Runs of ventricular tachycardia vs. another phenomenon

Ashman Phenomenon

Ashman phenomenon is an intraventricular conduction abnormality caused by a change in the heart rate. Aberrantly conducted beats (usually seen in atrial fibrillation) are often mistaken for PVCs or ventricular tachycardia, causing diagnostic confusion. Ashman phenomenon is an ECG finding that is usually linked to benign conduction irregularity, but it is an important finding to be aware of to avoid misdiagnosis.

• First reported in 1947 by Gouaux and Ashman, they showed that the earlier in the cardiac cycle a premature atrial contraction (PAC) occurs, and the longer the preceding cycle is, the more likely that PAC conduction will deviate from the normal pathway and be conducted with aberration
• Ashman phenomenon can occur in any supraventricular rhythm (most commonly atrial fibrillation, may even occur in sinus rhythm occasionally)
• Physiological aberrancy of ventricular conduction is due to a change in the QRS cycle length
  • • Typically follows a long-short cycle, and is especially likely to occur with a short-long-short cycle
• The refractory period of the ventricle is proportional to the heart rate and the duration of the preceding R-R interval
  • • Shorter R-R intervals are associated with a shorter duration action potential and vice versa
    • With longer R-R intervals the refractory period is longer, and if a short R-R interval follows with an atrial impulse arriving during the refractory period, the beat that terminates the cycle is likely to be conducted aberrantly
• Aberrant conduction results when a supraventricular impulse reaches the His-Purkinje system while one of its branches is still in the relative or absolute refractory period
  • • Typically conducted with a RBBB morphology (right bundle branch has a longer refractory period than the left), may have LBBB morphology as well but seen less frequently
    • When the aberrancy occurs in groups, it can resemble non-sustained ventricular tachycardia

Treatment

• No treatment needed for isolated complexes
  • • This is NOT ventricular tachycardia and antidysrhythmic medications and hospitalization is unnecessary
• Rate control and treatment of the underlying condition may be necessary

Take home points

The Ashman phenomenon

• Aberrant ventricular conduction that follows a short-long-short cycle in atrial fibrillation and other supraventricular arrhythmias
• Often occurs in groups and may be mistaken for non-sustained ventricular tachycardia or PVC’s
• Typically conducted in a RBBB morphology (right bundle branch has a longer refractory period than the left)
  • • Scrutinize lead V1
• Benign ECG manifestation of the underlying condition that usually responds to rate control
• Ventricular antiarrhythmics and admission for ventricular tachycardia is unnecessary