Atrial Fibrillation

Arrhythmias are heart rate or rhythm disorders. They cause the heart to beat too fast (tachycardia), too slow (bradycardia), or irregularly.

Among these, atrial fibrillation (AF) is the most common, responsible for one-third of hospital admissions for heart rhythm disorders and is the leading cause of stroke.

What is atrial fibrillation?

Atrial fibrillation is the chaotic and uncoordinated activation of the heart's atria, resulting in the loss of the contractile capacity. This is due to abnormalities that alter the formation or conduction of electrical impulses in the atria. These abnormalities may be structural (inflammation, fibrosis, hypertrophy, and dilatation), or electrical.

It may present in the form of rapid and irregular pulses. Dyspnea, fatigue, and intolerance to the effort are also frequent, although sometimes the patient can only report an indefinite discomfort. Less commonly: syncope, angina pectoris, hypotension, or embolism may also be part of the first clinical manifestation. A significant concern with atrial fibrillation is the possibility of developing blood clots within the heart's upper chambers.

It is estimated that 1 in 4 adults in Europe will suffer from atrial fibrillation in their lifetime, and the incidence increases with age. From the age of 40, a person has a 26% chance of developing atrial fibrillation. It currently affects approximately 1-2% of the world's population, with more than five million new cases annually.

What are the causes of atrial fibrillation?

Atrial fibrillation is associated with certain cardiovascular diseases: ischemic and hypertensive heart disease, heart failure, coronary artery disease, and valvular heart disease. Other risk factors include arterial hypertension, obesity, excessive alcohol consumption, diabetes mellitus, smoking, and sleep apnea, just to name a few.

It has been shown that, in the case of atrial fibrillation, risk factors have a cumulative or additive nature. The chances of suffering from the disease increase progressively with the increasing accumulation of risk factors presented by a particular patient.

Some studies have shown that the disease has a genetic component. Although men are more likely to suffer from it, it is associated with an adjusted increase in mortality of 2 times in women and 1.5 times in men. Causes of death directly related to atrial fibrillation include stroke, heart failure, and sudden death.

The progressive aging of the population, the more prolonged survival of patients with heart disease, and the increase in risk factors (especially obesity) contribute to a progressive growth in atrial fibrillation. Its prevalence is expected to double in Spain in the coming decades.

How is atrial fibrillation diagnosed?

Although clinical suspicion is established by detecting an irregular pulse, the definitive diagnosis is made through an electrocardiogram, which captures the specific pattern of this type of arrhythmia: absence of P waves, which are replaced by F waves of different voltage and frequency, while accompanied by absolutely irregular RR intervals in the absence of AV block.

Current clinical practice guidelines of the European Society of Cardiology propose a classification based on the presentation, duration, and mode of termination of atrial fibrillation. Thus, five patterns are described:

First-episode AF: it is so termed when it is documented for the first time, regardless of its duration and associated symptomatology.
Paroxysmal AF: the most common form of AF, episodes usually end spontaneously or after cardioversion (between the first 48 hours and seven days).
Persistent AF: this type is considered when the arrhythmia lasts more than seven days, even after cardioversion (drugs or electrical cardioversion).
Long-standing persistent AF: this is AF that has lasted for a year or more, when a rhythm control strategy is adopted.
Permanent AF: this type is considered when the patient and physician accept the arrhythmia, and any option of intervention to revert to sinus rhythm is abandoned, leaving only heart rate control.

As the atria remodel, the episodes increase in duration in most patients, from paroxysmal to persistent forms. However, European guidelines have also proposed a new classification that has a more substantial clinical and pathophysiological basis but is still less widely used:

AF secondary to structural heart disease: occurs in the presence of significant structural heart disease. The appearance of the arrhythmia usually implies substantial clinical deterioration.
Focal AF: usually occurs in young patients with highly symptomatic paroxysmal forms.
Polygenic AF: in carriers of normal genetic variants, but associated with AF development at an early age.
Postoperative AF: occurs in subjects who have undergone major surgery, usually cardiovascular, in previous sinus rhythm, and without a history of AF.
AF in patients with mitral stenosis or mechanical valve prostheses: associated with the hemodynamic disturbances produced by such valve diseases.
AF in athletes: usually paroxysmal forms, closely related to the duration and intensity of exercise.
Monogenic AF: occurs in subjects with hereditary heart disease, including channelopathies.

