The R on T phenomenon is a dangerous pattern most associated with which arrhythmia?

• A. Premature ventricular contraction
• B. Atrial flutter
• C. Sinus tachycardia
• D. Bundle branch block

Answer: (A)

R on T is a dangerous timing of a ventricular extra beat. It happens when a premature ventricular contraction lands on the T wave of the preceding beat, during the vulnerable period of ventricular repolarization. That ectopic impulse can trigger a rapid, chaotic ventricular arrhythmia, such as ventricular tachycardia or ventricular fibrillation. Because this pattern hinges on a premature ventricular event, the association is with premature ventricular contractions. In contrast, atrial flutter, sinus tachycardia, or bundle branch block do not inherently involve a premature ventricular impulse landing on the T wave to provoke a dangerous ventricular rhythm.