A 34-year-old man is presenting to the Emergency Department with severe pain in his back due to a sickle cell crisis, precipitated by exposure to cold and no chest pain:

• Sinus tachycardia with frequent premature atrial complexes with aberrant conduction
• Ventricular rate 107/min

This is good example of aberration due to abrupt change in cardiac cycle (a long cycle followed by a short cycle), known as the “Ashman phenomenon”.