Atrial Fibrillation

Atrial fibrillation was the subject of a CRQ question in March 2022 (43.2% pass rate) and examiners lamented a lack of knowledge of the Resus Council's tachycardia algorithm in "the worst performing question on the paper".

Resources

Atrial fibrillation is a supraventricular tachyarrhythmia characterised by uncoordinated atrial electrical activity and consequent ineffective atrial contraction

This manifests as an absence of P-waves on ECG and the characteristic 'irregularly irregular' R-R intervals

There may, however, be regular R-R intervals if there is concomitant AV nodal block

The diagnosis of AF requires rhythm documentation with an ECG demonstrating an episode of AF of (by convention) at least 30s duration

These are muddy waters and the classification of AF seems to be an evolving beast, though the ones below are taken from the ESC guidelines
It can be grossly classified as symptomatic or unsymptomatic

Generally, it is referred to as being:

First-diagnosed AF: AF not diagnosed before, irrespective of its duration or the presence/severity of AF-related symptoms
Paroxysmal: AF that terminates spontaneously or with intervention within 7 days of onset
Persistent: AF that is continuously sustained beyond 7 days, including episodes terminated by cardioversion (drugs or electrical cardioversion) after ≥7 days
Long-standing persistent: Continuous AF of >12 months’ duration when decided to adopt a rhythm control strategy
Permanent: In short, no further attempts to restore/maintain sinus rhythm will be undertaken

AF is the commonest arrhythmia
Although the overall prevalence is in the realm of 2%, the incidence increases with age such that in the general population is 5% by 65yrs and 10% by 75yrs

It has a ∽1.5x male preponderance and is more common in Caucasians

Perioperative and critical care

AF is (naturally) also a common arrhythmia in theatre, in post-operative and critical care patients
It is more common in these patient cohorts than the general population
Peak incidence is between 2 and 4 days post-operatively

Clinical setting	Prevalence of (post-operative) AF
Vascular or major colorectal surgery	5 - 10%
Non-cardiac thoracic surgery	10 - 30%
Cardiac surgery	25 - 50%
Critical care (all-comers)	4 - 15%
Critical care (septic shock)	Up to 40%

The pathophysiology is polyfactorial, involving some blend of:

Enhanced automaticity in 'sleeves' of atrial tissue extending into the pulmonary veins or vena caval junctions

These act as trigger points to generate atrial ectopics, leading to AF
Ablation of these foci may provide a permanent cure

Multiple re-entering, randomly circulating wavelets of electrical activity which create a chaotic electrical state and maintain dysrhythmia
Electrical and structural remodelling of atrial tissue leads to shortening of refractory periods, which promotes a treatment-resistant state

This mechanism can transform paroxysmal AF into persistent AF at a rate of up to 15%/yr

Haemodynamic sequelae

Loss of atrial systole ('atrial kick') reduces LV filling and thus compromises cardiac output
Decreased diastolic filling time due to rapid ventricular rate
'Tachycardiomyopathy' i.e. a global cardiomyopathy associated with the rapid rate
Generation of atrial thrombus due to turbulent flow and subsequent risk of systemic embolism

The previously used term 'lone' AF is no longer recommended, with every case of AF felt to have underlying cause(s)
In theatre and on ICU the cause is typically due to physiological disturbance e.g. shock, sepsis, electrolyte derangement, hypoxaemia, exogeneous catecholamines
Otherwise the causes can be classified according to whether they are cardiac in nature or not:

Cardiovascular causes	Non-cardiac causes
Post-MI	Diabetes mellitus
Hypertension, esp. if LVH	Acute illness e.g. sepsis
Valvular heart disease, especially mitral	Catecholamine surges e.g. stress, surgery, phaeochromocytoma, exogenous infusions, SAH
Myocarditis or pericarditis or endocarditis	Pulmonary embolism
Congenital cardiac disease esp. ASD	Pulmonary HTN inc. that due to OSA
Sick sinus syndrome	Alcohol (binges)
Cardiac surgery	Hyperthyroidism
Atrial myxoma	Electrolyte disturbances, particularly hypokalaemia
	Stimulants e.g. caffeine, nicotine

Symptoms	Signs
Palpitation	Myocardial ischaemia
(Pre-)syncope	Tachycardia (typically 120-180bpm)
Dyspnoea	Hypotension
Chest tightness/pain	Acute cardiac failure ± pulmonary oedema
Fatigue/lethargy	Cardiogenic shock
Reduced exercise tolerance	Loss of 'a' wave and 'x' descent on JVP

Outcome	Notes
Stroke	AF responsible for 20 - 30% if ischaemic stroke
LV dysfunction or failure	Occurs in 20 - 30% of patients with AF
Cognitive decline	Hazard ratio 1.4 (independent of stroke history)
Vascular dementia	Hazard ratio 1.6 (independent of stroke history)
Depression	In 16 - 20%
Post-operative complications	↑ Infections ↑ Bleeding ↑ Renal complications
↓ QoL	QoL impaired in >60% of patients
Hospitalisation	10 - 40% of AF patients annually ↑ Length of stay ↑ Healthcare costs
Mortality	↑ 1.5 - 3.5x vs. baseline

Management of AF involves:

Restoring sinus rhythm
Maintaining sinus rhythm
Restoring an acceptable heart rate
Reducing the risk of thromboembolic sequelae

