Atrial fibrillation (Afib) is a common type of supraventricular tachyarrhythmia characterized by uncoordinated atrial activation that results in an irregular ventricular response. While the exact mechanisms of Afib are poorly understood, associations with a number of cardiac (e.g., valvular heart disease, coronary artery disease) and noncardiac (e.g., hyperthyroidism, electrolyte imbalances) risk factors have been established. Individuals with Afib are typically asymptomatic. When symptoms do occur, they usually include palpitations, lightheadedness, and shortness of breath. Physical examination typically reveals an irregularly irregular pulse. Ineffective atrial emptying as a result of Afib can lead to stagnation of blood and clot formation in the atria, which in turn increases the risk of stroke and other thromboembolic complications. Diagnosis is confirmed with ECG showing absent P waves with irregular QRS intervals. Echocardiography is used to rule out structural heart disease and to evaluate for any atrial thrombi. Immediate synchronized cardioversion is required in hemodynamically unstable patients. In stable patients, treatment involves the correction of modifiable risk factors, rate or rhythm control strategies, and anticoagulation. Rate-control therapy typically involves the use of beta blockers or nondihydropyridine calcium channel blockers. Rhythm control strategies include synchronized electrical cardioversion, the use of pharmacological antiarrhythmics (e.g., flecainide, propafenone, or amiodarone), and ablation of the arrhythmogenic tissue. Patients are typically started on anticoagulation depending on their thrombotic and bleeding risk.
Atrial flutter is another common type of supraventricular tachyarrhythmia that is usually caused by a single macroreentrant rhythm within the atria. The risk factors for atrial flutter are similar to those of Afib. In atrial flutter, the ventricular rhythm is usually regular. Treatment is also similar to that of Afib, consisting of anticoagulation and strategies to control heart rate and rhythm. Atrial flutter is typically more responsive to than Afib. Atrial flutter frequently progresses to Afib.
Risk factors 
|Risk factors for atrial fibrillation|
|Cardiovascular risk factors|
|Intrinsic cardiac disorders|| |
|Noncardiac disorders|| |
Reversible causes of atrial fibrillation 
- Hyperthyroidism, thyrotoxicosis
- Electrolyte imbalances
- Cardiothoracic surgery
- Myocardial infarction
- Alcohol use
- Excess caffeine
- Fever of any cause
- Recreational or pharmacological drug use
- Pulmonary embolism
- Other triggers of tachycardia: e.g., pain, hypovolemia, anemia
Remember PARASITE to memorize the major risk factors for acute Afib: P – Pulmonary disease; A – Anemia; R – Rheumatic heart disease; A – Atrial myxoma; S – Sepsis; I – Ischemia; T – Thyroid disease; E – Ethanol.
Hemodynamic stability 
- Unstable Afib: Afib manifesting with signs of hemodynamic instability (e.g., chest pain, altered mental status, acute pulmonary edema, hypotension, or cardiogenic shock)
- Stable Afib: Afib without signs of hemodynamic instability
Ventricular rate 
- Afib with rapid ventricular response: Afib with a ventricular rate > 100–110/minute (tachycardic Afib) 
- Afib with slow ventricular response: Afib with a ventricular rate < 60/minute (bradycardic Afib or slow Afib) 
Onset and duration 
- Paroxysmal Afib: Afib that resolves within 7 days of onset either following treatment or spontaneously; the frequency of recurring episodes may vary.
- Persistent Afib: continuous Afib for > 7 days
- Long-standing persistent Afib: continuous Afib for > 1 year
- Permanent Afib: persistent Afib in which therapeutic attempts are no longer made to convert to or maintain sinus rhythm unless the patient and the treating physician agree to do so 
Method of detection 
- Clinical Afib: an episode of Afib lasting ≥ 30 seconds that is documented on a surface ECG; may be symptomatic or asymptomatic
- Subclinical Afib: asymptomatic Afib not previously detected on a surface ECG that is discovered on implanted cardiac devices and confirmed on intracardiac electrograms 
Valvular heart conditions 
Moderate to severe mitral stenosis or a mechanical heart valve
- Significantly increased risk of thromboembolic events
- Previously classified as valvular Afib 
- Any other valvular heart disease or no valvulopathy
Patients with Afib should always be evaluated for mitral valve involvement!