Treatment

Once atrial fibrillation has been diagnosed, a clinical approach should be made to the patient to assess the severity of symptoms, the arrhythmia pattern, and hemodynamic stability and control associated risk factors. The European Society of Cardiology recommends the determination of the subject's functional status by applying the modified EHRA scale in its clinical practice guidelines.

After the initial assessment, a protocolized study will be planned that will include:

A basic blood test to estimate the state of renal function, rule out anemia and thyroid dysfunction.
A chest X-ray to rule out associated pulmonary pathology.
A transthoracic echocardiogram to know the state of ventricular function, the size of the cardiac chambers (with a particular interest in the left atrium), and the presence of valvulopathies.

Other studies may be necessary. Continuous electrocardiographic monitoring may be helpful in subjects aimed at heart rate control or in whom there are doubts about the symptomatology produced by paroxysmal episodes of atrial fibrillation. Transesophageal echocardiography is more accurate than transthoracic echocardiography in assessing certain valve diseases (especially mitral insufficiency) and ruling out the presence of thrombi in the left atrium if an early cardioversion strategy is decided.

The choice of treatment for atrial fibrillation depends on the objective proposed according to the patient's needs: management of the acute episode, mitigation of risk factors and associated comorbidities, heart rate control, and cardiac rhythm control strategy.

Heart rate control: Indicated in subjects whose recovery of sinus rhythm is not contemplated or is impossible. The objective is to avoid symptoms due to elevated heart rate and prevent the eventual deterioration of ventricular function through the use of beta-blocking drugs.

Heart rhythm control: This strategy aims to maintain the patient's sinus rhythm, using antiarrhythmic drugs or an invasive approach by ablation. Maintenance of sinus rhythm is associated with a better vital prognosis and a reduction in symptoms and is used in young patients (under 70 years old).

Symptomatic patients (usually due to exertional dyspnea or palpitations), but in a stable clinical situation and without significant underlying heart disease, should benefit from restoring sinus rhythm as soon as possible, allowing symptom control and stopping atrial remodeling. Two aspects should be considered: the anticoagulation status of the subject and the chronology of the onset of the arrhythmia.

In very symptomatic patients (dyspnea at rest, angina, syncope, or presyncope), with an unstable hemodynamic situation (due to arterial hypotension or heart failure), or with severe underlying heart disease (severe left ventricular systolic dysfunction, mitral stenosis, severe aortic valve stenosis), the acute episode should be treated intensively in addition to the usual supportive measures (oxygen therapy, ventilatory support) and treatment of the underlying cardiac or extracardiac disease.

In patients with symptomatic but hemodynamically stable atrial fibrillation in whom cardioversion is considered, pharmacological or electrical cardioversion can be considered, depending on patient preference and availability of resources. The efficacy and safety profile of the different drugs used for cardioversion is usually not as effective in severe patients or those with severe heart disease, so electrical cardioversion should be chosen in this situation.

Invasive treatment of atrial fibrillation by electrical isolation of the pulmonary veins using cryoablation (cold) or RF ablation (heat) is becoming increasingly important, avoiding the continuous use of antiarrhythmic drugs and their side effects.

In the long-term management of patients with atrial fibrillation, several fundamental aspects must be considered: symptom relief, adequate management of a concomitant cardiovascular disease or other arrhythmia-related diseases, prevention of thromboembolic events, and heart rate control or maintenance of sinus rhythm.

Recommendations of the Spanish Heart Foundation for patients with atrial fibrillation

Control blood pressure
Moderate alcohol consumption
Reduce stimulants (coffee, tea, sugary drinks).
Quit smoking.
Moderate exercise. Walking every day and moving around is essential, but long-distance running, long bicycle rides, and sports that involve a great deal of cardiovascular effort should be avoided.