Fusion beat
Also calledfusion complex · summation beat · combination beat
Definition
A single QRS complex produced when two wavefronts depolarize the ventricles at the same time, typically an impulse conducted from the atria and an impulse arising in the ventricles, giving a hybrid shape between the two pure beats. Fusion beats are seen with premature ventricular complexes, ventricular tachycardia, ventricular parasystole and ventricular pre-excitation. In a wide-complex tachycardia, fusion beats (like capture beats) come from atrial impulses conducting during AV dissociation and strongly suggest ventricular tachycardia. With a pacemaker, a fusion beat is a hybrid of the paced activation and the patient's own (spontaneous) depolarization.
Sources
- Wellens HJ, Bär FW, Lie KI. The value of the electrocardiogram in the differential diagnosis of a tachycardia with a widened QRS complex. Am J Med. 1978;64(1):27-33. doi.org/10.1016/0002-9343(78)90176-6
- Samesima N, God EG, Kruse JCL, et al. Brazilian Society of Cardiology guidelines on the analysis and issuance of electrocardiographic reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680. doi.org/10.36660/abc.20220623
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.