R-on-T phenomenon
Also calledR on T · RonT · R-on-T PVC · R-on-T PVC phenomenon · R wave on T wave
Definition
A premature ventricular complex that falls on the T wave of the preceding beat, that is, during that beat's repolarization. Early observations and experimental work, built on the idea of a vulnerable period during repolarization, suggested that such a beat could start ventricular tachycardia or ventricular fibrillation, and R-on-T beats are a recognized trigger of both. Most R-on-T beats, however, do not set off an arrhythmia and are often seen in people who never develop ventricular fibrillation; the phenomenon matters most where repolarization is prolonged and uneven, as in long-QT syndrome.
Clinical noteWhether a beat is R-on-T depends on when its R wave occurs relative to the end of the preceding T wave, not simply on how premature it is: in one study of implanted-defibrillator recordings, a risk score based on that timing rose from isolated ectopic beats to nonsustained VT to sustained VT or VF, whereas the prematurity index of the initiating beat showed no such trend.
Sources
- Engel TR, Meister SG, Frankl WS. The "R-on-T" phenomenon: an update and critical review. Ann Intern Med. 1978;88(2):221-225. doi.org/10.7326/0003-4819-88-2-221
- 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
- Yap R, Calian D, Wright M, et al. Premature ventricular complexes. Clin Med (Lond). 2026;26(4):100609. doi.org/10.1016/j.clinme.2026.100609
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.