific Tx. • DO NOT combine verapamil with beta-blockers as risk of bradycardia & reduced CO .

Drugs for HR control Metoprolol 25 to 100 mg orally, BD Propanolol 30-160mg/day in divided doses Diltiazem 40-120 mg daily TDS Verapamil 40-120 mg daily TDS Digoxin loading: 250-500mcg q4-6hrs, to a max of 1.5mg. Maintenance: 125-250mcg OD (rarely up to 500mcg daily) • Halve the digoxin dosage in elderly and renal impairment patient. Monitor serum digoxin level to prevent toxicity. • • • • •

• When taking digoxin, best to obtain potassium level of 4-5.5mmol/l. • If use with amiodarone, halve the digoxin dose due to risk of toxicity. • Signs of toxicity: PR interval prolongation, xanthopsia(yellow vision), delirium • Digoxin alone is insufficiet in slowing rapid ventricular rate associate with increased sympathetic tone (exercise, hyperthyroidism, fever). Consider alternative or combining with beta-blockers, verapamil or diltiazem.

Anticoagulants • Patients with AF usually have a significantly increased risk of stroke (up to 7x that of the general population). • Hence, preventing the formation of blood clots is an important part of treating AF . • Warfarin is the most effective medicine in prevention of stroke. • It reduces the risk of stroke by 60%, while the reduction with aspirin is about 20%. • Aspirin is used when warfarin is C/I.

3 risk categories for thromboembolism: • High risk patient: patients with a previous thromboembolic event thought to be secondary to their fibrillation and patients with longstanding mitral valve disease. Should all be on long-term warfarin unless there are very strong C/I aspirin 75-300mg/day • Intermediate risk: The presence of a history of hypertension, age >65yrs, LV dysfunction or history of HF. Based on GP’s clinical judgment on whether or not to introduce warfarin or aspirin.

• Low risk: patient <65yrs, with an echocardiographically normal heart and no history of HTN or any of the other risk factors for thromboembolism. Probably do not need treatment with warfarin. • Recent results of the Stroke Prevention in Atrial Fibrillation III (SPAF III) trial demonstrated a 75 percent reduction in the risk of stroke for people taking adjusted dose of warfarin in AF.

INR • Recommended warfarin dose is 5mg/day. • Target INR range for warfarin is 2 to 3 • Except perhaps in patients who have already suffered thromboembolic events with an INR in this range, a target of 2.5 to 3.5 may seems reasonable. • In patients age >75yrs who are at risk of major bleeding, a target INR of 1.8-2.5 may be a reasonable compromise.

Counselling on warfarin • Ensure patient understand the INR values. • Diet issue- a normal constant amount of vitamin K intake (green leafty veges i.e spinach, green tea, cabbage & animal liver etc) • Do not take any OTC products/supplements before consulting with your doctor. • Purple toe syndrome- bilateral, painful purple lesions on toes. Stop medication & seek medical advise immediately.

References • Australian Medical Handbook.2006 • Sarawak Handbook of Medical Emergencies. 2nd edition.2005. • Adjusted-dose warfarin versus low-intensity, fixeddose warfarin plus aspirin for high-risk patients with atrial fibrillation: Stroke Prevention in Atrial Fibrillation III randomized clinical trial." The Lancet, September 7, 1996, 348, 633-638. • Therapeutic Guidelines. 2003. Australia • www.mims.com.my