Rhythms and Arrhythmia
Atrial fibrillation is a common arrhythmia that is usually due to constant conduction within the atria caused by multiple circuits. Certain parts of the atria are depolarising whilst other parts are repolarising. This causes a loss of atrial contraction due to the ineffective quiver of the muscle.
P waves are absent from the ECG and the baseline consists of irregular waveforms that continuously change in shape, duration, amplitude, and direction. These irregular waveforms are referred to as fibrillatory waves. The resulting ventricular response (seen as QRS complexes) is completely irregular.
In the ECG trace below, the QRS complexes (arrowed) form an irregular rhythm with an average rate of 78 bpm. The ECG baseline (shaded) shows fibrillatory waveforms.
Approximately one in five strokes can be attributed to atrial fibrillation, causing this particular arrhythmia to be a significant public health concern. Prevalence increases with age such that it is present in more than 10% of the population over 75 years old.
Patients are categorised clinically based on whether their atrial fibrillation is paroxysmal (self-terminating), persistent (can be converted to sinus rhythm), or permanent (unable to convert or maintain sinus rhythm).