Atrial Fibrillation

Atrial Fibrillation is the most common sustained arrhythmia in adults. It arises from loss of organized atrial activity, with multiple impulses sent to the AV node, causing irregular and often rapid ventricular response. Clinically, atrial fibrillation places patients at increased risk of thromboembolic events, congestive heart failure, and dementia.

Physiology

 * Originates from multiple wandering re-entrant circuits in the atria leading to disorganized atrial contractions. Atrial rate often >350bpm.
 * Ventricular response is variable due to the refractory phase of the AV node. Rates ~110-160.

Presentation

 * Stable atrial fibrillation can be asymptomatic. Some people c/o of palpitations
 * Unstable atrial fibrillation is caused by rapid uncontrolled irregular ventricular response leading to Chest pain, shortness of breath, hypotension, heart failure, death
 * Untreated AF = 5x risk of venous thromboembolism and stroke. Also, at risk of cardiomyopathy.
 * Stroke incidence related to AF increases with age, with 1.5% at age 50–59 years to 23.5% at age 80–89 years.
 * Stroke patients with AF have been found to have greater disability, longer in-hospital patient stays and lower rate of discharge home.

Etiology
Atrial fibrillation etiology mnemonic: PIRATES
 * Most common sustained arrhythmia in adults.
 * The prevalence increases with age: < 1% in those aged 55–59 years, increases to 5–15% in those 80 years of age and older
 * More prevalent in men than women: the lifetime risk of developing AF after age 55 is 24% in men and 22% in women.

P-pulmonary embolism, disease, post-op

I-Ischemic heart disease, idiopathic, infectious

R- rheumatic valvular disease

A-anemia, alcohol, age, autonomic tone

T – thyroid, toxins

E – elevated BP, electrolytes

S- sleep apnea, sepsis, surgery

ECG

 * Irregularly irregular rhythm with no distinct P waves
 * Variable ventricular rate. QRS usually narrow unless pre-existing BBB
 * Fibrillatory waves may be visible and can mimic P waves leading to misdiagnosis
 * Fine (amplitude <0.5mm) or coarse (amplitude >0.5mm)

Work-up

 * CBC, Electrolytes, TSH, Echo, +/- Holter

Atrial flutter

 * Originates from a large re-entrant circuit over a large depolarized atrial area as compared to fibrillation


 * Characteristic pattern is sawtooth waves on ECG with atrial rates of 200-350bpm

Atrial fibrillation

 * Rapid ventricular rate HR>110
 * Slow AF HR < 60
 * First episode AF
 * Recurrent AF (> 2episodes)
 * Paroxysmal AF (rhythm alternates between NSR and AF)
 * Permanent AF

Treatment
Treatment depends on the stability of the patient and the duration of the arrhythmia. Need to consider rate/rhythm control and need for anticoagulation.

Rate/Rhythm control

 * Stable patient
 * If low risk stoke (onset <48 h or therapeutic OAC -oral anticoagulation >3 weeks)
 * Cardioversion
 * Anticoagulation as per CCS algorithm criteria (see below)
 * If high risk VTE ( > 48h sx, no OAC >3 weeks, stroke/TIA < 6mts, mechanical/rheumatic valve d/o)
 * Rate control initially (B-blocker/CCB)
 * Therapeutic OAC x 3 weeks prior to outpatient cardioversion
 * Continue OAC >4 weeks post cardioversion
 * Unstable patient
 * TEE guided cardioversion (if available) + immediate OAC for > 4 weeks
 * Urgent cardioversion + immediate OAC for > 4 weeks
 * Rate controllers:
 * B-blockers, CCB.
 * Rhythm controllers:
 * Pill in pocket: good option for paroxysmal a.fib
 * Note amiodarone and procainamide are pharmocologic forms of cardioversion
 * Catheter ablation is an alternative treatment option
 * Special Case: In wolf-parkinson white with AF DO NOT USE  B-blockers or Ca channel blockers


 * ​ Blocking the AV node can lead to increased activity through the accessory pathway and lead to VT/VF
 * Screen_Shot_2015-12-13_at_2.23.58_PM.png

Anti-coagulation

 * All patients with atrial fibrillation no matter if paroxysmal or persistent should be stratified
 * Based on the CHADS2 score and age as per new CCS guidelines
 * Congestive Heart Failure -1
 * Hypertension - 1
 * Age >/= 75 years old - 1
 * Diabetes -1
 * Prior stroke/TIA - 2

Anticoagulation options

 * NOAC (new oral anticoagulant) for non-valvular AF non-inferior to warfarin
 * Dabigatran
 * Rivaroxaban
 * Apixaban
 * Warfarin/Coumadin: rheumatic mitral stenosis, eGFR < 30, mechanical valve, mitral valve repair

Extra Links/Resources
1) LITFL (All images courtesy of LITFL)

2) Canadian Cardiovascular Society Atrial Fibrillation Guidelines 2014