Coupling interval
Also calledcoupling interval PVC · ectopic coupling interval · CI
Definition
The time from a preceding normal (usually sinus) beat to the premature ectopic beat that follows it. Ectopic beats whose coupling interval stays nearly constant are called fixed coupled (one study defined this as a variation of 80 ms or less); fixed coupling is usually taken to mean reentry, although it does not prove it. A coupling interval that varies widely while the intervals between the ectopic beats themselves stay nearly constant suggests parasystole. If an ectopic beat comes early enough to fall on the T wave of the preceding beat (R-on-T phenomenon), it can trigger ventricular tachycardia or ventricular fibrillation.
Sources
- Yu R, Qi J, Wang X. Pediatric premature atrial contractions: clinical characteristics, diagnosis, and management: a literature review. Am Heart J Plus. 2026;68:100811. doi.org/10.1016/j.ahjo.2026.100811
- Michelson EL, Morganroth J, Spear JF, et al. Fixed coupling: different mechanisms revealed by exercise-induced changes in cycle length. Circulation. 1978;58(6):1002-1009. doi.org/10.1161/01.cir.58.6.1002
- Ren Z, Zhou J, Xu G, et al. The diagnostic criteria for classic parasystole. Chin Med J (Engl). 1999;112(11):992-994. pubmed.ncbi.nlm.nih.gov/11721482/
- Lian J, Muessig D, Lang V. Risk assessment of R-on-T event based on modeled QT-RR relationship. Pacing Clin Electrophysiol. 2011;34(6):700-708. doi.org/10.1111/j.1540-8159.2011.03058.x
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.