Epidemiology and Etiology
Epidemiology
- Most common form of cardiac arrhythmia
- Incidence increases with age
- 70% of patients with atrial fibrillation (AF) are > 65 years old
- More common in men (but if affected, women are more likely to be symptomatic and develop complications)
- More common in Caucasians than African Americans, Hispanics, and Asians
General risk factors for cardiovascular disease
- Advanced age
- Hypertension
- Diabetes mellitus
- Smoking
- Obesity
- Sleep apnea
Risk factors for AF
- Usually associated with some underlying heart disease
- Most common chronic disease associations are hypertensive heart disease and coronary heart disease
- 15%–30% of cases are idiopathic or not associated with any known risk factor
| Cardiac risk factors | Non-cardiac risk factors |
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| P | Pulmonary diseases:
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| I |
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| R |
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| A |
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| T |
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| E |
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| S |
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Pathophysiology and Classification
Pathophysiology
- AF is caused by re-entrant electric conduction.
- Re-entrant pathways can be due to:
- Fibrosed tissue
- Atrial dilation (e.g., congenital defect or post-MI)
- Abnormal accessory pathways (e.g., WPW syndrome)
- Most common site of the rapid atrial firing that triggers AF is the pulmonary veins.
The pathophysiology of re-entrant pathways
- An ectopic focus initiates a cardiac action potential, which travels in the form of a unidirectional conduction wave. If a conduction barrier is present (e.g., cardiac tissue damaged by ischemia), the wave will travel around it.
- In healthy tissue, the conductive wave will meet refractory tissue upon completing the circuit.
- If the refractory period is shorter than the time it takes the wave to complete the circuit, re-entrant electric conduction may occur.
- If the conduction barrier becomes large enough, the conduction wave will meet repolarized tissue and re-entry may occur.
- If the conduction wave is slowed down by a damaged section of atrial tissue, re-entry may occur.
- Heart rate:
- Atrial rate > 300/min
- Some beats are irregularly modulated by the atrioventricular (AV) node
- Ventricular rate = 90–170/min
- Effects:
- Atrial remodeling: irregular impulses and contractions lead to progressive dilation and fibrosis of the atria → higher risk for AF → vicious cycle of pathology
- Asynchronous contractility → atria lose systolic function
- Rapid uncontrolled atrial contractions ( > 300/min) → slower pass through the AV node → uncoordinated ventricular contractions (90–170/min) → tachycardia
- Decreased cardiac output → stasis of blood → promotes thromboembolism
- Decreased cardiac output → heart failure
Classification
- Paroxysmal: AF that starts spontaneously and terminates spontaneously or with intervention within 7 days of onset; episodes may occur with variable frequency
- Persistent: AF that fails to self-terminate within 7 days, requires pharmacologic or electrical cardioversion to terminate
- Long-standing persistent: AF that has lasted for more than 12 months
- Permanent: AF that is unresponsive to treatment, patient and doctor decide to no longer pursue a rhythm control strategy
- Lone: paroxysmal, persistent, or permanent AF with no structural heart disease, typically in persons < 60 years old, the lowest risk of complications → patients have a CHA2DS2-VASc score of “0”
- Secondary: due to underlying condition, treatment focuses on the underlying condition to resolve AF
- Subclinical: AF in asymptomatic individuals without a prior diagnosis of AF, often found in the context of implantable cardiac monitoring devices
Clinical Presentation
- AF is often asymptomatic.
- If patients experience symptoms, these are often nonspecific and variable.
