Pacemaker fusion beat
Also calledPacemaker fusion · Paced fusion beat · Paced fusion complex
Definition
A complex produced when a paced stimulus and the heart's own depolarization activate the same chamber at the same time, giving a QRS (or P wave) whose shape lies between a fully paced beat and a native beat. A pacing spike is present, and the complex can be narrower than a fully paced beat because part of the chamber is depolarized by the native impulse. It is consistent with normal pacemaker behavior, not a malfunction. A pseudofusion beat differs in that the spike falls on a native complex without contributing to its depolarization, so the complex looks like the native beat.
Clinical noteFusion and pseudofusion are normal pacemaker behavior; in pseudofusion the spike does not change the complex.
Sources
- Safavi-Naeini P, Saeed M. Pacemaker troubleshooting: common clinical scenarios. Tex Heart Inst J. 2016;43(5):415-418. doi.org/10.14503/THIJ-16-5918
- Barold SS, Herweg B. Usefulness of the 12-lead electrocardiogram in the follow-up of patients with cardiac resynchronization devices. Part II. Cardiol J. 2011;18(6):610-624. doi.org/10.5603/cj.2011.0024
- 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.