Atrial Fibrillation

Definition

• Uncoordinated atrial activation with atrial mechanical dysfunction.
• Major risk of cardioembolism causing ischaemic stroke.
• Assess with risk score.

Aetiology

• Atrial fibrosis, loss of atrial muscle mass.
• Increased automaticity or multiple re-entrant wavelets.
• Atrial ‘rate’ of AF is 400–600/min, but it is the ventricular response that matters.
  • Ventricular rate held in check by AV node at <200/min, slows with age and conduction disease.
  • An accessory bundle (WPW) can allow faster rates to conduct AV causing VF.

Haemodynamics

• ↑ HR shortens diastole and limits LV filling and coronary perfusion. LV filling may already be compromised by loss of atrial systole.
  • Rate control with drugs, treat failure and DC shock if needed.
  • Impaired LV function or mitral stenosis makes things much worse!

Clinical

• Asymptomatic.
• Palpitations, dyspnoea, chest discomfort.
• Cardioembolic stroke, mesenteric emboli, limb emboli, dyspnoea.
• Fatigue and worsening heart failure, syncope, dizziness.
• ↓BP with fast/slow AF, irregularly irregular pulse.
• Pulse deficit.
• Murmurs suggesting valve disease, signs of thyroid disease, hypertension.

Causes

• Ischaemic / valvular / rheumatic / hypertensive heart disease / cardiomyopathy / post cardiac surgery / thyrotoxicosis / alcohol – acute binge or chronic / sick sinus syndrome / congenital heart disease / pulmonary embolism / pneumonia / sarcoidosis / amyloidosis  / haemochromatosis / lone AF (idiopathic) / pericarditis / myocarditis.

   

  Classification of atrial fibrillation
  ● Persistent: lasts >7 days. ● Paroxysmal: 2+ episodes self-terminating lasting <7 days.	● Permanent: lasts >1 year and fails to cardiovert. ● Lone AF: aged <60 y, no HTN, normal echo, no risk factors.

Investigations

• Bloods
  • FBC – ↓Hb
  • ↑WCC – sepsis
  • U&E
  • Mg, Ca, K
  • TFT – thyrotoxicosis
  • LFTs – alcohol, haemochromatosis.
• CXR
  • cardiomegaly
  • pulmonary oedema
  • infection
  • post cardiac surgery effusion
• Troponin
  • ↑with ACS or myocarditis
  • minor rise with DC shock
• ECG
  • Absent ‘P’ waves – no organised atrial activity
  • Fibrillatory waves that vary in amplitude, shape and timing
  • QRS complexes which are irregularly irregular
  • Aberrantly conducted AF: wide complex and fast but irregular.
  • Pre-excited AF: QRS 160–300/min and slurred up or down stroke of delta waves seen giving wide complex appearance but very irregular; the irregularity means that it is not VT.

Dangerous if it conducts to ventricles at 1:1 and can precipitate VT/VF. This depends on the character of the accessory pathway. If there are RR intervals <260 ms this is considered unsafe and needs inpatient cardiology review for ablation. If unstable simply DC cardiovert.

Capturing PAF

• 24 h tape in those with suspected asymptomatic episodes or symptomatic episodes less than 24 h apart.
• Use an event recorder ECG in those with symptomatic episodes more than 24 h apart. Some may use 7 day tape.

Echo

• Transthoracic echocardiogram
  • assess LV function
  • valve disease
  • LA size
• Anticoagulation rarely depends on the echo.
• Transoesophageal echocardiogram
  • closer inspection of valves
  • mitral disease
  • ASD
  • endocarditis
  • LA thrombus may be seen and can help assess risk of thromboembolism

Coronary angiography

• If IHD suspected.

Atrial Fibrillation anticoagulation risk assessment

• CHA2DS2VaSc score, assesses stroke risk in those with AF.
  • Adjusted annual stroke risk by score:
    • (0) 0% / (1) 1.3% / (2) 2.2% / (3) 3.3% / (4) 4.0% / (5) 6.7% / (6) 9.8% / (7) 9.6% / (8) 6.7% / (9) 15.2%
• HAS-BLED score, assesses bleeding risk.
  • A score of 3 or more indicates increased 1 year bleed risk on anticoagulation sufficient to justify caution or more regular review.
  • Risk is for intracranial bleed, bleed requiring hospitalisation or a haemoglobin drop >2 g/L or that needs transfusion.

Management

For all:

• ABC, high flow oxygen as needed.
• IV fluids cautiously if at all in LVF or fluid overloaded.
• Start treatment dose LMWH in all with AF and not anticoagulated with no contraindications.
• Look for and treat any cause: chest infection, thyrotoxicosis, ACS, PE, sepsis, MI/ACS, pulmonary oedema, PE, alcohol excess or withdrawal.

