Atrial fibrillation (AF) is one of the most common clinical arrhythmias. It is characterized by the loss of regular and orderly electrical activity in the atria, which is replaced by rapid and disordered fibrillation waves. The atria deteriorate or lose pumping function due to the loss of effective contraction and diastole, and result in an extremely irregular response of the ventricles.
I. Classification of atrial fibrillation
According to the characteristics of atrial fibrillation episodes, atrial fibrillation can be divided into three categories: paroxysmal AF, persistent AF and permanent AF.
Paroxysmal AF refers to AF of < 7 d duration, usually < 24 h, and is mostly self-limiting.
Persistent AF: Atrial fibrillation with a duration >7 d. It is usually not self-resetting and the success rate of pharmacological resetting is low, and electrical resetting is often required.
Permanent atrial fibrillation: Atrial fibrillation that fails to maintain sinus rhythm or for which there is no indication for resetting.
A variety of diseases and predisposing factors can lead to AF. Isolated atrial fibrillation is defined as age less than 60 years with no (not found) clinical or cardiac ultrasound evidence of cardiopulmonary disease (including hypertension). Such patients have a low risk of thromboembolism and death and a better prognosis. However, over time, patients no longer fall under this category as they age and develop abnormalities of cardiac structure such as left atrial enlargement. Non-valvular atrial fibrillation occurs in patients without rheumatic heart disease, prosthetic valve replacement or valve repair.
Second, the danger of atrial fibrillation
Patients with atrial fibrillation are at increased risk of distant stroke, heart failure, and all-cause mortality, especially in women. Mortality is doubled in patients with atrial fibrillation compared with those in sinus rhythm. The incidence of ischemic stroke in patients with nonvalvular AF is 5%/year, which is 2 to 7 times higher than in those without AF. When transient ischemic attack (TIA) and asymptomatic stroke were considered, the incidence of ischemic attack with AF was 7%/year. Patients with rheumatic heart disease in atrial fibrillation had a 17-fold increased risk of stroke compared with age-matched controls; compared with patients with nonrheumatic atrial fibrillation, the risk was increased 5-fold. The incidence of embolism in patients with atrial fibrillation increased with age, with an annual incidence of stroke due to atrial fibrillation of 1.5% in patients aged 50 to 59 years, rising to 23.5% in those aged 80 to 89 years. The incidence of embolism was higher in male patients than in females at all ages.
The incidence of atrial fibrillation is increased in patients with heart failure, and atrial fibrillation worsens cardiac function. In patients with cardiac function class I (NYHA classification), the incidence of atrial fibrillation is ≤5%. As cardiac function deteriorates, the incidence of atrial fibrillation increases and occurs in nearly half of patients with cardiac function class IV. Patients with atrial fibrillation in combination with heart failure have a significantly higher morbidity and mortality rate than patients with atrial fibrillation without heart failure.
Atrial fibrillation can also cause tachycardia cardiomyopathy in patients with persistent increases in ventricular rate. After the tachycardia is controlled, the enlarged heart and cardiac function can be partially or completely restored to normal.
Clinical manifestations, diagnosis and preliminary evaluation of atrial fibrillation
1.Clinical symptoms
The clinical manifestations of atrial fibrillation are diverse. Most patients have symptoms such as palpitations, dyspnea, chest pain, fatigue, dizziness and blackness. The symptoms of patients with atrial fibrillation are related to various factors such as the ventricular rate at the time of attack, cardiac function, concomitant diseases, the duration of atrial fibrillation and the sensitivity of patients to perceive symptoms. In patients with permanent atrial fibrillation, symptoms diminish or even disappear over time. Some patients with atrial fibrillation have no symptoms, and some are detected only when serious complications of atrial fibrillation occur, such as stroke, embolism or heart failure.
2.History and physical examination
The diagnosis of atrial fibrillation is based on a history and physical examination, and requires confirmation by at least one single-lead ECG or Holter recording. The initial evaluation of a patient with atrial fibrillation includes determining the type of atrial fibrillation, identifying the cause, looking for cardiac and extracardiac factors associated with atrial fibrillation, and the status of previous consultations. For example, the patient is evaluated for the presence of underlying cardiac disease such as hypertension, valvular disease, and thyroid disease. Physical examination reveals unequal strength of heart sounds, absolute arrhythmia, and pulse dystocia often suggest the presence of atrial fibrillation.
3.Electrocardiogram performance
In atrial fibrillation, the electrocardiogram shows the disappearance of P waves, replaced by fibrillation waves of irregular size, shape and time limit, and the ventricular rate is mostly irregular.
4.Cardiac ultrasound and X-ray chest examination
In the initial evaluation, all patients with atrial fibrillation need to undergo cardiac ultrasound to evaluate the left atrial and left ventricular diameters and wall thickness, and to exclude valvular disease, cardiomyopathy, and pericardial disease. Assessment of left ventricular systolic and diastolic function helps guide the protocol for antiarrhythmic and anticoagulant therapy. Transesophageal ultrasonography can detect thrombus in the left atrium. x-ray chest radiographs can evaluate heart size and lung condition.