Step 1: Cardiovert to sinus rhythm

In short, follow the Resus Council tachycardia algorithm
Amiodarone is often a winner, with a reported 80% cardioversion rate
Slightly more left-field Class III anti-arrhythmic agents have also been used, such as the 'kalants' (vernakalant and nifekalant) and ibutilide

They are purportedly specific to ion channels in atrial cardiac myocytes, thus mitigating some of the negative effects of more generalised anti-arrhythmics
Only vernakalant is licensed by NICE, and appears to rapidly cardiovert AF to sinus rhythm following IV administration
Presumably these come under the "seek expert help" part of the Resus Council algorithm…

Steps 2 & 3: Maintenance therapy and rate control

Multiple studies from the early 2000's (AFFIRM, RACE, PIAF and STAF) concluded rate control was preferable to rhythm control, although the latter prevents long-term atrial remodelling
The minutiae of which drug to choose to acheive this, from the smorgasbord of available agents, is beyond the necessary level of detail
An array of drugs are suitable, including Class 1C sodium channel antagonists, beta-blockers, digoxin, non-DHP calcium channel antagonists and amiodarone
Although amiodarone is highly effective at preventing relapse, its extra-cardiac toxic effects make it a less suitable first line maintenance agent
Which rate to aim for? The ESC guidelines aim for <100bpm in post-operative AF

Perioperative and critical care

Management in this setting is largely the same
DCCV of new-onset AF with haemodynamic instability in the critical care setting has a success rate of 48 - 100%, but the recurrence rate appears to be about 15%
Amiodarone is often next in the barrel of the syringe, but in terms of cardioverting AF it may be:

Only equally effective as other agents such as magnesium and diltiazem
Less effective than beta blockers (esmolol or metoprolol) or flecainide

Which to choose?
The ESC guidelines cite a "lack of evidence from large RCTs" in the acute drug treatment of perioperative AF, but go on to say that "amiodarone is the most frequently used drug for prevention of perioperative AF"
The above-linked systematic review follows suit, stating they are "unable to distinguish a hierarchy of effectiveness between direct current cardioversion, amiodarone, β-antagonists, calcium channel blockers, and magnesium at achieving cardioversion to sinus rhythm or heart rate control in new-onset AF"

If the patient has AF of any type, you need to consider anticoagulating them to reduce thromboembolic risk
The ESC say: "[The] clinical pattern of AF (first-detected, paroxysmal, permanent, persistent, long-standing persistent) should not condition the indication to thromboprophylaxis"

Stroke risk in AF is stratified according to the CHA₂DS₂-Vasc score

It determines the 1yr risk of thromboembolism in a patient with non-valvular AF
All patients with a CHA₂DS₂-Vasc score ≥2 should be offered anticoagulation
All men with a CHA₂DS₂-Vasc score >1 should be offered anticoagulation

The plot thickens, however, as one must also assess the bleeding risk in these patients to be able to engage in a risk/benefit, shared decision with them
NICE say we should use the ORBIT score to do this, the ESC say we should use HAS-BLED

Anticoagulants

First line:

Apixaban 5mg BD [or 2.5mg BD in those with certain criteria]
Edoxaban 60mg OD [or 30mg if weight <61kg]
Rivaroxiban 20mg OD
Dabigatran 110 - 150mg BD [depends on age]

Second line:

Vitamin K antagonist i.e. warfarin with target INR 2-3

Perioperative management of the patient with atrial fibrillation

History and examination, with focus on:

AF-related symptoms and pattern of disease
Concomitant cardiovascular and pulmonary comorbidities

Investigations

FBC, U&E, LFTs, clotting screen ± TFT's
Consider BNP/NT-ProBNP, troponin and CRP
12-lead ECG ± ambulatory monitoring
TTE if concern about myocardial or valvular function
Cardiovascular functional capacity assessment e.g. CPET
Consider:

CTCA/Angiography in those with concerns over CAD
Brain CT/MRI in those with suspected CVA

Optimisation

Ensure rate control optimised prior to elective surgery and taken on morning of surgery
Ensure electrolytes inc. Mg²⁺ within normal range
Consider first on list to reduce dehydration
Liaise with surgical and haematological colleagues about perioperative anticoagulation
Consider HDU bed if significant cardiovascular comorbidities

Maintain normal homeostatic milieu to avoid decompensation, in particular:

Avoid hypoxia or hypercarbia
Avoid hypovolaemia
Avoid acidosis
Maintain normal potassium and magnesium levels

If AF does occur, one should:

Correct any underlying physiological derangements as above
Rate control the AF with a β-blocker, amiodarone or diltiazem

Outside the domain of cardiac surgery, there is no need for prophylactic anti-arrhythmics
The ESC say: "beta-blockers should not be used routinely for the prevention of post-operative AF in patients undergoing non-cardiac surgery"

Continue rate control medication
Follow pre-operative anticoagulant plan inc. appropriate 'bridging' or other VTE prophylaxis
Multi-modal analgesia; avoid catecholamine surges
Multi-modal anti-emesis; avoid dehydration and electrolyte disturbances

New AF in the post-operative period should be managed as per the sections above; amiodarone or beta-blockers are likely to be the pharmacological agents of choice
COP-AF is an ongoing RCT of whether colchicine reduces perioperative AF and myocardial injury vs. placebo in patients undergoing major, non-cardiac thoracic surgery