Atrial Fibrillation (AF)

Definition

Chaotic, irregular atrial rhythm at 300-600 bpm

Aetiology

·         cardiac

MI, HTN, cardiac failure, mitral valve disease, cardiomyopathy, constrictive pericarditis, SSS, atrial myxoma, endocarditis

·         Others

                                 i.            Lung – Pneumonia, PE, lung ca

                               ii.            Endocrine – Thyrotoxicosis, phaechromocytoma

                              iii.            Metabolic ↓K, ↓Mg, alcohol

                             iv.            Infiltration - Haemochromatosis, sarcoid

                               v.            Post-op

Pathophysiology

1.       Rapid firing foci

2.       Multiple re-entrant circuits sweeping around the atrial myocardium

3.       Loss of synchronized atrial contraction

4.       Only a few of the impulses (variable and unpredictable) transmit through AV node

5.       To produce an irregular ventricular response

Classification

        I.            Paroxysmal        Intermittent, self-terminating

      II.            Persistent          Prolong, Reversible by electric / chemical cardioversion

    III.            Permanent        Not reversible

Symptoms

Asymptomatic

Palpitation, chest pain, dyspnoea, faintness

Signs

Irregularly irregular rhythm, apical pulse is greater than radial pulse, 1^st heart sound of variable intensity, sign of LVF

I(x)

ECG

ECG characteristics of a.fib:

•       Absence of P waves

•       Atrial rate 350 – 600 bpm (fwave)

•       Irregular ventricular rhythm

•       Ventricular rate 100 – 180 bpm

Blood

U&E, cardiac enzyme, TFT

Echo

Left atrial enlargement, mitral valve disease, poor left ventricular function

Managements

Principle

                                I.            Treat underlying causes

                              II.            Rate vs. rhythm control – same mortality

Rate control

Indications

                                                         i.            >65 years old

                                                       ii.            Underlying coronary artery disease

                                                      iii.            Unsuitable for cardioversion

                                                     iv.            Contraindicated for anti-arrhythmic drugs

Aim: < 80bpm at rest,

Drugs involved

·         Diltiazem            60-120mg/8h PO; or

·         Verapamil          40-120mg/8h PO; or

·         Metoprolol       50mg/12h PO, or just 10mg/8h if LV function poor

·         Digoxin (Class IV)

o   Used in elderly, not ambulatory

o   Less effective in active ppl

o   Because only block AVN at rest

o   If exercise SNS control AVN

Rhythm control

Indications

                                                         i.            Symptomatic

                                                       ii.            Younger

                                                      iii.            AF secondary to corrected precipitant (e.g. unstable U&E)

Methods to control rhythm

1.       Pharmacological

·         Flecainide          (if no structural abn)

§  Monitor ECG (flecainide is strong negative inotrope)

·         Amiodarone     (Structural abn √)

Note: Pre-cardioversion echo is required to look for any structural heart   abnormality

Indication

·         No structural heart disease e.g. atrium not dilated

·         CI to long-term anti-coagulant

2.       Electrical cardioversion

·         Cardioversion regime (after 48 hours anti-coagulant)

O₂àITU/CCUàGA or IV sedation à200Jà360Jà360J

                            III.            Anticoagulant

Maintenance – warfarin vs aspirin –CHADS₂ score

Rapid acting – Warfarin vs heparin (UFH, LMWH) vs factor X_a inhibitor vs dabigatran

CHADS score

estimating the risk of stroke in patients with non-rheumatic atrial fibrillation (AF)

used to determine whether or not treatment is required with anticoagulation therapy or antiplatelet therapy

Condition	Points	Scores
C	Congestive heart failure	1
H	Hypertension: blood pressure consistently above 140/90 mmHg (or treated hypertension on medication)	1
A	Age >/=75 years	1
D	Diabetes Mellitus	1
S2	Prior Stroke or TIA	2
P	Peripheral vascular disease	1

Anticoagulation based on the CHADS₂ score

Score	Risk	Anticoagulation Therapy	Considerations
0	Low	Aspirin	Aspirin daily
1	Moderate	Aspirin or Warfarin	Aspirin daily or raise INR to 2.0-3.0, depending on factors such as patient preference
2 or greater	Moderate or High	Warfarin	Raise INR to 2.0-3.0, unless contraindicated (e.g. clinically significant GI bleeding, inability to obtain regular INR screening)