Circulation

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

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Presentation below by Dr Dave Sharman (Cons Cardiologist – click the pic!)

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