Atrial arrhythmias

doi:10.1136/bmj.324.7337.594

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Steve Goodacre,
Richard Irons

In adults a tachycardia is any heart rate greater than 100 beats per minute. Supraventricular tachycardias may be divided into two distinct groups depending on whether they arise from the atria or the atrioventricular junction. This article will consider those arising from the atria: sinus tachycardia, atrial fibrillation, atrial flutter, and atrial tachycardia. Tachycardias arising from re-entry circuits in the atrioventricular junction will be considered in the next article in the series.

Supraventricular tachycardias

From the atria or sinoatrial node

Sinus tachycardia
Atrial fibrillation
Atrial flutter
Atrial tachycardia

From the atrioventricular node

Atrioventricular re-entrant tachycardia
Atrioventricular nodal re-entrant tachycardia

Clinical relevance

The clinical importance of a tachycardia in an individual patient is related to the ventricular rate, the presence of any underlying heart disease, and the integrity of cardiovascular reflexes. Coronary blood flow occurs during diastole, and as the heart rate increases diastole shortens. In the presence of coronary atherosclerosis, blood flow may become critical and anginal-type chest pain may result. Similar chest pain, which is not related to myocardial ischaemia, may also occur. Reduced cardiac performance produces symptoms of faintness or syncope and leads to increased sympathetic stimulation, which may increase the heart rate further.

Electrocardiographic characteristics of atrial arrhythmias

Sinus tachycardia

P waves have normal morphology
Atrial rate 100-200 beats/min
Regular ventricular rhythm
Ventricular rate 100-200 beats/min
One P wave precedes every QRS complex

Atrial tachycardia

Abnormal P wave morphology
Atrial rate 100-250 beats/min
Ventricular rhythm usually regular
Variable ventricular rate

Atrial flutter

Undulating saw-toothed baseline F (flutter) waves
Atrial rate 250-350 beats/min
Regular ventricular rhythm
Ventricular rate typically 150 beats/min (with 2:1 atrioventricular block)
4:1 is also common (3:1 and 1:1 block uncommon)

Atrial fibrillation

P waves absent; oscillating baseline f (fibrillation) waves
Atrial rate 350-600 beats/min
Irregular ventricular rhythm
Ventricular rate 100-180 beats/min

As a general rule the faster the ventricular rate, the more likely the presence of symptoms—for example, chest pain, faintness, and breathlessness. Urgent treatment is needed for severely symptomatic patients …