trigeminy

Ventricular beats are grouped in groups of 3, the first 2 beats are normal beats, the third premature. A compensatory pause after the premature beat separates the triplets of beats. The premature beat generally arises from an ectopic focus in the atria or ventricles. An acceleration of heart rate may normalize the rhythm. A similar pattern is produced by a second degree AV block with a ratio of 4:3; however, this pattern is not converted to a normal rhythm by an acceleration of heart rate.

References

DeGowin & DeGowin's Diagnostic Examination, 6th edition, RL DeGowin (ed), McGraw Hill, NY 1994, pg 356