Let us now discuss capture and fusion beats, which are also very helpful in the differential diagnosis of a wide QRS tachycardia. Captures and fusions are sinus activated QRS’s which occur in the midst of a tachycardia, due to AV dissociation. A capture is slightly early and has a narrow QRS configuration just like a normal beat. A fusion beat is a merging of the sinus QRS morphology and the ventricular QRS morphology with the resulting QRS morphology lying somewhere between the configuration of the sinus activation and the ventricular morphology. In a patient with a wide QRS rhythm, AV dissociation alone is highly suggestive of a ventricular origin, but may be difficult to identify; however, narrow premature QRS capture beats, and/or fusion beats, are virtually pathognomonic of a ventricular origin.