In the case of atrial fibrillation impulses originates not from the sinus node, but from different parts of the atria. The impulses are very frequent. Atrial fibrillation describes when muscle fibers of the atria contract at different times. In such case atria don’t contract coordinately, they twitch or quiver or fibrillate. There is no effective atrial contraction; there are only many uncoordinated muscle fiber contractions.
Normally, the atria eject small amount of the blood into the ventricles, this is called the “atrial kick”. In the case of atrial fibrillation, ventricles lose this amount of the blood.
Risk factors for the atrial fibrillation involve valvular heart disease, hypertension, coronary artery disease, previous myocardial infarction, underlying heart failure, obesity, diabetes mellitus, thyroid dysfunction, smoking, alcohol consumption, chronic obstructive pulmonary disease, obstructive sleep apnoea, sport, genetic factors and other. But age is the main risk factor for the atrial fibrillation.
Patient may complaint of shortness of breath, palpitations, feeling of irregular heartbeats, general fatigue, dizziness. Some patients feel chest pain.
Diagnosis of atrial fibrillation is based on ECG. There is no obvious P wave, which normally responds atrial depolarization. But you can see small f-waves of different amplitude and duration. Ventricular complexes are irregular and often frequent (heart rate exceeds 100 bpm). Often paroxysmal atrial fibrillation cannot be found during routine ECG, because it may self-terminate before record. In such case devices for long-term ECG registration (e.g. Holter-ECG or loop recorders) is helpful.
Transthoracic echocardiography usually reveals increase in left atrial volume. The possibility of atrial fibrillation and frequency of paroxysms is well-correlated with the left atrial size. Also, transmitral blood flow changes in the case of atrial fibrillation. What is this? Left atrium and left ventricle are separated by mitral valve. Blood is transferred to left ventricle in two steps: early left ventricular filling during ventricle relaxation and late ventricular filling during atrial contraction, also called “atrial kick”. Atrial contractions are responsible for only 15-25% of general left ventricular filling. Ratio between peak blood flow during early ventricular filling and during atrial contraction is called E/A ratio. Transmitral flow is M-shaped. In the case of atrial fibrillation A component is absent.