- Atrial fibrillation is a .
- The exact mechanisms of Afib are not well understood. Suggested mechanisms include:
The new onset of Afib triggers a vicious circle that can ultimately lead to long-standing Afib with atrial remodeling:
- Afib is triggered by one or both of the following
- Afib is sustained by re-entry rhythms and/or rapid focal ectopic firing
- Electrophysiological changes in the atria occur within a few hours of Afib onset (electrical modeling).
- If Afib persists, atrial fibrosis and dilatation (structural remodeling) occur within a few months.
- Electrical and structural remodeling increase susceptibility to Afib, resulting in a vicious circle.
- Effects of Afib
- All patients
- : more likely to occur in patients with Afib with RVR and/or underlying cardiopulmonary disease
- Complications of Afib
Individuals with Afib may be asymptomatic for a long time before a diagnosis is made.
- Diagnostic confirmation
- Identification of the underlying (e.g., , )
- Evaluation for factors that affect treatment
- Comorbid conditions: e.g., ,
- Complications: e.g., ,
- Initial investigative study to confirm Afib
- Signs of comorbid conditions and/or underlying etiologies 
|Characteristic ECG findings in atrial fibrillation |
|P waves|| |
|QRS complex|| |
Wide QRS complex may indicate or .
Laboratory studies 
- CBC: assessment for anemia and signs of infection
- Serum electrolytes (Na+, K+, Mg2+, and Ca2+): to identify electrolyte imbalances
- BUN, serum creatinine: to identify chronic kidney disease (CKD) 
- Coagulation studies: to guide anticoagulation therapy
Additional cardiac evaluation is guided by clinical suspicion.
- : e.g., troponin
- : e.g., and/or BNP or NT-proBNP 
- Others: See “CAD diagnostics” and “Diagnosis of hypertension.”
Obtain additional laboratory studies based on suspected underlying etiology, e.g.:
- TFTs: to screen for thyrotoxicosis
- : e.g., D-dimer levels in patients with low Wells score for PE 
- Goal: to assess cardiac function and rule out underlying structural heart disease (e.g., mitral valve stenosis)
- New Afib diagnosis
- Known Afib with clinical deterioration of unclear etiology
Echocardiographic findings in Afib 
- The heart may be structurally normal (more common in young people).
- Left atrial thrombus may be visible
- Atrial enlargement
- Chaotic atrial movements that are not coordinated with ventricles
- Decreased left atrial compliance and volume
- Evidence of underlying etiology, e.g., ↓ LVEF (due to cardiomyopathy), valvular heart disease, pericardial effusion
TEE for Afib 
- Indications (prior to cardioversion)
- Findings of concern
TEE is usually not required for patients undergoing and those undergoing who have Afib onset < 48 hours or have received ≥ 3 weeks of therapeutic anticoagulation. 
Chest imaging 
- Goal: to evaluate for underlying cardiopulmonary comorbidities or etiologies
- CXR: e.g., , ,
- : See “Findings” in “CTPA.”
Cardiac rhythm monitoring 
- Findings: episodes of paroxysmal Afib; may reveal additional arrhythmias, e.g., atrial flutter
- Cardiac stress test: if underlying ischemic heart disease is suspected or to assess the adequacy of rate control 
- EP study 
- Sleep study: if obstructive sleep apnea is suspected 
- Palpitations 
- Other symptoms
Irregularly irregular may represent Afib with , , or . If in doubt, treat it as .
The differential diagnoses listed here are not exhaustive.
Tachycardic or unstable patients
- Unstable Afib: Perform emergency electrical cardioversion (see “Management of unstable tachycardia” for details).
- Heart rate > 100–110/minute: Start .
- Suspected : See “Afib with WPW.”
Patients with unstable Afib should be treated with immediate electrical cardioversion!
