Atrial fibrillation

What it is

Atrial fibrillation is an irregular, narrow QRS (atrial) tachycardia. On the ECG the rhythm is irregularly irregular, P waves are absent, there is no isoelectric baseline, and the ventricular rate is variable. Because the rhythm is irregular, the rate is read from the number of QRS complexes on the strip multiplied by 6, so 12 complexes is 72 bpm. Compare atrial flutter, the other narrow QRS atrial rhythm. In flutter the QRS complexes are regular, the atrial rate is around 300 bpm with saw-tooth P waves, and the causes are heart failure (most common), rheumatic heart disease and atrial septal defect. Treatment of flutter is similar to that of atrial fibrillation. Atrial fibrillation is itself typed by how long it lasts, and the four types are:

1. Paroxysmal: self-terminates within less than 7 days, usually under 48 h.
2. Persistent: more than 7 days, or it requires intervention to convert.
3. Permanent: ongoing, and attempts to convert have failed.
4. Lone AF: in younger patients, with no structural heart disease and no risk factors.

Put another way, atrial fibrillation is a rhythm disturbance of the atria that results in irregular, chaotic ventricular waveforms. That chaotic activity reduces cardiac output through the loss of coordinated atrial contractions and through a rapid ventricular rate, both of which limit diastolic filling and the stroke volume of the ventricles. On the ECG, fibrillatory waves are seen, accompanied by an irregular QRS pattern.