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Figure 2 Relationship between atrial ectopic activity and sinus node cycle length, as assessed in a baseline 24-h electrocardiogram Holter monitoring. The R-R interval trend graph (top) of time intervals selected from the continuous electrocardiogram recording shows that when the sinus node cycle length is short, or relatively short, no ectopic atrial premature impulses occur (left). A slight increase of sinus node cycle length (left arrow) is enough to trigger single (panel A) or repetitive (panel B) atrial premature impulses. This causes wide variations in the R-R intervals, with an apparent predominance of short (corresponding to atrial premature impulses) over long R-R intervals (corresponding to sinus node pauses following single or repetitive atrial impulses), which is denoted by the different densities of the superior and inferior lines in the graph. The right arrow indicates the disappearance of the arrhythmia, which occurs simultaneously with a critical shortening of sinus node cycle length. The arrhythmia is also absent when the sinus node rate slows down (right), during night sleep (panel C).
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