New diagnosis in stable patients 
- Onset ≥ 48 hours or unknown
Onset < 48 hours
- Consider or on an individual basis.
- See “ ” for details.
- Begin if favored by risk assessment.
- Identify and treat reversible causes of Afib.
- Provide supportive care for Afib.
- Manage complications.
Patients with known Afib
- For acutely decompensated rapid Afib, see “Afib with RVR.”
- For all other stable patients:
- Assess adherence to therapy (e.g., rate control medications, anticoagulation for Afib).
- Identify and manage .
- Evaluate for and address conditions that could alter treatment efficacy (e.g., new-onset AKI, medication interactions).
- Follow any existing treatment plan for rate control or rhythm control.
- Consult the patient's treating cardiologist as needed.
- Manage complications and comorbid conditions on an individual basis.
Supportive care for Afib
The following measures can be applied in inpatient or outpatient settings.
- Optimize long-term therapy for chronic underlying Afib etiologies and related comorbidities.
- Manage OSA management, reduction of alcohol consumption.  and encourage lifestyle modifications, e.g., weight loss, exercise,
- Monitor kidney and liver function regularly for patients on anticoagulation. 
- Educate patients on thromboembolism, and risks of anticoagulation and/or antiarrhythmic drugs. , risk of
- The workup and management of new stable Afib are typically started in emergency care settings and can continue in inpatient or outpatient settings depending on multiple factors, e.g.:
- For emergency department patients, follow local protocols for hospital admission vs. discharge with rapid follow-up in consultation with a cardiologist.
- For inpatients who develop new Afib or experience recurrence or decompensation, consult cardiology.
There are two strategies for arrhythmia treatment in patients with Afib: , which aims to reduce the heart rate, and , which aims to restore normal sinus rhythm. For the management of patients with Afib with RVR,” “Afib with WPW,” and “Management of unstable tachycardia.”, see “
Rate control vs. rhythm control 
There are no strict indications for either strategy. The choice should involve risk factors and preferences. with a specialist and varies based on disease characteristics and comorbidities, prior treatment responses, and individual patient
Rate control is typically favored 
- Longstanding persistent or recurrent Afib 
- High risk of thromboembolism, e.g., new Afib with onset ≥ 48 hours or unknown, known atrial thrombus, suboptimal anticoagulation
- High risk of adverse reactions to pharmacological cardioversion or electrical cardioversion
Rhythm control is typically favored 
- Recent-onset (< 12 months) Afib with known cardiovascular disease, especially heart failure 
- Patients < 70 years of age 
- Failure of prior rate control strategy to control symptoms or achieve target heart rate
- cardioversion)  (interventional
Rate control 
- Goal: reduction of the ventricular response rate to relieve symptoms, improved quality of life, and decreased risk of developing tachycardia-induced cardiomyopathy
Target resting heart rate 
- < 110/minute: in patients with normal LV systolic function whose symptoms are well controlled at this rate 
- < 80/minute: in patients with LV systolic dysfunction or who remain symptomatic at higher rates
- Beta blockers: e.g., metoprolol , atenolol , propranolol 
OR nondihydropyridine calcium channel blockers (ndHP CCBs): e.g., diltiazem , verapamil 
- Avoid in patients with .
- Can be safely used in heart failure with preserved normal LV systolic function.
- Second-line: digoxin ; preferred initial therapy for patients with 
- Third-line: amiodarone ; typically reserved for patients in whom all other options have failed 
AV nodal ablation and implantation of a permanent ventricular pacemaker
- Irreversible procedure
- Eliminates the need for rate-controlling medications but leads to lifelong dependence on a pacemaker.
- Recurrent Afib
- Afib refractory to medical rate control
- Patients who do not tolerate the pharmacological options for Afib management
Rhythm control 
For goals and indications in acute settings, see “Rhythm control” in “Afib with RVR.” Agents and dosages for pharmacological cardioversion are the same regardless of the setting. Consultation with cardiology is advised.
