Atrial Fibrillation
Atrial fibrillation (AF) is the most prevalent sustained arrhythmia in clinical practice.1
It is a supraventricular tachyarrhythmia characterized by disorganized atrial electrical activation, leading to the loss of effective atrial mechanical contraction and subsequent blood stasis within the atria. This prothrombotic state increases the risk of thromboembolic events.1
The atrioventricular (AV) node filters the high-frequency atrial impulses, resulting in an absolutely irregular ventricular response, typically at a lower rate than the atrial frequency.
Symptomatology of Atrial Fibrillation
Symptoms related to atrial fibrillation episodes are variable and not limited to typical palpitations; even nonspecific symptoms, such as fatigue, are often more frequent.2
90% of patients with AF describe symptoms of varying severity. Asymptomatic atrial fibrillation episodes can occur even in symptomatic patients.2
The presence or absence of symptoms is not correlated with the incidence of stroke, systemic embolism, or mortality. However, symptoms significantly affect the patient's quality of life.2
Recommendations for the Diagnosis of Atrial Fibrillation
- In patients with no known history of atrial fibrillation, it is recommended that the initial diagnosis be made via visual interpretation of electrocardiographic signals by a physician, regardless of the rhythm type or monitoring device.1
- In patients with an intracardiac rhythm device capable of diagnosing AF (such as an atrial pacemaker lead), the diagnosis of AF should only be made after visual confirmation by reviewing intracardiac tracings to exclude signal artifacts and other arrhythmias.1
- For patients who have experienced a systemic thromboembolic event with no known history of AF, and in whom maximum sensitivity for AF detection is sought, an implantable cardiac monitor (loop recorder) is reasonable.1
Atrial Fibrillation on the Electrocardiogram
The electrocardiogram of atrial fibrillation is characterized by presenting completely irregular R-R intervals.
It is often termed the "arrhythmia par excellence," as the R-R intervals are irregular without following any pattern.
Furthermore, due to chaotic atrial stimulation, there are no P waves. However, small atrial waves with variable morphology, called f waves (fibrillatory waves), may be observed.
Conduction to the ventricles occurs via the normal conduction system; therefore, QRS complexes are narrow, unless other alterations exist (bundle branch block, accessory pathway) or aberrant conduction occurs (see Ashman phenomenon).
Atrial Fibrillation on the Electrocardiogram
- Totally irregular R-R intervals.
- Absence of P waves.
- Small, irregular waves called f-waves may be seen.
- QRS complexes with morphology similar to sinus rhythm QRS complexes.
Heart Rate
Heart rate in atrial fibrillation is highly variable.
In patients without antiarrhythmic treatment, it frequently presents with elevated heart rates, whereas with optimized treatment, AF usually presents with rates within the normal range or even with bradycardia.
Atrial Fibrillation with Rapid Ventricular Response (RVR)
When atrial fibrillation presents with a HR > 110 bpm, it is usually because the patient is untreated, treatment is not optimized, or due to decompensation from another pathology (respiratory infection, anemia, hypoxemia).
In patients with permanent AF, it appears in the same scenarios as sinus tachycardia in normal patients.
Atrial Fibrillation with Slow Ventricular Response
Usually observed in patients with excess treatment or AV node dysfunction. When the HR is very slow or prolonged pauses are present, high-grade AV block should be suspected.
If the electrocardiogram shows AF with slow ventricular response and rhythmic QRS complexes, atrial fibrillation with complete AV block and an escape rhythm must be suspected.
Classification of atrial fibrillation
From the 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation and from the 2024 ESC Guidelines for the management of atrial fibrillation.1 2
- First diagnosed atrial fibrillation: first episode of AF, regardless of duration, severity, or related symptoms.
- Paroxysmal atrial fibrillation: terminates spontaneously within the first 7 days of onset or with the aid of an intervention.
- Persistent atrial fibrillation: duration exceeding 7 day.
- Long-standing persistent atrial fibrillation: arbitrarily defined as continuous AF of at least 12 months duration where rhythm control remains a treatment option in selected patients, distinguishing it from permanent AF.
- Permanent atrial fibrillation: AF where no further attempts to restore sinus rhythm are made.
In patients with permanent AF where a rhythm control strategy is adopted, it is redefined as long-standing persistent atrial fibrillation.
Management of Atrial Fibrillation
Once AF develops, three important care processes must be specifically addressed with all patients and aligned with their therapeutic goals:1
- Stroke risk evaluation and treatment, if applicable.
- Optimization of all modifiable risk factors.
- Symptom management via rate and rhythm control strategies, considering the AF burden in the context of each patient's needs.
