Atrial Fibrillation

OVERVIEW

Atrial fibrillation (AF) is the most common sustained dysrhythmia and is characterised by disorganised atrial electrical activity and contraction resulting in an “irregularly irregular” ventricular response (“fibrillation waves”)

• AF may be acute, transient, paroxysmal, or chronic and may or may not be rate-controlled
• Patients with AF may be stable or unstable
• AF has multiple possible underlying causes
• The incidence and prevalence of AF is increasing, with a lifetime risk for people over the age of 40 years of ~25%
• AF prevalence increases with age
• AF is a common occurrence post cardiac surgery (10-40%, typically day 2 to 3)

CAUSE

The classification below is according to pathophysiological mechanism

• Alternatively, can causes can be classified according to a ‘surgical sieve’ (e.g. vascular, inflammatory, trauma, etc)

Catecholamine excess or increased sensitivity

• Exogenous (eg. adrenaline infusion, hydrocarbon exposure)
• Endogenous
  • Subarachnoid haemorrhage
  • Stress
  • Phaeochromocytoma
  • Thyrotoxicosis

Atrial distension

• Pulmonary hypertension
  • primary
  • secondary, such as OSA, PE, pulmonary fibrosis
• Septal defects
• Valvular disease (e.g. mitral stenosis), including infective endocarditis

Abnormality of conducting system

• Congenital cardiac disease, eg. septal defect
• Infiltrative cardiac disease, eg. amyloidosis, sarcoidosis
• Ischaemic heart disease
• Age-related fibrotic changes
• Haemochromatosis/iron overload
• Hypothermia

Increased atrial automaticity / irritation

• Alcohol (“holiday heart”)
• Caffeine
• Catecholamines
• Electrolyte derangement (hypokalaemia, hypomagnesaemia)
• Myocarditis

COMPLICATIONS

Adverse effects on haemodynamics:

• loss of atrial systole (aka “atrial kick”) (normally responsible for about 20% of ventricular filling)
• Decreased diastolic filling time due to tachycardia
• Rate-related cardiomyopathy (can occur over weeks)

Atrial thrombus formation

• Systemic embolism, especially stroke
• Pulmonary embolism

Annual risk of embolic stroke from AF

• The CHA₂DS₂-VASc scoring system is recommended for estimating the risk of stroke (Lip et al, 2002; January et al, 2014)
• There are 3 categories:
  • score 0: negligible risk of stroke (~ 0%/y) (very few patients!)
  • score 1: 1.3%/y risk of stroke
  • score >1 (2 or more): >2.2% risk of stroke (high risk category)
• The maximum score of 9 predicts a 15.2%/y risk of stroke
• A CHA2DS2VASC calculator is available on MDCalc

C	Congestive heart failure (or Left ventricular systolic dysfunction)	1
H	Hypertension: blood pressure consistently above 140/90 mmHg (or treated hypertension on medication)	1
A2	Age ≥75 years	2
D	Diabetes Mellitus	1
S2	Prior Stroke or TIA or thromboembolism	2
V	Vascular disease (e.g. peripheral artery disease, myocardial infarction, aortic plaque)	1
A	Age 65–74 years	1
Sc	Sex category (female sex score 1 point)	1

INVESTIGATIONS

Bedside

• 12 lead ECG
• blood gas (e.g. hypokalaemia)

Laboratory

• UEC (e.g. hypokalaemia)
• CaMgPO4 (e.g. hypomagnesemia)
• FBC (e.g. anaemia)
• TFTs (e.g. hyperthyroidism)

Imaging

• CXR (e.g. cardiomegaly, atrial dilation, pulmonary odema, other lung disease)
• Echocardiography (e.g. structural heart disease, TOE to exclude atrial thrombus)

MANAGEMENT

Resuscitation

• address life threats, determine if stable or unstable
• Unstable features (if significant and attributable to AF)
  • chest pain
  • dyspnoea
  • heart failure
  • hypotension
• Electrical cardioversion
  • start at 100J (synhronised), then increased to 150J (ALS guidelines, in practice 50J may be successful)
  • provide procedural sedation

Specific treatments for stable AF patients (see below)

• rate control versus rhythm control
• anticoagulation

Seek and treat underlying cause and complications

• replace electrolytes (e.g. K > 4 mmol/L, Mg > 0.9 mmol/L)
• treat cause (e.g. ischaemia, sepsis, thyroid function)

Ablation therapy is indicated if:

• permanent AF where ventricular rate difficult to control and persistent symptoms/LV dysfunction
• rate-related cardiomyopathy due to refractory AF
• refractory symptomatic paroxysmal AF

