Sinus Pauses

Report:

Sinus rhythm

Sinus pauses, probably sinus arrests

Atrial escape beats

Comment:

The first beat in each group has a different-contoured P wave and is probably an atrial escape beat. This prevents the pause being measured, but it is already more than two sinus cycles long.

The main differential diagnosis is from blocked atrial ectopics; multiple leads may be required to exclude it. Sino-atrial exit block would be expected to have a pause shorter than two sinus cycles (Möbitz 1) or exactly two sinus cycles (Möbitz 2). Another possibility is sinus beats separated by short runs of atrial rhythm 96 – 98/min.

Sinus pauses is a convenient term to describe the pause without having to specify its mechanism.

The patient received 0.5 mg IV and 0.25 mg orally of Digoxin for AF, which reverted to sinus rhythm (probably spontaneously). Digoxin toxicity (or even therapeutic effect) is not very likely here. The patient has just been demonstrated to have bradycardia-tachycardia (sick sinus) syndrome.

Below (Fig 87a) is a similar trace, from an 82 year old woman with confusion and weakness: she was digoxin-toxic, event though there is no first degree AV block or obvious QT interval shortening. Her pauses are longer and the escape beats are junctional. The biphasic T waves merging into small U waves mime, in their terminal part, blocked SVEBs, especially before the pauses; but they are the same everywhere.