Fascicular tachycardia is uncommon. Patients frequently do not have any underlying structural heart disease and the origin of the tachycardia is the posterior fascicle (or less commonly the anterior fascicle) of the left bundle branch.

As the wave of depolarisation originates in specialised conducting tissue, the resultant QRS complex is of a relatively short duration (0.11-0.14 seconds). Consequently this arrhythmia is frequently misdiagnosed as an SVT.

Looking for ECG features of monomorphic ventricular tachycardia, such as capture beats, fusion beats, or dissociated P waves, can help to identify a fascicular tachycardia rather that SVT.