Disposition

• stable patients may be discharged with outpatient follow up following cardioversion or rate-control
• cardiology referral for patients requiring specialist follow-up
• patients with a significant underlying cause or comorbidities require admission to hospital
  • some require cardiac monitoring
  • those with critical illness require HDU/ ICU

RATE CONTROL VERSUS RHYTHM CONTROL

Rate control with anticoagulation is the strategy of choice, rather than rhythm control, for most patients

• Prior to the 2000s, rhythm control was preferred due to theoretical benefits from preventing cardiac remodelling due to chronic AF
• However, rate control was supported by a number of studies from the early 2000s (AFFRIM, RACE, STAF, and PIAF)
• A subsequent meta-analysis of 8 high-quality studies (n=7499) by Caldeira et al, 2012 found:
  • no clear survival benefit for rate control over rhythm control
  • composite endpoint (death, stroke and recurrent hospitalisation) favours rate-control

Rate control strategies

• Recommendations based on the 2014 AHA guideline:
  • β-blocker or calcium channel blocker for paroxysmal AF
    • can be given IV if hemodynamically stable (CCBs preferred in COPD patients)
  • IV amiodarone for critically ill patients
  • AV nodal blockade (e.g. BB, CCB, amiodarone) is not recommended in patients with pre-excitation (e.g. Wolff-Parkinson-White) – procainamide (not widely available in Australia) or electrical cardioversion is the better choice
  • avoid calcium channel blockers in decompensated heart failure (digoxin or amiodarone are preferred). Combination of digoxin and a β-blocker recommended for long-term management of compensated heart failure patients.
  • target a rate of 80 as the endpoint, however, higher rates (e.g. ~110/min) are acceptable in stable patients with preserved LV function
• Digoxin is slow acting and ineffective in patients with increased sympathetic tone (most critically ill patients)

Rhythm control strategies

• DC cardioversion
  • essential in unstable patients
  • is also an effective strategy when performed electively using procedural sedation within 48 hours of AF onset or later following adequate anticoagulation and TOE
• Pharmacological options for cardioversion can be used in hemodynamically stable patients
  • amiodarone
  • flecanide (only an option in structurally normal hearts, as associated with sudden cardiac death in structurally abnormal hearts)
  • propafenone
  • vernakalant
• Options for maintenance of sinus rhythm inlcude:
  • amiodarone
  • disopyramide
  • flecanide
  • sotolol

ANTICOAGULATION STRATEGIES

2014 AHA recommendations for anticoagulation:

• No anticoagulation is reasonable choice if the AF <48 hours and the CHA₂DS₂-VASc score is 0
  • risk of stroke is 0.2% pa
  • If AF <48 hours and the score is >0, therapeutic anticoagulation (e.g. IV heparin, enoxaparin)
• If AF >48 hours: therapeutic anticoagulation (e.g. IV heparin, enoxaparin)
• Anticoagulation should continue for at least 3 weeks before and 4 weeks after TOE-cardioversion
  • aspirin is an option if CHA₂DS₂-VASc score =1
  • Warfarin (INR 2-3) or equivalent if CHA₂DS₂-VASc score >1 (e.g. all patients >75-years-old)

The effectiveness of different anticoagulation therapies for stroke prevention per year:

• Warfarin: RRR 62%; ARR 2.8%
• Aspirin: RRR 22%; ARR 1.5%
• Warfarin plus aspirin: no additional benefit over warfarin alone
• Dabigatran: RRR 35% compared to warfarin

Benefits of anticoagulation should always be weighed against the harms (e.g. falls risk, coexistent bleeding diathesis)

• No anticoagulation is also reasonable if there is increased bleeding risk and/or AF is likely transient (e.g. post-cardiac surgery, many ICU patients)

CONSIDERATIONS IN THE ICU MANAGEMENT OF ATRIAL FIBRILLATION

Most textbooks and literature focus on the management of AF in the ward, emergency department, or outpatient setting.

Differences in the ICU include:

• AF is often transient (only about 15% of patients with AF in ICU will still be in AF at the time of ICU discharge (Artucio et al, 1990).
• AF is usually caused by reversible, non-cardiac underlying illnesses (Kanji et al, 2012), such as hypoxia, electrolyte abnormalities, and sepsis
• implications for patient outcomes are different for ICU patients with AF
  • unclear if AF is a cause of, or secondary marker of, greater illness severity in ICU patients overall
  • death from stroke is less likely
  • multi-organ dysfunction is more likely (e.g. worsening shock state)
• a standardised approach to pharmacotherapy is lacking (Kanjii et al, 2008)
  • Amiodarone is commonly used but has a relatively poor cardioversion success rate (40-76% at 12 h)
  • Cardioversion success rate at 12h for other options:
    • Esmolol and flecainide: 60-100%
    • Magnesium: 51-93%
• many ICU patients with AF have a higher risk of bleeding (e.g. post-cardiac surgery), so anticoagulation for persistent AF is typically delayed

