Case B14: Atrial Fibrillation. St Emlyn’s ECG Library

History

The ECG was recorded from a 71 year old man with chronic obstructive airways disease who was taking digoxin to control the heart rate in atrial fibrillation.

ECG

Rhythm: No recognizable P waves or other form of co-ordinated auial activity is seen in any lead. The baseline is irregular and chaotic atrial activity is best seen in lead VI where a waveform irregular in both amplitude and frequency is recorded. The QRS complexes are irregular and the R – R intervals vary unpredictably. There is no recognizable relationship between the QRS complexes and atrial activity: atrial fibrillation is present. Morphology: There are downwards sloping ST segments in leads II, III and aVF. In V5 and V6 the ST segments slope downwards and the T waves are flat. These changes are non specific and may be caused by digoxin; it is not possible to diagnose ischaemia from this record.

Comment

Atrial fibrillation is the most common arrhythmia encountered in clinical practice. The process of atrial depolarization is uncoordinated and appears to occur in a chaotic random fashion, often best recorded in leads V1 and V2, unlike atrial flutter where regular saw tooth waves at a rate near 300 per minute are usually best seen in the inferior leads. An irregular waveform usually at a frequency between 400 and 600 per minute reflects the electrical events in the atrial myocardium. The variation in size and shape of these T waves and the total lack of a fixed relationship to the QRS complexes should prevent any confusion with other supraventricular rhythms. Transmission of atrial depolarization to the ventricles is through the AV junction and depends on the refractory
period of the dssues involved. In the absence of treatment or pre-existing disease of the AV node the resulting ventricular rate will be rapid as many of the atrial impulses which arrive at the AV node will be conducted. A ventricular rate in the range of 120 – 200 beats per minute often results. This is detected clinically as a pulse that is irregular in both timing and volume.

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