A 38-year-old man is in the Emergency Department with severe abdominal and back pain due to a sickle cell crisis. For the past year he has complained of palpitation precipitated by stress:

• Sinus tachycardia, 107/min
• Frequent premature atrial complexes in a pattern of bigeminy and trigeminy, with right bundle branch block aberrancy

Comment: This is a good example of Ashman phenomenon (aberration due to short cycle preceded by a long cycle). All the PACs have the same short interval from the preceding sinus complex. Aberration, however, occurs only with the bigeminal sequence, because “the long cycle that precedes the PAC is longer than that of the first or fifth PAC“.