Stroke or Thromboembolism Prevention
Atrial fibrillation is a major risk factor for thromboembolism, regardless of the AF type.1, 2
If untreated, and depending on other patient-specific factors, the risk of ischemic stroke in atrial fibrillation increases fivefold, and one in five strokes is associated with AF.2
Therefore, the default approach should be to provide oral anticoagulation to all patients with a high risk of stroke or thromboembolism.1 2
Antiplatelet agents (aspirin or aspirin combined with clopidogrel) are not recommended for stroke prevention in atrial fibrillation.1 2
The CHA2DS2-VASc score is considered the most validated and popular risk score for determining stroke or thromboembolism risk in AF.1 2
The inclusion of gender complicates clinical practice for both professionals and patients; therefore, the 2024 ESC Guidelines2 have effectively implemented the CHA2DS2-VA score (excluding gender) for stroke risk assessment.
Any patient with atrial fibrillation or atrial flutter, with a CHA2DS2-VASc score of 2 or more in men, 3 in women, or 2 points on the CHA2DS2-VA scale, must receive oral anticoagulation, unless contraindicated.1, 2
Rate Control Strategy in Atrial Fibrillation
Atrial fibrillation with rapid ventricular response around 120 bpm
Rate control is an appropriate strategy for many patients with AF.1 Decreasing the heart rate is often sufficient to improve AF-related symptoms.
Currently, the accepted goal is to maintain a resting HR below 110 bpm. Only in cases where symptoms persist should a stricter control (less than 80 bpm) be attempted.2
Rhythm Control Strategy in Atrial Fibrillation
The rhythm control strategy refers to treatments dedicated to restoring and maintaining sinus rhythm. These treatments include electrical cardioversion, antiarrhythmic drugs, or percutaneous catheter ablation.2
The main reason to consider long-term rhythm control treatment is the reduction of atrial fibrillation symptoms.1 2
In patients presenting with both atrial fibrillation and reduced left ventricular function, or who develop reduced LV function following an initial AF diagnosis where no identifiable cause is observed, a rhythm control strategy is also recommended.1
Electrical Cardioversion
Until the recent 2024 ESC Guidelines, cardioversion was typically considered when the definitive duration of AF was less than 48 hours. According to these new guidelines:
- Cardioversion is not recommended if the duration of AF is greater than 24 hours, unless the patient has received at least three weeks of anticoagulation or a transesophageal echocardiogram (TEE) is performed to exclude the presence of an intracardiac thrombus.2
- In acute patients or when early cardioversion is necessary, a TEE can be performed to exclude intracardiac thrombi before cardioversion.1 2
- If a thrombus is detected, anticoagulation must be initiated for a minimum of 4 weeks, followed by a repeat TEE to ensure thrombus resolution.2
- Oral anticoagulation must be continued for at least 4 weeks post-cardioversion.1 2
Catheter Ablation for Atrial Fibrillation
Catheter ablation is an invasive technique aimed at curing AF. It is the treatment with the best results for maintaining sinus rhythm in the long term, although late recurrences may occur.
It is primarily indicated in patients with symptomatic paroxysmal AF, with normal atria and normal systolic function. Also in patients with symptomatic persistent AF despite antiarrhythmic treatment.
Special Cases of Atrial Fibrillation
Patients with AF may also present with other types of arrhythmias. For example, a complete AV block, conduction through an accessory pathway of AF stimuli in Wolff-Parkinson-White syndrome or as bradycardia-tachycardia syndrome.
Atrial Fibrillation and Complete AV Block
Absence of P waves or presence of f-waves with rhythmic QRS complexes accompanied by significant bradycardia. The QRS morphology depends on the location of the escape rhythm.
Atrial Fibrillation and Wolff-Parkinson-White Syndrome
AF impulses in WPW patients are conducted mainly through the accessory pathway, producing a tachycardia characterized by wide and arrhythmic QRS complexes. Due to high ventricular rates, it can degenerate into ventricular tachycardia or ventricular fibrillation.
This is a medical emergency and requires urgent electrical cardioversion.
Bradycardia-Tachycardia Syndrome
Atrial fibrillation may appear in the context of sick sinus syndrome following significant sinus pauses. It is usually self-limited and followed by another prolonged sinus pause.
References
- 1. Joglar JA, Chung MK, Armbruster AL, et al. 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2023; 149(1). doi: 10.1161/CIR.0000000000001193.
- 2. Van Gelder IC, Rienstra M, Bunting KV, et al. 2024 ESC Guidelines for the management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS): Developed by the task force for the management of atrial fibrillation of the European Society of Cardiology (ESC), with the special contribution of the European Heart Rhythm Association (EHRA) of the ESC. Endorsed by the European Stroke Organisation (ESO). Eur. Heart J. 2024; 45(36): 3314–3414. doi: 10.1093/eurheartj/ehae176.