5.Exercise test
Patients with suspected myocardial ischemia should undergo an exercise test before applying class Ic antiarrhythmic drugs. Exercise test can also evaluate ventricular rate control during activity in patients with persistent or permanent atrial fibrillation.
IV. Treatment
(A) Treatment principles
1. Objectives
The goals of treatment for atrial fibrillation include finding and correcting the cause and etiology, ventricular rate control, prevention of thromboembolic complications, and restoration of sinus rhythm (rhythm control). The ventricular rate control strategy is to keep the ventricular rate under control by pharmacological means without attempting to restore or maintain sinus rhythm. Rhythm control aims to restore or maintain sinus rhythm.
Ventricular rate control is recommended for the following patients with atrial fibrillation.
① Patients with asymptomatic atrial fibrillation who must be converted to sinus rhythm for no particular reason.
(ii) In patients with atrial fibrillation that has persisted for several years, it is difficult to maintain sinus rhythm even after conversion to sinus rhythm.
(iii) In patients whose risk of conversion and maintenance of sinus rhythm with antiarrhythmic drugs is greater than the risk of atrial fibrillation itself.
(iv) Ventricular rate control is as effective as rhythm control in patients who are old (>65 years of age) or have uncorrected etiology of organic heart disease (including coronary artery disease, mitral stenosis, and left atrial internal diameter >55 mm).
2. Selection of pharmacological and non-pharmacological treatment of atrial fibrillation
Both pharmacologic and ablative therapy are effective for rhythm control and ventricular rate control. Drug is the preferred treatment for rhythm control, and radiofrequency ablation is suitable for patients with paroxysmal atrial fibrillation whose drug therapy is ineffective or whose side effects are intolerable and whose symptoms are severe; for persistent or permanent atrial fibrillation without organic heart disease, catheter ablation can also be considered if antiarrhythmic drug therapy fails. At this stage, the reference indications for catheter ablation of atrial fibrillation are: paroxysmal atrial fibrillation in patients <75 years of age with no or mild organic heart disease, anterior and posterior diameters of the left atrium <50mm, recurrent episodes, severe symptoms and unsatisfactory drug control. At this stage, radiofrequency ablation of atrial fibrillation is significantly more difficult to perform and has a higher risk of potentially serious complications (e.g., pulmonary vein stenosis, stroke, atrioventricular-esophageal fistula) than catheter radiofrequency ablation of conventional arrhythmias, so it is recommended that this treatment be performed under the supervision of an experienced electrophysiology center or an experienced physician.
Intraoperative maze or left atrial ablation for atrial fibrillation is a reasonable option for patients preparing for coronary artery bypass grafting or valve replacement.
(ii) Ventricular rate control
1. Objective
Patients with good ventricular rate control at rest are at risk of rapid heart rate during exercise, leading to restricted ventricular filling and myocardial ischemia; therefore, it is necessary to evaluate the change in heart rate of patients during subextreme exercise or over 24 hours, especially in patients with significant symptoms during activity. The goal of ventricular rate control in patients with atrial fibrillation is a ventricular rate range of 60 to 80 beats/min at rest and a heart rate of 90 to 115 beats/min maintained for moderate exercise.
2. Drugs
Medications that inhibit conduction within the AV node and prolong its induction period are recommended to slow ventricular rate, relieve symptoms, and improve hemodynamics, including beta blockers, calcium antagonists, digitalis, and certain antiarrhythmic drugs.
Beta blockers and non-dihydropyridine calcium antagonists are used to control ventricular rate in patients with persistent or permanent atrial fibrillation or atrial fibrillation requiring emergency management. Digitalis analogs are used in patients with rapid ventricular rates at rest and in patients with heart failure and a resting lifestyle. β-blockers or non-dihydropyridine calcium antagonists in combination with digitalis analogs can help control ventricular rates, but dosage should be monitored to avoid bradycardia. Intravenous digitalis and amiodarone may be considered in patients with decompensated heart failure combined with atrial fibrillation without atrioventricular bypass. When other drugs are ineffective or contraindicated, intravenous amiodarone is beneficial for ventricular rate control.
Beta blockers should be used with caution in patients with decompensated heart failure. Calcium antagonists are not recommended in patients with atrial fibrillation in the presence of heart failure. Digitalis alone is not recommended for ventricular rate control in patients with paroxysmal atrial fibrillation. Digitalis, non-dihydropyridine calcium antagonists and β-blockers are contraindicated in patients with atrial fibrillation in combination with pre-excitation syndrome because inhibition of atrial excitation via the atrioventricular node in atrial fibrillation may accelerate its forward transmission via the atrioventricular bypass, resulting in a significant acceleration of the ventricular rate, which may cause severe hemodynamic disturbances and even induce ventricular tachycardia and/or ventricular fibrillation. Patients with asthma and pulmonary heart disease can choose non-dihydropyridine calcium antagonists.
3.Non-pharmacological treatment
For patients with atrial fibrillation whose ventricular rate cannot be effectively controlled by drug therapy and who have severe symptoms, atrioventricular node ablation combined with pacing therapy can effectively reduce the symptoms.