R-on-T phenomenon

R-·on-·T phe·nom·e·non

a premature ventricular (QRS) complex in the electrocardiogram interrupting the T wave of the preceding beat; often predisposes to serious ventricular arrhythmias.

R-on-T phenomenon

Cardiology A premature ventricular depolarization so early in the cardiac cycle that it falls on the apex of the preceding T wave, possibly presaging ventricular tachycardia or fibrillation; 'R-on-T' indicates a need to ↑ antiarrhythmics–eg, lidocaine