What is the R on T phenomenon?

The R on T phenomenon refers specifically to the occurrence of a premature ventricular contraction (PVC) that falls on the T wave of a preceding heartbeat. This is particularly significant because the T wave represents the phase of ventricular repolarization. When a PVC occurs during this vulnerable period, it can disrupt the normal electrical cycle of the heart and potentially lead to more severe arrhythmias, such as ventricular tachycardia or fibrillation.

The timing of the PVC is crucial; if it occurs during the T wave, it can lead to serious consequences, as the heart's muscle may not be fully repolarized and ready to respond to another contraction. This makes understanding the R on T phenomenon important for recognizing and managing potential life-threatening cardiac events.