R-on-T phenomenon
Occurrence of a ventricular premature beat during the vulnerable period of ventricular repolarization, corresponding to the T wave of the preceding beat.
Full Definition
The R-on-T phenomenon describes the occurrence of a ventricular premature complex (VPC) that falls during the vulnerable period of ventricular repolarization, typically landing on or near the T wave of the preceding normal beat. This timing is particularly dangerous because it occurs during the relative refractory period when ventricular tissue has heterogeneous repolarization, making it susceptible to triggering sustained ventricular arrhythmias including ventricular tachycardia or ventricular fibrillation. The vulnerable period corresponds roughly to the peak of the T wave and represents approximately 20-40 milliseconds during the cardiac cycle. While not all R-on-T events lead to sustained arrhythmias, they represent a higher risk scenario, especially in patients with underlying heart disease, electrolyte abnormalities, or QT prolongation. Recognition of this pattern is important for risk stratification and arrhythmia prevention.
Usage
Usage note: Always hyphenate as R-on-T, not R on T or RonT.
In Context
- "The Holter monitor captured an R-on-T phenomenon that initiated a 12-beat run of ventricular tachycardia." — Holter monitor interpretation
- "Frequent R-on-T premature beats in this acute MI patient warranted continuous cardiac monitoring." — CCU progress note