AF and unwell:

• Remember AF and fast AF can be a response to an infective, inflammatory or metabolic/toxic cause.
• Treatment must balance to focus on treating the underlying cause as well as using rate control drugs.
• Look for causality.
• If fast AF is causing compromise: ↓? BP, LVF, angina then DC cardioversion, which may be done without anticoagulation, but start LMWH [NICE 2014].
• If not severely compromised consider
  • AMIODARONE 150–300 mg IV, 30–60 min via a large bore cannula or preferably a central line.
    • Any deterioration then emergency DC cardioversion.
    • Further amiodarone infusions require a central line.
  • Alternatives include DIGOXIN loading or a BETA-BLOCKER.
  • Consider cardioversion if arrhythmia is less than 48 h, and start rate control if AF duration >48 h or is uncertain. Anticoagulate both.
  • Consider Bisoprolol, Atenolol or Metoprolol (avoid Sotalol) especially if angina or hypertension.
  • Digoxin can be loaded (check not on it already) useful especially if in LVF
    • DIGOXIN 500 mcg PO/slow IV over 1 h  
    • Then 250–500 mcg PO/slow IV 6 h later.
    • Digoxin slows resting rate and is an inotrope and best for those with CCF or a sedentary life. Reduce dose with renal failure.
    • Rhythm control AF >48 h must wait until anticoagulated for a minimum of 3 weeks.

AF and well

• Ventricular rate 60–120/min and haemodynamically well. Determine and manage cause. The question will be between rate control – slowing the AF – or rhythm control by trying to chemically or electrically cardiovert the patient to sinus rhythm and maintaining it.
• Assess need for anticoagulation and if needed start LMWH/UFH acutely or DOAC.

Rate control

• Consider oral Beta-blocker or rate limiting CCB.
• Digoxin may be considered if sedentary lifestyle.
• Avoid Amiodarone long term as side effects significant.
• Rhythm control – repeated attempts to remain in SR – DC cardioversion

Anticoagulation and cardioversion

• DC
  • You can electrically or chemically cardiovert immediately if you can be certain that AF duration is <48 h or a TOE shows that there is no LA appendage thrombus, or it is clinical indicated due to instability.
  • For those where the above is not the case, Start LMWH or IV Heparin immediately and continue for at least 3 weeks.
  • If elective cardioversion is planned, then anticoagulate for 3 weeks before and at least 3 weeks after.
• Chemical cardioversion
  • Consider Amiodarone (limited duration) or Dronedarone.
  • Flecainide can be used if LV function normal and no significant IHD.

Aim to get SR (rhythm control): when patient is unstable and SR would improve haemodynamics, in younger symptomatic patients or those with stroke or cardiomyopathy. Overall prognosis, however, is the same.

Specific scenarios

Pre-excited AF and WPW syndrome

• Use IV PROCAINAMIDE / IV AMIODARONE IV Sotalol or IV Flecainide
• If unstable, then immediate DC cardioversion.

Avoid digoxin, beta-blockers and Verapamil or Diltiazem in pre-excited AF. They may increase risk of VF.

• Assess for anticoagulation.

Prevention and management of postoperative AF

• With cardiothoracic surgery reduce postoperative AF by offering either amiodarone, a standard beta-blocker (not sotalol), or a rate-limiting calcium antagonist.
• DO NOT offer digoxin.
• Continue any pre-existing beta blockade.
• Postop, offer a rhythm based strategy.
  • For postop AF, use appropriate antithrombotic therapy and correct identifiable precipitants (U&E, low SpO2) [NICE 2014].

Atrial flutter

• Also needs rate control, risk assessment and anticoagulation.
• Beta blockade, diltiazem or digoxin for rate control.
• Cardioversion should be considered with same assessment and anticoagulation as for AF.
• AMIODARONE is useful for rapid rate control.

Remember – Anticoagulation consideration in all with AF, atrial flutter or PAF. Determine CHA2DS2VaSc score and HAS-BLED score and assess risk/benefits of anticoagulation.

Other considerations

• Control hypertension, review need for aspirin or NSAIDs, stop/reduce alcohol.
• Do not avoid anticoagulation purely on ‘risk of falls’. Quantify risk and intervene to reduce falls where possible.
• Anticoagulate
  • CHA2DS2VaSc > 1 in men
  • >2 in women.
  • If non-valvular AF (those severe MS or AS or with a metal valve must have warfarin or LMWH) then consider Warfarin or a DOAC (Apixaban, Dabigatran or Rivaroxaban, etc.).
  • High CHA2DS2VaSc score needs urgent commencement on LMWH or a DOAC or Warfarin.
  • If anticoagulation contraindicated or not acceptable then consider cardiology referral for Left atrial appendage occlusion.

Bridging anticoagulation

• Interruptions in anticoagulation can increase embolic risk.
• It is common to give LMWH bridging in the perioperative period but this may lead to risk of bleeding.
  • A recent study in the NEJM has looked at this.
    • The study excluded those with mechanical heart valves, stroke/TIA/systemic embolization within 12 weeks, major bleeding within 6 weeks, renal insufficiency, ↓? platelets or planned cardiac, brain or spinal surgery were excluded.
    • The conclusion was that bridging is not warranted for most AF patients with CHA2DS2VaSc scores of <4, for low-risk procedures.
    • This study must be interpreted along with local expert guidance balancing the risk of peri-procedure bleeding and embolic risk.

See also