Atrial fibrillation is a cardiac arrhythmia that involves the two upper chambers of the heart. It can often be identified by taking a pulse and observing that the heartbeats don't occur at regular intervals. Atrial fibrillation is the most common arrhythmia, risk increases with age. Atrial fibrillation can be chronic and sustained, or brief and intermittent (paroxysmal). Paroxysmal atrial fibrillation refers to intermittent episodes of atrial fibrillation lasting, for example, minutes to hours. The heart rate reverts to normal between episodes. In chronic, sustained atrial fibrillation, the atria fibrillate all of the time. Chronic, sustained atrial fibrillation is not difficult to diagnose.
Atrial fibrillation is associated with many cardiac conditions, including cardiomyopathy, coronary artery disease, valvular heart disease, ventricular hypertrophy and other associated conditions. This pathological state has been associated with hyperthyroidism, acute alcohol intoxication, changes in the autonomic nervous system and is common after cardiac surgery. The most common condition associated with atrial fibrillation is high blood pressure. Some people have atrial fibrillation with no obvious source or associated condition. This is more frequent in younger people and it is called «alone» atrial fibrillation. It is likely that people who have this form of atrial fibrillation have had some inflammatory process or trauma to the atrium. Some people have a focal source that originates from the pulmonary veins. Many conditions can cause disorganized electrical activity in the atria to develop. In many cases, a «leaky» or a sticky (stenotic) mitral valve can result in an enlarged (dilated) atria. Patients with a history of high blood pressure (hypertension) can develop atrial fibrillation, because high blood pressure eventually begins to affect the atria. Blocks in the arteries that supply the heart with blood (coronary arteries), heart attacks, and an overactive thyroid gland can also lead to atrial fibrillation. Excessive consumption of alcohol acts as a toxin on the heart, and patients who binge drink or chronically drink large amounts of alcohol are at risk for developing this arrhythmia.
In atrial fibrillation the regular impulses produced by the sinus node to provide rhythmic contraction of the heart are overwhelmed by the rapid randomly generated electrical discharges produced by larger areas of atrial tissue, often localized to the pulmonary veins. It can be distinguished from atrial flutter, which is a more organized electrical circuit usually in the right atrium that produces characteristic saw-toothed F-waves on the ECG; in atrial flutter, the discharges circulate rapidly at a rate of 300 to 600 beats per minute (bpm) around the atrium.
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Figure 34 — Atrial fibrillation
ECG signs of atrial fibrillation:
Irregularly irregular rhythm.
Ventricular rate varies extensively to 180/minute, but atrial rate is undeterminable.
P wave is replaced by multiply f wave.
QRS duration is normal, but shape is changed with every constriction.
T wave is indiscernible.
Atrial fibrillation often causes no symptoms at all. When symptoms do occur, there may be palpitations (awareness of a rapid heartbeat), fainting, dizziness, weakness, shortness of breath and angina pectoris (chest pain caused by a reduced blood supply to the heart muscle). Some people with atrial fibrillation have periods of completely normal heartbeats. The condition may be discovered incidentally, when a physician notices that the patient’s heart rate is no longer regular. Sometimes, the development of shortness of breath or of fatigue compels a patient to seek medical attention. But, some patients do not see a doctor until they have suffered a stroke.
Electrical cardioversion is an option used in the treatment and management of atrial fibrillation, atrial flutter and supraventricular paroxysmal tachycardia. It involves the use of a synchronized direct current electrical countershock that depolarizes all the cells simultaneously, allowing the SA node to resume the pacemaker role. The electrical discharge is synchronized with or triggered by the client’s QRS complex for avoidance of accidental discharge during the repolarization phase, when the ventricle is vulnerable to the development of ventricular fibrillation.