OTHER CONSIDERATIONS

If AF with slow ventricular response, suspect:

• Severe AV nodal disease
• Hypothermia
• Medications: Digoxin toxicity, Calcium-channel blocker / beta-blocker toxicity

References and Links

FOAM and web resources

• Wiesbauer F. Atrial Fibrillation Management Essentials. Medmastery
• Academic Life in EM — Paucis Verbis card: Anticoagulation in Atrial Fibrillation
• Crashingpatient.com — Dysrhythmias
• EMCrit Podcast 20 – The Crashing Atrial Fibrillation Patient

Journal articles

• Van Gelder IC, Hagens VE, Bosker HA, Kingma JH, Kamp O, Kingma T, Said SA, Darmanata JI, Timmermans AJ, Tijssen JG, Crijns HJ; Rate Control versus Electrical Cardioversion for Persistent Atrial Fibrillation Study Group. A comparison of rate control and rhythm control in patients with recurrent persistent atrial fibrillation. N Engl J Med. 2002 Dec 5;347(23):1834-40
• Wyse DG, Waldo AL, DiMarco JP, Domanski MJ, Rosenberg Y, Schron EB, Kellen JC, Greene HL, Mickel MC, Dalquist JE, Corley SD; Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) Investigators. A comparison of rate control and rhythm control in patients with atrial fibrillation. N Engl J Med. 2002 Dec 5;347(23):1825-33
• Hohnloser SH, Kuck KH, Lilienthal J. Rhythm or rate control in atrial fibrillation–Pharmacological Intervention in Atrial Fibrillation (PIAF): a randomised trial. Lancet. 2000 Nov 25;356(9244):1789-94.
• Carlsson J, Miketic S, Windeler J, Cuneo A, Haun S, Micus S, Walter S, Tebbe U; STAF Investigators. Randomized trial of rate-control versus rhythm-control in persistent atrial fibrillation: the Strategies of Treatment of Atrial Fibrillation (STAF) study. J Am Coll Cardiol. 2003 May 21;41(10):1690-6.
• Kanji S, Stewart R, Fergusson DA, McIntyre L, Turgeon AF, Hébert PC. Treatment of new-onset atrial fibrillation in noncardiac intensive care unit patients: a systematic review of randomized controlled trials. Crit Care Med. 2008 May;36(5):1620-4
• Morrison LJ, Deakin CD, Morley PT, Callaway CW, Kerber RE, Kronick SL, Lavonas EJ, Link MS, Neumar RW, Otto CW, Parr M, Shuster M, Sunde K, Peberdy MA, Tang W, Hoek TL, Böttiger BW, Drajer S, Lim SH, Nolan JP; Advanced Life Support Chapter Collaborators. Part 8: Advanced life support: 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. Circulation. 2010 Oct 19;122(16 Suppl 2):S345-421.
• Lip GY, Nieuwlaat R, Pisters R, Lane DA, Crijns HJ. Refining clinical risk stratification for predicting stroke and thromboembolism in atrial fibrillation using a novel risk factor-based approach: the euro heart survey on atrial fibrillation. Chest. 2010 Feb;137(2):263-72.
• Caldeira D, David C, Sampaio C. Rate versus rhythm control in atrial fibrillation and clinical outcomes: updated systematic review and meta-analysis of randomized controlled trials. Arch Cardiovasc Dis. 2012 Apr;105(4):226-38
• Kanji S, Williamson DR, Yaghchi BM, Albert M, McIntyre L; Canadian Critical Care Trials Group. Epidemiology and management of atrial fibrillation in medical and noncardiac surgical adult intensive care unit patients. J Crit Care. 2012 Jun;27(3):326.e1-8
• Arrigo M, Bettex D, Rudiger A. Management of atrial fibrillation in critically ill patients. Crit Care Res Pract. 2014;2014:840615.
• January CT, Wann LS, Alpert JS, Calkins H, Cigarroa JE, Cleveland JC Jr, Conti JB, Ellinor PT, Ezekowitz MD, Field ME, Murray KT, Sacco RL, Stevenson WG, Tchou PJ, Tracy CM, Yancy CW; ACC/AHA Task Force Members. 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on practice guidelines and the Heart Rhythm Society. Circulation. 2014 Dec 2;130(23):2071-104
• Sibley S, Muscedere J. New-onset atrial fibrillation in critically ill patients. Can Respir J. 2015 May-Jun;22(3):179-82
• Yoshida T, Fujii T, Uchino S, Takinami M. Epidemiology, prevention, and treatment of new-onset atrial fibrillation in critically ill: a systematic review. J Intensive Care. 2015 Apr 23;3(1):19.

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