- Termination of atrial fibrillation (or flutter)
- Restoration and maintenance of sinus rhythm
- Symptom improvement
- Prevention of atrial remodeling
- Cardioversion options
- Long-term antiarrhythmic drug therapy: Consider in patients with a low risk of adverse effects.
Planned electrical cardioversion 
- Gradually increasing strengths of direct current shock (synchronized with the R wave) are administered under procedural sedation until sinus rhythm is restored.
- The adjunctive use of antiarrhythmic drugs prior to shock delivery may increase the likelihood of success.
- See “ ” for the approach to emergency .
- Consider in pharmacological cardioversion. or if the patient prefers
- Most likely to be effective for arrhythmias of < 7 days duration 
- Consultation with a specialist (e.g., cardiologist, electrophysiologist) is strongly recommended.
- More effective for atrial flutter than Afib, but there is a risk of conversion to 1:1 conduction with propafenone and flecainide 
Pharmacological cardioversion agents for Afib 
The following are inpatient regimens of IV or oral antiarrhythmics:
Several antiarrhythmic agents can precipitate other arrhythmias (e.g., in patients with QTc prolongation) and clinical deterioration in patients with structural heart disease. Only start these medications in controlled settings and in consultation with a specialist.
Pill-in-pocket approach 
- A single, self-administered dose of an anti-arrhythmic (e.g., flecainide , propafenone ) used outside of the hospital to terminate atrial fibrillation
- Typically given in conjunction with a beta blocker or ndHP CCB
- May be used in patients with recent onset of Afib with infrequent episodes and no history of structural or ischemic heart disease
- Patients should be monitored on the regimen in the hospital environment before they can self-administer.
Interventional cardioversion 
- Description: Creation of scar tissue that prevents the spread of ectopic impulses.
- Indications: patients undergoing cardiac surgery for other reasons, symptomatic refractory Afib, patient preference, concurrent CHF with reduced LVEF 
Pericardioversion anticoagulation for Afib 
Patients with moderate to severe mitral stenosis, mechanical heart valves, or hypertrophic cardiomyopathy are at high risk of thromboembolism regardless of duration since Afib onset or CHA2DS2-VASc score. If not already anticoagulated, consult cardiology for optimal pericardioversion management.
|Pericardioversion anticoagulation for Afib |
|Onset < 48 hours|| |
(CHA2DS2-VASc score 0 in men and 1 in women)
(CHA2DS2-VASc score 1 in men and 2 in women)
CHA2DS2-VASc score ≥ 2 in men and ≥ 3 in women)
|Onset ≥ 48 hours or unknown||Stable patients|| |
Base decisions about postcardioversion thrombotic and bleeding risk profiles.  on individual
Use the same risk-benefit profile assessment for all types of Afib and atrial flutter (e.g., paroxysmal Afib, persistent Afib, or permanent Afib) and regardless of treatment strategy (i.e., rate control and/or rhythm control) or apparent maintenance of sinus rhythm. 
- Assess thrombotic risk.
- Assess bleeding risk.
- Identify .
- Calculate HAS-BLED score.
- Choose the appropriate based on the individual risk profile.
- Consider interventional alternatives for patients with thrombotic risk. and a high
Prevention of thromboembolism with long-term anticoagulation is typically indicated in patients with moderate to severe mitral stenosis, mechanical heart valves, HCM, and/or a CHA2DS2-VASc score ≥ 2 in men and ≥ 3 in women.
Always consider the bleeding risk when initiating anticoagulation.
Risk assessment 
|Thrombotic risk in Afib and atrial flutter|
|High risk|| |
|Moderate risk|| |
|Low risk|| |
- A validated scoring system for assessing the risk of stroke in Afib. 
- Avoid use in patients with moderate to severe mitral stenosis, mechanical heart valves, or HCM. 
|CHA2DS2-VASc score |
|Congestive heart failure or LV dysfunction||1|
|Age ≥ 75 years||2|
|Prior stroke, transient ischemic attack, or thromboembolism||2|
|Age 65–74 years||1|
|Sex: female ||1|
Risk of stroke 
HAS-BLED score 
- Most often used to assess the risk of bleeding in patients starting anticoagulation. 
