weird definitions

Question 1

fusion beats

Answer 1

A fusion beat occurs when a supraventricular and a ventricular impulse coincide to produce a hybrid complex.
It indicates that there are two foci of pacemaker cells firing simultaneously: a supraventricular pacemaker (e.g. the sinus node) and a competing ventricular pacemaker (source of ventricular ectopics).
The fusion beats are of intermediate width and morphology to the supraventricular and ventricular complexes.

Causes

Fusion beats are seen with:

Ventricular tachycardia
Accelerated idioventricular rhythm (AIVR)