Table Of Contents
Atrial Fibrillation
Atrial fibrillation is an irregular atrial rhythm at a heart rate of 300 – 600 bpm.
It peaks at 70+ years, and affects men slightly more than women.
Classification of atrial fibrillation
| Classification | Description |
|---|---|
| Primary (lone) atrial fibrillation | Atrial fibrillation in patients < 60 years of age without clinical or echocardiographic evidence of cardiopulmonary disease |
| Secondary atrial fibrillation | Atrial fibrillation that is associated with hypertension, coronary artery disease, chronic lung disease, and hyperthyroidism |
| Valvular atrial fibrillation | Atrial fibrillation with rheumatic mitral valve disease, prosthetic heart valve, or mitral valve repair |
| Non-valvular atrial fibrillation | Atrial fibrillation without specific valvular heart disease |
Classification of atrial fibrillation based on duration of episodes
| Classification | Description |
|---|---|
| Paroxysmal atrial fibrillation | Atrial fibrillation that self-terminates in 48 hours to 7 days. It recurs with variable frequency |
| Persistent atrial fibrillation | Atrial fibrillation that lasts more than 7 days. Long-term episodes can be sustained for a year or more. This may require pharmacological or electrical cardioversion for termination. |
| Long-standing persistent atrial fibrillation | Atrial fibrillation that lasts for more than a year. |
| Permanent atrial fibrillation | The presence of atrial fibrillation is accepted by either the patient or the clinician. Rhythm control strategies are no longer pursued. |
Pillars of treatment of atrial fibrillation
| Treatment | Description |
|---|---|
| Anticoagulation | Prevents stroke formation in the atria. This is decided using CHA₂DS₂-VASc. DOACs are preferred. Warfarin is used if there is a mechanical valve or mitral stenosis. Heparin is used in the acute setting. |
| Rate control | This regulates how fast the ventricles beat (< 90 bpm at rest). Atrial fibrillation continues, but the heart rate is kept safe. Drugs include beta-blockers, calcium channel blockers, and digoxin. |
| Rhythm control | This restores and maintains normal sinus rhythm. Methods include: cardioversion (electrical and pharmacological); antiarrhythmic drugs (amiodarone, flecainide, and propafenone); and catheter ablation |
- Risk factors
- Increasing age
- Male sex
- Hypertension
- Ischaemic heart disease
- Heart failure
- Cardiomyopathy
- Cardiothoracic surgery
- Diabetes mellitus
- Obesity
- Pneumonia
- Smoking
- Obstructive sleep apnoea
- Thyrotoxicosis
- Caffeine
- Alcohol excess
- Chronic kidney disease
- Pathophysiology
- Triggers (initiation)
- Commonly from the pulmonary veins
- Enhanced automaticity → ectopic cells fire faster than the SA node
- Triggered activity (abnormal after-depolarisation – Ca2+ influx)
- Micro-reentry (small localised re-entry circuits)
- Substrate (maintenance environment)
- Structural and electrical changes allow atrial fibrillation to persist
- Shortened action potential duration and reduced refractory period promote multiple re-entry wavelets
- Atrial enlargement and fibrosis also facilitate re-entry
- Perpetuators (”AF begets AF”)
- Atrial dilatation → increased dispersion of refractoriness and fibrosis (due to increased angiotensin II)
- Fibrosis → conduction heterogeneity → sustains atrial fibrillation
- Ionic remodelling (reduced L-type Ca2+ channels) → alters action potential
- Loss of atrial contraction → irregular ventricular response → blood stasis → thrombus → stroke
- Triggers (initiation)
- Signs and symptoms
- Asymptomatic atrial fibrillation
- Irregularly irregular pulse
- Heartbeats follow each other in an entirely random pattern
- Haemodynamic compromise
- Cardiac chest pain
- Heart rate > 150 bpm
- Blood pressure < 90 mmHg
- Syncope or pre-syncope
- Signs of acute heart failure
- Signs of cardiogenic shock
- Differentials
- Irregular pulse
- Atrial flutter
- AVNRT and AVRT
- Ventricular ectopic beats
- Sinus tachycardia
- Anxiety and anxiety attacks
- Thyroid disease
- Endocarditis
- AV block
- Atrial flutter
- Ventricular fibrillation
- Hyperkalaemia
- Investigation
- 12-lead echocardiogram
- Irregularly irregular rhythm
- Absent P waves
- Variable ventricular response
- Transthoracic echocardiogram (TTE)
- Rule out left atrial appendage thrombus (LAA), particularly if onset > 48 hours
- Blood tests (UECs, cardiac enzymes, and TFTs) to identify potential reversible causes
- 12-lead echocardiogram
- Acute treatment
- Unstable
- Immediate electrical cardioversion +/- amiodarone if unsuccessful
- Stable < 48 hours
- Rate control or rhythm control
- Start heparin in case cardioversion is delayed
- Stable ≥ 48 hours
- Rate control
- Anticoagulate for > 3 weeks first if rhythm control is chosen
- Correct electrolyte imbalances and associated illnesses
- Consider anticoagulation
- Unstable
- Long-term treatment
- Rate control strategy for patients > 65 years old, or a history of ischemic heart disease
- Beta-blockers or rate-limiting calcium channel blockers are first-line
- Digoxin is second-line. It is only used as monotherapy in sedentary patients.
