Atrial Fibrillation
last authored: March 2011, David LaPierre
last reviewed:
Introduction
Atrial fibrillation (AF) is a heart rhythm in which the atrial rate is so fast, or so chaotic, that discrete P waves are no longer discernible. Ventricular rate is irregularly irregular and is frequently 140-160 bpm.
AF can be paroxysmal, with self-limiting episodes of less than 7 days. Persistent AF lasts greater than one week and requires medication or cardioversion to restore rhythm. Permanent AF is present when sinus rhythm cannot be restored.
AF can be asymtomatic, or it can be serious. Rapid ventricular rates can decrease cardiac output, leading to presyncope, fatigue, and poor function. Severe symptoms include angina, syncope, and dyspnea. Atrial thrombi often form, particularly in the left atrial appendage, posing risk for emobolus and infarction, most ominously in the brain as a stroke. Up to 15% of strokes are caused by AF, which leads to a 3-5 fold increase in stroke. Lastly, in patients with electrical conductance problems, AF can lead to a rapid ventricular tachycardia that can end in ventricular fibrillation and death. Mortality doubles in age-matched people.
AF is extremely common; over 20% of people over 40 will develop it. AF affects 5% of people over 70, 10% of people over 80%.
Atrial flutter is a related condition, in which atrial rate is often 250-350. There is usually 2:1 or 4:1 conduction, so pulse is frequently regular.
The Case of Tony Liu
Tony is a 86 year-old man who comes to you with palpitations that have been present for 2 days. He is otherwise asymptomatic. You check his pulse, and his rate is 134 and irregular.
- is this atrial fibrillation?
- what do you do?
Causes and Risk Factors
Aging, hypertension, and heart failure are the most common causes.
It is important to first assess for reversible causes:
- alcohol
- caffeine
- hyperthyroidism
Other risk factors include:
- male sex
- valvular heart disease
- coronary artery disease
- acute myocardial infarction
- pulmonary embolus
- cardiomyopathy
- sick sinus syndrome: ECG diagnosis (sinus bradycardia, sinus arrest, tachyarrhytmia)
- cardiac surgery
- pericarditis: viral, tumour infiltration
- WPW: Wolff-Parkinson-White syndrome: accessory bundle
- lung cancer
- idiopathic
Pathophysiology
Atrial fibrillation frequently follows atrial fibrosis, stretching, or injury. This can occur with hypertension, heart failure, or mitral stenosis.
The sino-atrial (SA) node can become fibrotic or sclerotic, and the atrioventricular (AV) node will only allow so many beats through.
Atrial ectopy can trigger fribrillation, using triggered or automatic. An abnormal atrium, scarred and stretched, is easily put into fibrillation by triggers, due to easy reentry.
Signs and Symptoms
- history
- physical exam
History
Some people with AF can be asymptomatic, while others can feel terrible. Symptoms can include:
- palpitations
- fatigue
- dyspnea
- lightheadedness/pre-syncope/syncope
- chest pain/angina (if with coronary artery disease)
- symptoms of congestive heart failure (if with valvular disease)
Symptoms of stroke can follow embolus with AF.
Physical Exam
An irregularly irregular, rapid pulse is the classic finding with atrial fibrillation.
Other signs include:
- variable first heart sound
- variable systolic blood pressure
- absent a wave on JVP
Assess heart rate at heart apex, as some beats will not be palpable at the wrist.
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
TSH is helpful to screen for hypothyroidism.
INR/PT is necessary for patients who will be treated with warfarin
Diagnostic Imaging
EKG is diagnostic, revealing fibrillations without P waves. QRS complexes are often irregularly irregular. It is difficult to diagnose exactly how long AF must be present to pose a risk, but American and European guidelines suggest at least 30 seconds.
A stress test can be used to exacerbate abnormal rhythms. A 24-hour Holter monitor can be used to assess response to medication. A loop monitor can be useful for symptoms that occur a few times monthly.
Chest X ray may detect cardiomyopathy.