- Palpitations
- Tachycardia
- Chest pain
- Fatigue
- Dyspnea
- Syncope
- Confusion
- Mild dyspnea
- Embolic event
- If symptoms are atypical → notice signs of the underlying disorder (e.g., exophthalmos in hyperthyroidism, murmur in the case of a valvular defect)
- Complications of long-standing AF:
- Signs of heart failure (pulmonary edema, orthopnea, paroxysmal nocturnal dyspnea, dyspnea at rest, pitting edema, S3, S4)
- Signs of embolization (stroke/transient ischemic attack [TIA] presenting with focal neurologic deficits such as paresis, vision loss, or renal, splenic, or intestinal infarct)
Diagnosis
Electrocardiogram (ECG): confirms diagnosis
- Irregularly irregular (pathognomonic)
- RR intervals follow no repetitive pattern
- No distinct P waves
- Narrow QRS complexes (< 0.12 seconds)
Echocardiogram: used to identify etiology and complications, not for diagnosis
- Transthoracic echocardiogram (TTE)
- Used to assess cardiac function
- Rules out or confirms structural cardiac disease (e.g., valve stenosis)
- Transesophageal echocardiogram (TEE)
- Rules out or confirms the structural cardiac disease
- Indicated if AF lasted for > 48 hrs or if the duration is unknown
- Indicated if planning cardioversion on patients who haven’t received anticoagulation therapy for at least 3 weeks
- Used to detect thrombi within the left atrium or left atrial appendage
Other tests to rule out underlying conditions:
- Cardiac enzymes → myocardial infarction
- BNP → heart failure
- TSH/fT4 → hyperthyroidism
- CBC → infection/sepsis
- BUN, creatinine → kidney function
- CT pulmonary angiography → pulmonary embolism
- Electrolytes (potassium, calcium, or magnesium) → electrolyte imbalances
- Urine drug screen → cocaine, amphetamines, digoxin, or alcohol
- Exercise testing → ischemic heart disease, also guides pharmacotherapy
ECG shows an irregularly irregular rhythm of atrial fibrillation in a thyrotoxic patient
Image: “Initial electrocardiogram (ECG) at presentation to the emergency room” by ST4 Diabetes and Endocrinology Princess of Wales Hospital Bridgend, CF31 1RQ UK. License: CC BY 3.0
Example of an ECG tracing showing atrial fibrillation with irregularly irregular RR intervals and loss of P waves
Image: “Electrocardiogram showing atrial fibrillation with rapid ventricular rate” by Division of Hematology and Oncology, Sylvester Comprehensive Cancer Center, Miami, FL, USA. License: Image: “” by . License: CC BY 2.0
Thrombus formed on the lateral wall of the left atrium (white arrow)
Image: “Fourteen days after cardiac surgery, a thrombus had formed over the lateral left atrium wall (white arrow)” by U.S. National Library of Medicine. License: CC BY 4.0
Management
Algorithm for the management of atrial fibrillation
Image by Lecturio.AF management consists of the following:
- Determination of hemodynamic status
- Rate control OR rhythm control
- Anticoagulation therapy
- Treatment of the underlying cause
Special considerations:
- Newly discovered AF < 24-48 hours → electrical cardioversion (without anticoagulation)
- If concurrent WPW syndrome → IV procainamide or IV amiodarone (not nodal blockers)
- Ablative therapy for tracts or pulmonary vein foci (long-term management)
- Use heparin only if there is a current clot in the atrium.
| Hemodynamic status |
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|---|---|---|
| Rate control vs. rhythm control | Rate control Indication:
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| Rhythm control Indication:
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| Anticoagulation | Warfarin, novel oral anticoagulants (NOAC) | Indication:
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| Aspirin | Indication:
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| Cardioversion protocol (electrical or pharmacological) | 3 weeks prior and 4 weeks post-cardioversion | |
| Treat underlying cause | Hypertension, coronary artery disease, valvular heart disease, chronic obstructive pulmonary disease, thyrotoxicosis, sick sinus syndrome, etc. | |
| C | Congestive heart failure | 1 |
|---|---|---|
| H | Hypertension | 1 |
| A | Age (≥ 75 years) | 2 |
| D | Diabetes mellitus | 1 |
| S | Stroke, TIA, or thromboembolism | 2 |
| V | Vascular disease | 1 |
| A | Age 65–74 years | 1 |
| Sc | Sex category (female) | 1 |
Differential Diagnosis
The following conditions are differential diagnoses for AF:
- Atrial flutter: an irregular heart rhythm of the atria. It is classified as supraventricular tachycardia. Symptoms include palpitations. Complications include increased risk of stroke and congestive heart failure.
- Key difference: Flutter is a regular rhythm whereas fibrillation is irregular.
- Paroxysmal supraventricular tachycardia: a type of supraventricular tachycardia characterized by narrow QRS complexes and a fast heart rhythm, typically between 150 and 240 beats per minute
- Multifocal atrial tachycardia: a type of atrial arrhythmia characterized by rapid heart rate with at least 3 or more P wave morphologies. It is called multifocal since the signals arise from various zones within the atria other than the sinus node.
- Premature atrial contractions: common ectopic beats generated from foci in atria, triggering premature heartbeats