- Consider addressing modifiable risk factors, e.g., uncontrolled hypertension, alcohol use, NSAID, or aspirin use, and reevaluating risk.
- A high-risk HAS-BLED score is not necessarily a reason to withhold anticoagulation; these patients require more frequent monitoring. 
|HAS-BLED score |
|Abnormal renal or liver function||1 point each (max. 2)|
|Bleeding history or predisposition||1|
|Elderly individuals (age > 65)||1|
|Drugs that predispose to bleeding or alcohol use||1 point each (max. 2)|
Anticoagulation regimens in atrial fibrillation and atrial flutter 
- The choice of anticoagulant is predominantly based on individual patient factors.
- Educate patients on treatment adherence, bleeding risk, and risk-mitigating behavior modifications. 
- Antiplatelets are no longer recommended as an alternative to anticoagulation for stroke prevention in Afib or atrial flutter. 
- See “Pericardioversion anticoagulation in Afib” for indications and agents for anticoagulation prior to cardioversion for rhythm control.
|Long-term anticoagulation options in atrial fibrillation and flutter |
|Clinical applications||Options||Special considerations|
|Vitamin K antagonists (VKAs)|| |
Interventional alternatives to anticoagulation 
- Incidence: 88 per 100,000 person-years (increases with age)
- Sex: ♂ > ♀ (incidence in men is 2.5 times greater than in women)
- Similar to atrial fibrillation (see “Etiology” section above)
- May additionally result from the treatment of Afib 
- Type I (common; ; typical or isthmus-dependent flutter): caused by a counterclockwise (more common) or clockwise (less common) macroreentrant activation of cardiac muscle fibers in the right atrium that travels along the tricuspid annulus and passes through the cavotricuspid isthmus
- Type II (rare; atypical atrial flutter): various reentrant rhythms that do not involve the cavotricuspid isthmus, are not well-defined, and/or occur in the left atrium
- Most patients are asymptomatic.
- Less commonly: symptoms of , such as palpitations, dizziness, syncope, fatigue, and or dyspnea
- Tachycardia with a regular pulse
- Symptoms of the underlying disease (e.g., murmurs of mitral stenosis) may be present.
- Similar to atrial fibrillation except for ECG findings (see “Diagnosis of atrial fibrillation”)
- Characteristic ECG findings of atrial flutter
- Rate: typically 75–150/minute (depending on conduction) 
- Atrial rate ≥ ventricular rate
- Regular, narrow QRS complexes
- The rhythm may be:
- Sawtooth appearance of P waves: identical flutter waves (F waves) that occur in sequence at a rate of ∼ 300/minute
- Predominantly negative deflections in leads II, III, aVF
- Flat deflections in I and aVL
Consult cardiology for all patients.
- Acute is the same as the .
- Long-term arrhythmia management is very similar to with some minor differences:
- Anticoagulation recommendations are the same as for .
- Frequently degenerates into atrial fibrillation
- 1:1 conduction can lead to life-threatening ventricular tachycardia
- One-Minute Telegram 67-2023-1/3: Freezing the progression of atrial fibrillation
- One-Minute Telegram 65-2022-1/3: 2022 U.S. Preventive Services Task Force: summary of recommendations
- One-Minute Telegram 63-2022-1/3: Apixaban: the right pick for atrial fibrillation?
- One-Minute Telegram 63-2022-3/3: No revelations on the best anticoagulant for patients with end-stage kidney disease
- One-Minute Telegram 62-2022-1/3: K+ may be more than OK at making bad rhythms go away
- One-Minute Telegram 59-2022-3/3: The rhythm is gonna get you: early rhythm control in low-risk AF
- One-Minute Telegram 44-2022-2/4: To screen or not to screen for atrial fibrillation: 2022 updated USPSTF recommendations
- One-Minute Telegram 15-2020-3/4: Anticoagulation for patients with bioprosthetic mitral valves: is it time for a DOAC?
- One-Minute Telegram 12-2020-4/4: Levothyroxine and AFib in older patients: what’s the right dose?
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