CT with pulmonary angiography, or ventilation-perfusion scan, can be done if pulmonary embolus is suspected.
Echocardiography can detect valvular heart disease or heart failure.
Transesophageal echo can be done to identify atrial thrombus if cardioversion is planned.
Differential Diagnosis
The differential includes:
- multifocal atrial tachycardia
- sinus tachycardia with frequent premature atrial beats
- atrial flutter
Treatments
Treatment depends on diagnosis and underlying disease, desire for rhythm vs rate control, and risk of stroke.
- anticoagulation
- rate control
- rhythm control
- cardioversion
- electrical ablation
Anticoagulation
All patients with atrial fibrillation should be on anticoagulation, but the specific medication depends on risk of stroke.
CHADS2 (low risk =0, med=1, high>2)
|
CHA2DS2-VASc (low risk =0, 1 high risk >2
|
Low risk - ASA 81-325 mg, or clopidogrel.
Medium or high risk - warfarin (INR of 2-3), or dabigatran. Warfarin is an effective drug, but can be very difficult to maintain patients as therapeutic and requires frequent monitoring by bloodwork. Supertherapeutic levels increase the risk of bleeding.
Dabigatran is a direct thrombin inhibitor that does not require INR monitoring. The risk of bleeding is the same as that of warfarin, but the risk of intracranial bleeding is about half of warfarin. The major side effect is GI symptoms
If a mechanical heart valve, or mitral stenosis, is present, INR should be 2.5-3.5. Dabigatran is not indicated
HAS-BLED is a validated tool used to calculate risk for bleeding. A score of three or more predicts increased risk for bleeds (Pisters et al, 2010).
Hypertension
Abnormal renal, liver function
Sroke
Bleeding history or disposition
Labile INR
Elderly (>65)
Drugs or alcohol concurrent use
Rate Control
- beta blockers: propanalol, metoprolol, atenolol, nadalol
- non-dihydropyridine calcium channel blockers (verapamil, diltiazem)
- digoxin may be used in the elderly; in younger people, heart rate will increase with activity
- amiodarone, more acute
AVN ablation and pacing.
For patients with AF and HF, rate control = rhythm control in terms of cardiovascular mortality. Rate control reduces cardioversion and hospitalization, and should be the primary approach
Rhythm control
Electrical cardioversion
pharmacological cardioversion - amiodorone.
drugs to maintain NSR. Antiarrhytmics can have adverse effects.
Cardioversion
Cardioversion should be carried out if the patient is hemodynamically unstable, and may be considered if AF has been present for less than 48 hours.
If arrhythmia has been present for >48 hours, cardioversion should not be done unless systemic anticoagulation has been given for at least three weeks.
2 days of symptoms - check for clot with TEE
warfarin for 3 weeks, and consistently therapeutic
cardioversion
1 month post-cardioversion of treatment
emergent cardioversion
Heparin or LMWH bolus, cardiovert, treat with warfarin.
electrical ablation:
AIFFIRM 2002: rhythm control (cardioversion + antiarrhytmics) vs rate control (beta blocker plus digoxin). Very similar, but rate control appeared better.
Pulmonary vein ablation vs AV node ablation.
PVI: 6 months post, 80% AF-free.
Kahn et al. 2008. NEJM
AV-node ablaion and BVI:
- long-standing, persistent AF
- LA diameter 55-60
- bradycardia
- need for ICD
LA ablation
- absence of previous features
- paroxysmal AF
Consequences and Course
AF can cause atrial thrombus in appendage.
The thromboemboli are bigger for A-Fib.
can also get tachycardia-induced cardiomopathy
HF can predispose for AFib, while AFib can cause or worsen CHF.
Additional Resources
Pisters R. 2010. A novel user-friendly score (HAS-BLED) to assess 1-year risk of major bleeding in patients with atrial fibrillation: the Euro Heart Survey. Chest. 138(5):1093-100.
ccsguidelineprograms.ca
Topic Development
authors:
reviewers:
 |