Atrial fibrillation is defined by an anarchic atrial electrical activity with a frequency of 350-600 beats / minute, with the cancellation of atrial mechanical function. Ventricular rhythm is completely irregular, usually with a frequency between 100 and 150 beats / minute. Irregular ventricular rhythm is due to a hidden driving trough atrioventricular junction.
Clinical classification of atrial fibrillation is done according to guidelines proposed by the American Heart Association, in the following types:
- Paroxysmal atrial fibrillation: lasts several minutes, hours or up to 7 days and resolves spontaneously;
- Recurrent atrial fibrillation: the patient had repeated episodes of atrial fibrillation, remitted either spontaneously or with treatment;
- Persistent atrial fibrillation: lasting more than seven days and dose not resolves spontaneously;
- Permanent atrial fibrillation (chronic), which can not be remitted with treatment.
Atrial Fibrilation Causes:
Paroxysmal atrial fibrillation may occur in a healthy heart in the following situations:
- Acute alcoholism;
- Coffee and tobacco abuse;
In a diseased heart, paroxysmal atrial fibrillation occurs in the following situations:
- Myocardial infarction;
- During invasive investigations and during interventions: cardiac catheterization, coronary arteriography, surgical interventions;
- In other situations: acute hypoxia, hypercapnia, electrolyte disturbances, hypotension, cardiogenic shock, etc.
Permanent atrial fibrillation, appears in the following situations:
- In heart disease: coronary artery disease, mitral stenosis, aortic stenosis, mitral regurgitation, aortic regurgitation, hypertrophic cardiomyopathy, dilated cardiomyopathy, hypertensive cardiomyopathy, myocarditis, pericarditis, chronic pulmonary heart disease;
- Other medical conditions: hypoxia and hypercapnia, in chronic hyperthyroidism;
- In 15% of cases, permanent atrial fibrillation is idiopathic, especially in men.
In terms of pathophysiology, atrial fibrillation, causes the following changes:
- Reduced cardiac output by atrial systole loss, cardiac output is reduced by 20-30% and by shortening of the diastole, cardiac output is reduced in proportion to the increase of ventricular rate;
- Worsening of hemodynamic status, particularly in patients with heart failure, mitral stenosis and ventricular diastolic dysfunction;
- The occurrence of angina pectoris, in cases of atrial fibrillation with increased ventricular rate by increasing the myocardial oxygen consumption and by the shortening of diastole, will appear the reduction of coronary perfusion.
- Atrium thrombus formation, with the risk of systemic embolism and of pulmonary embolism.
Atrial Fibrilation Diagnosis
Symptoms of atrial fibrillation are polymorphic. The patient may feel palpitations, anginal pain, the worsening of heart failure symptoms, syncope (if ventricular rate is very high or very low). Atrial fibrillation with ventricular rate close to normal may be asymptomatic.
Physical examination may reveal the following aspects:
- Total irregular heart rhythm, usually with an accelerated rate (100-160 beats / minute) and heart sounds unequal in intensity;
- Peripheral arterial pulse is irregular and unequal in amplitude. At accelerated ventricular rates is present a pulse deficit, due to excessive shortening of diastole, with reduction of the end diastolic volume and therefore will appear a reduce in systolic flow, so that aortic valve does not open. So, not all cases of atrial fibrillation have pulse deficit, but only the forms with marked tachycardia. The effort accentuates the symptoms and signs of atrial fibrillation.
- ECG shows the following: absence of P waves, atrial electrical activity is replaced by “f” waves, with small amplitude, irregular and with a frequency between 350-600 beats / minute. Ventricular rhythm is irregular, with a rate between 100 and 150 beats / minute. QRS complex has a shorter duration than normal.
Sino-carotid massage may cause a transient reduction in heart rate and is useful in the differentiation of atrial fibrillation form atrial flutter.
The prognosis of atrial fibrillation, depends in particular on:
- Ventricular myocardium state, which is dependent on the underlying disease, will dictate the degree of hemodynamic deterioration.
- The presence of atrial thrombus, which is leading to an increased incidence of thromboembolic accidents, of which 75% are cerebrovascular accidents (strokes).
Atrial Fibrilation Treatment
Treatment of atrial fibrillation has the following objectives:
- Conversion to sinus rhythm (electric or medication), when is indicated and possible;
- Relapse prevention;
- Prevention of thromboembolic complications;
- Control of ventricular function when converting and maintaining of sinus rhythm are not possible.
The choice of therapeutic methods, in the treatment of atrial fibrillation is individualized and should consider the etiologic substrate of atrial fibrillation.
Treatment for paroxysmal atrial fibrillation access:
- Treatment of paroxysmal atrial fibrillation with hemodynamic deterioration associated with myocardial ischemia or Wolff-Parkinson-White syndrome, is electric conversion to sinus rhythm.
- In the case of hemodynamically stable atrial fibrillation, are performed the following:
- Rate control is the main therapeutic target that can be achieved rapidly by intravenous administration of beta-blockers (metoprolol, bisoprolol) or calcium channel blockers (diltiazem).
- Pharmacological conversion to sinus rhythm can be achieved by administration of antiarrhythmic agents from class III (amiodarone, sotalol), class IA (disopyramide) or class IC (propafenone, flecainide).
- Electric conversion is performed if pharmacological conversion attempt failed for 24 hours.
In the case of electrical or pharmacological conversion of atrial fibrillation, is required the prevention of thromboembolic complications, by the following measures:
- In patients with atrial fibrillation which was installed in less than 48 hours and the patients will be subjected to conversion to sinus rhythm, anticoagulation therapy management is optional, depending primarily on the associate risk of embolism.
- If the occurrence of atrial fibrillation happened in more than 48 hours, and the patient has a higher risk for embolism, then the treatment with oral anticoagulants is required at least with 2 weeks before conversion and must be continued 2 weeks after conversion to sinus rhythm.
- Emergency defibrillation involves anticoagulation with intravenous heparin, initially in bolus and then in continuous infusion in a dose that prolongs the APTT with 1.5-2 times compared to its reference value. After defibrillation, oral anticoagulation therapy should be continued for a period of 2 weeks.
Prevention of recurrence of atrial fibrillation:
Prevention of atrial fibrillation recurrence is performed by administering antiarrhythmic drugs from class IA, class IC and class III. An alternative therapy to prevent relapse of atrial fibrillation, is represented by atrial pacemaker implant, with the anti-tachycardia function.
Treatment of permanent atrial fibrillation:
This type of atrial fibrillation has low chances of conversion to sinus rhythm, especially if left atrial diameter exceeds 5 cm.
Heart rate control in permanent atrial fibrillation is performed, electively, with digoxin, which may be associate with low-dose of beta-blocker, verapamil or amiodarone. Optimal therapeutic effect is considered to be obtained when heart rate reaches 60 to 80 beats / minute.
In the case of bad tolerated chronic atrial fibrillation, is practice atrio-ventricular node ablation or ablation of His fascicle by radiofrequency current, followed by permanent pacemaker implantation.