- Amiodarone is third-line
- Beta-blockers should not be given with verapamil
- Rhythm control strategy for younger patients, first presentation, lone AF, or secondary AF
- Elective DC cardioversion
- Elective pharmacological cardioversion (flecainide, amiodarone or propafenone)
- Atrioventricular node ablation with pacing
- Pulmonary vein ablation
- Maze procedure
- For paroxysmal atrial fibrillation:
- ‘Pill in the pocket’ (sotalol or flecainide PRN) if infrequent AF, BP > 100 mmHg systolic and no past LV dysfunction
- Anticoagulation
- Ablation if symptomatic or frequent episodes
- Rate control strategy for patients > 65 years old, or a history of ischemic heart disease
- Complications
- Stroke
- Heart failure
- Cardiomyopathy
- Reduced quality of life
Anticoagulation in Atrial Fibrillation
Atrial fibrillation results in loss of coordinated atrial contraction, which increases the risk of thrombus formation (especially in the left atrial appendage). Anticoagulation prevents stroke in patients with atrial fibrillation.
- Acute atrial fibrillation < 48 hours
- Thrombus formation is unlikely
- Heparin (UFH or LMWH) + immediate cardioversion
- Long-term anticoagulation can be assessed using CHA2DS2-VASC
- Acute atrial fibrillation > 48 hours
- High risk of atrial thrombus
- Delay cardioversion and anticoagulate for:
- ≥ 3 weeks before cardioversion
- ≥ 4 weeks after cardioversion
- Transesophageal echocardiography (TEE) can be used to check for a thrombus and guide cardioversion
- Haemodynamically unstable atrial fibrillation
- Immediate electrical cardioversion without anticoagulation
- Start anticoagulation as soon as possible after
- Chronic atrial fibrillation
CHA2DS2-VASC score
| Risk factor | Point |
|---|---|
| Congestive Heart Failure | 1 |
| Hypertension (or treated hypertension) | 1 |
| Age ≥ 75 years | 2 |
| Age 65 – 74 years | 1 |
| Diabetes | 1 |
| Prior stroke or transient ischemic attack | 2 |
| Vascular disease (including ischaemic heart disease and peripheral arterial disease) | 1 |
| Sex (female) | 1 |
Interpretation
| Score | Anticoagulation |
|---|---|
| 0 | No treatment |
| ≥ 2 | Consider anticoagulation in men |
| ≥ 3 | Consider anticoagulation in women |
The HAS-BLED scoring system can be used to assess the 1-year risk of bleeding in patients with atrial fibrillation who are on anticoagulation.
Bleeding is defined as intracranial haemorrhage, hospitalisation, Hb decrease > 2 g/L and/or transfusion.
HAS-BLED
| Risk factor | Points |
|---|---|
| Hypertension (uncontrolled systolic BP > 160 mmHg) | 1 |
| Abnormal renal function or liver function | 1 for each |
| Stroke, history of | 1 |
| Bleeding, history or tendency | 1 |
| Labile INR | 1 |
| Elderly > 65 years | 1 |
| Drugs predisposing to bleeding or alcohol use | 1 for each |
A score ≥ 3 suggests a high risk of bleeding