fusion beat
Cardiac beat resulting from simultaneous activation of the ventricles by two different impulse sources.
Full Definition
A fusion beat occurs when the ventricles are simultaneously activated by two different electrical impulses, typically one from a supraventricular source and another from a ventricular source. This results in a QRS complex that has morphological characteristics of both contributing rhythms. Fusion beats are commonly seen during ventricular tachycardia when an occasional supraventricular impulse conducts to the ventricles and merges with the ventricular tachycardia wavefront. They serve as important diagnostic criteria for ventricular tachycardia, helping to distinguish it from supraventricular tachycardia with aberrancy. Fusion beats can also occur in patients with pacemakers when intrinsic conduction competes with paced beats.
Usage
Usage note: Often used in plural form when describing multiple occurrences.
In Context
- "The presence of fusion beats during the wide-complex tachycardia confirmed the diagnosis of ventricular tachycardia." — ECG interpretation report
- "Intermittent fusion beats were observed when the patient's intrinsic rhythm competed with ventricular pacing." — Device interrogation report