Electrocardiographical clues to a mechanism of pre-syncope.

This is the case of a 73 year-old female who presented to clinic complaining of pre-syncope. A 24-hour Holter monitor revealed multiple episodes of 2–2.5 s pauses associated with non-conducted P waves (Fig. 1). Careful examination of the rhythm strip revealed high-frequency, low-amplitude signal during and immediately prior to the pauses. This high-frequency low-amplitude signal was particularly marked during the pause. The PR interval was observed to lengthen slightly in the beats prior to the pause and there was slight slowing of the sinus rate.